arXiv subjects

E. Hatziminaoglou

Publications and source records attributed to E. Hatziminaoglou.

At least 91 records · Page 5Linked to original sources

arXiv2009

Resolved Dust Emission in a Quasar at z=3.65

We present submillimetre observations of the z=3.653 quasar SDSS160705+533558 together with data in the optical and infrared. The object is unusually bright in the far-IR and submm with an IR luminosity of ~10^14 L_sun. We ascribe this luminosity to a combination of AGN and starburst emission, with the starburst forming stars at a rate of a few thousand solar masses per year. Submillimetre Array (SMA) imaging observations with a resolution ~1" show that the submm (850 micron) emission is extended on scales of 10--35kpc and is offset from the optical position by ~10 kpc. This morphology is dissimilar to that found in submm galaxies, which are generally un- or marginally resolved on arcsecond scales, or submm-luminous AGN where the AGN lies at the peak of the submm or molecular emission. The simplest explanation is that the object is in the early stages of a merger between a gas rich galaxy, which hosts the starburst, and a gas-poor AGN-host galaxy, which is responsible for the quasar emission. It is also possible that jet induced star formation might contribute to the unusual morphology.

astro-ph.CO↗

arXiv2009

A Deep XMM-Newton Serendipitous Survey of a middle-latitude area. II. New deeper X-ray and optical observations

The radio-quiet neutron star 1E1207.4-5209 has been the target of several XMM-Newton observations, with a total exposure of ~350 ks. The source is located at intermediate galactic latitude (b~10 degrees), i.e. in a sky region with an extremely interesting mix of both galactic and extra-galactic X-ray sources. The aim of our work is to investigate the properties of both the intermediate-latitude galactic and extra-galactic X-ray source populations in the 1E1207.4-5209 field. We performed a coherent analysis of the whole XMM-Newton observation data set to build a catalogue of serendipitous X-ray sources detected with high confidence and to derive information on the source flux, spectra, and time variability. In addition, we performed a complete multi-band (UBVRI) optical coverage of the field with the Wide Field Imager (WFI) of the ESO/MPG 2.2m telescope (La Silla) to search for candidate optical counterparts to the X-ray sources, down to a V-band limiting magnitude of ~24.5. We detected a total of 144 serendipitous X-ray sources. Thanks to the refined X-ray positions and to the WFI observations, we found candidate optical counterparts for most of the X-ray sources in our compilation. For most of the brightest ones we proposed a likely classification based on both the X-ray spectra and the optical colours. Our results indicate that at intermediate galactic latitude the X-ray source population is dominated by the extra-galactic component, but with a significant contribution from the galactic component in the soft energy band, below 2 keV.

astro-ph.HE↗

arXiv2009

A multi-wavelength survey of AGN in the XMM-LSS field: I. Quasar selection via the KX technique

AIMS: We present a sample of candidate quasars selected using the KX-technique. The data cover 0.68 deg^2 of the X-ray Multi-Mirror (XMM) Large-Scale Structure (LSS) survey area where overlapping multi-wavelength imaging data permits an investigation of the physical nature of selected sources. METHODS: The KX method identifies quasars on the basis of their optical (R and z') to near-infrared (Ks) photometry and point-like morphology. We combine these data with optical (u*,g'r',i',z') and mid-infrared (3.6-24 micron) wavebands to reconstruct the spectral energy distributions (SEDs) of candidate quasars. RESULTS: Of 93 sources selected as candidate quasars by the KX method, 25 are classified as quasars by the subsequent SED analysis. Spectroscopic observations are available for 12/25 of these sources and confirm the quasar hypothesis in each case. Even more, 90% of the SED-classified quasars show X-ray emission, a property not shared by any of the false candidates in the KX-selected sample. Applying a photometric redshift analysis to the sources without spectroscopy indicates that the 25 sources classified as quasars occupy the interval 0.7 < z < 2.5. The remaining 68/93 sources are classified as stars and unresolved galaxies.

