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The Survey for Ionization in Neutral Gas Galaxies. I. Description and Initial Results
We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG),a census of star formation in H I-selected galaxies. The survey consistsof Hα and R-band imaging of a sample of 468 galaxies selected fromthe H I Parkes All Sky Survey (HIPASS). The sample spans three decadesin H I mass and is free of many of the biases that affect otherstar-forming galaxy samples. We present the criteria for sampleselection, list the entire sample, discuss our observational techniques,and describe the data reduction and calibration methods. This paperfocuses on 93 SINGG targets whose observations have been fully reducedand analyzed to date. The majority of these show a single emission linegalaxy (ELG). We see multiple ELGs in 13 fields, with up to four ELGs ina single field. All of the targets in this sample are detected inHα, indicating that dormant (non-star-forming) galaxies withMHI>~3×107 Msolar are veryrare. A database of the measured global properties of the ELGs ispresented. The ELG sample spans 4 orders of magnitude in luminosity(Hα and R band), and Hα surface brightness, nearly 3 ordersof magnitude in R surface brightness and nearly 2 orders of magnitude inHα equivalent width (EW). The surface brightness distribution ofour sample is broader than that of the Sloan Digital Sky Survey (SDSS)spectroscopic sample, the EW distribution is broader than prism-selectedsamples, and the morphologies found include all common types ofstar-forming galaxies (e.g., irregular, spiral, blue compact dwarf,starbursts, merging and colliding systems, and even residual starformation in S0 and Sa spirals). Thus, SINGG presents a superior censusof star formation in the local universe suitable for further studiesranging from the analysis of H II regions to determination of the localcosmic star formation rate density.
| Discovery Among the Disks
Not Available
| Dust properties of UV bright galaxies at z ~ 2
We investigate the properties of the extinction curve in the rest-frameUV for a sample of 34 UV-luminous galaxies at 2 < z < 2.5,selected from the FORS Deep Field (FDF) spectroscopic survey. A newparametric description of the rest-frame UV spectral energy distributionis adopted; its sensitivity to properties of the stellar populations orof dust attenuation is established with the use of models. The latterare computed by combining composite stellar population models andcalculations of radiative transfer of the stellar and scatteredradiation through the dusty interstellar medium (ISM) for a dust/starsconfiguration describing dust attenuation in local starbursts. In thefavoured configuration the stars are enveloped by a shell with atwo-phase, clumpy, dusty ISM. The distribution of the z 2UV-luminous FDF galaxies in several diagnostic diagrams shows that theirextinction curves range between those typical of the Small and LargeMagellanic Clouds (SMC and LMC, respectively). For the majority ofstrongly reddened objects having a UV continuum slope β > -0.4 asignificant 2175 Å absorption feature (or "UV bump") is inferred,indicating an LMC-like extinction curve. On the other hand, the UVcontinua of the least reddened objects are mostly consistent withSMC-like extinction curves, lacking a significant UV bump, as for thesample of local starbursts investigated by Calzetti and collaborators.Furthermore, the most opaque (β 0) and, thus (for ourmodels), dustiest UV-luminous FDF galaxies tend to be among the mostmetal-rich, most massive, and largest systems at z 2, indicating< Z > 0.5 {-} 1 Zȯ, < Mstars> 6 × 1010 Mȯ, and 4 kpc, respectively. The presence of the UVbump does not seem to depend on the total metallicity, as given by theequivalent width (EW) of the C IV doublet. Conversely, it seems to beassociated with a large average EW of the six most prominentinterstellar low-ionisation absorption lines falling in the FORSspectra. The average EW of these saturated lines offers a proxy for theISM topology. We interpret these results as the evidence for adifference in the properties of the dusty ISM among the most evolvedUV-luminous, massive galaxies at z 2.
| Principal component analysis of International Ultraviolet Explorer galaxy spectra
We analyse the UV spectral energy distribution of a sample of normalgalaxies listed in the International Ultraviolet Explorer (IUE) NewlyExtracted Spectra (INES) Guide No. 2 - Normal Galaxies using a principalcomponent analysis. The sample consists of the IUE short-wavelength (SW)spectra of the central regions of 118 galaxies, where the IUE apertureincluded more than 1 per cent of the galaxy size. The principalcomponents are associated with the main components observed in theultraviolet (UV) spectra of galaxies. The first component, accountingfor the largest source of diversity, may be associated with the UVcontinuum emission. The second component represents the UV contributionof an underlying evolved stellar population. The third component issensitive to the amount of activity in the central regions of galaxiesand measures the strength of star-formation events.In all the samples analysed here, the principal component representativeof star-forming activity accounts for a significant percentage of thevariance. The fractional contribution to the spectral energydistribution (SED) by the evolved stars and by the young population aresimilar.Projecting the SEDs on to their eigenspectra, we find that none of thecoefficients of the principal components can outline an internalcorrelation or can correlate with the optical morphological types. In asubsample of 43 galaxies, consisting of almost only compact and BCDgalaxies, the third principal component defines a sequence related tothe degree of starburst activity of the galaxy.
