arXiv subjects

F. J. Carrera

Publications and source records attributed to F. J. Carrera.

At least 73 records · Page 4Linked to original sources

arXiv2013

Submm-bright QSOs at z~2: signposts of co-evolution at high z

We have assembled a sample of 5 X-ray and submm-luminous z~2 QSOs which are therefore both growing their central black holes through accretion and forming stars copiously at a critical epoch. Hence, they are good laboratories to investigate the co-evolution of star formation and AGN. We have performed a preliminary analysis of the AGN and SF contributions to their UV-to-FIR SEDs, fitting them with simple direct (disk), reprocessed (torus) and star formation components. All three are required by the data and hence we confirm that these objects are undergoing strong star formation in their host galaxies at rates 500-2000 Msun/y. Estimates of their covering factors are between about 30 and 90%. In the future, we will assess the dependence of these results on the particular models used for the components and relate their observed properties to the intrinsice of the central engine and the SF material, as well as their relevance for AGN-galaxy coevolution.

astro-ph.CO↗

arXiv2012

Analysis of Spitzer-IRS spectra of hyperluminous infrared galaxies

Hyperluminous infrared galaxies (HLIRG) are the most luminous persistent objects in the Universe. They exhibit extremely high star formation rates, and most of them seem to harbour an AGN. They are unique laboratories to investigate the most extreme star formation, and its connection to super-massive black hole growth. The AGN and SB relative contributions to the total output in these objects is still debated. Our aim is to disentangle the AGN and SB emission of a sample of thirteen HLIRG. We have studied the MIR low resolution spectra of a sample of thirteen HLIRG obtained with the IRS on board Spitzer. The 5-8 μm range is an optimal window to detect AGN activity even in a heavily obscured environment. We performed a SB/AGN decomposition of the continuum using templates, successfully applied for ULIRG in previous works. The MIR spectra of all sources is largely dominated by AGN emission. Converting the 6 μm luminosity into IR luminosity, we found that ~80% of the sample shows an IR output dominated by the AGN emission. However, the SB activity is significant in all sources (mean SB contribution ~30%), showing star formation rates ~300-3000 solar masses per year. Using X-ray and MIR data we estimated the dust covering factor (CF) of these HLIRG, finding that a significant fraction presents a CF consistent with unity. Along with the high X-ray absorption shown by these sources, this suggests that large amounts of dust and gas enshroud the nucleus of these HLIRG, as also observed in ULIRG. Our results are in agreement with previous studies of the IR SED of HLIRG using radiative transfer models, and we find strong evidence that all HLIRG harbour an AGN. This work provides further support to the idea that AGN and SB are both crucial to understand the properties of HLIRG. Our study of the CF supports the hypothesis that HLIRG can be divided in two different populations.

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arXiv2012

The XMM deep survey in the CDF-S II. a 9-20 keV selection of heavily obscured active galaxies at z>1.7

We present results on a search of heavily obscured active galaxies z>1.7 using the rest-frame 9-20 keV excess for X-ray sources detected in the deep XMM-CDFS survey. Out of 176 sources selected with the conservative detection criteria (>8 sigma) in the first source catalogue of Ranalli et al., 46 objects lie in the redshift range of interest with the median redshift z~2.5. Their typical rest-frame 10-20 keV luminosity is 1e+44 erg/s, as observed. Among optically faint objects that lack spectroscopic redshift, four were found to be strongly absorbed X-ray sources, and the enhanced Fe K emission or absorption features in their X-ray spectra were used to obtain X-ray spectroscopic redshifts. Using the X-ray colour-colour diagram based on the rest-frame 3-5 keV, 5-9 keV, and 9-20 keV bands, seven objects were selected for their 9-20 keV excess and were found to be strongly absorbed X-ray sources with column density of nH > 0.6e+24 cm-2, including two possible Compton thick sources. While they are emitting at quasar luminosity, ~3/4 of the sample objects are found to be absorbed by nH > 1e+22 cm-2. A comparison with local AGN at the matched luminosity suggests an increasing trend of the absorbed source fraction for high-luminosity AGN towards high redshifts.

