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Star Formation in Galaxies with Large Lower Surface Brightness Disks
We present B, R, and Hα imaging data of 19 large disk galaxieswhose properties are intermediate between classical low surfacebrightness galaxies and ordinary high surface brightness galaxies. Weuse data taken from the Lowell 1.8 m Perkins telescope to determine thegalaxies' overall morphology, color, and star formation properties.Morphologically, the galaxies range from Sb through Irr and includegalaxies with and without nuclear bars. The colors of the galaxies varyfrom B-R=0.3 to 1.9, and most show at least a slight bluing of thecolors with increasing radius. The Hα images of these galaxiesshow an average star formation rate lower than is found for similarsamples with higher surface brightness disks. In addition, the galaxiesstudied have both higher gas mass-to-luminosity ratios and more diffuseHα emission than is found in higher surface brightness samples.
| The AGN and gas disc in the low surface brightness galaxy PGC045080
We present radio observations and optical spectroscopy of the giant lowsurface brightness (LSB) galaxy PGC045080 (or 1300+0144). PGC045080 is amoderately distant galaxy having a highly inclined optical disc andmassive HI gas content. Radio continuum observations of the galaxy werecarried out at 320, 610MHz and 1.4GHz. Continuum emission was detectedand mapped in the galaxy. The emission appears extended over the innerdisc at all three frequencies. At 1.4GHz and 610MHz it appears to havetwo distinct lobes. We also did optical spectroscopy of the galaxynucleus; the spectrum did not show any strong emission lines associatedwith active galactic nucleus (AGN) activity but the presence of a weakAGN cannot be ruled out. Furthermore, comparison of the Hα fluxand radio continuum at 1.4GHz suggests that a significant fraction ofthe emission is non-thermal in nature. Hence we conclude that a weak orhidden AGN may be present in PGC045080. The extended radio emissionrepresents lobes/jets from the AGN. These observations show thatalthough LSB galaxies are metal poor and have very little starformation, their centres can host significant AGN activity. We alsomapped the HI gas disc and velocity field in PGC045080. The HI discextends well beyond the optical disc and appears warped. In the HIintensity maps, the disc appears distinctly lopsided. The velocity fieldis disturbed on the lopsided side of the disc but is fairly uniform inthe other half. We derived the HI rotation curve for the galaxy from thevelocity field. The rotation curve has a flat rotation speed of~190kms-1.
| Exploring Infrared Properties of Giant Low Surface Brightness Galaxies
We present an analysis of Spitzer Space Telescope observations of thethree low surface brightness (LSB) optical giant galaxies Malin 1, UGC6614, and UGC 9024. Mid- and far-infrared morphology, spectral energydistributions, and integrated colors are used to derive the dust mass,dust-to-gas mass ratio, total infrared luminosity, and star formationrate (SFR). We also investigate UGC 6879, which is intermediate betweenhigh surface brightness (HSB) and LSB galaxies. The 8 μm imagesindicate that polycyclic aromatic hydrocarbon (PAH) molecules arepresent in the central regions of all three metal-poor LSB galaxies. Thediffuse optical disks of Malin 1 and UGC 9024 remain undetected at mid-and far-infrared wavelengths. The dustiest of the three LSB galaxies,UGC 6614, has infrared morphology that varies significantly withwavelength; 160 μm (cool) dust emission is concentrated in two clumpson the northeast and northwest sides of a distinct ring seen in the 24and 8 μm images (and a broken ring at 70 μm) at a radius of ~40"(18 kpc) from the galaxy center. The 8 and 24 μm emission iscospatial with Hα emission previously observed in the outer ringof UGC 6614. The estimated dust-to-gas ratios, from less than10-3 to 10-2, support previous indications thatthe LSB galaxies are relatively dust-poor compared to the HSB galaxies.The total infrared luminosities are approximately 1/3 to 1/2 theblue-band luminosities, suggesting that old stellar populations are theprimary source of dust heating in these LSB objects. The SFR estimatedfrom the infrared data ranges ~0.01-0.88 Msolaryr-1, consistent with results from optical studies.
| Spitzer Observations of Low-Luminosity Isolated and Low Surface Brightness Galaxies
We examine the infrared properties of five low surface brightnessgalaxies (LSBGs) and compare them with related but higher surfacebrightness galaxies, using Spitzer Space Telescope images and spectra.All the LSBGs are detected in the 3.6 and 4.5 μm bands, representingthe stellar population. All but one are detected at 5.8 and 8.0 μm,revealing emission from hot dust and aromatic molecules, although manyare faint or pointlike at these wavelengths. Detections of LSBGs at thefar-infrared wavelengths of 24, 70, and 160 μm are varied inmorphology and brightness, with only two detections at 160 μm,resulting in highly varied spectral energy distributions. Consistentwith previous expectations for these galaxies, we find that detectabledust components exist for only some LSBGs, with the strength of dustemission dependent on the existence of bright star-forming regions.However, the far-infrared emission may be relatively weak compared withnormal star-forming galaxies.
