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Propriétés statistiques des AGN de faibles luminositées

Abstract : In the recent years, majors surveys have been collecting several ten thousands of QSO spectra, demonstrating the high efficiency of optical color pre-selection techniques and providing a new level of statistics in describing the properties of the QSO population. The drawback of these pre-selection techniques is that some subset of the underlying QSO population may be under-represented in these survey thereby possibly biasing our current understanding.

This ph D thesis is devoted to the study of the properties of the faint population of type-1 AGN. For this purpose we use a spectroscopic sample of 130 broad line AGN, extracted from a large galaxy survey, the VIRMOS VLT Deep Survey (VVDS). This AGN sample present two-major interests: (1) a selection function free of pre-selection biases, which enables us to census the population of optical type-1 AGN from redshift 0 to 5 in a coherent way; (2) a very faint limiting magnitude (respectively Iab=22.5 and Iab=24 for the wide and deep sample) that was previously reached for catalogs of this size only by photometric studies.

Our measured surface density (~472+/-48 BLAGN per square degree with Iab <= 24) is significantly higher than that of any other optically selected sample of BLAGN with spectroscopic confirmation.

Because of the contamination of the AGN light by their host galaxy at the faint magnitude explored by our sample, we observe that a significant fraction of AGN in our sample would be missed by the usual UV excess and morphological criteria used for the pre-selection of optical QSO candidates. This contamination is as well seen in our composite spectrum. We observe an extension of the anti-correlation between luminosity and equivalent-width of high-ionization emission-lines to the fainter luminosities probed by our sample for a given redshift (Baldwin effect).

The luminosity function derived from this sample shows a relatively steep faint end at low redshift (11.5). This behavior fit into the picture of an anti-hierarchical growth of galactic black holes, as it was first suggested by X-ray selected AGN studies.

Preliminary results on the black hole mass estimates of our objects suggest that most of faint optical AGN are triggered by intermediate-mass galactic black-holes (~100 million of solar mass) accreting at relatively low Eddington rates (~< 10%).
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Submitted on : Thursday, January 11, 2007 - 10:25:29 AM
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  • HAL Id : tel-00123824, version 1



Isabelle Gavignaud. Propriétés statistiques des AGN de faibles luminositées. Physique [physics]. Université Paul Sabatier - Toulouse III, 2006. Français. ⟨tel-00123824⟩



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