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arXiv2009

Mid-infrared spectroscopy of infrared-luminous galaxies at z~0.5-3

We present results on low-resolution mid-infrared (MIR) spectra of 70 infrared-luminous galaxies obtained with the Infrared Spectrograph (IRS) onboard Spitzer. We selected sources from the European Large Area Infrared Survey (ELAIS) with S15 > 0.8 mJy and photometric or spectroscopic z > 1. About half of the sample are QSOs in the optical, while the remaining sources are galaxies, comprising both obscured AGN and starbursts. We classify the spectra using well-known infrared diagnostics, as well as a new one that we propose, into three types of source: those dominated by an unobscured AGN (QSOs), obscured AGN, and starburst-dominated sources. Starbursts concentrate at z ~ 0.6-1.0 favored by the shift of the 7.7-micron PAH band into the selection 15 micron band, while AGN spread over the 0.5 < z < 3.1 range. Star formation rates (SFR) are estimated for individual sources from the luminosity of the PAH features. An estimate of the average PAH luminosity in QSOs and obscured AGN is obtained from the composite spectrum of all sources with reliable redshifts. The estimated mean SFR in the QSOs is 50-100 Mo yr^-1, but the implied FIR luminosity is 3-10 times lower than that obtained from stacking analysis of the FIR photometry, suggesting destruction of the PAH carriers by energetic photons from the AGN. The SFR estimated in obscured AGN is 2-3 times higher than in QSOs of similar MIR luminosity. This discrepancy might not be due to luminosity effects or selection bias alone, but could instead indicate a connection between obscuration and star formation. However, the observed correlation between silicate absorption and the slope of the near- to mid-infrared spectrum is compatible with the obscuration of the AGN emission in these sources being produced in a dust torus.

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arXiv2008

Properties of dusty tori in AGN: I. The Case of SWIRE/SDSS Quasars

We derive the properties of dusty tori in Active Galactic Nuclei (AGN) from the comparison of observed Spectral Energy Distributions (SEDs) of SDSS quasars and a precomputed grid of torus models. The observed SEDs comprise SDSS photometry, 2MASS J, H, and K data, whenever available and mid-Infrared (MIR) data from the Spitzer Wide-area InfraRed Extragalactic (SWIRE) Survey. The adopted model is that of Fritz et al., 2006. The fit is performed by standard chi^2 minimisation, the model however can be multi-component comprising a stellar and a starburst components, whenever necessary. Models with low equatorial optical depth, tau_9.7, were allowed as well as ``traditional'' models with tau_9.7 > 1.0, corresponding to A_V > 22 and the results were compared. Fits using high optical depth tori models only produced dust more compactly distributed than in the configuration where all tau_9.7 models were permitted. Tori with decreasing dust density with the distance from the centre were favoured while there was no clear preference for models with or without angular variation of the dust density. The computed outer radii of the tori are of some tens of parsecs large but can reach, in a few cases, a few hundreds of parsecs. The mass of dust, M_Dust, and infrared luminosity, L_IR, integrated in the wavelength range between 1 and 1000 micron, do not show significant variations with redshift, once the observational biases are taken into account. Objects with 70 micron detections, representing 25% of the sample, are studied separately and the starburst contribution (whenever present) to the IR luminosity can reach, in the most extreme but very few cases, 80%.

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arXiv2007

The VVDS type-1 AGN sample: The faint end of the luminosity function

In a previous paper (Gavignaud et al. 2006), we presented the type-1 Active Galactic Nuclei (AGN) sample obtained from the first epoch data of the VIMOS-VLT Deep Survey (VVDS). The sample consists of 130 faint, broad-line AGN with redshift up to z=5 and 17.5< I <24.0, selected on the basis of their spectra. In this paper we present the measurement of the Optical Luminosity Function up to z=3.6 derived from this sample, we compare our results with previous results from brighter samples both at low and at high redshift. Our data, more than one magnitude fainter than previous optical surveys, allow us to constrain the faint part of the luminosity function up to high redshift. By combining our faint VVDS sample with the large sample of bright AGN extracted from the SDSS DR3 (Richards et al., 2006b) and testing a number of different evolutionary models, we find that the model which better represents the combined luminosity functions, over a wide range of redshift and luminosity, is a luminosity dependent density evolution (LDDE) model, similar to those derived from the major X-surveys. Such a parameterization allows the redshift of the AGN space density peak to change as a function of luminosity and explains the excess of faint AGN that we find at 1.0< z <1.5. On the basis of this model we find, for the first time from the analysis of optically selected samples, that the peak of the AGN space density shifts significantly towards lower redshift going to lower luminosity objects. This result, already found in a number of X-ray selected samples of AGN, is consistent with a scenario of "AGN cosmic downsizing", in which the density of more luminous AGN, possibly associated to more massive black holes, peaks earlier in the history of the Universe, than that of low luminosity ones.