| Extended, regular HI structures around early-type galaxies
We discuss the morphology and kinematics of the H I of a sample of 30southern gas-rich early-type galaxies selected from the H I ParkesAll-Sky Survey (HIPASS). This is the largest collection ofhigh-resolution H I data of a homogeneously selected sample. Given thesensitivity of HIPASS, these galaxies represent the most H I-richearly-type galaxies. In two-thirds of the galaxies, we find the H I tobe in a large, regular disk- or ring-like structure that in some casesis strongly warped. In the remaining cases we find the H I distributedin irregular tails or clouds offset from the galaxy. The giant, regularH I structures can be up to ~200 kpc in diameter and contain up to1010~M_ȯ of H I. The incidence of irregular H Istructures appears to be somewhat higher in elliptical galaxies, but thelarge, regular structures are observed in both elliptical and S0galaxies and are not strictly connected to the presence of a stellardisk. If these two types of galaxies are the result of differentformation paths, this is not strongly reflected in the characteristicsof the H I. The size and the regular kinematics of the H I structuresimply that the neutral hydrogen must have settled in these galaxiesseveral Gyr ago. Merging as well as gas accretion from the IGM areviable explanations for the origin of the gas in these galaxies. Theaverage column density of the H I is low so that little star formationis expected to occur and these early-type galaxies can remain gas richfor very long periods of time. The large H I structures likely representkey structures for tracing the origin and evolution of these galaxies.
| A Normal Stellar Disk in the Galaxy Malin 1
Since its discovery, Malin 1 has been considered the prototype and mostextreme example of the class of giant low surface brightness diskgalaxies. Examination of an archival Hubble Space Telescope I-band imagereveals that Malin 1 contains a normal stellar disk that was notpreviously recognized, having a central I-band surface brightness ofμ0=20.1 mag arcsec-2 and a scale length of 4.8kpc. Out to a radius of ~10 kpc, the structure of Malin 1 is that of atypical SB0/a galaxy. The remarkably extended, faint outer structuredetected out to r~100 kpc appears to be a photometrically distinctcomponent and not a simple extension of the inner disk. In terms of itsdisk scale length and central surface brightness, Malin 1 was originallyfound to be a very remote outlier relative to all other known diskgalaxies. The presence of a disk of normal size and surface brightnessin Malin 1 suggests that such extreme outliers in disk propertiesprobably do not exist, but underscores the importance of the extendedouter disk regions for a full understanding of the structure andformation of spiral galaxies.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the Data Archive at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| Constraints on galaxy structure and evolution from the light of nearby systems
We review knowledge of galaxy structures obtained by their emitted lightand in the local universe where they can be studied in great detail. Wediscuss the shapes of, and stellar motions within, galaxies,compositional clues derived from their spectra, and what luminous matterimplies about their dark matter content. Implications on the currenttheory of hierarchical galaxy formation are explored.
| A massive spiral galaxy in the Zone of Avoidance
We report the discovery of a very HI-massive disc galaxy, HIZOAJ0836-43,at a velocity of vhel = 10689kms-1, correspondingto a distance of 148Mpc (assuming H0 =75kms-1Mpc-1). It was found during the course of asystematic HI survey of the southern Zone of Avoidance (ZOA) (|b| <=5°) with the multibeam system at the 64-m Parkes radio telescope.Follow-up observations with the Australia Telescope Compact Array revealan extended HI disc. We derive an HI mass of 7.5 ×1010Msolar. Using the HI radius, we estimate atotal dynamical mass of 1.4 × 1012Msolar,similar to the most massive known disc galaxies such as Malin1.HIZOAJ0836-43 lies deep in the ZOA where the optical extinction is veryhigh, AB = 9.8mag. However, in the near-infrared (NIR)wavebands, where the extinction is considerably lower, HIZOAJ0836-43 isclearly detected by both the Deep Near Infrared Survey of the SouthernSky (DENIS) and Two-Micron All-Sky Survey (2MASS). Deep Anglo-AustralianTelescope NIR (Ks and H band) images show that HIZOAJ0836-43is an inclined disc galaxy with a prominent bulge (scalelength 2.5arcsecor 1.7kpc), and an extended disc (scalelength 7arcsec or 4.7kpc) whichcan be traced along the major axis out to a radius of 20arcsec or13.4kpc (at 20magarcsec-2 in Ks). The HI disc ismuch more extended, having a radius of 66kpc at1Msolarpc-2. Detections in the radio continuum at1.4GHz and at 60μm (IRAS) are consistent with HIZOAJ0836-43 formingstars at a rate of ~35Msolaryr-1. We compare theproperties of HIZOAJ0836-43 with those of the most HI-massive galaxiescurrently known, UGC4288, UGC1752 and Malin1, all of which areclassified as giant low surface brightness galaxies.The observations were obtained with the Australia Telescope which isfunded by the Commonwealth of Australia for operations as a NationalFacility managed by CSIRO.E-mail: jdonley@as.arizona.edu
