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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
| A Three-dimensional Study of the Local Environment of Bright IRAS Galaxies: The Active Galactic Nucleus-Starburst Connection
We present a three-dimensional study of the local (<=100h-1 kpc) and the large scale (<=1 h-1 Mpc)environment of bright IRAS balaxies (BIRGs). For this purpose we use 87BIRGs located at high Galactic latitudes (with 0.008<=z<=0.018),as well as a control sample of nonactive galaxies having the samemorphological, redshift, and diameter size distributions as thecorresponding BIRG sample. Using the Center for Astrophysics and theSouthern Sky Redshift Survey galaxy catalogs (mb<~15.5),as well as our own spectroscopic observations (mb<~19.0),for a subsample of the original BIRG sample, we find that the fractionof BIRGs with a close neighbor is significantly higher than that oftheir control sample. Comparing with a related analysis of Seyfert 1 andSeyfert 2 galaxies by Koulouridis and coworkers, we find that BIRGs havea similar environment to that of Seyfert 2 galaxies, although thefraction of BIRGs with a bright, close neighbor is even higher than thatfor Seyfert 2 galaxies. An additional analysis of the relation betweenFIR colors and the type of activity of each BIRG shows a significantdifference between the colors of strongly interacting and noninteractingstarbursts and a resemblance between the colors of noninteractingstarbursts and Seyfert 2 galaxies. Our results support the view thatclose interactions can drive molecular clouds toward the galacticcenter, triggering starburst activity and obscuring the nuclearactivity. When the close neighbor moves away, starburst activity isreduced with the simultaneous appearance of an obscured (type 2) activegalactic nucleus (AGN). Finally, the complete disentanglement of thepair gives birth to an unobscured (type 1) AGN.
| Near-Infrared and Star-forming Properties of Local Luminous Infrared Galaxies
We use Hubble Space Telescope (HST) NICMOS continuum and Paαobservations to study the near-infrared and star formation properties ofa representative sample of 30 local (d~35-75 Mpc) luminous infraredgalaxies (LIRGs, infrared [8-1000 μm] luminosities oflogLIR=11-11.9 Lsolar). The data provide spatialresolutions of 25-50 pc and cover the central ~3.3-7.1 kpc regions ofthese galaxies. About half of the LIRGs show compact (~1-2 kpc)Paα emission with a high surface brightness in the form of nuclearemission, rings, and minispirals. The rest of the sample show Paαemission along the disk and the spiral arms extending over scales of 3-7kpc and larger. About half of the sample contains H II regions withHα luminosities significantly higher than those observed in normalgalaxies. There is a linear empirical relationship between the mid-IR 24μm and hydrogen recombination (extinction-corrected Paα)luminosity for these LIRGs, and the H II regions in the central part ofM51. This relation holds over more than four decades in luminosity,suggesting that the mid-IR emission is a good tracer of the starformation rate (SFR). Analogous to the widely used relation between theSFR and total IR luminosity of R. Kennicutt, we derive an empiricalcalibration of the SFR in terms of the monochromatic 24 μm luminositythat can be used for luminous, dusty galaxies.
| Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydrodynamical Models
We have performed detailed non-local thermodynamic equilibrium (NLTE)spectral synthesis modeling of two types of one-dimensionalhydrodynamical models: the very highly parameterized deflagration modelW7, and two delayed-detonation models. We find that, overall, bothmodels do about equally well at fitting well-observed SNe Ia nearmaximum light. However, the Si II λ6150 feature of W7 issystematically too fast, whereas for the delayed-detonation models it isalso somewhat too fast but significantly better than that of W7. We findthat a parameterized mixed model does the best job of reproducing the SiII λ6150 line near maximum light, and we study the differences inthe models that lead to better fits to normal SNe Ia. We discuss what isrequired of a hydrodynamical model to fit the spectra of observed SNe Ianear maximum light.
