Extremely Metal-Poor Galaxies: The HI Content
M. E. Filho, B. Winkel, Sánchez Almeida, J. A. Aguerri, R. Amorín, Y. Ascasibar, B. G. Elmegreen, D. M. Elmegreen, J. M. Gomes, A. Humphrey, P. Lagos, A. B. Morales-Luis, C. Muñoz-Tuñón, P. Papaderos, J. M. Vílchez
aa r X i v : . [ a s t r o - ph . C O ] J u l Astronomy & Astrophysics manuscript no. cometary˙v19˙astro c (cid:13)
ESO 2018June 18, 2018
Extremely Metal-Poor Galaxies: The H i Content
M. E. Filho ⋆ , B. Winkel , J. S´anchez Almeida , , J. A. Aguerri , , R. Amor´ın , , Y. Ascasibar , B. G.Elmegreen , D. M. Elmegreen , J. M. Gomes , A. Humphrey , P. Lagos , A. B. Morales-Luis , , C.Mu˜noz-Tu˜n´on , , P. Papaderos , and J. M. V´ılchez Centro de Astrof´ısica da Universidade do Porto, 4150-762, Porto, Portugal Max-Planck-Institut f¨ur Radioastronomie (MPIfR), Auf dem H¨ugel 69, 53121 Bonn, Germany Instituto de Astrof´ısica de Canarias, E-38200 La Laguna (Tenerife), Spain Departamento de Astrof´ısica, Universidad La Laguna, E-38206 La Laguna (Tenerife), Spain Instituto de Astrof´ısica de Andaluc´ıa, E-18008 Granada, Spain INAF - Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Rome, Italy Universidad Aut´onoma de Madrid, E-28049 Madrid, Spain IBM, T. J. Watson Research Center, Yorktown Heights, New York 10598, USA Vassar College, Department of Physics and Astronomy, Poughkeepsie, New York 12604, USA
ABSTRACT
Context.
Extremely metal-poor (XMP) galaxies are chemically, and possibly dynamically, primordial objects in the localUniverse.
Aims.
Our objective is to characterize the H i content of the XMP galaxies as a class, using as a reference the list of140 known local XMPs compiled by Morales-Luis et al. (2011). Methods.
We have observed 29 XMPs, which had not been observed before at 21 cm, using the Effelsberg radio telescope.This information was complemented with H i data published in literature for a further 53 XMPs. In addition, opticaldata from the literature provided morphologies, stellar masses, star-formation rates and metallicities. Results.
Effelsberg H i integrated flux densities are between 1 and 15 Jy km s − , while line widths are between 20 and120 km s − . H i integrated flux densities and line widths from literature are in the range 0.1 – 200 Jy km s − and 15– 150 km s − , respectively. Of the 10 new Effelsberg detections, two sources show an asymmetric double-horn profile,while the remaining sources show either asymmetric (seven sources) or symmetric (one source) single-peak 21 cm lineprofiles. An asymmetry in the H i line profile is systematically accompanied by an asymmetry in the optical morphology.Typically, the g -band stellar mass-to-light ratios are ∼ i gas mass-to-light ratios may be up to twoorders of magnitude larger. Moreover, H i gas-to-stellar mass ratios fall typically between 10 and 20, denoting thatXMPs are extremely gas-rich. We find an anti-correlation between the H i gas mass-to-light ratio and the luminosity,whereby fainter XMPs are more gas-rich than brighter XMPs, suggesting that brighter sources have converted a largerfraction of their H i gas into stars. (abridged) Conclusions.
XMP galaxies are among the most gas-rich objects in the local Universe. The observed H i componentsuggests kinematical disruption and hints at a primordial composition. Key words. galaxies: fundamental parameters – radio lines: galaxies – techniques: spectroscopic
1. Introduction
According to the hierarchical paradigm of structure forma-tion, massive galaxies assemble through mergers and can-nibalism of smaller systems. Interactions between galax-ies and secular processes induce episodes of star-formation.Stellar winds and the death of stars chemically enrich boththe interstellar medium and the subsequent stellar genera-tions. In this scenario, extremely metal-poor dwarf galaxies(XMPs) should be common in the early Universe, whereasthey should be very rare at low redshift (York et al. 2000;Pustilnik et al. 2005; Guseva et al. 2007; Izotov, Thuan &Guseva 2012; Mamon et al. 2012). Indeed, one of the mostrecent searches in the Sloan Digital Sky Survey (SDSS)Data Release 7 (DR7; Abazajian et al. 2009) and in lit-erature, has yielded only 140 XMPs in the local Universe,corresponding to 0.1% of the galaxies in the local volume(Morales-Luis, S´anchez Almeida, Aguerri & Mu˜noz-Tu˜n´on ⋆ E-mail: mfi[email protected]
1. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content of the star-forming galaxies in the Kiso survey of UV-brightgalaxies (Miyauchi-Isobe, Maehara & Nakajima 2010) arecometary (Elmegreen et al. 2012).There are various interpretations for the asymmetric op-tical morphology of these galaxies. They could be diffuseedge-on disks in the early stages of evolution, with mas-sive star-forming regions viewed from the side (Elmegreen& Elmegreen 2010), resulting from the spontaneous excita-tion of gravitational instabilities (Elmegreen et al. 2009).Alternatively, these structures may also arise from gravita-tional triggering due to a merger with a low-mass compan-ion (Straughn et al. 2006) or it may be self-propagation ofthe star-formation activity within an already existing gas-rich galaxy or chemically pristine gas cloud (Papaderos etal. 1998, 2008). The large starburst that gives rise to theasymmetry could also be due to the infall of pristine exter-nal gas (S´anchez Almeida et al. 2013).In the few XMPs where the H i has been investigatedwith interferometric observations, the H i spatial distribu-tions and velocity profiles are found to be distorted (Ekta,Chengalur & Pustilnik 2008; Ekta & Chengalur 2010a), in-dicating infall of external unenriched gas that may feedthe starburst and drop the metallicity (Kewley, Geller &Barton 2006) or gas stripping forced by an interaction withan external medium (Gavazzi et al. 2001; Elmegreen &Elmegreen 2010). In the latter case, the asymmetric star-burst results from the ram compression by the intergalacticmedium: gas-rich disks with star-formation at the leadingedge and the rest of the disk visible as the tail, or with star-formation at the leading edge and a tail of star-formationin the stripped gas. In any case, the study of the dynam-ical, stellar, ionized gas and neutral atomic gas structureis crucial to disentangle the nature of the XMPs and theirassociation with a particular morphology.Our team is involved in the full observational character-ization of a representative sample of local XMP galaxies.Their H i gas content is particularly important, since thesegalaxies are expected to have large gas reservoirs respon-sible for many of their observational properties, includingsustaining the current star-formation episode and even di-luting the interstellar gas to yield their low metallicity. Thiswork aims at describing and quantifying, for the first time,the H i content of the XMPs as a class.In Sect. 2.1 we present a compilation of published H i information for the reference list of XMPs in ML11. The ex-isting data were completed with new observations obtainedwith the 100-meter single-dish Effelsberg radio telescope.The observations, data reduction (following a novel tech-nique) and properties of the detected sources are describedin Sect. 2.2. Because derived parameters, such as dynami-cal masses, rely on ancillary optical data, we have compiledthis information from the SDSS optical images and spectra(Sect. 3). Global galaxy parameters are derived combiningthe H i and optical data, as explained in Sect. 4. The re-sults of our investigation, namely, the description of the H i content of the XMP galaxies with respect to other physi-cal properties, such as the Tully – Fisher relation, are de-scribed in Sect. 5. In Sect. 6 we describe properties thatrely exclusively on optical data, such as the morphology.Our conclusions are summarized in Sect. 7.Throughout this paper, we adopt the cosmological pa-rameters Ω m = 0 .
27, Ω Λ = 0 .
73 and H = 73 km s − Mpc − .
2. H i Radio Data
The sources presented in this analysis were extracted fromthe work of ML11, which contains 140 extremely metal-poor galaxies selected from the SDSS DR7 (Abazajian etal. 2009), including 11 new XMP candidates, and com-pleted with all the galaxies in literature having an oxygenmetallicity less than a tenth of the solar value (explicitly,12 + log (O/H) ≤ i gas data comes partly from literature (Sect. 2.1)and is complemented by new observations (Sect. 2.2).
53 out of the 140 XMP galaxies possess published H i line observations, 5 of which were non-detections. The H i data were primarily gathered from the Arecibo LegacyFast ALFA Survey (ALFALFA; Giovanelli et al. 2007), H i Parkes All-Sky Survey (HIPASS; Barnes et al. 2001) andThe H i Nearby Galaxy Survey (THINGS; Walter et al.2008), as well as sources observed with the Nan¸cay RadioTelescope (NRT; Pustilnik & Martin 2007), the GreenBank Telescope (GBT; Schneider et al. 1992; Hogg et al.2007), the Australia Telescope Compact Array (ATCA;Warren, Jerjen & Koribalski 2006; O’Brien et al. 2010),the Westerbork Synthesis Radio Telescope (WSRT; Kova˘c,Osterloo & van der Hulst 2009), the Giant Metrewave RadioTelescope (GMRT; Begum et al. 2006, 2008), the EffelsbergRadio Telescope (Huchtmeier, Krishna & Petrosian 2005)and the Very Large Array (VLA; Thuan, Hibbard & L´evrier2004).These observations have yielded typical H i integratedflux densities, S H i , in the 0.1 – 200 Jy km s − range andline widths, at 50% of the peak flux density level, w , inthe 15 – 150 km s − range.In Table 1 we list the compilation of H i line observa-tions from literature. In addition to the H i integrated fluxdensity, which can be used to estimate the H i mass (Eq. 4;Sect. 4), Table 1 includes the H i diameter, d H i , the sys-temic heliocentric or local group-corrected radial velocity(optical convention; Eq. 2; Sect. 4), v sys , and the line width, w . The systemic radial velocity is the midpoint of the H i emission-line profile and can be used to estimate a redshiftdistance using the Hubble law. The line width provides ameasure of the Doppler broadening and, together with theH i diameter, can be used to estimate the dynamical mass(Eq. 3; Sect. 4). Original references and observational facil-ities or surveys are also listed in Table 1. H i Observations
Of the 87 sources with no published H i line observations, wechose the subsample of 29 targets, with declinations above − ◦ , suitable for the latitude of Effelsberg, and observableduring the period July through November 2012. To obtain measurements of the H i flux density, S ν , atfrequency ν , we performed pointed observations with the100-m single-dish Effelsberg radio telescope using the cen-tral feed of the 7-beam L-band receiver and the AFFTS i Content
Table 1.
Compilation of the H i data from literature for 53 XMP galaxies in the local Universe. Col. 1: Source name.Col. 2: Right Ascension. Col. 3: Declination. Col. 4: H i integrated flux density and error. ” < ” designates an upperlimit. Data from references (a) are corrected for pointing, (b) are flux density-corrected for beam resolution and (h)are self-absorption-corrected line flux densities. Col. 5: H i systemic heliocentric or local group-corrected ( ⋆ ) radialvelocity (optical convention) and error. Col. 6: H i line width at 50% of the peak flux density and error. Col. 7: H i diameter at a column density of ∼ atoms cm − . Col. 8: Telescope or survey. Col. 9: Bibliographical reference.(a) - Green Bank Telescope (GBT) – Schneider et al. 1992; (b) - Nan¸cay Radio Telescope (NRT) – Pustilnik &Martin 2007; (c) - The H i Parkes All Sky Survey (HIPASS) – Koribalski et al. 2004; (d) - Australia TelescopeCompact Array (ATCA) – Warren, Jerjen & Koribalski 2006; (e) - Giant Metrewave Radio Telescope (GMRT) –Begum et al. 2008; (f) - Arecibo Radio Telescope – Lu et al. 1993; (g) - Giant Metrewave Radio Telescope (GMRT)– Ekta & Chengalur 2010a; (h) - Arecibo Radio Telescope – Springob et al. 2005; (i) - The H i Parkes All Sky Survey(HIPASS) – Doyle et al. 2005; (j) - Giant Metrewave Radio Telescope (GMRT) – Ekta, Pustilnik & Chengalur 2009;(k) - Effelsberg Radio Telescope – Huchtmeier, Karachentsev & Karachentsev 2003; (l) - The H i Nearby GalaxySurvey (THINGS) performed with the Very Large Array (VLA) – Walter et al. 2008; (m) - Giant Metrewave RadioTelescope (GMRT) – Chengalur et al. 2006; (n) Very Large Array (VLA) - ACS Nearby Galaxy Survey Treasury(VLA-ANGST) – Ott et al. 2012; (o) - H i catalog A General Catalog of H i Observations of Galaxies – Huchtmeier &Richter 1989; (p) - Green Bank Telescope (GBT) – Hogg et al. 2007; (q) - Effelsberg Radio Telescope – Huchtmeier,Krishna & Petrosian 2005; (r) - Giant Metrewave Radio Telescope (GMRT) – Begum et al. 2006; (s) - Parkes RadioTelescope – Barnes & de Blok 2004; (t) - Very Large Array (VLA) – Thuan, Hibbard & L´evrier 2004; (u) - GiantMetrewave Radio Telescope (GMRT) – Ekta, Chengalur & Pustilnik 2006; (v) - The Arecibo Legacy Fast ALFASurvey (ALFALFA) – Giovanelli et al. 2007; (w) - Westerbork Synthesis Radio Telescope (WSRT) – Kova˘c, Osterloo& van der Hulst 2009; (x) - Green Bank Telescope (GBT) – O’Neil 2004; (y) - Giant Metrewave Radio Telescope(GMRT) – Ekta, Chengalur & Pustilnik 2008; (z) - Australia Telescope Compact Array (ATCA) – O’Brien et al.2010.
