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An IRAS High Resolution Image Restoration (HIRES) Atlas of All Interacting Galaxies in the IRAS Revised Bright Galaxy Sample
The importance of far-infrared observations for our understanding ofextreme activity in interacting and merging galaxies has beenillustrated by many studies. Even though two decades have passed sinceits launch, the most complete all-sky survey to date from which far-IRselected galaxy samples can be chosen is still that of the InfraredAstronomical Satellite (IRAS). However, the spatial resolution of theIRAS all-sky survey is insufficient to resolve the emission fromindividual galaxies in most interacting galaxy pairs, and hence previousstudies of their far-IR properties have had to concentrate either onglobal system properties or on the properties of very widely separatedand weakly interacting pairs. Using the HIRES image reconstructiontechnique, it is possible to achieve a spatial resolution ranging from30" to 1.5m (depending on wavelength and detector coverage), whichis a fourfold improvement over the normal resolution of IRAS. This issufficient to resolve the far-IR emission from the individual galaxiesin many interacting systems detected by IRAS, which is very importantfor meaningful comparisons with single, isolated galaxies. We presenthigh-resolution 12, 25, 60, and 100 μm images of 106 interactinggalaxy systems contained in the IRAS Revised Bright Galaxy Sample (RBGS,Sanders et al.), a complete sample of all galaxies having a 60 μmflux density greater than 5.24 Jy. These systems were selected to haveat least two distinguishable galaxies separated by less than threeaverage galactic diameters, and thus we have excluded very widelyseparated systems and very advanced mergers. Additionally, some systemshave been included that are more than three galactic diameters apart,yet have separations less than 4' and are thus likely to suffer fromconfusion in the RBGS. The new complete survey has the same propertiesas the prototype survey of Surace et al. We find no increased tendencyfor infrared-bright galaxies to be associated with other infrared-brightgalaxies among the widely separated pairs studied here. We find smallenhancements in far-IR activity in multiple galaxy systems relative toRBGS noninteracting galaxies with the same blue luminosity distribution.We also find no differences in infrared activity (as measured byinfrared color and luminosity) between late- and early-type spiralgalaxies.
| 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.
| 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 infrared supernova rate in starburst galaxies
We report the results of our ongoing search for extincted supernovae(SNe) at near-infrared wavelengths. We have monitored at 2.2 mu m asample of 46 Luminous Infrared Galaxies and detected 4 SNe. The numberof detections is still small but sufficient to provide the firstestimate of supernova rate at near-infrared wavelengths. We measure a SNrate of SNNIR_r=7.6+/- 3.8 SNu which is an order of magnitudelarger than observed in quiescent galaxies. On the other hand, theobserved near-infrared rate is still a factor 3-10 smaller than thatestimated from the far-infrared luminosity of the galaxies. Amongvarious possibilities, the most likely scenario is that dust extinctionis so high (AV>30) to obscure most SNe even in thenear-IR.The role of type Ia SNe is also discussed within this context. We derivethe type Ia SN rate as a function of the stellar mass of the galaxy andfind a sharp increase toward galaxies with higher activity of starformation. This suggests that a significant fraction of type Ia SNe areassociated with young stellar populations.Finally, as a by-product, we give the average K-band light curve ofcore-collapse SNe based on all the existing data, and review therelation between SN rate and far-infrared luminosity.Based on observations collected at the European Southern Observatory,Chile (proposal 66.B-0417), at the Italian Telescopio Nazionale Galileo(TNG) operated on the island of La Palma by the Centro Galileo Galileiof the INAF (Istituto Nazionale di Astrofisica), and at the StewardObservatory 61'' telescope.
| 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.
| 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.
| Accurate Positions for MCG Galaxies
We have measured accurate celestial coordinates for 4741 extragalacticobjects, primarily drawn from a list of MCG galaxies with no recentlypublished accurate positions. The standard deviations in the newpositions depend slightly on the measurement method but are on the orderof 1.0" to 1.2". Standard deviations in the original MCG positions areconfirmed to be at the 1.5′-2.0′ level. These new positionswere integrated into NED in 1997 December.