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arXiv2006

A 15um selected sample of high-z starbursts and AGNs

We report results from a Spitzer GO-1 program of IRS spectroscopy of a large sample of Luminous Infrared Galaxies and quasars selected from the European Large Area ISO Survey (ELAIS) which have a wide multiwavelength coverage, including ISOCAM, ISOPHOT, IRAC and MIPS (from SWIRE), and optical photometry. We present the sample selection and results from the IRS spectroscopy.

astro-ph↗

arXiv2006

XMM-Newton and ESO observations of the two unidentified gamma-ray sources 3EG J0616-3310 and 3EG J1249-8330

The limited angular resolution of gamma-ray telescopes prevents a direct identification of the majority of sources detected so far. This is particularly true for the low latitude, probably galactic, ones only 10 % of which has been identified. Most counterparts of the identified low-latitude gamma-ray sources are Isolated Neutron Stars (INS), both radio-loud and radio-quiet (Geminga-like) objects, which are characterised by an extremely high value of the X-ray-to-optical flux ratio f_X/f_opt. Therefore, the systematic X-ray and optical coverage of low-latitude unidentified gamma-ray sources aiming at high f_X/f_opt sources seems one of the most promising ways to spot INS candidate counterparts. Since low latitude sources are heavily affected by the interstellar absorption at both X-ray and optical wavelengths, we have focussed on two middle-latitude, probably galactic, GRO/EGRET sources: 3EG J0616-3310 and 3EG J1249-8330. These two sources, which could belong to a local galactic population, have been selected owing to their relatively good positional accuracy, spectral shape and lack of candidate extragalactic radio counterparts. Here we report on X-ray observations of the two gamma-ray error boxes performed with XMM-Newton and on their optical follow-up carried on with the Wide Field Imager at the ESO/MPG 2.2m telescope. Less than half of the ~300 sources detected by the X-ray coverage have no optical counterparts. Among those, we have selected few interesting sources with f_X/f_opt > 100, which we consider promising INS candidates.

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arXiv2006

XMM and Chandra measurements of the AGN intrinsic absorption: dependence on luminosity and redshift

We combine bright XMM data with the Chandra Deep Field South observations in order to explore the behavior of the intrinsic AGN absorption, as a function of redshift and luminosity.Our sample consists of 359 sources selected in the hard 2-8 keV band, spanning the flux range 6\times10^{-16}-$3\times10^{-13} erg s^-1 cm^-2 with a high rate of spectroscopic or photometric redshift completeness (100 and 85 per cent respectively for the Chandra and XMM data. We derive the column density values using X-ray spectral fits. We find that the fraction of obscured AGN falls with increasing luminosity in agreement with previous findings. The fraction of obscured AGN shows an apparent increase at high redshifts (z>2). Simulations show that this effect can be most probably attributed to the fact that at high redshifts the column densities are overestimated.

astro-ph↗

arXiv2006

Luminosity functions for galaxies and quasars in the Spitzer Wide-Area Infrared Extra-galactic (SWIRE) Legacy survey

We construct rest-frame luminosity functions at 3.6, 4.5, 5.8, 8 and 24 microns over the redshift range 0<z<2 for galaxies and 0<z<4 for optical QSOs, using optical and infrared data from the Spitzer Wide-area InfraRed Extragalactic survey. The 3.6 and 4.5 micron galaxy LFs show evidence for moderate positive luminosity evolution up to z~1.5, consistent with the passive ageing of evolved stellar populations. Their comoving luminosity density was found to evolve passively, gradually increasing out to z~0.5-1 but flattening, or even declining, at higher redshift. Conversely, the 24 micron galaxy LF, which is more sensitive to obscured star formation and/or AGN activity, undergoes strong positive evolution, with the derived IR energy density and SFR density proportional to (1+z)^gamma with gamma=4.5^{+0.7}_{-0.6} and the majority of this evolution occurring since z~1. Optical QSOs, however, show positive luminosity evolution in all bands, out to the highest redshifts (3<z<4). Modelling as L* proportional to (1+z)^gamma gave gamma=1.3^{+0.1}_{-0.1} at 3.6 micron, gamma=1.0^{+0.1}_{-0.1} at 4.5 micron and stronger evolution at the longer wavelengths (5.8, 8 and 24 micron), of gamma~3. Comparison of the galaxy LFs to predictions from a semi-analytic model based on CDM indicate that an IMF skewed towards higher mass star formation in bursts compared to locally is preferred. As a result the currently inferred massive star formation rates in distant sub-mm sources may require substantial downwards revision.