| The Millennium Galaxy Catalogue: a census of local compact galaxies
We use the Millennium Galaxy Catalogue (MGC) to study the effect ofcompact galaxies on the local field galaxy luminosity function (LF).Here, we observationally define as `compact' galaxies that are too smallto be reliably distinguished from stars using a standard star-galaxyseparation technique. In particular, we estimate the fraction ofgalaxies that are misclassified as stars due to their compactness.We have spectroscopically identified all objects to BMGC =20mag in a 1.14-deg2 subregion of the MGC, regardless ofmorphology. From these data we develop a model of the high surfacebrightness (SB) incompleteness and estimate that ~1 per cent of galaxieswith BMGC < 20mag are misclassified as stars, with anupper limit of 2.3 per cent at 95 per cent confidence. However, sincethe missing galaxies are preferentially sub-L* their effect on the faintend of the LF is substantially amplified: we find that they contribute~6 per cent to the total LF in the range -17 < MB <-14mag, which raises the faint end slope α by0.03+0.02-0.01. Their contribution to the totalB-band luminosity density is ~2 per cent. Roughly half of the missinggalaxies have already been recovered through spectroscopy ofmorphologically stellar targets selected mainly by colour. We find thatthe missing galaxies mostly consist of intrinsically small, blue, starforming, sub-L* objects.In combination with the recent results of Driver et al. we have nowdemonstrated that the MGC is free from both high- and low-SB selectionbias for giant galaxies (MB <~ -17mag). Dwarf galaxies, onthe other hand, are significantly affected by these selection effects.To gain a complete view of the dwarf population will require both deeperand higher-resolution surveys.
| Morphology and star formation in nearby low surface brightness galaxies
We present observations (B, R, K, Hα and HI) of six nearby lowsurface brightness galaxies (LSBGs). They show an astonishing amount ofvariety; while some systems appear smooth and featureless, othersresolve into loose assemblies of gas clouds. We have derived rotationcurves, gas surface density profiles and star formation thresholds forthree of the galaxies.The results have been used to test two ideas describing their starformation: one in which star formation depends solely on the HI gassurface density, and one that depends on differential rotation. We findthat a critical HI surface density criterion in the range 2.6-12.6× 1020cm-2(2.1-10.1Msolarpc-2) best describes thestar-forming ability of these galaxies on local and global scales. Acritical gas surface density based on the rotation of the gas is alsoable to describe the results on a global scale for two of the threegalaxies for which we were able to derive rotation curves.
| On Star Formation and the Nonexistence of Dark Galaxies
We investigate whether a baryonic dark galaxy or ``galaxy withoutstars'' could persist indefinitely in the local universe, whileremaining stable against star formation. To this end, a simple model hasbeen constructed to determine the equilibrium distribution andcomposition of a gaseous protogalactic disk. Specifically, we determinethe amount of gas that will transit to a Toomre unstable cold phase viathe H2 cooling channel in the presence of a UV-X-ray cosmicbackground radiation field. All but one of the models are predicted tobecome unstable to star formation: we find that, in the absence of aninternal radiation field, the majority of gas will become Toomreunstable in all putative dark galaxies with baryonic masses greater than109 Msolar, and in at least half of those greaterthan 106 Msolar. Moreover, we find that all ourmodel objects would be detectable via H I line emission, even in thecase that star formation is potentially avoided. These results areconsistent with the nondetection of isolated extragalactic H I cloudswith no optical counterpart (galaxies without stars) by the H I ParkesAll-Sky Survey. Additionally, where star formation is predicted tooccur, we determine the minimum interstellar radiation field required torestore gravothermal stability, which we then relate to a minimum globalstar formation rate. This leads to the prediction of a previouslyundocumented relation between H I mass and star formation rate that isobserved for a wide variety of dwarf galaxies in the H I mass range108-1010 Msolar. The existence of sucha relation strongly supports the notion that the well-observedpopulation of dwarf galaxies represents the minimum rates ofself-regulating star formation in the universe.
