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The distribution of atomic gas and dust in nearby galaxies - III. Radial distributions and metallicity gradients
The radial distribution of dust and gas in 38 nearby galaxies isinvestigated, using a sample of galaxies for which matched resolution(25 arcsec) neutral hydrogen (HI) and 850-μm images are available.Most of these radial profiles are fitted well by an exponential model,and the derived 850-μm scalelengths are proportional to the HIscalelengths. From this relation, it is found that the metallicitygradients of these galaxies are much shallower than previous studies,unless the dust temperature is constant within the disc, or asignificant component of molecular gas exists at large radii that is nottraced by CO observations.
| Revised masses of dust and gas of SCUBA Local Universe Survey far-infrared bright galaxies based on a recent CO survey
Recent CO measurements of an essentially complete subsample of galaxiesfrom the SCUBA Local Universe Survey (SLUGS) are used to examine theirimplications for dust and gas masses in this sample. Estimates of dustmasses are affected by a contribution to the SCUBA brightnessmeasurements by CO(3-2) emission, and molecular gas masses by the use ofa modified value of the CO-to-H2 conversion factor X. Theaverage dust mass is reduced by 25-38 per cent, which has no bearing onearlier conclusions concerning the shape of the dust mass luminosityfunction derived from the SLUGS. The value of X found from the COsurvey, when applied together with the reduction in dust masses, leadsto lower estimates for the mean gas-to-dust mass ratios, where the gasincludes both H2 and H I. For the CO sample, the mean globalratio is reduced from approximately 430 to about 320-360, but is furtherreduced to values near 50 when applied to the nuclear regions relevantto the CO observations. We discuss these results and suggest that thedifferences between the nuclear and outer regions may simply reflectdifferences in metallicity or the existence of considerable amounts ofunobserved cold dust in the outer regions of these galaxies.
| The ISOPHOT 170 μm Serendipity Survey II. The catalog of optically identified galaxies%
The ISOPHOT Serendipity Sky Survey strip-scanning measurements covering≈15% of the far-infrared (FIR) sky at 170 μm were searched forcompact sources associated with optically identified galaxies. CompactSerendipity Survey sources with a high signal-to-noise ratio in at leasttwo ISOPHOT C200 detector pixels were selected that have a positionalassociation with a galaxy identification in the NED and/or Simbaddatabases and a galaxy counterpart visible on the Digitized Sky Surveyplates. A catalog with 170 μm fluxes for more than 1900 galaxies hasbeen established, 200 of which were measured several times. The faintest170 μm fluxes reach values just below 0.5 Jy, while the brightest,already somewhat extended galaxies have fluxes up to ≈600 Jy. For thevast majority of listed galaxies, the 170 μm fluxes were measured forthe first time. While most of the galaxies are spirals, about 70 of thesources are classified as ellipticals or lenticulars. This is the onlycurrently available large-scale galaxy catalog containing a sufficientnumber of sources with 170 μm fluxes to allow further statisticalstudies of various FIR properties.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) areMPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena,Imperial College London.Full Table 4 and Table 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/39
| Dust masses and star formation in bright IRAS galaxies. Application of a physical model for the interpretation of FIR observations
We address the problem of modeling the far-infrared (FIR) spectrum andderiving the star-formation rate (SFR) and the dust mass of spiralgalaxies. We use the realistic physical model of Popescu et al.(\cite{popescu}) to describe the overall ultra-violet (UV), optical andFIR spectral energy distribution (SED) of a spiral galaxy. The modeltakes into account the 3-dimensional old and young stellar distributionsin the bulge and the disk of a galaxy, together with the dust geometry.The geometrical characteristics of the galaxy and the intrinsic opticaland near-infrared spectra are determined by the galaxy's observed K-bandphotometry. The UV part of the spectrum is assumed to be proportional tothe SFR through the use of population synthesis models. By solving theradiative transfer equation, we are able to determine the absorbedenergy, the dust temperature and the resulting FIR spectrum. The modelhas only three free parameters: SFR, dust mass, and the fraction of theUV radiation which is absorbed locally by dense dust in the HII regions.Using this model, we are able to fit well the FIR spectra of 62 brightIRAS galaxies from the ``SCUBA Local Universe Galaxy Survey" of Dunne etal. (\cite{dunne1}). As a result, we are able to determine, amongothers, their SFR and dust mass. We find that, on average, the SFR (inabsolute units), the star-formation efficiency, the SFR surface densityand the ratio of FIR luminosity over the total intrinsic luminosity, arelarger than the respective values of typical spiral galaxies of the samemorphological type. We also find that the mean gas-to-dust mass ratio isclose to the Galactic value, while the average central face-on opticaldepth of these galaxies in the V band is 2.3. Finally, we find a strongcorrelation between SFR or dust mass and observed FIR quantities liketotal FIR luminosity or FIR luminosity at 100 and 850 μm. Thesecorrelations yield well-defined relations, which can be used todetermine a spiral galaxy's SFR and dust-mass content from FIRobservations.
