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Dust and CO emission towards the centers of normal galaxies, starburst galaxies and active galactic nuclei. I. New data and updated catalogue
Aims.The amount of interstellar matter in a galaxy determines itsevolution, star formation rate and the activity phenomena in thenucleus. We therefore aimed at obtaining a data base of the12CO line and thermal dust emission within equal beamsizesfor galaxies in a variety of activity stages. Methods: .We haveconducted a search for the 12CO (1-0) and (2-1) transitionsand the continuum emission at 1300 μm towards the centers of 88galaxies using the IRAM 30 m telescope (MRT) and the Swedish ESOSubmillimeter Telescope (SEST). The galaxies are selected to be brightin the far infrared (S100~μ m 9 Jy) and opticallyfairly compact (D25≤ 180 arcsec). We have applied opticalspectroscopy and IRAS colours to group the galaxies of the entire sampleaccording to their stage of activity into three sub-samples: normal,starburst and active galactic nuclei (AGN). The continuum emission hasbeen corrected for line contamination and synchrotron contribution toretrieve the thermal dust emission. For the latter we have determinedthe radio spectral indices of the individual sources and extrapolatedthe synchrotron emission corresponding to our millimeter beams to 1300μm. Results: .We present new observational data for the12CO (1-0) and (2-1) transitions and the thermal dustemission at 1300 μm for 88 galaxies. In conjunction with our previousdata, the new observations are used to compile an updated catalogue fora total of 160 galaxies.Based on observations collected at ESO, La Silla, Chile, and IRAM, PicoVeleta, Spain. Appendices A and B are only available in electronic format http://www.aanda.org
| X-ray observations of three young, early-type galaxies
Massive haloes of hot plasma exist around some, but not all ellipticalgalaxies. There is evidence that this is related to the age of thegalaxy. In this paper, new X-ray observations are presented for threeearly-type galaxies that show evidence of youth, in order to investigatetheir X-ray components and properties. NGC 5363 and NGC 2865 were foundto have X-ray emission dominated by purely discrete stellar sources.Limits are set on the mass distribution in one of the galaxies observedwith XMM-Newton, NGC 4382, which contains significant hot gas. We detectthe X-ray emission in NGC 4382 out to 4re. The mass-to-lightratio is consistent with a stellar origin in the inner regions but risessteadily to values indicative of some dark matter by 4re.These results are set in context with other data drawn from theliterature, for galaxies with ages estimated from dynamical orspectroscopic indicators. Ages obtained from optical spectroscopyrepresent central luminosity-weighted stellar ages. We examine the X-rayevolution with age, normalized by B- and K-band luminosities. Low valuesof Log(LX/LB) and Log(LX/LK)are found for all galaxies with ages between 1 and 4 Gyr. Luminous X-rayemission only appears in older galaxies. This suggests that theinterstellar medium is removed and then it takes several gigayears forhot gas haloes to build up, following a merger. A possible mechanism forgas expulsion might be associated with feedback from an active nucleustriggered during a merger.
| Outflows in Infrared-Luminous Starbursts at z < 0.5. II. Analysis and Discussion1,
We have performed an absorption-line survey of outflowing gas in 78starburst-dominated, infrared-luminous galaxies. This is the largeststudy of superwinds at z<~3. Superwinds are found in almost allinfrared-luminous galaxies, and changes in detection rate with SFR-windsare found twice as often in ultraluminous infrared galaxies (ULIRGs) asin less-luminous galaxies-reflect different wind geometries. The maximumvelocities we measure are 600 km s-1, though most of theoutflowing gas has lower velocities (100-200 km s-1). (Onegalaxy has velocities exceeding 1000 km s-1.) Velocities inLINERs are higher than in H II galaxies, and outflowing ionized gasoften has higher velocities than the neutral gas. Wind properties(velocity, mass, momentum, and energy) scale with galaxy properties(SFR, luminosity, and galaxy mass), consistent with ram-pressure drivingof the wind. Wind properties increase strongly with increasing galacticmass, contrary to expectation. These correlations flatten at high SFR(>~10-100 Msolar yr-1), luminosities, andmasses. This saturation is due to a lack of gas remaining in the wind'spath, a common neutral gas terminal velocity, and/or a decrease in theefficiency of thermalization of the supernovae energy. It means thatmass entrainment efficiency, rather than remaining constant, declines ingalaxies with SFR>10 Msolar yr-1 andMK<-24. Half of our sample consists of ULIRGs, which hostas much as half of the star formation in the universe at z>~1. Thepowerful, ubiquitous winds we observe in these galaxies imply thatsuperwinds in massive galaxies at redshifts above unity play animportant role in the evolution of galaxies and the intergalacticmedium.Some of the observations reported here were obtained at the MMTObservatory, which is a joint facility of the Smithsonian Institutionand the University of Arizona.Some of the observations reported here were obtained at the Kitt PeakNational Observatory, National Optical Astronomy Observatory, which isoperated by the Association of Universities for Research in Astronomy,Inc. (AURA), under cooperative agreement with the National ScienceFoundation.
