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Mid-infrared Properties of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. I. Emission-line Diagnostics
We compare mid-infrared emission-line properties from high-resolutionSpitzer spectra of a hard X-ray (14-195 keV) selected sample of nearby(z < 0.05) active galactic nuclei (AGNs) detected by the Burst AlertTelescope (BAT) aboard Swift. The luminosity distribution for themid-infrared emission lines, [O IV] 25.89 ?m, [Ne II] 12.81 ?m,[Ne III] 15.56 ?m, and [Ne V] 14.32/24.32 ?m, and hard X-raycontinuum show no differences between Seyfert 1 and Seyfert 2populations; however, six newly discovered BAT AGNs are under-luminousin [O IV], most likely the result of dust extinction in the host galaxy.The overall tightness of the mid-infrared correlations and BAT fluxesand luminosities suggests that the emission lines primarily arise in gasionized by the AGNs. We also compare the mid-infrared emission lines inthe BAT AGNs with those from published studies of ULIRGs, Palomar-Greenquasars, star-forming galaxies, and LINERs. We find that the BAT AGNsample falls into a distinctive region when comparing the [Ne III]/[NeII] and the [O IV]/[Ne III] ratios. These line ratios are lower insources that have been previously classified in the mid-infrared/opticalas AGNs than those found for the BAT AGNs, suggesting that, in our X-rayselected sample, the AGNs represent the main contribution to theobserved line emission. These ratios represent a new emission linediagnostic for distinguishing between AGNs and star-forming galaxies.
| Infrared Spectral Energy Distributions of Seyfert Galaxies: Spitzer Space Telescope Observations of the 12 μm Sample of Active Galaxies
The mid-infrared spectral energy distributions (SEDs) of 83 activegalaxies, mostly Seyfert galaxies, selected from the extended 12 μmsample are presented. The data were collected using all threeinstruments, Infrared Array Camera (IRAC), Infrared Spectrograph (IRS),and Multiband Imaging Photometer for Spitzer (MIPS), aboard the SpitzerSpace Telescope. The IRS data were obtained in spectral mapping mode,and the photometric data from IRAC and IRS were extracted from matched,20'' diameter circular apertures. The MIPS data were obtained in SEDmode, providing very low-resolution spectroscopy (R ~ 20) between ~55and 90 μm in a larger, 20'' × 30'' synthetic aperture. Wefurther present the data from a spectral decomposition of the SEDs,including equivalent widths and fluxes of key emission lines; silicate10 μm and 18 μm emission and absorption strengths; IRACmagnitudes; and mid-far-infrared spectral indices. Finally, we examinethe SEDs averaged within optical classifications of activity. We findthat the infrared SEDs of Seyfert 1s and Seyfert 2s with hidden broadline regions (HBLRs, as revealed by spectropolarimetry or othertechnique) are qualitatively similar, except that Seyfert 1s showsilicate emission and HBLR Seyfert 2s show silicate absorption. Theinfrared SEDs of other classes within the 12 μm sample, includingSeyfert 1.8-1.9, non-HBLR Seyfert 2 (not yet shown to hide a type 1nucleus), LINER, and H II galaxies, appear to be dominated by starformation, as evidenced by blue IRAC colors, strong polycyclic aromatichydrocarbon emission, and strong far-infrared continuum emission,measured relative to mid-infrared continuum emission.
| Spitzer-IRS High-Resolution Spectroscopy of the 12 μm Seyfert Galaxies. II. Results for the Complete Data Set
We present our Spitzer-Infrared Spectrometer (IRS) spectroscopic surveyfrom 10 μm to 37 μm of the Seyfert galaxies of the 12 μm GalaxySample, collected in a high-resolution mode (R ~ 600). The new spectraof 61 galaxies, together with the data we already published, give us atotal of 91 12 μm Seyfert galaxies observed, out of 112. We discussthe mid-IR emission lines and features of the Seyfert galaxies, using animproved active galactic nucleus (AGN) classification scheme: instead ofadopting the usual classes of Seyfert 1's and Seyfert 2's, we use thespectropolarimetric data from the literature to divide the objects intocategories "AGN 1" and "AGN 2," where AGN 1's include all broad-lineobjects, including the Seyfert 2's showing hidden broad lines inpolarized light. The remaining category, AGN 2's, contains only Seyfertswith no detectable broad lines in either direct or polarizedspectroscopy. We present various mid-IR observables, such asionization-sensitive and density-sensitive line ratios, the polycyclicaromatic hydrocarbon (PAH) 11.25 μm feature and the H2S(1) rotational line equivalent widths (EWs), the (60-25 μm) spectralindex, and the source extendedness at 19 μm, to characterizesimilarities and differences in the AGN populations, in terms of AGNdominance versus star formation dominance. We find that the mid-IRemission properties characterize all the AGN 1's objects as a singlefamily, with strongly AGN-dominated spectra. In contrast, the AGN 2'scan be divided into two groups, the first one with properties similar tothe AGN 1's except without detected broad lines, and the second withproperties similar to the non-Seyfert galaxies, such as LINERs orstarburst galaxies. We computed a semianalytical model to estimate theAGN and the starburst contributions to the mid-IR galaxy emission at 19μm. For 59 galaxies with appropriate data, we can separate the 19μm emission into AGN and starburst components using the measuredmid-IR spectral features. We use these to quantify the brightnessthresholds that an AGN must meet to satisfy our classifications: AGN 1'shave an AGN contribution >=73% and AGN 2 >= 45% of their totalemission at 19 μm. The detection of [Ne V] lines turns out to be analmost perfect signature of energy production by an AGN. Only four(~7.5%) of 55 AGN 1's and two (10%) out of 20 AGN 2's do not have [Ne V]14.3 μm down to a flux limit of ~4 × 10-15 ergs-1 cm-2. We present mean spectra ofthe various AGN categories. Passing from AGN-dominated tostarburst-dominated objects, the continuum steepens, especially atwavelengths shorter than 20 μm, while the PAH feature increases inits EW and the high ionization lines decrease. We estimate H2mass and excitation temperature through the measurement of the S(1)rotational line of this molecule. Finally, we derive the first localluminosity functions for the brightest mid-IR lines and the PAH featureat 11.25 μm. No statistical difference is apparent in the spacedensities for Seyfert 1's and 2's of a given line luminosity, or for thenew classes of AGN 1's and 2's. We use the correlation between [Ne V]line and nonstellar IR continuum luminosity to derive the global outputof accretion-powered galactic nuclei in the local universe.