Name RA(J2000) DEC(J2000) S H i v sys w d H i Telescope Ref. h m s ◦ ′ ′′
Jy km s − km s − km s − ′ or Survey(1) (2) (3) (4) (5) (6) (7) (8) (9)UGC12894 00 00 22 +39 29 44 6.75 ± ± ± < ±
30 50 . . . NRT bESO473-G024 00 31 22 -22 45 57 7.2 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
11 . . . NRT bUGCA20 01 43 15 +19 58 32 11.43 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
10 . . . NRT bSBS940+544 09 44 17 +54 11 34 < ± ± ± ± ± ± ± ± ± ± ±
12 324 ± i Content
Table 1.
Compilation of the H i data from literature for 53 XMP galaxies in the local Universe. Continued. Name RA(J2000) DEC(J2000) S H i v sys w d H i Telescope Ref. h m s ◦ ′ ′′
Jy km s − km s − km s − ′ or Survey(1) (2) (3) (4) (5) (6) (7) (8) (9)KUG1013+381 10 16 24 +37 54 44 1.51 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± a VLA t14.1 -103 ± ± ± ± ± ± ± ± < ±
15 . . . . . . NRT bSBS1211+540 12 14 02 +53 45 17 0.63 894 ± ± ± ± ± < ±
50 . . . . . . NRT bVCC0428 12 20 40 +13 53 22 0.65 ± ± ± ± ± ± ± ± ⋆ ± ± ± ± ± ± ±
16 . . . GBT xDD0167 13 13 23 +46 19 22 3.7 ± ± ± ± ± ± ± ±
15 . . . NRT bSagDIG 19 29 59 -17 40 41 23.0 ± ± ± ± ± ± ± ± ± ± < ±
20 50 . . . NRT b a Quoted value is for the major axis diameter only. backend. The latter is a Field Programmable Gate Array(FPGA)-based Fast Fourier Transform (FFT) spectrome-ter (Klein et al. 2006), providing 16k spectral channels overa bandwidth of 100 MHz (spectral resolution of 7.1 kHz).This results in a velocity resolution at 21 cm of 1.5 km s − .Each of the candidate sources was observed for aboutone hour in on-off mode (effective observing time is ∼ σ outliers in the residual (peaks in excess of 8 times thenoise standard deviation or rms ). The associated spectral channels in the spectrum were subsequently replaced withthe median-filtered values.The spectra have been flux-calibrated using a noveltechnique (Winkel, Kraus & Bach 2012), which accountsfor the frequency dependence of the system temperatureand, as such, provides an unbiased calibration over thefull bandwidth. This new method requires good knowledgeof the temperature of the calibration diode, T cal , whichwe have measured repeatedly using the calibration sourcesNGC 7027, 3C 48 and 3C 147 during the observing sessionsin July and November 2012. For the most accurate ab-solute flux calibration, total-power measurements of the(Galactic) target S7 (Kalberla, Mebold & Reif 1982) wereused to fix T cal at the frequency of 1420.1 MHz. The latterusually leads to an uncertainty of less than 3% for the 7-beam system (Winkel et al. 2010), while we find a scatter ofthe individually determined T cal spectra of about 5%, withrespect to the average of all T cal spectra.Using the SIMBAD Astronomical Database, we ob-tained the radial velocity (heliocentric, converted from the
4. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content optical to the radio convention; Eq. 2; Sect. 4) value forthe sources, in order to directly extract the relevant partof each spectrum. Residual baselines were removed using apolynomial fit. For each resulting profile, the residual rms and integrated flux density of the source, if detected, wasdetermined. The baseline rms can also be used to calcu-late a theoretical flux limit ( σ ) for a hypothetical sourcewith a Gaussian-like H i profile of width w = 50 km s − (equal to the full width at half maximum, FWHM, for aGaussian).Of the 29 observed sources, there were seven (excludingJ0014-0044; Sect. 2.2.2) detections ( ≫ σ ), three marginaldetections ( > σ ), six uncertain detections ( ∼ σ ) and 12non-detections ( ≪ σ ). i Properties
Figure 1 displays H i spectra and SDSS Data Release 9(DR9; Ahn et al. 2012) composite images of the 10 de-tected sources (including marginal detections) ordered byright ascension, and also of J0014-0044 in the field of UCG139 (see below).Table 2 contains the Effelsberg H i parameters. In ad-dition to the H i integrated flux density and line width,Table 2 contains the effective observing time on-source, t , the systemic local standard-of-rest radial velocity (ra-dio convention; Eq. 2; Sect. 4), v lsrsys , the 5 σ detection limitand a characterization of the H i line profile shape.The H i integrated flux density, S H i = R S ν dν , sys-temic radial velocities and line widths were derived fromthe 21 cm baseline-subtracted profiles obtained with thesingle-dish observations. Typically, the Effelsberg flux den-sity errors are in the range 5 – 10%. In the cases where theH i profile is double-horn (J0014-0044 in the field of UGC139; Fig. 1 and see below; J0113+0052 and J0204-1009),we marked the positions of 50% of the peak on each sideof the double-horn profile, and estimated the line width atthese points (e.g., Springob et al. 2005).Usually H i sources are relatively isolated. However,given the large Effelsberg beam ( ∼ ′ ), we have checked thefields in which the XMPs reside, in order to assess possibleH i contamination. For this, we have visually analyzed theSDSS DR9 images (Fig. 1) in a field of view of about 6 ′ .The results of this inspection are detailed in the list below. • J0014-0044 – The SDSS image (Fig. 1) shows atwo-knot source next to a large spiral (SBc) galaxy (UGC139). The NASA/IPAC Extragalactic Database (NED )has flagged the brightest SDSS XMP knot as a WesternH ii region of UGC 139. Indeed, SDSS spectroscopy of thebright knot and UGC 139 put them at a similar redshiftof ∼ i profile is double-horn sym-metric, typical of ordered disk rotation, with a large linewidth ( ∼
320 km s − ; Table 2). Therefore, the H i line de-tected with Effelsberg is primarily associated with the spiralgalaxy UGC 139 and the source has been excluded from thefollowing analysis. • J0015+0104, J0113+0052, J0204-1009, J0301-0052, J0315-0024 and PHL293B – The SDSS images(Fig. 1) show knotted or cometary structures in relativelyclean fields. Therefore, we are confident that the detectedH i flux density is associated with the XMP galaxies. For different widths the flux density limit scales with √ w . http://ned.ipac.caltech.edu/ • J0126-0038 and J2104-0035 – These sources showcometary structures (Fig. 1) and are found in fields withnearby stars and small red objects, the latter likely highredshift galaxies. Therefore, it is unlikely that there is con-tamination of the H i data. • J2053+0039 – This source (Fig. 1) is found in aSDSS field with nearby stars and small red objects, likelyto be high redshift galaxies. However, there is a small bluecloud to the Northwest of the original XMP position (topright-hand corner; Fig. 1), with a SDSS photometric red-shift of 0.17 ± i data will likely contain information from both thesecomponents. • J2150+0033 – In the SDSS image (Fig. 1), thissymmetric XMP shows a nearby galaxy in projection. TheSDSS redshifts for the XMP source and the galaxy are 0.02and 0.06, respectively. Therefore, the H i data is not likelyto be affected by contamination.
3. Auxiliary Optical Data
In order to estimate physical parameters like dynamical andH i gas masses, we have compiled from literature opticalsizes, inclinations, distances, g -band magnitudes, H ii gas-phase metallicities and other relevant observables. Theseare included in Tables 3, 4 and 5. Hubble flow distances (Table 5), D, are obtained from NEDand are corrected for Virgocentric infall. The optical radii(Table 3), r opt , have been obtained from the SDSS data,as the radii containing 90% of the galaxy light in the g -band. When these values are not available, we use NEDSDSS r -band Petrosian radii, or the average between thesemi-major axis, θ M , and the semi-minor axis, θ m , at the 25mag arcsec − isophote. The inclination angle of the source(Table 3), i , is computed as:sin i = vuut − (cid:16) θ m θ M (cid:17) − q , (1)where q = 0 .
25, which implicitly assumes galaxies to bedisks of intrinsic thickness q (e.g., S´anchez-Janssen et al.2010). Absolute g -band magnitudes, M g , have been ob-tained from the Hubble flow Virgocentric infall-correcteddistances (Table 5) and SDSS DR7 Petrosian g -band mag-nitudes (Table 3), included in Table 1 and 2 of ML11. The g -band luminosity has been obtained from the absolutemagnitude, assuming a solar absolute g -band magnitudeof 5.12 . Metallicity values are H ii gas-phase metallicities(Table 3) taken from Table 1 and 2 of ML11 (and refer-ences therein). They have been derived using the direct(T e ) method or strong-line methods, based on empiricalcalibrations consistent with the direct method. i Content T [ K ] J0014-0044Flux: 29.28 K km/sFlux: 15.25 Jy km/sFlux limit: 0.71 Jy km/s(5-sigma, 50km/s)Base RMS: 19.35 mK
J0014−0044 T [ K ] J0015+0104Flux: 2.91 K km/sFlux: 1.52 Jy km/sFlux limit: 0.61 Jy km/s(5-sigma, 50km/s)Base RMS: 16.69 mK600 800 1000 1200 1400 1600vlsr (radio) [km/s]−0.050.000.050.100.150.200.25 T [ K ] J0113+0052Fl)+: 11.06 K km/sFl)+: 5.76 Jy km/sFl)+ limi(: 0.69 Jy km/s(5-sigma, 50km/s)Base RMS: 18.65 mK
Fig. 1. H i Effelsberg spectra (left) and SDSS fields (right) of the detected (including marginal) XMP galaxies. The H i spectra of J0014-0044 is dominated by the H i gas of the nearby spiral galaxy UGC 139 (Sect. 2.2.2). In the spectra,the blue vertical solid lines mark the radial velocity from SIMBAD (heliocentric; converted from the optical to the radioconvention), the blue vertical dashed lines mark the regions for the baseline computation and flux density integration,and the red lines represent a smoothed version of the spectrum, using a Gaussian kernel of width σ sm = 21 .
22 km s − .The smoothing kernel was chosen such that the resulting spectral resolution becomes σ res = 21 .
25 km s − , which isoptimally suited to detect a (Gaussian) feature of line width √ σ res = 50 km s − (FWHM). Note that the integratedflux densities and limits were derived from the full-resolution spectra/ rms . We have adapted, completed and/or revised, using theSDSS DR9 composite images, the optical morphologicalclassification, based on the simple scheme presented inML11 – symmetric for a spherical, elliptical or disk-likesymmetric structure, cometary for a head-tail structure,with or without a clear knot at the head, and a diffusetail, two-knot for a structure with two knots, with or with-out a head-tail morphology, and multi-knot for a diffusestructure with multiple star-formation knots. In Fig. 2 wesupply SDSS DR9 postage stamp images illustrating this scheme, while Table 3 includes the individual morphologi-cal classification for the XMPs.We have also parametrized the asymmetric optical mor-phology, by measuring the degree of optical asymmetry orspatial offset, ∆R/r, in the cometary galaxies (and in somecases, also in two-knot or multi-knot sources with cometary-like morphology) from the SDSS images. ∆R is the differ-ence between the position of the brightest star-formation re-gion and the position of the center of the galaxy (estimatedfrom the outer isophote, measured at 25 mag arcsec − ) andr is the radius of the same outer isophote. The results areincluded in Table 3.
6. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content T [ K ] J0126-0038Flux: 5.11 K km/sFlux: 2.66 Jy km/sFlux limit: 0.63 Jy km/s(5-sigma, 50km/s)Base RMS: 17.24 mK1400 1600 1800 2000 2200 2400vlsr (radio) [ m/s]−0.050.000.050.100.150.200.25 T [ K ] J0204-1009Flux: 19.00 K km/sFlux: 9.89 Jy km/sFlux limit: 0.67 Jy km/s(5-sigma, 50km/s)Base RMS: 18.16 mK1600 1800 2000 2200 2400 2600vlsr (radio) [ m/s]−0.050.000.050.100.150.200.25 T [ K ] J0301-0052Flux: 4.11 K km/sFlux: 2.14 Jy km/sFlux limit: 0.65 Jy km/s(5-sigma, 50km/s)Base RMS: 17.73 mK
Fig. 1.
Continued from Fig. 1.
The Max-Planck Institute for Astrophysics–Johns HopkinsUniversity (MPA–JHU) group provides a number of de-rived physical parameters for all galaxies in the SDSS(Kauffmann et al. 2003; Brinchmann et al. 2004). We in-clude in Table 4 the relevant parameters from this database:best-fit spectroscopic redshift, z (heliocentric, optical con-vention; Eq. 2; Sect. 4), velocity offset of the Balmer,∆v Balmer , and forbidden, ∆v forbidden , emission lines, andthe total stellar mass and star-formation rate (SFR). 1 σ errors for the Balmer and fobidden emission-line velocityoffsets, and the stellar masses are also provided in Table 4.The best-fit spectroscopic redshift is measured usingseveral nebular and stellar lines, via a code developed byDavid Schlegel . The resulting radial velocity, v z = c z (he-liocentric, optical convention; Eq.; Sect. 4; Table 5), is ameasurement of the average nebular/stellar component ra- http://spectro.princeton.edu/ dial velocity and shall be designated hereinafter as the best-fit radial velocity.The MPA-JHU group also provides measurements of theBalmer and forbidden emission-line shifts relative to thebest-fit radial velocity, after removing the contribution ofthe stellar component from the spectra, via stellar popula-tion synthesis models. Balmer and forbidden emission-linevelocities (Table 5) have been calculated from the Balmerand forbidden line velocity offsets relative to the best-fitradial velocity.The stellar masses are the median of the distributionof the total mass estimates obtained using SDSS modelphotometry and include a correction for aperture effectsand nebular emission . However, we stress that the stellarmass values are uncertain, as they are obtained by con-verting light into stellar mass via a mass-to-light (M/L)ratio that assumes a constant or exponentially decreas- i Content T [ K ] J0315-0024Flux: 2.50 K km/sFlux: 1.30 Jy km/sFlux limit: 0.63 Jy km/s(5-sigma, 50km/s)Base RMS: 17.09 mK3400 3600 3800 4000 4200 4400vlsr (radio) [km/s]−0.050.000.050.100.150.200.25 T [ K ] J2053+0039Flux: 3.09 K km/sFlux: 1.61 J+ km/sFlux l m t: 0.68 J+ km/s(5-sigma, 50km/s)Base RMS: 18.44 mK800 1000 1200 1400 1600 1800vlsr (radio) [km/s]−0.050.000.050.100.150.200.25 T [ K ] J2104-0035Flux: 2.86 K km/sFlux: 1.49 Jy km/sFlux limit: 0.67 Jy km/s(5-sigma, 50km/s)Base RMS: 18.15 mK
Fig. 1.
Continued from Fig. 1.ing star-formation history. This assumption is, however,not entirely appropriate for BCDs (and therefore also notfor XMPs), since the young starburst component in thesesystems contributes a significant amount to the total B -band luminosity (Papaderos et al. 1996b; also Cair´os etal. 2001; Gil de Paz & Madore 2005; Amor´ın et al. 2007,2009). Consequently, stellar mass determinations based onthe integrated luminosity and a standard M/L ratio areoverestimated by, typically, a factor of 2 (0.3 dex). This,and the strong contribution of nebular (line and contin-uum) emission in most XMPs (e.g., Papaderos et al. 2008;also Papaderos & ¨Ostlin 2012) conspires, along with aper-ture effects, to produce large uncertainties in stellar massdeterminations.In order to have an idea of the potential bias affect-ing the stellar mass estimates, we have also computed thestellar masses in an alternative way, using the correlationsfrom Bell & de Jong (2001). We have adopted the cali-bration obtained by assuming a mass-dependent formationepoch model with bursts, and a scaled-down Salpeter ini- tial mass function (IMF; see their Table 1), using the SDSS g − r colours to estimate the stellar M/L values, and there-fore, the stellar masses. We note, however, that this methodmay also suffer from similar uncertainties as those describedabove, as well as those related to model assumptions.The colour-determined stellar masses are comparedwith the MPA-JHU-determined stellar masses in Fig. 3.There appears to be a break in the one-to-one relationat about log M ⋆ = 7.5 M ⊙ . MPA-JHU stellar masses be-low this value are underestimated according to the color-determined value, whereas stellar masses above this valueare overestimated. The differences between these two meth-ods of stellar mass determation is, however, rarely above1 dex.By default, we use the MPA-JHU-determined stellarmasses in the subsequent analysis. However, we also presentcolor-determined stellar mass results when the outcomemay depend on the stellar mass determination, in orderto have an idea of potential uncertainties.
8. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content T [ K ] J2150+0033Flux: 2.07 K km/sFlux: 1.08 J+ km/sFlux l m t: 0.62 J+ km/s(5-sigma, 50km/s)Base RMS: 16.81 mK1000 1200 1400 1600 1800 2000vlsr (radio) [km/s]/0.050.000.050.100.150.200.25 T [ K ] PHL293BFlu−: 1.27 K km/sFlu−: 0.66 J. km/sFlu− limit: 0.50 J. km/s(5-sigma, 50km/s)Base RMS: 13.68 mK
Fig. 1.
Continued from Fig. 1.
Fig. 3.
The comparison between the MPA-JHU- and color-determined stellar masses. The color code parametrizes themorphology as follows: red = symmetric, black = cometary,blue = two-knot, green = multi-knot and grey = no mor-phological information. The magenta line is the one-to-onerelation.The total SFRs are computed using the nebular emis-sion lines and galaxy photometry . The specific star for-mation rate (sSFR) is the SFR divided by the total stellarmass.
4. Multi-wavelength Analysis
Combining the H i , SDSS and other online data, we deriveglobal galaxy parameters for the XMP galaxies, includingbulk velocities and masses (Table 5).When multiple H i entries are available from literature(12 sources; Table 1), we preferably chose interferometricvalues to provide better constraints on the H i gas param-eters. Sources HS0122+0743, J0133+1342, J1105+6022,J1121+0324, J1201+0211, J1215+5223 and HS1442+4250are documented in Pustilnik & Martin (2008) as belongingto merger systems or as having possible companions. Thismay produce possible H i contamination and consequently(artifically) increase the value of the H i mass.We do not correct the Effelsberg H i line widths(Table 2) for instrumental effects, turbulence, inclinationand redshift stretching; these corrections are estimated tobe small at low redshift (e.g., Springob et al. 2005). Indeed,even if line widths are small and the sources faint (Table 2),the errors in the line widths are dominated by the muchlarger errors generated in the estimation of line widths fromlow signal-to-noise spectra.The Effelsberg H i systemic radial velocities (Table 2)have been converted from the local to the barycentricstandard-of-rest using the coordinates of each galaxy. Thecorresponding velocity corrections range from -30 to 13km s − . The velocities have not been converted from thebarycentric to the heliocentric standard-of-rest, since thiscorrection has a maximum amplitude of 0.012 km s − , muchsmaller than the H i gas velocity and velocity offset errors.We further converted the Effelsberg systemic radial veloci-ties from the radio to the optical convention, according tothe formula:
9. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Table 2.
The H i parameters from our new Effelsberg observations for 29 XMP galaxies in the local Universe.Col. 1: Source name. Col. 2: Right Ascension. Col. 3: Declination. Col. 4: Effective integration time on-source.Col. 5: Systemic local standard-of-rest radial velocity (radio covention). Col. 6: H i line width at 50% of the peakflux density. Col. 7: H i integrated flux density. Col. 8: 5 σ error in integrated flux density. Col. 9: Note on detection.Detections are ≫ σ , non-detections are ≪ σ , marginal detections are > σ and uncertain detections are ∼ σ .Col. 10: Profile of the H i line, single (s)- or double (d)-peaked and symmetric (sym) or asymmetric (asym). Name RA(J2000) DEC(J2000) t v lsrsys w S H i σ Detection Profile h m s ◦ ′ ′′ min km s − km s − Jy km s − Jy km s − (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)J0004+0025 00 04 21.6 +00 25 36 30 . . . . . . . . . 0.7 uncertain . . .J0014-0044 a
00 14 28.8 -00 44 44 30 3915.17 320.07 15.3 0.7 yes d-symJ0015+0104 00 15 20.679 +01 04 36.99 30 2036.79 27.87 1.5 0.6 yes s-asymJ0016+0108 00 16 28.254 +01 08 01.92 60 . . . . . . . . . 0.5 no . . .J0029-0108 00 29 04.73 -01 08 26.3 30 . . . . . . . . . 0.7 uncertain . . .J0029-0025 00 29 49.497 -00 25 39.89 30 . . . . . . . . . 0.8 no . . .J0057-0022 00 57 12.603 -00 21 57.67 30 . . . . . . . . . 0.6 uncertain . . .J0107+0001 01 07 50.817 +00 01 28.42 30 . . . . . . . . . 0.6 no . . .J0113+0052 01 13 40.45 +00 52 39.2 30 1156.22 34.58 5.8 0.7 yes d-asymJ0126-0038 01 26 46.4 -00 38 39 30 1898.32 49.91 2.7 0.6 yes s-asymJ0135-0023 01 35 44.037 -00 23 16.89 30 . . . . . . . . . 0.6 uncertain . . .HKK97L14 02 00 09.9 +28 49 57 30 . . . . . . . . . 0.6 uncertain . . .J0204-1009 02 04 25.55 -10 09 36.0 30 1906 112.04 9.9 0.7 yes d-asymJ0254+0035 02 54 28.94 +00 35 50.4 30 . . . . . . . . . 0.7 no . . .J0301-0059 03 01 26.3 -00 59 26 30 . . . . . . . . . 0.6 no . . .J0301-0052 b
03 01 49.03 -00 52 57.4 30 2107.85 110.2 2.1 0.7 yes s-asymJ0303-0109 03 03 31.3 -01 09 47 30 . . . . . . . . . 0.8 no . . .J0313+0010 03 13 01.57 +00 10 40.3 30 . . . . . . . . . 0.6 no . . .J0315-0024 03 15 59.9 -00 24 26 30 6649.89 91.71 1.3 0.6 marginal s-asymJ0341-0026 03 41 18.1 -00 26 28 30 . . . . . . . . . 0.6 no . . .J2053+0039 20 53 12.597 +00 39 14.25 30 3906.98 52.79 1.6 0.7 yes s-asymJ2104-0035 21 04 55.3 -00 35 22 30 1404.00 52.04 1.5 0.7 yes s-asymJ2105+0032 21 05 08.6 +00 32 23 30 . . . . . . . . . 0.7 no . . .J2120-0058 21 20 25.937 -00 58 26.53 30 . . . . . . . . . 0.6 uncertain . . .J2150+0033 21 50 31.957 +00 33 05.07 30 4382.42 64.45 1.1 0.6 marginal s-symPHL293B 22 30 36.8 -00 06 37 60 1590.99 44.84 0.7 0.5 marginal s-asymJ2238+1400 22 38 31.1 +14 00 29 30 . . . . . . . . . 0.5 no . . .J2259+1413 22 59 00.86 +14 13 43.5 30 . . . . . . . . . 0.6 no . . .J2302+0049 23 02 10.0 +00 49 39 30 . . . . . . . . . 0.6 no . . . a The H i line is dominated by the H i gas in the nearby spiral galaxy UGC 139 (Sect. 2.2.2). b Baseline problems. v opt = v rad − v rad /c , (2)where v opt is the systemic radial velocity in the optical con-vention, v rad is the systemic radial velocity in the radioconvention and c is the speed of light. The difference be-tween the radio and optical convention stems from the useof the frequency (radio) or the wavelength (optical) to inferthe line shifts.The H i velocity offset, ∆v H i , has been defined as thedisplacement of the H i systemic radial velocity (heliocen-tric, optical convention; Tables 1 and 2) with respect to thebest-fit radial velocity, v z (heliocentric, optical convention;Sect. 3.3 and Table 4). The error in the H i velocity offsetcontains the corresponding error in the H i systemic radialvelocity (Tables 1 and 2) and a 1 km s − error in the best-fit radial velocity determination. When the former is notavailable, we adopt a value of 5 km s − for the H i systemicradial velocity error.In order to compute dynamical masses, we require H i galaxy sizes. From the H i (Table 1) and optical (Table 3)radii, we estimate that, on average, the H i -to-optical size ratio ∼ H i = 3 × r opt .The dynamical mass, defined as the total baryonic plusnon-baryonic mass contained within a certain radius, is es-timated assuming a spherical system in dynamical equilib-rium. We have determined the dynamical mass using theformula : M dyn M ⊙ = 2 . × (cid:16) w (cid:17) r H i , (3)where w is the (uncorrected) H i line width in km s − (Tables 1 and 2) and r H i is the H i radius in kpc (see above).We stress that the dynamical mass calculated in this waymay be an underestimation, since the H i radius may notinclude the full extent of the galaxy.The H i mass estimate assumes the neutral atomic gasmass to be optically thin (Wild 1952). The formula forderiving the H i mass is: i Content
Fig. 2.