| Outflows in Infrared-Luminous Starbursts at z < 0.5. I. Sample, Na I D Spectra, and Profile Fitting1,
We have conducted a spectroscopic survey of 78 starburstinginfrared-luminous galaxies at redshifts up to z=0.5. We usemoderate-resolution spectroscopy of the Na I D interstellar absorptionfeature to directly probe the neutral phase of outflowing gas in thesegalaxies. Over half of our sample are ultraluminous infrared galaxiesthat are classified as starbursts; the rest have infrared luminositiesin the range log(LIR/Lsolar)=10.2-12.0. The sampleselection, observations, and data reduction are described here. Theabsorption-line spectra of each galaxy are presented. We also discussthe theory behind absorption-line fitting in the case of a partiallycovered, blended absorption doublet observed at moderate-to-highresolution, a topic neglected in the literature. A detailed analysis ofthese data is presented in a companion paper.Some of the observations reported here were obtained at the MMTObservatory, a joint facility of the Smithsonian Institution and theUniversity of Arizona.Some of the observations reported here were obtained at the Kitt PeakNational Observatory, National Optical Astronomy Observatory, which isoperated by the Association of Universities for Research in Astronomy,Inc. (AURA), under cooperative agreement with the National ScienceFoundation.
| EGRET Upper Limits and Stacking Searches of Gamma-Ray Observations of Luminous and Ultraluminous Infrared Galaxies
We present a stacking analysis of EGRET γ-ray observations at thepositions of luminous and ultraluminous infrared galaxies. The latterwere selected from the recently presented HCN survey, which is thoughtto contain the most active star-forming regions of the universe.Different sorting criteria are used, and since there is no positivecollective detection of γ-ray emission from these objects, wedetermined both collective and individual upper limits. The uppermostexcess we find appears in the case of ULIRGs ordered by redshift, at avalue of 1.8 σ.
| Principal component analysis of International Ultraviolet Explorer galaxy spectra
We analyse the UV spectral energy distribution of a sample of normalgalaxies listed in the International Ultraviolet Explorer (IUE) NewlyExtracted Spectra (INES) Guide No. 2 - Normal Galaxies using a principalcomponent analysis. The sample consists of the IUE short-wavelength (SW)spectra of the central regions of 118 galaxies, where the IUE apertureincluded more than 1 per cent of the galaxy size. The principalcomponents are associated with the main components observed in theultraviolet (UV) spectra of galaxies. The first component, accountingfor the largest source of diversity, may be associated with the UVcontinuum emission. The second component represents the UV contributionof an underlying evolved stellar population. The third component issensitive to the amount of activity in the central regions of galaxiesand measures the strength of star-formation events.In all the samples analysed here, the principal component representativeof star-forming activity accounts for a significant percentage of thevariance. The fractional contribution to the spectral energydistribution (SED) by the evolved stars and by the young population aresimilar.Projecting the SEDs on to their eigenspectra, we find that none of thecoefficients of the principal components can outline an internalcorrelation or can correlate with the optical morphological types. In asubsample of 43 galaxies, consisting of almost only compact and BCDgalaxies, the third principal component defines a sequence related tothe degree of starburst activity of the galaxy.
| HCN Survey of Normal Spiral, Infrared-luminous, and Ultraluminous Galaxies
We report systematic HCN J=1-0 (and CO) observations of a sample of 53infrared (IR) and/or CO-bright and/or luminous galaxies, including sevenultraluminous infrared galaxies, nearly 20 luminous infrared galaxies,and more than a dozen of the nearest normal spiral galaxies. This is thelargest and most sensitive HCN survey of galaxies to date. All galaxiesobserved so far follow the tight correlation between the IR luminosityLIR and the HCN luminosity LHCN initially proposedby Solomon, Downes, & Radford, which is detailed in a companionpaper. We also address here the issue of HCN excitation. There is noparticularly strong correlation between LHCN and the 12 μmluminosity; in fact, of all the four IRAS bands, the 12 μm luminosityhas the weakest correlation with the HCN luminosity. There is also noevidence of stronger HCN emission or a higher ratio of HCN and COluminosities LHCN/LCO for galaxies with excess 12μm emission. This result implies that mid-IR radiative pumping, orpopulating, of the J=1 level of HCN by a mid-IR vibrational transitionis not important compared with the collisional excitation by densemolecular hydrogen. Furthermore, large velocity gradient calculationsjustify the use of HCN J=1-0 emission as a tracer of high-densitymolecular gas (>~3×104/τcm-3) andgive an estimate of the mass of dense molecular gas from HCNobservations. Therefore, LHCN may be used as a measure of thetotal mass of dense molecular gas, and the luminosity ratioLHCN/LCO may indicate the fraction of moleculargas that is dense.