| Secular Evolution and the Formation of Pseudobulges in Disk Galaxies
The Universe is in transition. At early times, galactic evolution wasdominated by hierarchical clustering and merging, processes that areviolent and rapid. In the far future, evolution will mostly be secularthe slow rearrangement of energy and mass that results from interactionsinvolving collective phenomena such as bars, oval disks, spiralstructure, and triaxial dark halos. Both processes are important now.This review discusses internal secular evolution, concentrating on oneimportant consequence, the buildup of dense central components in diskgalaxies that look like classical, merger-built bulges but that weremade slowly out of disk gas. We call these pseudobulges.
| Early-Type Galaxies in Extremely Isolated Environments: Typical Ellipticals?
We have conducted a BVR imaging survey of nine early-type galaxiespreviously verified to exist in extremely isolated environments. Ourgoals are to establish a baseline of morphological and photometricproperties for spheroidal systems evolving in extremely low-densityenvironments and to compare these properties with signatures predictedfor merged galaxy groups. We find that these isolated systems areunderluminous by at least a magnitude compared with objects identifiedas merged group remnants in other studies. Image processing techniquessensitive to shell features produced no detections, a result in strongcontrast to the high frequency of such structures found in otherisolated elliptical galaxies. Two objects, KIG 164 and KIG 870, appearto be merger remnants, as indicated by their disturbed morphology,apparent tidal features, and blue colors. KIG 164 exhibits an asymmetricnuclear morphology and a low surface brightness ``bridge'' between itand a possible dwarf satellite. KIG 870 shows both fan-shaped emissionat large radii and a possible double nucleus. Two other galaxies, KIG412 and KIG 792, are also blue, but without any morphologicalpeculiarities, suggesting that these systems are advanced mergers, olderthan KIG 164 and KIG 870. Two systems appear to be isolated lenticulargalaxies with no evidence of a merger history. Based on their redcolors, good fit to a R1/4-law light distribution, and thelack of morphological peculiarities, two other galaxies, KIG 557 and KIG824, are found to be excellent candidates for passively evolvingprimordial elliptical galaxies formed early in cosmic time. Optical datawere obtained with the 2.1 m Otto Struve telescope at McDonaldObservatory, which is operated by the University of Texas at Austin.
| The evolution of stars and gas in starburst galaxies
In systems undergoing starbursts the evolution of the young stellarpopulation is expected to drive changes in the emission-line properties.This evolution is usually studied theoretically, with a combination ofevolutionary synthesis models for the spectral energy distribution ofstarbursts and photoionization calculations. In this paper we present amore empirical approach to this issue. We apply empirical populationsynthesis techniques to samples of starburst and HII galaxies in orderto measure their evolutionary state and correlate the results with theiremission-line properties. A couple of useful tools are introduced thatgreatly facilitate the interpretation of the synthesis: (1) anevolutionary diagram, the axes of which are the strengths of the young,intermediate age and old components of the stellar population mix; and(2) the mean age of stars associated with the starburst, . These toolsare tested with grids of theoretical galaxy spectra and found to workvery well even when only a small number of observed properties(absorption-line equivalent widths and continuum colours) is used in thesynthesis.Starburst nuclei and HII galaxies are found to lie on a well-definedsequence in the evolutionary diagram. Using the empirically defined meanstarburst age in conjunction with emission-line data, we have verifiedthat the equivalent widths of Hβ and [OIII] decrease for increasing. The same evolutionary trend was identified for line ratios indicativeof the gas excitation, although no clear trend was identified formetal-rich systems. All these results are in excellent agreement withlong-known, but little tested, theoretical expectations.
