Abstract
We aim to illustrate the potentiality of the Advanced Large, Homogeneous Area, Medium-Band Redshift Astronomical (ALHAMBRA) survey to investigate the high redshift universe through the detection of quasi stellar objects (QSOs) at redshifts larger than 5. The search for z>5 QSOs candidates was done by fitting an extensive library of spectral energy distributions --including active and non-active galaxy templates as well as stars-- to the photometric database of the ALHAMBRA survey (composed of 20 optical medium-band plus the 3 broad-band JHKs filters). Our selection over ~1 square degree of ALHAMBRA data (~1/4 of the total area covered by the survey), combined with GTC/OSIRIS spectroscopy, has yielded the identification of an optically faint QSO at very high redshift (z = 5.41). The QSO has an absolute magnitude of ~-24 at the 1450{\AA} continuum, a bolometric luminosity of ~2x10^46 erg/s and an estimated black hole mass of ~10^8 Msolar. This QSO adds itself to a reduced number of known UV faint sources at these redshifts. The preliminary derived space density is compatible with the most recent determinations of the high-z QSO luminosity functions (QLF). This new detection shows how ALHAMBRA, as well as forthcoming well designed photometric surveys, can provide a wealth of information on the origin and early evolution of this kind of objects.
Highlights
It is widely accepted that the release of gravitational energy, as matter falls into a supermassive black hole (∼106−9 M ; SMBH), is the main generation mechanism for the high luminosities observed in AGN
Over the redshift range z = [5.0, 6.2], fewer than 10% of the known quasi stellar objects (QSOs) (23 objects; Mahabal et al 2005; Jiang et al 2009; Willott et al 2010b; Masters et al 2012; McGreer et al 2013) sample the faint part of the QSO luminosity function (QLF) (M1450 > −25 where M1450 is the monocromatic luminosity at rest frame 1450 Å)
We report the discovery of ALH023002+004647, a new, intrinsically faint, QSO at z = 5.41
Summary
It is widely accepted that the release of gravitational energy, as matter falls into a supermassive black hole (∼106−9 M ; SMBH), is the main generation mechanism for the high luminosities observed in AGN. Over the redshift range z = [5.0, 6.2], fewer than 10% of the known QSOs (23 objects; Mahabal et al 2005; Jiang et al 2009; Willott et al 2010b; Masters et al 2012; McGreer et al 2013) sample the faint part of the QLF (M1450 > −25 where M1450 is the monocromatic luminosity at rest frame 1450 Å) This restrains our knowledge of the true number of faint QSOs at these redshifts and severely hampers the derived accuracy of the overall QLF (given the high correlation between the LF parameters). All magnitudes are given in the AB system
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