| Theoretical Modeling of the Diffuse Emission of Gamma Rays from Extreme Regions of Star Formation: The Case of ARP 220
Our current understanding of ultraluminous infrared galaxies suggeststhat they are recent galaxy mergers in which much of the gas in theformer spiral disks, particularly that located at distances less than 5kpc from each of the premerger nuclei, has fallen into a common center,triggering a huge starburst phenomenon. This large nuclear concentrationof molecular gas has been detected by many groups, and estimates ofmolecular mass and density have been made. Not surprisingly, theseestimates were found to be orders of magnitude larger than thecorresponding values found in our Galaxy. In this paper, aself-consistent model of the high-energy emission of the superstarburstgalaxy Arp 220 is presented. The model also provides an estimate of theradio emission from each of the components of the central region of thegalaxy (western and eastern extreme starbursts and molecular disk). Thepredicted radio spectrum is found as a result of the synchrotron andfree-free emission and absorption of the primary and secondary steadypopulation of electrons and positrons. The latter is the output ofcharged pion decay and knock-on leptonic production, subject to a fullset of losses in the interstellar medium. The resulting radio spectrumis in agreement with subarcsecond radio observations, which is whatallows us to estimate the magnetic field. In addition, the FIR emissionis modeled with dust emissivity, and the computed FIR photon density isused as a target for inverse Compton process as well as to give anaccount of losses in the γ-ray escape. Bremsstrahlung emission andneutral pion decay are also computed, and the γ-ray spectrum isfinally predicted. Future possible observations with GLAST and theground-based Cerenkov telescopes are discussed.
| Luminous Infrared Galaxies as Plausible Gamma-Ray Sources for the Gamma-Ray Large Area Space Telescope and the Imaging Atmospheric Cerenkov Telescopes
We argue that luminous infrared galaxies may constitute a newlydetectable population of γ-ray sources for the next generation ofground- and space-based high-energy telescopes. In addition, we reportfor the first time upper limits on their fluxes using data obtained withthe EGRET telescope.
| The Star Formation Rate and Dense Molecular Gas in Galaxies
HCN luminosity is a tracer of dense molecular gas,n(H2)>~3×104cm-3, associatedwith star-forming giant molecular cloud (GMC) cores. We present theresults and analysis of our survey of HCN emission from 65 infraredgalaxies, including nine ultraluminous infrared galaxies (ULIGs,LIR>~1012Lsolar), 22 luminousinfrared galaxies (LIGs,1011Lsolar0.06 are LIGs or ULIGs. Normal spiralsall have similar and low dense gas fractionsLHCN/LCO=0.02-0.05. The global star formationefficiency depends on the fraction of the molecular gas in a densephase.
| 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.
