EDP Sciences
Free access
Volume 507, Number 2, November IV 2009
Page(s) 781 - 793
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361/200912730
Published online 01 October 2009
A&A 507, 781-793 (2009)
DOI: 10.1051/0004-6361/200912730

Low redshift AGN in the Hamburg/ESO survey

I. The local AGN luminosity function
A. Schulze, L. Wisotzki, and B. Husemann

Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
    e-mail: aschulze@aip.de

Received 19 June 2009 / Accepted 17 September 2009

We present a determination of the local ($z\approx0$) luminosity function of optically selected type 1 (broad-line) active galactic nuclei. Our primary resource is the Hamburg/ESO survey (HES), which provides a well-defined sample of more than 300 optically bright AGN with redshifts z<0.3 and blue magnitudes $B \la 17.5$. AGN luminosities were estimated in two ways, always taking care to minimise photometric biases due to host galaxy light contamination. Firstly, we measured broad-band BJ (blue) magnitudes of the objects over small apertures of the size of the seeing disk. Secondly, we extracted H$\alpha$ and H$\beta$ broad emission line luminosities from the spectra which should be entirely free of any starlight contribution. Within the luminosity range covered by the HES ( $-19 \ga M_{B_J} \ga - 26$), the two measures are tightly correlated. The resulting AGN luminosity function (AGNLF) is consistent with a single power law, also when considering the effects of number density evolution within the narrow redshift range. We compared our AGNLF with the H$\alpha$ luminosity function of lower luminosity Seyfert 1 galaxies by Hao et al. (2005a, AJ, 129, 1795) and found a smooth transition between both, with excellent agreement in the overlapping region. From the combination of HES and SDSS samples we constructed a single local AGNLF spanning more than 4 orders of magnitude in luminosity. It shows only mild curvature which can be well described as a double power law with slope indices of -2.0 for the faint end and -2.8 for the bright end. We predicted the local AGNLF in the soft X-ray domain and compared this to recent literature data. The quality of the match depends strongly on the adopted translation of optical to X-ray luminosities and is best for an approximately constant optical/X-ray ratio. We also compared the local AGNLF with results obtained at higher redshifts and find strong evidence for luminosity-dependent evolution, in the sense that AGN with luminosities around $M_B \simeq -19$ are as common in the local universe as they were at z=1.5. This supports the “AGN downsizing” picture first found from X-ray selected AGN samples.

Key words: galaxies: active -- galaxies: nuclei -- quasars: general

© ESO 2009

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.