SDSS images illustrating our optical morphology classification scheme: J1003+4504 (top left) showing symmetric,J0119-0935 (top right) showing cometary, J1151-0222 (also known as UM 461; bottom left) showing two-knot, and HS0122+0743 (bottom right) showing multi-knot optical morphology.M H i M ⊙ = 2 . × D S H i , (4)where S H i is the integrated flux density in Jy km s − (Tables 1 and 2) and D is the Virgocentric infall-correctedHubble flow distance in Mpc (Table 5).The dark matter mass has been estimated as:M DM = M dyn − M ⋆ − M H i − M He , (5)where M He , the helium mass, is 0.34 × M H i , the value typ-ical for standard Big Bang nucleosynthesis (Alpher et al.1948; Coc et al. 2012).The error determination in the dynamical mass includesa 20% error in r H i and the corresponding error in the linewidth (Table 1). When the latter is not available, we haveadopted a conservative error of 5 km s − . For the H i gasmass, the error was estimated assuming a conservative errorin integrated flux density (10%; Sect. 2.2.2) and the errorin the Virgocentric infall-corrected Hubble flow distance, asprovided by NED. In the few cases when the latter is notavailable, we have attributed a conservative distance errorof 10%. The helium mass error determination follows fromthe propogation of the error in H i gas mass. We adoptthe 1 σ stellar mass errors (Sect. 3.3 and Table 4) which,typically, are of the order of 0.5 dex (Fig. 3). For the dark matter mass, the final error estimation includes the errorin dynamical, H i gas, helium and stellar mass.All quoted velocities are in the heliocentric standard-of-rest and in the optical convention. Correlations found inliterature for absolute B -band magnitudes have been con-verted to absolute g -band magnitudes using the standardSDSS conversion factors (e.g., Jester et al. 2005).Unless otherwise explicitly stated, metallicities refer toH ii gas-phase metallicities (Table 3).We call attention to the six sources with the lowest g -band luminosity – UGC2684, DD053, LeoA, SextansB,UGCA292 and GR8. These are all nearby (D <
5. Results
In this section, and in Fig. 4 – 12, we present the proper-ties of the XMP galaxy class, particularly the H i content.All plots use a common color code to parametrize the mor-phology. The morphological color code is red for symmetric,black for cometary, blue for two-knot, green for multi-knotand grey for sources with no morphological information.
11. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content H i Line Profile – Optical Morphology Relation
If we include the three marginal detections (and excludeJ0014-0044), H i Effelsberg integrated flux densities rangefrom 1 to 15 Jy km s − and (uncorrected) line widths rangefrom 20 to 120 km s − (Sect. 2.2 and Table 2). The lineprofile shapes are varied (Fig. 1 and Table 2) – two sourcesshow asymmetric double-horn profiles, one source shows asymmetric single-peak profile and the remaining seven haveasymmetric single-peak profiles. Double-horn profiles aretypical of disk rotation, while single-peak profiles may arisefrom non-rotation, face-on disk rotation or preponderanceof random motions (relative to ordered motions) in the gas.An asymmetry in the line profile suggests an asymmetry inthe kinematics or possible companions (Fig. 1, Tables 2 and3). We have excluded the latter hypothesis in the case of theEffelsberg observations (Sect. 2.2.2). In the two double-hornsources, the highest intensity and/or widest peak occurs onthe (spectral) blue side (Fig. 1).The optical morphology of the Effelsberg targets showsthe varied nature of the optical structures (Fig. 1 andTable 3) and an association with the H i line pro-file (Table 2). The two asymmetric double-horn profilesources show cometary or multiple star-formation knotsin the SDSS images. The remaining asymmetric single-peak sources are cometary (five sources), multi-knot (onesource) or two-knot (one source), while the only single-peaksymmetric source has a symmetric optical morphology. Wefind that an asymmetry in the H i kinematics, as suggestedby the H i line shape, is systematically associated with anasymmetry in the optical morphology. Figure 4 contains the relation between the mass of the dif-ferent XMP galaxy constituents and the absolute g -bandmagnitude.Though the scatter is large, a trend is observed betweenthe (dynamical, H i and stellar) mass and the luminosity, re-flecting that the more massive galaxies are more luminous.The largest deviations occur at low luminosities, in thelow-surface brightness, nearby galaxies UGC2684, DD053,LeoA, SextansB, UGCA292 and GR8. At a given stellarmass, these galaxies are significantly offset to lower lumi-nosities compared with most XMPs. The XMP (H ii gas-phase) metallicity and absolute g -bandmagnitude are plotted as a function of the stellar (M ⋆ /L g )and the H i gas (M H i /L g ) M/L ( g -band) ratio in Fig. 5,where we have excluded the dynamical M/L ratio for clar-ity. The M H i /L g and M ⋆ /L g ratios measured for the XMPsare typically .
10 and ∼ H i /L g >
10. The estimatedM ⋆ /L g ratios likely reflect the M/L ratios of the galaxy tem-plates used as input in the photometry fitting-based stellarmass determinations (Sect. 3.3). Papaderos et al. (1996b)have determined the average M/L ratio of the star-formingcomponent in BCDs to be ∼ Fig. 4.
The mass – luminosity relation of the XMP galaxies.The color code parametrizes the morphology as follows: red= symmetric, black = cometary, blue = two-knot, green =multi-knot and grey = no morphological information. Top:the symbol code is (cid:3) = M dyn and × = M ⋆ . Bottom: thesymbol code is • = M H i and △ = M He .& Madore 2005; Amor´ın et al. 2007, 2009). We recall thatnearby XMPs are commonly found to be BCDs (Sect. 1).These values can be compared to the typical stellar M/Lratios observed in star-forming galaxies ( <
1; cyan line; top;Fig. 5), spirals (4 – 6; magenta line; top; Fig. 5), lenticulars( ∼
10; cyan dashed line; top; Fig. 5), dwarf irregulars (10 –15; orange dashed line; top; Fig. 5) and elliptical ( ∼
20; ma-genta dashed line; top; Fig. 5) galaxies (Faber & Gallagher1979).Regarding the absolute g -band magnitude versus theM H i /L g ratio (bottom; Fig. 5), we confirm previous pub-lished results found for a sample of dwarfs (cyan line;bottom; Fig. 5; Staveley-Smith, Davies & Kinman 1992).We find an anti-correlation between the M H i /L g ratio andthe luminosity, whereby fainter XMPs are more gas-richthan brighter XMPs. The result suggests that the less lu-minous sources have converted a smaller fraction of theirH i gas into stars. However, our sources deviate from theobserved correlation found for dwarf galaxies (cyan line;bottom; Fig. 5; Staveley-Smith, Davies & Kinman 1992)particularly at low luminosities, which correspond to thelow-surface brightness, nearby galaxies UGC2684, DD053,LeoA, SextansB, UGCA292 and GR8. In this low luminos-
12. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Fig. 5.
The H ii gas-phase metallicity and g -band magni-tude of the XMP galaxies as a function of the stellar and H i gas M/L ratio. The color code parametrizes the morphol-ogy as follows: red = symmetric, black = cometary, blue= two-knot, green = multi-knot and grey = no morpholog-ical information. The symbol code is • = M H i /L g and × = M ⋆ /L g . Top: the plot includes a range of stellar mass-to-light ratios found in spirals (magenta line), lenticulares(cyan dashed line), dwarf irregulars (orange dashed line)and ellipticals (magenta dashed line), an upper limit foundin star-forming (cyan line) galaxies (Faber & Gallagher1979) and an average value (orange line) found for BCDs(Papaderos et al 1996a). Bottom: we plot in cyan the H i gasM/L ratio-to-luminosity correlation found for dwarf galax-ies (Staveley-Smith, Davies & Kinman 1992).ity regime, the XMP galaxies appear to be 10 to 100 timesmore gas-rich than typical dwarf galaxies. Figures 6 and 7 show the relation between the mass andthe mass fraction of the different XMP galaxy constituents.In the figures, we mark the one-to-one (magenta line; top;Fig. 6; Fig. 7) and 0.1 × Mass (cyan line; top; Fig. 6) rela-tion for reference. We recall that the dynamical mass esti-mation is a lower limit (Eq. 3; Sect. 4) and that the darkmatter content is the fraction of dynamical mass which isnot stellar, H i or helium mass (Eq. 4; Sect. 4). In 12 of thesources with H i and dynamical mass determinations, M H i > M dyn by less than 0.5 dex (top; Fig. 6); these sourcesshall be excluded from the following discussion.Typically, the stellar component constitutes less than5% of the total (baryonic and non-baryonic) mass in theXMP systems (middle; Fig. 6). The H i gas mass fraction,relative to the dynamical mass, falls typically between 20and 60% (middle and bottom; Fig. 6), higher than the val-ues found in late-type systems (4 – 25%; Young & Scoville1991). Moreover, the H i gas mass is 10 to 20 times largerthan the stellar mass (middle; Fig. 6; Fig. 7), denoting thatXMPs are extremely gas-rich. As expected, this ratio de-pends on the stellar mass estimate. If we use the color-determined stellar masses (Sect. 3.3 and Fig.3), the H i -to-stellar mass ratios fall, typically, to about 5 – 10 (Fig. 7),which are still large values. As a comparison, H i gas-to-stellar mass ratios in excess of 100 are observed in some ofthe lowest metallicity BCDs (Pustilnik et al. 2001), whileratios of less than 4 are commonly observed in spirals andirregulars (Swaters 1999; Dalcanton 2007).Although our statistics are poor (16 sources), the val-ues for the putative dark matter content in XMPs show awide range, with a peak at 65% of the dynamical mass, andskewed to higher values (bottom; Fig. 6). These latter esti-mates are typically larger than those observed in the innerparts of spirals (10 – 15%; magenta dashed line; bottom;Fig. 6) and elliptical (30 – 50%; cyan dashed line; bottom;Fig. 6) galaxies (Swaters 1999; Borriello, Salucci & Danese2003; Cappellari et al. 2006; Thomas et al. 2007; Williamset al. 2009). Supernova-driven outflows or accretion of external gas maybe partially responsible for the observed low metallicitiesin XMP galaxies (e.g. Kunth & ¨Ostlin 2000) and in low-metallicity starbursts (Amor´ın, P´erez-Montero & V´ılchez2010; Amor´ın et al. 2012a). In a closed box model (no in-flow or outflow), as the gas is converted into stars, the gasmass fraction decreases and the gas metallicity increases.Deviations from this model, signaling outflow or inflow, areinvestigated using the effective yield (e.g., Dalcanton 2007):y eff = Z gas ln(1 / f gas ) , (6)where Z gas is the fraction of the gas mass in metals andf gas is the gas mass fraction, defined as the H i , helium andmetal mass divided by the total (H i , helium, stellar andmetal) mass.For a galaxy that evolves as a closed box, the effec-tive yield must coincide with the theoretical yield, y, de-rived from stellar evolution models (e.g., Edmunds 1990).Therefore, differences between y and y eff provide a directtool to diagnose gas inflows and outflows.Figure 8 (top) shows the effective yields of the XMPs asa function of the gas fraction (as defined above), for MPA-JHU- and color-determined stellar masses (Sect. 3.3 andFig. 3). The yields were computed assuming the metallicityfrom the optical emission lines (Table 3) to be the metal-licity of the H i gas, i.e., Z gas ≃ × O/H (e.g., Pilyugin,V´ılchez & Contini 2004). Figure 8 (top) also shows, for ref-erence, the effective yields for the set of spirals and dwarfirregular galaxies compiled by Pilyugin, V´ılchez & Contini(2004). The gas fraction from Pilyugin, V´ılchez & Contini
13. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Fig. 6.
