Arp 299: a second merging system with two active nuclei?

Recent BeppoSAX observations of Arp 299, a powerful far-IR merging starburst system composed of IC 694 and NGC 3690, clearly unveiled for the first time in this system the presence of a strongly absorbed active galactic nucleus (AGN). However the system was not spatially resolved by BeppoSAX. Here we present the analysis of archival Chandra and (for the first time) XMM-Newton observations, which allow us to disentangle the X-ray emission of the two galaxies. The detection of a strong 6.4 keV line in NGC 3690 clearly demonstrates the existence of an AGN in this galaxy, while the presence of a strong 6.7 keV Fe-Kalpha line in the spectrum of IC 694 suggests that also this nucleus might harbor an AGN. This would be the second discovery of two AGNs in a merging system after NGC 6240

X-ray redshifts with the International X-ray Observatory (IXO)

7 páginas, 4 figuras, 1 tabla.-- El pdf del artículo es la versión pre-print.We explore the capabilities of the future space science mission IXO (International X-ray Observatory) for obtaining cosmological redshifts of distant Active Galactic Nuclei (AGNs) using the X-ray data only. We first find in which regions of the X-ray luminosity (LX) versus redshift (z) plane the weak but ubiquitous Fe Ka narrow emission line can deliver an accurate redshift (dz < 5%) as a function of exposure time, using a CCD-based Wide Field Imager (IXO/WFI) as the one baselined for IXO. Down to a 2–10 keV X-ray flux of 10-14 erg cm-2 s-1 IXO/WFI exposures of 100 ks, 300 ks and 1Ms will deliver 20%, 40% and 60% of the redshifts. This means that in a typical 18' - 18' IXO/WFI field of view, 4, 10 and 25 redshifts will be obtained for free from the X-ray data alone, spanning a wide range up to z - 2–3 and fairly sampling the real distribution. Measuring redshifts of fainter sources will indeed need spectroscopy at other wavebands.We acknowledge partial financial support from the Spanish Ministerio de Ciencia e Innovación project AYA2009-08059. N. Castelló thanks the Spanish Ministerio de Ciencia e Innovación for a pre-doctoral fellowship.Peer reviewe

X-ray properties of a sample of NLS1 selected from the SDSS

Galaxy surveys have revealed the existence of Narrow Emission Line Galaxies (NELG) which are spectroscopically classified as starforming (SF), but whose X-ray luminosity exceeds 1042 erg s?1 which unambiguously signals the presence of an AGN. The origin for such a discrepancy is not understood. In order to addres this issue, we present a study using a large sample of 239 NELG (FWHM(H? ) < 1200 km/s) from the SDSS, for which we can construct the BPT diagram and that are detected in the hard (2?10 keV) X-ray band within the 2XMM X-ray source catalogue. We find that 33 of these objects are diagnosed as starforming galaxies but their X-ray luminosity exceeds 1042 erg s?1 . We conducted a detailed analysis of this population, using other optical spectral features,like the FWHM of the H? emission line and the X-ray spectral properties. We find that the bulk of this misclassified population, which represents over 10% of our full sample of hard X-ray detected NELGs, is constituted by NLS1 galaxies.Partial financial support for this work was provided by the spanish Ministry of Science and Innovation, through grant AYA2009-08059

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

[Context]: The optical and ultraviolet emission lines of galaxies are widely used to distinguish star-forming (SF) galaxies from active galactic nuclei (AGNs). However, this type of diagnostic has some associated uncertainties, because AGNs can be of low luminosity and/or heavily obscured, and the optical emission lines may be dominated by a stellar component. On the other hand, and despite its limitations, X-ray emission can be used as a reliable tracer of luminous AGNs. Several well-studied examples exist where the optical diagnostics are indicative of SF galaxy, but the X-ray properties reveal the presence of an AGN. [Aims]: 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. [Methods]: We construct a large sample of 211 narrow emission line galaxies (NELGs, which have full widths at half maximum (FWHMs) H β emission line star-forming>, we find a bimodal distribution in which 28 have X-ray luminosities in excess of 10 42 erg/s, large thickness parameters (T = F 2-10 keV/F [OIII] > 1) and large X-ray to optical flux ratios (X/O > 0.1), while the rest are consistent with being simply starforming galaxies. Those 28 galaxies exhibit the broadest H β line widths (FWHMs from ~300 to 1200 km s -1), and their X-ray spectrum is steeper than average and often displays a soft excess. [Conclusions]: 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 narrow line Seyfert 1s (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. © ESO, 2012.N. Castelló-Mor gratefully acknowledges the Spanish Ministerio de Ciencia e Innovación for a pre-doctoral fellowship. N.C.-M., X.B., L.B., and F.J.C. acknowledge partial financial support from the Spanish Ministerio de Ciencia e Innovación, through project AYA2010-21490-C02-01.Peer Reviewe

X-ray redshifts with the International X-ray Observatory (IXO)