| CO Molecular Gas in Infrared-luminous Galaxies
We present the first statistical survey of the properties of the12CO(1-0) and 12CO(3-2) line emission from thenuclei of a nearly complete subsample of 60 infrared (IR) luminousgalaxies selected from SCUBA Local Universe Galaxy Survey (SLUGS). Thissubsample is flux limited at S60μm>=5.24 Jy with far-IR(FIR) luminosities mostly at LFIR>1010Lsolar. We compare the emission line strengths of12CO(1-0) and (3-2) transitions at a common resolution of~15". The measured 12CO(3-2) to (1-0) line intensity ratiosr31 vary from 0.22 to 1.72, with a mean value of 0.66 for thesources observed, indicating a large spread of the degree of excitationof CO in the sample. These CO data, together with a wide range of dataat different wavelengths obtained from the literature, allow us to studythe relationship between the CO excitation conditions and the physicalproperties of gas/dust and star formation in the central regions ofgalaxies. Our analysis shows that there is a nonlinear relation betweenCO and FIR luminosities, such that their ratioLCO/LFIR decreases linearly with increasingLFIR. This behavior was found to be consistent with theSchmidt law relating star formation rate to molecular gas content, withan index N=1.4+/-0.3. We also find a possible dependence of the degreeof CO gas excitation on the efficiency of star-forming activity. Usingthe large velocity gradient (LVG) approximation to model the observeddata, we investigate the CO-to-H2 conversion factor X for theSLUGS sample. The results show that the mean value of X for the SLUGSsample is lower by a factor of 10 compared to the conventional valuederived for the Galaxy, if we assume the abundance of CO relative toH2, ZCO=10-4. For a subset of 12galaxies with H I maps, we derive a mean total face-on surface densityof H2+HI of about 42 Msolar pc-2 withinabout 2 kpc of the nucleus. This value is intermediate between that ingalaxies like our own and those with strong star formation.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| An Hα survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge-on spiral galaxies. I. How common are gaseous halos among non-starburst galaxies?
In a series of two papers we present results of a new Hα imagingsurvey, aiming at the detection of extraplanar diffuse ionized gas inhalos of late-type spiral galaxies. We have investigated a sample of 74nearby edge-on spirals, covering the northern and southern hemisphere.In 30 galaxies we detected extraplanar diffuse emission at meandistances of |z| ~ 1-2 kpc. Individual filaments can be traced out to|z|<=6 kpc in a few cases. We find a good correlation between the FIRflux ratio (S60/S100) and the SFR per unit area(LFIR/D225), based on thedetections/non-detections. This is actually valid for starburst, normaland for quiescent galaxies. A minimal SFR per unit area for the lowestS60/S100 values, at which extended emission hasbeen detected, was derived, which amounts to dotEA25thres = (3.2+/-0.5)*E40ergs-1 kpc-2. There are galaxies where extraplanaremission was detected at smaller values ofLFIR/D225, however, only in combinationwith a significantly enhanced dust temperature. The results corroboratethe general view that the gaseous halos are a direct consequence of SFactivity in the underlying galactic disk.Based on observations collected at the European Southern Observatory,Chile (ESO No. 63.N-0070, ESO No. 64.N-0034, ESO No. 65.N.-0002).
| The 2dF Galaxy Redshift Survey: the population of nearby radio galaxies at the 1-mJy level
We use redshift determinations and spectral analysis of galaxies in the2dF Galaxy Redshift Survey to study the properties of local radiosources with S>=1mJy. 557 objects (hereafter called the spectroscopicsample) drawn from the FIRST survey, corresponding to 2.3 per cent ofthe total radio sample, are found in the 2dFGRS catalogue within thearea9h48m<~RA(2000)<~14h32m and -2.77°<~Dec.(2000)<~2.25°, down to a magnitudelimit bJ=19.45. The excellent quality of 2dF spectra allowsus to divide these sources into classes, according to their opticalspectra. Absorption-line systems make up 63 per cent of thespectroscopic sample. These may or may not show emission lines due toAGN activity, and correspond to `classical' radio galaxies belongingmainly to the FRI class. They are characterized by relatively highradio-to-optical ratios, red colours, and high radio luminosities(1021<~P1.4GHz/WHz-1sr-1<~1024). Actively star-forming galaxies contributeabout 32 per cent of the sample. These objects are mainly found at lowredshifts (z<~0.1) and show low radio-to-optical ratios, blue coloursand low radio luminosities. We also found 18 Seyfert 2 galaxies (3 percent) and four Seyfert 1s (1 per cent). Analysis of the local radioluminosity function (LF) shows that radio galaxies are well described bymodels that assume pure luminosity evolution, at least down to radiopowersP1.4GHz<~1020.5WHz-1sr-1.Late-type galaxies, whose relative contribution to the radio LF is foundto be lower than was predicted by previous works, present an LF which iscomparable with the IRAS galaxy LF. This class of sources thereforeplausibly constitutes the radio counterpart of the dusty spirals andstarbursts that dominate the counts at 60μm.
| The distribution of atomic gas and dust in nearby galaxies - I. Presentation of matched-resolution VLA H I and SCUBA 850-μm maps
We present matched-resolution VLA HI and SCUBA 850-μm maps of 20IRAS-bright galaxies. Of the galaxies observed, two were not detected inHI and two were detected in absorption. The HI distributions of thegalaxies have a range of morphologies. Some of the systems appear HIdeficient in the central regions which could be due to a high conversionrate of HI into molecules or HI absorption. In contrast to the HI, the850-μm emission has a smooth distribution which is concentratedtowards the optical centre of each galaxy. We also find evidence for850-μm emission extending to the periphery of the optical disc insome of the galaxies. Finally, we note that the relative lack of850-μm emission when compared with HI does not necessarily mean thatthe atomic gas and dust do not have similar mass distributions.