The mass fraction of the various XMP galaxy con-stituents. Top: the color code parametrizes the morphol-ogy as follows: red = symmetric, black = cometary, blue =two-knot, green = multi-knot and grey = no morphologicalinformation. The symbol code is (cid:3) = M DM , • = M H i , △ =M He and × = M ⋆ . The magenta and cyan line are, respec-tively, the one-to-one and 0.1 × Mass relation. Middle: thedistribution of the mass fractions relative to the dynamicalor H i mass. The color code is blue = M H i M dyn , red = M ⋆ M dyn andgreen = M ⋆ M H i . Bottom: the distribution of the dark matterand H i mass fractions relative to the dynamical mass, inpercentage. The color code is blue = M H i M dyn and red = M DM M dyn .The magenta and cyan dashed lines are, respectively, therange for dark matter mass fractions in spiral and ellipticalgalaxies. Fig. 7.
The H i -to-stellar mass relation of the XMP galax-ies. The color code parametrizes the morphology as follows:red = symmetric, black = cometary, blue = two-knot, green= multi-knot and grey = no morphological information.The symbol code is • = MPA-JHU-determined stellar massvalues and ◦ = color-determined stellar mass values. Themagenta line is the one-to-one relation.(2004) includes molecular hydrogen, but its contribution isnegligible.The theoretical oxygen yield is log y ≃ -2.4 (magentaline; top; Fig. 8; Dalcanton et al. 2007; Meynet & Maeder2002), which coincides with the average effective yield ofthe gas-poor galaxies in the reference set, as is expectedto happen in chemical evolution models, when the gasis exhausted (K¨oppen & Hensler 2005; Dalcanton 2007).However, many XMPs have yields which largely exceedthe theoretical limit. There are two ways in which this ex-cess could be explained. Either the theoretical yield of ourXMPs is significantly larger than that of regular spirals,or the metallicity of the H i gas is much lower than themetallicity of the ionized H ii gas.Regarding the former explanation, a dependence of theIMF on the metallicity may play a role (e.g., Bromm &Larson 2004). In particular, a top-heavy IMF will increasethe oxygen yields by significant amounts (e.g., Meynet &Maeder 2002). The second possibility, which we explain be-low, is the extremely low metallicity of the H i gas, thatmust be much lower than the already low metallicity mea-sured in the H ii regions of the XMPs.When the gas mass fraction is large, as is the case inXMPs, one can easily show the effective yield to be theratio between the mass of metals in the gas, Z gas M gas , andthe stellar mass: y eff ≃ Z gas M gas M ⋆ , (7)where M gas stands for the mass of the gas. This expres-sion shows how difficult it is to increase the effective yieldbeyond the theoretical yield because, taken at face value,y eff > y implies creating more metals than those allowedby the stellar evolution that produced the mass in stars.However, if the gas metallicity has been overestimated bya significant amount, this would artificially increase the ef-fective yields (Eq. 7). In other words, the large effectiveyields that we infer may be easily explained if the H i gas
14. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content is mostly pristine (Thuan, Lecavelier des Etangs & Izotov2005), with a metallicity much lower than the already lowmetallicity measured in the gas forming stars at present(H ii gas-phase metallicity; Table 3).As a sanity check, we have also computed y eff using thecolor-determined stellar masses (Sect. 3.3 and Fig. 3; top;Fig. 8). Equation 6 shows how an increase in stellar massdecreases y eff . However, it does not suffice to explain theobserved y eff > y, in most cases.The H i gas metallicity reproducing both the theory andobservations can be estimated assuming that the mass ofmetals in the H i gas coincides with the mass of metalsproduced by the stars, i.e., y = Z gas M gas /M ⋆ . The ratiobetween the effective yield and the true yield is then givenby the ratio between the metallicity measured in the H ii regions, Z H ii , used to compute y eff , and the true H i gasmetallicity, Z H i (bottom; Fig. 8). Explicitly:Z H ii / Z H i ≃ y eff / y . (8)The results show that the ratio Z H ii / Z H i falls, typically,between 1 and 10 (bottom; Fig. 8). This is in agreementwith the findings of Lebouteiller et al. (2013) on the metal-licity of the H i gas in the XMP prototype, IZw18. The H i region abundances were found to be lower by a factor of ∼ ii regions, and it may contain pocketsof pristine gas, with an essentially null metallicity. The mass – metallicity relation, or equivalently the lu-minosity – metallicity relation (for similar M/L ratios;Lequeux et al. 1979), reflects the fundamental role thatthe mass plays in galaxy chemical evolution. We recall thatthe metallicity pertains to the H ii gas-phase metallicity(Table 3).Besides the mass – metallicity relation for the XMPs,Fig. 9 (top) includes the empirical relations for extremestarburst galaxies called green peas (magenta line; top;Fig. 9; Amor´ın, P´erez-Montero & V´ıchez 2010) and for ex-tremely metal-poor BCDs (cyan line; top; Fig. 9; Papaderoset al. 2008). The latter is determined from the luminosity ofthe underlying host, after the subtraction of the starburstcontamination using surface photometric techniques, andtherefore, refers to the stellar mass.The XMP galaxies show a large scatter in the mass –luminosity relation, with a significant fraction of the stel-lar mass points falling to the left of the correlations (top;Fig. 9). This is similar to what is found in more distant low-metallicity galaxies (e.g. z > Fig. 8.
The effective yield and the H ii -to-H i metallicityratio of the XMP galaxies as a function of the gas massfraction. The color code parametrizes the morphology asfollows: red = symmetric, black = cometary, blue = two-knot, green = multi-knot and grey = no morphological in-formation. Top: the symbol code is • = XMPs with MPA-JHU-determined stellar masses, ◦ = XMPs with color-determined stellar masses, (cid:3) = spiral and N = irregulargalaxies. The spiral and irregular galaxy data were ob-tained from Pilyugin, V´ılchez & Contini (2004). The ma-genta line represents the theoretical yield limit for a closed-box model. Bottom: the symbol code is • = XMPs withMPA-JHU-determined stellar masses and ◦ = XMPs withcolor-determined stellar masses.metal-poor for their luminosity. The largest deviations fromthe correlation occur at low luminosities, correspondingto the low-surface brightness, nearby galaxies UGC2684,DD053, LeoA, SextansB, UGCA292 and GR8. In this lowluminosity regime, the inverse situation occurs; the XMPsare underluminous for their metallicity. The Tully – Fisher (TF) relation (Tully & Fisher 1977) isan empirical correlation found for spiral galaxies, reflectingthe fact that the bigger or brighter the galaxy, the fasterit rotates. Indeed, all galaxies are found to follow the samebaryonic mass – TF relation, including low-surface bright-
15. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Fig. 9.
The mass – and luminosity – H ii gas-phasemetallicity relation of the XMP galaxies. The color codeparametrizes the morphology as follows: red = symmetric,black = cometary, blue = two-knot, green = multi-knotand grey = no morphological information. Top: the sym-bol code is (cid:3) = M dyn , • = M H i and × = M ⋆ . The fig-ure includes the empirical correlation established for BCDsby Papaderos (2008; cyan line) and for green pea starburstgalaxies (magenta line; Amor´ın, P´erez-Montero & V´ılchez2010). Bottom: the figure shows the luminosity – metallic-ity relation found for a sample of dwarf irregular galaxies(magenta line; Skillman, Kennicutt & Hodge 1989) and fora sample of SDSS star-forming galaxies (cyan line; Gusevaet al. 2009).ness (LSB) galaxies, that contain a large amount of H i gas(e.g., van de Kruit & Freeman 2011).As pointed out in Kannappan et al. (2002), the disper-sion in the TF relation, particularly regarding the dwarfgalaxy population, is mainly related to recent perturba-tions in their evolution, which is consistent with Kassin etal. (2007) and de Rossi, Tissera & Pedrosa (2012), whoargue that the dispersion and residuals correlate with themorphology and kinematical indicators.Figure 10 (top) contains the luminosity – TF relation forthe XMPs, together with the empirical relation found forearly- and late-type dwarf and giant galaxies (cyan and ma-genta line, respectively; top; Fig. 10; de Rijcke et al. 2007)and their 1 σ errors (cyan and magenta dashed line, respec-tively; top; Fig. 10; de Rijcke et al. 2007), extrapolated to fainter and slower rotating galaxies. We note that the 1 σ lower limit for the late-type dwarf and giant luminosity –TF relation (magenta dashed line; top; Fig. 10; de Rijckeet al. 2007) falls almost on top of the early-type dwarf andgiant luminosity – TF relation (cyan line; top; Fig. 10; deRijcke et al. 2007). We have converted the circular velocityused in de Rijcke et al. (2007) to w , assuming a Gaussianshape for the line profile, such that v circ = 1.52 × w /2(e.g., Gurovich et al. 2010).The majority of the XMP galaxies follow the luminos-ity – TF relation (top; Fig. 10) within 1 σ , with a widespread in luminosity. However, differences are particularlylarge in the lowest luminosity targets, which correspondto the low-surface brightness, nearby galaxies UGC2684,DD053, LeoA, SextansB, UGCA292 and GR8. Indeed, for agiven stellar luminosity, the line widths are too broad com-pared to late- and early-type giant and dwarf galaxies. Inthese sources, the main support against gravity comes fromrandom motions rather than from rotation (e.g., Carignan,Beaulieu & Freeman 1990).Figure 10 (bottom) contains the mass – TF relationfor the XMPs, together with the mass – TF relation forthe dwarf and giant early- and late-type galaxy samples byde Rijcke et al. (2007), in terms of stellar mass (magentaline; bottom; Fig. 10) and gas plus stellar (baryonic) mass(cyan line; bottom; Fig. 10), and their 1 σ errors (magentaand cyan dashed line, respectively; bottom; Fig. 10), ex-trapolated to lower masses and line widths. We define thebaryonic mass, M baryon , as the total stellar, H i and heliummass.The stellar mass points fall generally below the (stel-lar) correlation, with a large scatter. The majority of thesepoints are not within 1 σ of the (stellar) correlation; theirstellar masses are unusually low for their potential wells.This is comparable to what has been observed for BCDs(Amor´ın et al. 2009). In simulations performed by de Rossi,Tissera & Pedrosa (2010), it is shown that the tendency forslowly rotating galaxies (low-mass systems) to lie below thestellar mass – TF relation can be explained by the actionof supernova feedback and stellar winds.The XMPs do follow the baryonic mass – TF relation; acorrelation is present between the line width and the H i gasand the baryonic mass, as expected for extremely gas-richgalaxies (e.g., McGaugh et al. 2000; Gurovich et al. 2010).These results suggest that the H i gas is largely virializedand may be partially rotationally supported. In Fig. 11 we investigate the presence of velocity differ-ences (offsets) between the H i gas, Balmer emission linesand forbidden emission lines, measured relative to the best-fit radial velocity (Sect. 3.3 and Tables 4 and 5). We plotonly non-zero velocity offsets. Balmer line, forbidden lineand H i velocity offsets are only considered reliable if theoffset is larger than 3 times the respective error (Table 4).The error in the H i gas offset is dominated by the error inthe systemic velocity estimation, which is typically 5 kms − . However, H i offsets lower than the intrinsic H i gas ve-locity dispersion in a dwarf galaxy (typically ∼
10 km s − )were considered unreliable. Best-fit (spectroscopic) redshifterrors for these sources are quite low (e.g. Maddox et al.2013), resulting in best-fit radial velocity errors of about 1km s − . Furthermore, because of the typical velocity disper-
16. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Fig. 10.