| Pre-heating by pre-virialization and its impact on galaxy formation
We use recent observations of the HI mass function to constrain galaxyformation. The data conflict with the standard model where most of thegas in a low-mass dark matter halo is assumed to settle into a disc ofcold gas that is depleted by star formation and supernova-drivenoutflows until the disc becomes gravitationally stable. Assuming a starformation threshold density supported by both theory and observations,this model predicts HI masses that are much too large. The reason issimple: supernova feedback requires star formation, which in turnrequires a high surface density for the gas. Heating by the ultravioletbackground can reduce the amount of cold gas in haloes with masses<109.5h-1 Msolar, but isinsufficient to explain the observed HI mass function. A consistentmodel can be found if low-mass haloes are embedded in a pre-heatedmedium, with a specific gas entropy ~10 keV cm2. In addition,such a model simultaneously matches the faint-end slope of the galaxyluminosity function without the need for any supernova-driven outflows.We propose a pre-heating model where the medium around low-mass haloesis pre-heated by gravitational pancaking. Because gravitational tidalfields suppress the formation of low-mass haloes while promoting that ofpancakes, the formation of massive pancakes precedes that of thelow-mass haloes within them. We demonstrate that the progenitors ofpresent-day dark matter haloes with M<~ 1012h-1Msolar were embedded in pancakes of masses ~5 ×1012h-1 Msolar at z~ 2. The formationof such pancakes heats the gas to a temperature of 5 ×105 K and compresses it to an overdensity of ~10. Such gashas a cooling time that exceeds the age of the Universe at z<~ 2, andhas a specific entropy of ~15 keV cm2, almost exactly theamount required to explain the stellar and HI mass functions.
| The Gas Content in Galactic Disks: Correlation with Kinematics
We consider the relationship between the total HI mass in late-typegalaxies and the kinematic properties of their disks. The mass M HI forgalaxies with a wide variety of properties, from dwarf dIrr galaxieswith active star formation to giant low-brightness galaxies, is shown tocorrelate with the product V c R 0 (V c is the rotational velocity, andR 0 is the radial photometric disks cale length), which characterizesthe specific angular momentum of the disk. This correlation, along withthe decrease in the relative mass of the gas in a galaxy with increasingV c, can be explained in terms of the previous assumption that the gasdensity in the disks of most galaxies is maintained at a level close tothe threshold (marginal) stability of a gaseous layer to localgravitational perturbations. In this case, the regulation mechanism ofthe star formation rate associated with the growth of localgravitational instability in the gaseous layer must play a crucial rolein the evolution of the gas content in the galactic disk.
| The cosmological significance of low surface brightness galaxies found in a deep blind neutral hydrogen survey
Minchin et al. have recently placed limits on the cosmologicalsignificance of gas-rich low surface brightness (LSB) galaxies as aproportion of the total population of gas-rich galaxies by carrying outa very deep survey (HIDEEP) for neutral hydrogen (HI) with the Parkesmultibeam system. Such a survey avoids the surface brightness selectioneffects that limit the usefulness of optical surveys for finding LSBgalaxies. To complement the HIDEEP survey, we have digitally stackedeight 1-h R-band Tech Pan films from the UK Schmidt Telescope covering36 deg2 of the survey area to reach a very deep isophotallimit of 26.5 Rmag arcsec-2. At this level, we find that allof the 129 HI sources within this area have optical counterparts andthat 107 of them can be identified with individual galaxies. We haveused the properties of the galaxies identified as the opticalcounterparts of the HI sources to estimate the significance of LSBgalaxies (defined to be those at least 1.5 mag dimmer in effectivesurface brightness than the peak in the observed distribution seen inoptical surveys). Two different methods of correcting for ease ofdetection do not yield significantly different results: LSB galaxiesmake up 62 +/- 37 per cent of gas-rich galaxies by number according toour first method (weighting by HI mass function), which includes acorrection for large-scale structure, or 51 +/- 20 per cent whencalculated by our second method (1/Vmax correction). We alsofind that LSB galaxies provide 30 +/- 10 per cent of the contribution ofgas-rich galaxies to the neutral hydrogen density of the Universe, 7 +/-3 per cent of their contribution to the luminosity density of theUniverse, 9 +/- 4 of their contribution to the baryonic mass density ofthe Universe, 20 +/- 10 per cent of their contribution to the dynamicalmass density of the Universe, and 40 +/- 20 per cent of theircross-sectional area. We do not find any `crouching giant' LSB galaxiessuch as Malin 1, nor do we find a population of extremely low surfacebrightness galaxies not previously found by optical surveys. Suchobjects must be either rare, gas-poor or outside the survey detectionlimits.