| The SCUBA Local Universe Galaxy Survey - I. First measurements of the submillimetre luminosity and dust mass functions
This is the first of a series of papers presenting results from theSCUBA Local Universe Galaxy Survey (SLUGS), the first statistical surveyof the submillimetre properties of the local Universe. As the initialpart of this survey, we have used the SCUBA camera on the James ClerkMaxwell Telescope to observe 104 galaxies from the IRAS Bright GalaxySample. We present here the 850-μm flux measurements. The 60-, 100-,and 850-μm flux densities are well fitted by single-temperature dustspectral energy distributions, with the sample mean and standarddeviation for the best-fitting temperature beingTd=35.6+/-4.9K and for the dust emissivity indexβ=1.3+/-0.2. The dust temperature was found to correlate with60-μm luminosity. The low value of β may simply mean that thesegalaxies contain a significant amount of dust that is colder than thesetemperatures. We have estimated dust masses from the 850-μm fluxesand from the fitted temperature, although if a colder component ataround 20K is present (assuming a β of 2), then the estimated dustmasses are a factor of 1.5-3 too low. We have made the first directmeasurements of the submillimetre luminosity function (LF) and of thedust mass function. Unlike the IRAS 60-μm LF, these are well fittedby Schechter functions. The slope of the 850-μm LF at lowluminosities is steeper than -2, implying that the LF must flatten atluminosities lower than we probe here. We show that extrapolating the60-μm LF to 850μm using a single temperature and β does notreproduce the measured submillimetre LF. A population of `cold' galaxies(Td<25K) emitting strongly at submillimetre wavelengthswould have been excluded from the 60-μm-selected sample. If suchgalaxies do exist, then this estimate of the 850-μm flux is biased(it is underestimated). Whether such a population does exist is unknownat present. We correlate many of the global galaxy properties with theFIR/submillimetre properties. We find that there is a tendency for lessluminous galaxies to contain hotter dust and to have a greater starformation efficiency (cf. Young). The average gas-to-dust ratio for thesample is 581+/-43 (using both the atomic and molecular hydrogen), whichis significantly higher than the Galactic value of 160. We believe thatthis discrepancy is probably due to a `cold dust' component atTd<=20K in our galaxies. There is a surprisingly tightcorrelation between dust mass and the mass of molecular hydrogen,estimated from CO measurements, with an intrinsic scatter of ~=50percent.
| Absorption-Line Probes of Gas and Dust in Galactic Superwinds
We have obtained moderate resolution (R=few thousand) spectra of the NaI λλ5890, 5896 (Na D) absorption line in a sample of 32far-IR-bright starburst galaxies. In 18 cases, the Na D line in thenucleus is produced primarily by interstellar gas, while cool starscontribute significantly in the others. In 12 of the 18``interstellar-dominated'' cases the Na D line is blueshifted by over100 km s-1 relative to the galaxy systemic velocity (the``outflow sources''), while no case shows a net redshift of more than100 km s-1. The absorption-line profiles in these outflowsources span the range from near the galaxy systemic velocity to amaximum blueshift of ~400-600 km s-1. The outflow sources aregalaxies systematically viewed more nearly face-on than the others. Wetherefore argue that the absorbing material consists of ambientinterstellar material that has been entrained and accelerated along theminor axis of the galaxy by a hot starburst-driven superwind. The Na Dlines are optically thick, but indirect arguments imply total hydrogencolumn densities of NH~few×1021cm-2. This implies that the superwind is expelling matter ata rate comparable to the star formation rate. This outflowing materialis evidently very dusty: we find a strong correlation between the depthof the Na D profile and the line-of-sight reddening. Typical impliedvalues are E(B-V)=0.3-1 over regions several-to-10 kpc in size. Webriefly consider some of the potential implications of theseobservations. The estimated terminal velocities of superwinds inferredfrom the present data and extant X-ray data are typically 400-800km-1, are independent of the galaxy rotation speed, and arecomparable to (substantially exceed) the escape velocities forL* (dwarf) galaxies. The resulting selective loss of metalsfrom shallower potential wells can establish the mass-metallicityrelation in spheroids, produce the observed metallicity in theintracluster medium, and enrich a general IGM to of order10-1 solar metallicity. If the outflowing dust grains cansurvive their journey into the IGM, their effect on observations ofcosmologically distant objects would be significant.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| The Supernova Rate in Starburst Galaxies
We conducted an optical CCD search for supernovae in a sample of 142bright [m(B) <= 16 mag], nearby (z<=0.03) starburst galaxies overthe period 1988 December to 1991 June, to a limiting R-band magnitude of18. Five supernovae were found, in all cases outside the host galaxy'snucleus. We determine supernova rates (in supernova units or SNU) in theextranuclear regions to be 0.7 h^2 SNU for Type Ia, 0.7 h^2 SNU for TypeIb/c, and ~0.6 h^2 SNU for Type II, with large uncertainties but upperlimits of 2.2 h^2, 2.5 h^2, and 1.7 h^2 SNU, respectively. These ratesare similar to those measured in ``normal'' galaxies. We found noevidence for a supernova-induced brightening in any galactic nucleusand, with a few reasonable assumptions, can place upper limits of 9 h^2,12 h^2, and 7 h^2 SNU on the rates of unobscured supernovae Types Ia,Ib/c, and II, respectively, inside the nuclei.