| Absolute Magnitude Distributions and Light Curves of Stripped-Envelope Supernovae
The absolute visual magnitudes of three Type IIb, 11 Type Ib, and 13Type Ic supernovae (collectively known as stripped-envelope supernovae)are studied by collecting data on the apparent magnitude, distance, andinterstellar extinction of each event. Weighted and unweighted meanabsolute magnitudes of the combined sample, as well as various subsetsof the sample, are reported. The limited sample size and theconsiderable uncertainties, especially those associated with extinctionin the host galaxies, prevent firm conclusions regarding differencesbetween the absolute magnitudes of supernovae of Types Ib and Ic, andregarding the existence of separate groups of overluminous andnormal-luminosity stripped-envelope supernovae. The spectroscopiccharacteristics of the events of the sample are considered. Three of thefour overluminous events are known to have had unusual spectra. Most butnot all of the normal-luminosity events have had typical spectra. Thelight curves of stripped-envelope supernovae are collected and compared.Because SN 1994I in M51 was very well observed, it often is regarded asthe prototypical Type Ic supernova, but it has the fastest light curvein the sample. Light curves are modeled by means of a simple analyticaltechnique that, combined with a constraint on E/M from spectroscopy,yields internally consistent values of ejected mass, kinetic energy, andnickel mass.
| Using Line Profiles to Test the Fraternity of Type Ia Supernovae at High and Low Redshifts
Using archival data of low-redshift (z<0.01 Center for Astrophysicsand SUSPECT databases) Type Ia supernovae (SNe Ia) and recentobservations of high-redshift (0.161.7] SNe Ia, which are also subluminous. Inaddition, we give the first direct evidence in two high-z SN Ia spectraof a double-absorption feature in Ca II λ3945, an event alsoobserved, although infrequently, in low-redshift SN Ia spectra (6 out of22 SNe Ia in our local sample). Moreover, echoing the recent studies ofDessart & Hillier in the context of Type II supernovae (SNe II), wesee similar P Cygni line profiles in our large sample of SN Ia spectra.First, the magnitude of the velocity location at maximum profileabsorption may underestimate that at the continuum photosphere, asobserved, for example, in the optically thinner line S II λ5640.Second, we report for the first time the unambiguous and systematicintrinsic blueshift of peak emission of optical P Cygni line profiles inSN Ia spectra, by as much as 8000 km s-1. All the high-z SNeIa analyzed in this paper were discovered and followed up by the ESSENCEcollaboration and are now publicly available.Based in part on observations obtained at the Cerro TololoInter-American Observatory, which is operated by the Association ofUniversities for Research in Astronomy (AURA), Inc., under cooperativeagreement with the National Science Foundation (NSF); the EuropeanSouthern Observatory, Chile (ESO program 170.A-0519) the GeminiObservatory, which is operated by AURA under a cooperative agreementwith the NSF on behalf of the Gemini partnership (the NSF [UnitedStates], the Particle Physics and Astronomy Research Council [UnitedKingdom], the National Research Council [Canada], CONICYT [Chile], theAustralian Research Council [Australia], CNPq [Brazil], and CONICET[Argentina]) (programs GN-2002B-Q-14, GN-2003B-Q-11, and GS-2003B-Q-11)the Magellan Telescopes at Las Campanas Observatory; the MMTObservatory, a joint facility of the Smithsonian Institution and theUniversity of Arizona; and the F. L. Whipple Observatory, which isoperated by the Smithsonian Astrophysical Observatory. Some of the datapresented herein were obtained at the W. M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California, and the National Aeronauticsand Space Administration. The Observatory was made possible by thegenerous financial support of the W. M. Keck Foundation.
| Hydrogen and helium traces in type Ib-c supernovae
Aims.To investigate the spectroscopic properties of a selected opticalphotospheric spectra of core collapse supernovae (CCSNe). Specialattention is devoted to traces of hydrogen at early phases. The impacton the physics and nature of their progenitors is emphasized.Methods: .The CCSNe-sample spectra are analyzed with the parameterizedsupernova synthetic spectrum code "SYNOW" adopting some simplifyingapproximations. Results: .The generated spectra are found to matchthe observed ones reasonably well, including a list of only 23 candidateions. Guided by SN Ib 1990I, the observed trough near 6300 Å isattributed to Hα in almost all type Ib events, although in someobjects it becomes too weak to be discernible, especially at laterphases. Alternative line identifications are discussed. Differences inthe way hydrogen manifests its presence within CCSNe are highlighted. Intype Ib SNe, the Hα contrast velocity (i.e. line velocity minusthe photospheric velocity) seems to increase with time at early epochs,reaching values as high as 8000 km s-1 around 15-20 daysafter maximum and then remains almost constant. The derived photosphericvelocities, indicate a lower velocity for type II SNe 1987A and 1999emas compared to SN Ic 1994I and SN IIb 1993J, while type Ib eventsdisplay a somewhat larger variation. The scatter, around day 20, ismeasured to be ~5000 km s-1. Following two simple approaches,rough estimates of ejecta and hydrogen masses are given. A mass ofhydrogen of approximately 0.02 M_ȯ is obtained for SN 1990I, whileSNe 1983N and 2000H ejected ~0.008 M_ȯ and ~0.08 M_ȯ ofhydrogen, respectively. SN 1993J has a higher hydrogen mass, ~0.7M_ȯ with a large uncertainty. A low mass and thin hydrogen layerwith very high ejection velocities above the helium shell, is thus themost likely scenario for type Ib SNe. Some interesting and curiousissues relating to oxygen lines suggest future investigations.