| Star formation rate in galaxies from UV, IR, and Hα estimators
Infrared (IR) luminosity of galaxies originating from dust thermalemission can be used as an indicator of the star formation rate (SFR).Inoue et al. (\cite{inoue00}, IHK) have derived a formula for theconversion from dust IR luminosity to SFR by using the following threequantities: the fraction of Lyman continuum luminosity absorbed by gas(f), the fraction of UV luminosity absorbed by dust (epsilon ), and thefraction of dust heating from old (ga 108 yr) stellarpopulations (eta ). We develop a method to estimate those threequantities based on the idea that the various way of SFR estimates fromultraviolet (UV) luminosity (2000 Å luminosity), Hαluminosity, and dust IR luminosity should return the same SFR. Afterapplying our method to samples of galaxies, the following results areobtained in our framework. First, our method is applied to a sample ofstar-forming galaxies, finding that f ~ 0.6, epsilon ~ 0.5, and eta ~0.4 as representative values. Next, we apply the method to a starburstsample, which shows larger extinction than the star-forming galaxysample. With the aid of f, epsilon , and eta , we are able to estimatereliable SFRs from UV and/or IR luminosities. Moreover, the Hαluminosity, if the Hα extinction is corrected by using the Balmerdecrement, is suitable for a statistical analysis of SFR, because thesame {correction factor for the Lyman continuum extinction (i.e. 1/f)}is applicable to both normal and starburst galaxies over all the rangeof SFR. The metallicity dependence of f and epsilon is also tested:Only the latter proves to have a correlation with metallicity. As anextension of our result, the local (z=0) comoving density of SFR can beestimated with our dust extinction corrections. We show that all UV,Hα , and IR comoving luminosity densities at z=0 give a consistentSFR per comoving volume ( ~ 3x 10-2h M_sun yr-1Mpc-3). Useful formulae for SFR estimate are listed.Tables 1 and 2, and Appendix A are only available in electronic form athttp://www.edpsciences.org
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| An empirical calibration of star formation rate estimators
The observational determination of the behaviour of the star formationrate (SFR) with look-back time or redshift has two main weaknesses: (i)the large uncertainty of the dust/extinction corrections, and (ii) thatsystematic errors may be introduced by the fact that the SFR isestimated using different methods at different redshifts. Mostfrequently, the luminosity of the Hα emission line, that of theforbidden line [O II] λ3727 and that of the far-ultravioletcontinuum are used with low-, intermediate- and high-redshift galaxies,respectively. To assess the possible systematic differences among thedifferent SFR estimators and the role of dust, we have compared SFRestimates using Hα, [O II] λ3727 Å, ultraviolet (UV)and far-infrared (FIR) luminosities [SFR(Hα), SFR(O II), SFR(UV)and SFR(FIR), respectively of a sample comprising the 31 nearbystar-forming galaxies that have high-quality photometric data in the UV,optical and FIR. We review the different `standard' methods for theestimation of the SFR and find that while the standard method providesgood agreement between SFR(Hα) and SFR(FIR), both SFR(O II) andSFR(UV) are systematically higher than SFR(FIR), irrespective of theextinction law. We show that the excess in the SFR(O II) and SFR(UV) ismainly due to an overestimation of the extinction resulting from theeffect of underlying stellar Balmer absorptions in the measured emissionline fluxes. Taking this effect into consideration in the determinationof the extinction brings the SFR(O II) and SFR(UV) in line with theSFR(FIR), and simultaneously reduces the internal scatter of the SFRestimations. Based on these results, we have derived `unbiased' SFRexpressions for the SFR(UV), SFR(OII) and SFR(Hα). We have usedthese estimators to recompute the SFR history of the Universe using theresults of published surveys. The main results are that the use of theunbiased SFR estimators brings into agreement the results of allsurveys. Particularly important is the agreement achieved for the SFRderived from the FIR/millimetre and optical/UV surveys. The `unbiased'star formation history of the Universe shows a steep rise in the SFRfrom z =0 to z =1 with SFR ~(1+z)4.5, followed by a declinefor z>2 where SFR ~(1+z)-1.5. Galaxy formation models tendto have a much flatter slope from z=0 to z=1
| A New Database of Observed Spectral Energy Distributions of Nearby Starburst Galaxies from the Ultraviolet to the Far-Infrared
We present a database of UV-to-FIR data of 83 nearby starburst galaxies.The galaxies are selected based upon the availability of IUE data. Wehave recalibrated the IUE UV spectra for these galaxies by incorporatingthe most recent improvements. For 45 of these galaxies we useobservations by Storchi-Bergmann et al. and McQuade et al. for thespectra in the optical range. The NIR data are from new observationsobtained at the NASA/IRTF and the Mount Laguna Observatory, combinedwith the published results from observations at the Kitt Peak NationalObservatory. In addition, published calibrated ISO data are included toprovide mid-IR flux densities for some of the galaxies. Theoptical-to-IR data are matched as closely as possible to the IUE largeaperture. In conjunction with IRAS and ISO FIR flux densities, all thesedata form a set of observed spectral energy distributions (SEDs) of thenuclear regions of nearby starburst galaxies. The SEDs should be usefulin studying star formation and dust/gas attenuation in galaxies. We alsopresent the magnitudes in the standard BVRI and various HST/WFPC2bandpasses synthesized from the UV and optical wavelength ranges ofthese SEDs. For some of the galaxies, the HST/WFPC2 magnitudessynthesized from the SEDs are checked with those directly measured fromWFPC2 images to test the photometric errors of the optical data andtheir effective matching of apertures with the UV data. The implicationsof the new SEDs on the star formation rates and dust/gas attenuation arebriefly discussed.