| A Complete Redshift Survey to the Zwicky Catalog Limit in a 2^h X 15 deg Region around 3C 273
We compile 1113 redshifts (648 new measurements, 465 from theliterature) for Zwicky catalog galaxies in the region (-3.5d <= delta<= 8.5d, 11h5 <= alpha <= 13h5). We include redshifts for 114component objects in 78 Zwicky catalog multiplets. The redshift surveyin this region is 99.5% complete to the Zwicky catalog limit, m_Zw =15.7. It is 99.9% complete to m_Zw = 15.5, the CfA Redshift Survey(CfA2) magnitude limit. The survey region is adjacent to the northernportion of CfA2, overlaps the northernmost slice of the Las CampanasRedshift Survey, includes the southern extent of the Virgo Cluster, andis roughly centered on the QSO 3C 273. As in other portions of theZwicky catalog, bright and faint galaxies trace the same large-scalestructure.
| Toward a Unified Model for the ``Diffuse Ionized Medium'' in Normal and Starburst Galaxies
The ``diffuse ionized medium'' (DIM) makes up a significant fraction ofthe mass and ionization requirements of the interstellar medium of theMilky Way and is now known to be an energetically significant componentin most normal star-forming galaxies. Observations of the ionized gas instarburst galaxies have revealed the presence of gas with strikingsimilarities to the DIM in normal galaxies: relatively low surfacebrightness and strong emission from low-ionization forbidden lines like[S II] lambdalambda6716, 6731. In this paper we analyze Hα imagesand long-slit spectra of samples of normal and starburst galaxies tobetter understand the nature of this diffuse, low surface brightnessgas. We find that in both samples there is a strong inverse correlationbetween the Hα surface brightness (Sigma_Hα) and the [SII]/Hα line ratio at a given location in the galaxy. However, thecorrelation for the starbursts is offset brightward by an order ofmagnitude in Hα surface brightness at a given line ratio. Incontrast, we find that all the galaxies (starburst and normal alike)define a universal relation between line ratio and the relative Hαsurface brightness (Sigma_Hα/Sigma_e, where Sigma_e is the meanHα surface brightness within the galaxy half-light radius). Weshow that such a universal correlation is a natural outcome of a modelin which the DIM is photoionized gas that has a characteristic thermalpressure (P) that is proportional to the mean rate of star formation perunit area in the galaxy (Sigma_SFR). Good quantitative agreement withthe data follows if we require the constant of proportionality to beconsistent with the values of P and Sigma_SFR in the local disk of theMilky Way. Such a scaling between P and Sigma_SFR may arise eitherbecause feedback from massive stars heats the ISM or because Sigma_SFRis determined (or limited) by the mean gas pressure.
| The Nature of Starburst Galaxies
Utilizing a large sample of infrared-selected starburst galaxies havingoptical images and long-slit spectra, we explore the interrelationshipsbetween the properties of starbursts and relate these properties tothose of the "host" galaxy. We find that the half-light radius of theHα-emitting region (r_e,Hα_) enters into severalcorrelations that suggest it is physically related to the actualstarburst radius. Most suggestively, the effective IR surface brightness(L_IR_/πr^2^_e,Hα_) correlates strongly with the far-IR colortemperature. This can be reproduced roughly with an idealized model of asurrounding dust screen whose far-IR emissivity is determined by thelocal energy density of UV starburst light. Typical values forr_e,Hα_ are a few hundred pc to a few kpc (with the Hαemission being significantly more compact than the red starlight). Thisconfirms the "circumnuclear" scales of typical starbursts. We show alsothat starbursts seem to obey a limiting IR surface brightness of about10^11^L_sun_ kpc^2^, corresponding to a maximum star formation rate ofabout 20 M_sun_ yr^-1^ kpc^2^ for a normal initial mass function. Weargue that this upper limit suggests that starbursts are self-regulatingin some way. We show that most of these galaxies have relatively normal,symmetric rotation curves. This implies that the galactic disk need notsuffer severe dynamical damage in order to "fuel" a typical starburst.We show also that the starbursts occur preferentially in the innerregion of solid-body rotation. This may reflect both bar-driven inflowof gas to the region between the inner Lindblad resonances and thedominance of gravitational instability over tidal shear in this region.Most of the starbursts reside in galaxies with rotation speeds of120-200 km s^-1^ (compared to 220 km s^-1^ for a fiducial L^*^ galaxylike the Milky Way). The lack of a correlation between galaxy rotationspeed and starburst luminosity means that even relatively modestgalaxies (masses~10% of the Milky Way) can host powerful starbursts. Weargue on the basis of causality that the internal velocity dispersion ina starburst sets an upper limit to the star formation rate. The mostextreme starbursts approach this limit, but most are well below.Finally, we show that the relative narrowness of the nuclear emissionlines in starbursts (relative to the galaxy rotation speed) arisesbecause the gas in the nuclear "bin" usually does not sample fully thesolid-body part of the rotation curve. The narrow lines do notnecessarily imply that the starburst is not in dynamical equilibrium.