| Starbursts in barred spiral galaxies. VI. HI observations and the K-band Tully-Fisher relation
This paper reports a study of the effect of a bar on the neutralhydrogen (HI) content of starburst and Seyfert galaxies. We also makecomparisons with a sample of ``normal'' galaxies and investigate howwell starburst and Seyfert galaxies follow the fundamental scalingTully-Fisher (TF) relation defined for normal galaxies. 111 Markarian(Mrk) IRAS galaxies were observed with the Nançay radiotelescope,and HI data were obtained for 80 galaxies, of which 64 are newdetections. We determined the (20 and 50%) linewidths, the maximumvelocity of rotation and total HI flux for each galaxy. Thesemeasurements are complemented by data from the literature to form asample of Mrk IRAS (74% starburst, 23% Seyfert and 3% unknown) galaxiescontaining 105 unbarred and 113 barred ones. Barred galaxies have lowertotal and bias-corrected HI masses than unbarred galaxies, and this istrue for both Mrk IRAS and normal galaxies. This robust result suggeststhat bars funnel the HI gas toward the center of the galaxy where itbecomes molecular before forming new stars. The Mrk IRAS galaxies havehigher bias-corrected HI masses than normal galaxies. They also showsignificant departures from the TF relation, both in the B and K bands.The most deviant points from the TF relation tend to have a strongfar-infrared luminosity and a low oxygen abundance. These resultssuggest that a fraction of our Mrk IRAS galaxies are still in theprocess of formation, and that their neutral HI gas, partly of externalorigin, has not yet reached a stationary state.Based on observations obtained at the large radiotelescope ofObservatoire de Nançay, operated by Observatoire de Paris.Tables 5 and 6 are only (and Table 4 also) available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/416/515
| The evolution of stars and gas in starburst galaxies
In systems undergoing starbursts the evolution of the young stellarpopulation is expected to drive changes in the emission-line properties.This evolution is usually studied theoretically, with a combination ofevolutionary synthesis models for the spectral energy distribution ofstarbursts and photoionization calculations. In this paper we present amore empirical approach to this issue. We apply empirical populationsynthesis techniques to samples of starburst and HII galaxies in orderto measure their evolutionary state and correlate the results with theiremission-line properties. A couple of useful tools are introduced thatgreatly facilitate the interpretation of the synthesis: (1) anevolutionary diagram, the axes of which are the strengths of the young,intermediate age and old components of the stellar population mix; and(2) the mean age of stars associated with the starburst, . These toolsare tested with grids of theoretical galaxy spectra and found to workvery well even when only a small number of observed properties(absorption-line equivalent widths and continuum colours) is used in thesynthesis.Starburst nuclei and HII galaxies are found to lie on a well-definedsequence in the evolutionary diagram. Using the empirically defined meanstarburst age in conjunction with emission-line data, we have verifiedthat the equivalent widths of Hβ and [OIII] decrease for increasing. The same evolutionary trend was identified for line ratios indicativeof the gas excitation, although no clear trend was identified formetal-rich systems. All these results are in excellent agreement withlong-known, but little tested, theoretical expectations.
| Evolutionary spectral energy distribution diagnostics of starburst galaxies: signature of bimodality
We construct an evolutionary spectral energy distribution (SED) model ofa starburst region, from the ultraviolet to submillimetre wavelengths.This model allows us to derive the star formation rate, optical depth bydust and apparent effective radius of starburst regions at variouswavelengths; as a result, the intrinsic surface brightness of starburstregions can be derived. Using this SED model, we analyse 16ultraviolet-selected starburst galaxies and 10 ultraluminous infraredgalaxies. The derived star formation rates and optical depths arecompared with emission-line measurements and are found to be consistent.The derived apparent effective radii are also consistent withobservations. From the SED analysis, we find a bimodal property of thestar formation rate with the optical depth and the compactness ofstellar distributions. While mild starbursts have a limiting intrinsicsurface brightnessLbolr-2e~= 1012Lsolar kpc-2, intense starbursts tend to be moreheavily obscured and concentrated within a characteristic scale ofre~= 0.3 kpc. We suggest that the mild starbursts can betriggered by a self-gravitating disc instability in which feedback iseffective in the shallow gravitational potential. On the other hand, theintense starbursts can be induced via an external dynamical perturbationsuch as galaxy merging, in which feedback is less effective owing to thedeep gravitational potential attained by the large gas concentrationwithin the central starburst region.
| 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.
| Star formation rate in galaxies from UV, IR, and Hα estimators