| A Hubble Space Telescope Survey of the Mid-Ultraviolet Morphology of Nearby Galaxies
We present a systematic imaging survey of 37 nearby galaxies observedwith the Hubble Space Telescope (HST) Wide Field and Planetary Camera 2(WFPC2) in the mid-UV F300W filter, centered at 2930 Å, as well asin the I-band (F814W) filter at 8230 Å. Eleven of these galaxieswere also imaged in the F255W filter, centered at 2550 Å. Oursample is carefully selected to include galaxies of sufficiently smallradius and high predicted mid-UV surface brightness to be detectablewith WFPC2 in one orbit and covers a wide range of Hubble types andinclinations. The mid-UV (2000-3200 Å) spans the gap betweenground-based UBVR(IJHK) images, which are available or were acquired forthe current study, and far-UV images available from the Astro/UITmissions for 15 galaxies in our sample. The first qualitative resultsfrom our study are as follows:1. Early-type galaxies show a significantdecrease in surface brightness going from the red to the mid-UV,reflecting the absence of a dominant young stellar population and insome cases the presence of significant (central) dust lanes. Galaxiesthat are early types in the optical show a variety of morphologies inthe mid-UV that can lead to a different morphological classification,although not necessarily as later type. Some early-type galaxies becomedominated by a blue nuclear feature or a point source in the mid-UV,e.g., as a result of the presence of a Seyfert nucleus or a LINER. Thisis in part due to our mid-UV surface brightness selection, but it alsosuggests that part of the strong apparent evolution of weak AGNs inearly-type galaxies may be due to surface brightness dimming of theirUV-faint stellar population, which renders the early-type host galaxiesinvisible at intermediate to higher redshifts.2. About half of themid-type spiral and star-forming galaxies appear as a latermorphological type in the mid-UV, as Astro/UIT also found primarily inthe far-UV. Sometimes these differences are dramatic (e.g., NGC 6782shows a spectacular ring of hot stars in the mid-UV). However, not allmid-type spiral galaxies look significantly different in the mid-UV.Their mid-UV images show a considerable range in the scale and surfacebrightness of individual star-forming regions. Almost without exception,the mid-type spirals in our sample have their small bulges bisected by adust lane, which often appears to be connected to the inner spiral armstructure.3. The majority of the heterogeneous subset of late-type,irregular, peculiar, and merging galaxies display F300W morphologiesthat are similar to those seen in F814W, but with important differencesdue to recognizable dust features absorbing the bluer light and to hotstars, star clusters, and star formation ``ridges'' that are bright inthe mid-UV. Less than one-third of the galaxies classified as late typein the optical appear sufficiently different in the mid-UV to result ina different classification.Our HST mid-UV survey of nearby galaxiesshows that, when observed in the rest-frame mid-UV, early- to mid-typegalaxies are more likely to be misclassified as later types thanlate-type galaxies are to be misclassified as earlier types. This isbecause the later type galaxies are dominated by the same young and hotstars in all filters from the mid-UV to the red and so have a smaller``morphological K-correction'' than true earlier type galaxies. Themorphological K-correction can thus explain part, but certainly not all,of the excess faint blue late-type galaxies seen in deep HST fields.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute (STScI), which isoperated by the Association of Universities for Research in Astronomy(AURA), Inc., under NASA contract NAS 5-26555. Also based in part onobservations made with the Vatican Advanced Technology Telescope: theAlice P. Lennon Telescope and the Thomas J. Bannan AstrophysicsFacility.
| An Infrared Space Observatory Atlas of Bright Spiral Galaxies
In this first paper in a series we present an atlas of infrared imagesand photometry from 1.2 to 180 μm for a sample of bright spiralgalaxies. The atlas galaxies are an optically selected,magnitude-limited sample of 77 spiral and S0 galaxies chosen from theRevised Shapley-Ames Catalog (RSA). The sample is a representativesample of spiral galaxies and includes Seyfert galaxies, LINERs,interacting galaxies, and peculiar galaxies. Using the Infrared SpaceObservatory (ISO), we have obtained 12 μm images and photometry at60, 100, and 180 μm for the galaxies. In addition to its imagingcapabilities, ISO provides substantially better angular resolution thanis available in the IRAS survey, and this permits discrimination betweeninfrared activity in the central regions and global infrared emission inthe disks of these galaxies. These ISO data have been supplemented withJHK imaging using ground-based telescopes. The atlas includes 2 and 12μm images. Following an analysis of the properties of the galaxies,we have compared the mid-infrared and far-infrared ISO photometry withIRAS photometry. The systematic differences we find between the IRASFaint Source Catalog and ISO measurements are directly related to thespatial extent of the ISO fluxes, and we discuss the reliability of IRASFaint Source Catalog total flux densities and flux ratios for nearbygalaxies. In our analysis of the 12 μm morphological features we findthat most but not all galaxies have bright nuclear emission. We find 12μm structures such as rings, spiral arm fragments, knotted spiralarms, and bright sources in the disks that are sometimes brighter thanthe nuclei at mid-infrared wavelengths. These features, which arepresumably associated with extranuclear star formation, are common inthe disks of Sb and later galaxies but are relatively unimportant inS0-Sab galaxies. Based on observations with the Infrared SpaceObservatory (ISO), an ESA project with instruments funded by ESA MemberStates (especially the PI countries: France, Germany, Netherlands, andUnited Kingdom) and with the participation of ISAS and NASA.
