We discuss the X-ray luminosity function and number counts of normal spiral galaxies. A detailed comparison is performed of the LFs compiled at infrared, radio and optical wavelengths and converted ...into XLFs using available relations in the literature with the XLF directly estimated in the 0.5–2 keV energy band from X-ray surveys. We find that the XLF from the local sample of IRAS galaxies provides a good representation of all available data samples; pure luminosity evolution of the form $(1+z)^\eta$, with $\eta\la 3$, is favoured over pure density evolution. We also find that the local X-ray luminosity density is well defined, $3\times 10^{37} \pm 30\%$ erg s-1 Mpc-3. We discuss different estimates of the galaxies Log N-Log S, selected from the Chandra Deep Field surveys with different selection criteria, and find that these have similar slopes, but normalisations scattered within a factor ~2 (which is not far from the Poissonian error on the number counts). We then compare the observed galaxies Log N-Log S with the counts predicted by the integration of our reference $z=0$ XLF. From the analysis of number counts alone, it is not possible to discriminate between density and luminosity evolution; however, the evolution of galaxies must be stopped in both cases at a redshift $z\sim 1{-}2$. The contribution of galaxies to the cosmic X-ray background is found to be in the range $6\%{-}12\%$. By means of a complementary analysis with cosmic star formation models, we also find that the observed X-ray number counts might be not compatible with very high star formation rates at $z\sim 3$ as suggested by sub-mm observations. Concerning the content of current and, possibly, future X-ray surveys, we determine the fraction of normal galaxies around the current flux limit. At ~$3\times 10^{-17}$ erg s-1 cm-2 in the 0.5-2.0 keV band, the normal galaxies in the Chandra Deep Field surveys are about the $(30\pm 12)\%$ of the total number of objects. At fainter fluxes the fraction of galaxies will probably rise, and exceed the counts from AGN at fluxes $\la$10-17 erg s-1 cm-2.
As the mid-IR luminosity represents a good isotropic proxy of the AGN power, a low X-ray to mid-IR luminosity ratio is often claimed to be a reliable indicator of Compton-thick AGN. We assess the ...efficiency of the X-ray to mid-IR luminosity ratio diagnostic by examining the 12 μm IRAS AGN sample (intrinsic L2−10 keV > 1042 erg s-1) for which high signal-to-noise ratio XMM-Newton observations are now available. We find that the vast majority (ten out of eleven) of the AGN that were classified as Compton-thick on the basis of X-ray spectroscopy by Brightman & Nandra have a low LX/L6 μm luminosity ratio, i.e. lower than a few percent of the average AGN ratio, as is typical of reflection-dominated Compton-thick sources. At low LX/L6 μm ratios, we also find a comparable number of AGN, most of which are heavily absorbed but not Compton-thick. This implies that although most Compton-thick AGN have low LX/L6 μm ratios, at least in the local, Universe, the converse is not necessarily true. We then extend our analysis to higher redshifts. We perform the same analysis in the Chandra Deep Field South, for which excellent quality Chandra (4 Ms) and XMM-Newton (3 Ms) X-ray spectra are available. We derive accurate X-ray luminosities for Chandra sources using X-ray spectral fits, as well as 6 μm luminosities from spectral energy distribution fits. We find in total eight AGN (intrinsic L2−10 keV > 1042 erg s-1) with low LX/L6 μm ratios, after excluding one source where the 6 μm emission primarily comes from star-formation. One of these sources has been already found to host a Compton-thick nucleus, while for another one at a redshift of z = 1.22 we argue it is most likely Compton-thick on the basis of its combined Chandra and XMM-Newton spectrum. In agreement with the low redshift sample, we find a large number of non Compton-thick “contaminants” with low X-ray to mid-IR luminosity ratios. Our results suggest that a low LX/L6 μm ratio alone cannot help us to ascertain whether a Compton-thick AGN is present, albeit the majority of low LX/L6 μm AGN are heavily obscured. More interestingly, the two most reliable Compton-thick AGN in the high redshift Universe have high LX/L6 μm ratios, showing that this method cannot provide complete Compton-thick AGN samples.
