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An Integrated Spectrophotometric Survey of Nearby Star-forming Galaxies
We present integrated optical spectrophotometry for a sample of 417nearby galaxies. Our observations consist of spatially integrated,S/N=10-100 spectroscopy between 3600 and 6900 Å at ~8 Å FWHMresolution. In addition, we present nuclear (2.5"×2.5")spectroscopy for 153 of these objects. Our sample targets a diverserange of galaxy types, including starbursts, peculiar galaxies,interacting/merging systems, dusty, infrared-luminous galaxies, and asignificant number of normal galaxies. We use population synthesis tomodel and subtract the stellar continuum underlying the nebular emissionlines. This technique results in emission-line measurements reliablycorrected for stellar absorption. Here we present the integrated andnuclear spectra, the nebular emission-line fluxes and equivalent widths,and a comprehensive compilation of ancillary data available in theliterature for our sample. In a series of subsequent papers we use thesedata to study optical star formation rate indicators, nebular abundancediagnostics, the luminosity-metallicity relation, the dust properties ofnormal and starburst galaxies, and the star formation histories ofinfrared-luminous galaxies.
| Local and Large-Scale Environment of Seyfert Galaxies
We present a three-dimensional study of the local (<=100h-1 kpc) and the large-scale (<=1 h-1 Mpc)environment of the two main types of Seyfert AGN galaxies. For thispurpose we use 48 Seyfert 1 galaxies (with redshifts in the range0.007<=z<=0.036) and 56 Seyfert 2 galaxies (with0.004<=z<=0.020), located at high galactic latitudes, as well astwo control samples of nonactive galaxies having the same morphological,redshift, and diameter size distributions as the corresponding Seyfertsamples. Using the Center for Astrophysics (CfA2) and Southern SkyRedshift Survey (SSRS) galaxy catalogs (mB~15.5) and our ownspectroscopic observations (mB~18.5), we find that within aprojected distance of 100 h-1 kpc and a radial velocityseparation of δv<~600 km s-1 around each of ourAGNs, the fraction of Seyfert 2 galaxies with a close neighbor issignificantly higher than that of their control (especially within 75h-1 kpc) and Seyfert 1 galaxy samples, confirming a previoustwo-dimensional analysis of Dultzin-Hacyan et al. We also find that thelarge-scale environment around the two types of Seyfert galaxies doesnot vary with respect to their control sample galaxies. However, theSeyfert 2 and control galaxy samples do differ significantly whencompared to the corresponding Seyfert 1 samples. Since the maindifference between these samples is their morphological typedistribution, we argue that the large-scale environmental differencecannot be attributed to differences in nuclear activity but rather totheir different type of host galaxies.
| The relation between mergers and AGN activity. Results from radio galaxy and luminous infrared galaxy studies
There is morphological evidence that the activity in powerful radiogalaxies could be triggered by mergers and galaxy interactions. However,nothing is known about the timescales, order of events, and the type ofinteraction involved. It is not yet known whether there exists anevolutionary link between radio galaxies and other merger systems suchas very luminous and ultraluminous infrared galaxies (VLIRGs andULIRGs). Here, we report preliminary results obtained from the analysisof near-ultraviolet and optical spectroscopic observations of samples ofRadio Galaxies and VLIRGs-ULIRGs to investigate, through age-dating oftheir young stellar population, whether an evolutionary link existsbetween VLIRGs/ULIRGs-Radio Galaxies-normal elliptical galaxies. Theseresults will help to understand the genesis events that lead to theformation of radio jet and quasar activity, and they will allow us toplace radio galaxies in the context of hierarchical evolution models forthe population of giant elliptical galaxies.
| Spitzer IRS Spectra of a Large Sample of Seyfert Galaxies: A Variety of Infrared Spectral Energy Distributions in the Local Active Galactic Nucleus Population
We are conducting a large observing program with the Spitzer SpaceTelescope to determine the mid- to far-IR spectral energy distributionsof a well-defined sample of 87 nearby, 12 μm-selected Seyfertgalaxies. In this paper we present the results of Spitzer IRSlow-resolution spectroscopy of a statistically representative subsampleof 51 of the galaxies (59%), with an analysis of the continuum shapesand a comparison of the Seyfert types. We find that the spectra clearlydivide into groups based on their continuum shapes and spectralfeatures. The largest group (47% of the sample of 51) shows a very redcontinuum suggestive of cool dust and strong emission featuresattributed to polycyclic aromatic hydrocarbons. Sixteen objects (31%)have a power-law continuum with spectral indices of α5-20μm=-2.3 to -0.9 that flatten to α20-35μm=-1.1 to 0.0 at ~20 μm. Clear silicate emission featuresat 10 and 18 μm are found in two of these objects (Mrk 6 and Mrk335). A further 16% of the sample show power-law continua withunchanging slopes of α5-35 μm=-1.7 to -1.1. Twoobjects are dominated by a broad silicate absorption feature. One objectin the sample shows an unusual spectrum dominated by emission features,which is unlike any of the other spectra. Some spectral features areclearly related to a starburst contribution to the IR spectrum, whilethe