| The Palermo Swift-BAT hard X-ray catalogue. II. Results after 39 months of sky survey
Aims: We present the Palermo Swift-BAT hard X-ray catalogueobtained from the analysis of data acquired during the first 39 monthsof the Swift mission. Methods: We developed a dedicated softwareto perform the data reduction, mosaicking, and source detection of theBAT survey data. We analyzed the BAT dataset in three energy bands(14-150 keV, 14-30 keV, 14-70 keV), obtaining a list of 962 detectionsabove a significance threshold of 4.8 standard deviations. Theidentification of the source counterparts was pursued using threestrategies: cross-correlation with published hard X-ray catalogues,analysis of field observations of soft X-ray instruments, andcross-correlation with SIMBAD databases. Results: The surveycovers 90% of the sky down to a flux limit of 2.5×10-11 erg cm-2 s-1 and 50% ofthe sky down to a flux limit of 1.8 ×10-11 ergcm-2 s-1 in the 14-150 keV band. We derived acatalogue of 754 identified sources, of which ˜69% areextragalactic, ˜27% are Galactic objects, and ˜4% arealready known X-ray or gamma ray emitters, whose nature has yet to bedetermined. The integrated flux of the extragalactic sample is ˜1%of the cosmic X-ray background in the 14-150 keV range.Table 2 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/510/A48
| Accurate classification of 17 AGNs detected with Swift/BAT
Through an optical campaign performed at 5 telescopes located in thenorthern and the southern hemispheres, plus archival data from two online sky surveys, we have obtained optical spectroscopy for 17counterparts of suspected or poorly studied hard X-ray emitting activegalactic nuclei (AGNs) detected with Swift/BAT in order to determine orbetter classify their nature. We find that 7 sources of our sample aretype 1 AGNs, 9 are type 2 AGNs, and 1 object is an X-ray brightoptically normal galaxy; the redshifts of these objects lie in a rangebetween 0.012 and 0.286. For all these sources, X-ray data analysis wasalso performed to estimate their absorption column and to search forpossible Compton thick candidates. Among our type 2 objects, we did notfind any clear Compton thick AGN, but at least 6 out of 9 of them arehighly absorbed (NH > 1023 cm-2),while one does not require intrinsic absorption; i.e., it appears to bea naked Seyfert 2 galaxy.Based on observations obtained from the following observatories:Telescopio Nazionale Galileo at the Observatorio del Roque de losMuchachos of the Instituto de Astrofísica de Canarias (CanaryIslands, Spain); Astronomical Observatory of Bologna in Loiano (Italy);Astronomical Observatory of Asiago (Italy); Cerro Tololo InteramericanObservatory (Chile); Observatorio Astronómico Nacional (San PedroMártir, Mexico).
| The Mid-Infrared Continua of Seyfert Galaxies
An analysis of archival mid-infrared (mid-IR) spectra of Seyfertgalaxies from the Spitzer Space Telescope observations is presented. Wecharacterize the nature of the mid-IR active nuclear continuum bysubtracting a template starburst spectrum from the Seyfert spectra. Thelong wavelength part of the spectrum contains a strong contribution fromthe starburst-heated cool dust; this is used to effectively separatestarburst-dominated Seyferts from those dominated by the active nuclearcontinuum. Within the latter category, the strength of the activenuclear continuum drops rapidly beyond ~20 μm. On average, type 2Seyferts have weaker short-wavelength active nuclear continua ascompared to type 1 Seyferts. Type 2 Seyferts can be divided into twotypes, those with strong polycyclic aromatic hydrocarbon (PAH) bands andthose without. The latter type show polarized broad emission lines intheir optical spectra. The PAH-dominated type 2 Seyferts and Seyfert1.8/1.9s show very similar mid-IR spectra. However, after thesubtraction of the starburst component, there is a striking similarityin the active nuclear continuum of all Seyfert optical types.PAH-dominated Seyfert 2s and Seyfert 1.8/1.9s tend to show weak activenuclear continua in general. A few type 2 Seyferts with weak/absent PAHbands show a bump in the spectrum between 15 and 20 μm. We suggestthat this bump is the peak of a warm (~200 K) blackbody dust emission,which becomes clearly visible when the short-wavelength continuum isweaker. This warm blackbody emission is also observed in other Seyfertoptical subtypes, suggesting a common origin in these active galacticnuclei.