| 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 Starburst-AGN Connection. II. The Nature of Luminous Infrared Galaxies as Revealed by VLBI, VLA, Infrared, and Optical Observations
We present here detailed results of an 18 cm VLBI survey of 31 luminous(LFIR > 1011.25 Lȯ), radio-compact ( theta <~ 0."25) infraredgalaxies (LIGs). High-resolution VLA maps at 15 and 22 GHz are presentedfor 14 of these galaxies that exhibit compact milliarcsecond-scaleemission, providing information about radio structure of LIGs on scalesfrom 0."004 to 1."0. We also present new optical spectrophotometricobservations. Over half the sample galaxies show high brightnesstemperature radio emission from the VLBI data, with Tb > 105 K andstructure on scales of 5-150 mas, as previously reported in Lonsdale,Smith, & Lonsdale. The median VLBI power for detected sources is logPVLBI = 22.0 (W Hz-1), and the mean ratio of VLBI to total 1.6 GHz fluxdensity is = 0.12. Further structure is observedon the larger VLA scales. No highly significant (P < 1%) statisticalcorrelations are found between the presence or strength of the VLBIemission and other observed quantities, including total radio power,radio spectral index, IR luminosity and colors, radio-infrared ratio,molecular gas mass, and optical excitation. Statistical analysis doessuggest that the infrared luminosity, molecular gas emission, and radioemission on VLA and VLBI scales are physically related. Previous work(Lonsdale, Smith, & Lonsdale) demonstrated that hidden(dust-enshrouded) active galactic nuclei (AGNs) are capable of poweringLIGs and giving rise to the observed VLBI- and VLA-scale structures;here we investigate the complementary question of whether a starburstcan completely explain the observed characteristics, including the highbrightness temperature radio emission. Simple starburst models show thatthe far-infrared luminosity can be explained by starbursts in all casesexcept Mrk 231, although for some objects the constraints imposed on theinitial mass function are severe. Using our starburst models we modelthe VLBI data for 11 galaxies with detailed radio structural informationusing complexes of radio supernovae. The required supernova rates are nusn ~ 0.1-2 yr-1, consistent with the rates derived from the starburstmodel to explain the observed far-infrared luminosities. However in allcases we require complexes of extremely luminous radio supernovae (RSNs)to explain the high-Tb emission. In some cases the RSN must haveimplausibly high radio powers, more than an order of magnitude largerthan any previously reported RSNs; in our view these sources representAGN radio cores. In most cases an acceptable fit requires that the RSNbe clustered on parsec scales. Furthermore, only a few clumps may beactive in the radio at a given time. Based on this analysis we concludethat 7/11 systems can be plausibly explained as starbursts. Fourgalaxies, UGC 2369, Mrk 231, UGC 5101, and NGC 7469, almost certainlyhouse AGN radio cores. From our modeling, coupled with other recent VLBIand infrared evidence, we conclude that Arp 220 is dominated by amassive starburst at radio and infrared wavelengths.
| Spectroscopy of Luminous Infrared Galaxies at 2 Microns. II. Data for Galaxies with 11.2 <= (L IR/L ) 11.9
Spectra across the infrared K band are presented for a flux-limitedsample of powerful, bright, "infrared" galaxies. The sample in thepresent paper, consisting of 43 systems (47 individual galaxies) withinfrared luminosities LIR in the range 11.2 <~ log (LIR/Lȯ)<~ 11.9, was chosen from the IRAS Bright Galaxy Catalogue. Thespectra have resolving powers of ~340--680. When combined with the 13spectra we have already published for the "ultraluminous" galaxies,those with log (LIR/Lȯ) >~ 12.0, this constitutes the largestdatabase of high-quality infrared spectra yet assembled for awell-defined sample of galaxies. The spectra are, in general, dominatedby emission lines, which are due to the Br gamma hydrogen recombinationline and to several quadrupole transitions of excited molecularhydrogen. Emission from He I also appears frequently. Deep absorptionbands from CO are present in virtually all the spectra, as are a varietyof weaker stellar absorption features. The data are analyzed in acompanion paper (Paper III).