| Ionized Gas in the Halos of Edge-on Starburst Galaxies: Evidence for Supernova-driven Superwinds
Supernova-driven galactic winds ("superwinds") have been invoked toexplain many aspects of galaxy formation and evolution. Such windsshould arise when the supernova rate is high enough to create a cavityof very hot shock-heated gas within a galaxy. This gas can then expandoutward as a high-speed wind that can accelerate and heat ambientinterstellar or circum-galactic gas causing it to emit optical lineradiation and/or thermal X-rays. Theory suggests that such winds shouldbe common in starburst galaxies and that the nature of the winds shoulddepend on the star formation rate and distribution. In order tosystematize our observational understanding of superwinds (determinetheir incidence rate and the dependence of their properties on the starformation that drives them) and to make quantitative comparisons withthe theory of superwinds, we have analyzed data from an opticalspectroscopic and narrow-band imaging survey of an infrared flux-limited(S_60 microns_ >= 5.4 Jy) sample of about 50 IR-warm (S_60microns_/S_100 microns_ > 0.4), starburst galaxies whose stellardisks are viewed nearly edge-on (b/a ~> 2). This sample containsgalaxies with infrared luminosities from ~10^10^-10^12^ L_sun_ andallows us to determine the properties of superwinds over a wide range ofstar formation rates. We have found that extraplanar emission-line gasis a very common feature of these edge-on, IR-bright galaxies and theproperties of the extended emission-line gas are qualitatively andquantitatively consistent with the superwind theory. We can summarizethese properties as morphological, ionization, dynamical, and physical.1. Morphological properties.-Extraplanar filamentary and shell-likeemission-line morphologies on scales of hundreds of parsecs to 10 kpcare common, there is a general "excess" of line emission along the minoraxis, the minor axis emission-line "excess" correlates with "IRactivity," and the minor axis emission-line "excess" also correlateswith the relative compactness of the Hα emission. 2. Ionizationproperties.-Line ratios become more "shocklike" (high ratios of [N II]λ6583/Hα, [S II] λλ6716, 6731/Hα, and[O I] λ6300/Hα) at more extreme IR properties, the most"shocklike" line ratios occur far out along the minor axis, "shocklike"line ratios corresponds to broad emission lines, and the most extremeline ratios correspond to the most extreme IR properties, especially forthe emission-line gas farthest out along the minor axis. 3. Dynamicalproperties.-Lines are broader along the minor axis than along the majoraxis, line widths correlate with the "IR activity," line widthscorrelate with line ratios, line widths do not correlate with rotationspeed, minor axis shear (a measure of the systematic velocity changealong the minor axis) correlates with "IR activity," minor axis shearcorrelates with axial ratio and implies that a face-on galaxy would havean outflow/inflow speed of 170_-80_^+150^ km s^-1^, and the starburstsshow statistically blueward line profile asymmetries. 4. Physicalproperties.-Pressures in the nuclei of these galaxies are 3 orders ofmagnitude higher than the ambient pressure in the interstellar medium ofour galaxy, and the pressure falls systematically with radius. Whilenone of these results are in themselves proof of the superwind model, webelieve that when the results are taken as a whole, the superwindhypothesis is very successful in explaining what we have observed. Inaddition, these results have implications for galaxy evolution and thenature of the intergalactic medium. Those galaxies with the bestevidence for driving superwinds are those with large IR luminosities(L_IR_ ~> 10^44^ ergs s^-1^), large IR excesses (L_IR_/L_OPT_ ~>2), and warm far-IR colors (S_60 microns_/S_100 microns_ ~> 0.5).Integrating over the local far-IR luminosity function for galaxiesmeeting the above criteria, multiplying by the age of the universe, andthen dividing by the local space density of galaxies implies thatsuperwinds have carried out ~5 x 10^8^ M_sun_ in metals and 10^59^ ergsin kinetic plus thermal energy per average (Schecter L^*^) galaxy overthe history of the universe. We note that these two quantities areapproximately equal to the mass of metals contained inside an averagegalaxy and the gravitational binding energy of an average galaxy,respectively. Even with the conservative assumptions of this calculation(we have neglected that star formation rates were presumably higher inthe early universe), it is obvious that superwinds may have a majorimpact on the evolution of individual galaxies and the intergalacticmedium by injecting mass, metals, and kinetic energy into the galactichalo and potentially the intergalactic medium.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| The bar-enhanced star-formation activities in spiral galaxies.