Infrared (IR) luminosity of galaxies originating from dust thermalemission can be used as an indicator of the star formation rate (SFR).Inoue et al. (\cite{inoue00}, IHK) have derived a formula for theconversion from dust IR luminosity to SFR by using the following threequantities: the fraction of Lyman continuum luminosity absorbed by gas(f), the fraction of UV luminosity absorbed by dust (epsilon ), and thefraction of dust heating from old (ga 108 yr) stellarpopulations (eta ). We develop a method to estimate those threequantities based on the idea that the various way of SFR estimates fromultraviolet (UV) luminosity (2000 Å luminosity), Hαluminosity, and dust IR luminosity should return the same SFR. Afterapplying our method to samples of galaxies, the following results areobtained in our framework. First, our method is applied to a sample ofstar-forming galaxies, finding that f ~ 0.6, epsilon ~ 0.5, and eta ~0.4 as representative values. Next, we apply the method to a starburstsample, which shows larger extinction than the star-forming galaxysample. With the aid of f, epsilon , and eta , we are able to estimatereliable SFRs from UV and/or IR luminosities. Moreover, the Hαluminosity, if the Hα extinction is corrected by using the Balmerdecrement, is suitable for a statistical analysis of SFR, because thesame {correction factor for the Lyman continuum extinction (i.e. 1/f)}is applicable to both normal and starburst galaxies over all the rangeof SFR. The metallicity dependence of f and epsilon is also tested:Only the latter proves to have a correlation with metallicity. As anextension of our result, the local (z=0) comoving density of SFR can beestimated with our dust extinction corrections. We show that all UV,Hα , and IR comoving luminosity densities at z=0 give a consistentSFR per comoving volume ( ~ 3x 10-2h M_sun yr-1Mpc-3). Useful formulae for SFR estimate are listed.Tables 1 and 2, and Appendix A are only available in electronic form athttp://www.edpsciences.org
| An empirical calibration of star formation rate estimators
The observational determination of the behaviour of the star formationrate (SFR) with look-back time or redshift has two main weaknesses: (i)the large uncertainty of the dust/extinction corrections, and (ii) thatsystematic errors may be introduced by the fact that the SFR isestimated using different methods at different redshifts. Mostfrequently, the luminosity of the Hα emission line, that of theforbidden line [O II] λ3727 and that of the far-ultravioletcontinuum are used with low-, intermediate- and high-redshift galaxies,respectively. To assess the possible systematic differences among thedifferent SFR estimators and the role of dust, we have compared SFRestimates using Hα, [O II] λ3727 Å, ultraviolet (UV)and far-infrared (FIR) luminosities [SFR(Hα), SFR(O II), SFR(UV)and SFR(FIR), respectively of a sample comprising the 31 nearbystar-forming galaxies that have high-quality photometric data in the UV,optical and FIR. We review the different `standard' methods for theestimation of the SFR and find that while the standard method providesgood agreement between SFR(Hα) and SFR(FIR), both SFR(O II) andSFR(UV) are systematically higher than SFR(FIR), irrespective of theextinction law. We show that the excess in the SFR(O II) and SFR(UV) ismainly due to an overestimation of the extinction resulting from theeffect of underlying stellar Balmer absorptions in the measured emissionline fluxes. Taking this effect into consideration in the determinationof the extinction brings the SFR(O II) and SFR(UV) in line with theSFR(FIR), and simultaneously reduces the internal scatter of the SFRestimations. Based on these results, we have derived `unbiased' SFRexpressions for the SFR(UV), SFR(OII) and SFR(Hα). We have usedthese estimators to recompute the SFR history of the Universe using theresults of published surveys. The main results are that the use of theunbiased SFR estimators brings into agreement the results of allsurveys. Particularly important is the agreement achieved for the SFRderived from the FIR/millimetre and optical/UV surveys. The `unbiased'star formation history of the Universe shows a steep rise in the SFRfrom z =0 to z =1 with SFR ~(1+z)4.5, followed by a declinefor z>2 where SFR ~(1+z)-1.5. Galaxy formation models tendto have a much flatter slope from z=0 to z=1
| A New Database of Observed Spectral Energy Distributions of Nearby Starburst Galaxies from the Ultraviolet to the Far-Infrared
We present a database of UV-to-FIR data of 83 nearby starburst galaxies.The galaxies are selected based upon the availability of IUE data. Wehave recalibrated the IUE UV spectra for these galaxies by incorporatingthe most recent improvements. For 45 of these galaxies we useobservations by Storchi-Bergmann et al. and McQuade et al. for thespectra in the optical range. The NIR data are from new observationsobtained at the NASA/IRTF and the Mount Laguna Observatory, combinedwith the published results from observations at the Kitt Peak NationalObservatory. In addition, published calibrated ISO data are included toprovide mid-IR flux densities for some of the galaxies. Theoptical-to-IR data are matched as closely as possible to the IUE largeaperture. In conjunction with IRAS and ISO FIR flux densities, all thesedata form a set of observed spectral energy distributions (SEDs) of thenuclear regions of nearby starburst galaxies. The SEDs should be usefulin studying star formation and dust/gas attenuation in galaxies. We alsopresent the magnitudes in the standard BVRI and various HST/WFPC2bandpasses synthesized from the UV and optical wavelength ranges ofthese SEDs. For some of the galaxies, the HST/WFPC2 magnitudessynthesized from the SEDs are checked with those directly measured fromWFPC2 images to test the photometric errors of the optical data andtheir effective matching of apertures with the UV data. The implicationsof the new SEDs on the star formation rates and dust/gas attenuation arebriefly discussed.