mechanisms producing observed power-law continuum shapes, attributedto an active galactic nucleus (AGN) component, may be dust or nonthermalemission. The IR spectral types appear to be related to the Seyferttypes. Principal component analysis results suggest that the relativecontribution of starburst emission may be the dominant cause of variancein the observed spectra. The derived starburst component of eachspectrum, however, contributes <40% of the total flux density. Wecompare the IR emission with the optically thin radio emissionassociated with the AGN and find that Seyfert 1 galaxies have higherratios of IR to radio emission than Seyfert 2 galaxies, as predicted bythe unified model if the torus is optically thick in the mid-IR.However, smooth-density torus models predict a much larger differencebetween Seyfert types 1 and 2 than the factor of 2 difference observedin our sample; the observed factor of ~2 difference between the type 1and type 2 galaxies in their IR-to-radio ratios above 15 μm requiresthe standard smooth-density torus models to be optically thin at thesewavelengths. However, the resulting low torus opacity requires that thehigh observed columns detected in X-ray absorption be produced in gaswith a very low dust-to-gas ratio (perhaps within the dust sublimationregion). On the other hand, our observations may be consistent withclumpy torus models containing a steep radial distribution of opticallythick dense clumps. The selection of our sample at 12 μm, where thetorus may be optically thick, implies that there may beorientation-dependent biases in the sample; however, we do not find thatthe sample is biased toward Seyfert 2 galaxies with more luminouscentral engines, as would be expected. We find that the Seyfert 2galaxies typically show stronger starburst contributions than theSeyfert 1 galaxies in the sample, contrary to what is expected based onthe unified scheme for AGNs. This may be due to the selection effectthat only those Seyfert 2 galaxies with strong starburst contributionshad high enough integrated 12 μm flux densities to fall above theflux limit of the sample.
| A Survey of Merger Remnants. II. The Emerging Kinematic and Photometric Correlations
This paper is the second in a series exploring the properties of 51optically selected, single-nuclei merger remnants. Spectroscopic datahave been obtained for a subsample of 38 mergers and combined withpreviously obtained infrared photometry to test whether mergers exhibitthe same correlations as elliptical galaxies among parameters such asstellar luminosity and distribution, central stellar velocity dispersion(σ0), and metallicity. Paramount to the study is totest whether mergers lie on the fundamental plane. Measurements ofσ0 have been made using the Ca triplet absorption lineat 8500 Å for all 38 mergers in the subsample. Additionalmeasurements of σ0 were made for two of the mergers inthe subsample using the CO absorption line at 2.29 μm. The resultsindicate that mergers show a strong correlation among the parameters ofthe fundamental plane but fail to show a strong correlation betweenσ0 and metallicity (Mg2). In contrast toearlier studies, the σ0 values of the mergers areconsistent with objects that lie somewhere between intermediate-mass andluminous giant elliptical galaxies. However, the discrepancies withearlier studies appear to correlate with whether the Ca triplet or COabsorption lines are used to derive σ0, with the latteralmost always producing smaller values. Finally, the photometric andkinematic data are used to demonstrate for the first time that thecentral phase-space densities of mergers are equivalent to those inelliptical galaxies. This resolves a long-standing criticism of themerger hypothesis.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.
| Molecular hydrogen and [FeII] in active galactic nuclei - II. Results for Seyfert 2 galaxies
Near-infrared spectroscopy is used to study the kinematics andexcitation mechanisms of H2 and [FeII] lines in a sampledominated by Seyfert 2 galaxies. The spectra simultaneously cover theJHK bands, allowing us to compare line fluxes emitted in the interval0.8-2.4 μm and avoiding aperture and seeing effects. TheH2 lines are systematically narrower than the narrow-lineregion lines, suggesting that, very likely, the H2 does notoriginate from the same parcel of gas that forms the narrow-line region.Emission-line ratios between H2 lines favour thermalexcitation mechanisms for the molecular gas in active galactic nuclei.It was found that non-thermal excitation contributes, at most, 30 percent of the observed H2. Thermal excitation is also confirmedby the rather similar vibrational and rotational temperatures in theobjects (~2000 K). The mass of hot H2 ranges from102 to 103Msolar, with nearly half ofobjects showing values of <500 Msolar. It shows that thefraction of molecular mass present in the nuclear region and emitting inthe near-infrared is a very small fraction of the warm molecular masspresent in the centre. A diagnostic diagram composed of the line ratiosH2/Brγ and [FeII]/Paβ proves to be a useful toolin the near-infrared for separating emission-line objects by theirdegree of nuclear activity. We found that active galactic nuclei arecharacterized by H2 2.121 μm/Brγ and [FeII] 1.257μm/Paβ flux ratios between 0.6 and 2. Starburst/HII galaxiesdisplay line ratios <0.6 while low-ionization nuclear emission-lineregions are characterized by values larger than 2 in either ratio.
