This thesis presents and discusses an analysis of the multiwavelength obser- vations (from mid-infrared to X-rays) of the central 0.6 square degrees of the ELAIS-S1 field . It makes use of data from four great observatories: XMM-Newton selects a large sample of Active Galactic Nuclei (AGN), so disclosing the accretion processes onto super-massive black holes (SMBH), Chandra provides arcsec positions for the X-ray sources, ESO/VLT provides photometry, spectroscopy (redshift and source classification), and the Spitzer mid-infrared bands probe obscured AGNs and dusty star-forming galaxies. The main main goals of this survey are: 1) to obtain a complete census of accreting SMBHs population in the Universe, combining different selection methods, and 2) to study the AGN environment and compare it to that non accreting passive and star-forming galaxies. 1) Unobscured and moderately obscured AGNs are selected using hard X-ray data, while obscured AGNs can be selected using mid-infrared data. Once obtained AGN samples, the multiwavelength properties of X-ray and infrared selected AGNs have then be studied in detail. The first step was the identification of the X-ray sources’ counterparts. This allowed the generation of a multiwavelength AGN catalogue. Subsequently, we analyzed the optical spectroscopic properties of X-ray sources, determined the galaxy redshift, AGN classification and spectral parameters. Among the most interesting sources studied, there are those showing high F(2-10 keV)/F(R) ratios (X/O). These sources are very bright in the 2-10 keV energy band, and are usually faint in the optical band (R>23). Due to their faint optical flux most of these AGNs are missed in optical surveys. They are in any case difficult to identify spectroscopically with even 8 m class telescopes. The absence of an optical active nucleus suggests that they are obscured by dust and gas, and, given their bright hard X-ray emission, they are probably obscured QSOs. Spitzer mid-infrared data allowed us to identify AGNs even more obscured than the high X/O sources. These Spitzer selected AGNs shine in the mid-infrared but are faint even at X-ray wavelengths, implying extreme obscuring column densities of the order of 1024 cm−2 or higher. We studied the broad band optical-to-infrared spectral energy distribu- tions (SEDs) of the X-ray sources and compared these SEDs to the spectro- scopic classifications of their optical counterparts. We also used the multi- wavelenght catalogue to obtain reliable photometric redshifts of the X-ray sources without optical spectroscopy by comparing the observed SED to galaxy templates. 2) Nuclear activity may be linked to environment in which the galaxies are located. The survey contiguos area allows us addressing this topic. Do the X- ray sources reside in overdense regions with respect to non-acitve galaxies? We compared the X-ray sample against galaxies selected in the NIR and MIR, which are therefore biased towards red R-K colors. We found that the average overdensity populated by X-ray sources is similar to that populated by these infrared selected sources, in agreement with previous studies. This is not surprising, given the fact that red galaxies are known to reside already in dense environments.
Feruglio, C. (2008). The multiwavelength survey of the ELAIS-S1 field.
|Titolo:||The multiwavelength survey of the ELAIS-S1 field|
|Data di pubblicazione:||26-nov-2008|
|Anno Accademico:||A.A. 2005/2006|
|Settore Scientifico Disciplinare:||Settore FIS/05 - Astronomia e Astrofisica|
|Tipologia:||Tesi di dottorato|
|Citazione:||Feruglio, C. (2008). The multiwavelength survey of the ELAIS-S1 field.|
|Appare nelle tipologie:||07 - Tesi di dottorato|