| Reddening, Absorption, and Decline Rate Corrections for a Complete Sample of Type Ia Supernovae Leading to a Fully Corrected Hubble Diagram to v < 30,000 km s-1
Photometric (BVI) and redshift data corrected for streaming motions arecompiled for 111 ``Branch-normal,'' four 1991T-like, seven 1991bg-like,and two unusual supernovae of Type Ia (SNe Ia). Color excessesE(B-V)host of normal SNe Ia, due to the absorption of thehost galaxy, are derived by three independent methods, giving excellentagreement leading to the intrinsic colors at maximum of(B-V)00=-0.024+/-0.010 and (V-I)00=-0.265+/-0.016if normalized to a common decline rate of Δm15=1.1. Thestrong correlation between redshift absolute magnitudes (based on anarbitrary Hubble constant of H0=60 km s-1Mpc-1), corrected only for the extrinsic Galactic absorption,and the derived E(B-V)host color excesses leads to thewell-determined yet abnormal absorption-to-reddening ratios ofRBVI=3.65+/-0.16, 2.65+/-0.15, and 1.35+/-0.21.Comparison with the canonical Galactic values of 4.1, 3.1, and 1.8forces the conclusion that the law of interstellar absorption in thepath length to the SN in the host galaxy is different from the localGalactic law, a result consistent with earlier conclusions by others.Improved correlations of the fully corrected absolute magnitudes (on thesame arbitrary Hubble constant zero point) with host galaxymorphological type, decline rate, and intrinsic color are derived. Werecover the result that SNe Ia in E/S0 galaxies are ~0.3 mag fainterthan in spiral galaxies for possible reasons discussed in the text. Thenew decline rate corrections to absolute magnitudes are smaller thanthose by some authors for reasons explained in the text. The fourspectroscopically peculiar 1991T-type SNe are significantly overluminousas compared to Branch-normal SNe Ia. The overluminosity of the seven1999aa-like SNe is less pronounced. The seven 1991bg types in the sampleconstitute a separate class of SNe Ia, averaging in B 2 mag fainter thanthe normal Ia. New Hubble diagrams in B, V, and I are derived out to~30,000 km s-1 using the fully corrected magnitudes andvelocities, corrected for streaming motions. Nine solutions for theintercept magnitudes in these diagrams show extreme stability at the0.02 mag level using various subsamples of the data for both low andhigh extinctions in the sample, proving the validity of the correctionsfor host galaxy absorption. We shall use the same precepts for fullycorrecting SN magnitudes for the luminosity recalibration of SNe Ia inthe forthcoming final review of our Hubble Space Telescope Cepheid-SNexperiment for the Hubble constant.
| 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.
| 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.
| 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.
| Optical and Infrared Photometry of the Nearby Type Ia Supernovae 1999ee, 2000bh, 2000ca, and 2001ba
We present near-infrared photometry of the Type Ia supernova (SN)1999ee; also, optical and infrared photometry of the Type Ia SNe 2000bh,2000ca, and 2001ba. For SNe 1999ee and 2000bh, we present the first-everSN photometry at 1.035 μm (the Y band). We present K-corrections thattransform the infrared photometry in the observer's frame to thesupernova rest frame. Using our infrared K-corrections and stretchfactors derived from optical photometry, we construct JHK templates thatcan be used to determine the apparent magnitudes at maximum if one hassome data in the window -12 to +10 days with respect toT(Bmax). Following up previous work on the uniformity of Vminus IR loci of Type Ia supernovae of midrange decline rates, wepresent unreddened loci for slow decliners. We also discuss evidence fora continuous change of color at a given epoch as a function of declinerate.
