The HI Morphology and Stellar Properties of Strongly Barred Galaxies: support for bar quenching in massive spirals
Lucy Newnham, Kelley Hess, Karen Masters, Sandor Kruk, Samanta Penny, Tim Lingard, Rebecca Smethurst
MMNRAS , 1– ?? (2018) Preprint January 7, 2019 Compiled using MNRAS L A TEX style file v3.0
The HI Morphology and Stellar Properties of StronglyBarred Galaxies: support for bar quenching in massivespirals
L. Newnham, (cid:63) Kelley M. Hess, , Karen L. Masters, , Sandor Kruk, † Samantha J. Penny , Tim Lingard, R. J. Smethurst, Institute of Cosmology & Gravitation, University of Portsmouth, Dennis Sciama Building, Portsmouth PO1 3FX, UK Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD, Groningen, The Netherlands ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo, The Netherlands Department of Physics and Astronomy, Haverford College, 370 Lancaster Ave, Haverford, PA 19041, USA European Space Agency, ESTEC, Keplerlaan 1, PO Box 299, 2200AG Noordwijk, The Netherlands Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
Accepted XXX. Received YYY; in original form ZZZ
ABSTRACT
Galactic bars are able to affect the evolution of galaxies by redistributing gas in galaxy,possibly contributing to the cessation of star formation. Several recent works point to‘bar quenching’ playing an important role in massive disk galaxies like our own MilkyWay.We construct the largest ever sample of gas rich and strongly barred disc galaxieswith resolved HI observations making use of both the Giant Meter Radio Telescope(GMRT) and the Karl Jansky Very Large Array (VLA) to collect data. This sample ofgalaxies, which we call HIRB (HI Rich Barred) galaxies, were identified with the help ofGalaxy Zoo - to find galaxies hosting a strong bar, and the Arecibo Legacy Fast AreciboL-band Feed Array (ALFALFA) blind HI survey- to identify galaxies with an high HIcontent.We measure the gas fractions, HI morphology and kinematics in each galaxy, and usearchival optical data from the Sloan Digital Sky Survey (SDSS) to reveal star-formationhistories and bar properties. The HIRB galaxies presented here support a picture inwhich bar quenching is playing, or will soon play an important role in their evolution.They also support models which show how the presence of cold gas delays and slows thedevelopment of a strong bar. The galaxies with the lowest gas fractions (still very highfor their mass) show clear HI holes, dynamical advanced bars and low star formationrates, while those with the highest gas fractions show little impact from their bar onthe HI morphology, and are still actively star-forming. How such unusual galaxies cameto be is an open question. Several of the HIRBs have local gas rich companions. Tidalinteractions with these lower mass galaxies could result in an early triggering of the barand/or accretion of HI between them. The role of environment in the evolution of theHIRB galaxies will be explored in a future paper.
Key words: galaxies: general – galaxies: star formation – galaxies: structure – galaxies:spiral – galaxies : evolution – galaxies: morphology (cid:63)
E-mail: [email protected] † ESA Research Fellow
Within a galaxy, a bar is a structure in the central regionmade up of stars, gas and dust following elongated orbits.Bars are found in 30-70% of disc galaxies within 0.01 < z < © a r X i v : . [ a s t r o - ph . GA ] J a n Newnham et al. in molecular clouds,which then cool further, collapse, and forms new stars. Even-tually the HI will run out in the galaxy and star formationwill cease. Star formation may also cease if the HI is unableto cool due to significant torque or other dynamical processes(e.g. bar torques Tubbs 1982). The general picture that HIrich galaxies are star forming holds well, with a clear corre-lation between star formation properties and HI content (e.gSaintonge et al. 2012).Numerical simulations of bar formation in disc galaxiescan now realistically include a dissipative gas counterpart,and the effects of that on the galaxy. The formation of a barin these is shown to aid the movement of material; with an-gular momentum being transported outwards and materialtransported in, towards the centre, in the inner bar regions(Bournaud & Combes 2002). The gas is especially influencedby this since it is dynamically cold, it responds to gravita-tional perturbations (e.g. as explored in Athanassoula 2013)Kraljic et al. (2012), exploring zoomed-in cosmologicalsimulations and Athanassoula et al. (2013) uses detailed N-body and Smooth Particle Hydrodynamics (SPH) simulationto show the formation and growth of a bar with hydrody-namic models of gas flow, and present gas morphology as wellas stars. In particular, Athanassoula et al. (2013) and Spinosoet al. (2017) predict the HI kinematics of strongly barredgalaxies, the gas within the bar cororation radius (bar region)infalls to the very centre (inner kpc) where it enhances starformation. Gas outside of this region is also prevented fromentering due to the bar, therefore creating a ‘hole’. The gas isprevented from entering the central region as it cannot crosspast co-rotation when the strong bar has been established.The gas is also transfered along the bar towards the centre.This agrees extremely well with the THINGS observations of MNRAS , 1– ?? (2018) IRB-I M95 (Walter et al. 2008) which show a large HI hole in thebar region. In this paper we will further test the predictionsof these simulations in a sample of strongly barred gas-richgalaxies.We introduce a sample of galaxies we are calling “HI RichBarred” (HIRB) galaxies. This study was initiated to help re-veal the evolution of galaxies with strong bars and large quan-tities of neutral hydrogen (HI). As mentioned above, galaxiestend not to host a strong bar and have a large reserve ofHI (Masters et al. 2012). This is likely because the presenceof significant quantities of gas inhibits and slows bar forma-tion (Athanassoula et al. 2013; Villa-Vargas et al. 2010). TheHIRB galaxies are unusual as they all host a strong bar andstill have large reserves of HI, such that they would be con-sidered HI rich galaxies relative to typical scaling relations(Huang et al. 2012).The paper is organised as follows: in Section 2 we dis-cuss the data collected for this study, a description of thesample selection criteria, the available archival optical andspectroscopic data, and finally the resolved HI data collectedfor them by us using the VLA (NSF’s Karl G. Jansky VeryLarge Array ) and the GMRT (the Giant Metrewave RadioTelescope in Pune, India). In Section 3 we discuss the prop-erties of the six HIRB galaxies revealed by these data. InSection 4 we compare our results to simulations, and pro-vide a plausible physical picture of the galaxies. We concludeand summarize our results in Section 5. Where distances areneeded to calculate physical lengths or other properties weuse H =
70 km/s/Mpc to convert from redshift.
We introduce here the “HI-Rich Barred” (HIRB) galaxy sam-ple. This sample has been designed to investigate a rare typeof disc galaxy which are both strongly barred and very HIgas-rich. The parent sample consisted of 2090 almost face-ondisc galaxies (selected through the Sloan Digital Sky Survey(SDSS)), with HI gas content detections from the ALFALFA40% survey (which was the part of ALFALFA available atthe time the HIRB galaxy survey was initiated Haynes et al.2011) and bar identifications from Galaxy Zoo (GZ2 Willettet al. 2013) that were the basis of the study published in(Masters et al. 2012). This sample was built from a volumelimited subset of the Galaxy Zoo sample, with . < z < . (in order to allow for reliable distance measurements and anadequate angular resolution to detect bars in the galaxies).The SDSS spectroscopic limiting magnitude of r = 17.7 cor-responds to a volume limited sample of galaxies with M r < -19.0 out to z = 0.05.For more details of the selection of the parent samplefrom Galaxy Zoo and ALFALFA see (Masters et al. 2012).We show in Figure 1 HI gas fraction from ALFALFA (Hayneset al. 2011) against an estimate of the stellar mass, from K-correction fit to Petrosian magnitudes, for the entire sample The National Radio Astronomy Observatory is a facility of theNational Science Foundation operated under cooperative agree-ment by Associated Universities, Inc.
