Type 1 low z AGN. I. Emission properties

TL;DR

This study analyzes the emission properties of a large sample of type 1 AGN, revealing that their spectral energy distributions and host galaxy characteristics are primarily driven by luminosity, with implications for understanding AGN and galaxy co-evolution.

Contribution

It provides a comprehensive analysis of emission properties across a broad luminosity range, highlighting the role of luminosity in shaping AGN SEDs and host galaxy features, and introduces new correlations between X-ray and optical emissions.

Findings

H-alpha FWHM distribution is luminosity-independent.

Optical-UV SED matches scaled quasar templates plus host contribution.

Host galaxy properties correlate with AGN luminosity and star formation.

Abstract

We analyze the emission properties of a new sample of 3,579 type 1 AGN, selected from the SDSS DR7 based on the detection of broad H-alpha emission. The sample extends over a broad H-alpha luminosity L_bHa of 10^40 - 10^44 erg s^-1 and a broad H-alpha FWHM of 1,000 - 25,000 km s^-1, which covers the range of black hole mass 10^6<M_BH/M_Sun<10^9.5 and luminosity in Eddington units 10^-3 < L/L_Edd < 1. We combine ROSAT, GALEX and 2MASS observations to form the SED from 2.2 mic to 2 keV. We find the following: 1. The distribution of the H-alpha FWHM values is independent of luminosity. 2. The observed mean optical-UV SED is well matched by a fixed shape SED of luminous quasars, which scales linearly with L_bHa, and a host galaxy contribution. 3. The host galaxy r-band (fibre) luminosity function follows well the luminosity function of inactive non-emission line galaxies (NEG), consistent with a fixed fraction of ~3% of NEG hosting an AGN, regardless of the host luminosity. 4. The hosts of lower luminosity AGN have a mean z band luminosity and u-z colour which are identical to NEG with the same redshift distribution. With increasing L_bHa the AGN hosts become bluer and less luminous than NEG. The implied increasing star formation rate with L_bHa is consistent with the relation for SDSS type 2 AGN of similar bolometric luminosity. 5. The optical-UV SED of the more luminous AGN shows a small dispersion, consistent with dust reddening of a blue SED, as expected for thermal thin accretion disc emission. 6. There is a rather tight relation of nuL_nu(2 keV) and L_bHa, which provides a useful probe for unobscured (true) type 2 AGN. 7. The primary parameter which drives the X-ray to UV emission ratio is the luminosity, rather than M_BH or L/L_Edd.