ISOPHOT Observations of Narrow-Line Seyfert 1 Galaxies

Broad infrared spectra (7-200 micrometer) of four NLS1 galaxies, obtained with the imaging photo-polarimeter (ISOPHOT) on board the Infrared Space Observatory (ISO), are presented. The infrared luminosities and temperatures, opacities and sizes of the emitting dust components are derived. A comparison between the observed infrared spectra and the optical emission line fluxes of a sample of 16 NLS1 galaxies suggests that these objects suffer different degrees of dust absorption according to the inclination of the line of sight with respect to the dust distribution.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho

XMM-Newton discovery of very high obscuration in the candidate Supergiant Fast X-ray Transient AX J1714.1-3912

We have analysed an archival XMM-Newton EPIC observation that serendipitously covered the sky position of a variable X-ray source AX J1714.1-3912, previously suggested to be a Supergiant Fast X-ray Transient (SFXT). During the XMM-Newton observation the source is variable on a timescale of hundred seconds and shows two luminosity states, with a flaring activity followed by unflared emission, with a variability amplitude of a factor of about 50. We have discovered an intense iron emission line with a centroid energy of 6.4 keV in the power law-like spectrum, modified by a large absorption (NH around 1e24 cm-2), never observed before from this source. This X-ray spectrum is unusual for an SFXT, but resembles the so-called "highly obscured sources", high mass X-ray binaries (HMXBs) hosting an evolved B[e] supergiant companion (sgB[e]). This might suggest that AX J1714.1-3912 is a new member of this rare type of HMXBs, which includes IGR J16318-4848 and CI Camelopardalis. Increasing this small population of sources would be remarkable, as they represent an interesting short transition evolutionary stage in the evolution of massive binaries. Nevertheless, AX J1714.1-3912 appears to share X-ray properties of both kinds of HMXBs (SFXT vs sgB[e] HMXB). Therefore, further investigations of the companion star are needed to disentangle the two hypothesis.Comment: Accepted for publication in MNRA

The far-infrared energy distributions of Seyfert and starburst galaxies in the Local Universe: ISO photometry of the 12 micron active galaxy sample

New far-infrared photometry with ISOPHOT, onboard the Infrared Space Observatory, is presented for 58 galaxies with homogeneous published data for another 32 galaxies all belonging to the 12 micron galaxy sample. In total 29 Seyfert 1's, 35 Seyfert 2's and 12 starburst galaxies, about half of the 12 micron active galaxy sample, plus 14 normal galaxies for comparison. The ISO and the IRAS data are used to define color-color diagrams and spectral energy distributions (SED). Thermal dust emission at two temperatures (one cold at 15-30K and one warm at 50-70K) can fit the 60-200 micron SED, with a dust emissivity law proportional to the inverse square of the wavelength. Seyfert 1's and Seyfert 2's are indistinguishable longward of 100 micron, while, as already seen by IRAS, the former have flatter SEDs shortward of 60 micron. A mild anti-correlation is found between the [200 - 100] color and the "60 micron excess". We infer that this is due to the fact that galaxies with a strong starburst component, and thus a strong 60 micron flux, have a steeper far-infrared turnover. In non-Seyfert galaxies, increasing the luminosity corresponds to increasing the star formation rate, that enhances the 25 and 60 micron emission. This shifts the peak emission from around 150 micron in the most quiescent spirals to shorter than 60 micron in the strongest starburst galaxies.Comment: Accepted for publication in The Astrophysical Journal AASTeX preprint with 49 pages and 20 figures Also available at http://orion.ifsi.rm.cnr.it/publ.htm

Near Infrared Adaptive Optics Imaging of QSO Host Galaxies

We report near-infrared (primarily H-band) adaptive optics (AO) imaging with the Gemini-N and Subaru Telescopes, of a representative sample of 32 nearby (z<0.3) QSOs selected from the Palomar-Green (PG) Bright Quasar Survey (BQS), in order to investigate the properties of the host galaxies. 2D modeling and visual inspection of the images shows that ~36% of the hosts are ellipticals, \~39% contain a prominent disk component, and ~25% are of undetermined type. 30% show obvious signs of disturbance. The mean M_H(host) = -24.82 (2.1L_H*), with a range -23.5 to -26.5 (~0.63 to 10 L_H*). At <L_H*, all hosts have a dominant disk component, while at >2 L_H* most are ellipticals. "Disturbed" hosts are found at all M_H(host), while "strongly disturbed" hosts appear to favor the more luminous hosts. Hosts with prominent disks have less luminous QSOs, while the most luminous QSOs are almost exclusively in ellipticals or in mergers (which presumably shortly will be ellipticals). At z<0.13, where our sample is complete at B-band, we find no clear correlation between M_B(QSO) and M_H(host). However, at z>0.15, the more luminous QSOs (M_B<-24.7), and 4/5 of the radio-loud QSOs, have the most luminous H-band hosts (>7L_H*), most of which are ellipticals. Finally, we find a strong correlation between the "infrared-excess", L_IR/L_BB, of QSOs with host type and degree of disturbance. Disturbed and strongly disturbed hosts and hosts with dominant disks have L_IR/L_BB twice that of non-disturbed and elliptical hosts, respectively. QSOs with "disturbed" and "strongly-disturbed" hosts are also found to have morphologies and mid/far-infrared colors that are similar to what is found for "warm" ultraluminous infrared galaxies, providing further evidence for a possible evolutionary connection between both classes of objects.Comment: 80 pages, accepted for publication in ApJ Supp

Obscured and unobscured AGN populations in a hard-X-ray selected sample of the XMDS survey

