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

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

Understanding the build-up of SMBH and Galaxies

Trabajo presentado a la Conferencia: Exploring the Hot and Energetic Universe: The first scientific conference dedicated to the Athena X-ray observatory; celebrada en Madrid (España) del 8 a 10 de septiembre de 2015.One of the main open questions in modern Astrophysics is understanding the coupled growth of supermassive black holes by accretion and their host galaxies via star formation, from their peak at redshifts z~ 1-4 to the present time. The generic scenario proposed involves an early phase of intense black hole growth that takes place behind large obscuring columns of inflowing dust and gas clouds. It is postulated that this is followed by a blow-out stage during which some form of AGN feedback controls the fate of the interstellar medium and hence, the evolution of the galaxy. X-rays are essential for testing this scenario as they uniquely probe AGN at both the early heavily obscured stage and the later blow-out phase. X-ray spectral analysis can identify the smoking gun evidence of heavily obscured black hole growth (e.g. intense iron Kalpha line). It therefore provides the most robust method for compiling clean samples of deeply shrouded AGN with well-defined selection functions and unbiased determinations of their intrinsic properties (accretion luminosity, obscuring column). X-rays are also the best window for studying in detail AGN feedback. This process ultimately originates in the innermost regions close to the supermassive black hole and is dominated, in terms of energy and mass flux, by highly ionised material that remains invisible at other wavelengths. The most important epoch for investigating the relation between AGN and galaxies is the redshift range z~1-4, when most black holes and stars we see in the present-day Universe were put in place. Unfortunately, exhaustive efforts with current high-energy telescopes only scrape the tip of the iceberg of the most obscured AGN population. Moreover, Xray studies of the incidence, nature and energetics of AGN feedback are limited to the local Universe. The Athena observatory will provide the technological leap required for a breakthrough in our understanding of AGN and galaxy evolution at the heyday of the Universe. The excellent survey capabilities of Athena/WFI (effective area, angular resolution, field of view) will allow to measure the incidence of feedback in the shape of warm absorbers and Ultra Fast Outflows among the general population of AGN, as well as to complete the census of black hole growth by detecting and characterising significant samples of the most heavily obscured (including Compton thick) AGN, to redshifts z~3-4. The outstanding spectral throughput and resolution of Athena/X-IFU will permit measuring the energetics of those outflows to assess their influence on their host galaxies. The demographics of the heavily obscured and outflowing populations relative to their hosts are fundamental for understanding how major black hole growth events relate to the build-up of galaxies.Peer Reviewe

The XMM deep survey in the CDF-S: IV. Compton-thick AGN candidates

The Chandra Deep Field is the region of the sky with the highest concentration of X-ray data available: 4 Ms of Chandra and 3 Ms of XMM-Newton data, allowing excellent quality spectra to be extracted even for faint sources. We took advantage of this to compile a sample of heavily obscured active galactic nuclei (AGN) using X-ray spectroscopy. We selected our sample among the 176 brightest XMM-Newton sources, searching for either flat X-ray spectra (Γ < 1.4 at the 90% confidence level) suggestive of a reflection dominated continuum or an absorption turn-over suggestive of a column density higher than ≈ 1024 cm-2. We found a sample of nine heavily-obscured sources satisfying the above criteria. Four of these show statistically significant FeKα lines with large equivalent widths (three out of four have equivalent widths consistent with 1 keV) suggesting that these are the most certain Compton-thick AGN candidates. Two of these sources are transmission dominated while the other two are most probably reflection dominated Compton-thick AGN. Although this sample of four sources is by no means statistically complete, it represents the best example of Compton-thick sources found at moderate-to-high redshift with three sources at z = 1.2–1.5 and one source at z = 3.7. Using Spitzer and Herschel observations, we estimate with good accuracy the X-ray to mid-IR (12 μm) luminosity ratio of our sources. These are well below the average AGN relation, independently suggesting that these four sources are heavily obscured.I.G. and A.C. acknowledge the Marie Curie fellowship FP7-PEOPLE-IEF-2008 Prop. 235285. We acknowledge financial contribution from the agreement ASI-INAF I/009/10/0. P.R. acknowledges the receipt of a fellowship (proposal no. P9-3493) from the Greek Secretariat of Research and Technology in the framework of the project “Support to postdoctoral researchers”. N.C. acknowledges financial support from the Della Riccia foundation. F.J.C. acknowledges partial financial support by the Spanish Ministry of Economy and Competitiveness through the grant AYA2010-21490-C02-01.Peer Reviewe