We report the results from a 2011 Suzaku observation of the nearby low-ionization broad absorption line (BAL) quasar/ULIRG Markarian 231 (Mrk 231). These data reveal that the X-ray spectrum has ...undergone a large variation from the 2001 XMM-Newton and BeppoSAX observations. We interpret this finding according to a scenario whereby the X-ray continuum source is obscured by a two-component partial-covering absorber with N
H ∼ 1022 and ∼1024 cm−2, respectively. The observed spectral change is mostly explained by a progressive appearance of the primary continuum at <10 keV due to the decrease of the covering fraction of the denser absorption component. The properties of the X-ray obscuration in Mrk 231 match well with those of the X-ray shielding gas predicted by the theoretical models for an efficient radiatively driven acceleration of the BAL wind. In particular, the X-ray absorber might be located at the extreme base of the outflow. We measure a 2-10 keV luminosity of L
2-10 = 3.3 × 1043 erg s−1 for the 2011 data set, i.e. an increase of 30 per cent with respect to the 2001 value.
The XMM Deep Survey in the CDF-S Antonucci, M; Talavera, A; Vagnetti, F ...
Astronomy and astrophysics (Berlin),
2/2015, Letnik:
574
Journal Article
Recenzirano
The XMM-Newton X-ray observatory has repeatedly observed the Chandra Deep Field-South (CDF-S) in 33 epochs through the XMM-CDFS Deep Survey. We present the UV catalogue of the XMM-CDFS Deep Survey. ...Its main purpose is to provide complementary UV average photometric measurements of known optical/UV sources in the CDF-S, taking advantage of the unique characteristics of the survey. We re-processed the XMM-OM data of the survey and stacked the exposures from consecutive observations using the standard Science Analysis System (SAS) tools to process the data obtained during single observations. Photometric data of 1129 CDF-S sources are provided in the catalogue, and optical/UV/X-ray photometric and spectroscopic information from other surveys are also included. The comparison with the available measurements in similar spectral bands confirms the validity of the XMM-OM calibration.
We report results from a spectral and timing analysis of M82 X-1, one of the brightest known ultraluminous X-ray sources. Data from a new 105-ks XMM—Newton observation of M82 X-1, performed in 2004 ...April, and of archival RossiXTE observations are presented. A very soft thermal component is present in the XMM spectrum. Although it is not possible to rule out a residual contamination from the host galaxy, modelling it with a standard accretion disc would imply a black hole (BH) mass of ≈103 M⊙. An emission line was also detected at an energy typical for fluorescent Fe emission. The power density spectrum of the XMM observation shows a variable Quasi-Periodic Oscillation (QPO) at frequency of 113 mHz with properties similar to those discovered by Strohmayer and Mushotzky. The QPO was also found in seven archival RXTE observations, that include those analysed by Strohmayer and Mushotzky, and Fiorito and Titarchuk. A comparison of the properties of this QPO with those of the various types of QPOs observed in Galactic black hole candidates strongly suggests an association with the type-C, low-frequency QPOs. Scaling the frequency inversely to the BH mass, the observed QPO frequency range (from 50 to 166 mHz) would yield a BH mass anywhere in the interval few tens to 1000 M⊙.
Stellar and Gaseous Abundances in M82 Origlia, L; Ranalli, P; Comastri, A ...
The Astrophysical journal,
05/2004, Letnik:
606, Številka:
2
Journal Article
Recenzirano
The near-infrared (near-IR) absorption spectra of starburst galaxies show several atomic and molecular lines from red supergiants that can be used to infer reliable stellar abundances. The metals ...locked in stars give a picture of the galaxy metallicity prior to the last burst of star formation. The enrichment of the new generation of stars born in the last burst can be traced by measuring the hot gas in the X-rays. For the first time, detailed stellar abundances in the nuclear region of the starburst galaxy M82 have been obtained. They are compared with those of the hot gas, as derived from an accurate reanalysis of the XMM-Newton and Chandra nuclear X-ray spectra. The cool stars and the hot gas suggest image =-0.35 plus or minus 0.2 dex and an overall Si/Fe and Mg/Fe enhancement by approx0.4 and 0.5 dex, respectively. This is consistent with a major chemical enrichment by Typ IIE supernova explosions in recursive bursts on short timescales. Oxygen is more puzzling to interpret, since it is enhanced by approx0.3 dex in stars and depleted by approx0.2 dex in the hot gas. None of the standard enrichment scenarios can fully explain such a behavior compared with that of the other alpha-elements.