We use the ratio L_FIR_/L_B_ and the IRAS color index S_25_/S_12_ (bothwidely used as indices of relative star formation rates in galaxies) toanalyse subsets (containing no known AGNs or merging/interactinggalaxies) of: (a) the IRAS Bright Galaxy Sample, (b) galaxies from theoptically complete RSA sample which have IRAS detections in all fourbands, and (c) a volume-limited IR-unselected sample. We confirm thatIR-bright barred (SB) galaxies do, on average, have very significantlyhigher values of the FIR-optical and S_25_/S_12_ ratios (and presumably,higher relative star formation rates, SFR) than that do unbarred ones;the effect is most obvious in the IR colors. We also confirm that thesedifferences are confined to early-type (S0/a-Sbc) spirals and are notevident among late-type systems (Sc-Sdm). Unlike others, we see noenhancement of the SFR in weakly-barred (SAB) galaxies. We furtherconfirm that the effect of bars on the SFR is associated with therelative IR luminosity and show that it is detectable only in galaxieswith L_FIR_/L_B_>1/3, suggesting that as soon as they have anyeffect, bars translate their host galaxies into this relativelyIR-luminous group. Conversely, for galaxies with L_FIR_/L_B_ below ~0.1this luminosity ratio is lower among barred than unbarred systems, againconfirming and quantifying an earlier result. Although there is nosimple physical relation between H I content and star formation, astrong correlation of H I content with the presence of bars has beenfound for early-type spirals with L_FIR_/L_B_>1/3. This suggests thatthe availability of fuel is the factor determining just which galaxiesundergo bar-induced starbursts.
| A comparative study of morphological classifications of APM galaxies
We investigate the consistency of visual morphological classificationsof galaxies by comparing classifications for 831 galaxies from sixindependent observers. The galaxies were classified on laser print copyimages or on computer screen using scans made with the Automated PlateMeasuring (APM) machine. Classifications are compared using the RevisedHubble numerical type index T. We find that individual observers agreewith one another with rms combined dispersions of between 1.3 and 2.3type units, typically about 1.8 units. The dispersions tend to decreaseslightly with increasing angular diameter and, in some cases, withincreasing axial ratio (b/a). The agreement between independentobservers is reasonably good but the scatter is non-negligible. In spiteof the scatter, the Revised Hubble T system can be used to train anautomated galaxy classifier, e.g. an artificial neural network, tohandle the large number of galaxy images that are being compiled in theAPM and other surveys.
| Optical Spectroscopy of Luminous Infrared Galaxies. II. Analysis of the Nuclear and Long-Slit Data
A spectroscopic survey of a sample of 200 luminous IRAS galaxies (LIGs:L_ir_^7^ > 3 x 10^10^ L_sun_; H_0_ = 75 km s^-1^ Mpc^-1^) was carriedout using the Palomar 5 meter and University of Hawaii 2.2 m telescopes.Kim et al. (1995) described the data-taking and data-reductionprocedures and presented line and continuum measurements extracted fromthe nucleus of these objects. In this paper, the nuclear data arecombined with circumnuclear measurements on 23 of these galaxies toinvestigate the properties of the line-emitting gas and underlyingstellar population in and out of the nucleus. The nuclear spectra ofthese galaxies were classified as H II region-like" or "AGN-like" usinga large number of line-ratio diagnostics corrected for the underlyingstellar absorption features. This correction is an important source oferrors in some previous studies. The emission-line spectra of many AGNswere found to-be of relatively low ionization level and were thereforeclassified as LINER. We confirm that both the fraction of LIGs with AGNspectra and the fraction of Seyferts among the AGN increase withinfrared luminosity, reaching values of 62% and 54% at the highestobserved luminosities, respectively. The fraction of LINERs, on theother hand, is relatively constant at ~27%. The source of the ionizationof the emission-line gas often is a function of the distance from thenucleus. Based on the emission-line ratios and the strengths of thestellar absorption features, circumnuclear starburst activity is acommon feature of LIGs, regardless of their nuclear spectral types. Theemission-line, absorption-line, continuum, radio, and IRAS properties ofthe LINERs suggest that most of the LINER emission in theseinfrared-selected galaxies is produced through shock ionization ratherthan photoionization by a genuine active nucleus. The nuclear region ofSeyfert LIGs is found to be slightly less reddened than that of theLINERs and H II galaxies. The dust distribution generally isconcentrated toward the nucleus, in agreement with the often peakydistribution of the molecular gas observed in these galaxies. Inverteddust profiles in which the nucleus appears less dusty than thecircumnuclear region are observed in only three LIGs, all of which haveAGN emission-line characteristics (one Seyfert 2 galaxy and two LINERs).Low nuclear dust content appears to favor the detection of activenuclei. This may be due to selection effects or may reflect realphysical differences between these classes of objects: galaxies withSeyfert emission lines may be at a more advanced stage of dustdestruction/expulsion than H II LIGs. Complex optical depth effects mayalso explain these results without invoking a smaller amount of dust inthe nucleus. The Hβ and Mg I b absorption features are stronger inthe nuclei of AGNs (especially among the LINERs) than in H II LIGs,suggesting that AGN LIGs are at a more advanced stage of stellarevolution than H II LIGs. Further support for this scenario comes fromthe fact that AGNs are found more frequently in advanced mergers than HII galaxies (only two Seyfert galaxies are detected in systems withwell-separated nuclei). However, this last result may be a luminosityeffect rather than an effect related to the dominant nuclear source ofionization. Moreover, the absorption-line data may simply reflect thefact that galaxies with powerful H II regions show evidence for youngstars while galaxies with AGNs do not. The radial variations of theHβ and Mg I b absorption features indicate the presence of a strongsource of featureless continuum in the nucleus of nearly all LIGs,regardless of their nuclear spectral types. Contamination by thecircumnuclear starburst prevents us from determining the extent of thiscontinuum source. The [O III] profiles of both Seyfert and LINER LIGswere found to be broader on average than those of H II objects. Nearly20% of the LIGs in our sample have line widths larger than 600 km s^-1^.We find that most of the galaxies in which we could determine the radialvariations of the [O III] line width present broader profiles in thecircumnuclear region than at the nucleus. When combined with publisheddata on a few other well-studied LIGs, these results suggest thatlarge-scale nuclear winds are common in these objects and are anefficient way of getting rid of the obscuring material in the nuclearregion. The spatially extended LINER emission observed in many of theseobjects is probably due to shock ionization resulting from theinteraction of the wind-accelerated gas with the ambient material of thehost galaxy.