Figure 1.
HI content (from ALFALFA; Haynes et al. 2018), ex-pressed relative to the stellar mass versus the stellar mass ofgalaxies in our sample (See Section 2.1). A volume limited sub-set of ALFLAFA100 galaxies are plotted in grey and the orangepoints show all galaxies within that sample that host a strong bar( p bar > . ). The blue line fits the trend between the HI massfraction and the stellar mass, with the black dotted line showing atrend 3 σ more gas rich than that. The individually coloured shapesrepresent the six HIRB galaxies observed and detailed in this pa-per - the rainbow colour order reveals the absolute bar length (seeSection 3.1.2). (grey points) with strongly barred galaxies hi-lighted in or-ange. Solid lines show the best fit relation for all (blue) andjust strongly barred (orange) galaxies, while the dashed lineis 3 σ above this mean line. Our HIRB galaxies are shown bythe large coloured stars, the colour of which, in rainbow orderreveals a ranking by the physical size of the bar (which wediscuss later in Section 3.1.1).Using this large sample we started by selecting objectswhich fit the criteria to be a HIRB galaxy, namely HI-richand strongly barred. In Masters et al. (2012) it was shownthat these are rare. We define the gas-rich sample to have agas fraction, log ( M H i / M ∗ ) greater than 3 σ more than themean value for their stellar mass as shown in Figure 1. Wefind that only 2% (48 galaxies) of the entire parent samplemeet both these criteria. These 48 galaxies equate to 17%of those galaxies with comparable HI mass for their stellarmass.Since these strongly barred, gas-rich galaxies are rare, itis hard to find a large sample of them nearby. We have to goto larger volumes (and therefore higher redshifts) in order tohave a reasonable sample. However, to be able to observe theHI at high enough resolution to resolve the bar region andwith the column density sensitivity required to detect thedisk requires tens of hours of observing for a single source atz > MNRAS , 1– ?? (2018) Newnham et al. hours of telescope time on the GMRT and VLA combined.Unfortunately the data from one source was corrupted by anearby continuum source (see 2.3 for details on the observingand data reduction).The properties of our final six galaxies are summarized inTable 1, where you can see they still span a range of variousproperties, while all being gas rich and strongly barred. SDSSoptical g ri images are shown for all six in Figure 2.Our HIRB galaxies share many properties with those inthe (HI) HIghMass Survey ongoing at the JVLA (Hallenbecket al. 2014) in that they are unusually massive and gas-rich,and so like HIghMass, make good z ∼ analogues of the typesof galaxies which will dominate detections in SKA surveys (aswell as the similar HI mass and gas-rich galaxies in HIGHzat z ∼ . ; Catinella & Cortese 2015). HIghMass galaxieswere selected without any reference to visual morphology, andthere are no obvious strongly barred galaxies in that sample.The general conclusion from the five HIghMass galaxies withresolved HI is that they must be galaxies about to transitionfrom a gas rich but relatively inactive state, to a state ofvigorous star-formation (Hallenbeck et al. 2014).There are other ongoing surveys of HI-rich galaxieswhich are also relevant for comparison. The Bluedisks project(Wang et al. 2013) is using Westerbork Synthesis Radio Tele-scope (WSRT) observations to investigate the reason for ex-cess HI in some galaxies over that predicted from scaling rela-tions, while Lemonias et al. (2014) present VLA C configura-tion observations of a sample of HI rich, but not star-formingspirals (including for UGC 4109 in our sample). MeanwhileLee et al. (2014)’s “HI Monsters” survey is a CO survey ofvery HI rich galaxies. None of these surveys use informationon galaxy morphology for selection, nor comment on it intheir results, while it is central to the HIRBs selection. Inboth Blue disks and HI Monsters, they find that HI rich (butnot necessarily high HI fraction) spirals are simply scaled upversions of lower mass spirals, and sit on all the typical scalingrelations. The passive HI rich spirals of Lemonias et al. (2014)however show more extended and lower surface brightness HIthan is typical, and it is interesting to note that roughly halfof them appear to host relatively strong bars (see their Fig-ure 3; although we have not explored the significance of thisfraction). All optical photometric and spectroscopic data used in thispaper is taken from the final release of the first phase of theSloan Digital Sky Survey (SDSS Data Release 7, Abazajianet al. 2009), and all HIRB galaxies (and their parent sample)are part of the Main Galaxy Sample of SDSS (MGS, Strausset al. 2002)We make use of morphologies from the second phase ofGalaxy Zoo (GZ2, Willett et al. 2013). These come from theaggregation of classifications made by numerous volunteers onimages from the SDSS for the brightest 25% of MGS galaxies(those with m r < ). In GZ2 a median of 45 people lookingat each galaxy. The GZ2 classification process starts with thequestion: ‘Is this galaxy simply smooth and rounded, with nosigns of a disc?’, where one of the options were ‘features ordisc’, followed by ‘Could this be a disc viewed edge-on?’. The weighted and debiased fraction of users answering a specificway to a single question in GZ2 is denoted, p X . The sampledefined in Masters et al 2012 used p features p not edge − on > p bar and define this as the percentageof ‘yes’ votes to that question (although note that it is not ex-actly this, following a correction for redshift bias as describedin Willett et al. 2013). For example, a galaxy with p bar =0.5suggests that 50% of the people asked if there is a visible barresponded ‘yes’. A comparison with other bar idenfiticationsis shown in Appendix A of Masters et al. (2012, and alsosee Willett et al. 2013). Using this, p bar > u g riz -bands, andwith a variety of apertures. In the NASA Sloan Atlas Blan-ton et al. (2005) provide matched aperture photometry alsoincluding NUV and FUV photometry from the GALEX satel-lite (Martin et al. 2005). We use the Absolute magnitude inrest-frame GALEX/SDSS FN u g riz , from Petrosian aperturesto generate colours, and the stellar mass from K-correctionfit to Petrosian magnitudes. A colour-mass diagram is shownfor the parent sample in Figure 3, with the six HIRB galaxieshi-lighted with the large coloured symbols. As is obvious fromthat diagram HIRB galaxies span a range of optical colours.The SDSS images can also be used to provide more quan-titative details of the bar structures. Following the methoddescribed in Kruk et al. (2017) we obtained two or three com-ponent decompositions for each galaxy in the sample. This isparticularly useful in providing bar lengths and bar positionangles. We give more details on how bar lengths are obtainedin Section 3.1.1 below.We further make use of the SDSS fiber spectra to obtainmeasurements related to the stellar populations and ionizedgas in these galaxies. We note that the SDSS fibre has a 3”size, which represents only 1.2–2.9 kpc at the distance of theHIRB galaxies, as such these spectra measure the proper-ties of only the central parts of these galaxies, well withinthe bar radius. A full spectral fitting is beyond the scope ofthis work, however we make use of line fluxes and spectralindex measurements provided by the Max Planck Institutefor Astrophysics and John’s Hopkins University collaboration(MPA-JHU) . These star formation rates are found using thetechnique described in Brinchmann et al. (2004) while updat-ing the procedure for aperture corrections. This procedure in-cluded calculating the light outside the fiber per galaxy, thenfitting stochastic models to the photometry, akin to thoseused in Salim et al. (2007) . Our HI observations were designed to resolve the optical barat the center of the galaxy in addition to the rest of the , 1– ?? (2018) IRB-I Figure 2.
