arXiv subjects

Ezequiel Treister

Publications and source records attributed to Ezequiel Treister.

154 records · Page 9Linked to original sources

arXiv2006

The Extended Chandra Deep Field-South Survey: X-ray Point-Source Catalog

The Extended Chandra Deep Field-South (ECDFS) survey consists of 4 Chandra ACIS-I pointings and covers $\approx$ 1100 square arcminutes ($\approx$ 0.3 deg$^2$) centered on the original CDF-S field to a depth of approximately 228 ks. This is the largest Chandra survey ever conducted at such depth, and only one XMM-Newton survey reaches a lower flux limit in the hard 2.0--8.0 keV band. We detect 651 unique sources -- 587 using a conservative source detection threshold and 64 using a lower source detection threshold. These are presented as two separate catalogs. Of the 651 total sources, 561 are detected in the full 0.5--8.0 keV band, 529 in the soft 0.5--2.0 keV band, and 335 in the hard 2.0--8.0 keV band. For point sources near the aim point, the limiting fluxes are approximately $1.7 \times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ and $3.9 \times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ in the 0.5--2.0 keV and 2.0--8.0 keV bands, respectively. Using simulations, we determine the catalog completeness as a function of flux and assess uncertainties in the derived fluxes due to incomplete spectral information. We present the differential and cumulative flux distributions, which are in good agreement with the number counts from previous deep X-ray surveys and with the predictions from an AGN population synthesis model that can explain the X-ray background. In general, fainter sources have harder X-ray spectra, consistent with the hypothesis that these sources are mainly obscured AGN.

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arXiv2005

Spitzer Number Counts of AGN in the GOODS fields

We present mid-infrared observations of AGN in the GOODS fields, performed with the Spitzer Space Telescope. These are the deepest infrared and X-ray fields to date and cover a total area of ~0.1 square degrees. AGN are selected on the basis of their hard (2-8 keV) X-ray emission. The median AGN infrared luminosity is at least 10 times larger than the median for normal galaxies with the same redshift distribution, suggesting that the infrared emission is dominated by the central nucleus. The X-ray to infrared luminosity ratios of GOODS AGN, most of which are at 0.5<z<1.5, are similar to the values obtained for AGN in the local Universe. The observed infrared flux distribution has an integral slope of ~1.5 and there are 1000 sources per square degree brighter than ~50 uJy at 3-6 microns. The counts approximately match the predictions of models based on AGN unification, in which the majority of AGN are obscured. This agreement confirms that the faintest X-ray sources, which are dominated by the host galaxy light in the optical, are obscured AGN. Using these Spitzer data, the AGN contribution to the extragalactic infrared background light is calculated by correlating the X-ray and infrared catalogues. This is likely to be a lower limit given that the most obscured AGN are missed in X-rays. We estimate the contribution of AGN missed in X-rays, using a population synthesis model, to be ~45% of the observed AGN contribution, making the AGN contribution to the infrared background at most ~2-10% in the 3-24 micron range, depending on wavelength, lower than most previous estimates. The AGN contribution to the infrared background remains roughly constant with source flux in the IRAC bands but decreases with decreasing flux in the MIPS 24 um band, where the galaxy population becomes more important.

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arXiv2005

Obscured and Unobscured AGN Evolution and the X-ray background

The Great Observatories Origins Deep Survey (GOODS) combines deep HST and Spitzer imaging with the deepest Chandra/XMM observations to probe obscured AGN at higher redshifts than previous multiwavelength surveys. We present a self-consistent implementation of the AGN unification paradigm, which postulates obscured AGN wherever there are unobscured AGN, to successfully explain the infrared, optical, and X-ray number counts of X-ray sources detected in the GOODS fields. Assuming either a constant ratio of obscured to unobscured AGN of 3:1 (the local value), or a ratio that decreases with luminosity, and including Compton-thick sources, we can explain the spectral shape and normalization of the extragalactic X-ray "background" as a superposition of unresolved AGN, predominantly at z~0.5-1.5 and L_x~10^43-10^44 ergs/s. The possible dependence of the obscured to unobscured ratio with redshift is not well constrained; present data allow it to decrease or increase substantially beyond z~1.