The luminosity and mass – TF relation of theXMP galaxies. The color code parametrizes the morphol-ogy as follows: red = symmetric, black = cometary, blue =two-knot, green = multi-knot and grey = no morphologi-cal information. Top: the figure contains the luminosity –TF relation found for early-type (cyan line; de Rijcke et al.2007) and late-type (magenta line; de Rijcke et al. 2007)dwarf and giant galaxies and 1 σ errors (cyan and magentadashed line, respectively; de Rijcke et al. 2007). We notethat the 1 σ lower limit for the late-type dwarf and giantluminosity – TF relation (magenta dashed line; de Rijckeet al. 2007) falls almost on top of the early-type dwarf andgiant luminosity – TF relation (cyan line; de Rijcke et al.2007). Bottom: the symbol code is (cid:3) = M baryon , • = M H i and × = M ⋆ . The magenta and cyan lines show the mass –TF correlation for a sample of dwarf and giant early- andlate-type galaxies (de Rijcke et al. 2007), in terms of stellarmass and H i gas plus stellar mass, respectively, and their1 σ errors (magenta and cyan dashed line, respectively; deRijcke et al. 2007).sion of the warm gas (20 – 30 km s − ), we have disregardedBalmer and forbidden line offsets below 10 km s − .The majority (80 – 90%) of the XMPs with measuredBalmer and forbidden emission-line velocities show no shift(Table 4). However, in 60% of the sources with H i gas andoptical data, we find a small offset (10 – 40 km s − ) betweenthe systemic velocity of the H i gas and the best-fit radialvelocity (top; Fig. 11; Table 5; e.g. Maddox et al. 2013). Wehave verified the SDSS DR9 images to find that the major- ity of these sources are cometary or knotted (Table 3) andthat the SDSS fiber position for the spectra is generally lo-cated at the head or at the brightest star-forming knot, notat the center of the XMP system. We recall that the spatialoffset we defined (Sect. 3.2 and Table 3) is a measurementof this displacement. Therefore, this could, in principle, ex-plain the small velocity offsets observed between the H i gasand the nebular/stellar emission. However, we find no ev-idence for a correlation between the spatial offset and theH i gas velocity offset (bottom; Fig. 11). The result suggeststhat the H i gas and the nebular/stellar component are nottightly coupled in these XMPs.In the three XMP sources where the H i gas, Balmerline or forbidden line offsets are larger ( >
50 km s − ), wesearched the SDSS DR9 and radio continuum (NVSS andFIRST; Condon et al. 1998; Becker, White & Helfand 1995)fields (6 ′ radius) for potential galaxy contaminants. We dis-cuss these below. • J0301-0052 – This cometary XMP (Table 3) hasbeen observed with Effelsberg (Table 2) and shows a largeH i gas offset ( ∼
100 km s − ; Table 5). We had previouslydiscarded H i contamination (Sect. 2.2.2) by checking theSDSS spectroscopic or photometric redshifts of the neigh-bours and found no sources within 200 km s − of the target.In addition, the nearest radio continuum source (NVSS)present in the field is about 1 ′ away and has a flux of3.2 mJy. The SDSS has classified this source as a starburstat a redshift of 0.0073 (Table 4). Indeed, the SDSS spectraof the source shows narrow emission lines, with weak [O i ]and [S ii ], typical of a star-forming galaxy. This is consistentwith the observed [N ii ] λ α and [O iii ] λ β ratios and their location on the so-called BPT diagram (af-ter Baldwin, Phillips & Terlevich 1981). The fact that theSDSS spectra has been taken at the head of the cometarystructure could explain the large velocity displacement rel-ative to the H i gas. • SDSSJ1025+1402 – This red symmetric (Table 3)source shows Balmer and forbidden line offsets in excess of60 km s − (Table 4). The neighbouring sources in the SDSSfield show typically lower redshifts, which discards possibleH i contamination, and the nearest radio continuum source(NVSS) lies 5 ′ away. The SDSS classifies this source as abroad-line quasar at a redshift of 0.1004 (Table 4). The[N ii ] λ α and [O iii ] λ β ratios put thissource in the realm of star-forming galaxies in the BPTdiagram. However, the red color, broad H α line, large red-shift and large instrinsic luminosity indicate that the sourcemay host an Active Galactic Nuclei (AGN; Izotov, Thuan& Guseva 2007). The interaction of the AGN jet with theNarrow Line Region (NLR) may explain the Balmer andforbidden line offsets. • J1644+2734 – This disk-like symmetric (Table 3)source shows a large forbidden line offset (-140 km s − ;Table 4). Sources in the SDSS field show higher radial ve-locities, which discards possible H i contamination, and thenearest radio continnum source (NVSS) is at a distance of3 ′ . The SDSS classifies this source as a quasar at a redshiftof 0.0232 (Table 4). The [N ii ] λ α and [O iii ] λ β ratios put this source in the realm of compositegalaxies in the BPT diagram. The disk-like morphology,associated with the presence of broad H α emission indicatethat the source may host an AGN (Izotov, Thuan & Guseva2007). The large forbidden line offset may be the result of
17. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Fig. 11.
The velocity offset of the XMP galaxies as a func-tion of the best-fit radial velocity and spatial offset. TheH i , Balmer emission-line and forbidden emission-line ve-locity offsets, ∆v H i , ∆v Balmer and ∆v forbidden , respectively,are the displacements of the H i systemic radial velocity,Balmer lines and forbidden lines with respect to the best-fitradial velocity, v z (Sect. 3.3 and Table 5). Only non-zerovalues are plotted. The color code parametrizes the mor-phology as follows: red = symmetric, black = cometary,blue = two-knot, green = multi-knot and grey = no mor-phological information. The symbol code is • = ∆v H i , (cid:3) = ∆v forbidden and △ = ∆v Balmer . The magenta line definesthe null velocity offset.cloud motion in the NLR, as a result of the interaction withthe AGN jet.See Izotov, Thuan & Guseva (2007) for a discussionon the presence of broad-line emission and AGN in XMPgalaxies.
6. Complementary Results From Optical Data
Our optical morphological classification scheme (Sect. 3.2;Table 3; Fig. 1 and 2) has yielded 27 symmetric, 60cometary, 11 two-knot and 18 multi-knot galaxies. Of the116 out of 140 sources with SDSS DR9 information, ∼ i and stellar masses, (H i gas andstellar) mass fractions and (H i gas and stellar) mass-to-light ratios, faintest/brightest magnitudes and the narrow-est/widest line widths of the XMP galaxies. Figure 12 contains the SFR and sSFR as a function of thestellar mass.The XMP SFRs (top; Fig. 12), which measure the globalstar-formation rate, are similar to those typically observedin BCDs (log SFR ∼ -3.6 – 0.4, for log M ⋆ = 6 – 10 M ⊙ ;S´anchez Almeida et al. 2009). However, more luminousBCDs can show SFRs up to 60 M ⊙ yr − and sSFRs upto 10 − yr − (Cardamone et al. 2009; Amor´ın et al. 2012b;also Izotov, Guseva & Thuan 2011). The XMPs SFR valuesare lower than the range of SFRs that are typically observedin the disks of large spiral galaxies ( <
20 M ⊙ yr − ; magentaline; top; Fig. 12; Kennicutt 1998). Given the positive cor-relation between the SFR and the stellar mass (top; Fig.12), this is expected, given the low masses of the XMPs.Regarding the sSFR (bottom; Fig. 12), we observe awide range of values. We find some high sSFRs comparedto local SDSS samples (Tremonti et al. 2004; also Peeples,Pogge & Stanek 2008, 2009). The timescale to double theirstellar mass, at the present SFR, 1/sSFR, is typically lowerthan 1 Gyr, smaller than the age of the galaxies, if we as-sume that they are about the age of the Universe ( ∼
14 Gyr;e.g., Caon et al. 2005; Amor´ın et al. 2007). This implies thatXMPs are now undergoing a major starburst episode, whichcan not be sustained for very long.
7. Conclusions
We have investigated the H i content of local XMP galax-ies as a class, using the 140 sources compiled by ML11.These sources were selected either as showing negliglible[N ii ] lines in the SDSS DR7 (Abazajian et al. 2009) spec-tra, or H ii gas-phase metallicities smaller than a tenth thesolar value.53 of these galaxies have published H i data, providingintegrated flux densities and line widths in the range 0.1 –200 Jy km s − and 15 – 150 km s − , respectively (Sect. 2.1and Table 1). We have also obtained new Effelsberg obser-vations for 29 sources with no published 21 cm data, yield-ing 10 new detections (Sect. 2.2 and Table 2). Effelsberg in-tegrated flux densities are in the range 1 – 15 Jy km s − andline widths cover a wide spectrum (20 – 120 km s − ). TheEffelsberg line profiles are varied; one source shows a sym-metric single-peak profile, seven show skewed single-peakprofiles, demonstrating an asymmetry in the kinematics ofthe H i gas, and two show asymmetric double-horn profiles(Fig. 1 and Table 2). Combining the optical morphologywith the H i line profile shapes (Fig.1, Tables 2 and 3), wefind that the double-horn sources are associated with multi-knot or cometary optical morphology. Single-peak asym-metric profiles are associated with either cometary, two-knot or multi-knot morphology, while the single-peak sym-metric profile is associated with a symmetric source. We
18. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Fig. 12.
The SFR and sSFR of the XMP galaxies as a func-tion of stellar mass. The color code parametrizes the mor-phology as follows: red = symmetric, black = cometary,blue = two-knot, green = multi-knot and grey = no mor-phological information. Top: the magenta line provides theupper limit to the SFRs typically observed in the disks oflocal spiral galaxies.conclude that an asymmetry in the H i gas line profile issystematically associated with an asymmetry in the opticalmorphology (Sect. 5.1 and Fig. 1).When the new Effelsberg and literature data are takentogether, typically, the estimated dynamical, H i and stellarmasses are in the range 10 . − . , 10 . − . and 10 − M ⊙ ,respectively (Sect. 5, Fig. 6 and Table 5). H i gas-to-stellarmass ratios are about 10 – 20 (Sect. 5.4, Fig. 6 and 7). Wefind that brighter XMPs have converted a larger fraction oftheir H i gas into stars (Sect. 5.3 and Fig. 5). Moreover,M ⋆ /L g ratios are found to be on average 0.1, whereasM H i /L g ratios may be up to 100 times larger (Sect. 5.3 andFig. 5). Therefore, we conclude that local XMP galaxies areextremely gas-rich. The H i gas and stellar mass constitute20 – 60% and <
5% of the dynamical mass, respectively(Sect. 5.4 and Fig. 6). Furthermore, dark matter mass con-tent (Sect. 5.4 and Fig. 6) spans a wide range of values forXMP systems, but in some cases it accounts for over 65% ofthe dynamical mass, higher than the values determined forspirals and ellipticals (10 – 50%; Swaters 1999; Borriello,Salucci & Danese 2003; Cappellari et al. 2006; Thomas etal. 2007; Williams et al. 2009). The global SFRs (Sect. 6.2, Table 4 and Fig. 12) inXMPs are found to similar to those found in typical BCDs(S´anchez Almeida et al. 2009). The apparent low SFRs aredue to the lower stellar masses of the XMPs, because thesSFRs (SFR per unit mass) are high and are, on average,higher than those observed for local galaxies (Tremonti etal. 2004), with timescales to double their stellar mass, atthe current rate, of typically less than 1 Gyr.XMPs are found to fall off of the mass – and luminos-ity – metallicity relations (Sect. 5.6 and Fig. 9) found forBCDs (Papaderos et al. 2008), extreme starburst galax-ies (Amor´ın, P´erez-Montero & V´ılchez 2010), SDSS star-forming galaxies (Guseva et al. 2009) and dwarf irregulars(Skillman, Kennicutt & Hodge 1989), signaling the presenceof pristine material. XMPs generally uphold the baryonicmass – and luminosity – TF relation (Sect. 5.7 and Fig. 10)found for samples of late- and early-type dwarf and giantgalaxies (de Rijcke et al. 2007). The results suggest that theH i gas is partly virialized and may contain some rotationalsupport. However, for the lowest luminosity XMPs, most ofthe gravitational support comes from random motions.The effective yield of oxygen in XMPs is often largerthan the theoretical yield (Sect. 5.5 and Fig. 8). This is un-usual and suggests that either the theoretical yields areunderestimating the production of oxygen in these low-metallicity environments, or the H i gas metallicity is 0.1 – 1times that measured in the H ii regions. This second possi-bility is in agreement with the recent work of Leboutellier etal. (2013) on the metallicity of the H i gas of the XMP pro-totype, IZw18 (also Thuan, Lecavelier des Etangs & Izotov2005).We have also completed and/or revised the optical mor-phological classification presented in ML11, bringing up to83% the percentage of classified sources (Sect. 3.2, Sect. 6.1,Fig. 2 and Table 3). Of the 116 sources with SDSS imaging, ∼
80% present an asymmetric optical morphology, signatureof asymmetric star-formation. 27 galaxies show a symmet-ric spherical, elliptical or disk-like structure, 60 present aclear head-tail cometary morphology, 11 show a two-knotstructure, and 18 present a multiple knot structure due tothe presence of multiple star-forming regions.Velocity offsets between the H i gas and the neb-ular/stellar component have also been investigated(Sect. 5.8, Table 5 and Fig. 11). We find that in 60% ofthe XMPs with H i and optical data, small displacements(10 – 40 km s − ) occur and these do not correlate with themorphology. This result suggests that, in these sources, theH i gas is not highly coupled to the nebular/stellar compo-nent.We conclude that XMP galaxies are extremely gas-rich,with evidence that the H i component is kinematically dis-turbed and relatively metal-free. Acknowledgements.
We would like to thank J. Brinchmann for hishelp regarding the MPA-JHU data and the anonymous referee fortheir suggestions and comments.M. E. F. is supported by a Post-Doctoral grantSFRH/BPD/36141/2007, by the Funda¸c˜ao para a Ciˆencia eTecnologia (FCT, Portugal). J. M. G. is supported by a Post-Doctoral grant SFRH/BPD/66958/2009 by the FCT (Portugal).P. L. is supported by a Post-Doctoral grant SFRH/72308/2010,funded by the FCT (Portugal). P. P. is supported by a Ciˆencia2008 Contract, funded by the FCT/MCTES and POPH/FSE (EC).A. H. is supported by a Marie Curie Fellowship, cofunded by theFCT and the FP7. Y. A. receives financial support from projectAYA2010-21887-C04-03, from the former Ministerio de Cienciae Innovaci´on (MICINN, Spain), as well as the Ram´on y Cajal
19. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
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21. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Table 3.