Our goal is to probe the populations of obscured and unobscured AGN investigating their optical-IR and X-ray properties as a function of X-ray flux, luminosity and redshift within a hard X-ray selected sample of 136 X-ray sources in the XMM Medium Deep Survey (XMDS) with wide multiwavelength coverage. The XMDS area is covered with optical photometry from the VVDS and CFHTLS surveys and infrared Spitzer data. Based on the X-ray luminosity and X-ray to optical ratio, 132 sources are likely AGN, of which 122 have unambiguous optical - IR identification. The observed optical and IR spectral energy distributions of sources are fitted with AGN/galaxy templates in order to classify them and compute photometric redshifts. 70% of the AGN are fitted by a type 2 AGN or a star forming galaxy template and are grouped together in a single class of ``optically obscured'' AGN. They have ``red'' optical colors and generally show significant X-ray absorption from X-ray spectra or hardness ratios (N$_H > 10^{22}$ cm$^{-2}$). Sources with SEDs typical of type 1 AGN have ``blue'' optical colors and exhibit X-ray absorption in about 30% of cases. We performed a stacking analysis for obscured and type 1 AGN. The stacked X-ray spectrum of obscured AGN is flatter than that of type 1 AGN and has an average spectral slope of Gamma = 1.6. The subsample of objects fitted by a galaxy template has an even harder stacked spectrum, with Gamma = 1.2 - 1.3. The obscured fraction is larger at lower fluxes, lower redshifts and lower luminosities. X-ray absorption is less common than ``optical'' obscuration and its incidence is nearly constant with redshift and luminosity. This implies that X-ray absorption is not necessarily related to optical obscuration.Comment: 33 pages, 21 figures, accepted for publication in A&

Synchrotron radio emission in radio-quiet AGNs

The basic mechanism responsible for radio emission in radio-loud active galactic nuclei (AGNs) is assumed to be synchrotron radiation. We suggest here that radio emission in radio-quiet objects is also due to synchrotron radiation of particles accelerated in shocks. We consider generic shocks and study the resulting synchrotron properties. We estimate the synchrotron radio luminosity and compare it with the X-ray component produced by inverse Compton emission. We obtain that the radio to X-ray luminosity ratio is much smaller than unity, with values typical of radio-quiet sources. The predicted trends on source parameters, black hole mass and accretion rate, may account for the anticorrelation between radio-loudness and Eddington ratio observed in different AGN samples.Comment: 5 pages, accepted for publication in Astronomy and Astrophysic

Detections of CO Molecular Gas in 24um-Bright ULIRGs at z~2 in the Spitzer First Look Survey

We present CO observations of 9 ULIRGs at z~2 with S(24\mu m)>1mJy, previously confirmed with the mid-IR spectra in the Spitzer First Look Survey. All targets are required to have accurate redshifts from Keck/GEMINI near-IR spectra. Using the Plateau de Bure millimeter-wave Interferometer (PdBI) at IRAM, we detect CO J(3-2) [7 objects] or J(2-1) [1 object] line emission from 8 sources with integrated intensities Ic ~(5-9)sigma. The CO detected sources have a variety of mid-IR spectra, including strong PAH, deep silicate absorption and power-law continuum, implying that these molecular gas rich objects at z~2 could be either starbursts or dust obscured AGNs. The measured line luminosity L'[CO] is (1.28-3.77)e+10[K km/s pc^2]. The averaged molecular gas mass M(H2) is 1.7e+10Msun, assuming CO-to-H2 conversion factor of 0.8Msun/[K km/s pc^2]. Three sources (33%) -- MIPS506, MIPS16144 & MIPS8342 -- have double peak velocity profiles. The CO double peaks in MIPS506 and MIPS16144 show spatial separations of 45kpc and 10.9kpc, allowing the estimates of the dynamical masses of 3.2e+11*sin^(-2)(i)Msun and 5.4e+11*sin^{-2}(i)Msun respectively. The implied gas fraction, M(gas)/M(dyn), is 3% and 4%, assuming an average inclination angle. Finally, the analysis of the HST/NIC2 images, mid-IR spectra and IR SED revealed that most of our sources are mergers, containing dust obscured AGNs dominating the luminosities at (3-6)um. Together, these results provide some evidence suggesting SMGs, bright 24um z~2 ULIRGs and QSOs could represent three different stages of a single evolutionary sequence, however, a complete physical model would require much more data, especially high spatial resolution spectroscopy.Comment: 15 pages, 8 figures, accepted for publication in ApJ

Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources

We have measured mid-infrared radiation from an orientation-unbiased sample of 3CRR galaxies and quasars at redshifts 0.4 < z < 1.2 with the IRS and MIPS instruments on the Spitzer Space Telescope. Powerful emission (L_24micron > 10^22.4 W/Hz/sr) was detected from all but one of the sources. We fit the Spitzer data as well as other measurements from the literature with synchrotron and dust components. The IRS data provide powerful constraints on the fits. At 15 microns, quasars are typically four times brighter than radio galaxies with the same isotropic radio power. Based on our fits, half of this difference can be attributed to the presence of non-thermal emission in the quasars but not the radio galaxies. The other half is consistent with dust absorption in the radio galaxies but not the quasars. Fitted optical depths are anti-correlated with core dominance, from which we infer an equatorial distribution of dust around the central engine. The median optical depth at 9.7 microns for objects with core-dominance factor R > 10^-2 is approximately 0.4; for objects with R < 10^-2, it is 1.1. We have thus addressed a long-standing question in the unification of FR II quasars and galaxies: quasars are more luminous in the mid-infrared than galaxies because of a combination of Doppler-boosted synchrotron emission in quasars and extinction in galaxies, both orientation-dependent effects.Comment: 42 pages, 14 figures plus two landscape tables. Accepted for publication in Ap