Optical SDSS gri images of each of the six galaxies in the HIRB sample.MNRAS , 1– ?? (2018) Newnham et al.
Table 1.
Properties of the seven HIRB galaxies used in sample selection. Column 4 is the debiased fraction of GZ users identifying a bar,7 is the global width from ALFALFA (Haynes et al. 2011) (8) Shape and colour used to represent in plotsName R.A. and Dec z p bar log ( M (cid:63) log ( M HI W50 Shape and Colour(J2000) / M (cid:12) ) / M (cid:12) ) km s − (1) (2) (3) (4) (5) (6) (7) (8)UGC 5830 10 42 38.0 +23 57 07 0.044 0.62 11.17 10.40 624UGC 4109 07 56 16.6 +11 39 41 0.046 0.91 11.04 10.46 304 Red SquareUGC 9362 14 33 17.5 +03 54 10 0.030 0.75 10.50 10.34 113 Orange TriangleUGC 9244 14 26 08.4 +05 14 15 0.028 0.59 10.94 10.36 414 Yellow CircleUGC 6871 11 53 46.3 +10 24 10 0.022 0.54 10.55 10.29 346 Green StarUGC 7383 12 20 01.3 +08 36 26 0.025 0.58 10.10 10.38 294 Blue xUGC 8408 13 23 00.3 +13 57 02 0.024 0.88 10.19 10.26 290 Purple Diamond Figure 3.
A colour-mass diagram showing the volume limited AL-FALFA100 galaxies (grey), those of which are strongly barred (or-ange) and with the HIRB galaxies hi-lighted with individual shapesand colours. Two of the HIRBs are at the high mass end of theblue cloud, two are at opposing sides of the green valley (withinthe green lines (Schawinski et al. 2014)) and the remaining twoare in the red sequence. The percentage numbers adjacent to eachHIRB galaxy displays the gas fraction that galaxy has. disk. However the scarcity of gas-rich, strongly barred galax-ies meant that the majority of our targets are at relativelylarge distances ( . < z < . ) compared to typical HIinterferometric targets ( z < . ). The small beam requiredto resolve the centers of these galaxies, necessitated observ-ing with the B-configuration of the VLA with its maximumbaseline of 10 km. The GMRT is comprised of 30 antennassimilarly arranged in a fixed “Y”-configuration with a max-imum baseline of 25 km, but also has 14 antennas concen-trated within 1 km. The combination of long baselines witha compact core mean that the performance of the GMRT isoften compared to the VLA in B-configuration. In balancingresolution with column density sensitivity, our galaxies werechallenging targets to observe. In this section we describe our observing, imaging, and source finding strategies. Table2 summarizes the properties of the final data cubes for all sixgalaxies. We observed UGC 5830, UGC 4109, UGC 6871, and UGC7383 with the VLA in B-configuration between November2013 - January 2014 (Project ID: 13B-142). Each observationwas centered on the H i systemic velocity of the galaxy mea-sured by ALFALFA. The bandwidth spanned 8 MHz dividedinto 512 channels, resulting in a 3.3 km s − resolution overapproximately 1700 km s − . We observed each galaxy for 6x2hours, including calibration, resulting in a total of 10 hourson-source. The data were calibrated and imaged using stan-dard methods in Common Astronomy Software Applications(CASA; McMullin et al. 2007). The final images were madewith natural weighting to provide the best column densitysensitivity.We imaged each 2 hour observing session individually toinspect the quality of the data before combining all sessionstogether. However, UGC 7383 required special attention. Al-though we were able to image all the individual sessions andachieve the expected rms, σ , for unknown reasons the CASA clean task was unable to properly combine the first sessionwith the remaining five. Instead, we imaged the first sessionindividually, the last five sessions together, and combined thetwo resulting cubes in the image plane, weighting them by / σ to create a final dirty (not yet cleaned) image cube ofthe full 10 hours. We performed the same weighting com-bination procedure on the synthesized dirty beam cubes. Inorder to clean the dirty image cubes, we imported the datato the Astronomical Image Processing System (AIPS; Greisen2003) and cleaned the channels individually using the AIPStask APCLN .For UGC 5830, we realized after imaging that a > . Jy source lay at the half power point of the primary beam,causing significant difficulties for imaging and continuum sub-traction. We attempted to do self-calibration on the field, andto subtract the continuum with a number of higher orderpolynomials, but could not completely remove the interferingcontinuum source. We concluded that “third generation” cal-ibration techniques–which include direction dependent gaincalibration–would be required, but given the faintness of H i profile from ALFALFA (UGC 5830 has the second highestredshift in our sample), the effort to make a reliable H i map MNRAS , 1– ?? (2018) IRB-I outweighed the benefits. In the rest of the paper, we excludeUCG 5830 from the analysis. We observed UGC 9244, UGC 9362, UGC 8408 with theGMRT for 22-24 hours each including calibration, with a to-tal of approximately 18-19 hours on source. The observationstook place in February-March 2016 and February 2017, whilethe galaxies were up at night to avoid solar interference andto minimize the incidence of other ground based radio fre-quency interference. We observed using the GMRT’s spec-tral zoom mode with 256 channels across 4 MHz bandwidthcentered on the ALFALFA HI redshift of the galaxy. Thisprovided 3.3 km s − spectral resolution over approximately800 km s − . Unfortunately, due to roll-off at the edges ofthe sideband, less of the band was useable. In the worst case,combined with RFI, the final cube covered 460 km s − , whichfortunately included the galaxy and a few channels for con-tinuum subtraction.We calibrated the data in the standard way using AIPSwhile on site at the GMRT. For imaging purposes the datawere spectrally averaged as little as possible to be able to de-tect reliable signal in individual channels, while still resolvingthe motion of the gas in the disk. The galaxies were imagedwith natural weighting to provide the best column densitysensitivity as possible given the long baselines. In addition,UGC 9362 benefited from self calibration in AIPS which re-duced the noise in the final image by approximately 1/3.Despite careful flagging we found that there were stillstripes in some of the images suggesting bad baselines whichwe had been unable to isolate from looking at the individualvisibilities. Stripes in the image plane are equivalent to a highpoint in the UV plane, and its complex conjugate which hasthe same value. From the orientation and width of the stripeswe can predict the location of the high points in the UVplane. Thus, in order to eliminate the stripes, for each galaxywe Fourier transformed the image cube using the fft task inMiriad (Sault et al. 2011), we blanked the outlier points inthe resulting UV plane data cubes (each image cube producesan amplitude and phase cube) and we performed the inverseFourier transform to return to the image plane. (The inversealso produces an amplitude and phase cube but the phases ofsky image are zero everywhere.) In the end we eliminated theworst offending stripes, and reduced the noise in the cubesby a factor of approximately 1.055.Finally, we spatially smoothed the data of UGC 6871 sothe final spatial resolution and column density sensitivity wasof comparable to those of the other galaxies (see Table 2). In order to create moment maps from the relatively lowsignal-to-noise data we used the automated H i source finderSoFiA, the Source Finding Application (Serra et al. 2015).We used the “smooth and clip” method with a large mergeradius and pixel dilation to capture the large-scale low sur-face brightness flux in each galaxy. The source finder worksiteratively, to find sources in the data down to a user speci-fied signal-to-noise, mask them, smooth the data and search again. The mask is iterated upon and grows with eachsmoothing run. We used kernels which smoothed the data upto only 2 channels in velocity, since our cubes were alreadyaveraged significantly in velocity, and up to × or × pixels spatially. This allowed us to identify and include lowcolumn density gas in our final images, while the momentmaps are presented at full spatial resolution to resolve thecentral regions of each galaxy. The length of a bar is often difficult to define and there isno standard way of measuring it. In this study, we use barlength or refer to twice the bar radius. Commonly used tech-niques to measure bar sizes are based on (1) visual bar lengthmeasurements (for example drawing a line on top of the bar,used in Galaxy Zoo studies, (Hoyle et al. 2011), (2) bar ma-jor axis surface brightness profiles (obtained from photomet-ric decompositions, Kruk et al. (2018)) and (3) ellipse fits togalaxy isophotes (where the bar length is assumed to be atthe maximum of the ellipticity, Sheth et al. (2003); Erwin(2005)).We have used all the three methods to determine the barsizes for the six galaxies in the HIRB Galaxy Survey. First,we measured the bar lengths using visual estimation directlyfrom the SDSS i -band images (which are less prone to dust,and hence better probe the mass distribution). In the secondmethod, the bar size is assumed to be the effective radius of aS´ersic fit to the brightness profile along the bar major axis, ina detailed disc+bar+bulge photometric decomposition donein Kruk et al. (2018) The multi-component decompositionalso allows the position angle of the bar and of the disc to bemeasured. Finally, we used the iraf ellipse routine to fit el-liptical isophotes to the galaxy i -band images and determinedthe bar size at the maximum of the ellipticity. The bar lengthmeasurements agree (within ∼
10% of each other). In general,the bar effective radius is shorter than the manually measurebar length, which is shorter than the estimated value basedon maximum ellipticity. Henceforth, we use the visually mea-sured bar lengths, which are the often the median value ofthe three measurement methods, while the position anglesare based on the disc+bar+bulge decompositions.While bar length cannot be used as any kind of abso-lute chronometer for bar age, all simulations show monotonicincrease in bar length with time (e.g. Athanassoula 2013;Martinez-Valpuesta et al. 2006). We therefore use absolutebar length (measured in kpc) as a proxy for bar age, and tagthe HIRB galaxies in order of their bar length as revealed bythe colour coding of their symbols in all plots (see Figures 1,3, 4, 5 and 6).