| The IRAS Revised Bright Galaxy Sample
IRAS flux densities, redshifts, and infrared luminosities are reportedfor all sources identified in the IRAS Revised Bright Galaxy Sample(RBGS), a complete flux-limited survey of all extragalactic objects withtotal 60 μm flux density greater than 5.24 Jy, covering the entiresky surveyed by IRAS at Galactic latitudes |b|>5°. The RBGS includes629 objects, with median and mean sample redshifts of 0.0082 and 0.0126,respectively, and a maximum redshift of 0.0876. The RBGS supersedes theprevious two-part IRAS Bright Galaxy Samples(BGS1+BGS2), which were compiled before the final(Pass 3) calibration of the IRAS Level 1 Archive in 1990 May. The RBGSalso makes use of more accurate and consistent automated methods tomeasure the flux of objects with extended emission. The RBGS contains 39objects that were not present in the BGS1+BGS2,and 28 objects from the BGS1+BGS2 have beendropped from RBGS because their revised 60 μm flux densities are notgreater than 5.24 Jy. Comparison of revised flux measurements forsources in both surveys shows that most flux differences are in therange ~5%-25%, although some faint sources at 12 and 25 μm differ byas much as a factor of 2. Basic properties of the RBGS sources aresummarized, including estimated total infrared luminosities, as well asupdates to cross identifications with sources from optical galaxycatalogs established using the NASA/IPAC Extragalactic Database. Inaddition, an atlas of images from the Digitized Sky Survey with overlaysof the IRAS position uncertainty ellipse and annotated scale bars isprovided for ease in visualizing the optical morphology in context withthe angular and metric size of each object. The revised bolometricinfrared luminosity function, φ(Lir), forinfrared-bright galaxies in the local universe remains best fit by adouble power law, φ(L)~Lα, withα=-0.6(+/-0.1) and α=-2.2(+/-0.1) below and above the``characteristic'' infrared luminosityL*ir~1010.5Lsolar,respectively. A companion paper provides IRAS High Resolution (HIRES)processing of over 100 RBGS sources where improved spatial resolutionoften provides better IRAS source positions or allows for deconvolutionof close galaxy pairs.
| An Hα survey aiming at the detection of extraplanar diffuse ionized gas in halos of edge-on spiral galaxies. I. How common are gaseous halos among non-starburst galaxies?
In a series of two papers we present results of a new Hα imagingsurvey, aiming at the detection of extraplanar diffuse ionized gas inhalos of late-type spiral galaxies. We have investigated a sample of 74nearby edge-on spirals, covering the northern and southern hemisphere.In 30 galaxies we detected extraplanar diffuse emission at meandistances of |z| ~ 1-2 kpc. Individual filaments can be traced out to|z|<=6 kpc in a few cases. We find a good correlation between the FIRflux ratio (S60/S100) and the SFR per unit area(LFIR/D225), based on thedetections/non-detections. This is actually valid for starburst, normaland for quiescent galaxies. A minimal SFR per unit area for the lowestS60/S100 values, at which extended emission hasbeen detected, was derived, which amounts to dotEA25thres = (3.2+/-0.5)*E40ergs-1 kpc-2. There are galaxies where extraplanaremission was detected at smaller values ofLFIR/D225, however, only in combinationwith a significantly enhanced dust temperature. The results corroboratethe general view that the gaseous halos are a direct consequence of SFactivity in the underlying galactic disk.Based on observations collected at the European Southern Observatory,Chile (ESO No. 63.N-0070, ESO No. 64.N-0034, ESO No. 65.N.-0002).