| Dust Morphology of Hidden Broad-Line Region and Non-Hidden Broad-Line Region Seyfert 2 Galaxies
We investigate the nuclear dust properties of hidden broad-line region(HBLR) and non-HBLR Seyfert 2 galaxies. Optical images obtained from theHubble Space Telescope for a selected sample of HBLR and non-HBLRSeyfert 2 galaxies are fitted with the Galfit package to probe the innerstructures of these galaxies within the central 1 kpc regions. Most ofthe galaxies show complicated dust features in these regions. However,the dust morphology shows no significant difference between the HBLR andnon-HBLR Seyfert 2 galaxies. Dust masses inside the 1 kpc nuclearregions (M1kpc) are estimated from the obscuration levels inthe central regions of these galaxies. We compare our results with otherobserved properties, including [O III], far-infrared, and radioemission. We find that the HBLR and non-HBLR Seyfert 2 galaxies showdifferent near-infrared colors and M1kpc-FIR correlations,indicating that these two classes of Seyfert 2 galaxies are dominated bydifferent emission mechanisms. We suggest that they are intrinsicallydifferent and cannot be explained by the standard unification model.
| X-ray obscuration and obscured AGN in the local universe
We discuss the X-ray properties of 49 local (z<0.035) Seyfert 2galaxies with HST/WFC2 high-resolution optical coverage. It includes theresults of 26 still unpublished Chandra and XMM-Newton observations,which yield 25 (22) new X-ray detections in the 0.5-2 keV (2-10 keV)energy band. Our sample covers a range in the 2-10 keV observed flux,F2-10, from 3 × 10-11 to 6 ×10-15 erg cm-2 s-1. The percentage ofobjects that are likely obscured by Compton-thick matter (columndensity, NH ≥ σt-1 ≃1.6 × 1024 cm-2) is ≃50%, and reaches≃80% for log (F2-10) < 12.3. Hence, Kαfluorescent iron lines with large Equivalent Width ({EW} > 0.6 keV)are common in our sample (6 new detections at a confidence level≥2σ). They are explained as due to reflection off theilluminated side of optically thick material. We confirm a correlationbetween the presence of a 100-pc scale nuclear dust in the WFC2 imagesand Compton-thin obscuration. We interpret this correlation as due tothe large covering fraction of gas associated with the dust lanes. TheX-ray spectra of highly obscured AGN invariably present a prominent softexcess emission above the extrapolation of the hard X-ray component.This soft component can account for a very large fraction of the overallX-ray energy budget. As this component is generally unobscured - andtherefore likely produced in extended gas structures - it may lead to asevere underestimation of the nuclear obscuration in z 1 absorbedAGN, if standard X-ray colors are used to classify them. As a by-productof our study, we report the discovery of a soft X-ray, luminous(≃7 × 1040 erg s-1) halo embedding theinteracting galaxy pair Mkn 266.
| NIR spectroscopy of luminous infrared galaxies and the hydrogen recombination photon deficit
We report on near-infrared medium-resolution spectroscopy of a sample ofluminous and ultraluminous infrared galaxies (LIRGs-ULIRGs), carried outwith SOFI at the ESO 3.5 m New Technology Telescope. Because ofwavelength dependence of the attenuation, the detection of the Paαor Brγ line in the Ks band should provide relevant constraints onSFR and the contribution of an AGN. We find, however, that theintensities of the Paα and Brγ lines, even corrected forslit losses, are on average only 10% and 40%, respectively, of thatexpected from a normal starburst of similar bolometric luminosity. Thecorresponding star formation rates, after correcting for the attenuationderived from the NIR-optical emission line ratios, are 14% and 60% ofthat expected if the far infrared luminosity were entirely powered bythe starburst. This confirms the existence of a recombination photondeficit, particularly in the case of the Paα line, already foundin the Brγ line in other infrared galaxies of similar luminosity.In discussing the possible causes of the discrepancy, we find unlikelythat it is due to the presence of an AGN, though two objects showevidence of broadening of the Paα line and of the presence ofcoronal line emission. In fact, from our own observations and datacollected from the literature we argue that the studied galaxies appearto be predominantly powered by a nuclear starburst. Two scenarioscompatible with the present data are that either there exists a highlyattenuated nuclear star forming region, and/or that a significantfraction (≃80%) of the ionizing photons are absorbed by dustwithin the HII regions. We suggest that observations in the Brαspectral region could constitute a powerful tool to disentangle thesetwo possibilities.
| Search for Active Galaxies Using the First Byurakan Survey
The First Byurakan Survey (FBS) low-dispersion spectra allow selectionof different types of objects by their SEDs and/or emission orabsorption lines. This method is especially good for the search of AGNs.Markarian survey, the 2nd part of the FBS, optical identifications ofIRAS sources, as well as cross-correlations of radio, IR, X-ray catalogswith optical data (APS and USNO) revealed a vast amount of new AGNs andtheir candidates. Spectroscopic observations for a number of them haveconfirmed their nature. The digitization of the FBS will make theseworks more efficient. It will be a unique observational database forsearch for new interesting objects, including AGNs.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Comparison of Nuclear Starburst Luminosities between Seyfert 1 and 2 Galaxies Based on Near-Infrared Spectroscopy
We report on infrared K- (2-2.5 μm) and L-band (2.8-4.1 μm) slitspectroscopy of 23 Seyfert 1 galaxies in the CfA and 12 μm samples. Apolycyclic aromatic hydrocarbon (PAH) emission feature at 3.3 μm inthe L band is primarily used to investigate nuclear star-formingactivity in these galaxies. The 3.3 μm PAH emission is detected in 10sources (=43%), demonstrating that detection of nuclear star formationin a significant fraction of Seyfert 1 galaxies is now feasible. For thePAH-detected nuclei, the surface brightness values of the PAH emissionare as high as those of typical starbursts, suggesting that the PAHemission probes the putative nuclear starbursts in the dusty tori aroundthe central active galactic nuclei (AGNs). The magnitudes of the nuclearstarbursts are quantitatively estimated from the observed 3.3 μm PAHemission luminosities. The estimated starburst luminosities relative tosome indicators of AGN powers in these Seyfert 1 galaxies are comparedwith 32 Seyfert 2 galaxies in the same samples that we have previouslyobserved. We find that there is no significant difference in nuclearstarburst to AGN luminosity ratios of Seyfert 1 and 2 galaxies and thatnuclear starburst luminosity positively correlates with AGN power inboth types. Our results favor a slightly modified AGN unification model,which predicts that nuclear starbursts occurring in the dusty tori ofSeyfert galaxies are physically connected to the central AGNs, ratherthan the classical unification paradigm, in which the dusty tori simplyhide the central AGNs of Seyfert 2 galaxies and reprocess AGN radiationas infrared dust emission in Seyfert galaxies. No significantdifferences in nuclear star formation properties are recognizablebetween Seyfert 1 galaxies in the CfA and 12 μm samples.