| Star formation and dust extinction in nearby star-forming and starburst galaxies
We study the star formation rate and dust extinction properties of asample of nearby star-forming galaxies as derived from Hα and UV (~ 2000 Å) observations and we compare them to those of a sample ofstarburst galaxies. The dust extinction in Hα is estimated fromthe Balmer decrement and the extinction in UV using the FIR to UV fluxratio or the attenuation law for starburst galaxies of Calzetti et al.(\cite{calzetti5}). The Hα and UV emissions are stronglycorrelated with a very low scatter for the star-forming objects and witha much higher scatter for the starburst galaxies. The Hα to UVflux ratio is found to be larger by a factor ~ 2 for the starburstgalaxies. We compare both samples with a purely UV selected sample ofgalaxies and we conclude that the mean Hα and UV properties ofnearby star-forming galaxies are more representative of UV-selectedgalaxies than starburst galaxies. We emphasize that the Hα to UVflux ratio is strongly dependent on the dust extinction: the positivecorrelation found between FHα/FUV andFFIR/FUV vanishes when the Hα and UV fluxare corrected for dust extinction. The Hα to UV flux ratiosconverted into star formation rate and combined with the Balmerdecrement measurements are tentatively used to estimate the dustextinction in UV.
| A catalogue and analysis of X-ray luminosities of early-type galaxies
We present a catalogue of X-ray luminosities for 401 early-typegalaxies, of which 136 are based on newly analysed ROSAT PSPC pointedobservations. The remaining luminosities are taken from the literatureand converted to a common energy band, spectral model and distancescale. Using this sample we fit the LX:LB relationfor early-type galaxies and find a best-fit slope for the catalogue of~2.2. We demonstrate the influence of group-dominant galaxies on the fitand present evidence that the relation is not well modelled by a singlepower-law fit. We also derive estimates of the contribution to galaxyX-ray luminosities from discrete-sources and conclude that they provideLdscr/LB~=29.5ergs-1LBsolar-1. Wecompare this result with luminosities from our catalogue. Lastly, weexamine the influence of environment on galaxy X-ray luminosity and onthe form of the LX:LB relation. We conclude thatalthough environment undoubtedly affects the X-ray properties ofindividual galaxies, particularly those in the centres of groups andclusters, it does not change the nature of whole populations.
| The anomalous properties of Markarian 1460
We present and discuss optical, near-infrared and Hi measurements of thegalaxy Markarian 1460 at a distance of 19Mpc in the Ursa Major Cluster.This low-luminosity (MB=-14) galaxy is unusual because (i) itis blue (B-R=0.8) and has the spectrum of an Hii galaxy, (ii) it has alight profile that is smooth and well fitted by an r1/4 andnot an exponential function at all radii larger than the seeing, and(iii) it has an observed central brightness of aboutμB=20magarcsec-2, intermediate between those ofelliptical galaxies (on the bright μB side) and normallow-luminosity dwarf irregular (on the low μB side)galaxies. No other known galaxy exhibits all these properties inconjunction. On morphological grounds this galaxy looks like a normaldistant luminous elliptical galaxy, since the Fundamental Plane tells usthat higher luminosity normal elliptical galaxies tend to have lowersurface-brightnesses. Markarian 1460 has2×107Msolar of Hi and a ratioM(Hi)/LB of 0.2, which is low compared to the typical valuesfor star-forming dwarf galaxies. From the high surface-brightness andr1/4 profile, we infer that the baryonic component ofMarkarian 1460 has become self-gravitating through dissipativeprocesses. From the colours, radio continuum, Hi and optical emissionline properties, and yet smooth texture, we infer that Markarian 1460has had significant star formation as recently as ~1Gyr ago but nottoday.
| Strömgren Photometry from z=0 to z~1. I. The Method
We use rest-frame Strömgren photometry to observe clusters ofgalaxies in a self-consistent manner from z=0 to z=0.8. Strömgrenphotometry of galaxies is intended as a compromise between standardbroadband photometry and spectroscopy, in the sense that it is moresensitive to subtle variations in spectral energy distributions than theformer, yet much less time-consuming than the latter. principalcomponent analysis is used to facilitate extraction of information fromthe Strömgren data. By calibrating the principal components usingwell-studied galaxies, as well as models of stellar populations, wedevelop a purely empirical method to detect, and subsequently classify,cluster galaxies at all redshifts smaller than 0.8. Interlopers arediscarded with unprecedented efficiency (up to 100%). The firstprincipal component essentially reproduces the Hubble sequence and canthus be used to determine the global star formation history of clustermembers. The (PC2, PC3) plane allows us to identify Seyfert galaxies(and distinguish them from starbursts) based on photometric colorsalone. In the case of E/S0 galaxies with known redshift, we are able toresolve the age-dust-metallicity degeneracy, albeit at the accuracylimit of our present observations. We use this technique in later papersto probe galaxy clusters well beyond their cores and to faintermagnitudes than spectroscopy can achieve, because the faint end of theluminosity function as well as the outer cluster regions seem to exhibitthe strongest evolutionary trends. We are able to directly compare thesedata over the entire redshift range without a priori assumptions becauseour observations do not require first-order k-corrections. Thecompilation of such data for different cluster types over a wideredshift range is likely to set important constraints on the evolutionof galaxies and on the clustering process.