7 páginas, 4 figuras, 1 tabla.-- El pdf del artículo es la versión pre-print.We explore the capabilities of the future space science mission IXO (International X-ray Observatory) for obtaining cosmological redshifts of distant Active Galactic Nuclei (AGNs) using the X-ray data only. We first find in which regions of the X-ray luminosity (LX) versus redshift (z) plane the weak but ubiquitous Fe Ka narrow emission line can deliver an accurate redshift (dz < 5%) as a function of exposure time, using a CCD-based Wide Field Imager (IXO/WFI) as the one baselined for IXO. Down to a 2–10 keV X-ray flux of 10-14 erg cm-2 s-1 IXO/WFI exposures of 100 ks, 300 ks and 1Ms will deliver 20%, 40% and 60% of the redshifts. This means that in a typical 18' - 18' IXO/WFI field of view, 4, 10 and 25 redshifts will be obtained for free from the X-ray data alone, spanning a wide range up to z - 2–3 and fairly sampling the real distribution. Measuring redshifts of fainter sources will indeed need spectroscopy at other wavebands.We acknowledge partial financial support from the Spanish Ministerio de Ciencia e Innovación project AYA2009-08059. N. Castelló thanks the Spanish Ministerio de Ciencia e Innovación for a pre-doctoral fellowship.Peer reviewe

Decoupling absorption and continuum variability in the Seyfert 2 NGC 4507

We present the results of the Suzaku observation of the Seyfert 2 galaxy NGC 4507. This source is one of the X-ray brightest Compton-thin Seyfert 2s and a candidate for a variable absorber. Suzaku caught NGC 4507 in a highly absorbed state characterized by a high column density (NH ~ 8 × 1023 cm-2), a strong reflected component (R ~ 1.9) and a high equivalent width FeKα emission line (EW ~ 500 eV). The FeKα emission line is unresolved at the resolution of the Suzaku CCDs [σ < 30 eV or full width at half-maximum (FWHM) < 3000 km s-1] and most likely originates in a distant absorber. The Fe Kβ emission line is also clearly detected and its intensity is marginally higher than the theoretical value for low ionization Fe. A comparison with previous observations performed with XMM-Newton and BeppoSAX reveals that the X-ray spectral curvature changes on a time-scale of a few months. We analysed all these historical observations, with standard models as well as with a most recent model for a toroidal reprocessor and found that the main driver of the observed 2-10 keV spectral variability is a change of the line-of-sight obscuration, varying from ~4 × 1023 to ~9 × 1023 cm-2. The primary continuum is also variable, although its photon index does not appear to vary, while the FeKα line and reflection component are consistent with being constant across the observations. This suggests the presence of a rather constant reprocessor and that the observed line-of-sight NH variability is either due to a certain degree of clumpiness of the putative torus or due to the presence of a second clumpy absorber. © 2012 The Authors.Peer Reviewe

XMM–Newton first X-ray detection of the low-ionization broad absorption line quasar PG 1700+518

7 páginas, 5 figuras, 2 tablas.-- El Pdf del artículo es la versión pre-print: arXiv:1104.2003v1We report the first high-energy detection of PG 1700+518, a well-known low-ionization broad absorption line quasar (quasi-stellar object, QSO). Due to previous X-ray non-detection, it was classified as soft X-ray weak QSO. We observed PG 1700+518 with XMM–Newton for about 60 ks divided in three exposures. The spectrum below 2 keV is very steep, Γ∼ 2.4–3.8, while at higher energies the extremely flat emission (photon index Γ∼ 0.15, when modelled with a power law) suggests the presence of strong absorption (NH, pl∼ 2 × 1023 cm−2, Γ fixed to 1.8) or a reflection-dominated continuum. The broad-band flux is consistent with previous non-detection. Simultaneous European Photon Imaging Camera (EPIC) and Optical Monitor (OM) data confirm its X-ray weakness (observedαox∼−2.2). The level of obscuration derived from the X-ray spectra of PG 1700+518 cannot explain its soft X-ray nuclear weakness unless a column density of NH≳ 2 × 1024 cm−2 is present.LB acknowledges support from the SpanishMinistry of Science and Innovation through a ‘Juan de la Cierva’ fellowship. Financial support for this work was provided by the Spanish Ministry of Science and Innovation, through research grant AYA2009-08059. Support from the Italian Space Agency is acknowledged by EP (contract ASI/INAF I/088/06/0) and CV (contracts I/088/06/0 and I/009/10/0).Peer reviewe

XMM–Newton first X-ray detection of the low-ionization broad absorption line quasar PG 1700+518