| Near-infrared K-Band Spectroscopic Investigation of Seyfert 2 Nuclei in the CfA and 12 Micron Samples
We present near-infrared K-band slit spectra of the nuclei of 25 Seyfert2 galaxies in the CfA and 12 μm samples. The strength of the COabsorption features at 2.3-2.4 μm produced by stars is measured interms of a spectroscopic CO index. A clear anticorrelation between theobserved CO index and the nuclear K-L color is present, suggesting thata featureless hot dust continuum heated by an active galactic nucleus(AGN) contributes significantly to the observed K-band fluxes in thenuclei of Seyfert 2 galaxies. After correction for this AGNcontribution, we estimate nuclear stellar K-band luminosities for allsources and CO indices for sources with modestly large observed COindices. The corrected CO indices for 10 (=40%) Seyfert 2 nuclei arefound to be as high as those observed in star-forming or elliptical(=spheroidal) galaxies. We combine the K-band data with measurements ofthe L-band 3.3 μm polycyclic aromatic hydrocarbon (PAH) emissionfeature, another powerful indicator for star formation, and find thatthe 3.3 μm PAH to K-band stellar luminosity ratios are substantiallysmaller than those of starburst galaxies. Our results suggest that the3.3 μm PAH emission originates in the putative nuclear starbursts inthe dusty tori surrounding the AGNs, because of its high surfacebrightness, whereas the K-band CO absorption features detected at thenuclei are dominated by old bulge (=spheroid) stars and thus may not bea powerful indicator for the nuclear starbursts. We see no cleardifference in the strength of the CO absorption and PAH emissionfeatures between the CfA and 12 μm Seyfert 2 galaxies.
| 10 Micron Imaging of Seyfert Galaxies from the 12 Micron Sample
We present small-aperture (1.5") photometry and new high-resolutionimages at 10 μm (N band) for 87 Seyfert galaxies from the Extended 12μm Sample drawn from the IRAS database. With this data we hope totest the predictions of the unified model for active galactic nuclei andto search for bright, extended circumnuclear 10 μm emission. Wedetected 62 Seyfert galaxies, 18 of which have no previously publishedsmall-aperture photometry. All the detected sources, both Seyfert 1'sand Seyfert 2's, show a central point source. The 31 Seyfert 1's and 31Seyfert 2's that we detected have similar luminosity distributions.Except for previously known bright extended 10 μm structure aroundArp 220, NGC 1068, and NGC 7469, we see definitive evidence for brightextended emission around only one new object: Mrk 1239. Four otherSeyfert 1's and six other Seyfert 2's show evidence of faint, low-levelextended emission. One Seyfert 1 and two Seyfert 2's show evidence ofsignificantly increased flux over previously published small-aperturevalues. We also compared the N-band data with the J-Ks colorthat we derived from the Two Micron All Sky Survey (2MASS). There is adistinct trend of redder central bulge J-Ks colorscorresponding to brighter absolute N-band magnitudes. In color-magnitudespace there is a definite grouping of Seyfert 1's and Seyfert 2's, withtwo sets of outliers.
| A Deep K-Band Photometric Survey of Merger Remnants
We present K-band photometry for 51 candidate merger remnants to assessthe viability of whether spiral-spiral mergers can produce bona fideelliptical galaxies. Using both the de Vaucouleurs r1/4 andSérsic r1/n fitting laws, it is found that the stellarcomponent in a majority of the galaxies in the sample has undergoneviolent relaxation. However, the sample shows evidence for incompletephase mixing. The analysis also indicates the presence of ``excesslight'' in the surface brightness profiles of nearly one-third of themerger remnants. Circumstantial evidence suggests that this is due tothe effects of a starburst induced by the dissipative collapse of thegas. The integrated light of the galaxies also shows that mergers canmake L* elliptical galaxies, in contrast to earlier infrared studies.The isophotal shapes and related structural parameters are alsodiscussed, including the fact that 70% of the sample show evidence fordisky isophotes. The data and results presented are part of a largerphotometric and spectroscopic campaign to thoroughly investigate a largesample of mergers in the local universe.