In this section we provide some discussion and comments onthe optical morphology of each of the six HIRB galaxies.
MNRAS , 1– ?? (2018) Newnham et al.
Table 2.
Properties of the HIRB galaxy final data cubes. Columns are (2) The spatial resolution of the final image, (4) The rms of thefinal image, (5) The resolution of the restoring clean beam.Galaxy Spectral Resolution Robustness rms Resolution HI Column Density ObservatoryName (km s − ) (Weighting) (Jy beam − chan − ) (arcsec) atoms cm − km s − (1) (2) (3) (4) (5) (6) (7)UGC 4109 19.8 natural . × − . × . . × VLAUGC 9362 31.9 natural . × − . × . . × GMRTUGC 9244 27.5 natural . × − . × . . × GMRTUGC 6871 19.8 natural . × − . × . . × VLA” ” smoothed . × − . × . . × ”UGC 7383 9.9 natural . × − . × . . × VLAUGC 8408 27.5 natural . × − . × . . × GMRT
Table 3.
Optical Properties of the HIRB galaxy sample Columnsare (3) Diameter of the disc (4) Bar to Galaxy ratio, (5) Optical ( u − r ) Name Bar length r Petro
Relative bar ( u − r ) (kpc) (kpc) length(1) (2) (3) (4) (5)UGC 4109 14.48 48.26 0.29 2.76UGC 9362 11.5 30.33 0.36 2.47UGC 9244 8.22 28.60 0.28 2.75UGC 6871 6.36 17.55 0.36 2.08UGC 7383 5.12 14.97 0.30 1.73UGC 8408 4.26 20.85 0.21 1.81 • UGC 4109: is a flocculent spiral which was classified asSB(r)b in (Corwin et al. 1994, hereafter RC3), denoting anSb type with a strong bar and ring. In GZ2, 41/45 classifiersidentified the bar, and four out of five users asked also notedthe ring (questions about rings in Galaxy Zoo are in a sub-menu, often missed). According to our measurements, thisgalaxy has the longest bar of all of the galaxies in the HIRBsample (with a length of 14.5 kpc), which stretches across29% of the optical extent of the galaxy. This galaxy is alsoone of the most massive of the sample, with a stellar mass of . M (cid:12) , and one of the ‘reddest’ of the HIRBs. This galaxyis shown as the red square icon in all sample plots. • UGC 9362: like UGC4109, UGC 9362 is a flocculentspiral galaxy. It was classified as Sbc in the RC3 who somehowmissed the very obvious bar on photographic plates; 21/28GZ2 users identified the obvious bar. It has the second longestbar of the HIRB sample, with a length of 11.5 kpc whichhowever covers 36% of the total extent of it’s optical disc (i.e.more of the galaxy than the bar in UGC 4109). This, which isthe third most massive in the HIRB sample is optically foundin the green valley (close to the red side) and is shown as theorange triangle icon in all sample plots. • UGC 9244: this galaxy has some obvious interactionwith a very close neighbour to the North-East. This has re-sulted in the northern most spiral arm being significantly dis-torted. UGC 9244 has two primary arms and a third smallerone. It was classifed as SBbc in the RC3. It hosts the thirdlongest bar of the sample at 8.2 kpc, or 28% of the diameterof the disc. It has a stellar mass of . M (cid:12) , making it thesecond most massive galaxy of the sample. It is also anotherof the ‘redder’ galaxies in the sample. This galaxy is shownas the yellow circle icon in all sample plots. • UGC 6871: is central in the range of optical colours andstellar masses of the HIRB sample. It has a mass of . M (cid:12) and appears to be on the blue side of the green val-ley. Although UGC 6871 is clearly another flocculent spiral,there is a distortion in one of the arms at the lower left ofthe galaxy. It appears to be stretching out from the galaxytowards the end of the arm. Curiously the RC3 classifies thisas an SB0 (perhaps due to the limitations of photographicimages blurring the flocculent arms together), while Nair &Abraham (2010a) classify it as Sc, missing the fairly obviousbar. In GZ2, 21 out of 39 classifiers indicated the presenceof the bar. The bar is the third shortest of the sample at 6.4kpc or 36% of the diameter of the disc. This galaxy is shownas the green star icon in all sample plots. • UGC 7383: is an obviously blue galaxy. It also has astellar mass of . M (cid:12) , making it the least massive of thesample. Accordingly, UGC 7383 has one of the physicallyshortest bars of the sample at 5.1 kpc, which however stillcovers 30% of the extent of the optical disc. The optical im-age of this galaxy shows two defined, tightly wound spiralarms, without much evidence of interaction with any nearbygalaxies. The RC3 classifies this as Sab, again missing the ob-vious bar, spotted by 22 out of 38 GZ2 classifiers. This galaxyis shown as the blue x icon in all sample plots. • UGC 8408: is also known as NGC 5115. This is thefinal HIRB galaxy and has the shortest actual bar length at4.26 kpc, which is less than third of the length of the longestbar in the sample. While UGC 8408’s bar still covers 21%of the disc’s optical extent, this is the shortest relative barlength of the entire sample, which hints that it might be themost recently formed.UGC 8408 is one of the ‘bluest’ galaxies we observed, itis also the second least massive galaxy with a stellar massvalue of . M (cid:12) . There is some obvious distortion to theoptical morphology of this galaxy. It appears to be a granddesign spiral, with two main arms which are clearly defined.However it seems to also have an extra ‘arm’ which does notquite reach the centre.In the RC3 this galaxy was classified as SBcd. This galaxyis shown as the purple diamond icon in all sample plots. The HIRB sample span a range of properties including gasfraction (Figure 1), galaxy total color (Figure 3), and starformation rate (Figure 4), despite covering a relatively narrowrange in stellar mass (approximately one order of magnitude).From Fig 3 we see that our galaxies span the blue cloud, greenvalley and red sequence. In the following sections we present
MNRAS , 1– ?? (2018) IRB-I Figure 4.