| Star formation and dust extinction in nearby star-forming and starburst galaxies
We study the star formation rate and dust extinction properties of asample of nearby star-forming galaxies as derived from Hα and UV (~ 2000 Å) observations and we compare them to those of a sample ofstarburst galaxies. The dust extinction in Hα is estimated fromthe Balmer decrement and the extinction in UV using the FIR to UV fluxratio or the attenuation law for starburst galaxies of Calzetti et al.(\cite{calzetti5}). The Hα and UV emissions are stronglycorrelated with a very low scatter for the star-forming objects and witha much higher scatter for the starburst galaxies. The Hα to UVflux ratio is found to be larger by a factor ~ 2 for the starburstgalaxies. We compare both samples with a purely UV selected sample ofgalaxies and we conclude that the mean Hα and UV properties ofnearby star-forming galaxies are more representative of UV-selectedgalaxies than starburst galaxies. We emphasize that the Hα to UVflux ratio is strongly dependent on the dust extinction: the positivecorrelation found between FHα/FUV andFFIR/FUV vanishes when the Hα and UV fluxare corrected for dust extinction. The Hα to UV flux ratiosconverted into star formation rate and combined with the Balmerdecrement measurements are tentatively used to estimate the dustextinction in UV.
| Strömgren Photometry from z=0 to z~1. I. The Method
We use rest-frame Strömgren photometry to observe clusters ofgalaxies in a self-consistent manner from z=0 to z=0.8. Strömgrenphotometry of galaxies is intended as a compromise between standardbroadband photometry and spectroscopy, in the sense that it is moresensitive to subtle variations in spectral energy distributions than theformer, yet much less time-consuming than the latter. principalcomponent analysis is used to facilitate extraction of information fromthe Strömgren data. By calibrating the principal components usingwell-studied galaxies, as well as models of stellar populations, wedevelop a purely empirical method to detect, and subsequently classify,cluster galaxies at all redshifts smaller than 0.8. Interlopers arediscarded with unprecedented efficiency (up to 100%). The firstprincipal component essentially reproduces the Hubble sequence and canthus be used to determine the global star formation history of clustermembers. The (PC2, PC3) plane allows us to identify Seyfert galaxies(and distinguish them from starbursts) based on photometric colorsalone. In the case of E/S0 galaxies with known redshift, we are able toresolve the age-dust-metallicity degeneracy, albeit at the accuracylimit of our present observations. We use this technique in later papersto probe galaxy clusters well beyond their cores and to faintermagnitudes than spectroscopy can achieve, because the faint end of theluminosity function as well as the outer cluster regions seem to exhibitthe strongest evolutionary trends. We are able to directly compare thesedata over the entire redshift range without a priori assumptions becauseour observations do not require first-order k-corrections. Thecompilation of such data for different cluster types over a wideredshift range is likely to set important constraints on the evolutionof galaxies and on the clustering process.
| Cold gas and star formation in a merging galaxy sequence
We explore the evolution of the cold gas (molecular and neutralhydrogen) and star formation activity during galaxy interactions, usinga merging galaxy sequence comprising both pre- and post-mergercandidates. Data for this study come from the literature, but aresupplemented by some new radio observations presented here. First, weconfirm that the ratio of far-infrared luminosity to molecular hydrogenmass (LFIRM(H2); star formation efficiency)increases close to nuclear coalescence. After the merging of the twonuclei there is evidence that the star formation efficiency declinesagain to values typical of ellipticals. This trend can be attributed toM(H2) depletion arising from interaction induced starformation. However, there is significant scatter, likely to arise fromdifferences in the interaction details (e.g., disc-to-bulge ratio,geometry) of individual systems. Secondly, we find that the centralmolecular hydrogen surface density, ΣH2,increases close to the final stages of the merging of the two nuclei.Such a trend, indicating gas inflows caused by gravitationalinstabilities during the interaction, is also predicted by numericalsimulations. Furthermore, there is evidence for a decreasing fraction ofcold gas mass from early interacting systems to merger remnants,attributed to neutral hydrogen conversion into other forms (e.g., stars,hot gas) and molecular hydrogen depletion resulting from ongoing starformation. The evolution of the total-radio to blue-band luminosityratio, reflecting the total (disc and nucleus) star formation activity,is also investigated. Although this ratio is on average higher than thatfor isolated spirals, we find a marginal increase along the mergingsequence, attributed to the relative insensitivity of disc starformation to interactions. However, a similar result is also obtainedfor the nuclear radio emission, although galaxy interactions arebelieved to significantly affect the activity (star formation, AGN) inthe central galaxy regions. Nevertheless, the nuclear-radio to blue-bandluminosity ratio is significantly elevated compared with that forisolated spirals. Finally, we find that the FIR-radio flux ratiodistribution of interacting galaxies is consistent with star formationbeing the main energizing source.