| Modelling the Spectral Energy Distribution of compact luminous infrared galaxies: Constraints from high frequency radio data
We have performed 23 GHz VLA observations of 7 compact, luminousinfrared galaxies, selected as showing evidence of starburst activity.New and published multi-frequency data are combined to obtain thespectral energy distributions of all 7 galaxies from the near-infraredto the radio (at 1.4 GHz). These SEDs are compared with new models, fordust enshrouded galaxies, which account for both starburst and AGNcomponents.In all 7 galaxies the starburst provides the dominant contribution tothe infrared luminosity; in 4 sources no contribution from an AGN isrequired. Although AGN may contribute up to 50 percent of the totalfar-infrared emission, the starbursts always dominate in the radio. TheSEDs of most of our sources are best fit with a very high optical depthof 50 at 1 μm.The scatter in the far-infrared/radio correlation, found among luminousIRAS sources, is due mainly to the different evolutionary status oftheir starburst components. The short time-scale of the star formationprocess amplifies the delay between the far-infrared and radio emission.This becomes more evident at low radio frequencies (below about 1 GHz)where synchrotron radiation is the dominant process. In the far-infrared(at wavelengths shorter than 100 μm) an additional source of scatteris provided by AGN, when present. AGN may be detected in thenear-infrared by the absence of the knee, typical of stellarphotospheres. However, near-infrared data alone cannot constrain thelevel at which AGN contribute because the interpretation of theirobserved properties, in this wave-band, depends strongly on modelparameters.
| The relation between AGN hard X-ray emission and mid-infrared continuum from ISO spectra: Scatter and unification aspects
We use mid-infrared spectral decomposition to separate the 6 μmmid-infrared AGN continuum from the host emission in the ISO lowresolution spectra of 71 active galaxies and compare the results toobserved and intrinsic 2-10 keV hard X-ray fluxes from the literature.We find a correlation between mid-infrared luminosity and absorptioncorrected hard X-ray luminosity, but the scatter is about an order ofmagnitude, significantly larger than previously found with smallerstatistics. Main contributors to this scatter are likely variations inthe geometry of absorbing dust, and AGN variability in combination withnon-simultaneous observations. There is no significant differencebetween type 1 and type 2 objects in the average ratio of mid-infraredand hard X-ray emission, a result which is not consistent with the mostsimple version of a unified scheme in which an optically andgeometrically thick torus dominates the mid-infrared AGN continuum. Mostprobably, significant non-torus contributions to the AGN mid-IRcontinuum are masking the expected difference between the two types ofAGN.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/465Based on observations with ISO, an ESA project with instruments fundedby ESA member states (especially the PI countries: France, Germany, TheNetherlands, and the UK) with the participation of ISAS and NASA.
| A joint mid-infrared spectroscopic and X-ray imaging investigation of LINER galaxies
We present a comprehensive comparative high resolution mid-IRspectroscopic and X-ray imaging investigation of LINERs using archivalobservations from the ISO-SWS and the Chandra Advanced CCD ImagingSpectrometer. Although the sample is heterogenous and incomplete, thisis the first comprehensive study of the mid-infrared fine structure lineemission of LINERs. These results have been compared with similarobservations of starburst galaxies and AGN. We find that LINERs veryclearly fall between starbursts and AGN in their mid-IR fine structureline spectra, showing L[OIV]26 μm/LFIR andL[OIV]26 μm/L[NeII]12.8 μm ratios, bothmeasures of the dominant nuclear energy source in dust-enshroudedgalaxies, intermediate between those of AGN and starbursts. Chandraimaging observations of the LINERs reveal hard nuclear point sourcesmorphologically consistent with AGN in most (67%) of the sample, with aclear trend with IR-brightness. Most LINERs that show a single dominanthard compact X-ray core are IR-faint (LFIR/LB <1), whereas most LINERs that show scattered X-ray sources are IR-bright.A comparative X-ray/mid-IR spectroscopic investigation of LINERs revealssome puzzling results. Objects that display strong hard nuclear X-raycores should also display high excitation lines in the IR. However, wefind two LINERs disagree with this expectation. The galaxy NGC 404 showsweak soft X-ray emission consistent with a starburst but has the mostprominent highest excitation mid-IR spectrum of our entire sample. UsingIR emission line diagnostics alone, this galaxy would be classified ashosting a dominant AGN. Conversely, the IR luminous LINER NGC 6240 hasan extremely luminous binary AGN as revealed by the X-rays but showsweak IR emission lines. With the advent of SIRTF, and future IR missionssuch as Herschel and JWST, it is increasingly critical to determine theorigin of these multiwavelength anomalies.Table 2 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/825Table 3 is only available in electronic form athttp://www.edpsciences.org
| Compact Nuclear Starbursts in Seyfert 2 Galaxies from the CfA and 12 Micron Samples
We present infrared 2.8-4.1 μm slit spectra of 32 Seyfert 2 galaxiesin the CfA and 12 μm samples. The 3.3 μm polycyclic aromatichydrocarbon (PAH) emission feature was used to estimate the absolutemagnitude of a compact nuclear starburst (less than a few hundredparsecs in size) that is presumed to have occurred in the outer regionof an obscuring dusty molecular torus around a central supermassiveblack hole. We detected 3.3 μm PAH emission in 11 of the 32 Seyfert 2nuclei in our sample, providing evidence for the presence of compactnuclear starbursts in a significant fraction of Seyfert 2 nuclei.However, the rest-frame equivalent widths of the 3.3 μm PAH emissionand the 3.3 μm PAH-to-infrared luminosity ratios measured in thisstudy suggest that compact nuclear starbursts generally do notcontribute significantly to the observed 3-4 μm nuclear fluxes or tothe infrared luminosities of Seyfert 2 galaxies. Absorption features at3.4 μm from bare dust were clearly detected in only two of thenuclei, and features at 3.1 μm from ice-covered dust were detected inonly one nucleus. If the dust properties in the direction of theseSeyfert 2 nuclei do not differ significantly from the Galacticinterstellar medium, then these small absorption optical depths suggestthat dust extinction toward the 3-4 μm continuum emitting region inthe innermost part of the obscuring dusty torus is modest:AV<50-60 mag. Finally, the 3.3 μm PAH emissionluminosities measured in this study were found to be significantlycorrelated with IRAS 12 and 25 μm and nuclear N-band (10.6 μm)luminosities. If these three luminosities trace the power of the activegalactic nucleus (AGN), then the luminosities of compact nuclearstarbursts and AGNs are correlated. This correlation is in agreementwith theories predicting that the presence of a compact nuclearstarburst in the torus leads to an enhancement of the mass accretionrate onto the central supermassive black hole.