The optical data for the 140 XMP galaxies in the local Universe. Col. 1: Source name. Col. 2:Right Ascension. Col. 3: Declination. Col. 4: SDSS g -band Petrosian magnitude, from ML11. Col. 5: Opticalradius containing 90% of the g -band galaxy light, from the SDSS. Otherwise, NED SDSS r -band Petrosianradius ( ⋆ ) or the average source size at isophote 25 mag arcsec − ( † ), is used. Col. 6: Inclination angle of thesource from the SDSS g -band data, NED SDSS r -band Petrosian data ( ⋆ ) or estimated from the NED sourcesize ( † ). Col. 7: Metallicity, 12 + log (O/H), from ML11. Tabulated values are based on the direct methodor strong-line method ( ‡ ; see ML11 for details). Col. 8: SDSS optical morphology adapted from ML11 orobtained from SDSS DR9 images ( ∗ ). Symmetric (spherical, elliptical or disk-like symmetric structure), two-knot (two-knot structure), multi-knot (multiple knot structure) and cometary (head-tail structure), are used.Col. 9: Spatial offset, ∆R/r, where ∆R is the difference between the position of the brightest star-formationregion and the position of the center of the galaxy and r is the radius of the outer isophote. Name RA(J2000) DEC(J2000) m g r opt sin i
12 + log (O/H) Optical Spatial h m s ◦ ′ ′′ mag ′′ Morphology Offset(1) (2) (3) (4) (5) (6) (7) (8) (9)UGC12894 00 00 22 +39 29 44 . . . 27.0 ⋆ . . . 7.64 . . . . . .J0004+0025 00 04 22 +00 25 36 19.4 5.23 0.70 7.37 symmetric ∗ . . .J0014-0044 a
00 14 29 -00 44 44 18.7 1.43 ⋆ ⋆ ∗ . . .J0016+0108 00 16 28 +01 08 02 18.9 4.54 0.57 7.53 symmetric ∗ . . .HS0017+1055 00 20 21 +11 12 21 . . . . . . . . . 7.63 cometary ∗ ∗ ⋆ ⋆ ∗ . . .ESO473-G024 00 31 22 -22 45 57 . . . 25.5 † † ‡ symmetric . . .AndromedaIV 00 42 32 +40 34 19 . . . 34.5 † † ⋆ ⋆ ∗ . . .IC1613 01 04 48 +02 07 04 . . . 460.5 † † ∗ . . .J0107+0001 01 07 51 +00 01 28 19.4 1.30 0.63 7.23 cometary ∗ † † ∗ ∗ ⋆ ⋆ ∗ ∗ . . .J0135-0023 01 35 44 -00 23 17 18.9 2.23 ⋆ ⋆ ∗ . . .UGCA20 01 43 15 +19 58 32 18.0 58.5 † † ∗ ∗ ‡ cometary . . .HKK97L14 02 00 10 +28 49 53 . . . 13.5 † † ∗ ∗ . . .J0205-0949 02 05 49 -09 49 18 15.3 21.39 0.98 7.61 multi-knot ∗ . . .J0216+0115 02 16 29 +01 15 21 17.4 9.22 0.73 7.44 cometary ∗ † † ∗ ⋆ ⋆ ∗ ⋆ ⋆ ∗ ‡ cometary 0.5J0313+0010 03 13 02 +00 10 40 18.9 4.35 0.43 7.44 symmetric ∗ . . .J0315-0024 03 16 00 -00 24 26 20.2 1.48 ⋆ ⋆ ∗ ∗ † † † † ∗ ⋆ ⋆ ∗ † † † † ∗ . . .Tol0618-402 06 20 02 -40 18 09 . . . 10.5 † † a Although this source has been selected as an XMP galaxy in ML11, NED has flagged this as a Western H ii regionof UGC 139 (Sect. 3.2.2).22. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Table 3.
The optical data for the 140 XMP galaxies in the local Universe. Continued.
Name RA(J2000) DEC(J2000) m g r opt sin i
12 + log (O/H) Optical Spatial h m s ◦ ′ ′′ mag ′′ Morphology Offset(1) (2) (3) (4) (5) (6) (7) (8) (9)ESO489-G56 06 26 17 -26 15 56 15.6 22.5 † † ⋆ ⋆ ∗ † † ‡ symmetric . . .HS0822+03542 08 25 55 +35 32 31 17.8 4.45 0.92 7.35 cometary ∗ † † ∗ . . .UGC4483 08 37 03 +69 46 31 15.1 31.5 † † ∗ ‡ cometary 0.4HS0846+3522 08 49 40 +35 11 39 18.2 5.80 0.79 7.65 cometary ∗ ∗ . . .J0910+0711 09 10 29 +07 11 18 16.9 11.61 0.94 7.63 cometary ∗ ∗ ∗ ∗ ‡ cometary 0.4CGCG007-025 09 44 02 -00 38 32 16.0 9.47 0.82 7.65 multi-knot ∗ . . .SBS940+544 09 44 17 +54 11 34 19.1 0.63 ⋆ ⋆ ∗ . . .LeoA 09 59 26 +30 44 47 19.0 124.5 † † ∗ . . .SextansB 10 00 00 +05 19 56 20.5 129.0 † † ∗ . . .J1003+4504 10 03 48 +45 04 57 17.5 3.40 0.59 7.65 ‡ symmetric . . .SextansA 10 11 00 -04 41 34 . . . 162.0 † † ⋆ ⋆ ∗ . . .UGCA211 10 27 02 +56 16 14 16.2 2.11 0.38 7.56 cometary ∗ ∗ . . .J1044+0353 10 44 58 +03 53 13 17.5 4.16 0.86 7.44 cometary 0.4HS1059+3934 11 02 10 +39 18 45 17.9 7.89 0.71 7.62 multi-knot ∗ . . .J1105+6022 11 05 54 +60 22 29 16.4 17.08 0.91 7.64 cometary ∗ ∗ ∗ † † ⋆ ⋆ ∗ ‡ cometary 0.4J1151-0222 11 51 32 -02 22 22 16.8 11.30 0.52 7.78 two-knot 0.6J1157+5638 11 57 54 +56 38 16 16.9 10.39 0.61 7.83 ‡ cometary 0.5J1201+0211 12 01 22 +02 11 08 17.6 10.28 0.88 7.49 cometary 0.6SBS1159+545 12 02 02 +54 15 50 18.7 2.33 0.40 7.41 two-knot ∗ ∗ . . .Tol1214-277 12 17 17 -28 02 33 . . . 2.4 † . . . 7.55 . . . . . .VCC0428 12 20 40 +13 53 22 17.0 11.73 0.91 7.64 cometary ∗ ∗ . . .Tol65 12 25 47 -36 14 01 17.5 6.0 † . . . 7.54 . . . . . .J1230+1202 12 30 49 +12 02 43 16.7 4.88 0.86 7.73 cometary 0.3KISSR85 12 37 18 +29 14 55 19.9 3.16 0.56 7.61 cometary ∗ ∗ . . .HS1236+3937 12 39 20 +39 21 05 18.5 8.54 1.00 7.47 two-knot ∗ ∗ . . .SBS1249+493 12 51 52 +49 03 28 18.0 3.00 0.84 7.64 cometary ∗ ⋆ ⋆ ∗ . . .KISSR1490 13 13 16 +44 02 30 19.0 5.60 0.85 7.56 cometary ∗ ∗ ∗ ⋆ ⋆ ‡ symmetric . . . 23. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Table 3.
The optical data for the 140 XMP galaxies in the local Universe. Continued.
Name RA(J2000) DEC(J2000) m g r opt sin i
12 + log (O/H) Optical Spatial h m s ◦ ′ , ′′ mag ′′ Morphology Offset(1) (2) (3) (4) (5) (6) (7) (8) (9)J1331+4151 13 31 27 +41 51 48 17.1 3.80 0.74 7.75 cometary 0.3ESO577-G27 13 42 47 -19 34 54 . . . 28.5 † † ∗ ∗ ∗ ‡ cometary 0.4J1422+5145 14 22 51 +51 45 16 20.2 2.01 0.73 7.41 symmetric ∗ . . .J1423+2257 14 23 43 +22 57 29 17.9 2.36 0.66 7.72 symmetric . . .J1441+2914 14 41 58 +29 14 34 20.1 2.25 0.55 7.47 symmetric ∗ . . .HS1442+4250 14 44 13 +42 37 44 15.9 20.04 1.00 7.54 cometary ∗ ∗ ∗ ∗ . . .J1644+2734 16 44 03 +27 34 05 17.7 10.05 1.00 7.48 symmetric ∗ . . .J1647+2105 16 47 11 +21 05 15 17.3 9.16 0.82 7.75 multi-knot . . .W1702+18 17 02 33 +18 03 06 18.4 1.57 0.56 7.63 symmetric ∗ . . .HS1704+4332 17 05 45 +43 28 49 18.4 3.49 0.75 7.55 cometary ∗ ∗ ∗ ⋆ ⋆ ∗ ⋆ ⋆ ∗ . . .HS2134+0400 21 36 59 +04 14 04 . . . . . . . . . 7.44 cometary ∗ ∗ . . .ESO146-G14 22 13 00 -62 04 03 . . . 52.5 † † † † ⋆ ⋆ ∗ † † ∗ . . .J2259+1413 22 59 01 +14 13 43 19.1 4.03 0.85 7.37 cometary ∗ ⋆ ⋆ ∗ i Content
Table 4.
The SDSS MPA-JHU data for the 140 XMP galaxies in the localUniverse. Col. 1: Source name. Col. 2: Best-fit spectroscopic redshift, z =v z /c (heliocentric, optical convention). Col. 3: Balmer emission-line velocityoffset and error, measured relative to the best-fit radial velocity (v z ). Col. 4:Forbidden emission-line velocity offset and error, measured relative to thebest-fit radial velocity (v z ). Col. 5: Logarithm of the stellar mass and 1 σ error. Col. 6: Logarithm of the star-formation rate. Name z ∆v Balmer ∆v forbidden log M ⋆ log SFRkm s − km s − M ⊙ M ⊙ yr − (1) (2) (3) (4) (5) (6)UGC12894 . . . . . . . . . . . . . . .J0004+0025 0.0126 2.4 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± i Content
Table 4.
The SDSS MPA-JHU data for the 140 XMP galaxies in the localUniverse. Continued.
Name z ∆v Balmer ∆v forbidden log M ⋆ log SFRkm s − km s − M ⊙ M ⊙ yr − (1) (2) (3) (4) (5) (6)IZw18 0.0024 12.9 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± i Content
Table 4.
The SDSS MPA-JHU data for the 140 XMP galaxies in the localUniverse. Continued.
Name z ∆v Balmer ∆v forbidden log M ⋆ log SFRkm s − km s − M ⊙ M ⊙ yr − (1) (2) (3) (4) (5) (6)KISSR1013 0.0249 3.1 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± i Content
Table 5.
