G. G. C. Palumbo

Evidence for ultra-fast outflows in radio-quiet AGNs★ I. Detection and statistical incidence of Fe K-shell absorption lines

Context. Blue-shifted Fe K absorption lines have been detected in recent years between 7 and 10 keV in the X-ray spectra of several radio-quiet AGNs. The derived blue-shifted velocities of the lines can often reach mildly relativistic values, up to 0.2–0.4c. These findings are important because they suggest the presence of a previously unknown massive and highly ionized absorbing material outflowing from their nuclei, possibly connected with accretion disk winds/outflows. Aims. The scope of the present work is to statistically quantify the parameters and incidence of the blue-shifted Fe K absorption lines through a uniform analysis on a large sample of radio-quiet AGNs. This allows us to assess their global detection significance and to overcome any possible publication bias. Methods. We performed a blind search for narrow absorption features at energies greater than 6.4 keV in a sample of 42 radio-quiet AGNs observed with XMM-Newton. A simple uniform model composed by an absorbed power-law plus Gaussian emission and absorption lines provided a good fit for all the data sets. We derived the absorption lines parameters and calculated their detailed detection significance making use of the classical F-test and extensive Monte Carlo simulations. Results. We detect 36 narrow absorption lines on a total of 101 XMM-Newton EPIC pn observations. The number of absorption lines at rest-frame energies higher than 7 keV is 22. Their global probability to be generated by random fluctuations is very low, less than 3 × 10 −8 , and their detection have been independently confirmed by a spectral analysis of the MOS data, with associated random probability 7 keV and to overcome their publication bias. These lines indicate that UFOs are a rather common phenomenon observable in the central regions of these sources and they are probably the direct signature of AGN accretion disk winds/ejecta. The detailed photo-ionization modeling of these absorbers is presented in a companion paper.

Dynamical properties of compact groups of galaxies

Radial velocities are presented for 457 galaxies in the 100 Hickson compact groups. More than 84 percent of the galaxies measured have velocities within 1000 km/s of the median velocity in the group. Ninety-two groups have at least three accordant members, and 69 groups have at least four. The radial velocities of these groups range from 1380 to 42,731 km/s with a median of 8889 km/s, corresponding to a median distance of 89/h Mpc. The apparent space density of these systems ranges from 300 to as much as 10 exp 8 sq h/sq Mpc, which exceeds the densities in the centers of rich clusters. The median projected separation between galaxies is 39/h kpc, comparable to the sizes of the galaxies themselves. A significant correlation is found between crossing time and the fraction of gas-rich galaxies in the groups, and a weak anticorrelation is found between crossing time and the luminosity contrast of the first-ranked galaxy.

An XMM-Newton hard X-ray survey of ultraluminous infrared galaxies

XMM-Newton observations of 10 ULIRGs are reported. The aim is to investigate in hard X-rays a complete ULIRG sample selected from the bright IRAS 60

Asca and rosat x-ray spectra of high-redshift radio-loud quasars

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The XMM-Newton and BeppoSAX view of the Ultra Luminous Infrared Galaxy MKN 231

m catalogue. All sources are detected in X-rays, 5 of which for the first time. These observations confirm that ULIRGs are intrinsically faint X-rays sources, their observed X-ray luminosities being typically L(2-10 keV) 1E45 erg/s. In all sources we find evidence for thermal emission from hot plasma with kT~0.7keV, dominating the X-ray spectra below 1keV, and likely associated with a nuclear or circumnuclear starburst. This thermal emission appears uncorrelated with the FIR luminosity, suggesting that,in addition to the ongoing rate of star formation, other parameters may also affect it. The soft X-ray emission appears to be extended on a scale of ~30kpc for Mkn231 and IRAS19254-7245, possible evidence of galactic superwinds. In these 2 sources, in IRAS20551-4250 and IRAS23128-5919 we find evidence for the presence of hidden AGNs, while a minor AGN contribution may be suspected also in IRAS20100-4156. In particular, we have detected a strong Fe line at 6.4keV in the spectrum of IRAS19254-7245 and a weaker one in Mkn231, suggestive of deeply buried AGNs. For the other sources, the X-ray luminosities and spectral shapes are consistent with hot thermal plasma and X-ray binary emissions of mainly starburst origin. We find that the 2-10keV luminosities in these sources, most likely due to high-mass X-ray binaries, are correlated with L_FIR: both luminosities are good indicators of the current global SFR in the galaxy. The composite nature of ULIRGs is then confirmed, with hints for a predominance of the starburst over the AGN phenomenon in these objects.