| Star formation in distant starburst galaxies
This paper discusses the stellar population content of distant (5 000 kms^{-1} <== V_R<=16 000 km s^{-1}) galaxies with enhancedstar-formation activity. Distinction is made between isolated galaxiesand galaxies morphologically disturbed, with clear signs of interactionsuch as mergers. In these galaxies the International UltravioletExplorer (M_BoxIUE) large aperture samples most of the galaxy's body.Consequently, the resulting integrated spectra arise primarily from bluestellar populations of different ages together with significantcontributions from intermediate and old age components, subject tovarying reddening amounts. Instead of analysing individual, usually lowSignal-to-Noise ratio (S/N) spectra, our approach is to coadd thespectra of objects with similar spectral properties in the UV,considering as well their properties in the visible/near-infraredranges. Consequently, the resulting high (S/N) template spectra containthe average properties of a rather uniform class of objects, andinformation on spectral features can now be analysed with moreprecision. Three groups have been found for the interacting galaxies,corresponding to a red, blue and very blue continuum. Isolated galaxieshave been separated into two groups, one with a flat/red continuum andthe other with a blue continuum. For comparison, we also include in thepresent analysis two groups of nearby disturbed galaxies. Stellarpopulations are analysed by means of a synthesis algorithm based on starcluster spectral components of different ages which fit the observedspectra both in terms of continuum distribution and spectral features.Flux fractions of the different age groups found in the synthesis havebeen transformed into mass fractions, allowing inferences on the starformation histories. Young stellar populations (age <500 Myr) are themain flux contributors, except for the groups with a red spectrum notdue to extinction, arising from the intermediate (age ~1 - 2 Gyr) andold age populations. We also study the reddening values and theextinction law: a Small Magellanic Cloud-like extinction law isappropriate for all cases. As compared to nearby galaxies with enhancedstar-formation, the distant starburst galaxy spectral groups exhibitlarger contributions from the intermediate and old age populations. Thiseffect is mainly accounted for by the larger spatial area sampled by theM_BoxIUE slit in the distant galaxies, including not only the entirebulge but also evolved disk populations. The present results provide aquantitative measure of the star-forming activity in interactinggalaxies, compared to isolated galaxies. Based upon data collected withthe International Ultraviolet Explorer (IUE) Satellite, supported byNASA, SERC and ESA.
| 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.
| Age and Dust Degeneracy for Starburst Galaxies Solved?
We present a newly built spectral evolution model of galaxies thatincludes both stellar and dust effects. Applying the model to 22 nearbystarburst galaxies shows that far-infrared (FIR) luminosity of galaxieshelps to break the age-dustiness degeneracy. We have derived a uniquesolution of age and the dustiness for each starburst galaxy. Theresulting starburst ages and optical depths are in the range 10<=t(Myr)<=500 and 0.5<=tau_V<=5.0, respectively. The result isrobust and is almost independent of model assumptions such as dustdistributions, extinction curves, and burst strengths. With the rapidlygrowing sensitivity of submillimeter detectors, it should becomepossible in the near future to determine the age and tau_V ofstar-forming galaxies at redshifts z~=3 and beyond. Accurate estimatesof tau_V for Lyman-break galaxies and high-z galaxies might require asubstantial revision of the previously claimed picture of star formationhistory over the Hubble time.
| Dust Absorption and the Ultraviolet Luminosity Density at Z~3 as Calibrated by Local Starburst Galaxies
We refine a technique to measure the absorption-corrected ultraviolet(UV) luminosity of starburst galaxies using rest-frame UV quantitiesalone and apply it to Lyman-limit U dropouts at z~3 found in the HubbleDeep Field (HDF). The method is based on an observed correlation betweenthe ratio of far-infrared (FIR) to UV fluxes with spectral slope beta (aUV color). A simple fit to this relation allows the UV flux absorbed bydust and reprocessed to the FIR to be calculated, and hence thedust-free UV luminosity to be determined. International UltravioletExplorer spectra and Infrared Astronomical Satellite fluxes of localstarbursts are used to calibrate the F_FIR/F_1600 versus beta relationin terms of A_1600 (the dust absorption at 1600 Å) and thetransformation from broadband photometric color to beta. Bothcalibrations are almost completely independent of theoreticalstellar-population models. We show that the recent marginal andnondetections of HDF U dropouts at radio and submillimeter wavelengthsare consistent with their assumed starburst nature and our calculatedA_1600. This is also true of recent observations of the ratio of opticalemission-line flux to UV flux density in the brightest U dropouts. Thislatter ratio turns out not to be a good indicator of dust extinction. InU dropouts, absolute magnitude M_1600,0 correlates with beta: brightergalaxies are redder, as is observed to be the case for local starburstgalaxies. This suggests that a mass-metallicity relationship is alreadyin place at z~3. The absorption-corrected UV luminosity function of Udropouts extends up to M_1600,0~-24 AB mag, corresponding to a starformation rate ~200 M_solar yr^-1 (H_0=50 km s^-1 Mpc^-3 and q_0=0.5 areassumed throughout). The absorption-corrected UV luminosity density atz~3 is rho_1600,0>=1.4x10^27 ergs^-1 Hz^-1 Mpc^-1. It is still alower limit since completeness corrections have not been done andbecause only galaxies with A_1600<~3.6 mag are blue enough in the UVto be selected as U dropouts. The luminosity-weighted meandust-absorption factor of our sample is 5.4+/-0.9 at 1600 Å.
