S. A. Pustilnik

Strong Emission Line H II Galaxies in the Sloan Digital Sky Survey. I. Catalog of DR1 Objects with Oxygen Abundances from Te Measurements

We present the first edition of the SDSS H II galaxies with Oxygen abundances Catalog (SHOC), which is a listing of strong emission-line galaxies (ELGs) from the Sloan Digital Sky Survey (SDSS). Oxygen abundances have been obtained with the classic Te method. We describe the method exploiting the SDSS database to construct this sample. The selection procedures are described and discussed in detail, as well as some problems encountered in the process of deriving reliable emission line parameters. The method was applied to the SDSS Data Release 1 (DR1). We present 612 SDSS emission-line galaxies (624 separate SDSS targets in total), for which the oxygen abundances 12 + log(O/H) have rms uncertainties ≤0.20 dex. The subsample of 263 ELGs (272 separate SDSS targets) have an uncertainty ≤0.10 dex, while 459 ELGs (470 separate SDSS targets) have an uncertainty ≤0.15 dex. The catalog includes the main parameters of all selected ELGs, the intensities and equivalent widths of hydrogen and oxygen emission lines, as well as oxygen abundances with their uncertainties. The information on the presence of Wolf-Rayet blue and/or red bumps in 109 galaxies is also included. With the use of combined g, r, i SDSS images we performed visual morphological classification of all SHOC galaxies. Four hundred sixty-one galaxies (~75%) are classified as confident or probable blue compact galaxies (BCG/BCG?), 78 as irregular ones, 20 as low surface brightness galaxies (LSBG), 10 as obviously interacting, and 43 as spiral galaxies. In creating the catalog, 30 narrow-line active galactic nuclei and 69 LINERs were also identified; these are also presented apart of the main catalog. We outline briefly the content of the catalog, and the prospects of its use for statistical studies of the star formation and chemical evolution issues. Some of these studies will be presented in the forthcoming paper. Finally, we show that the method presented by Kniazev et al. for calculating O+/H+ using intensities of the [O II] λλ7320, 7330 lines for SDSS emission-line spectra in the absence of [O II] λ3727 line appears to yield reliable results over a wide range of studied oxygen abundances: 7.10 < 12 + log(O/H) < 8.5.

The metallicity extremes of the Sagittarius dSph: SALT spectroscopy of PNe

In this work we present the first spectroscopic results obtained with the Southern African Large Telescope (SALT) during its performance-verification phase. We find that the Sagittarius dwarf spheroidal galaxy (Sgr) contains a youngest stellar population with [O/H] ≈ -0.2 and age t > 1 Gyr, and an oldest population with [O/H] = -2.0. The values are based on spectra of two planetary nebulae (PNe), using empirical abundance determinations. We calculated abundances for O, N, Ne, Ar, S, Cl, Fe, C and He. We confirm the high abundances of PN StWr2-21 with 12 + log(O/H) = 8.57 ± 0.02 dex. The other PN studied, BoBn 1, is an extraordinary object in that the neon abundance exceeds that of oxygen. The abundances of S, Ar and Cl in BoBn 1 yield the original stellar metallicity, corresponding to 12 + log(O/H) = 6.72 ± 0.16 dex which is 1/110 of the solar value. The actual [O/H] is much higher: third dredge-up enriched the material by a factor of ∼12 in oxygen, ∼240 in nitrogen and ∼70 in neon. Neon as well as nitrogen and oxygen content may have been produced in the intershell of low-mass asymptotic giant branch (AGB) stars. Well defined broad WR lines are present in the spectrum of StWr2-21 and absent in the spectrum of BoBn 1. This puts the fraction of [WR]-type central PNe stars to 67 per cent for dSph galaxies.

Low Surface Brightness Galaxies in the Sloan Digital Sky Survey. I. Search Method and Test Sample

In this paper we present results of a pilot study to use imaging data from the Sloan Digital Sky Survey (SDSS) to search for low surface brightness (LSB) galaxies. For our pilot study we use a test sample of 92 galaxies from the Impey et al. catalog distributed over 93 SDSS fields of the Early Data Release (EDR). Many galaxies from the test sample are either LSB or dwarf galaxies. To deal with the SDSS data most effectively, a new photometry software was created, which is described in this paper. We present the results of the selection algorithms applied to these 93 EDR fields. Two galaxies from the Impey et al. test sample are very likely artifacts, as confirmed by follow-up imaging. With our algorithms we were able to recover 87 of the 90 remaining test sample galaxies, implying a detection rate of ~96.5%. The three missed galaxies fall too close to very bright stars or galaxies. In addition, 42 new galaxies with parameters similar to the test sample objects were found in these EDR fields (i.e., ~47% additional galaxies). We present the main photometric parameters of all identified galaxies and carry out first statistical comparisons. We tested the quality of our photometry by comparing the magnitudes for our test sample galaxies and other bright galaxies with values from the literature. All these tests yielded consistent results. We briefly discuss a few unusual galaxies found in our pilot study, including an LSB galaxy with a two-component disk and 10 new giant LSB galaxies.