X-ray evidence for a mildly relativistic and variable outflow in the luminous Seyfert 1 galaxy Mrk 509

Results are presented on the X-ray properties of 9 high-redshift (1.2 < z < 3.4) radio-loud quasars (RLQs) observed by the Advanced Satellite for Cosmology and Astrophysics (ASCA; 10 observations) and ROSAT (11 observations, for a subset of six quasars). New ASCA observations of S5 0014+81 (z = 3.38) and S5 0836+71 (z = 2.17) and ROSAT observations of PKS 2126-158 for which results were never presented elsewhere are included. A simple model consisting of a power law plus cold, uniform absorption gives acceptable fits to the spectra of all sources. The ASCA spectra of the six brightest objects show evidence for absorption in excess of the Galactic value at a 99% confidence level. Comparison with the ROSAT data suggests that absorption has significantly varied (ΔNH ~ 8 × 1020 cm-2) in the case of S5 0836+71, on a timescale of approximately 0.8 yr in the quasar frame. For the remaining five sources for which ROSAT spectra were available, the two instruments gave consistent results, and the data were combined yielding unprecedented spectral coverage (typically about 0.4-40 keV in the quasar frame) for high-z quasars. This allows us to put severe limits on several different descriptions of the continuum (e.g., broken power law, bremsstrahlung, reflection component). No Fe Kα emission line is detected in any of the ASCA spectra. An absorption edge consistent with Fe Kα at the quasar redshift is marginally detected in S5 0014+81. Possible origins for the observed low energy absorption are discussed. In particular, contributions from the molecular clouds and dust present in our Galaxy (usually disregarded) are carefully considered. In light of the new results for S5 0836+71 and S5 0014+81, absorption intrinsic to the quasars is considered and discussed. The average slope obtained from the eight ASCA spectra in the observed ~0.5-10 keV energy band is Γ0.5-10 keV 1.61 ± 0.04, with a dispersion σ0.5-10 keV 0.10 ± 0.03. The average photon index in the observed 2-10 keV band, where the effect of absorption is negligible, is Γ2-10 keV 1.53 ± 0.05, with a dispersion σ2-10 keV 0.12. Furthermore, the implications of the present results on the calculations of the contribution of quasars to the cosmic X-ray and γ-ray backgrounds are briefly discussed.

Probing the Hard X-Ray Properties of High-Redshift Radio-Quiet Quasars with ASCA

We discuss XMM-Newton and BeppoSAX observations of MKN 231, the lowest-redshift Broad Absorption Line (BAL) QSO known so far and one of the best-studied Ultra Luminous Infrared Galaxies. By combining the XMM-Newton spectral resolution and the high-energy bandpass of BeppoSAX we have been able to study in more detail than previ- ously possible its 0.2-50 keV spectral properties. The BeppoSAX PDS data unveiled, for the first time, a highly absorbed (NH ∼ 2 × 10 24 cm −2 ) power-law component. We find that: a) below 10 keV we are seeing only reprocessed radiation through reflection and/or scattering; b) the intrinsic 2-10 keV luminosity of MKN 231 is 1 +1.0 −0.5 × 10

Infrared emission from compact groups of galaxies

Context. There is growing evidence for the presence of blueshifted Fe K absorption lines in a number of radio-quiet AGNs and QSOs. These may be fundamental to probe flow dynamics near supermassive black holes. Aims. Here we aim to verify and better characterise the existence of such Fe K absorption at ∼8–10 keV in the luminous Seyfert 1 galaxy Mrk 509, one of the most promising target for these studies. Methods. We present a comprehensive spectral analysis of the six XMM-Newton observations of the source (for a total of ∼200 ks), focusing on a detailed and systematic search for absorption features in the high-energy data. Results. We detect several absorption features at rest-frame energies ∼8–8.5 keV and ∼9.7 keV. The lines are consistent with being produced by H-like iron Kα and Kβ shell absorptions associated with an outflow with a mildly relativistic velocity of ∼0.14–0.2 c. The lines are found to be variable in energy and, marginally, in intensity, implying variations in either the column density, geometry and/or ionization structure of the outflow are common.

Variable X-ray absorption in the mini-BAL QSO PG 1126-041

This paper reports the X-ray spectral analysis of five high-redshift (z≥2), radio-quiet quasars observed by ASCA. A simple power-law continuum plus cold Galactic absorption model well fits all the spectra (typically between ~2 and 30 keV in the sources frame). Neither the X-ray spectral hardening, which is attributed to a reflection component and observed in Seyfert galaxies, nor the excess absorption previously detected in high-redshift, radio-loud quasars have been revealed. Only marginal evidence of a neutral or mildly ionized FeKα line is found in one of the quasars. The average spectral slope in the observed 0.7-10 keV energy range, Γ=1.67 ± 0.11 (dispersion σ ~0.07), appears to be flatter than that of low-z, radio-quiet quasars (Γ 1.9-2) and slightly steeper but consistent with Γ=1.61 ± 0.04 (σ ~0.10) of high-z, radio-loud quasars.

High-Energy Spectra of Active Galactic Nuclei. II. Absorption in Seyfert Galaxies

A search of the IRAS Point Source Catalog, Version 2 has revealed infrared sources within 1 arcmin of the optical centers of 54 galaxies in Hicksons catalog of compact groups of galaxies. The 60-micron luminosity function for these galaxies has the same shape as the luminosity function of the IRAS bright galaxy sample. The space density of IRAS galaxies in compact groups is 60 times smaller than the space density of IRAS bright galaxies, indicating that of order 1 percent of all bright IRAS galaxies are in compact groups. The infrared emission from these galaxies is compared with the emission from samples of isolated galaxies by Keel et al. (1985) and cluster galaxies studied by Bicay and Giovanelli (1987). The fractional distribution of the ratio of far-infrared to optical luminosity of compact group galaxies is significantly larger than that of the isolated galaxies and comparable to that of the cluster galaxies. These results indicate that infrared emission is enhanced in the compact group galaxies, probably because of interactions. 24 refs.