astro-ph↗

arXiv2006

Infrared Constraints on AGN Tori Models

This work focuses on the properties of dusty tori in active galactic nuclei (AGN) derived from the comparison of SDSS type 1 quasars with mid-Infrared (MIR) counterparts and a new, detailed torus model. The infrared data were taken by the Spitzer Wide-area InfraRed Extragalactic (SWIRE) Survey. Basic model parameters are constraint, such as the density law of the graphite and silicate grains, the torus size and its opening angle. A whole variety of optical depths is supported. The favoured models are those with decreasing density with distance from the centre, while there is no clear tendency as to the covering factor, ie small, medium and large covering factors are almost equally distributed. Based on the models that better describe the observed SEDs, properties such as the accretion luminosity, the mass of dust, the inner to outer radius ratio and the hydrogen column density are computed.

astro-ph↗

arXiv2006

Cosmic evolution of the galaxy mass and luminosity functions by morphological type from multi-wavelength data in the CDF-South

We constrain the evolution of the galaxy mass and luminosity functions from the analysis of (public) multi-wavelength data in the Chandra Deep Field South (CDFS) area, obtained from the GOODS and other projects, and including very deep high-resolution imaging by HST/ACS. Our reference catalogue of faint high-redshift galaxies, which we have thoroughly tested for completeness and reliability, comes from a deep (S(3.6micron)>1 microJy) image by IRAC on the Spitzer Observatory. These imaging data in the field are complemented with extensive optical spectroscopy by the ESO VLT/FORS2 and VIMOS spectrographs, while deep K-band VLT/ISAAC imaging is also used to derive further complementary statistical constraints and to assist the source identification and SED analysis. We have selected a highly reliable IRAC 3.6micron sub-sample of 1478 galaxies with S(3.6)>10microJy, 47% of which have spectroscopic redshift, while for the remaining objects both COMBO-17 and Hyperz are used to estimate the photometric redshift. This very extensive dataset is exploited to assess evolutionary effects in the galaxy luminosity and stellar mass functions, while luminosity/density evolution is further constrained with the number counts and redshift distributions. The deep ACS imaging allows us to differentiate these evolutionary paths by morphological type, which our simulations show to be reliable at least up to z=1.5 for the two main early- (E/S0) and late-type (Sp/Irr) classes. These data, as well as our direct estimate of the stellar mass function above M=10^(10)M_sun for the spheroidal subclass, consistently evidence a progressive dearth of such objects to occur starting at z=0.7, paralleled by an increase in luminosity. (abridged)

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arXiv2005

Revisiting the Infrared Spectra of Active Galactic Nuclei with a New Torus Emission Model

We describe improved modelling of the emission by dust in a toroidal--like structure heated by a central illuminating source within Active Galactic Nuclei (AGN). We chose a simple but realistic torus geometry, a flared disc, and a dust grain distribution function including a full range of grain sizes. The optical depth within the torus is computed in detail taking into account the different sublimation temperatures of the silicate and graphite grains, which solves previously reported inconsistencies in the silicate emission feature in type-1 AGN. We exploit this model to study the spectral energy distributions (SEDs) of 58 extragalactic (both type-1 and type-2) sources using archival optical and infrared (IR) data. We find that both AGN and starburst contributions are often required to reproduce the observed SEDs, although in a few cases they are very well fitted by a pure AGN component. The AGN contribution to the far-IR luminosity is found to be higher in type-1 sources, with all the type-2 requiring a substantial contribution from a circum-nuclear starburst. Our results appear in agreement with the AGN Unified Scheme, since the distributions of key parameters of the torus models turn out to be compatible for type-1 and type-2 AGN. Further support to the unification concept comes from comparison with medium-resolution IR spectra of type-1 AGN by the Spitzer observatory, showing evidence for a moderate silicate emission around 10 \mums which our code reproduces. From our analysis we infer accretion flows in the inner nucleus of local AGN characterized by high equatorial optical depths ($A_V\simeq 100$), moderate sizes ($R_{max}<100 pc$) and very high covering factors ($f\simeq 80$ per cent) on average.