The XMM deep survey in the CDF-S Castello-Mor, N; Carrera, F J; Alonso-Herrero, A ...
Astronomy and astrophysics (Berlin),
08/2013, Letnik:
556
Journal Article
Recenzirano
Odprti dostop
Accretion onto supermassive black holes is believed to occur mostly in obscured active galactic nuclei (AGN). Such objects are proving rather elusive in surveys of distant galaxies, including those ...at X-ray energies. Our main goal is to determine whether the revised IRAC criteria of Donley et al., are effective at selecting X-ray type-2 AGN. We present the results from the X-ray spectral analysis of 147 AGN selected by cross-correlating the highest spectral quality ultra-deep XMM-Newton and the Spitzer/IRAC catalogues in the Chandra Deep Field South. Consequently it is biased towards sources with high S/N X-ray spectra. In order to measure the amount of intrinsic absorption in these sources, we adopt a simple X-ray spectral model that includes a power-law modified by intrinsic absorption at the redshift of each source and a possible soft X-ray component. We therefore conclude that the IR power-law method is efficient in finding X-ray-absorbed sources. We would then expect that the long-sought dominant population of absorbed AGN is abundant among IR power-law spectral shape sources not detected in X-rays.
The XMM Deep survey in the CDF-S Falocco, S; Carrera, F J; Corral, A ...
Astronomy and astrophysics (Berlin),
07/2013, Letnik:
555
Journal Article
Recenzirano
Odprti dostop
X-ray spectroscopy of active galactic nuclei (AGN) offers the opportunity to directly probe the inner regions of the accretion disk. Reflection of the primary continuum on the circumnuclear accreting ...matter produces features in the X-ray spectrum that help to explore the physics and the geometry of the innermost region, close to the central black hole. We present the results of our analysis of average AGN XMM-Newton X-ray spectra in the Chandra Deep Field South observation (hereafter, XMM CDFS), in order to explore the Fe line features in distant AGN up to z~3.5. Thanks to the high quality of the XMM CDFS spectra and to the detailed modelling of the continuum and instrumental effects, we have shown that the most distant AGN exhibit a highly significant iron emission feature. The EW of both features are similar to those observed in individual nearby AGN, hence they must be a widespread characteristic of AGN, since otherwise the average values would be smaller than observed.
We present an X-ray spectroscopic study of optically selected (SDSS) Seyfert 2 (Sy2) galaxies. The goal is to study the obscuration of Sy2 galaxies beyond the local universe, using good quality X-ray ...spectra in combination with high S/N optical spectra for their robust classification. We analyzed all available XMM-Newton archival observations of narrow emission line galaxies that meet the above criteria in the redshift range 0.05 <z< 0.35. We initially selected narrow line AGN using the SDSS optical spectra and the BPT classification diagram. We further modeled and removed the stellar continuum, and we analyzed the residual emission line spectrum to exclude any possible intermediate-type Seyferts. Our final catalog comprises 31 Sy2 galaxies with median redshift z ~ 0.1. X-ray spectroscopy is performed using the available X-ray spectra from the 3XMM and the XMMFITCAT catalogs. Implementing various indicators of obscuration, we find seven (~23%) Compton-thick AGN. The X-ray spectroscopic Compton-thick classification agrees with other commonly used diagnostics, such as the X-ray to mid-IR luminosity ratio and the X-ray to OIIIλ5007 luminosity ratio. Most importantly, we find four (~13%) unobscured Sy2 galaxies, at odds with the simplest unification model. Their accretion rates are significantly lower than the rest of our Sy2 sample, in agreement with previous studies that predict the absence of the broad line region below a certain Eddington ratio threshold.
The Chandra Deep Field South (CDF‐S) was observed by XMM‐Newton for about 3 Ms in many periods over the past decade (2001–2002 and 2008–2009). The main goal of the survey was to obtain good quality ...X‐ray spectroscopy of the active galactic nuclei responsible for the bulk of the X‐ray background. We present the scientific highlights of the XMM‐Newton survey and briefly discuss the perspectives of future observations to pursue XMM deep survey science with current and forthcoming X‐ray facilities.
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