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arXiv2012

Using the Bright Ultra-Hard XMM-Newton Survey to define an IR selection of luminous AGN based on WISE colours

We present a highly complete and reliable mid-infrared (MIR) colour selection of luminous AGN candidates using the 3.4, 4.6, and 12 um bands of the WISE survey. The MIR colour wedge was defined using the wide-angle Bright Ultra-Hard XMM-Newton Survey (BUXS), one of the largest complete flux-limited samples of bright (f(4.5-10 keV)>6x10^{-14} erg cm^-2 s^-1) "ultra-hard" (4.5-10 keV) X-ray selected AGN to date. BUXS includes 258 objects detected over a total sky area of 44.43 deg^2 of which 251 are spectroscopically identified and classified, with 145 being type-1 AGN and 106 type-2 AGN. Our technique is designed to select objects with red MIR power-law spectral energy distributions (SED) in the three shortest bands of WISE and properly accounts for the errors in the photometry and deviations of the MIR SEDs from a pure power-law. The completeness of the MIR selection is a strong function of luminosity. At L(2-10 keV)>10^{44} erg s^-1, where the AGN is expected to dominate the MIR emission, 97.1_{-4.8}^{+2.2}% and 76.5_{-18.4}^{+13.3}% of the BUXS type-1 and type-2 AGN meet the selection. Our technique shows one of the highest reliability and efficiency of detection of the X-ray selected luminous AGN population with WISE amongst those in the literature. In the area covered by the BUXS survey our selection identifies 2755 AGN candidates detected with SNR>5 in the three shorter wavelength bands of WISE with 38.5% having a detection at 2-10 keV X-ray energies. We also analyzed the possibility of including the 22um WISE band to select AGN candidates, but neither the completeness nor the reliability of the selection improves. This is likely due to both the significantly shallower depth at 22um compared with the first three bands of WISE and star-formation contributing to the 22um emission at the WISE 22um sensitivity.

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arXiv2012

Exploring X-ray and radio emission of type 1 AGN up to z ~ 2.3

X-ray emission from AGN is dominated by the accretion disk around a SMBH. The radio luminosity, however, has not such a clear origin except in the most powerful sources where jets are evident. The origin (and even the very existence) of the local bi-modal distribution in radioloudness is also a debated issue. By analysing X-ray, optical and radio properties of a large sample of type 1 AGN up to z>2, where the bulk of this population resides, we aim to explore the interplay between radio and X-ray emission in AGN, in order to further our knowledge on the origin of radio emission, and its relation to accretion. We analyse a large (~800 sources) sample of type 1 AGN and QSOs selected from the 2XMMi X-ray source catalogue, cross-correlated with the SDSS DR7 spectroscopic catalogue, covering a redshift range from z~0.3 to z~2.3. SMBH masses are estimated from the Mg II emission line, bolometric luminosities from the X-ray data, and radio emission or upper limits from the FIRST catalogue. Most of the sources accrete close to the Eddington limit and the distribution in radioloudness does not appear to have a bi-modal behaviour. We confirm that radioloud AGN are also X-ray loud, with an X-ray-to-optical ratio up to twice that of radioquiet objects, even excluding the most extreme strongly jetted sources. By analysing complementary radio-selected control samples, we find evidence that these conclusions are not an effect of the X-ray selection, but are likely a property of the dominant QSO population. Our findings are best interpreted in a context where radio emission in AGN, with the exception of a minority of beamed sources, arises from very close to the accretion disk and is therefore heavily linked to X-ray emission. We also speculate that the RL/RQ dichotomy might either be an evolutionary effect that developed well after the QSO peak epoch, or an effect of incompleteness in small samples.