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arXiv2005

Remarkable Disk and Off-nuclear Starburst Activity in the "Tadpole Galaxy" as revealed by the Spitzer Space Telescope

We present ground-based optical and Spitzer infrared imaging observations of the interacting galaxy UGC 10214, the "Tadpole Galaxy" (z = 0.0310), focusing on the star formation activity in the nuclear, disk, spiral arms and tidal tail regions. The major findings of this study are that the Tadpole is actively forming stars in the main disk outside of the nucleus and in the tidal plume, with an estimated mean star formation rate of ~2 to 4 M_sun/yr. The most prominent sites of mid-infrared emission define a "ring" morphology that, combined with the overall morphology of the system, suggest the interaction may belong to the rare class of off-center collisional ring systems that form both shock-induced rings of star formation and tidal plumes. The nuclear emission is solely powered by older stars, with little evidence for ongoing star formation at the center of the Tadpole. Extra-nuclear star formation accounts for >50% of the total star formation in the disk and spiral arms, featuring infrared-bright 'hot spots' that exhibit strong PAH emission, whose band strength is comparable to that of late-type star-forming disk galaxies. The tidal tail, which extends 2 arcmin (~75 kpc) into the intergalactic medium, is populated by super massive star clusters likely triggered by the galaxy-galaxy interaction that has distorted UGC 10214 into its current "tadpole" shape.

astro-ph↗

arXiv2005

Morphological Studies of the SWIRE Galaxy Population in the UGC 10214 HST/ACS field

We present results of a morphological analysis of a small subset of the Spitzer Wide-area InfraRed Extragalactic survey (SWIRE) galaxy population. The analysis is based on public ACS data taken inside the SWIRE N1 field, which are the deepest optical high-resolution imaging available within the SWIRE fields as of today. Our reference sample includes 156 galaxies detected by both ACS and SWIRE. Among the various galaxy morphologies, we disentangle two main classes, spheroids (or bulge-dominated galaxies) and disk-dominated ones, for which we compute the number counts as a function of flux. We then limit our sample to objects with IRAC fluxes brighter than 10 microJy, estimated ~90% completeness limit of the SWIRE catalogues, and compare the observed counts to model predictions. We find that the observed counts of the spheroidal population agree with the expectations of a hierarchical model while a monolithic scenario predicts steeper counts. Both scenaria, however, under-predict the number of late-type galaxies. These observations show that the large majority (close to 80 per cent) of the 3.6 and 4.5 micron galaxy population, even at these moderately faint fluxes, is dominated by spiral and irregular galaxies or mergers.

astro-ph↗

arXiv2005

Star counts in the Galaxy. Simulating from very deep to very shallow photometric surveys with the TRILEGAL code

We describe TRILEGAL, a new populations synthesis code for simulating the stellar photometry of any Galaxy field. The code attempts to improve upon several technical aspects of star count models, by: dealing with very complete input libraries of evolutionary tracks; using a stellar spectral library to simulate the photometry in any broad-band system; being very versatile allowing easy changes in the input libraries and in the description of all of its ingredients -- like the SFR, AMR, IMF, and geometry of Galaxy components. In a previous paper (Groenewegen et al. 2002), the code was first applied to describe the very deep star counts of the CDFS stellar catalogue. Here, we briefly describe its initial calibration using EIS-deep and DMS star counts, which are adequate samples to probe both the halo and the disc components of largest scale heights (oldest ages). We then present the changes in the calibration that were necessary to cope with some improvements in the model input data, and the use of more extensive photometry datasets: the relatively shallower 2MASS catalogue, which probes mostly the disc at intermediate ages, and the immediate solar neighbourhood as sampled by Hipparcos, which contains a somewhat larger fraction of younger stars than deeper surveys. Remarkably, the same model calibration can reproduce well the star counts in all the above-mentioned data sets, that span from the very deep magnitudes of CDFS (16<R<23) to the very shallow ones of Hipparcos (V<8). Significant deviations are found just for fields close to the Galactic Center and Plane, and for a single set of South Galactic Pole data. The TRILEGAL code is ready to use for the variety of wide-angle surveys in the optical/infrared that will become available in the coming years.