The HIRB galaxies plotted on a Star Formation Ratevs stellar mass (a galaxy star forming sequence) plot. The greypoints show our volume limited subset of ALFALFA100, while theorange points depict the strongly barred of those galaxies, and thecoloured symbols show the HIRB galaxies, with the rainbow orderindicating physical bar length. the optical properties and HI morphologies in relation to thebar length to attempt to explain how they vary with thetransition of galaxies with a high HI content from the bluecloud to the red sequence.We explore the star formation properties of the samplefurther in Figure 4 which makes use of star formation ratesfrom the MPA-JHU catalog. These star formation rates areused to plot the “star forming sequence” of galaxies. We showthe entire parent sample (ALFALFA detected GZ2 galaxies)in grey, with those with strong bars overplotted in orange.Five of the HIRB galaxies are hi-lighted, the final HIRBgalaxy (UGC 7383) has an unreliable flag on its SFR, andso is not plotted, but its optical colours and spectrum sug-gest it is star forming. We see that only two are clearly on thestar forming sequence, with two just below, and one well offit. This is despite all five having significantly more HI thanis expected for their stellar mass.While the SF rates shown in Figure 4 have been correctedfor H α emission from non- star forming sources it is reason-able to wonder if the presence of the strong bar might befeeding an AGN in these galaxies through the in-falling gas.This was shown as likely by Oh et al. (2012), but disputed byGalloway et al. (2015) and Cheung et al. (2015). According toa diagnostic “BPT” diagram (Baldwin et al. 1981), all six ofthe HIRB galaxies and their companions have line emissionwhich comes almost exclusively from star formation regions.None of these galaxies present any evidence for any emissionfrom an AGN.Another useful diagnostic diagram for the optical prop-erties of galaxies D n ( ) against H δ A . This diagram is di-agnostic of the fraction of star formation in the last 2 Gyrs which occured in bursts, versus continuous star formation(Kauffmann et al. 2003). We show this in Figure 5, whichcompares the position of the HIRB galaxies with similarHI masses (left) or similar bar properties (right). Modelsfrom Kauffmann et al. (2003) are indicated, which show re-gions which are populated by smooth star formation histories(green), currently starbursting (cyan) or post-starburst (blue)galaxies, with emission from galaxies with mixed star forma-tion found in the middle. As is noted, the HIRBs typicallylie in the quiescent part of this diagram, as is also normal forgalaxies with similar bar properties (at right), but lie to thelow star formation side of galaxies with similar HI masses.As will be discussed in Section 3.2.2, UGC 4109 (redsquare) and UGC 9244 (yellow circle) both have HI holesat their centre. This suggests the bar has already funneledthe gas towards the very centre, which might then lead toa concentration of H in the centre and therefore we expectyounger population of stars in the centre (e.g. as was observedby Ellison et al. 2011 in a sample of barred galaxies).The HIRB galaxies were run through the star formationhistory software tool starpy (Smethurst et al. 2015). starpy employs a Bayesian method along with ensemble MarkovChain Monte Carlo (Foreman-Mackey et al. 2013) to inferthe parameters describing a simple exponentially decliningstar formation history of a single galaxy. starpy makes useof the SDSS and GALEX optical photometry, specifically thePetrosian magnitude petroMag u and r wavebands, providedby SDSS Data Release 7 (Stoughton et al. 2002) and the NUV waveband from GALEX (Martin et al. 2005). starpy requires the observed u − r and NUV − u colours and redshift.Intrinsic dust is not taken into consideration or modeled for.The full description and method can be found in Section 3.2in Smethurst et al. (2015).Only five of the HIRB galaxies were able to go throughthe starpy software. UGC 6871 was not detected withGALEX; it was right on the edge of a field, meaning thatthe NUV value was not available. Three of the HIRBs (UGC4109, UGC 9244 and UGC 9362) have results which suggestedthey started to quench very early on in their history, and thequenching proceeded slowly so they are probably still starforming. The other two (UGC 8408 and UGC 7383) have be-gun quenching more recently and relatively rapidly. Figure 6shows the HIRB galaxies placement in comparison with thesample used in Smethurst et al. (2015), where we can see thattwo HIRB galaxies are relatively normal u − r colours, whilethree are very red in u − r for their NUV − u colours indicatingthe extremely slow quenching.While the star-formation properties and stellar ages re-vealed by the optical data on HIRB galaxies do not show amonotonic increase with bar length, there is clearly a generaltrend such that those HIRB galaxies with longer bars (red,orange and yellow) are more likely to be passive and haveold stellar populations for their stellar mass than those withshorter bars (blue and purple). This is particularly evident inFigure 6 where the two groups show quite different quenchinghistories. MNRAS , 1– ?? (2018) Newnham et al.
Figure 5. D n ( ) versus H δ A for: Left: all spiral galaxies with a strong bar ( P bar ). Right: spiral galaxies with a HI mass range similarto that shown by the HIRB’s (log( M (cid:12) / M H i ) = 10-10.5). D n ( ) correlates with the global stellar population age (larger is older), whileH δ A peaks in post-starburst galaxies. The background colours shows models of Kauffmann et al. (2003); green for quiescent galaxies, cyanfor starburst galaxies (burst occurred less that 1 Gyr ago), blue shows post-starburst galaxies (burst occurred over 1 Gyr ago) and grey areall other regions covered by the model galaxies Kauffmann et al. (2003). These values are from the 3” SDSS fiber, so we probe the stellarpopulation in the bulge. As with the other figures, the individual HIRB galaxies are shown by different shapes and colours. Table 4.