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arXiv2012

GOODS-Herschel: Ultra-deep XMM-Newton observations reveal AGN/star-formation connection

Models of galaxy evolution assume some connection between the AGN and star formation activity in galaxies. We use the multi-wavelength information of the CDFS to assess this issue. We select the AGNs from the 3Ms XMM-Newton survey and measure the star-formation rates of their hosts using data that probe rest-frame wavelengths longward of 20 um. Star-formation rates are obtained from spectral energy distribution fits, identifying and subtracting an AGN component. We divide the star-formation rates by the stellar masses of the hosts to derive specific star-formation rates (sSFR) and find evidence for a positive correlation between the AGN activity (proxied by the X-ray luminosity) and the sSFR for the most active systems with X-ray luminosities exceeding Lx=10^43 erg/s and redshifts z~1. We do not find evidence for such a correlation for lower luminosity systems or those at lower redshifts. We do not find any correlation between the SFR (or the sSFR) and the X-ray absorption derived from high-quality XMM-Newton spectra either, showing that the absorption is likely to be linked to the nuclear region rather than the host, while the star-formation is not nuclear. Comparing the sSFR of the hosts to the characteristic sSFR of star-forming galaxies at the same redshift we find that the AGNs reside mostly in main-sequence and starburst hosts, reflecting the AGN - sSFR connection. Limiting our analysis to the highest X-ray luminosity AGNs (X-ray QSOs with Lx>10^44 erg/s), we find that the highest-redshift QSOs (with z>2) reside predominantly in starburst hosts, with an average sSFR more than double that of the "main sequence", and we find a few cases of QSOs at z~1.5 with specific star-formation rates compatible with the main-sequence, or even in the "quiescent" region. (abridged)

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arXiv2012

The X-ray luminous galaxies optically classified as star forming are mostly narrow line Seyfert 1s

We aim to characterize the nature of galaxies whose optical emission line diagnostics are consistent with star formation, but whose X-ray properties strongly point towards the presence of an AGN. Understanding these sources is of particular importance in assessing the completeness of AGN samples derived from large galaxy surveys, selected solely on the basis of their optical spectral properties.We construct a large sample of 211 NELGs, which have FWHMs Hb emission line <1200 km/s from the SDSS-DR7 galaxy spectroscopic catalogue, for which we are able to construct a classical diagnostic diagram, [OIII]/Hb versus [NII]/Ha (hence z<0.4), and that are also detected in the hard energy band and present in the 2XMM catalogue. This sample offers a large database by which to investigate potential mismatches between optical diagnostics and X-ray emission. Among these 211 objects, which based on our selection criteria are all at z<0.4, we find that 145 galaxies are diagnosed as AGNs, having 2-10 keV X-ray luminosities that span a wide range, from 10^40 erg/s to above 10^44 erg/s. Out of the remaining 66 galaxies, which are instead diagnosed as SF, we find a bimodal distribution in which 28 have X-ray luminosities in excess of 10^42 erg/s, large T (>1), and large X/O ratio (>0.1), while the rest are consistent with being simply SF galaxies. Those 28 galaxies exhibit the broadest Hb line FWHMs, from ~300 to 1200 km/s, and their X-ray spectrum is steeper than average and often displays a soft excess. We therefore conclude that the population of X-ray luminous NELGs with optical lines consistent with those of a starforming galaxy (which represent 19% of our whole sample) is largely dominated by NLS1s. The occurrence of such sources in the overall optically selected sample is small (<2%), hence the contamination of optically selected galaxies by NLS1s is very small.