Global galaxy parameters for the 140 XMP galaxies in the local Universe. Col. 1: Source name. Col. 2:Best-fit radial velocity (v z =c z ; heliocentric, optical convention). Col. 3: H i gas radial velocity (heliocentric, opticalconvntion). Col. 4: H i gas velocity offset relative to the best-fit radial velocity. Col. 5: Radial velocity for the Balmeremission lines (heliocentric, optical convention). Col. 6: Radial velocity for the forbidden emission lines (heliocentric,optical convention). Col. 7: Hubble flow distance corrected for Virgocentric infall, from NED. Col. 8: Logarithm of thedynamical mass, estimated as M dyn /M ⊙ = 2.3 × (cid:0) w (cid:1) r H i , where w is the (uncorrected) H i line width (Tables 1and 2) in km s − and r H i is the H i radius (Table 1), assumed to be 3 × r opt (Table 3) in pc. Col. 9: Logarithm of theH i mass, estimated as M H i /M ⊙ = 2.36 × D S H i , where S H i is the integrated line flux density (Tables 1 and 2) inJy km s − and D is the Hubble flow distance corrected for Virgocentric infall in Mpc. Col. 10: Logarithm of the stellarmass (Table 4). Col. 11: Logarithm of the stellar M/L ratio in the g -band. Name v z v H i ∆v H i v Balmer v forbid D log M dyn log M H i log M ⋆ log M ⋆ /L g km s − km s − km s − km s − km s − Mpc M ⊙ M ⊙ M ⊙ M ⊙ /L ⊙ (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)UGC12894 . . . 335.00 . . . . . . . . . 8.36 8.34 8.05 . . . . . .J0004+0025 3786.00 . . . . . . 3783.58 3797.03 52.30 . . . . . . 7.72 2.04J0014-0044 4077.00 . . . . . . 4081.96 4083.42 56.70 . . . . . . 7.61 1.58J0015+0104 2058.00 2050.02 7.98 2061.42 2058.00 28.80 8.46 8.47 7.46 1.86J0016+0108 3111.00 . . . . . . 3111.00 3115.66 42.80 . . . . . . 7.64 1.94HS0017+1055 . . . 5630.00 . . . . . . . . . 78.10 . . . . . . . . . . . .J0029-0108 3948.00 . . . . . . 3948.00 3939.95 53.90 . . . . . . 7.88 2.10J0029-0025 4236.00 . . . . . . 4230.90 4236.00 59.10 . . . . . . 6.88 1.50ESO473-G024 . . . 542.00 . . . . . . . . . 7.15 8.32 7.84 . . . . . .J0036+0052 8469.00 . . . . . . 8470.20 8474.05 118.50 . . . . . . 8.36 1.73AndromedaIV . . . 237.00 . . . . . . . . . 6.30 9.17 8.26 . . . . . .J0057-0022 2811.00 . . . . . . 2811.00 2815.08 39.20 . . . . . . 7.46 1.91IC1613 . . . 234.00 . . . . . . . . . 0.74 8.21 7.45 . . . . . .J0107+0001 5439.00 . . . . . . 5444.38 5443.97 74.90 . . . . . . 7.86 1.87AM0106-382 . . . . . . . . . . . . . . . 7.50 . . . . . . . . . . . .J0113+0052 1143.00 1155.61 -12.61 1143.00 1143.00 15.80 7.71 8.53 6.77 2.41J0119-0935 1914.00 1932.00 -18.00 1911.15 1916.58 24.80 . . . 8.14 6.06 1.07HS0122+0743 2925.00 2926.00 -1.00 2915.68 2921.30 40.30 8.98 9.33 6.39 -0.54J0126-0038 1941.00 1904.70 36.30 1941.00 1936.53 25.80 8.24 8.63 7.63 2.17J0133+1342 2601.00 2580.00 21.00 2607.57 2601.00 36.10 8.27 7.49 6.60 0.72J0135-0023 5070.00 . . . . . . 5067.24 507. . . 69.50 . . . . . . 8.16 2.04UGCA20 . . . 498.00 . . . . . . . . . 8.63 9.25 8.30 . . . . . .UM133 . . . 1621.00 . . . . . . . . . 22.40 . . . 8.64 . . . . . .J0158+0006 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .HKK97L14 . . . . . . . . . . . . . . . 4.81 8.80 6.52 . . . . . .J0204-1009 1902.00 1907.72 -5.72 1902.00 1897.01 25.20 9.43 9.17 7.20 1.24J0205-0949 . . . 1885.00 . . . . . . . . . 25.30 9.76 9.29 . . . . . .J0216+0115 2802.00 . . . . . . 2802.00 2804.84 38.70 . . . . . . 8.20 1.98096632 . . . . . . . . . . . . . . . 12.90 . . . . . . . . . . . .J0254+0035 4458.00 . . . . . . 4458.00 4458.00 59.90 . . . . . . 7.61 1.98J0301-0059 11484.00 . . . . . . 11480.46 11490.10 155.60 . . . . . . 8.96 3.18J0301-0052 2196.00 2094.29 101.71 2204.43 2206.18 29.00 8.87 8.62 7.57 2.17J0303-0109 9120.00 . . . . . . 9120.00 9117.65 124.00 . . . . . . 8.33 2.06J0313+0006 8748.00 . . . . . . 8758.57 8763.53 122.50 . . . . . . 7.67 1.17J0313+0010 2322.00 . . . . . . 2322.00 2329.65 31.10 . . . . . . 7.57 2.14J0315-0024 6774.00 6787.09 -13.09 6774.00 6774.00 90.90 8.98 9.40 7.77 1.93UGC2684 . . . 350.00 . . . . . . . . . 5.95 7.88 7.94 . . . . . .SBS0335-052W . . . 4014.70 . . . . . . . . . 53.80 8.54 8.77 . . . . . .SBS0335-052E . . . 4053.60 . . . . . . . . . 54.00 8.88 8.62 . . . . . .J0338+0013 12795.00 . . . . . . 12790.03 12791.60 173.60 . . . . . . . . . . . .J0341-0026 9186.00 . . . . . . 9186.00 9193.79 123.50 . . . . . . 8.38 1.72ESO358-G060 . . . 808.00 . . . . . . . . . 8.90 9.10 8.30 . . . . . .G0405-3648 . . . . . . . . . . . . . . . 9.00 . . . . . . . . . . . .J0519+0007 . . . . . . . . . . . . . . . 180.40 . . . . . . . . . . . .Tol0618-402 . . . . . . . . . . . . . . . 140.0 . . . . . . . . . . . .ESO489-G56 . . . 492.30 . . . . . . . . . 4.23 7.65 6.95 . . . . . .J0808+1728 13263.00 . . . . . . 13265.01 13266.03 181.40 . . . . . . 7.41 0.57J0812+4836 525.00 . . . . . . 525.00 529.39 9.44 . . . . . . 6.35 0.80UGC4305 . . . 157.10 . . . . . . . . . 4.89 9.46 9.09 . . . . . .J0825+1846 11388.00 . . . . . . 11397.62 11401.95 156.10 . . . . . . 7.35 0.56HS0822+03542 750.00 726.60 23.40 781.37 782.90 11.72 7.31 6.94 6.04 1.02DD053 . . . 19.20 . . . . . . . . . 2.42 7.87 7.47 . . . . . .UGC4483 . . . . . . . . . . . . . . . 5.00 . . . 7.88 . . . . . .HS0837+4717 12588.00 . . . . . . 12556.84 12559.68 174.30 . . . . . . 7.97 0.5328. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Table 5.
Global galaxy parameters for the 140 XMP galaxies in the local Universe. Continued.
Name v z v H i ∆v H i v Balmer v forbid D log M dyn log M H i log M ⋆ log M ⋆ /L g km s − km s − km s − km s − km s − Mpc M ⊙ M ⊙ M ⊙ M ⊙ /L ⊙ (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)J0842+1033 3096.00 . . . . . . 3083.20 3082.23 49.50 . . . . . . 7.01 0.70HS0846+3522 . . . 2169.00 . . . . . . . . . 36.30 8.28 7.49 . . . . . .J0859+3923 . . . . . . . . . . . . . . . 9.50 . . . . . . . . . . . .J0910+0711 . . . . . . . . . . . . . . . 22.00 . . . . . . . . . . . .J0911+3135 756.00 . . . . . . 758.26 756.00 11.60 . . . . . . 6.14 1.13J0926+3343 528.00 . . . . . . 528.00 528.00 8.25 . . . . . . 6.05 1.34IZw18 726.00 745.00 -19.00 713.06 715.13 13.90 7.76 8.12 6.43 0.59J0940+2935 504.00 505.00 -1.00 504.00 505.80 7.23 8.77 7.40 6.30 1.18J0942+3404 6747.00 . . . . . . 6741.99 6748.69 94.10 . . . . . . 6.83 0.52CGCG007-025 1434.00 . . . . . . 1426.68 1421.95 20.80 . . . . . . 6.67 0.43SBS940+544 1623.00 . . . . . . 1623.00 1627.23 26.60 . . . . . . 7.05 1.84CS0953-174 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .J0956+2849 504.00 . . . . . . 511.75 516.53 5.85 . . . . . . 6.73 1.56LeoA . . . 21.70 . . . . . . . . . 1.54 7.75 7.37 . . . . . .SextansB . . . 300.50 . . . . . . . . . 1.63 8.41 7.66 . . . . . .J1003+4504 2766.00 . . . . . . 2763.54 2767.39 41.10 . . . . . . 7.03 0.80SextansA . . . 324.00 . . . . . . . . . 1.43 8.60 7.81 . . . . . .KUG1013+381 1164.00 1169.00 -5.00 1156.84 1154.56 19.90 8.30 8.15 6.58 0.34SDSSJ1025+1402 30129.00 . . . . . . 30018.59 30061.57 413.90 . . . . . . 10.22 3.15UGCA211 837.00 . . . . . . 837.00 837.00 15.50 . . . 8.23 7.18 1.28J1031+0434 1170.00 . . . . . . 1170.00 1170.00 18.10 . . . . . . 6.61 0.57HS1033+4757 1560.00 1541.00 19.00 1562.70 1565.65 25.60 9.04 8.31 7.08 1.26J1044+0353 3861.00 . . . . . . 3858.21 3857.27 53.50 . . . . . . 6.80 0.34HS1059+3934 . . . 3019.00 . . . . . . . . . 48.10 9.05 8.88 . . . . . .J1105+6022 1326.00 1333.00 -7.00 1327.49 1328.69 23.30 8.89 8.50 6.96 0.79J1119+5130 1338.00 . . . . . . 1340.89 1343.24 23.30 . . . . . . 6.48 0.51J1121+0324 1149.00 1171.00 -22.00 1149.00 1155.21 . . . 9.11 8.40 6.19 0.83UGC6456 . . . -93.69 . . . . . . . . . 1.42 7.74 6.68 . . . . . .SBS1129+576 . . . 1506.00 . . . . . . . . . 26.40 8.82 8.81 . . . . . .J1145+5018 1674.00 . . . . . . 1674.00 1680.04 27.70 . . . . . . 6.71 0.95J1151-0222 1056.00 . . . . . . 1052.91 1058.67 13.10 . . . . . . 6.65 1.14J1157+5638 417.00 . . . . . . 423.81 424.46 8.56 . . . . . . . . . . . .J1201+0211 975.00 974.00 1.00 977.00 976.96 8.60 7.80 7.22 6.09 1.26SBS1159+545 . . . 3560.00 . . . . . . . . . 53.30 . . . . . . . . . . . .SBS1211+540 918.00 894.00 24.00 932.92 932.58 17.20 8.26 7.64 6.02 0.51J1215+5223 153.00 159.00 -6.00 158.98 158.03 3.33 7.69 7.09 6.01 1.05Tol1214-277 . . . 7785.00 . . . . . . . . . 105.70 . . . . . . . . . . . .VCC0428 801.00 794.00 7.00 801.00 802.93 13.10 8.58 7.42 6.20 0.77HS1222+3741 12114.00 . . . . . . 12108.43 12108.51 170.90 . . . . . . 7.86 0.55Tol65 . . . 2790.00 . . . . . . . . . 37.90 8.49 8.86 . . . . . .J1230+1202 1254.00 1227.00 27.00 1249.42 1246.75 13.10 7.93 7.62 6.56 1.01KISSR85 . . . . . . . . . . . . . . . 104.60 . . . . . . . . . . . .UGCA292 . . . 308.30 . . . . . . . . . 3.41 6.50 7.59 . . . . . .HS1236+3937 . . . . . . . . . . . . . . . 79.00 . . . . . . . . . . . .J1239+1456 . . . . . . . . . . . . . . . 296.70 . . . . . . . . . . . .SBS1249+493 . . . . . . . . . . . . . . . 103.60 . . . . . . . . . . . .J1255-0213 15564.00 . . . . . . 15572.15 15575.00 213.70 . . . . . . 7.67 0.65GR8 219.00 217.00 2.00 219.00 226.21 1.43 7.28 6.64 6.02 2.87KISSR1490 . . . . . . . . . . . . . . . 53.00 . . . . . . . . . . . .DD0167 . . . 150.24 . . . . . . . . . 3.19 7.26 6.95 . . . . . .HS1319+3224 . . . . . . . . . . . . . . . 78.10 . . . . . . . . . . . .J1323-0132 6738.00 . . . . . . 6740.87 6743.93 92.50 . . . . . . 7.04 0.39J1327+4022 3150.00 . . . . . . 3154.24 3156.55 48.00 . . . . . . 6.27 0.51J1331+4151 3510.00 . . . . . . 3514.90 3519.01 52.60 . . . . . . 7.16 0.56ESO577-G27 . . . . . . . . . . . . . . . 21.30 . . . . . . . . . . . .J1355+4651 8433.00 . . . . . . 8429.22 8434.65 118.30 . . . . . . 6.90 0.47 29. E. Filho et al.: Extremely Metal-Poor Galaxies: The H i Content
Table 5.
Global galaxy parameters for the 140 XMP galaxies in the local Universe. Continued.
Name v z v H i ∆v H i v Balmer v forbid D log M dyn log M H i log M ⋆ log M ⋆ /L g km s − km s − km s − km s − km s − Mpc M ⊙ M ⊙ M ⊙ M ⊙ /L ⊙⊙