| Spectroscopy of Luminous Infrared Galaxies at 2 Microns. III. Analysis for Galaxies with log (L IR/L ) 11.2
We have obtained spectra across the K window for the first large sampleof luminous galaxies selected from the IRAS survey. This paper containsthe principal analysis of the 43 systems in our sample with luminositiesof 11.2 <~ log (LIR/Lȯ) <~ 11.9. The spectra themselves werepresented in a companion paper by Goldader et al. (Paper II). The Brgamma luminosities are proportional to LIR, at levels similar to thoseof star-forming regions. This strongly suggests that star formationaccounts for the bulk of the energy production in these objects, ingeneral agreement with previous studies. Good agreement is found for thecontinuous star formation models of Leitherer & Heckman with uppermass cutoffs well below 100 Msolar . The models accommodate arange in starburst ages of ~107 to 109 yr. Instantaneous starburstmodels fit the data but imply an unrealistically short range of ages forthe entire sample. It is difficult to avoid concluding that the initialmass functions are deficient in stars of less than ~1 Msolar. Strong emission lines from molecular hydrogen are detected. The H2 v =1--0 S(1) line luminosities are proportional to LIR; the correlationextends through the ultraluminous infrared galaxies. The H2 emission inthe galaxies tends to be more spatially extended than the Br gammaemission. Measured values and upper limits for the ratios of the variousH2 lines visible in our spectra indicate that the H2 seen in emission at2 mu m is consistent with being shock excited. However, othermechanisms, operating at sufficiently high densities that the H2 energylevels are thermalized by collisions, cannot be excluded. Based onenergy considerations, we suggest that the shocks are due to supernovaremnants expanding into the interstellar medium. The frequency of TypeII supernovae necessary to account for the H2 line emission agrees withfrequencies deduced from the starburst models and the radio/far-infraredcorrelation. However, there remain a number of galaxies that cannot bemade to fit this model. A decade after its discovery, a universalexplanation of the strong H2 emission in luminous infrared galaxiescontinues to elude us. No previously unrecognized broad-line activenuclei were discovered in our survey; either they are weak or absent orthe true optical depths at 2 mu m are much higher than indicated byconventional extinction measures. However, there are clear differencesbetween the K-band properties of galaxies that contain broad-line activenuclei and those that do not. The differences seem to be due to thepresence of strong nonstellar continuum emission coming from the activenuclei themselves. With the addition of the 13 ultraluminous galaxieswith log (LIR/Lȯ) >~ 12 from Goldader et al. (Paper I), thenumber of systems observed in this program totals 56. We haveincorporated these ultraluminous galaxies in some parts of the analysisto examine properties across the entire luminosity range of our sample.
| 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.
| 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.
| High resolution IRAS observations of interacting systems in the IRAS bright galaxy sample
Several conclusions have been drawn from IRAS observations and thedetermination of infrared fluxes of interacting bright galaxies. Theseare: (1) individual interacting galaxies are indistinguishable fromisolated galaxies of similar blue luminosity on the basis of infraredproperties; (2) no correlation was found between measures of interactionstrength and indicators of enhanced star formation; and (3) comparisonof the interacting and isolated samples indicates substantialdifferences between their distributions of far-infrared color ratios,luminosities, and surface brightnesses.
| On the origin of the radio emission in IRAS galaxies with high and ultrahigh luminosity - The starburst-AGN controversy
The radio emission detected in high-luminosity and ultraluminous IRASgalaxies is explained here in terms of violent circumnuclear starbursts.The radio luminosities of the compact radio sources detected in thenearby circumnuclear starburst galaxies NGC 253 and M82 are consistentwith their being a mixture of young radio SNe and old SNR. They must beintrinsically much brighter than the galactic SNR, i.e., radiohypernovae with peak luminosities 100 to 1000 times the luminosity ofCas A. In the starburst scenario, the radio luminosities ofhigh-luminosity and ultraluminous IRAS galaxies (HLIRG and ULIRG) aredominated by the nonthermal radio emission associated with SNe and SNR.These SNe must be radio hypernovae for which SN1979c is a prototype. Theobserved FIR luminosities, q parameters, and Br-alpha luminosities inHLIRG and ULIRG are best explained by a Salpeter IMF with upper masslimit of 60 solar masses.