| COLA. II. Radio and Spectroscopic Diagnostics of Nuclear Activity in Galaxies
We present optical spectroscopic observations of 93 galaxies taken fromthe infrared-selected COLA (compact objects in low-power AGNs) sample.These are all galaxies for which we have previously obtainedlow-resolution radio observations and high-resolution (<0.05")Australian Long Baseline Array snapshots. The sample spans the range offar-IR luminosities from normal galaxies to luminous infrared galaxiesand contains a significant number of galaxies involved in galaxy-galaxyinteractions. Of the galaxies observed, 78 (84%) exhibit emission linesindicating that they are either AGNs or actively forming stars(starburst galaxies). Using a newly developed, theoretically based,optical emission line scheme to classify the spectra, we find that 15%of the emission-line galaxies are Seyfert galaxies, 77% are starbursts,and the rest are either borderline AGN/starburst or show ambiguouscharacteristics. We find little evidence for an increase in the fractionof AGNs in the sample as a function of far-IR (FIR) luminosity, incontrast to previous studies, but our sample covers only a small rangein infrared luminosity(1010.5Lsolar<=LFIR<=1011.7 Lsolar), and thus a weak trend may be masked. Instead,as the infrared luminosity increases, so does the fraction of metal-richstarbursts, objects that on more traditional diagnostic diagrams wouldhave been classified as weak, low-ionization, narrow emission lineregions. As a whole the Seyfert galaxies exhibit a small, butstatistically significant, radio excess on the radio-FIR correlationcompared to the galaxies classified as starbursts. Compact (<0.05")radio cores are detected in 55% of the Seyfert galaxies, and thesegalaxies exhibit a significantly larger radio excess than the Seyfertgalaxies in which compact cores were not detected. Our results indicatethat there may be two distinct populations of Seyfert galaxies,``radio-excess'' Seyfert galaxies, which exhibit extended radiostructures and compact radio cores, and ``radio-quiet'' Seyfertgalaxies, in which the majority of the radio emission can be attributedto star formation in the host galaxy. No significant difference is seenbetween the IR and optical spectroscopic properties of Seyfert galaxieswith and without radio cores.
| The Unified Model and Evolution of Active Galaxies: Implications from a Spectropolarimetric Study
We extend the analysis presented in Paper I of a spectropolarimetricsurvey of the CfA and 12 μm samples of Seyfert 2 galaxies (S2s). Weconfirm that polarized (hidden) broad-line region (HBLR) S2s tend tohave hotter circumnuclear dust temperatures, show mid-IR spectra morecharacteristic of Seyfert 1 galaxies (S1s), and are intrinsically moreluminous than non-HBLR S2s. The levels of obscuration and circumnuclearstar formation, however, appear to be similar between HBLR and non-HBLRS2 galaxies, based on an examination of various observationalindicators. HBLR S2s, on average, share many similar large-scale,presumably isotropic, characteristics with S1s, as would be expected ifthe unified model is correct, while non-HBLR S2s generally do not. Theactive nuclear engines of non-HBLR S2s, then, appear to be truly weakerthan HBLR S2s, which in turn are fully consistent with being S1s viewedfrom another direction. There is also evidence that the fraction ofdetected HBLRs increases with the radio power of the active galacticnucleus. Thus, all S2 galaxies may not be intrinsically similar innature, and we speculate that evolutionary processes may be at work.
| 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.
