The space density of low-redshift active galactic nuclei

We present a new determination of the optical luminosity function (OLF) of active galactic nuclei (AGN) at low redshifts ( z <0.15) based on Hubble Space Telescope ( HST ) observations of X-ray-selected AGN. The HST observations have allowed us to derive a true nuclear luminosity function for these AGN. The resulting OLF illustrates a two power-law form similar to that derived for quasi‐stellar objects (QSOs) at higher redshifts. At bright magnitudes, M _B <−20, the OLF derived here exhibits good agreement with that derived from the Hamburg/European Southern Observatory (ESO) QSO survey. However, the single power-law form for the OLF derived from the Hamburg/ESO survey is strongly ruled out by our data at M _B >−20. Although the estimate of the OLF is best fitted by a power-law slope at M _B <−20.5 that is flatter than the slope of the OLF derived at z >0.35, the binned estimate of the low-redshift OLF is still consistent with an extrapolation of the z >0.35 OLF based on pure luminosity evolution.