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| Spitzer/IRS 5-35 μm Low-resolution Spectroscopy of the 12 μm Seyfert Sample
We present low-resolution 5.5-35 μm spectra for 103 galaxiesfrom the 12 μm Seyfert sample, a complete unbiased 12 μmflux limited sample of local Seyfert galaxies selected from the IRASFaint Source Catalog, obtained with the Infrared Spectrograph (IRS)on-board Spitzer Space Telescope. For 70 of the sources observed in theIRS mapping mode, uniformly extracted nuclear spectra are presented forthe first time. We performed an analysis of the continuum emission, thestrength of the polycyclic aromatic hydrocarbon (PAH) and astronomicalsilicate features of the sources. We find that on average, the15-30 μm slope of the continuum islangα15–30rang = –0.85 ± 0.61 forSeyfert 1s and –1.53 ± 0.84 for Seyfert 2s, and there issubstantial scatter in each type. Moreover, nearly 32% of the Seyfert1s, and 9% of the Seyfert 2s, display a peak in the mid-infraredspectrum at 20 μm, which is attributed to an additional hot dustcomponent. The PAH equivalent width decreases with increasing dusttemperature, as indicated by the global infrared color of the hostgalaxies. However, no statistical difference in PAH equivalent width isdetected between the two Seyfert types, 1 and 2, of the same bolometricluminosity. The silicate features at 9.7 and 18 μm in Seyfert 1galaxies are rather weak, while Seyfert 2s are more likely to displaystrong silicate absorption. Those Seyfert 2s with the highest silicateabsorption also have high infrared luminosity and high absorption(hydrogen column density NH > 1023cm–2) as measured from the X-rays. Finally, we proposea new method to estimate the active galactic nucleus contribution to theintegrated 12 μm galaxy emission, by subtracting the "starformation" component in the Seyfert galaxies, making use of the tightcorrelation between PAH 11.2 μm luminosity and 12 μmluminosity for star-forming galaxies.
| The Evolution of Swift/BAT Blazars and the Origin of the MeV Background
We use three years of data from the Swift/Burst Alert Telescope (BAT)survey to select a complete sample of X-ray blazars above 15 keV.This sample comprises 26 flat-spectrum radio quasars (FSRQs) and 12 BLLacertae (BL Lac) objects detected over a redshift range of 0.03 < z< 4.0. We use this sample to determine, for the first time in the15-55 keV band, the evolution of blazars. We find that, contrary tothe Seyfert-like active galactic nuclei (AGNs) detected by BAT, thepopulation of blazars shows strong positive evolution. This evolution iscomparable to the evolution of luminous optical quasi-stellar objects(QSOs) and luminous X-ray-selected AGNs. We also find evidence for anepoch dependence of the evolution as determined previously forradio-quiet AGNs. We interpret both these findings as a strong linkbetween accretion and jet activity. In our sample, the FSRQs evolvestrongly, while our best fit shows that BL Lac objects might not evolveat all. The blazar population accounts for 10%-20% (depending on theevolution of the BL Lac objects) of the cosmic X-ray background (CXB) inthe 15-55 keV band. We find that FSRQs can explain the entire CXBemission for energies above 500 keV solving the mystery of thegeneration of the MeV background. The evolution of luminous FSRQs showsa peak in redshift (zc = 4.3 ± 0.5) which is largerthan the one observed in QSOs and X-ray-selected AGNs. We argue thatFSRQs can be used as tracers of massive elliptical galaxies in the earlyuniverse.
| Dust Emission from Unobscured Active Galactic Nuclei
We use mid-infrared (MIR) spectroscopy of unobscured active galacticnuclei (AGNs) to reveal their native dusty environments. We concentrateon Seyfert 1 galaxies, observing a sample of 31 with the InfraredSpectrograph aboard the Spitzer Space Telescope, and compare them with21 higher luminosity quasar counterparts. Silicate dust reprocessingdominates the MIR spectra, and we generally measure the 10 and 18 μmspectral features weakly in emission in these galaxies. The strengths ofthe two silicate features together are sensitive to the dustdistribution. We present numerical radiative transfer calculations thatdistinguish between clumpy and smooth geometries, which are applicableto any central heating source, including stars as well as AGNs. In theobservations, we detect the obscuring "torus" of unified AGN schemes,modeling it as compact and clumpy. We also determine that star formationincreases with AGN luminosity, although the proportion of the galaxies'bolometric luminosity attributable to stars decreases with AGNluminosity.