| Properties of Molecular Gas in Massive Low Surface Brightness Galaxies, Including New 12CO Observations of Three Malin 1 ``Cousins''
To date, the only low surface brightness (LSB) galaxies that have beendetected in CO are the massive LSB (MLSB) galaxies. In 2003, O'Neil,Schinnerer, & Hofner hypothesized that it is the prominent bulgecomponent in MLSB galaxies, not present in less massive LSB galaxies,that gives rise to the detectable quantities of CO gas. To test thishypothesis, we have used the IRAM 30 m telescope to obtain three new,deep CO J(1-0) and J(2-1) observations of MLSB galaxies. Two of thethree galaxies observed were detected in CO-one in the J(1-0) line andthe other in both the J(1-0) and J(2-1) lines-bringing the total numberof MLSB galaxies with CO detections to five, out of a total of nine MLSBgalaxies observed at CO to date. The third object had no detection to 2mK at CO J(1-0). Comparing all MLSB galaxy CO results with surveys ofhigh surface brightness galaxies, we find that the MLSB galaxies'MH2 and MH2/MHIvalues fall within the ranges typically found for high surfacebrightness objects, albeit at the low end of the distribution, with thetwo MLSB galaxies detected at CO in this survey having the highestMH2/MHI values yet measured for any LSBsystem, by factors of 2-3.
| New Reference Galaxy Standards for H I Emission Observations
We have taken advantage of the improved baselines and higher sensitivityavailable with the upgraded Arecibo 305 m telescope to create a new H Ispectral line catalog of disk galaxies that can be used as a referencecatalog for anyone interested in 21 cm spectral line work. In all 108galaxies were observed, covering 24 hr of the sky at declinationsbetween 0° and 36° and velocities between 0 and 25,000 kms-1. The majority of the galaxies were observed at least twotimes on different nights to avoid problems with radio frequencyinterference, baseline fluctuations, etc. Comparing our measured valueswith all those available in the literature shows that although largeindividual variations may exist, the average difference between themeasurements is zero. In all we have considerable confidence in ourmeasurements, and the resulting catalog should be extremely useful as awell-defined reference catalog for anyone interested in 21 cm spectralline work.
| ESO 215-G?009: An Extreme H I-Rich Dwarf Irregular Galaxy
We present deep BVRI band images and H I line observations of thenearby, low surface brightness galaxy ESO 215-G?009, which were obtainedwith the Australian National University 2.3 m telescope and theAustralia Telescope Compact Array, respectively. ESO 215-G?009 wasselected from the HIPASS Bright Galaxy Catalog because it has the secondhighest H I mass-to-light ratio of the galaxies with measured B-bandapparent magnitudes. We find that it is an isolated dwarf irregulargalaxy with an old stellar population. We place an upper limit on thecurrent star formation rate of ~2.5×10-3Msolar yr-1. The extended H I disk showsregular rotation (vrot=51+/-8 km s-1) and, at acolumn density of ~5.0×1019 atoms cm-2, canbe traced out to over 6 times the Holmberg radius of the stellarcomponent (radius at μB=26.6 mag arcsec-2).After foreground star subtraction, we measure a B-band apparentmagnitude of 16.13+/-0.07 mag within a radius of 80". The H I fluxdensity is 122+/-4 Jy km s-1 within a radius of 370". Given aGalactic extinction of AB=0.95+/-0.15 mag, we derive an H Imass-to-light ratio of 22+/-4 Msolar/Lsolar,Bfor ESO 215-G?009. To our knowledge this is the highestMHI/LB ratio for a galaxy to be confirmed byaccurate measurement to date.
| Beyond the Galaxy Luminosity Function
With the advent of large-scale surveys (i.e. Legacy Surveys) it is nowpossible to start looking beyond the galaxy luminosity function (LF) tomore detailed statistical representations of the galaxy population, i.emultivariate distributions. In this review I first summarise the currentstate-of-play of the B-band global and cluster LFs and then brieflypresent two promising bivariate distributions: the luminosity-surfacebrightness plane (LSP) and the colour-luminosity plane (CLP). In bothplanes galaxy bulges and galaxy disks form marginally overlapping butdistinct distributions, indicating two key formation/evolutionaryprocesses (presumably merger and accretion). Forward progress in thissubject now requires the routine application of reliable bulge-diskdecomposition codes to allow independent investigation of these two keycomponents.