| Quantitative Morphology of Galaxies Observed in the Ultraviolet
We present a quantitative study of the far-ultraviolet (FUV) and opticalmorphology in 32 nearby galaxies and estimate the ``morphologicalk-correction'' expected if these objects were observed unevolved at highredshift. Using the common indices of central concentration (C) androtational asymmetry (A) to quantify morphology, we considerindependently two phenomena that give rise to this k-correction.Bandshifting, the decrease in the rest-frame wavelength of lightobserved through optical filters, is explored by measuring these indicesin several passbands for each galaxy, and it is found to be the primarydriver of changes in C and A. In general, the optical trend found fordecreasing C and increasing A when going to shorter wavelengths extendsto the FUV. However, the patchy nature of recent star formation inlate-type galaxies, which is accentuated in the FUV, results in poorquantitative correspondence between morphologies determined in theoptical and FUV. We then artificially redshift our FUV images into theHubble Deep Field (HDF) filters to simulate various cosmologicaldistance effects, such as surface brightness dimming and loss of spatialresolution. Hubble types of many galaxies in our sample are not readilyidentifiable at redshifts beyond z~1, and the galaxies themselves aredifficult to detect beyond z~3. Because only features of the highestsurface brightness remain visible at cosmological distances, the changein C and A between simulated high-z galaxies and their unredshiftedcounterparts depends on whether their irregular features are primarilybright or faint. Our simulations suggest that k-corrections alone areindeed capable of producing the peculiar morphologies observed at highredshift; for example, several spiral galaxies have C and A indicestypical of irregular or peculiar HDF objects viewed at z>=2. Webriefly discuss some elements of a scheme to classify rest-frame UVimages, mergers, protogalaxies, and other objects for which classicalHubble types do not adequately encompass the existing morphology.
| Gas properties of Hii and starburst galaxies: relation with the stellar population
We study the gas emission of galaxies with active star formation,consisting mostly of Hii and starburst galaxies, as well as some Seyfert2 galaxies, and determine chemical and physical parameters. The dataconsist of 19 high signal-to-noise ratio optical templates, a result ofgrouping 185 emission-line galaxy spectra. Underlying stellar populationmodels (from Raimann et al.) were subtracted from the templates in orderto isolate the pure emission component. We analyse the distribution ofthese improved signal-to-noise ratio emission spectra in diagnosticdiagrams and find that the Hii templates show a smaller spread inlog([Oiii]/Hβ) values than the individual galaxies, apparently as aresult of the population subtraction and a better signal-to-noise ratio.We thus suggest the template sequence as a fiducial observational locusfor Hii galaxies which can be used as reference for models. The sequenceof line ratios presented by the Hii galaxies in the diagramlog([Oiii]λ5007/Hβ) versus log([Nii]λ6584/Hα)is primarily owing to the gas metallicity, of which thelog([Nii]/Hα) ratio is a direct estimator. We also study theproperties of the starburst galaxies and those intermediate between Hiiand starburst galaxies, which are more metal rich and sit on moremassive galaxies. We discuss the present results in the frame of arecently proposed equivalent-width diagnostic diagram for emission-linegalaxies (by Rola et al.) and conclude that the observed ranges inW([Oii])/W(Hβ) and W(Hβ) are mostly owing to the non-ionizingstellar population contribution. We propose that W(Hβ) be used asan estimator of this contribution to the continuum, and briefly discussimplications to the cosmological use of Hii galaxies.
| Population synthesis of Hii galaxies
We study the stellar population of galaxies with active star formation,determining ages of the stellar components by means of spectralpopulation synthesis of their absorption spectra. The data consist ofoptical spectra of 185 nearby (z<=0.075) emission-line galaxies. Theyare mostly Hii galaxies, but we also include some starbursts and Seyfert2s, for comparison purposes. They were grouped into 19 highsignal-to-noise ratio template spectra, according to their continuumdistribution, absorption- and emission-line characteristics. Thetemplates were then synthesized with a star cluster spectral base. Thesynthesis results indicate that Hii galaxies are typically age-compositestellar systems, presenting important contributions from generations upto as old as 500Myr. We detect a significant contribution of populationswith ages older than 1Gyr in two groups of Hii galaxies. The agedistributions of stellar populations among starbursts can varyconsiderably despite similarities in the emission-line spectra. In thecase of Seyfert 2 groups we obtain important contributions from the oldpopulation, consistent with a bulge. From the diversity of starformation histories, we conclude that typical Hii galaxies in the localUniverse are not systems presently forming their first stellargeneration.