| Optical Photometry of the Type Ia Supernova 1999ee and the Type Ib/c Supernova 1999ex in IC 5179
We present UBVRIz light curves of the Type Ia SN 1999ee and the TypeIb/c SN 1999ex, both located in the galaxy IC 5179. SN 1999ee has anextremely well-sampled light curve spanning from 10 days beforeBmax through 53 days after peak. Near maximum, we findsystematic differences of ~0.05 mag in photometry measured with twodifferent telescopes, even though the photometry is reduced to the samelocal standards around the supernova using the specific color terms foreach instrumental system. We use models for our bandpasses andspectrophotometry of SN 1999ee to derive magnitude corrections(S-corrections) and remedy this problem. This exercise demonstrates theneed of accurately characterizing the instrumental system before greatphotometric accuracies of Type Ia supernovae can be claimed. It alsoshows that this effect can have important astrophysical consequences,since a small systematic shift of 0.02 mag in the B-V color canintroduce a 0.08 mag error in the extinction-corrected peak B magnitudeof a supernova and thus lead to biased cosmological parameters. The datafor the Type Ib/c SN 1999ex present us with the first ever observedshock breakout of a supernova of this class. These observations showthat shock breakout occurred 18 days before Bmax and supportthe idea that Type Ib/c supernovae are due to the core collapse ofmassive stars rather than thermonuclear disruption of white dwarfs.
| Optical and Infrared Spectroscopy of SN 1999ee and SN 1999ex
We report optical and infrared spectroscopic observations of the Type IaSN 1999ee and the Type Ib/c SN 1999ex, both of which were hosted by thegalaxy IC 5179. For SN 1999ee we obtained a continuous sequence with anunprecedented wavelength and temporal coverage beginning 9 days beforemaximum light and extending through day 42. Before maximum light SN1999ee displayed a normal spectrum with a strong Si II λ6355absorption, thus showing that not all slow-declining supernovae (SNe)are spectroscopically peculiar at these evolutionary phases. Acomparative study of the infrared spectra of SN 1999ee and other Type IaSNe shows that there is a remarkable homogeneity among the Branch-normalSNe Ia during their first 60 days of evolution. SN 1991bg-like objects,on the other hand, display spectroscopic peculiarities at infraredwavelengths. SN 1999ex was characterized by the lack of hydrogen lines,weak optical He I lines, and strong He I λλ10830, 20581,thus providing an example of an intermediate case between pure Ib and Icsupernovae. We conclude, therefore, that SN 1999ex provides the firstclear evidence for a link between the Ib and Ic classes and that thereis a continuous spectroscopic sequence ranging from the He-deficient SNeIc to the SNe Ib, which are characterized by strong optical He I lines.Based on observations collected at the European Southern Observatory,Chile (program ESO 164.H-0376).
| Local velocity field from sosie galaxies. I. The Peebles' model
Pratton et al. (1997) showed that the velocity field around clusterscould generate an apparent distortion that appears as tangentialstructures or radial filaments. In the present paper we determine theparameters of the Peebles' model (1976) describing infall of galaxiesonto clusters with the aim of testing quantitatively the amplitude ofthis distortion. The distances are determined from the concept of sosiegalaxies (Paturel 1984) using 21 calibrators for which the distanceswere recently calculated from two independent Cepheid calibrations. Weuse both B and I-band magnitudes. The Spaenhauer diagram method is usedto correct for the Malmquist bias. We give the equations for theconstruction of this diagram. We analyze the apparent Hubble constant indifferent regions around Virgo and obtain simultaneously the Local Groupinfall and the unperturbed Hubble constant. We found:[VLG-infall = 208 ± 9 km s-1] [\log H =1.82 ± 0.04 (H ≈ 66 ± 6 km s-1Mpc-1).] The front side and backside infalls can be seenaround Virgo and Fornax. In the direction of Virgo the comparison ismade with the Peebles' model. We obtain: [vinfall} =CVirgo/r0.9 ± 0.2] withCVirgo=2800 for Virgo and CFornax=1350 for Fornax,with the adopted units (km s-1 and Mpc). We obtain thefollowing mean distance moduli: [μVirgo=31.3 ± 0.2(r=18 Mpc )] [μFornax=31.7 ± 0.3 (r=22 Mpc). ] Allthese quantities form an accurate and coherent system. Full Table 2 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/57
| Homogenization of the Stellar Population along Late-Type Spiral Galaxies