| 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 cold gas properties of Markarian galaxies
A sample of 61 Markarian galaxies detected in the CO line was compiled.Using available HI, element H2, optical and radio continuumdata, the analysis of the gas kinematics and the star formationproperties for this sample of galaxies was performed. The mainconclusion can be summarized as follows: (1) The HI and CO line widthsare well correlated. Interaction between galaxies has no influence onthe CO line broadening. A rapidly rotating nuclear disk in the galaxymight lead to the CO line broadening with less influence on the HI line.(2) The atomic and molecular gas surface densities are well correlatedwith the blue, FIR and radio continuum surface brightness; however, thecorrelation for molecular component is stronger.\ (3) In general, thegalaxies with UV-excess (Markarian galaxies) do not differ in their starformation properties from the non-UV galaxies.
| Comparisons of Infrared Colors and Emission-line Intensities between Two types of Seyfert 2 Galaxies
We study the relation between the infrared colors, [OIII] emissionlines, gaseous absorbing column density (NH),and thedetectability of the polarized (hidden) broad-line region (HBLR) in alarge sample of 75 Seyfert 2 galaxies (Sy2s). From the indicators ofstar-formation activity, f60/f100 andLFIR/LB, we find some evidence that the Sy2swithout HBLR show higher star-formation activities than those with HBLR,in agreement with previous prediction. Also, we confirm that the HBLRSy2s tend to have a larger luminosity ratio of the core to the hostgalaxy, suggesting that the HBLR Sy2s display more powerful AGNactivity. However, the level of obscuration found in previous papers isnearly indistinguishable between the two types of Sy2s. The resultssupport the statement that the non-HBLR Sy2s, with a weaker corecomponent and a stronger star-formation activity component, areintrinsically different from the HBLR Sy2s, which are Sy1 systems with ahidden powerful AGN core and a low star-formation activity. Theindications are that the non-HBLR Sy2s might be at an earlierevolutionary phase than the HBLR Sy2s.
| Seyfert 2 Galaxies with Spectropolarimetric Observations
We present a compilation of radio, infrared, optical, and hard X-ray(2-10 keV) data for a sample of 90 Seyfert 2 galaxies (Sy2s) withspectropolarimetric observations (41 Sy2s with detection of polarizedbroad lines [PBLs] and 49 without PBLs). Compared to Sy2s without PBLs,Sy2s with PBLs tend to be earlier type spirals and show warmermidinfrared color and significant excess of emissions (including thehard X-ray [2-10 keV], [O III] λ5007, infrared [25 μm], andradio). Our analyses indicate that the majority of Sy2s without PBLs arethose sources having less powerful active galactic nucleus (AGN)activities, most likely caused by a low accretion rate. It implies thatthe detectability of the polarized broad emission lines in Sy2s maydepend on their central AGN activities in most cases. Based on theavailable data, we find no compelling evidence for the presence of twotypes of Sy2s; one of which has been proposed to be intrinsicallydifferent from Sy2s claimed in the unification model.
| The Far-Infrared Energy Distributions of Seyfert and Starburst Galaxies in the Local Universe: Infrared Space Observatory Photometry of the 12 Micron Active Galaxy Sample
New far-infrared photometry with ISOPHOT aboard the Infrared SpaceObservatory (ISO) is presented for 58 galaxies with homogeneouspublished data for another 32 galaxies, all belonging to the 12 μmgalaxy sample-in total, 29 Seyfert 1 galaxies, 35 Seyfert 2 galaxies,and 12 starburst galaxies, or about half of the 12 μm active galaxysample, plus 14 normal galaxies for comparison. ISO and InfraredAstronomical Satellite (IRAS) data are used to define color-colordiagrams and spectral energy distributions (SEDs). Thermal dust emissionat two temperatures (one cold at 15-30 K and one warm at 50-70 K) canfit the 60-200 μm SED, with a dust emissivity law proportional to theinverse square of the wavelength. Seyfert 1 galaxies and Seyfert 2galaxies are indistinguishable longward of 100 μm, while, as alreadyseen by IRAS, the former have flatter SEDs shortward of 60 μm. A mildanticorrelation is found between the [200-100] color and the ``60 μmexcess.'' We infer that this is due to the fact that galaxies with astrong starburst component and thus a strong 60 μm flux have asteeper far-infrared turnover. In non-Seyfert galaxies, increasing theluminosity corresponds to increasing the star formation rate, whichenhances the 25 and 60 μm emission. This shifts the peak emissionfrom around 150 μm in the most quiescent spirals to shorter than 60μm in the strongest starburst galaxies. To quantify these trendsfurther, we identified with the IRAS colors three idealized infraredSEDs: pure quiescent disk emission, pure starburst emission, and pureSeyfert nucleus emission. Even between 100 and 200 μm, the quiescentdisk emission remains much cooler than the starburst component. Seyfertgalaxies have 100-200 μm SEDs ranging from pure disks to purestarbursts, with no apparent contribution from their active nuclei atthose wavelengths. Based on observations with ISO, an ESA project withinstruments funded by ESA Member States (especially the PI countries:France, Germany, the Netherlands, and the United Kingdom) with theparticipation of ISAS and NASA.