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arXiv2012

Mining the Herschel-ATLAS: submillimeter-selected blazars in equatorial fields

The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) provides an unprecedented opportunity to search for blazars at sub-mm wavelengths. We cross-matched the FIRST radio source catalogue with the 11655 sources brighter than 35 mJy at 500μm in the \sim 135 square degrees of the sky covered by the H-ATLAS equatorial fields at 9 h and 15 h, plus half of the field at 12 h. We found that 379 of the H-ATLAS sources have a FIRST counterpart within 10 arcsec, including 8 catalogued blazars (plus one known blazar that was found at the edge of one the H-ATLAS maps). To search for additional blazar candidates we have devised new diagnostic diagrams and found that known blazars occupy a region of the log(S500μm/S350μm) vs. log(S500μm/S1.4GHz) plane separated from that of the other sub-mm sources with radio counterparts. Using this diagnostic we have selected 12 further candidates that turn out to be scattered in the (r-z) vs. (u-r) plane or in the WISE colour-colour diagram proposed by Massaro et al. (2012), where known blazars are concentrated in well defined strips. This suggests that the majority of them either are not blazars or have spectral energy distributions contaminated by their host galaxies. A significant fraction of true blazars are found to be hosted by star-forming galaxies. This finding, supported by an analysis of blazars detected in Planck 545 and 857 GHz bands, is at odds with the notion that blazar hosts are passive ellipticals and indicates that the sub-mm selection is providing a novel prospect on blazar properties. Based on an inspection of the available photometric data, including the WISE all-sky survey, the unpublished VIKING survey and new radio observations, we tentatively estimate that there are 11 blazars with synchrotron flux density S500μm > 35mJy over the considered area. This result already allows us to constrain blazar evolution models.

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arXiv2012

Herschel-ATLAS: Planck sources in the Phase 1 fields

We present the results of a cross-correlation of the Planck Early Release Compact Source Catalog (ERCSC) with the catalog of Herschel-ATLAS sources detected in the Phase 1 fields, covering 134.55 deg2. There are 28 ERCSC sources detected by Planck at 857 GHz in this area. As many as 16 of them are probably high Galactic latitude cirrus; 10 additional sources can be clearly identified as bright, low-z galaxies; one further source is resolved by Herschel as two relatively bright sources; and the last is resolved into an unusual condensation of low-flux, probably high-redshift point sources, around a strongly lensed Herschel-ATLAS source at z = 3.26. Our results demonstrate that the higher sensitivity and higher angular resolution H-ATLAS maps provide essential information for the interpretation of candidate sources extracted from Planck sub-mm maps.

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arXiv2011

Averaging the AGN X-ray spectra from deep Chandra fields

The X-ray spectra of Active Galactic Nuclei (AGN) carry the signatures of the emission from the central region, close to the Super Massive Black Hole (SMBH). For this reason, the study of deep X-ray spectra is a powerful instrument to investigate the origin of their emission. The emission line most often observed in the X-ray spectra of AGN is Fe K. It is known that it can be broadened and deformed by relativistic effects if emitted close enough to the central SMBH. In recent statistical studies of the X-ray spectra of AGN samples, it is found that a narrow Fe line is ubiquitous, while whether the broad features are as common is still uncertain. We present here the results of an investigation on the characteristics of the Fe line in the average X-ray spectra of AGN in deep Chandra fields. The average spectrum of the AGN is computed using Chandra spectra with more than 200 net counts from the AEGIS, Chandra Deep Field North and Chandra Deep Field South surveys. The sample spans a broader range of X-ray luminosities than other samples studied with stacking methods up to z=3.5. We analyze the average spectra of this sample using our own averaging method, checking the results against extensive simulations. Subsamples defined in terms of column density of the local absorber, luminosity and z are also investigated. We found a very significant Fe line with a narrow profile in all our samples and in almost all the subsamples that we constructed. The equivalent width (EW) of the narrow line estimated in the average spectrum of the full sample is 74 eV. The broad line component is significantly detected in the subsample of AGN with L<1.43 1E44 cgs and z<0.76, with EW=108 eV. We concluded that the narrow Fe line is an ubiquitous feature of the X-ray spectra of the AGN up to z=3.5.The broad line component is significant in the X-ray spectra of the AGN with low luminosity and low z.