| Optical Spectroscopy of Luminous Infrared Galaxies. I. Nuclear Data
A spectroscopic survey of a large sample of luminous infrared galaxies[log (L_ir_/L_sun_)^7^ ~ 10.5-12.5; H_0_ = 75 km s^-1^ Mpc^-1^] has beencarried out using the Palomar 5 m telescope,, and the University ofHawaii 2.2 m telescope. Long-slit spectra covering 375o-8000 A at aresolution of ~10 A were obtained of 200 IRAS galaxies, including 114objects from the IRAS Bright Galaxy Survey, and 86 objects with fainterinfrared fluxes selected on the basis of their "warm" far-infrared(S_60_/S_100_) colors. The methods of observation and data reduction arediscussed. An atlas of the spectra extracted from the nuclear region ofthese objects is presented along with a large number of parametersdescribing the properties of the emission lines, the stellar absorptionlines, and the continuum emission that were measured from the spectra.An analysis of these data is presented in a companion paper (Veilleux etal. 1995) along with a discussion of the spatial variations of theseparameters in a subsample of twenty-three objects.
| Ionized gas in the halos of edge-on, starburst galaxies: Data and results
We present narrowband H-alpha and broadband R images, as well aslong-slit spectra oriented along the minor and major axes of a sample ofabout 50 edge-on (a/b greater than or equal to 2), infrared-warm(S60 microns/S100 microns greater than 0.04),infrared-bright S60 microns greater than or equal to 5.4 Jygalaxies. The infrared luminosity of the sample ranges over1010 - 1012 solar luminosity. The spatiallyresolved spectroscopy includes the measurement of velocity relative tothe nuclear velocity, full width at half-maximum, total integrated fluxin the profile (for those spectra taken under photometric conditions)for the lines (N II) lambda lambda 6548, 6583, (O I) lambda 6300,H-alpha, and (S II) lambda lambda 6716, 6713 and line ratios as afunction of slit position along both the major and minor axes. Theresolution of the spectra are between about 3 and 5 A. The spectroscopicdata are presented for 5 bins along each axis -- a nuclear bin that is asum of the CCD rows that cover the half-light diameter centered on thenucleus of the galaxy, two near-nuclear bins which are sums of the CCDrows that cover from one to two half-light radii on each side of thenucleus, and two off-nuclear bins which are sums of the rows at nucleardistances greater than two half-light radii on each side of the nucleus.Additionally, we present recession velocities, nuclear line asymmetries,rotation speeds, minor axis velocity shears, H-alpha luminosities,R-band absolute magnitudes, minor axis H-alpha `excess' and effectiveradii of the galaxies in h-alpha and the R continuum. We deferdiscussion of the properties of the emission-line gas and theircorrelation with the infrared properties of this sample of galaxies to alater paper and limit ourselves to a presentation of the data andanalysis.
| X-ray study of starburst galaxies.
We present full results of a wide-energy, population study of X-rayemission from a sample of 51 candidate starburst galaxies selected fromthe IRAS Bright Galaxy Sample. Superposed low and high energy X-rayemission from these galaxies in the Einstein IPC and HEAO-1 A2 and A4energy bands, which span 0.5 to 160keV, is detected at the 99.99%confidence level, after allowing for confusion noise in the HEAO-1 data.Above 13keV the confidence level is only 85%. A power-law fit to themean spectral luminosity yields a (photon) index of 1.47+/-0.26. Weconsider and assess likely environments and mechanisms for X-rayemission in starburst galaxies. These include thermal emission frommassive binaries, supernova remnants, and galactic halos, and nonthermalemission resulting from Compton scattering of relativistic electrons bythe far IR and the cosmic microwave background radiation fields. Thecontribution of the population of sources represented by this sample tothe 3-50keV residual cosmic X-ray background is estimated to be at the3-4% level assuming no evolution. This contribution is significantlyhigher if the population evolved moderately.