| First Results from the COLA Project: The Radio-Far-Infrared Correlation and Compact Radio Cores in Southern COLA Galaxies
We present the first results from the COLA (compact objects in low-powerAGNs) project, which aims to determine the relationship between onefacet of AGN activity, the compact radio core, and star formation in thecircumnuclear region of the host galaxy. This will be accomplished bythe comparison of the multiwavelength properties of a sample of AGNswith compact radio cores to those of a sample of AGNs without compactcores and a matched sample of galaxies without AGNs. In this paper wediscuss the selection criteria for our galaxy samples and present theinitial radio observations of the 107 southern(δ<0deg) galaxies in our sample. Low-resolution ATCAobservations at 4.8, 2.5, and 1.4 GHz and high-resolution,single-baseline snapshots at 2.3 GHz with the Australian Long BaselineArray (LBA) are presented. We find that for the majority of the galaxiesin our sample, the radio luminosity is correlated with the far-infrared(FIR) luminosity. However, a small number of galaxies exhibit a radioexcess causing them to depart from the FIR-radio correlation. Compactradio cores are detected at fluxes greater than 1.5 mJy in nine of the105 galaxies observed with the LBA. The majority (8/9) of these galaxiesexhibit a radio excess, and 50% (7/14) of the galaxies that lie abovethe radio-FIR correlation by more than 1 σ have compact radiocores. The emission from the compact cores is too weak to account forthis radio excess, implying that there are radio structures associatedwith the compact cores that extend farther than the 0.05" resolution(corresponding to a linear scale 11-22 pc) of the LBA. There is noevidence that the radio luminosity of the compact cores is correlatedwith the FIR galaxy luminosity, indicating that the core contributeslittle to the overall FIR emission of the galaxy. The galaxies withcompact cores tend to be classified optically as AGNs, with two-thirds(6/9) exhibiting Seyfert-like optical emission line ratios, and theremaining galaxies classified either as composite objects (2/9) orstarburst (1/9). The galaxies classified optically as AGNs also exhibitthe largest radio excesses, and we therefore conclude that a large radioexcess on the radio-FIR correlation is a strong indication of an AGNwith a compact radio core.
| Mid-Infrared line diagnostics of active galaxies. A spectroscopic AGN survey with ISO-SWS
We present medium resolution (R ~ 1500) ISO-SWS 2.4-45 mu m spectra of asample of 29 galaxies with active nuclei. This data set is rich in finestructure emission lines tracing the narrow line regions and(circum-)nuclear star formation regions, and it provides a coherentspectroscopic reference for future extragalactic studies in themid-infrared. We use the data set to briefly discuss the physicalconditions in the narrow line regions (density, temperature, excitation,line profiles) and to test for possible differences between AGNsub-types. Our main focus is on new tools for determining the propertiesof dusty galaxies and on the AGN-starburst connection. We present mid-IRline ratio diagrams which can be used to identify composite (starburst +AGN) sources and to distinguish between emission excited by activenuclei and emission from (circum-nuclear) star forming regions. Forinstance, line ratios of high to low excitation lines like [O IV]25.9 mum/[Ne II]12.8 mu m, that have been used to probe for AGNs in dustyobjects, can be examined in more detail and with better statistics now.In addition, we present two-dimensional diagnostic diagrams that arefully analogous to classical optical diagnostic diagrams, but bettersuited for objects with high extinction. Finally, we discusscorrelations of mid-infrared line fluxes to the mid- and far-infraredcontinuum. We compare these relations to similar relations in starburstgalaxies in order to examine the contribution of AGNs to the bolometricluminosities of their host galaxies. The spectra are available inelectronic form from the authors. Based on observations with ISO, an ESAproject with instruments funded by ESA member states (especially the PIcountries: France, Germany, The Netherlands and the UK) and withparticipation of ISAS and NASA.
| Far infrared and radio emission in dusty starburst galaxies
We revisit the nature of the far infrared (FIR)/radio correlation bymeans of the most recent models of star forming galaxies, focusing inparticular on the case of obscured starbursts. We model the IR emissionwith our population synthesis code, GRASIL (Silva et al. \cite{Sil98}).For the radio emission, we revisit the simple model of Condon & Yin(\cite{Con90}). We find that a tight FIR/radio correlation is naturalwhen the synchrotron mechanism dominates over the inverse Compton, andthe electron cooling time is shorter than the fading time of thesupernova (SN) rate. Observations indicate that both these conditionsare met in star forming galaxies, from normal spirals to obscuredstarbursts. However, since the radio non-thermal (NT) emission isdelayed, deviations are expected both in the early phases of astarburst, when the radio thermal component dominates, and in thepost-starburst phase, when the bulk of the NT component originates fromless massive stars. We show that this delay allows the analysis ofobscured starbursts with a time resolution of a few tens of Myrs,unreachable with other star formation (SF) indicators. We suggest astrategy to complement the analysis of the deviations from the FIR/radiocorrelation with the radio slope (q-radio slope diagram) to obtaincharacteristic parameters of the burst, e.g. its intensity, age andfading time scale. The analysis of a sample of compact ULIRGs shows thatthey are intense but transient starbursts, to which one should not applyusual SF indicators devised for constant SF rates. We also discuss thepossibility of using the q-radio slope diagram to assess the presence ofobscured AGN. A firm prediction of the models is an apparent radioexcess during the post-starburst phase, which seems to be typical of aclass of star forming galaxies in rich cluster cores. Finally we discusshow deviations from the correlation, due to the evolutionary status ofthe starburst, affect the technique of photometric redshiftdetermination widely used for high-z sources.
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