| Comparing Galaxy Morphology at Ultraviolet and Optical Wavelengths
We have undertaken an imaging survey of 34 nearby galaxies infar-ultraviolet (FUV, ~1500 Å) and optical (UBVRI) passbands tocharacterize galaxy morphology as a function of wavelength. This sample,which includes a range of classical Hubble types from elliptical toirregular, with emphasis on spirals at low inclination angle, provides avaluable database for comparison with images of high-z galaxies whoseFUV light is redshifted into the optical and near-infrared bands.Ultraviolet data are from the Ultraviolet Imaging Telescope (UIT)Astro-2 mission. We present images and surface brightness profiles foreach galaxy, and we discuss the wavelength dependence of morphology fordifferent Hubble types in the context of understanding high-z objects.In general, the dominance of young stars in the FUV produces the patchyappearance of a morphological type later than that inferred from opticalimages. Prominent rings and circumnuclear star formation regions areclearly evident in FUV images of spirals, while bulges, bars, and old,red stellar disks are faint to invisible at these short wavelengths.However, the magnitude of the change in apparent morphology ranges fromdramatic in early-type spirals with prominent optical bulges to slightin late-type spirals and irregulars, in which young stars dominate boththe UV and optical emission. Starburst galaxies with centrallyconcentrated, symmetric bursts display an apparent ``E/S0'' structure inthe FUV, while starbursts associated with rings or mergers produce apeculiar morphology. We briefly discuss the inadequacy of the opticallydefined Hubble sequence in describing FUV galaxy images and estimatingmorphological k-corrections, and we suggest some directions for futureresearch with this data set.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| Spectral classification of emission-line galaxies
The main goal of this work is to further investigate the classificationof emission-line galaxies from the ``Spectrophotometric Catalogue of HII galaxies'' by Terlevich et al. (1991) in a homogeneous and objectiveway, using the three line-ratio diagrams, called diagnostic diagrams, ofVeilleux & Osterbrock (1987). On the basis of the resultingcatalogue, we critically discuss the classification methods in theoptical range. In particular we compare our classification scheme to theone done by Rola et al. (1997) which is efficient for the classificationof redshifted galaxies. We also propose a new diagnostic diagraminvolving the known intensity ratio R23=([O II],l 3727+[OIII] l 4959+{[O III] l 5007)/Hb which appears to be a very goodcriterion allowing to discriminate the Seyfert 2 from H ii galaxies. Therevised catalogue including 314 narrow-emission-line galaxies contains HII galaxies, Seyfert 2 galaxies, Low Ionization Nuclear Emission-LineRegions (hereafter LINERs) galaxies and some particular types ofgalaxies with the most intriguing ones, called ``ambiguous'', due to theambiguity of their location in the diagnostic diagrams. These galaxiesappear as H II galaxies and as active galactic nuclei (hereafter AGNs)in different diagrams of Veilleux & Osterbrock and constitutecertainly a sample of particularly interesting candidates for a thoroughstudy of connections between starbursts and AGNs. Available inelectronic form only via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| The QDOT all-sky IRAS galaxy redshift survey
We describe the construction of the QDOT survey, which is publiclyavailable from an anonymous FTP account. The catalogue consists ofinfrared properties and redshifts of an all-sky sample of 2387 IRASgalaxies brighter than the IRAS PSC 60-μm completeness limit(S_60>0.6Jy), sparsely sampled at a rate of one-in-six. At |b|>10deg, after removing a small number of Galactic sources, the redshiftcompleteness is better than 98per cent (2086/2127). New redshifts for1401 IRAS sources were obtained to complete the catalogue; themeasurement and reduction of these are described, and the new redshiftstabulated here. We also tabulate all sources at |b|>10 deg with noredshift so far, and sources with conflicting alternative redshiftseither from our own work, or from published velocities. A list of 95ultraluminous galaxies (i.e. with L_60μm>10^12 L_solar) is alsoprovided. Of these, ~20per cent are AGN of some kind; the broad-lineobjects typically show strong Feii emission. Since the publication ofthe first QDOT papers, there have been several hundred velocity changes:some velocities are new, some QDOT velocities have been replaced by moreaccurate values, and some errors have been corrected. We also present anew analysis of the accuracy and linearity of IRAS 60-μm fluxes. Wefind that the flux uncertainties are well described by a combination of0.05-Jy fixed size uncertainty and 8per cent fractional uncertainty.This is not enough to cause the large Malmquist-type errors in the rateof evolution postulated by Fisher et al. We do, however, find marginalevidence for non-linearity in the PSC 60-μm flux scale, in the sensethat faint sources may have fluxes overestimated by about 5per centcompared with bright sources. We update some of the previous scientificanalyses to assess the changes. The main new results are as follows. (1)The luminosity function is very well determined overall but is uncertainby a factor of several at the very highest luminosities(L_60μm>5x10^12L_solar), as this is where the remainingunidentified objects are almost certainly concentrated. (2) Thebest-fitting rate of evolution is somewhat lower than our previousestimate; expressed as pure density evolution with density varying as(1+z)^p, we find p=5.6+/-2.3. Making a rough correction for the possible(but very uncertain) non-linearity of fluxes, we find p=4.5+/-2.3. (3)The dipole amplitude decreases a little, and the implied value of thedensity parameter, assuming that IRAS galaxies trace the mass, isΩ=0.9(+0.45, -0.25). (4) Finally, the estimate of density varianceon large scales changes negligibly, still indicating a significantdiscrepancy from the predictions of simple cold dark matter cosmogonies.
| Galaxy Interactions: The HI Signature
Invited review in Session 3: Tidal Interactions.
| Age and Dust Degeneracy for Starburst Galaxies Solved?