| The extended 12 micron galaxy sample
We have selected an all-sky (absolute value of b greater than or equalto 25 deg) 12 micron flux-limited sample of 893 galaxies from the IRASFaint Source Catalog, Version 2 (FSC-2). We have obtained accurate totalfluxes in the IRAS wavebands by using the ADDSCAN procedure for allobjects with FSC-2 12 micron fluxes greater than 0.15 Jy and increasingflux densities from 12 to 60 microns, and defined the sample by imposinga survey limit of 0.22 Jy on the total 12 micron flux. Its completenessis verified, by means of the classical log N - log S andV/Vmax tests, down to 0.30 Jy, below which we have measuredthe incompleteness down to the survey limit, using the log N - log Splot, for our statistical analysis. We have obtained redshifts (mostlyfrom catalogs) for virtually all (98.4%) the galaxies in the sample.Using existing catalogs of active galaxies, we defined a subsample of118 objects consisting of 53 Seyfert 1s and quasars, 63 Seyfert 2s, andtwo blazars (approximately 13% of the full sample), which is the largestunbiased sample of Seyfert galaxies ever assembled. Since the 12 micronflux has been shown to be about one-fifth of the bolometric flux forSeyfert galaxies and quasars, the subsample of Seyferts (includingquasars and blazars) is complete not only to 0.30 Jy at 12 microns butalso with respect to a bolometric flux limit of approximately 2.0 x10-10 ergs/s/sq cm. The average value of V/Vmaxfor the full sample, corrected for incompleteness at low fluxes, is 0.51+/- 0.04, expected for a complete sample of uniformly distributedgalaxies, while the value for the Seyfert galaxy subsample is 0.46 +/-0.10. We have derived 12 microns and far-infrared luminosity functionsfor the AGNs, as well as for the entire sample. We extracted from oursample a complete subsample of 235 galaxies flux-limited (8.3 Jy) at 60microns. The 60 micron luminosity function computed for this subsampleis in satisfactory agreement with the ones derived from the brightgalaxy sample (BGS) and the deep high-galactic latitude sample, bothselected at 60 microns.
| The far-infrared properties of the CfA galaxy sample. I - The catalog
IRAS flux densities are presented for all galaxies in the Center forAstrophysics magnitude-limited sample (mB not greater than 14.5)detected in the IRAS Faint Source Survey (FSS), a total of 1544galaxies. The detection rate in the FSS is slightly larger than in thePSC for the long-wavelength 60- and 100-micron bands, but improves by afactor of about 3 or more for the short wavelength 12- and 25-micronbands. This optically selected sample consists of galaxies which are, onaverage, much less IR-active than galaxies in IR-selected samples. Itpossesses accurate and complete redshift, morphological, and magnitudeinformation, along with observations at other wavelengths.
| Very small grains and the infrared colors of galaxies
The contribution of very small grains with fluctuating temperature tothe IR emission of disk galaxies is evaluated in light of IRAS data, andthe abundance variation of these small grains among galaxies, relativeto the 'classical', thermally stable grains, is estimated. It issuggested that the low dispersion in the 'cold' galaxies isrepresentative of the true dispersion in the small-to-large grainabundance ratio among galaxies, while the larger dispersion among warmergalaxies results from increasing optical depth-heating dust effects dueto AGNs, in conjunction with the destruction of small dust grains athigh radiative energy densities.
| A 1.49 GHz atlas of the IRAS Bright Galaxy Sample
The VLA has been used in its A-, B-, C-, and D-configurations to make1.49 GHz maps of sources in both the original and revised IRAS BrightGalaxy Samples of strong extragalactic sources selected at a wavelengthof 60 microns. Integrated 1.49 GHz flux densities were obtained from thelowest resolution maps, and maps were made with higher resolution sothat nearly all of the radio sources have been at least partiallyresolved. Only NGC 1377 was not detected at 1.49 GHz. An atlas ofcontour maps, a table of total flux densities plus other radio sourceparameters, and references to published radio maps are given. Since theinfrared and radio continuum brightness distributions of IR-selectedgalaxies are usually similar, these high-resolution radio maps can beused as substitutes for the unavailable IR maps to indicate the sizesand precise locations of the IR-emitting regions.
| The IRAS Bright Galaxy Sample. IV - Complete IRAS observations
Total flux densities, peak flux densities, and spatial extents at 12,25, 60, and 100 microns are presented for the 330 sources in the IRASBright Galaxy Sample. The flux density ratios Snu (60microns)/Snu (100 microns) and Snu (12microns)/Sn (25 microns) are found to correlate with both theinfrared luminosity and the ratio of IR to visible flux. The relationbetween these two flux density ratios is shown to follow that foundpreviously, with different slopes appearing for the warmer and coldergalaxies in the sample. The results suggest that single photon heatingof small grains (often the dominant source of 12 and 25 micron radiationfrom galaxies) significantly affects the emission of some galaxies at 60microns, and that optical depth effects may alter the emergent radiationat 12 and 25 microns.
| 21 centimeter survey of luminous infrared galaxies
This paper presents the results from a 21-cm Arecibo survey of theatomic hydrogen and radio continuum in the most luminous IRAS galaxiesof the local universe. Ninety-two galaxies with FIR luminosities in therange of L(FIR) between the solar luminosity values of 2 x 10 to the10th and 2 x 10 to the 12th were surveyed. Eighty eight of these weredetected in the 21 cm line of atomic hydrogen; the radio continuum fluxwas determined for 80 galaxies. The data of this survey are compared theFIR and optical-wavelength band results. It is noted that luminous IRgalaxies show a striking statistical trend for the optical radialvelocities to be smaller than the systemic velocities derived from the21 H I profiles.
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