| The CaT strength in Seyfert nuclei revisited: analysing young stars and non-stellar light contributions to the spectra
In a former paper, we have presented spectra of 64 active, nine normaland five starburst galaxies in the region around the near-infraredcalcium triplet (CaT) absorption lines and the [SIII]?9069 line.In the present paper, we analyse the CaT strength (WCaT) andkinematical products derived in that study, namely stellar(?*) and ionized gas (?gas) velocitydispersions. Our main results may be summarized as follows. (1) Type 2Seyfert galaxies show no sign of dilution in WCaT withrespect to the values spanned by normal galaxies, even when opticalabsorption lines such as the CaII K band at 3933 Å are much weakerthan in old, bulge-like stellar populations. (2) The location of type 2Seyfert galaxies in the WCaT-WCaK plane isconsistent with evolutionary synthesis models. The implication is thatthe source responsible for the dilution of optical lines in these activegalactic nuclei (AGN) is a young stellar population, rather than an AGNfeatureless continuum, confirming the conclusion of the pioneer study ofTerlevich, Díaz & Terlevich. (3) In type 1 Seyfert galaxies,both W[SIII] and WCaT tend to be diluted due tothe presence of a non-stellar component, in agreement with theunification paradigm. (4) A comparison of ?* with?gas (obtained from the core of the [SIII] emittingline) confirms the existence of a correlation between the typicalvelocities of stars and clouds of the narrow line region. The strengthand scatter around this correlation are similar to those previouslyobtained from the [OIII]?5007 linewidth.
| X-Ray Spectral Properties of the BAT AGN Sample
The 9-month Swift Burst Alert Telescope (BAT) catalog provides the firstunbiased (NH < 1024 cm 2) look atlocal ( = 0.03) active galactic nuclei (AGNs). In this paper,we present the collected X-ray properties (0.3-12 keV) for the 153 AGNsdetected. In addition, we examine the X-ray properties for a completesample of nonbeamed sources, above the Galactic plane (b >= 15°).Of these, 45% are best fit by simple power law models, while 55% requirethe more complex partial covering model. One of our goals was todetermine the fraction of "hidden" AGNs, which we define as sources withscattering fractions less than or equal to 0.03 and ratios of soft tohard X-ray flux less than or equal to 0.04. We found that "hidden" AGNsconstitute a high percentage of the sample (24%), proving that they area very significant portion of local AGNs. Further, we find that thefraction of absorbed sources does increase at lower unabsorbed 2-10 keVluminosities, as well as accretion rates. This suggests that the unifiedmodel requires modification to include luminosity dependence, assuggested by models such as the "receding torus" model. Some of the mostinteresting results for the BAT AGN sample involve the host galaxyproperties. We found that 33% are hosted in peculiar/irregular galaxiesand only 5/74 are hosted in ellipticals. Further, 54% are hosted ininteracting/merger galaxies. Finally, we present both the average X-rayspectrum (0.1-10 keV) and log N-log S in the 2-10 keV band. With ouraverage spectrum, we have the remarkable result of reproducing themeasured CXB X-ray power law slope of Γ ≈ 1.4. From the logN-log S relationship, we show that we are complete to log S >= 11 inthe 2-10 keV band. Below this value, we are missing as many as 3000sources at log S = 12. Both the collected X-ray properties of ouruniform sample and the log N-log S relationship will now providevaluable input to X-ray background models for z ≈ 0.
| Constraining the Active Galactic Nucleus Contribution in a Multiwavelength Study of Seyfert Galaxies
We have studied the relationship between the high- and low-ionization [OIV] λ25.89 μm, [Ne III] λ15.56 μm, and [Ne II]λ12.81 μm emission lines with the aim of constraining theactive galactic nuclei (AGNs) and star formation contributions for asample of 103 Seyfert galaxies. We use the [O IV] and [Ne II] emissionas tracers for the AGN power and star formation to investigate theionization state of the emission-line gas. We find that Seyfert 2galaxies have, on average, lower [O IV]/[Ne II] ratios than Seyfert 1galaxies. This result suggests two possible scenarios: (1) Seyfert 2galaxies have intrinsically weaker AGNs, or (2) Seyfert 2 galaxies haverelatively higher star formation rates than Seyfert 1 galaxies. Weestimate the fraction of [Ne II] directly associated with the AGNs andfind that Seyfert 2 galaxies have a larger contribution from starformation, by a factor of ~1.5 on average, than what is found in Seyfert1 galaxies. Using the stellar component of [Ne II] as a tracer of thecurrent star formation, we found similar star formation rates in Seyfert1 and Seyfert 2 galaxies. We examined the mid- and far-infrared continuaand found that [Ne II] is well correlated with the continuum luminosityat 60 μm and that both [Ne III] and [O IV] are better correlated withthe 25 μm luminosities than with the continuum at longer wavelengths,suggesting that the mid-infrared continuum luminosity is dominated bythe AGN, while the far-infrared luminosity is dominated by starformation. Overall, these results test the unified model of AGNs andsuggest that the differences between Seyfert galaxies cannot be solelydue to viewing angle dependence.