Spectroscopy of two PN candidates in IC 10

We present the results of the first spectroscopic observations of two planetary nebula (PN) candidates in the Local Group dwarf irregular galaxy IC 10. Using several spectral classification diagrams, we show that the brightest PN candidate (PN 7) is not a PN, but rather a compact H II region consisting of two components with low electron number densities. After the rejection of this PN candidate, the IC 10 PN luminosity function cut-off becomes very close to the standard value. With the compiled spectroscopic data for a large number of extragalactic PNe, we analyse a series of diagnostic diagrams to generate quantitative criteria for separating PNe from unresolved H II regions. We show that, with the help of the diagnostic diagrams and the derived set of criteria, PNe can be distinguished from H II regions with an efficiency of ∼99.6 per cent. With the obtained spectroscopic data, we confirm that another, 1.7 mag fainter PN candidate (PN 9) is a genuine PN. We argue that, based on all currently available PNe data, IC 10 is located at a distance of 725 +63 −33 kpc [distance modulus (m − M) = 24.30 +0.18 −0.10 ].

Studies of galaxies in voids I. H i observations of Blue Compact Galaxies

We present here results of studies of the properties of galaxies located in very low density environments. We observed 26 blue compact galaxies (BCGs) from the Second Byurakan (SBS) and Case surveys located in voids with the radial velocities Vhel 11 000 km s 1 , two BCGs in the void behind the Virgo cluster and 11 BCGs in denser environments. H i fluxes and prole widths, as well as estimates of total H i masses, are presented for the 27 detected galaxies (of which 6 are in three galaxy pairs and are not resolved by the radiotelescope beam). Preliminary comparisons of void BCGs with similar objects from intermediate density regions { in the general eld and the Local Supercluster (sub-samples of BCGs in the SBS zone) and in the dense environment of the Virgo Cluster (a BCD sample) { are performed using the hydrogen-to-blue-luminosity ratio M(H i)/LB. We nd that for the same blue luminosity, for MB > 18: m 0, BCGs in lower density environment have on average more H i .T he slope of the M(H i)/LB L for BCGs shows a trend of steepening with decreasing bright galaxy density, being very close to zero for the densest environment considered here and reaching = 0.4 for voids.

H i in very metal‐poor galaxies: the SBS 0335–052 system

We present Giant Metrewave Radio Telescope (GMRT), H i 21cm observations of SBS 0335–052E and SBS 0335–052W, a close pair of dwarf galaxies, which are further unusual in being the most metal-poor star-forming galaxies known. We present images at several angular resolutions, ranging from �40 to 4 arcsec. These images show that SBS 0335–052 is a strongly interacting system, with a faint diffuse H i bridge seen at low resolution, and elongated tails seen at the higher resolutions. The overall morphology suggests that the pair represents a major (as both galaxies have similar H i masses) merger of extremely gas-rich galaxies, which is currently past the first close encounter. The low-resolution velocity field is dominated by the velocity difference between the two galaxies and the velocity gradient along the tidal features. However, for SBS 0335–052W at least, at high angular resolution, one sees a central velocity field that could be associated with the spin of the original undisturbed disc. The two galaxies have very similar H i masses, but very different optical properties and current star formation rates. A possible reason for this is the differing amounts of tidally-induced star formation, because of the different spin orientations of these interacting galaxies. The highest angular resolution H i images show that the ionized superbubble, identified by Thuan, Izotov & Lipovetsky (1997), in the Hubble Space Telescope (HST) images of SBS 0335–052E, is extended along one of the diffuse tidal features, and that there is a high-density H i clump at the other end of the superbubble. The star formation in SBS 0335–052E occurs mainly in a group of superstar clusters (SSCs) with a clear age gradient; the age decreases as one approaches the dense H i clump. We suggest that this propagating star formation is driven by the superbubble expanding into a medium with a tidally-produced density gradient. The high pressures associated with the compressed material would also naturally explain why current star formation is mainly concentrated in superstar clusters.

Study of galaxies in the Lynx–Cancer void – I. Sample description

The evolution of galaxies is influenced by the environment in which they reside. This effect should be strongest for the lowest-mass and -luminosity galaxies. To study dwarf galaxies in extremely low density environments, we have compiled a deep catalogue of dwarf galaxies in the nearby Lynx-Cancer void. This void hosts some of the most metal-poor dwarfs known to date. It borders the Local Volume at negative supergalactic Z(SGZ) coordinates and has a size of more than 16 Mpc. With a distance to its centre of only 18Mpc, it is close enough to allow a search for the faintest dwarfs. Within the void 75 dwarf (―11.9 > M B > ―18.0) and four subluminous (―18.0 > M B > ―18.4) galaxies have been identified. We present the parameters of the void galaxies and a detailed analysis of the completeness of the catalogue as a function of magnitude and surface brightness. The catalogue appears almost complete to M B < ―14 mag, but misses part of the fainter low surface brightness (LSB) face-on galaxies. This sample of void galaxies builds the basis of forthcoming observational studies that will provide insight into the main stellar population, H I mass-to-light ratio, metallicity and age for comparison with dwarfs in higher density regions. We briefly summarize the information on the unusual objects in the void and conclude that their concentration hints that voids are environments that are favourable for finding and studying unevolved dwarf galaxies.

