Previous abstract Next abstract
Session 109 - Seyferts.
Oral session, Thursday, January 16
We present the luminosity function for AGN/starburst nuclei to M_V\leq-13 at redshifts between 0.1 and 0.8. The objects are morphologically detected in Hubble Space Telescope WFPC2 images obtained in the V (F606W) and I (F814W) bands as part of the Medium Deep Survey (MDS). An important scientific aim of the MDS is to identify low luminosity AGNs from these images in order to measure the faint end of the AGN luminosity function as well as to study the host galaxies of AGNs and nuclear starburst systems. Understanding how the faint end of the AGN LF evolves is necessary to determine the frequency and total space density of these objects at earlier epochs.
We are able to identify candidate objects based on morphology. Candidates are selected by fitting imaged galaxies with multi-component models using maximum likelihood estimate techiniques to determine the best model fit. Our candidates are selected as those galaxies requiring an unresolved, point source component in the galaxy nucleus, in addition to a disk and/or bulge component, to adequately model the galaxy light.
We have searched 70 WFPC2 images for galaxies containing compact nuclei including 5 fields from the Groth strip and the Hubble Deep Field. We find 128 galaxies requiring a nuclear, unresolved point source component representing 9.4\pm0.8% of the 1366 galaxies in our survey. These nuclei typically comprise less than 20% of the total galaxy light. The majority of the host galaxies are spiral with little or no bulge component. We present the V-I colors of the nuclei in comparison with synthetic and observed colors for Seyfert 1s, Seyfert 2s and starburst galaxies at the full range of redshifts.
Spectroscopic redshifts have been obtained for 37 of our AGN/starburst candidates and photometric redshifts are estimated to an accuracy of \sigma_z\simeq0.1 for the remaining sample. We present the luminosity function for these nuclei out to z=0.8. Our LF extends from M_V=-13 to -20 with a mean density of 10^-3/Mpc^3/mag.
Program listing for Thursday