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arXiv2005

The Extended Chandra Deep Field-South Survey: Optical Properties of X-ray Detected Sources

The Extended Chandra Deep Field-South (E-CDF-S) survey consists of 4 Chandra ACIS-I pointings and covers ~1100 square arcminutes (~0.3 deg^2) centered on the original CDF-S field to a depth of approximately 228 ks (PI: Niel Brandt; Lehmer et al, 2005). This is the largest Chandra survey ever conducted at such depth. In our analysis (Virani et al, 2005), we detect 651 unique sources -- 587 using a conservative source detection limit and 64 using a lower source detection limit. Of these 651 sources, 561 are detected in the full 0.5--8.0 keV band, 529 in the soft 0.5--2.0 keV band, and 335 in the hard 2.0--8.0 keV band. For point sources near the aim point, the limiting fluxes are approximately $1.7 \times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ and $3.9 \times 10^{-16}$ $\rm{erg cm^{-2} s^{-1}}$ in the 0.5--2.0 keV and 2.0--8.0 keV bands, respectively. We present the optical properties of these X-ray sources, specifically the R-band magnitude distribution and a preliminary spectroscopic redshift distribution. One exciting result is the discovery of 7 new Extreme X-ray-to-Optical flux ratio objects (EXOs) found in the E-CDF-S field.

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arXiv2005

AGN Unification and the X-ray Background

Active Galactic Nuclei (AGN) unification, which implies a large number of obscured AGN, can explain the optical, infrared and X-ray content of deep multiwavelength surveys. Here, we show that the same model also successfully explains the spectral shape and intensity of the X-ray background. The simplest possible unified model assumes a constant ratio of obscured to unobscured AGN, independent of redshift or luminosity. With almost no free parameters, the predicted X-ray background agrees remarkably well with observations. Both the observed properties of deep AGN samples and the X-ray background can be explained by the same model without invoking different evolution for obscured and unobscured AGN. Recent observational evidence shows that the ratio of obscured to unobscured AGN may depend on luminosity. An AGN unification model that allows for such a dependence also fits the X-ray background spectrum, and the predicted numbers counts in the 2-10 keV X-ray band are in good agreement with observations. We present predictions for the source counts in hard X-rays (10-100 keV), which indicate that future missions like the Black Hole Finder will observe thousands of heavily obscured AGN.

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arXiv2005

Infrared Properties of AGN in the GOODS Fields: AGN in Stellar Dominated High-z Galaxies

We present analysis of spectral energy distributions (SEDs) from mid-infrared through X-ray of a sample of 420 hard X-ray selected, z-band and Spitzer/IRAC detected active galactic nuclei (AGN) and AGN candidates from the GOODS multiwavelength survey. We fit local empirical SED templates of both normal and active galaxies to the rest-frame luminosities calculated from spectroscopic (where available) and photometric redshifts. The majority of the optically stellar-dominated (with early-type galaxy fits) sources are moderately luminous (L_X,2-10 keV ~ 10^43 erg/s) hard X-ray sources with high X-ray hardness ratios (HR > 0.2), high MIR luminosities and red MIR colors in excess of a typical stellar dominated elliptical galaxy. These sources likely harbor heavily obscured (though Compton-thin) AGN. The observed ratio of obscured to unobscured AGN has an integrated mean of ~3.4:1 but declines with increasing redshift. This effect has been explained by Treister et al. (2004) as an observational bias triggered by the lack of spectroscopic redshifts at R > 24 which are predominantly higher redshift obscured sources.

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arXiv2004

Obscured AGN in Multiwavelength Surveys

Using a simple unification model for AGN, with a fixed ratio of obscured to unobscured AGN of 3:1, we explain the X-ray, optical and infrared properties of the X-ray sources in the GOODS fields. That is, the GOODS data are consistent with the existence of a large population of obscured AGN out to high redshifts. About half of these are so obscured that they are missed even by hard X-ray observations, and are detected only in deep infrared observations. The previously reported decreasing trend of obscured to total AGN ratio with increasing X-ray luminosity can be explained entirely as a selection effect.