7 páginas, 5 figuras, 2 tablas.-- El Pdf del artículo es la versión pre-print: arXiv:1104.2003v1We report the first high-energy detection of PG 1700+518, a well-known low-ionization broad absorption line quasar (quasi-stellar object, QSO). Due to previous X-ray non-detection, it was classified as soft X-ray weak QSO. We observed PG 1700+518 with XMM–Newton for about 60 ks divided in three exposures. The spectrum below 2 keV is very steep, Γ∼ 2.4–3.8, while at higher energies the extremely flat emission (photon index Γ∼ 0.15, when modelled with a power law) suggests the presence of strong absorption (NH, pl∼ 2 × 1023 cm−2, Γ fixed to 1.8) or a reflection-dominated continuum. The broad-band flux is consistent with previous non-detection. Simultaneous European Photon Imaging Camera (EPIC) and Optical Monitor (OM) data confirm its X-ray weakness (observedαox∼−2.2). The level of obscuration derived from the X-ray spectra of PG 1700+518 cannot explain its soft X-ray nuclear weakness unless a column density of NH≳ 2 × 1024 cm−2 is present.LB acknowledges support from the SpanishMinistry of Science and Innovation through a ‘Juan de la Cierva’ fellowship. Financial support for this work was provided by the Spanish Ministry of Science and Innovation, through research grant AYA2009-08059. Support from the Italian Space Agency is acknowledged by EP (contract ASI/INAF I/088/06/0) and CV (contracts I/088/06/0 and I/009/10/0).Peer reviewe

Dust-to-gas ratio in a complete sample of type-1 AGN

Resumen del póster presentado al XIII Scientific Meeting of the Spanish Astronomical Society, celebrado en la Universidad de Salamanca del 16 al 20 de julio de 2018.According to the Unified Model of Active Galactic Nuclei (AGN), unobscured AGN based on its optical spectrum (detection of rest-frame UV-optical broad emission lines, type-1 AGN) should appear as X-ray unabsorbed AGN. However, there is an important fraction (10-30%) of AGN whose optical and X-ray classifications do not match, and the origin of the discrepancy is not clear. To provide insight into this topic, we have conducted a statistical analysis of the optical obscuration and X-ray absorption properties of the optically type1 AGN from the Bright Ultra-hard XMM-Newton Survey (BUXS) with L2−10keV >1042 erg s−1 and z=0.05-1. We have high-quality spectra from XMM-Newton and either SDSS spectra or proprietary observations for the selected sample. In order to provide the most complete sample as possible, we have conducted a detailed analysis of the emission lines to provide a reliable classification of the AGNs. We derive the X-ray absorption by fitting their XMM-Newton spectra and the optical extinction using UV/optical spectral continuum fits. As BUXS is a flux limited X-ray selected sample at hard energies (f4.510keV ≤6×10−14 ergs−1cm−2), it is complete for NH column densities up to the Compton-thick limit (∼1024cm−2). Our preliminary results show that most type-1 AGN in our sample show consistent optical and X-ray classification, but there is a large fraction ( 20%) of objects with large NH column densities (NH >4×1021 cm−2)

WISE colours and star formation in the host galaxies of radio-loud narrow-line Seyfert 1

We investigate the mid-infrared (mid-IR) properties of the largest (42 objects) sample of radio-loud narrow-line Seyfert 1 (RL NLS1) collected to date, using data from the Wide-field Infrared Survey Explorer. We analyse the mid-IR colours of these objects and compare them to what is expected from different combinations of AGN and galaxy templates. We find that, in general, the host galaxy emission gives an important contribution to the observed mid-IR flux in particular at the longest wavelengths (W3, at 12 μm, and W4, at 22 μm). In about half of the sources (22 objects), we observe a very red mid-IR colour (W4 - W3 > 2.5) that can be explained only using a starburst galaxy template (M82). Using the 22 μm luminosities, corrected for the AGN contribution, we have then estimated the star formation rate (SFR) for 20 of these 'red' RL NLS1, finding values ranging from 10 to 500M⊙ yr-1. For the RLNLS1 showing bluer colours, instead, we cannot exclude the presence of a star-forming (SF) host galaxy although, on average, we expect a lower SFR. Studying the radio (1.4 GHz) to mid-IR (22 μm) flux ratios of the RL NLS1 in the sample, we found that in ~10 objects the SF activity could represent the most important component also at radio frequencies, in addition (or in alternative) to the relativistic jet. We conclude that both the mid-IR and the radio emission of RL NLS1 are a mixture of different components, including the relativistic jet, the dusty torus and an intense SF activity.Part of this work was supported by the COST Action MP0905 ‘Black Holes in a Violent Universe’ and by the European Commission Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 267251 Astronomy Fellowships in Italy (AstroFIt). The authors acknowledge financial support from the Italian Ministry of Education, Universities and Research (PRIN2010-2011, grant no. 2010NHBSBE). Support from the Italian Space Agency is acknowledged by LB (contract ASI INAF NuSTAR I/037/12/0). SM acknowledges funding from the Spanish Ministry of Economy and Competitiveness under grant AYA2012-31447, which is partly funded by the FEDER programme. SM acknowledges financial support from the ARCHES project (7th Framework of the European Union, no. 313146).Peer Reviewe