Our measurements of HI properties of HIRB Galaxies using the GMRT/VLA. Columns are (2) central velocity of HI detection,(3) HI mass Name Central v H I log M H i / M (cid:12) We measure the HI mass for each galaxy in the HIRB sam-ple using the interferometers (VLA and GMRT), and AL-FALFA had already measured the HI mass using the singledish telescope, Arecibo. The masses we measured differ bysmall amounts to the masses from ALFALFA, but this is tobe expected. ALFALFA’s M H i is shown in Table 1, column 6,and the M H i measured from the resolved HI data can be seenin Table 4, column 3. ALFALFA’s measurement was largerin four of the cases (UGC 9362, UGC 9244, UGC 6871, UGC8408). In the other two, where ALFALFA’s HI measurementwas lower than that collected by the interferometer (UGC 4109 & UGC 7383), the data was collected both times by theVLA rather than the GMRT.In all cases we believe the ALFALFA mass is more likelyto be a good measurement of the total HI mass. Single dishradio observations will collect and measure all of the HI de-tected within the beam, which is significantly larger than thebeam of interferometers like the VLA and the GMRT. Thismeans the measured M H i value may include some of flux fromHI in other nearby galaxies or structures at are too nearbyto differentiate between. While reducing resolved HI data, wecan disregard some of the HI we can see is coming from otherstructures, however synthesis imaging will also resolve outsome of the low surface brightness signal received. Becauseof this, synthesis imaging is known to miss HI mass, and itis common practise for the single dish data to be treated as MNRAS , 1– ?? (2018) IRB-I Figure 6. A NUV − U vs u − r plot for the 5 galaxies that were runthrough starpy . Compared to the Smethurst et al. (2015) sample,3 HIRB galaxies (UGC 4109, UGC 9362 and UGC 9244) are veryoptically red in comparison to their blue NUV colours. more reliable measure of total HI mass. We have determinedthat the any nearby galaxies to the HIRB galaxies are outsidethe Arecibo beam. In this section we will describe the HI morphology and con-tent from our VLA/GMRT observations. According to simu-lations (Athanassoula 2013), there should exist a correlationbetween gas fraction, the rate of development of a strongbar, the bar’s formation time, and the morphology of theHI remaining in the galaxy. In this section we investigate ifthis correlation is also present from the data collected by theHIRBs survey.The HI gas fractions ( M H i /( M H i + M ∗ )) for our six galax-ies are shown in Figure 3, and the morphologies shown foreach HIRB galaxy in Figures 7 and 8. We also summarizethis data in Table 4.It is clear from Figures 7 and 8 that there is a varietyof HI morphology revealed by the HIRB galaxies. Figure 9shows the intensity of HI in a slice aligned at the positionangle of the bar; the highlighted region shows exactly wherethe bar is to aid in our description of how HI morphologyrelates to the position of the bar.Both UGC 9362 and UGC 9244 show clear large scaleholes in their centres and Figure 9 shows the absence of anysiginificant amounts of HI in their bar regions at all.While UGC 4109, and UGC 6871 show large scale HIholes, they appear to be significantly offset from their centres.However when looking at the highlighted region in Figure 9we can see that there is still a dip in both of these galaxies’HI intensity at exact position of the bar. This could suggest that the bar is working towards sweeping the central region,but this still does not offer an explanation for the source ofthe large offset hole. It may be that tidal disruption plays arole in the HI morphology shown in these two galaxies.UGC 4109 has also been observed by the VLA in C-configuration in Lemonias et al. (2014). Named GASS 51390in that study, they show the HI intensity map in their Fig-ure 6. While this C configuation has lower spatial resolutionthan our data, we can clearly see there exists a hole in HI.Our observations reveal that the hole is slightly offset fromthe centre. On the opposite side to the offest hole there is adenser region - it is possible that a minor merger has occuredresulting in the unusual HI morphology.UGC 7383 and UGC 8408 are the HIRB galaxies withthe two lowest bar lengths, and neither appear to have ahole in the centre of their HI. Looking at the intensity alongthe exact section of the bar, there is still no evidence of anysignificant dip in the HI intensity. UGC 8408 on the otherhand does have a dip, albeit small enough to not notice whenlooking solely at the intensity map. So perhaps the bar isworking to clear the middle of gas after all.Our VLA observations of UGC 6871 did not detect all thegas associated with the blue-shifted side of the galaxy. Thisis evident from the HI spectrum in Figure 8 (top row, fourthcolumn), in which the emission which is blue shifted withrespect to the systemic velocity of the galaxy is seen in theALFALFA spectrum, but missing from the VLA spectrum.Examining the HI intensity map overlaid on the optical image(Figure 8), we see that the blue-shifted side of the HI disk(northwest) is not as extended compared to the stellar disk,as the red-shifted side of the gas disk is. Initially we thoughtthis asymmetry was tidal in origin, however given the missingflux in the HI profile, we suspect that the gas may be present,but at a column density below what we detect in the VLAobservations.In the first panel for each galaxy we overlay a conser-vative threshold for the HI density typically associated withstar formation (10 M (cid:12) pc − shown by the black contour). InUGC 4109 the majority of this higher density HI is found tothe left of the hole in the HI, in a dense region. UGC 9244and UGC 6871 reach the star formation threshold in manyplaces in the HI however their bar region HI holes are quiteevident. Our two blue galaxies with the shortest bars, UGC7383 and UGC 8408 have HI above the star formation thresh-old throughout their discs, which fits with the picture of themforming stars throughout. Finally UGC 9362 is the only oneof the six HIRB galaxies which does not reach this star form-ing in any significant area (there is a small part which doesaround RA: 14h33m18.5s, Dec: 3 °
54’ but it is too small to beof any significance morphologically). This galaxy does how-ever appear to be forming stars, which must be happening ata lower HI surface density than is typical.HI observations also provide velocity fields. we can seethat the velocity field for four of the HIRB galaxies are rotat-ing regularly (UGC 4109, UGC 9244, UGC 7383 and UGC8408). The remaining two galaxy’s velocities (UGC 9362 andUGC 6871) appear to be somewhat distorted. In UGC 9362,the ‘bluer’ velocities are distributed through the middle ve-locities (green) rather than collected on one side. Similarly,UGC 6871’s ‘redder’ velocities are concentrated in the middle
MNRAS , 1– ?? (2018) Newnham et al.
Figure 7.
HI resolved Data visualized for UGC 4109, UGC 9362 and UGC 9244. For each galaxy the panels from left to right are; (1) The HI total intensitymap depiciting the column density of each pixel. The black contour depicts the star formation threshold at 10 M (cid:12) pc − (Schaye 2004), (2) The SDSS r bandoptical image of the galaxy in greyscale with the contours of the HI total intensity map overlayed. Contour colours are; blue = 3 σ , yellow = 5 σ , green = 8 σ ,magenta = 10 σ , cyan = 20 σ , orange = 30 σ , red = 50 σ . (3) The HI velocity field of the galaxy, expressed in km/s. (4) A comparison of the HI ‘double peak’detected originally by ALFALFA (black) and by our observation with the VLA/GMRT (red). MNRAS , 1– ?? (2018) IRB-I Figure 8.
HI resolved Data visualized for UGC 6871, UGC 7383 and UGC 8408. For each galaxy the panels from left to right are; (1) The HI total intensitymap depiciting the column density of each pixel. The black contour depicts the star formation threshold at 10 M (cid:12) pc − (Schaye 2004), (2) The SDSS r bandoptical image of the galaxy in greyscale with the contours of the HI total intensity map overlayed. Contour colours are; blue = 3 σ , yellow = 5 σ , green = 8 σ ,magenta = 10 σ , cyan = 20 σ , orange = 30 σ , red = 50 σ . (3) The HI velocity field of the galaxy, expressed in km/s. (4) A comparison of the HI ‘double peak’detected originally by ALFALFA (black) and by our observation with the VLA/GMRT (red). MNRAS , 1– ?? (2018) Newnham et al.
Figure 9.