H i studies of extremely metal-deficient galaxies – II. Giant Metrewave Radio Telescope observations of SBS 1129+576

We present Giant Metrewave Radio Telescope H i observations of an extremely metal-deficient galaxy SBS 1129+576. SBS 1129+576 has a weighted mean oxygen abundance of 12 + log (O/H) = 7.41 ± 0.07, or 1/18 of the solar value. Our H i observations show that the galaxy is strongly interacting with a companion (projected separation ~ 27 kpc) galaxy, SBS 1129+577. HI emission from a third, smaller galaxy, SDSS J113227.68+572142.3, is also present in the data cube. We study the HI morphology and kinematics of this small group at angular resolutions ranging from ~ 40 to 8 arcsec. The low-resolution map shows a bridge of emission connecting the two larger galaxies and a large one-armed spiral distortion of the disc of SBS 1129+577. We measure HI masses of ~ 4.2 × 10 8 , ~ 2.7 × 10 9 and ~ 2.1 × 10 8 M ⊙ for SBS 1129+576, SBS 1129+577 and the gas in the bridge, respectively. Assuming that most of the bridge gas originally came from SBS 1129+576, approximately one-third of its original gas mass has been stripped off. The third smaller galaxy has an H i mass of (M HI ~ 1.1 × 10 7 M ⊙ ) and does not show any sign of interaction with the other two galaxies. The higher-resolution maps show that SBS 1129+577 has a central bar and a ring surrounding the bar; there is also a hint of an integral-shaped warp in SBS 1129+576. All these features are very likely to have been induced by the tidal interaction. In both SBS 1129+576 and SBS 1129+577, there is, in general, a good correspondence between regions with high H i column density and those with ongoing star formation. The two brightest H ii regions in SBS 1129+576 have (inclination-corrected) gas column densities of ~ 1.6 × 10 21 and ~ 1.8 × 10 21 atoms cm -2 , respectively. The inclination-corrected H i column density near the H ii regions in SBS 1129+577 is generally above ~ 2.0 × 10 21 atoms cm −2 . These values are close to the threshold density for star formation observed in other blue compact galaxies. In contrast to SBS 1129+576 and SBS 1129+577 which are very gas-rich, the third member of this group, SDSS J113227.68+572142.3, is gas-poor.

SDSS J092609.45+334304.1: a nearby unevolved galaxy

We present the results of observations of the very low surface brightness (VLSB) dwarf galaxy SDSS J092609.45+334304.1 with extreme parameters which indicate its unevolved status. Namely, its value of O/H, derived as an average of that in two adjacent H ii regions at the NE edge of the disc, corresponds to the parame- ter 12+log(O/H)=7.12±0.02, which is amongst two lowest known. The total HI flux measurement obtained with the Nancay Radio Telescope and the photometric results imply that the galaxy ratio M(HI)/LB �3.0, is among the top known in the Local Vol- ume. The galaxy is situated in the region of a nearby underdense region known as the Lynx-Cancer void, where other, unevolved galaxies, including DDO 68, HS 0832+3542 and SAO 0822+3545, are known to be present. The total mass of this almost edge-on VLSB galaxy is �8.3 times larger than its baryonic mass, implying the dynamical dominance of Dark Matter (DM) halo. The (u g),(g r) colours of outer parts of this galaxy are consistent with the ages of its main stellar population of 1-3 Gyr. Thanks to the galaxy isolation, the small effect of current or recent star formation (SF), its proximity and rather large HI flux (�2.5 Jy·km s −1 ), this VLSB dwarf is a good laboratory for the detailed study of DM halo properties through HI kinematics and the star formation processes in very metal-poor low surface density environment. This finding, along with the discovery of other unusual dwarf galaxies in this void, provides evidence for the relation between galaxy evolution and its very low-density environment for the baryonic mass range of 10 8 to 10 9 M⊙. This relation seems to be consistent with that expected in theCDM models of galaxy and structure formation.

HS 2134+0400—a new very metal-poor galaxy, a representative of the void population?

We present the 6-m SAO telescope spectroscopy of HS 2134+0400, a blue compact galaxy (BCG) discovered within the framework of a dedicated Hamburg/SAO survey for low-metallicity BCGs (HSS-LM). Its very low abundance of oxygen (12 + log(O/H) = 7.44) and other heavy elements (S, N, Ne, Ar) allows this dwarf galaxy to be assigned to the group of eight lowest-metallicity BCGs among the several thousand BCGs known in the nearby Universe. The measured heavy-element abundance ratios (S/O, Ne/O, N/O, and Ar/O) are in good agreement with the typical values found for other very metal-poor BCGs. The spatial location of HS 2134+0400 is atypical of the majority of BCGs: it lies in the Pegasus void, a large region with a very low density of galaxies with normal or higher luminosities. In addition to HS 2134+0400, we found a dozen more very metal-poor galaxies in voids. Therefore, we discuss the hypothesis that this type of objects may be representative for the population of dwarf galaxies in voids.