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arXiv2004

The Calan-Yale Deep Extragalactic Research (CYDER) Survey: Optical Properties and Deep Spectroscopy of Serendipitous X-ray Sources

We present the first results from the Calán-Yale Deep Extragalactic Research (CYDER) survey. The main goal of this survey is to study serendipitous X-ray sources detected by Chandra in an intermediate flux range ($10^{-15}-10^{-12}$ ergs s$^{-1}$) that comprises most of the X-ray background. 267 X-ray sources spread over 5 archived fields were detected. The $\log N-\log S$ distribution obtained for this sample is consistent with the results of other surveys. Deep $V$ and $I$ images were taken of these fields in order to calculate X-ray-to-optical flux ratios. Identifications and redshifts were obtained for 106 sources using optical spectroscopy from 8-m class telescopes to reach the optically faintest sources, to the same level as deeper X-ray fields like the Chandra Deep Fields, showing that the nature of sources detected depends mostly on the optical limit for spectroscopy. In general, sources optically classified as obscured Active Galactic Nuclei (AGNs) have redder optical colors than unobscured AGN. A rough correlation between $f_X/f_{\rm opt}$ and hard X-ray luminosity was found for obscured AGN confirming the prediction by existing models that in obscured AGN the optical light is completely dominated by the host galaxy. The previously claimed decrease of the obscured to unobscured AGN ratio with increasing X-ray luminosity is observed. However, this correlation can be explained as a selection effect caused by the lower optical flux of obscured AGN. Comparison between the observed $N_H$ distribution and predictions by existing models shows that the sample appears complete up to $N_H<3\times 10^{22}$ cm$^{-2}$, while for more obscured sources incompleteness plays an important role in the observed obscured to unobscured AGN ratio.

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arXiv2003

An X-ray Selected AGN at z=4.6 Discovered by the CYDER Survey

We present the discovery of a high redshift, X-ray selected AGN by the Calan-Yale Deep Extragalactic Research (CYDER) survey: CXOCY J033716.7-050153, located at $z=4.61$, the second high redshift AGN discovered by this survey. Here, we present its optical, near-IR and X-ray properties and compare it with other optical and X-ray selected high redshift AGN. The optical luminosity of this object is significantly lower than most optically selected high redshift quasars. It also has a lower rest frame UV to X-ray emission ratio than most known quasars at this redshift. This mild deviation can be explained either by dust obscuring the UV radiation of a normal radio quiet AGN emitting at 10% of its Eddington luminosity or because this is intrinsically a low luminosity radio loud AGN, with a super-massive Black Hole of $\sim 10^8M_\sun$ emitting at 1% of its Eddington luminosity. Deep radio observations can discriminate between these two hypotheses.

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arXiv2002

Properties of Low Surface Brightness Galaxies and Normal Spirals in the Near-IR

(Abridged) We present results for J and Ks near-IR imaging data on a large sample of 88 galaxies drawn from the catalogue of Impey et al. (1996). The near-IR data unveils many features of LSBGs not seen before in the optical. First, a high fraction of the observed LSBGs are very luminous in the near-IR, indicating that they have a well developed old stellar population, and that older LSBGs are more frequent in the universe than data from optical bands suggested. Second, the near-IR morphologies are often quite different than seen in the optical. Third, we find significant trends between the near-IR morphologies of the galaxies and their ratio of HI mass to near-IR luminosity. Fourth, we find no trend in disk surface brightness with absolute magnitude, but significant correlations when the bulge surface brightness is used. Finally, we find that the formation of a bulge requires a galaxy to have a total baryonic mass above ~ 10**10 Msun. A wide variety of other correlations are explored for the sample. The strongest of our correlations are with the ratio of HI mass to total baryonic mass, MHI/Mbaryonic, which tracks the evolutionary state of the galaxies as they convert gas into stars, and which ranges from 0.05 up to nearly 1 for the galaxies in our sample. We see also trends between MHI/Mbaryonic and central surface density, suggesting that increased star formation efficiency with increasing gas surface density strongly drives the conversion of gas into stars.

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