Left: The HI density map of each galaxy. A slice from the data is then taken along the bar and the HI density is then plotted(middle). The area of the bar is highlighted. Right: A slice from the data is taken perpendicular to the bar and the HI density is plotted.MNRAS , 1– ?? (2018) IRB-I of the galaxy rather than being on one side showing rotation.There is a clear disruption in the gas’s regular rotation. Itis possibly that the source of this distortion is nearby com-panions to these galaxies; this will be discussed further in afuture paper (L. Newnham et al. in prep.) The HIRB study was initiated with the goal of investigatingwhat a strong bar does to a gas rich galaxy, or equivalentlywhat a significant quantity of gas in a galaxy does to theevolution of a strong bar.Bar quenching is an idea which has been around in theliterature for some time (e.g. Tubbs 1982) but has recentlygained more attention due to the observation that passive spi-rals have large bar fractions (Masters et al. 2010), the strongtrend of bar fraction with optical colour (Masters et al. 2011;Nair & Abraham 2010a), and suggestions that bars can drivesecular growth of bulges, a morphological characteristic longagreed to correlate with quenched star formation (e.g. Che-ung et al. 2013; Kruk et al. 2018). Simulations of the impactof a bar on gas in a galaxy, demonstrate its ability to redis-tribute gas (e.g. Berentzen et al. 1998; Athanassoula et al.2013; Combes 2008; Villa-Vargas et al. 2010), more recentlysimulations have explicitly explored the possibility for theseflows to lead to global SF quenching (Gavazzi et al. 2015;James & Percival 2016; Spinoso et al. 2016; Khoperskov et al.2018; James & Percival 2018). However there is also a possi-bility that the torques from the bar simply prevent gas fromcollapsing and forming stars at the typical thresholds for star-formation (e.g. the model initially proposed by Tubbs 1982).In Athanassoula (2013) a galaxy’s gas fraction was foundto be influential in the rate of development of the bar itself,with higher gas fractions delaying the formation of the bar,and resulting in weaker bar. Evidence of this link betweengas fraction and the suppression of bar formation is presentin observations which show that bars are less likely to befound in gas rich spirals (or equivalently that barred galaxieshave lower gas content; Masters et al. 2012; Kim et al. 2017).We seek to use observations of HI morphology to provideconstraints on the mechanism of bar quenching, and to under-stand how unusual galaxies with high gas fractions and strongbars came to be. If gas redistribution is the main mechanismwe might expect to see clear evidence for it in the HI mor-phology (e.g. central holes), while if HI gas is present in largequantities and above the typical threshold for star formation( ∼ M (cid:12) pc − , Schaye 2004) in galaxies where star forma-tion is suppressed, we can argue that bar torques preventingthe gas from cool may be more important.Gas-rich and strongly barred galaxies have not beenstudied extensively with resolved HI observations, partly be-cause most surveys for resolved HI do not consider morphol-ogy in their selection, so are likely to miss strongly barredgalaxies, and while there are a small number of very nearbygalaxies with strong bars and resolved HI observations thesetend not to be particularly gas rich galaxies. However thereare resolved HI observations of very nearby galaxies withstrong bars.The HI Nearby Galaxy Survey (THINGS) (Walter et al.2008) survey reaches typical column densities of 4 x 10 cm − , which is comparable to the column densities we reachwith the HIRB sample. They present observations for one ofHIRB-like strongly-barred galaxy, M95, showing in extremedetail the distribution of the HI throughout the galaxy re-vealing a HI hole (and a small HI concentration in the verycentre was also found). Recently, George et al. (2018) tookthese data, along with other multi-wavelength data for M95to argue that redistribution of gas is likely to be the mainprocess for bar quenching in M95 (rather than heating frombar torques).The proto-typical strongly barred galaxy, NGC 1300,also has resolved HI data, taken in the 1980s with the VLA(England 1989). A re-analysis of those data show clearly theHI hole and gas streaming (Lindblad et al. 1997). A largeHI hole is also observed in nearby barred galaxies NGC 3992(Bottema & Verheijen 2002), and NGC 7479 (Laine & Gottes-man 1998), and while there is clear hints of a HI hole in thedate on NGC4123 presented by Weiner et al. (2001) theyalso note evidence for shocks caused by gas flow in the barregion. Contrary to this, the HI morphology in the very late-type barred spiral, NGC 3319 does not show a central hole,but rather gas and star formation all along its bar (Moore& Gottesman 1998). This difference is explained by Moore &Gottesman (1998), as NGC 3319 being a dynamically youngergalaxy than the early-type spirals with strong bars, obviousHI holes and lower gas fractions. Indeed it has a significantlyhigher gas fraction that the other galaxies (56% comparedto 6% gas in M95). It is worth noting that all of these verynearby galaxies with resolved HI have typical (or even low)HI gas fractions for their stellar mass, unlike our HIRB sam-ple which are all at least 3 σ gas-rich outliers in the HI massto stellar mass relation (see Figure 1, where are all HIRBgalaxies are well above the mean line, while these galaxies(not shown) would be on or below it).We will now discuss how the data presented in this pa-per for HIRB galaxies support, or reject the plausible barquenching mechanisms of gas redistribution and/or heatingdue to bar torques in very gas rich galaxies.We particularly compare our observations to the simula-tions of Athanassoula (2013). In that work it is shown thatthe time taken to develop a HI hole will vary from galaxy togalaxy, and also depends on the details of the gas fraction inthe galaxy, with observable HI holes being slow to developin gas rich galaxies even in the presence of a strong bar. Inthat work, the most gas rich galaxies did not develop clearHI holes by the end of the simulation (at 10 Gyrs). It is alsoknown that the bar mass impacts the ability of a bar to evac-uate HI, with Hunter (1990) showing that a bar needs to holdabout 10% of the disc mass to make a central HI depression.We start by now considering the sample in order of HI gasfraction and compare to the gas morphology and timescalesshown in Figure 4 of Athanassoula (2013): • Gas Fraction ∼ : From the simulations of Athanas-soula (2013), all strongly barred galaxies that have a total gasfraction around 20% develop the hole in the centre of the HIby 6 Gyr after the formation of a strong bar. The HIRB sam-ple’s two most gas poor galaxies UGC 4109 and UGC 9244with HI gas fractions of 21% and 17% show an offset hole,and central hole respectively (Figure 3, and Figure 7). Thesegalaxies are therefore consistent with being at this stage of MNRAS , 1– ?? (2018) Newnham et al. their evolution where they formed a bar at least 6 Gyr ago.These are also our two globally reddest galaxies, suggestinga global cessation of star formation, this is backed up, forthe central bulge region at least, by their fibre spectra whichreveal old central stellar populations (Figure 5) , and fur-ther while UGC 4109 (with an offset hole) is only just belowthe star forming sequence, UGC 9244 which has the largestcentral HI hole is well below the star forming sequence (seeFigure 4). M95, with a gas fraction of 6% by mass (Leroyet al. 2008) appears to be another example of this type ofdynamical advanced galaxy with a strong bar. • Gas Fraction ∼ :Three of our galaxies have HI gas fractions around 35-45%.One of these galaxies is in the redder edge of the green valley,one in the bluer edge and one in the blue sequence, as seenin Figure 3, with UGC 9362 (orange triangle) on the redside, UGC 6871 (green star) on the blue side and UGC 8408(purple diamond) well in the blue cloud.According to the simulations of (Athanassoula et al. 2013),a galaxy with 50% of its disc mass in cold gas and a barwhich formed at least 6 Gyr ago would already have a no-ticeable hole in the centre. Indeed both UGC 9362 (orangetriangle) and UGC 6871 (green star) have central HI holes(although UGC 6871’s is offset from the centre), howeverUGC 8408 (purple diamond) does not. This suggests thebar in UGC 8408 may be dynamically younger than thosein both UGC 9362 and UCG6871, and UGC8408’s more vig-orous star-formation and younger stellar population paints asimilar picture of a dynamically younger galaxy. • Gas Fraction ∼ :Our most gas rich galaxy, UGC 7383, despite having a stellarmass of M (cid:63) ∼ M (cid:12) , where gas fractions of around 30-40%are more typical, has a gas fraction of 66% (Figure 3) and dis-plays no evidence for a HI hole in the centre. However lookingat the most gas rich galaxies simulated in Athanassoula et al.(2013) we would not expect to see a HI hole in this type ofgalaxy unless the bar formed more than 10 Gyr ago, as galax-ies with these high gas fractions were not observed to form aHI hole before the end of the simulation.Overall our observations support a picture where bar for-mation is delayed, and therefore the development of a corre-sponding HI hole is delayed in galaxies with very high gasfractions, but that bars are apparently acting to clear HIholes in the centres of galaxies and therefore accelerate thecessation of star-formation globally.We will now look at how the star formation propertiesand optical morphology of the galaxies correlate with the HImorphology. If the development of HI holes are driving barquenching in HIRB galaxies we’d expect that those with holesare under star forming relative to typical galaxies with theirproperties, while those without holes may be more normal.In fact most of the galaxies in the HIRB sample appearto be relatively quiescent, with only two of them appearingin the middle of the star forming sequence (Figure 4), despitetheir large HI reserves. They also show a range of global op-tical colours. • Dynamically Old Bars (HI Hole)