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arXiv2011

The nature of X-ray absorbed QSOs

There exists a significant population of broad line, z~2 QSOs which have heavily absorbed X-ray spectra. Follow up observations in the submillimetre show that these QSOs are embedded in ultraluminous starburst galaxies, unlike most unabsorbed QSOs at the same redshifts and luminosities. Here we present X-ray spectra from XMM-Newton for a sample of 5 such X-ray absorbed QSOs that have been detected at submillimetre wavelengths. We also present spectra in the restframe ultraviolet from ground based telescopes. All 5 QSOs are found to exhibit strong C IV absorption lines in their ultraviolet spectra with equivalent width > 5 Angstroms. The X-ray spectra are inconsistent with the hypothesis that these objects show normal QSO continua absorbed by low-ionization gas. Instead, the spectra can be modelled successfully with ionized absorbers, or with cold absorbers if they posess unusually flat X-ray continuum shapes and unusual optical to X-ray spectral energy distributions. We show that the ionized absorber model provides the simplest, most self-consistent explanation for their observed properties. We estimate that the fraction of radiated power that is converted into kinetic luminosity of the outflowing winds is typically ~4 per cent, in agreement with recent estimates for the kinetic feedback from QSOs required to produce the M - sigma relation, and consistent with the hypothesis that the X-ray absorbed QSOs represent the transition phase between obscured accretion and the luminous QSO phase in the evolution of massive galaxies.

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arXiv2011

The X-ray spectral properties of the AGN population in the XMM-Newton bright serendipitous survey

We present here a detailed X-ray spectral analysis of the AGN belonging to the XMM-Newton bright survey (XBS) that comprises more than 300 AGN up to redshift ~ 2.4. We performed an X-ray analysis following two different approaches: by analyzing individually each AGN X-ray spectrum and by constructing average spectra for different AGN types. From the individual analysis, we find that there seems to be an anti correlation between the spectral index and the sources' hard X-ray luminosity, such that the average photon index for the higher luminosity sources (> 10E44 erg/s) is significantly flatter than the average for the lower luminosity sources. We also find that the intrinsic column density distribution agrees with AGN unified schemes, although a number of exceptions are found (3% of the whole sample), which are much more common among optically classified type 2 AGN. We also find that the so-called "soft-excess", apart from the intrinsic absorption, constitutes the principal deviation from a power-law shape in AGN X-ray spectra and it clearly displays different characteristics, and likely a different origin, for unabsorbed and absorbed AGN. Regarding the shape of the average spectra, we find that it is best reproduced by a combination of an unabsorbed (absorbed) power law, a narrow Fe Kalpha emission line and a small (large) amount of reflection for unabsorbed (absorbed) sources. We do not significantly detect any relativistic contribution to the line emission and we compute an upper limit for its equivalent width (EW) of 230 eV at the 3 sigma confidence level. Finally, by dividing the type 1 AGN sample into high- and low-luminosity sources, we marginally detect a decrease in the narrow Fe Kalpha line EW and in the amount of reflection as the luminosity increases, the "so-called" Iwasawa-Taniguchi effect.

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arXiv2011

The XMM Deep survey in the CDFS I. First results on heavily obscured AGN

We present the first results of the spectroscopy of distant, obscured AGN as obtained with the ultra-deep (~3.3 Ms) XMM-Newton survey in the Chandra Deep Field South (CDFS). One of the primary goals of the project is to characterize the X-ray spectral properties of obscured and heavily obscured Compton-thick AGN over the range of redhifts and luminosities that are relevant in terms of their contribution to the X-ray background. The ultra-deep exposure, coupled with the XMM detector's spectral throughput, allowed us to accumulate good quality X-ray spectra for a large number of X-ray sources and, in particular, for heavily obscured AGN at cosmological redshifts. Specifically we present the X-ray spectral properties of two high-redshift - z= 1.53 and z=3.70 - sources. The XMM spectra of both are very hard, with a strong iron Kalpha line at a rest-frame energy of 6.4 keV. A reflection-dominated continuum provides the best description of the X-ray spectrum of the z=1.53 source, while the intrinsic continuum of the z=3.70 AGN is obscured by a large column N_H ~ 10^24 cm-2 of cold gas. Compton-thick absorption, or close to it, is unambiguously detected in both sources. Interestingly, these sources would not be selected as candidate Compton thick AGN by some multiwavelength selection criteria based on the mid-infrared to optical and X-ray to optical flux ratios.