| A New H I Survey of Active Galaxies
We have conducted a new Arecibo survey for H I emission for 113 galaxieswith broad-line (type 1) active galactic nuclei (AGNs) out to recessionvelocities as high as ~35,000 km s-1. The primary aim of thestudy is to obtain sensitive H I spectra for a well-defined, uniformlyselected sample of active galaxies that have estimates of their blackhole masses in order to investigate correlations between H I propertiesand the characteristics of the AGNs. H I emission was detected in 66out of the 101 (65%) objects with spectra uncorrupted by radio frequencyinterference, among which 45 (68%) have line profiles with adequatesignal-to-noise ratio and sufficiently reliable inclination correctionsto yield robust deprojected rotational velocities. This paper presentsthe basic survey products, including an atlas of H I spectra,measurements of H I flux, line width, profile asymmetry, optical images,optical spectroscopic parameters, as well as a summary of a number ofderived properties pertaining to the host galaxies. To enlarge ourprimary sample, we also assemble all previously published H Imeasurements of type 1 AGNs for which we can estimate black hole masses,which total an additional 53 objects. The final comprehensivecompilation of 154 broad-line active galaxies, by far the largest sampleever studied, forms the basis of our companion paper, which uses the H Idatabase to explore a number of properties of the AGN host galaxies.
| Swift BAT Survey of AGNs
We present the results of the analysis of the first 9 months of data ofthe Swift BAT survey of AGNs in the 14-195 keV band. Using archivalX-ray data or follow-up Swift XRT observations, we have identified 129(103 AGNs) of 130 objects detected at |b|>15deg and withsignificance >4.8 ?. One source remains unidentified. Thesesame X-ray data have allowed measurement of the X-ray properties of theobjects. We fit a power law to the logN-logS distribution, and find theslope to be 1.42+/-0.14. Characterizing the differential luminosityfunction data as a broken power law, we find a break luminositylogL*(erg s-1) = 43.85 +/- 0.26, a low-luminositypower law slope a=0.84+0.16-0.22, and ahigh-luminosity power law slope b=2.55+0.43-0.30,similar to the values that have been reported based on INTEGRAL data. Weobtain a mean photon index 1.98 in the 14-195 keV band, with an rmsspread of 0.27. Integration of our luminosity function gives a localvolume density of AGNs above 1041 erg s-1 of2.4×10-3 Mpc-3, which is about 10% of thetotal luminous local galaxy density above M*=-19.75. We haveobtained X-ray spectra from the literature and from Swift XRT follow-upobservations. These show that the distribution of lognH isessentially flat from nH=1020 to 1024cm-2, with 50% of the objects having column densities of lessthan 1022 cm-2. BAT Seyfert galaxies have a medianredshift of 0.03, a maximum log luminosity of 45.1, and approximatelyhalf have lognH>22.
| BAT X-Ray Survey. I. Methodology and X-Ray Identification
We applied the maximum likelihood (ML) method, as an imagereconstruction algorithm, to the BAT X-Ray Survey (BXS). This method wasspecifically designed to preserve the full statistical information inthe data and to avoid mosaicking of many exposures with differentpointing directions, thus reducing systematic errors when co-addingimages. We reconstructed, in the 14-170 keV energy band, the image of a90×90 deg2 sky region, centered on (R.A.,decl.)=(105deg, -25deg), which BAT surveyed withan exposure time of ~1 Ms (in 2005 November). The best sensitivity inour image is ~0.85 mcrab or 2.0×10-11 ergscm-2. We detect 49 hard X-ray sources above the 4.5 σlevel; of these, only 12 were previously known as hard X-ray sources(>15 keV). Swift XRT observations allowed us to firmly identify thecounterparts for 15 objects, while 2 objects have Einstein IPCcounterparts (Harris et al. 1990); in addition to those, we found alikely counterpart for 13 objects by correlating our sample with theROSAT All-Sky Survey Bright Source Catalog (Voges et al. 1999). Sevenobjects remain unidentified. Analysis of the noise properties of ourimage shows that ~75% of the area is surveyed to a flux limit of ~1mcrab. This study shows that the coupling of the ML method to the mostsensitive, all-sky surveying, hard X-ray instrument, BAT, is able toprobe for the first time the hard X-ray sky to the millicrab flux level.The successful application of this method to BAT demonstrates that itcould also be applied with advantage to similar instruments such asINTEGRAL IBIS.
| Nuclear/Circumnuclear Starbursts and Active Galactic Nucleus Mass Accretion in Seyfert Galaxies
We investigated the correlation between nuclear/circumnuclear starburstsaround active galactic nuclei (AGNs) and the AGN activities for 43Seyfert galaxies in the CfA and 12 μm samples. We found that thecircumnuclear starburst luminosity, as well as the nuclear starburstluminosity, is positively correlated with the AGN luminosity. Moreover,the nuclear starburst luminosity is more strongly correlated with theAGN luminosity normalized with the AGN Eddington luminosity than is thecircumnuclear starburst luminosity. This implies that starbursts nearerthe AGN could have a greater effect on AGN mass accretion. We alsodiscuss these results from the viewpoint of the radiation effects fromstarbursts and sequential starbursts.