We present a study of the broadband UBV color profiles for 257 Sbcbarred and nonbarred galaxies, using photoelectric aperture photometrydata from the literature. Using robust statistical methods, we haveestimated the color gradients of the galaxies, as well as the total andbulge mean colors. A comparative photometric study using CCD images wasdone. In our sample, the color gradients are negative (reddish inward)in approximately 59% of the objects, are almost null in 27%, and arepositive in 14%, considering only the face-on galaxies, which representapproximately 51% of the sample. The results do not change, essentially,when we include the edge-on galaxies. As a consequence of this study wehave also found that barred galaxies are overrepresented among theobjects having null or positive gradients, indicating that bars act as amechanism of homogenization of the stellar population. This effect ismore evident in the U-B color index, although it can also be detected inthe B-V color. A correlation between the total and bulge colors wasfound that is a consequence of an underlying correlation between thecolors of bulges and disks found by other authors. Moreover, the meantotal color is the same irrespective of the gradient regime, whilebulges are bluer in galaxies with null or positive gradients, whichindicates an increase of the star formation rate in the central regionsof these objects. We have also made a quantitative evaluation of theamount of extinction in the center of these galaxies. This was doneusing the Wide Field Planetary Camera 2 (WFPC2) and the Near InfraredCamera and Multi-Object Spectrometer (NICMOS) Hubble Space Telescope(HST) archival data, as well as CCD B, V, and I images. We show thatalthough the extinction in the V-band can reach values up to 2 mag inthe central region, it is unlikely that dust plays a fundamental role inglobal color gradients. We found no correlation between color and O/Habundance gradients. This result could suggest that the color gradientsare more sensitive to the age rather than to the metallicity of thestellar population. However, the absence of this correlation may becaused by dust extinction. We discuss this result by considering apicture in which bars are a relatively fast, recurrent phenomenon. Theseresults are not compatible with a pure classical monolithic scenario forbulge and disk formation. On the contrary, they favor a scenario inwhich both these components are evolving in a correlated process inwhich stellar bars play a crucial role. Based partly on observationsmade at the Pico dos Dias Observatory (PDO/LNA-CNPq), Brazil.
| Absorption-Line Probes of Gas and Dust in Galactic Superwinds
We have obtained moderate resolution (R=few thousand) spectra of the NaI λλ5890, 5896 (Na D) absorption line in a sample of 32far-IR-bright starburst galaxies. In 18 cases, the Na D line in thenucleus is produced primarily by interstellar gas, while cool starscontribute significantly in the others. In 12 of the 18``interstellar-dominated'' cases the Na D line is blueshifted by over100 km s-1 relative to the galaxy systemic velocity (the``outflow sources''), while no case shows a net redshift of more than100 km s-1. The absorption-line profiles in these outflowsources span the range from near the galaxy systemic velocity to amaximum blueshift of ~400-600 km s-1. The outflow sources aregalaxies systematically viewed more nearly face-on than the others. Wetherefore argue that the absorbing material consists of ambientinterstellar material that has been entrained and accelerated along theminor axis of the galaxy by a hot starburst-driven superwind. The Na Dlines are optically thick, but indirect arguments imply total hydrogencolumn densities of NH~few×1021cm-2. This implies that the superwind is expelling matter ata rate comparable to the star formation rate. This outflowing materialis evidently very dusty: we find a strong correlation between the depthof the Na D profile and the line-of-sight reddening. Typical impliedvalues are E(B-V)=0.3-1 over regions several-to-10 kpc in size. Webriefly consider some of the potential implications of theseobservations. The estimated terminal velocities of superwinds inferredfrom the present data and extant X-ray data are typically 400-800km-1, are independent of the galaxy rotation speed, and arecomparable to (substantially exceed) the escape velocities forL* (dwarf) galaxies. The resulting selective loss of metalsfrom shallower potential wells can establish the mass-metallicityrelation in spheroids, produce the observed metallicity in theintracluster medium, and enrich a general IGM to of order10-1 solar metallicity. If the outflowing dust grains cansurvive their journey into the IGM, their effect on observations ofcosmologically distant objects would be significant.