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arXiv2011

A strongly starforming group: three massive galaxies associated with a QSO

We present here photometric redshift confirmation of the presence of large scale structure around the z=1.82 QSO RXJ0941, which shows an overdensity of submm sources. Radio imaging confirms the presence of the submm sources and pinpoints their likely optical-NIR counterparts. Four of the five submm sources present in this field (including the QSO) have counterparts with redshifts compatible with z=1.82. We show that our photometric redshifts are robust against the use of different spectral templates. We have measured the galaxy stellar mass of the submm galaxies from their rest-frame K-band luminosity obtaining log(M*/Msun)~11.5+-0.2, slightly larger than the Schechter mass of present day galaxies, and hence indicating that most of the stellar mass is already formed. We present optical-to-radio spectral energy distributions (SEDs) of the five SCUBA sources. The emission of RXJ0941 is dominated by reprocessed AGN emission in the observed MIR range, while the starburst contribution completely dominates in the submm range. The SEDs of the other three counterparts are compatible with a dominant starburst contribution above ~24um, with star formation rates SFR~2000Msun/yr, central dust masses log(Mdust/Msun)~9+-0.5 and hence central gas masses log(Mgas/Msun)~10.7. There is very little room for an AGN contribution. From X-ray upper limits and the observed 24um flux, we derive a maximum 2-10keV X-ray luminosity of 1e44 erg/s for any putative AGN, even if they are heavily obscured. This in turn points to relatively small black holes with log(MBH/Msun)<~8 and hence stellar-to-black hole mass ratios about one order of magnitude higher than those observed in the present Universe: most of their central black hole masses are still to be accreted. Local stellar-to-black hole masses ratios can be reached if ~1.3% of the available nuclear gas mass is accreted.

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arXiv2010

On the arcmin structure of the X-ray Universe

We present the angular correlation function of the X-ray population of 1063 XMM-Newton observations at high Galactic latitudes, comprising up to ~30000 sources over a sky area of ~125 sq. degrees in the energy bands: soft (0.5-2 keV) and hard (2-10 keV). This is the largest sample of serendipitous X-ray sources ever used for clustering analysis purposes to date and the results have been determined with unprecedented accuracy. We detect significant clustering signals in the soft and hard bands (~10 sigma and ~5 sigma, respectively). We deproject the angular correlation function via Limber's equation and calculate the typical spatial lengths. We infer that AGN at redshifts ~1 are embedded in dark matter halos with typical masses of log M ~ 12.6/h Msol and lifetimes in the range ~3-5 x 10^8 years, which indicates that AGN activity is a transient phase in the life of galaxies.