First Constraints from DAMIC-M on Sub-GeV Dark-Matter Particles Interacting with Electrons

We report constraints on sub-GeV dark matter particles interacting with electrons from the first underground operation of DAMIC-M detectors. The search is performed with an integrated exposure of 85.23 g days, and exploits the subelectron charge resolution and low level of dark current of DAMIC-M charge-coupled devices (CCDs). Dark-matter-induced ionization signals above the detector dark current are searched for in CCD pixels with charge up to 7e−. With this dataset we place limits on dark matter particles of mass between 0.53 and 1000  MeV/c2, excluding unexplored regions of parameter space in the mass ranges [1.6,1000]  MeV/c2 and [1.5,15.1]  MeV/c2 for ultralight and heavy mediator interactions, respectively

The DAMIC-M experiment: Status and first results

The DAMIC-M (DArk Matter In CCDs at Modane) experiment employs thick, fully depleted silicon charged-coupled devices (CCDs) to search for dark matter particles with a target exposure of 1 kg-year. A novel skipper readout implemented in the CCDs provides single electron resolution through multiple non-destructive measurements of the individual pixel charge, pushing the detection threshold to the eV-scale. DAMIC-M will advance by several orders of magnitude the exploration of the dark matter particle hypothesis, in particular of candidates pertaining to the so-called “hidden sector.” A prototype, the Low Background Chamber (LBC), with 20g of low background Skipper CCDs, has been recently installed at Laboratoire Souterrain de Modane and is currently taking data. We will report the status of the DAMIC-M experiment and first results obtained with LBC commissioning data

The XMM deep survey in the CDF-S VI. Obscured AGN selected as infrared power-law galaxies

Context. 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. Aims. Our main goal is to determine whether the revised IRAC criteria of Donley et al. (2012, ApJ, 748, 142; objects with an infrared (IR) power-law spectral shape), are effective at selecting X-ray type-2 AGN (i.e., absorbed NH > 1022 cm-2). Methods. 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. Results. We find 21/147 sources to be heavily absorbed but the uncertainties in their obscuring column densities do not allow us to confirm their Compton-Thick nature without resorting to additional criteria. Although IR power-law galaxies are less numerous in our sample than IR non-power-law galaxies (60 versus 87 respectively), we find that the fraction of absorbed (NHintr > 1022 cm-2) AGN is significantly higher (at about 3 sigma level) for IR-power-law sources (~2/3) than for those sources that do not meet this IR selection criteria (~1/2). This behaviour is particularly notable at low luminosities, but it appears to be present, although with a marginal significance, at all luminosities. Conclusions. 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

