Host galaxies of local hard X-ray selected AGN
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Date
2022
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Abstract
We investigate the evolutionary state of galaxies hosting active galactic nuclei (AGN) for a sample
of 138 hard X-ray selected AGN from the BAT AGN Spectroscopic Survey (BASS) catalog and which
have high-resolution (R ∼ 5000), VLT/X-SHOOTER 0.3–1 µm spectroscopy. We perform a stellar
population synthesis analysis via pPXF fitting of the stellar continuum, as well as fit specific emission
and absorption features (e.g., Lick indices, line ratios), to estimate AGN/star formation contributions,
dust obscuration, stellar age, metallicity and star formation histories. Additionally, we perform morphological classification on our sample to study possible correlations to said evolutionary state. We
compare our results to AGN X-ray properties and infrared (IR) derived SFRs to estimate the potential for AGN feedback. Using several cuts and selection criteria, we construct a comparison sample
from SDSS DR7 data in the MPA-JHU catalog to place our AGN sample in the context with overall
galaxy evolution. The X-SHOOTER spectra primarily probe the central regions of the AGN hosts,
which tend to be dominated by old (> 10 Gyr) stellar populations. However, we find our sample
primarily composed of main-sequence spirals (46%), followed by green valley spirals (14%) and green
valley ellipticals (14%), with almost no galaxies present in the red sequence according to our definition. Our spectral modeling suggests that most elliptical and blue spiral hosts of AGN experienced
strong episodes of star formation at intermediate ages (∼ 1–6 Gyr), which strongly correlate with
their apparent morphological features (tails, remnant features). In contrast, most red spirals seem to
follow a completely secular evolution. Comparison of IR and optically derived SFRs for 57 AGN in
the sample implies copious obscured star formation; this appears to push otherwise optically passive
elliptical hosts into the green valley or main sequence. As for the effect of AGN feedback, we only find
very mild correlations between the AGN and the host bulge properties, thereby implying weak links
between the current AGN event and their intermediate-age populations.
Description
Tesis (Magíster en Astronomía)--Pontificia Universidad Católica de Chile, 2022