| X-Ray Properties of an Unbiased Hard X-Ray-detected Sample of Active Galactic Nuclei
The Swift gamma-ray observatory's Burst Alert Telescope (BAT) hasdetected a sample of AGNs based solely on their hard X-ray flux (14-195keV). In this paper we present for the first time XMM-Newton X-rayspectra for 22 BAT AGNs with no previously analyzed X-ray spectra. Ifour sources are a representative sample of the BAT AGNs, as we claim,our results present for the first time global X-ray properties of anunbiased toward absorption (nH<3×1025cm-2), local (=0.03), AGN sample. We find 9/22 low-absorption(nH<1023 cm-2), simple power-lawmodel sources, where 4 of these sources have a statistically significantsoft component. Among these sources, we find the presence of a warmabsorber statistically significant for only one Seyfert 1 source,contrasting with the ASCA results of Reynolds and George and coworkers,who find signatures of warm absorption in half or more of their Seyfert1 samples at similar redshifts. In addition, the remaining sources(13/22) have more complex spectra, well fitted by an absorbed power lawat E>2.0 keV. Five of the complex sources are classified asCompton-thick candidates. Further, we find four more sources withproperties consistent with the hidden/buried AGNs reported by Ueda andcoworkers. Finally, we include a comparison of the XMM-Newton EPICspectra with available Swift X-Ray Telescope (XRT) observations. Fromthese comparisons, we find 6/16 sources with varying column densities,6/16 sources with varying power-law indices, and 13/16 sources withvarying fluxes, over periods of hours to months. Flux and power-lawindex are correlated for objects where both parameters vary.
| The Swift BAT X-Ray Survey. III. X-Ray Spectra and Statistical Properties
In this concluding part of the series of three papers dedicated to theSwift BAT hard X-ray survey (BXS), we focus on the X-ray spectralanalysis and statistical properties of the source sample. Using adedicated method to extract time-averaged spectra of BAT sources, weshow that Galactic sources have, generally, softer spectra thanextragalactic objects and that Seyfert 2 galaxies are harder thanSeyfert 1s. The averaged spectrum of all Seyfert galaxies is consistentwith a power-law with a photon index of 2.00+/-0.07. The cumulativeflux-number relation for the extragalactic sources in the 14-170 keVband is best described by a power-law with a slope α=1.55+/-0.20and a normalization of 9.6+/-1.9×10-3 AGNsdeg-2 (or 396+/-80 AGNs all-sky) above a flux level of2×10-11 ergs cm-2 s-1 (~0.85mcrab). The integration of the cumulative flux per unit area indicatesthat BAT resolves 1%-2% of the X-ray background emission in the 14-170keV band. A subsample of 24 extragalactic sources above the 4.5 σdetection limit is used to study the statistical properties of AGNs.This sample is composed of local Seyfert galaxies (z=0.026, medianvalue) and ~10% blazars. We find that 55% of the Seyfert galaxies areabsorbed by column densities of NH>1022 H atomscm-2 but that none is genuinely bona fide Compton thick. Thisstudy shows the capabilities of BAT to probe the hard X-ray sky to themillicrab level.
| Spitzer IRS Observations of Seyfert 1.8 and 1.9 Galaxies: A Comparison with Seyfert 1 and Seyfert 2
We present Spitzer mid-infrared spectra of 12 Seyfert 1.8 and 1.9galaxies over the 5-38 μm region. We compare the spectralcharacteristics of this sample to those of 58 Seyfert 1 and 2 galaxiesfrom the Spitzer archives. An analysis of the spectral shapes, thesilicate 10 μm feature and the emission-line fluxes have enabled usto characterize the mid-IR properties of Seyfert 1.8/1.9s. We find thatthe EWs of the 10 μm silicate feature are generally weak in allSeyfert galaxies, as previously reported by several studies. The fewSeyfert galaxies in this sample that show deep 10 μm silicateabsorption features are highly inclined and/or merging galaxies. It islikely that these absorption features originate primarily in the dustyinterstellar medium of the host galaxy rather than in a dusty torus onparsec scales close to the central engine. We find that the EW of thePAH band at 6.2 μm correlates strongly with the 20-30 μm spectralindex. Either of these quantities is a good indicator of the amount ofstarburst contribution to the mid-IR spectra. The spectra of Seyfert1.8s and 1.9s are dominated by these starburst features, similar to mostSeyfert 2s. They show strong PAH bands and a strong red continuum toward30 μm. The strengths of the high-ionization forbidden narrow emissionlines [O IV] 25.89 μm, [Ne III] 15.56 μm, and [Ne V] 14.32 μmrelative to [Ne II] 12.81 μm are weaker in Seyfert 1.8/1.9s andSeyfert 2s than in Seyfert 1s. The weakness of high-ionization lines inSeyfert 1.8-1.9s is suggestive of intrinsically weak AGN continua and/orstronger star formation activity leading to enhanced [Ne II]. We discussthe implications of these observational results in the context of theunified model of AGNs.