| The First CO Map of a Low Surface Brightness Galaxy
Using the Owens Valley Radio Observatory (OVRO) Millimeter-WavelengthArray, we have obtained the first CO map of a low surface brightness(LSB) galaxy. The studied galaxy, UGC 01922, was chosen for theseobservations because of both its previous CO detection with the IRAM 30m telescope and its classification as a Malin 1 ``cousin'' an LSB galaxywith MHI>=1010 Msolar. The OVRO mapdetected approximately 65% of the CO (1-0) flux found earlier with thesingle-dish measurements, giving a detected gas mass equivalent toMH2=1.1×109 Msolar.The integrated gas peak lies at the center of the galaxy and coincideswith both the optical and 1.4 GHz continuum emission peaks. Themolecular gas extends well beyond the OVRO beam size (~4" or 3 kpc),covering ~25% of the optical bulge. In all, perhaps the most remarkableaspect of this map is its unexceptional appearance. Given that it tookover 10 years to successfully detect molecular gas in any LSB system, itis surprising that the appearance and distribution of UGC 01922's CO issimilar to what would be expected for a high surface brightness galaxyin the same morphological class.
| Further Discoveries of 12CO in Low Surface Brightness Galaxies
Using the IRAM 30 m telescope we have obtained seven new, deep CO J(1-0)and J(2-1) observations of low surface brightness (LSB) galaxies. Fiveof the galaxies have no CO detected to extremely low limits [0.1-0.4 Kkm s-1 at J(1-0)], while two of the galaxies, UGC 01922 andUGC 12289, have clear detections in both line transitions. When theseobservations are combined with all previous CO observations taken of LSBsystems, we compile a total of 34 observations, in which only threegalaxies have had detections of their molecular gas. Comparing the LSBgalaxies with and without CO detections with a sample of high surfacebrightness (HSB) galaxies with CO observations indicates that it isprimarily the low density of baryonic matter within LSB galaxies that iscausing their low CO fluxes. Finally, we note that one of the massiveLSB galaxies studied in this project, UGC 06968 (a Malin 1 ``cousin''),has upper limits placed on both MH2 andMH2/MHI that are 10-20 times lower thanthe lowest values found for any galaxy (LSB or HSB) with similar globalproperties. This may be due to an extremely low temperature andmetallicity within UGC 06968 or simply due to the CO distribution withinthe galaxy being too diffuse to be detected by the IRAM beam.
| Properties of Low Surface Brightness Galaxies and Normal Spirals in the Near-Infrared
We present results for J and Ks near-IR imaging data on alarge sample of 88 galaxies drawn from the catalog of Impey et al. Thegalaxies span a wide range in optical and IR surface brightness andmorphology (although they were drawn from a catalog constructed toidentify low surface brightness galaxies [LSBGs]). They were alsoselected to include very low and high H I mass galaxies in order toensure that they span a wide range of evolutionary states. The near-IRdata unveil many features of LSBGs not seen before in the optical.First, a high fraction of the observed LSBGs are very luminous in thenear-IR, indicating that they have a well-developed old stellarpopulation and that older LSBGs are more frequent in the universe thandata from optical bands suggested. Second, the near-IR morphologies areoften quite different than those seen in the optical. Many diffuse LSBGsthat are apparently bulgeless when observed in blue bands insteadexhibit nuclei in J and Ks bands. Third, we find significanttrends between the near-IR morphologies of the galaxies and their ratioof H I mass to near-IR luminosity. Fourth, we find no trend in disksurface brightness with absolute magnitude but significant correlationswhen the bulge surface brightness is used. Finally, we find that theformation of a bulge requires a galaxy to have a total baryonic massabove ~1010 Msolar. A wide variety of othercorrelations are explored for the sample. We consider correlations amongmorphologies, surface brightnesses, near-IR colors, absolute magnitudes,and H I masses. In addition, using previous results by Bell & deJong, we convert the galaxies' near-IR luminosities to stellar masses onthe basis of color-dependent stellar mass-to-light ratios. This allowsus to consider correlations among more fundamental physical quantities,such as the H I mass, the stellar mass, the total baryonic mass, the gasmass fraction, the mass surface density, and the metallicity (via thehighly metal sensitive color index J-Ks). We find that thestrongest of our correlations are with the ratio of H I mass to totalbaryonic mass, MHI/Mbaryonic, which tracks theevolutionary state of the galaxies as they convert gas into stars andwhich ranges from 0.05 up to nearly 1 for the galaxies in our sample. Wefind strong systematic trends in how the metallicity-sensitiveJ-Ks color becomes redder with decreasingMHI/Mbaryonic, as would be expected for``closed-box'' models of chemical enrichment. However, the increasedscatter with increasing gas mass fraction and decreasing galaxy masssuggests that gas infall is increasingly significant in the gas-richlower mass systems. We argue that the overall range in J-Kscolor argues for at least a factor of 20 change in the mean stellarmetallicity across the mass range spanned by our sample. We also seestrong trends between MHI/Mbaryonic and centralsurface density, suggesting that increased star formation efficiencywith increasing gas surface density strongly drives the conversion ofgas into stars.
| The luminosity function of the Virgo Cluster from MB=-22 to -11
We measure the galaxy luminosity function (LF) for the Virgo Clusterbetween blue magnitudes MB=-22 and -11 from wide-fieldcharge-coupled device (CCD) imaging data. The LF is only graduallyrising for -22
| Ultra compact objects in the Fornax cluster of galaxies: Globular clusters or dwarf galaxies?