We present a newly built spectral evolution model of galaxies thatincludes both stellar and dust effects. Applying the model to 22 nearbystarburst galaxies shows that far-infrared (FIR) luminosity of galaxieshelps to break the age-dustiness degeneracy. We have derived a uniquesolution of age and the dustiness for each starburst galaxy. Theresulting starburst ages and optical depths are in the range 10<=t(Myr)<=500 and 0.5<=tau_V<=5.0, respectively. The result isrobust and is almost independent of model assumptions such as dustdistributions, extinction curves, and burst strengths. With the rapidlygrowing sensitivity of submillimeter detectors, it should becomepossible in the near future to determine the age and tau_V ofstar-forming galaxies at redshifts z~=3 and beyond. Accurate estimatesof tau_V for Lyman-break galaxies and high-z galaxies might require asubstantial revision of the previously claimed picture of star formationhistory over the Hubble time.
| The Taxonomy of Blue Amorphous Galaxies. II. Structure and Evolution
Dwarf galaxies play an important role in our understanding of galaxyformation and evolution, and starbursts are believed to affect thestructure and evolution of dwarf galaxies strongly. We have thereforeembarked on a systematic study of 12 of the nearest dwarf galaxiesthought to be undergoing bursts of star formation. These were selectedprimarily by their morphological type (blue ``amorphous'' galaxies). Weshow that these blue amorphous galaxies are not physicallydistinguishable from dwarfs selected as starbursting by other methods,such as blue compact dwarfs (BCDs) and H II galaxies. All these classesexhibit surface brightness profiles that are exponential in the outerregions (r>~1.5r_e) but often have a predominantly central blueexcess, suggesting a young burst in an older, redder galaxy. Typically,the starbursting ``cores'' are young (~10^7-10^8 yr) events compared tothe older (~10^9-10^10 yr) underlying galaxy (the ``envelope''). Theratio of the core to envelope in blue light ranges from essentially zeroto about 2. These starbursts are therefore modest events involving onlya few percent of the stellar mass. The envelopes have surfacebrightnesses that are much higher than typical dwarf irregular (dI)galaxies, so it is unlikely that there is a straightforward evolutionaryrelation between typical dIs and dwarf starburst galaxies. Instead wesuggest that amorphous galaxies may repeatedly cycle through starburstand quiescent phases, corresponding to the galaxies with strong andweak/absent cores, respectively. Once amorphous galaxies use up theavailable gas (either through star formation or galactic winds) so thatstar formation is shut off, the faded remnants would strongly resembledwarf elliptical galaxies. However, in the current cosmological epoch,this is evidently a slow process that is the aftermath of a series ofmany weak, recurring bursts. Present-day dE's must have experienced morerapid and intense evolution than this in the distant past.
| Neutral Hydrogen and Dark Matter in Spiral Galaxies
The first part presents a brief review of the main HI properties ofisolated, normal spiral galaxies and of the phenomena which seem tocharacterize and dominate their internal metabolism. In the second partattention is drawn to all those processes, such as tidal interactions,accretion and mergers, that depend on the galaxy environment and mayplay a significant role in galaxy formation and evolution. In the thirdpart the observational evidence for the dark matter component of spiralgalaxies is discussed.
| Redshifts of Galaxies around ARP 220 and Serendipitous Discovery of Three Star-forming Dwarf Galaxies at Redshift Z~0.5
We present redshift measurements of four faint galaxies around thearchetypal ultraluminous infrared galaxy Arp 220. These galaxies havesignificantly higher redshifts (z~0.036-0.091) than that of Arp 220(z~=0.018). Therefore, we conclude that they are background objects notphysically related to Arp 220. Three of these faint galaxies located tothe south of Arp 220 are a group of galaxies (or the brightest membersin a cluster of galaxies) at z~=0.09, as has been suggested previouslyon the basis of their associated soft X-ray emission. We also report theserendipitous discovery of three additional galaxies at redshift z~0.5,found along one of the slit positions. All three galaxies exhibit an [OII] lambda3727 emission line. The spectrum of the brightest galaxy(m_R~=24.4) shows other strong emission lines: Mg II lambda2798,Hβ, [O III] lambda4959, and[O III] lambda5007. The emission-lineproperties of these galaxies as well as their intrinsically lowluminosities (M_R>=-18.4) indicate that they are star-forming dwarfgalaxies.
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