Two of the HIRBs show obvious central HI Holes (UGC9362, orange triangle, and UGC 9244, yellow circle; Figure9), while two have apparently offset HI holes (UGC 4109, red square and UGC 6871, green star). These four have thelongest physical bars again supporting a picture that theirbars are dynamically the oldest among the HIRB galaxies.They do however show a range of star formation proper-ties, with UGC 9244 (yellow circle) well off the star forma-tion sequence, UGC 9362 (orange triangle) and UGC 4109(red square) at the lower edge and UGC 6871 (green star)appearing to still be forming stars at a typical rate. Look-ing at Dn as a tracer of stellar population age we againsee two galaxies with clearly old populations (UGC 4109, redsquare and UGC 9244, yellow circle), while the other two areyounger. Finally, the analysis of likely quenching history us-ing the technique of Smethurst et al. (2015) reveals that thethree galaxies with HI holes where this could be done (UGC6871 did not have a GALEX observation) show a clear sig-nature of unusually slow quenching (red u − r colours, whileremaining relatively blue in NUV − u ; see Figure 6).All in all this supports the idea that a HI hole corre-lates with secular (slow) quenching of star formation, possiblycaused by bar driving gas clearing, however the details of theindividual galaxies are, perhaps not surprisingly hinting at amore complex picture.We will come back to the role of local environment in moredetail in a future paper (L. Newnham et al. in prep.), but it’sclear from the HI morphology, and detections of companionsin the wider field of our data that local interactions may playa role in the history of these galaxies. For example, looking atthe HI distribution in UGC 9244 (Figure 7, bottom row, firstpanel) we can see that it is clearly interacting with a lowermass companion. The HI gas is extended in the directionof the companion, distorting the gas from an elliptical shape.This corresponds with the distortion of the spiral arm, visiblein the optical image of this galaxy (Figure 2, lower right.There is also evidence of interaction in the HI morphology ofUGC 9362 with it’s nearby companions, NSA 18045 (Figure7, middle row, first panel). Although the data has not pickedup any evidence of a HI bridge between the two, we can seethat the HI in NSA 18045 is heavily concentrated in the sideof the galaxy closest to UGC 9362.We have not commented on a mechanism which might cre-ate a offset HI hole not centred on the bar, or galaxy (as seein both UGC 4109 and UGC 6871). This may again pointto some tidal distortions caused by interactions, and perhapsgas rich low mass companions are the reason for HIRBs hav-ing such high gas fractions relative to their other properties.Curiously though, UGC 4109 has no companions which ap-pear local enough to this galaxy to account for it’s distortion,and its HI velocity field is very regular, so that explanationseems unlikely in this case. The other HIRB galaxy with anoffset HI hole, UGC 6871 is also fairly isolated and while it’sHI velocity field looks quite disturbed, we think the VLAdata may have missed some lower column density HI on theblue-shifted side which was detected in the single dish data. • Dynamically Young Bar (No HI Hole)
Both of our HIRB galaxies with no evidence for HI holes(UGC 7383; blue x, and UGC 8408; purple diamond) alsohave the shorter physical bars (and the highest gas fractions)supporting a picture where the gas has delayed bar formation,and the bar has not yet had time (or perhaps is not massiveenough) to sweep out cold gas in the bar region.
MNRAS , 1– ?? (2018) IRB-I These galaxies are both optically blue, and UGC 4808 isfound on the normal star-forming sequence (UGC 7383 hasan unreliable flag in the MPA-JHU derived star formationso we cannot comment on it’s relative location on that dia-gram), they also both have relatively young population ages,and in the models of Smethurst et al. (2015) appear on themain locus of points with evidence perhaps for recent quench-ing. The bar which has not swept out a HI hole in either ofthese, perhaps does not create enough heating to prevent starformation in them either.Despite their higher than average HI content (at least 3 σ above the average HI content for their stellar mass as shown inFigure 1), not all of the HIRB galaxies are actively star form-ing. Our observations of the HI morphology of HIRB galaxiessupport a picture where as a bar forms, grows and developsit sweeps out a hole in the HI gas. The central gas will bedisplaced quicker the lower the gas fraction of the galaxy, i.eUGC 4109 and UGC 9244 both have a low gas fraction andhave evidence of a hole at their centre (UGC9244) or offsetslightly (UGC 4109). So for those two galaxies the bar didn’tnecessarily have to age significantly before the HI morphol-ogy had been disrupted. This also fits with our two galaxieswith the shortest bars, neither UGC 7383 or UGC 8408 haveobvious holes in the centre and happen to be the galaxieswith the highest gas fractions in the sample. This suggeststhat bars need more time to grow to be able to sweep outthe gas from the centre. We can see a slight indent in theintensity of the HI in the centre of these two galaxies (Fig-ure 9) which might hint that the bar is staring to clear thegas. As seen by their range of optical colours (Figure 3) andthe inconsistencies with the star formation trends (Figure 4),these galaxies are in the transition from being star formingand blue, becoming red and ceasing to form stars due to thepresence of the bar. We have collected, reduced and imaged resolved HI data for6 galaxies making up the HI Rich Barred (HIRB) galaxy sur-vey. The galaxies were selected using the ALFALFA surveyand GZ2 morphologies, using the parent sample defined inMasters et al. (2012), and found to have a HI mass in therange of 10.25 < M H i / M (cid:12) < M H i / M ∗ ) more than 3 σ abovethe average for their M ∗ . Strongly barred galaxies were se-lected using the GZ2 bar “probability” of p bar > . . Anyvalue less than that would not be considered a strong bar,either a bar does not exist in that galaxy, or it is weak. Thisresulted in a sample of 48 galaxies which satisfied all of thecriteria, we needed to reduce the number further, in orderto observe and reduce the resolved HI data for them. We se-lected the nearest ten of these, six of which we were able toobtain HI total intensity and velocity fields for using with theGMRT or the VLA. These six galaxies have a range of opticalcolours and bulge sizes, making the sample representative ofthe local massive spiral population.The HIRB galaxies show a variety of star formation prop-erties, despite the presence of a strong bar, which usually correlates with passive spirals (Masters et al. 2010; Fraser-McKelvie et al. 2016) and the presence of large reserves ofHI which usually correlates with strong star formation (Sain-tonge et al. 2012). While some galaxies have central fiberspectra which place them on on the star formation sequenceof galaxies (Figure 4), they are all in the quiescent region ofthe D n δ A plot (Figure 5), although with a widerange of D n ACKNOWLEDGEMENTS.
We thank the staff of theGMRT who have made these observations possible. GMRTis run by the National Centre for Radio Astrophysics of theTata Institute of Fundamental Research. The Karl G. Jan-sky Very Large Array is operated by The National RadioAstronomy Observatory. AIPS and CASA are produced andmanaged by The National Radio Astronomy Observatory.The National Radio Astronomy Observatory is a facility ofthe National Science Foundation operated under coopera-
MNRAS , 1– ?? (2018) Newnham et al.
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