Optical studies of blazars, their host galaxies, and their environments

CELLONE, S. A.

Córdoba

Workshop; 5th Friends of Friends Meeting; 2015

IATE-OAC

The electromagnetic emission of BLAZARS spans the whole spectrum, from radio up to X and even gamma-rays, so their multi-wavelength study is mandatory. Within this context, optical studies can provide critical information to complement results from different frequency ranges.I summarize in this talk some results from optical studies of blazars, carried on by the GARRA group at La Plata, along recent years. The focus is set on several ongoing projects, based on observations obtained at Gemini and CAHA (Calar Alto, Spain). Two main topics can be identified: - Optical polarimetric studies of blazars, looking for fast fluctuations. We quantitatively evaluate the depolarizing effect introduced by their host galaxies, as well as systematic errors in the polarimetric light-curves when seeing conditions vary with time.- The BL Lac sub-class of blazars has -by definition- weak or absent lines in their optical spectra, thus many of them have still unreliable redshift determinations. We have undertaken an effort to measure redshifts of BL Lacs, based on Gemini-GMOS imaging and multi-object spectra of some selected objects. Even if no definite redshift can be obtained from the blazar's spectrum, at least a firm constraint can be provided by the (un)detection of the host galaxy and/or the redshift distribution of the galaxies in the immediate projected environment.