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arXiv2010

An excess of star-forming galaxies in the fields of high-redshift QSOs

We present submillimetre and mid-infrared imaging observations of five fields centred on quasi-stellar objects (QSOs) at 1.7<z<2.8. All 5 QSOs were detected previously at submillimetre wavelengths. At 850 (450) um we detect 17 (11) submillimetre galaxies (SMGs) in addition to the QSOs. The total area mapped at 850 um is ~28 arcmin^2 down to RMS noise levels of 1-2 mJy/beam, depending on the field. Integral number counts are computed from the 850 um data using the same analytical techniques adopted by `blank-field' submillimetre surveys. We find that the `QSO-field' counts show a clear excess over the blank-field counts at deboosted flux densities of 2-4 mJy; at higher flux densities the counts are consistent with the blank-field counts. Robust mid-infrared counterparts are identified for all four submillimetre detected QSOs and ~60 per cent of the SMGs. The mid-infrared colours of the QSOs are similar to those of the local ULIRG/AGN Mrk 231 if placed at 1<z<3 whilst most of the SMGs have colours very similar to those of the local ULIRG Arp 220 at 1<z<3. Mid-infrared diagnostics therefore find no strong evidence that the SMGs host buried AGN although we cannot rule out such a possibility. Taken together our results suggest that the QSOs sit in regions of the early universe which are undergoing an enhanced level of major star-formation activity, and should evolve to become similarly dense regions containing massive galaxies at the present epoch. Finally, we find evidence that the level of star-formation activity in individual galaxies appears to be lower around the QSOs than it is around more powerful radio-loud AGN at higher redshifts.

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arXiv2010

Spectral Energy Distribution of Hyper-Luminous Infrared Galaxies

The relationship between star formation and super-massive black hole growth is central to our understanding of galaxy formation and evolution. Hyper-Luminous Infrared Galaxies (HLIRGs) are unique laboratories to investigate the connection between starburst (SB) and Active Galactic Nuclei (AGN), since they exhibit extreme star formation rates, and most of them show evidence of harbouring powerful AGN. Our previous X-ray study of a sample of 14 HLIRGs shows that the X-ray emission of most HLIRGs is dominated by AGN activity. To improve our estimate of the relative contribution of the AGN and SB emission to its total bolometric output, we have built broad band spectral energy distributions (SEDs) for these HLIRGs, and we have fitted empirical AGN and SB templates to these SEDs. In broad terms, most sources are well fitted using this method, and we found AGN and SB contributions similar to those obtained by previous studies of HLIRGs. We have classified the HLIRGs SEDs in two groups, named class A and class B. Class A HLIRGs show a flat SED from the optical to the infrared energy range. Three out of seven class A sources can be modelled with a pure luminosity-dependent QSO template, while the rest of them require a type 1 AGN template and a SB template. The SB component is dominant in three out of four class A objects. Class B HLIRGs show SEDs with a prominent and broad IR bump. These sources can not trivially be modelled with a combination of pure AGN and pure SB, they require templates of composite objects, suggesting that >50% of their emission comes from stellar formation processes. We propose that our sample is actually composed by three different populations: very luminous QSO, young galaxies going through their maximal star formation period and the high luminosity tail of ULIRG population distribution.

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arXiv2010

A revision of the X-ray absorption nature of the BALQSOs

Broad absorption line quasars (BALQSOs) are key objects for studying the structure and emission/absorption properties of AGN. However, despite their fundamental importance, the properties of BALQSOs are still not well understood. In order to investigate the X-ray nature of these sources, as well as the correlations between X-ray and rest-frame UV properties, we compile a large sample of 88 BALQSOs observed by XMM-Newton. We performed a full X-ray spectral analysis on a sample of 39 sources with higher X-ray spectral quality, and an approximate HR analysis on the remaining sources. Using available optical spectra, we calculate the BALnicity index and investigate the dependence between this optical parameter and different X-ray properties. Using the neutral absorption model, we found that 36% of our BALQSOs have NH < 5x10^21 cm^-2, lower than the expected X-ray absorption for such objects. However, when we used a physically-motivated model for the X-ray absorption in BALQSOs, i.e. ionized absorption, \sim 90% of the objects are absorbed. The absorption properties also suggest that LoBALs may be physically different objects from HiBALs. In addition, we report on a correlation between the ionized absorption column density and BAL parameters. There is evidence (at 98% level) that the amount of X-ray absorption is correlated with the strength of high-ionization UV absorption. This correlation, not previously reported, can be naturally understood in virtually all BALQSO models, as driven by the total amount of gas mass flowing towards the observer.

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