| The host galaxy/AGN connection. Brightness profiles of early-type galaxies hosting Seyfert nuclei
We recently presented evidence of a connection between the brightnessprofiles of nearby early-type galaxies and the properties of the AGNthey host. The radio loudness of the AGN appears to be univocallyrelated to the host's brightness profile: radio-loud nuclei are onlyhosted by “core” galaxies while radio-quiet AGN are onlyfound in “power-law” galaxies. We extend our analysis hereto a sample of 42 nearby (V_rec < 7000 km s-1) Seyfertgalaxies hosted by early-type galaxies. From the nuclear point of view,they show a large deficit of radio emission (at a given X-ray or narrowline luminosity) with respect to radio-loud AGN, conforming with theiridentification as radio-quiet AGN. We used the available HST images tostudy their brightness profiles. Having excluded complex and highlynucleated galaxies, in the remaining 16 objects the brightness profilescan be successfully modeled with a Nuker law with a steep nuclear cuspcharacteristic of “power-law” galaxies (with logarithmicslope γ = 0.51-1.07). This result is what is expected for theseradio-quiet AGN based on our previous findings, thus extending thevalidity of the connection between brightness profile and radio loudnessto AGN of a far higher luminosity. We explored the robustness of thisresult against a different choice of the analytic form for thebrightness profiles, using a Sérsic law. In no object could wefind evidence of a central light deficit with respect to a pureSérsic model, the defining feature of “core” galaxiesin this modeling framework. We conclude that, regardless of the modelingstrategy, the dichotomy of AGN radio loudness can be univocally relatedto the host's brightness profile. Our general results can be re-phrasedas “radio-loud nuclei are hosted by core galaxies, whileradio-quiet AGN are found in non-core galaxies”.Based on observations obtained at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Incorporated, under NASA contract BAS 5-26555.
| Suppressed Star Formation in Circumnuclear Regions in Seyfert Galaxies
Feedback from black hole activity is widely believed to play a key rolein regulating star formation and black hole growth. A long-standingissue is the relation between star formation and the fueling of thesupermassive black holes in active galactic nuclei (AGNs). We compile asample of 57 Seyfert galaxies to tackle this issue. We estimate thesurface densities of gas and star formation rates in circumnuclearregions (CNRs). Comparing them with the well-known Kennicutt-Schmidt(K-S) law, we find that the star formation rates (SFRs) in the CNRs ofmost Seyfert galaxies are suppressed in this sample. Feedback issuggested to explain the suppressed SFRs.
| The Unified Model of Active Galactic Nuclei. II. Evolutionary Connection
We assemble a sample composed of 243 nearby Seyfert galaxies withredshifts z<=0.05 to test the unification scheme. The sample contains94 broad emission line Seyfert 1 galaxies (BLS1s), 44 narrow emissionline Seyfert 1s (NLS1s), 36 X-ray-absorbed hidden broad line regionSeyfert 2s (HBLR S2s), 42 X-ray-absorbed non-HBLR S2s, and 27X-ray-unabsorbed Seyfert 2s (unabsorbed non-HBLR S2s and HBLR S2s). Wefind that (1) NLS1s have less massive black hole masses than BLS1s, (2)HBLR S2s have the same mass distribution of black holes as BLS1s, (3)absorbed non-HBLR S2s have less massive black holes than HBLR S2s, and(4) unabsorbed non-HBLR S2s have the most massive black holes. We thushave a queue of black hole masses from small to large: narrow- tobroad-line Seyfert galaxies, providing new evidence for the evolutionarysequence. We find that the opening angles of the torus in NLS1s andabsorbed non-HBLR S2s are significantly smaller than those in BLS1s andHBLR S2s. We also find that the unabsorbed Seyfert 2 galaxies could becaused by low gas-to-dust ratios in the present sample. This indicatesthat the star formation histories could be different in the unabsorbedand absorbed Seyfert 2 galaxies, showing evidence for suppressed starformation by black hole activities. We outline a new unification schemebased on the orientation hypothesis: Seyfert galaxies can be unified byincluding the growth of black holes, Eddington ratios, changing openingangles of tori, and gas-to-dust ratios in tori. Seyfert galaxies tend tofinally evolve to unabsorbed non-HBLR Seyfert 2 galaxies, in which theblack holes accrete with low accretion rates and both the broad-lineregion and dusty torus disappear.
| Size and properties of the narrow-line region in Seyfert-1 galaxies from spatially-resolved optical spectroscopy
Context: .Spatially resolved emission-line spectroscopy is a powerfultool for determining the physical conditions in the narrow-line region(NLR) of active galactic nuclei (AGNs). We recently used opticallong-slit spectroscopy to study the NLRs of a sample of six Seyfert-2galaxies. We have shown that such an approach, in comparison to thecommonly used [O III] narrow-band imaging alone, allows us to probe thesize of the NLR in terms of AGN photoionisation. Moreover, severalphysical parameters of the NLR can be directly accessed. Aims: .Wehere apply the same methods to study the NLR of six Seyfert-1 galaxiesand compare our results to those of Seyfert-2 galaxies. Methods:.We employ diagnostically valuable emission-line ratios to determine thephysical properties of the NLR, including the core values and radialdependencies of density, ionisation parameter, and reddening. Trackingthe radial change of emission-line ratios in diagnostic diagrams allowsus to measure the transition between AGN-like and H II-like lineexcitation, and thus to measure the size of the NLR. Results: .Inthe diagnostic diagrams, we find a transition between line ratiosfalling in the AGN regime and those typical of H II regions in twoSeyfert-1 galaxies, thereby determining the size of the NLR. The centralelectron temperature and ionisation parameter are, in general, higher intype-1 Seyferts than in type 2s. In almost all cases, both electrondensity and ionisation parameter decrease with radius and the decreaseis faster in Seyfert-1 galaxies than in Sy 2s. In several objects, thegaseous velocity distribution is characteristic of rotational motion inan (inclined) emission-line disk in the centre. We give estimates of theblack-hole masses and discuss our findings in detail for each object.