| Molecular Gas Depletion and Starbursts in Luminous Infrared Galaxy Mergers
Most luminous infrared galaxies (LIGs) are closely interacting/mergingsystems that are rich in molecular gas. Here we study the relationshipbetween the stage of the galaxy-galaxy interactions, the molecular gasmass, and the star formation rate as deduced from the infraredluminosity L_IR in LIGs. We find a correlation between the CO (1-0)luminosity [a measure of molecular mass M(H_2)] and the projectedseparation of merger nuclei (the indicator of merging stages) in asample of 50 LIG mergers, which shows that the molecular gas contentdecreases as merging advances. The starburst is due to enhanced starformation in preexisting molecular clouds and not to the formation ofmore molecular clouds from atomic gas. Because of the starbursts, themolecular content is being rapidly depleted as merging progresses. Thisis further supported by an anticorrelation between L_IR/M(H_2), theglobal measure of the star formation rate per unit gas mass, and theprojected separation that implies an enhanced star formation``efficiency'' in late-stage mergers compared with that of earlymergers. This is the first evidence connecting the depletion ofmolecular gas with starbursts in interacting galaxies.
| Surface Brightness of Starbursts at Low and High Redshifts
Observations in the rest-frame ultraviolet from various space missionsare used to define the nearby starburst regions having the highestsurface brightness on scales of several hundred parsecs. The brightlimit is found to be 6 x 10^-16 ergs cm^-2 s^-1 Å^-1 arcsec^-2 forrest-frame wavelength of 1830 Å. Surface brightness in thebrightest pixel is measured for 18 galaxies in the Hubble Deep Fieldhaving z > 2.2. After correcting for cosmological dimming, we findthat the high-redshift starbursts have intrinsic ultraviolet surfacebrightness that is typically 4 times brighter than low-redshiftstarbursts. It is not possible to conclude whether this difference iscaused by decreased dust obscuration in the high-redshift starburstregions or by intrinsically more intense star formation. Surfacebrightness enhancement of starburst regions may be the primary factorfor explaining the observed increase with redshift of the ultravioletluminosity arising from star formation.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| X-ray observations of the interacting system ARP 284
We discuss the X-ray properties of the interacting system Arp 284,consisting of the active nuclear starburst galaxy NGC 7714 and itspost-starburst companion NGC 7715. A morphological signature of theinteraction, thought to have started <100 Myr ago, is an asymmetricstellar ring dominating the intensity profile of NGC 7714 in the innerdisk ( ~ 2 exponential scale lengths). In agreement to previousEinstein-data our ROSAT PSPC exposure shows the X-ray emission of Arp284 to be confined to NGC 7714. The bulk of the intrinsic X-rayluminosity in the ROSAT 0.1-2.4 keV band can be accounted for by thermalemission from hot ( ~ 5x 10(6) K) gas and amounts to ~ 2-4x 10(41) ergs(-1) . Follow-up observations with the ROSAT HRI revealed two distinctextended emitting regions contributing to the X-ray luminosity in NGC\7714. The more luminous of them (L_Xla 2x 10(41) erg s(-1) ) coincideswith the central starburst nucleus and can be explained this way. Thefainter one (L_X ~ 8x 10(40) erg s(-1) ) is located ~ 20'' off-centerand does not have any conspicuous optical counterpart. It is, likely,located at the borderline between the stellar ring and a massive(>10(9) M_ȯ) H I-bridge further to the east possiblyintersecting NGC 7714. The H I and X-ray morphology and the extensivestarburst nature of the nuclear energy source suggest differentscenarios for the formation of the eastern emission spot. Thepossibilities of (i) collisional heating of the outlying gas by astarburst-driven nuclear wind and (ii) infall of H I-clouds from thebridge onto the disk of NGC 7714 are discussed.
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