The relation between the Ultra Compact Objects (hereafter UCOs) recentlydiscovered in the Fornax cluster (Drinkwater et al. \cite{Drinkw00a};Hilker et al. \cite{Hilker99}) and the brightest globular clustersassociated with the central galaxy NGC 1399 has been investigated. Thequestion was adressed whether the UCOs constitute a distinct populationof objects not linked to globular clusters or whether there is a smoothtransition between both populations. Therefore, a spectroscopic surveyon compact objects in the central region of the Fornax cluster wascarried out with the 2.5 m du Pont telescope (LCO). UCOs and the brightNGC 1399 globular clusters with similar brightness were inspected. 12GCs from the bright end of the globular cluster luminosity function havebeen identified as Fornax members. Eight are new members, four wereknown as members from before. Their magnitude distribution supports asmooth transition between the faint UCOs and the bright globularclusters. There is no evidence for a magnitude gap between bothpopulations. However, the brightest UCO clearly stands out; it is toobright and too large to be accounted for by globular clusters. For theonly UCO included in our survey, a relatively high metallicity of [Fe/H]=~ -0.5 dex is measured.
| Gas-rich galaxies and the H I mass function
We have developed an automated cross-correlation technique to detect21cm emission in sample spectra obtained from the HI Parkes All SkySurvey. The initial sample selection was the nearest spectra to 2435low-surface-brightness galaxies in the catalogue of Morshidi-Esslinger,Davies and Smith. The galaxies were originally selected to haveproperties similar to Fornax cluster dE galaxies. As dE galaxies aregenerally gas poor it is not surprising that there were only 26 securedetections. All of the detected galaxies have very high values of(MH/LB)solar. Thus the HI selection offaint optical sources leads to the detection of predominately gas-richgalaxies. The gas-rich galaxies tend to reside on the outskirts of thelarge-scale structure delineated by optically-selected galaxies, butthey do appear to be associated with it. These objects appear to haverelative dark matter content similar to that of optically-selectedgalaxies. The HI-column densities are lower than the `critical density'necessary for sustainable star formation and they appear, relatively,rather isolated from companion galaxies. These two factors may explaintheir high relative gas content. We have considered the HI mass functionby looking at the distribution of velocities of HI detections in randomspectra on the sky. The inferred HI mass function is steep, thoughconfirmation of this result awaits a detailed study of the noisecharacteristics of the HI survey.
| High and Low Surface Brightness Galaxies in the Local Universe. IV. Optical and 21 Centimeter Spectroscopy
We present flux-calibrated spectra in the range 3500 to 8000 Å forthe nuclear regions of 250 galaxies and H I 21 cm line profiles for 238galaxies selected from the catalog of low surface brightness galaxiesidentified in Automated Plate Measuring Facility (APM) scans of UKSchmidt Telescope survey plates. For the optical spectra, common nebularabsorption- and emission-line equivalent widths and emission-line fluxeswere measured with typical errors of about 20%. H I mass and velocitywidths were measured from the 21 cm line emission, with 15% accuracy.Galaxies in this study span over 6 mag in surface brightness. Only about20% of these galaxies show spectroscopic evidence of active galacticnuclei. Derived quantities such as synthetic colors, metallicity, starformation rate, the ratio of neutral hydrogen mass to blue light, andgas mass fraction are presented in a companion paper.