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arXiv2004

Complete Multiwavelength Characterization of Faint Chandra X-ray Sources Seen in the Spitzer Wide-Area IR Extragalactic (SWIRE) Survey

We exploit deep combined observations with Spitzer and Chandra of the SWIRE survey in the ELAIS-N1 region, to investigate the nature of the faint X-ray and IR sources in common, to identify AGN/starburst diagnostics, and to study the sources of the X-ray and IR cosmic backgrounds. In the 17'x17' area of the Chandra ACIS-I image there are 3400 SWIRE near-IR sources with 4 sigma detections in at least 2 IRAC bands and 988 sources detected at 24micron with MIPS brighter than 0.1 mJy. Of these, 102 IRAC and 59 MIPS sources have Chandra counterparts, out of a total of 122 X-ray sources present in the area with S(0.5-8 kev)>10^(-15) erg/cm^2/s. We have constructed SEDs for each source using data from the 4 IRAC wavebands, Chandra fluxes, and optical follow-up data in the wavebands U, g', r', i', Z, and H. We fit a number of spectral templates to the SEDs at optical and infrared wavelengths to determine photometric redshifts and spectral categories, and also make use of diagnostics based on the X-ray luminosities, hardness ratios, X-ray to infrared spectral slopes and optical morphologies. Although we have spectroscopic redshifts for only a minority of the Chandra sources, the available SEDs constrain the redshifts for most of the sample sources, which turn out to be typically at 0.5<z<2. We find that 39% of the Chandra sources are dominated by type-1 AGN emission, 23% display optical/IR spectra typical of type-2 AGNs, while the remaining 38% fraction show starburst-like or even normal galaxy spectra. Since we prove that all these galaxies are dominated by AGN emission in X-rays this brings the fraction of type-1 AGNs to be 80% of the type-2: even assuming that all the Chandra sources undetected by Spitzer are type-2 AGNs, the type-1 fraction would exceed 1/3 of the total population (abridged).

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arXiv2004

On the use of photometric redshifts for X-ray selected AGNs

(Abridged) In this paper we present photometric redshift estimates for a sample of X-ray selected sources detected in the wide field (~2 deg^2), bright [f_{X} (0.5-8 keV)~10^{-14} cgs] XMM-Newton/2dF survey. Unlike deeper X-ray samples comprising a large fraction of sources with colours dominated by the host galaxy, our bright survey primarily probes the QSO X-ray population. Therefore photometric redshift methods employing both galaxy and QSO templates need to be used. We employ the photometric redshift technique of Hatziminaoglou, Mathez & Pello (2000) using 5-band photometry from the SDSS. We separate our X-ray sources according to their optical profile to point-like and extended. We apply QSO and galaxy templates to the point-like and extended sources respectively. X-ray sources associated with Galactic stars are identified and discarded from our point-like sample on the basis of their low X-ray--to--optical flux ratio and their broad band colours that are best fit by stellar templates. Comparison of our results with spectroscopic redshifts available, allows calibration of our method and estimation of the photometric redshift accuracy. For ~70 per cent of the point-like sources photometric redshifts are correct within dz <= 0.3 (or ~75 per cent have dz/(1+z) <= 0.2), and the rms scatter is estimated to be sigma_z = 0.30. For the optically extended objects the photometric redshifts work only in the case of red (g - r > 0.5 mag) sources yielding dz <= 0.15 and dz/(1+z) <= 0.2 for 73 and 93 per cent respectively. However, we find that the above photometric redshift technique does not work in the case of extended sources with blue colours (g - r < 0.5): such sources cannot be fit successfully by QSO or galaxy templates, or any linear combination of the two.

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