Abstract
We investigate the host galaxy and environment properties of a sample of 400 low z ($<$0.5) quasars that were imaged in the SDSS Stripe82. We can detect and study the properties of the host galaxy for more than 3/4 of the whole data set. We found that quasar hosts are dominated by luminous galaxies of absolute magnitude $M_* -3 < M(R) < M_*$ and that the galaxy number density of the quasar environments is comparable to that of the inactive galaxies with similar luminosities. For these quasars we undertake also a study in u,g,r,i and z SDSS bands and again we found that the mean colours of the quasar host galaxy are very similar to the values of the sample of inactive galaxies. For a subsample of low z sources the imaging study is complemented by spectroscopy of quasar hosts and of close companion galaxies. This study suggests that the fueling and triggering of the nuclear activity is only weakly dependent on the local environment of quasars. Contrary to past suggestions, for low redshift quasar there is a very modest connection between recent star formation and the nuclear activity.
Highlights
Quasar phenomenon assumes that the nuclear activity can be due to the major merger of two gasrich galaxies that feed the central engine and enable the growth of a spheroidal stellar component
A study by Bennert et al (2008) found that many low-z quasars show signs of recent or on-going interactions with nearby galaxies, suggesting a connection between the environment and the quasar activation. In spite of these imaging studies our knowledge of the physical association of the galaxies around quasars and their dynamical properties remains uncertain. To overcome these issues we recently carried out a systematic study of the the host galaxy and environment properties of a large (∼ 400) sample of low redshift (z < 0.5) quasars based on the deep images available from the Sloan Digital Sky Survey (SDSS) Stripe82 survey
In all 5 Sloan bands, the very close environment of quasars in our sample, we selected both from the full sample of 416 quasar and from the comparison sample only objects at z < 0.3 beyond this limit, the characterization of the quasar host galaxies becomes difficult at bluer filters due to the reduced contrast between the host galaxy and the nuclear emission
Summary
Quasar phenomenon assumes that the nuclear activity can be due to the major merger of two gasrich galaxies that feed the central engine and enable the growth of a spheroidal stellar component. In spite of these imaging studies our knowledge of the physical association of the galaxies around quasars and their dynamical properties remains uncertain To overcome these issues we recently carried out a systematic study of the the host galaxy and environment properties of a large (∼ 400) sample of low redshift (z < 0.5) quasars based on the deep images available from the SDSS Stripe survey. These coadded images are ∼2 magnitudes more profound with respect to the standard Sloan data and give the possibility to study both the quasar hosts and the immediate environments.
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