AGN samples, from the infrared to X-rays

Memoria presentada por Núria Castelló Mor para optar al título de Doctora por la Universidad de Cantabria.[ES]: En esta tesis doctoral hemos pretendido abordar el estudio de muestras de AGN, tanto a escala local como a distancias cosmológicas, con el objetivo de caracterizar los parámetros físicos esenciales en dichas galaxias activas y determinar así la naturaleza de las distintas muestras de núcleos activos que fueron seleccionadas en distintas bandas del espectro electromagnético. En la primera parte de esta tesis, que incluye los Capítulos 3 y 4, hemos seleccionado una muestra de galaxias activas mediante la obtención de cocientes de líneas de emisión en el óptico con la finalidad de caracterizar, por un lado, la naturaleza de las galaxias activas ópticamente clasificadas y, por otro lado, la de aquellas galaxias cuyos cocientes de líneas son consistentes con regiones de alta formación estelar, pero que por otro lado muestran inequívocamente la presencia de un AGN cuando se estudian en rayos X. Esta pesquisa concluye con el estudio de otro subgrupo de galaxias activas, las llamadas Seyfert 1 de líneas estrechas (NLS1, del inglés Narrow Line Seyfert 1). Estos objetos comparten algunas de las características espectrales en el óptico de los AGN de tipo 1, pero presentan líneas de Balmer más estrechas (FWHM<2000 km/s), además de una emisión muy intensa en Fe II y O I. En rayos X las NLS1 tienen propiedades que también las diferencian de los AGNs no oscurecidos, como un marcado exceso de emisión en rayos X blandos (0.5-2 keV) y variabilidad en escalas de tiempo muy cortas. Estas propiedades distintivas en rayos X se atribuyen principalmente a sus altos cocientes de Eddington (Lbol/LEdd ∼1-10) y a las bajas masas de sus agujeros negros con respecto a los de los AGNs de tipo 1 estándar (MBH ∼ 106−7M.). Las condiciones extremas en las que viven estos objetos pueden arrojar nuevas pistas sobre los parámetros fundamentales que dirigen la actividad nuclear. En la parte final de la tesis, Capítulo 5, hemos hecho uso del rango infrarrojo mediocercano. Debido a la reemisión en el infrarrojo de la radiación primaria del núcleo activo se deduce que una manera eficaz de detectar el mayor número posible de AGN oscurecidos es posiblemente con observaciones en el infrarrojo medio. En esta parte de la tesis hemos llevado a cabo un estudio sobre la eficiencia de selección de AGN absorbidos en el infrarrojo medio con respecto a una selección en los rayos X duros.[EN]: This dissertation begins with an introduction to the field of AGN and the methods that have been used to detect AGN focusing on type 2 Seyfert galaxies (Chapter 1). It is meant to provide background information on these objects and to convey the motivation for the research presented in this thesis. More detailed disquisitions on AGN can be found in the books by Robson (1996), Peterson (1997) and Osterbrock & Ferland (2006), as well as in Beckmann & Shrader (2012). This thesis work is based mainly on observations made with the XMM-Newton observatory, and complemented with data obtained at other optical and infrared facilities (Chapter 2). Chapter 3 starts with a study of a large sample of Narrow Emission Line Galaxies (NELGs) from the Sloan Digital Sky Survey (SDSS) with an X-ray counterpart detected by the XMM-Newton. The main goal for this inquiry is understanding the physical cause of why a fraction of galaxies exhibit optical line spectroscopy diagnostics compatible with star formation, yet have X-ray properties that are indicative of an AGN. It must relate to the demographics of AGN, black hole growth, and galaxy evolution. In contrast with previous works, the main finding of our work is that a NLS1 core can be identified in a large fraction of X-ray luminous galaxies but optically diagnosed as starforming, being ∼25% of hard X-ray-selected AGN. This work leads to study a population of NLS1 galaxies in order to achieve a comprehensive picture of this kind of galactic nuclei and to understand their role in the AGN framework. In Chapter 4, we have studied their broadband SED from optical to X-rays, to understand the lack of the soft-X-ray component, as well as the missing Fe II optical emission in a small fraction of NLS1. Chapter 5 is focused on the IRAC criteria of Donley et al. (2012) to evaluate the effectiveness on selecting type 2 AGN in the infrared. While absorbed AGN are rather elusive in surveys of distant galaxies (including those at X-ray energies), the midinfrared waveband has the advantage that the AGN’s primary emission is isotropically re-emitted in the mid-infrared. We found that the IR power-law method is efficient in finding X-ray-absorbed sources at any AGN luminosity. Finally, in Chapter 6, we conclude by summarizing our findings.Mi agradecimiento al programa de becas FPI del Ministerio, a través del cual este trabajo de investigación ha sido financiado en su mayor parte.Peer Reviewe

DAMIC-M experiment: Thick, silicon CCDs to search for light dark matter

On behalf of the DAMIC-M Collaboration.arXiv:2001.01476v1This report presents an overview of the unconventional use of charge-coupled devices (CCDs) to search for Dark Matter (DM). The DArk Matter in CCDs (DAMIC Experiment) employs the bulk silicon of thick, fully-depleted CCDs as a target for ionization signals produced by interations of particle dark matter from the galactic halo. The DAMIC collaboration has engaged in an extensive campaign of characterization efforts to understand the response of these CCDs to low-energy nuclear recoils and their unique capabilities, including the use of high spatial resolution for both the rejection and study of backgrounds. The preliminary results of DAMIC prove the performance of the detector, provide measurements of the background contamination and demonstrate the potentiality for DM searches, with only ~ 40 grams of detector mass. The next phase of the experiment, DAMIC-M (DArk Matter in CCDs at Modane), will consist of a kg-sized detector, implementing the most massive CCDs ever built. These CCDs will feature sub-electron noise and will be deployed in a low-radioactivity environment at the Laboratoire Souterrain de Modane in France.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