| Compact Radio Emission from Warm Infrared Galaxies
In this paper, we present a comparison between the optical spectroscopicdata and the incidence of compact radio emission for a sample of 60 warminfrared galaxies. We find that 80% of optically classified activegalactic nucleus (AGN)-type galaxies contain compact radio sources,while 37% of optically classified starburst galaxies contain compactradio sources. The compact radio luminosity shows a bimodaldistribution, indicating two populations in our sample. The majority ofthe higher radio luminosity class (L>104Lsolar) are AGNs, while the majority of the lower radioluminosity class (L<104 Lsolar) are starbursts.The compact radio emission in the starburst galaxies may be due toeither obscured AGNs or complexes of extremely luminous supernovae suchas that seen in Arp 220. The incidence of optically classified AGNsincreases with increasing far-infrared (FIR) luminosity. Using FIRcolor-color diagrams, we find that globally the energetics of 92% of thegalaxies in our sample are dominated by starburst activity, including60% of galaxies that we find to contain AGNs on the basis of theiroptical classification. The remainder are energetically dominated bytheir AGNs in the infrared. For starburst galaxies, electron densityincreases with dust temperature, consistent with the merger model forinfrared galaxies.
| The hard X-ray emission of luminous infrared galaxies
We present a study of the hard X-ray properties of a sample thatincludes all the Luminous Infrared Galaxies (LIGs, LIR >1011 L_sun) observed in the 2-10 keV energy band (new andarchival data). We find that a significant fraction of the sourcesoptically classified as AGNs do not show any indication of nuclearactivity in the X rays, thus suggesting heavy absorption along our lineof sight. The absence of strong emission in the 20-200 keV band in asubsample of LIGs observed with BeppoSAX suggests that in many casesthese sources are completely Compton thick (N_H > 1025cm-2). From a comparison between the infrared and the X-rayemission we deduce that the mid-IR emission is absorbed by a lowercolumn density than the X-ray emission or, alternatively, that thedust-to-gas ratio is lower than Galactic. We describe a simple modelthat reproduces the IR-X correlation by means of mixed AGN and starburstcontributions and we compare the predictions of this model with theobservational data at X-ray and optical wavelengths. Finally, we discussthe biases that affect the currently available samples of LIGs andbriefly analyze a small unbiased sample, finding that at least 50% ofthe sources host a (weak) AGN.
| Supernova 1999ex in IC 5179
IAUC 7310 available at Central Bureau for Astronomical Telegrams.
| Supernova 1999ee in IC 5179
IAUC 7284 available at Central Bureau for Astronomical Telegrams.
| Supernova 1999ee in IC 5179
IAUC 7272 available at Central Bureau for Astronomical Telegrams.
| The Durham/UKST Galaxy Redshift Survey - V. The catalogue
We present the radial velocities and blue, optical magnitudes for all ofthe galaxies within the Durham/UKST Galaxy Redshift Survey. Thiscatalogue consists of ~2500 galaxy redshifts to a limiting apparentmagnitude of B_J⋍17 mag, covering a ~1500-deg^2 area around theSouth Galactic Pole. The galaxies in this survey were selected from theEdinburgh/Durham Southern Galaxy Catalogue and were sampled, in order ofapparent magnitude, at a rate of one galaxy in every three. Thespectroscopy was performed at the 1.2-m UK Schmidt Telescope inAustralia using the FLAIR multi-object spectrograph. We show that ourradial velocity measurements made with this instrument have an empiricalaccuracy of +/-150 km s^-1. The observational techniques and datareduction procedures used in the construction of this survey are alsodiscussed. This survey demonstrates that the UKST can be used to make athree-dimensional map of the large-scale galaxy distribution, via aredshift survey to b_J⋍17 mag, over a wide area of the sky.
| 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.
| ^13CO (J = 1-0) Depression in Luminous Starburst Mergers
It is known that the class of luminous starburst galaxies tends to havehigher R=^12CO (J=1-0)/^13CO (J=1-0) integrated line intensity ratios(R>20) than normal spiral galaxies (R~10). Since most previousstudies investigated only R, it remains uncertain whether the luminousstarburst galaxies are overabundant in ^12CO or underabundant in ^13CO.Here we propose a new observational test to examine this problem. Ournew test is to compare far-infrared luminosities [L(FIR)] with those of^12CO and ^13CO [L(^12CO) and L(^13CO), respectively]. It is shown thatthere is a very tight correlation between L(^12CO) and L(FIR), as foundin many previous studies. However, we find that the ^13CO luminositiesof the high-R galaxies are lower by a factor of 3 on average than thoseexpected from the correlation for the remaining galaxies with ordinary Rvalues. Therefore, we conclude that the observed high R values for theluminous starburst galaxies are attributed to their lower ^13CO lineintensities.
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