| A 0.8-2.4 μm spectral atlas of active galactic nuclei
Aims.We present a near-infrared spectral atlas of 47 active galacticnuclei (AGN) of all degrees of activity in the wavelength interval of0.8-2.4 μm, including the fluxes of the observed emission lines. Weanalyze the spectroscopic properties of the continuum and emission linespectra of the sources. Methods: . In order to exclude apertureand seeing effects we used near-infrared spectroscopy in the shortcross-dispersed mode (SXD, 0.8-2.4 μm), taking the JHK-bands spectrasimultaneously. Results: .We present the most extensive NIRspectral atlas of AGN to date. This atlas offers a suitable database forstudying the continuum and line emission properties of these objects ina region full of interesting features. The shape of the continuum ofQSOs and Sy 1's are similar, being essentially flat in the H and Kbands, while a strong variation is found in the J band. In Seyfert 2galaxies, the continuum in the Fλ × λ space smoothlydecreases in flux from 1.2 μm redwards in almost all sources. In J,it smoothly rises bluewards in some sources, while in others a smalldecrease in flux is observed. The spectra are dominated by strongemission features of H I, He I, He II, [S III] and by conspicuousforbidden lines of low and high ionization species. Molecular lines ofH{2} are common features of most objects. The absence of O I and Fe IIlines in Seyfert 2 galaxies and the smaller FWHM of these lines relativeto that of H I in the Seyfert 1 give observational support to the factthat they are formed in the outermost portion of the broad-line region.The[P II] and coronal lines are detected for all degrees of activity.The [Fe II] 12 570 Å/16 436 Å line ratio becomes a reliablereddening indicator for the narrow-line region of Seyfert galaxies.
| Size and properties of the narrow-line region in Seyfert-2 galaxies from spatially-resolved optical spectroscopy
Context: .While [O III] narrow-band imaging is commonly used to measurethe size of the narrow-line regions (NLRs) in active galactic nuclei(AGNs), it can be contaminated by emission from surrounding starbursts.Recently, we have shown that long-slit spectroscopy provides a valuablealternative approach to probe the size in terms of AGN photoionisation.Moreover, several parameters of the NLR can be directly accessed.Aims: .We here apply the same methods developed and described for theSeyfert-2 galaxy NGC 1386 to study the NLR of five other Seyfert-2galaxies by using high-sensitivity spatially-resolved opticalspectroscopy obtained at the VLT and the NTT. Methods: .We probethe AGN-photoionisation of the NLR and thus, its "real" size usingdiagnostic line-ratio diagrams. We derive physical properties of the NLRsuch as reddening, ionisation parameter, electron density, and velocityas a function of distance from the nucleus. Results: .For NGC5643, the diagnostic diagrams unveil a similar transition between lineratios falling in the AGN regime and those typical for H II regions asfound for NGC 1386, thus determining the size of the NLR. For the otherfour objects, all measured line ratios fall in the AGN regime. In almostall cases, both electron density and ionisation parameter decrease withradius. Deviations from this general behaviour (such as a secondarypeak) seen in both the ionisation parameter and electron density can beinterpreted as signs of shocks from the interaction of a radio jet andthe NLR gas. In several objects, the gaseous velocity distribution ischaracteristic for rotational motion in an (inclined) emission-line diskin the centre. We compare our results to those of NGC 1386 and show thatthe latter can be considered as prototypical also for this largersample. We discuss our findings in detail for each object.
| A catalogue of quasars and active nuclei: 12th edition
Aims.This catalogue is aimed at presenting a compilation of all knownAGN in a compact and convenient form and we hope that it will be usefulto all workers in this field.Methods.Like the eleventh edition, itincludes position and redshift as well as photometry (U, B, V) and 6 cmflux densities when available. We now give 20 cm rather than 11 cm fluxdensities.Results.The present version contains 85 221 quasars,1122 BL Lac objects and 21 737 active galaxies (including 9628 Seyfert1s), almost doubling the number listed in the 11th edition. We also givea list of all known lensed and double quasars.
| The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Nuclear Dust Morphology and Starburst Rings
We present a study of the nuclear morphology of a sample of narrow- andbroad-line Seyfert 1 galaxies (NLS1s and BLS1s, respectively) based onbroadband images in the Hubble Space Telescope archives. In our previousstudy we found that large-scale stellar bars at >1 kpc from thenucleus are more common in NLS1s than BLS1s. In this paper we find thatNLS1s preferentially have grand-design dust spirals within ~1 kpc oftheir centers. We also find that NLS1s have a higher fraction of nuclearstar-forming rings than BLS1s. We find that many of the morphologicaldifferences are due to the presence or absence of a large-scale stellarbar within the spiral host galaxy. In general, barred Seyfert 1 galaxiestend to have grand-design dust spirals at their centers, confirming theresults of other researchers. The high fraction of grand-design nucleardust spirals and stellar nuclear rings observed in NLS1s' host galaxiessuggests a means for efficient fueling of their nuclei to support theirhigh Eddington ratios.
| 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.
| SWIFT/BAT Detections of Hard X-ray Sources II
Table of BAT survey source identifications described in ATEL #668.
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