| Compact starbursts in ultraluminous infrared galaxies
The 40 ultraluminous galaxies in the IRAS Bright Galaxy Sample ofsources stronger than S = 5.24 Jy at lambda = 60 microns were mappedwith approximately 0.25 arcsec resolution at 8.44 GHz. Twenty-fivecontain diffuse radio sources obeying the FIR-radio correlation; theseare almost certainly starburst galaxies. Fourteen other galaxies havenearly blackbody FIR spectra with color temperatures between 60 and 80 Kso their (unmeasured) FIR angular sizes must exceed approximately 0.25arcsec, yet they contain compact (but usually resolved) radio sourcessmaller than this limit. The unique radio and FIR properties of thesegalaxies can be modeled by ultraluminous nuclear starbursts so densethat they 67 are optically thick to free-free absorption at about 1.49GHz and dust absorption at about 25 microns. Only one galaxy (UGC 08058= Mrk 231) is a dominated by a variable radio source too compact to bean ultraluminous starburst; it must be powered by a 'monster'.
| 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. V - Multibeam photometry of galaxies with L(IR) greater than 10 to the 11th solar luminosities
With a view to studying the spatial distribution of the near-IR emissionin luminous IRAS galaxies, 47 galaxies with IR luminosities greater than10 to the 11th solar luminosities have been measured at 1.3, 1.65, and2.2 microns with beam diameters of 17, 33, and 55 arcsec, and used inconjunction with 5 and 10 arcsec observations. the unusually red near-IRcolors are found to be confined to the nuclear regions, while the outerdisk regions have near-IR colors appropriate to a normal stellarpopulation. Since most of the IR luminosity is coming from the nuclei,the global near-IR properties of IR luminous galaxies are not goodtracers of IR activity.
| 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.
| The IRAS Bright Galaxy Sample. III - 1-10 micron observations and coadded IRAS data for galaxies with L(IR) equal to or greater than 10 to the 11th solar luminosities
This paper presents the results of 1-10-micron observations and coaddedIRAS data on 61 galaxies from the Bright Galaxy Sample, with IRluminosities, L(IR), equal to or greater than 10 to the 11th solarluminosities. It was found that an increase in the total L(IR) above 10to the 11th solar luminosity is correlated with increased emission fromhot dust with characteristic temperatures about 800 K. This hot dustcontributes a substantial fraction of the 2.2- and 3.7-micron emission,resulting in a greatly increased dispersion in R(3.7/1.6) and R(2.2/1.6)for these high-luminosity galaxies, relative to lower-luminositygalaxies. This excess hot-dust emission appears to 'turn on' atluminosities of about 10 to the 11th solar luminosity. The spatialdistribution of the 10-micron emission indicated a substantial extendedcomponent for most of the galaxies in this sample, implying thatstar-formation processes contribute significantly to the luminosities.
| The IRAS bright galaxy sample. II - The sample and luminosity function
A statistically complete sample of 324 of the brightest infraredgalaxies discovered at 60 microns in the IRAS all-sky survey isdescribed. The results show that far-infrared emission is a significantluminosity component in the local universe, representing 25 percent ofthe luminosity emitted by stars in the same volume. Above 10 to the 11thsolar luminosities, the infrared luminous galaxies are the dominantpopulation of objects in the universe, being as numerous as the Seyfertgalaxies and more numerous than quasars at higher luminosities. Theinfrared luminosity appears to be independent of the optical luminosityof galaxies. Most infrared bright galaxies appear to require much of theinterstellar matter to be contributing to the observed infraredluminosity. Approximately 60-80 percent of the far-infrared luminosityof the local universe can be attributed, directly or indirectly, torecent or ongoing star formation.
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