| Ultracompact Dwarf Galaxies in the Fornax Cluster
By utilizing the large multiplexing advantage of the Two-degree Fieldspectrograph on the Anglo-Australian Telescope, we have been able toobtain a complete spectroscopic sample of all objects in a predefinedmagnitude range, 16.5
| The Ursa Major cluster of galaxies - III. Optical observations of dwarf galaxies and the luminosity function down to MR=-11
Results are presented of a deep optical survey of the Ursa Majorcluster, a spiral-rich cluster of galaxies at a distance of 18.6Mpcwhich contains about 30 per cent of the light but only 5 per cent of themass of the nearby Virgo cluster. Fields around known cluster membersand a pattern of blind fields along the major and minor axes of thecluster were studied with mosaic CCD cameras on the Canada-France-HawaiiTelescope. The dynamical crossing time for the Ursa Major cluster isonly slightly less than a Hubble time. Most galaxies in the localUniverse exist in similar moderate-density environments. The Ursa Majorcluster is therefore a good place to study the statistical properties ofdwarf galaxies, since this structure is at an evolutionary stagerepresentative of typical environments, yet has enough galaxies thatreasonable counting statistics can be accumulated. The mainobservational results of our survey are as follows. (i) The galaxyluminosity function is flat, with a logarithmic slope α=-1.1 for-17
| A Morphological Type Dependence in the μ0-log h Plane of Spiral Galaxy Disks
We present observational evidence for a galaxy ``type'' dependence tothe location of a spiral galaxy's disk parameters in theμ0-logh plane. With a sample of approximately 40 lowsurface brightness galaxies (both bulge- and disk-dominated) andapproximately 80 high surface brightness galaxies, the early-type diskgalaxies (<=Sc) tend to define a bright envelope in theμ0-logh plane, while the late-type (>=Scd) spiralgalaxies have, in general, smaller and fainter disks. Below the definingsurface brightness threshold for a low surface brightness galaxy (i.e.,more than 1 mag fainter than the 21.65 B mag arcsec-2 Freemanvalue), the early-type spiral galaxies have scale lengths greater than8-9 kpc, while the late-type spiral galaxies have smaller scale lengths.All galaxies have been modeled with a seeing-convolved Sérsicr1/n bulge and exponential disk model. We show that the trendof decreasing bulge shape parameter n with increasing Hubble type anddecreasing bulge-to-disk luminosity ratio, which has been observed amongthe high surface brightness galaxies, extends to the low surfacebrightness galaxies, revealing a continuous range of structuralparameters.
| The Z=0 Galaxy Luminosity Function. I. Techniques for Identification of Dwarf Galaxies at ~10 MPC
We present a program to study the galaxy luminosity function of the LeoI and Coma I Groups at ~10 Mpc. We have surveyed over 7 deg2in Leo I and ~11 deg2 in Coma I. In this paper, we detail themethod we have developed and implemented for identifying onmorphological grounds low surface brightness, MR<-10,dwarf galaxies at a distance of 10 Mpc. We also describe extensive MonteCarlo simulations of artificial galaxies, which we use to tune ourdetection algorithms and evaluate our detection efficiency and parameterrecovery as a function of R-band central surface brightnessμR(0) and total magnitude RT. We find for asubset of our Leo I data that at the 90% completeness level, we candetect dwarfs comparable to Antlia and Sculptor. Finally, we describepreliminary follow-up observations that confirm we are detecting dwarfspheroidal galaxies in Leo I at 10 Mpc.
| Galactosynthesis: halo histories, star formation and discs
We investigate the effects of a variety of ingredients that must enterinto a realistic model for disc galaxy formation, focusing primarily onthe Tully-Fisher (TF) relation and its scatter in several wavebands. Inparticular, we employ analytic distributions for halo formationredshifts and halo spins, empirical star formation rates and initialmass functions, realistic stellar populations, and chemical evolution ofthe gas. Our main findings are as follows. (a) The slope, normalizationand scatter of the TF relation across various wavebands are determinedlargely by the parent halo properties as dictated by the initialconditions, but are also influenced by star formation in the disc. (b)TF scatter in this model is due primarily to the spread in formationredshifts. The scatter can be measurably reduced by chemical evolution,and also by the weak anticorrelation between peak height and spin. (c)Multiwavelength constraints can be important in distinguishing betweenmodels that appear to fit the TF relation in I or K. (d) Assumingpassive disc evolution, successful models seem to require that the bulkof disc formation cannot occur too early (z>2-3) or too late(z<0.2), and are inconsistent with high values ofΩ0. (e) A simple, realistic model with the aboveingredients, and fewer free parameters than typical semi-analyticmodels, can reasonably reproduce the observed z=0 TF relation in allbands (B, R, I and K), as well as the observed B-band surfacebrightness-magnitude relation. In such a model, the near-infrared TFrelation at z=1 is similar to that at z=0, while bluer bands show amarkedly steeper TF slope at high redshift, consistent with limitedcurrent data. The remarkable agreement with observations suggests thatthe amount of gas that is expelled or poured into a disc galaxy may besmall (though small fluctuations might serve to align B-band predictionsbetter with observations), and that the specific angular momentum of thebaryons should roughly equal that of the halo; there is little room forangular momentum transfer. In Appendix A we present analytic fits tostellar population synthesis models.
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