1. LLAMA: Stellar populations in the nuclei of ultra hard X-ray selected AGN and matched inactive galaxies
- Author
-
Burtscher, L., Davies, R. I., Shimizu, T. T., Riffel, R., Rosario, D. J., Hicks, E. K. S., Lin, M. -Y., Riffel, R. A., Schartmann, M., Schnorr-Müller, A., Storchi-Bergmann, T., de Xivry, G. Orban, and Veilleux, S.
- Subjects
Astrophysics - Astrophysics of Galaxies - Abstract
The relation between nuclear ($\lesssim$ 50 pc) star formation and nuclear galactic activity is still elusive: theoretical models predict a link between the two, but it is unclear whether active galactic nuclei (AGNs) should appear at the same time, before or after nuclear star formation activity is ongoing. We present a study of this relation in a complete, volume-limited sample of nine of the most luminous ($\log L_{\rm 14-195 keV} > 10^{42.5}$ erg/s) local AGNs (the LLAMA sample), including a sample of 18 inactive control galaxies (6 star-forming; 12 passive) that are matched by Hubble type, stellar mass (9.5 $\lesssim$ log M_star/M_sun $\lesssim$ 10.5), inclination and distance. This allows us to calibrate our methods on the control sample and perform a differential analysis between the AGN and control samples. We perform stellar population synthesis on VLT/X-SHOOTER spectra in an aperture corresponding to a physical radius of $\approx$ 150 pc. We find young ($\lesssim$ 30 Myr) stellar populations in seven out of nine AGNs and in four out of six star-forming control galaxies. In the non-star-forming control population, in contrast, only two out of twelve galaxies show such a population. We further show that these young populations are not indicative of ongoing star-formation, providing evidence for models that see AGN activity as a consequence of nuclear star formation. Based on the similar nuclear star-formation histories of AGNs and star-forming control galaxies, we speculate that the latter may turn into the former for some fraction of their time. Under this assumption, and making use of the volume-completeness of our sample, we infer that the AGN phase lasts for about 5 % of the nuclear starburst phase., Comment: 53 pages, 44 figures, accepted for publication by A&A
- Published
- 2021
- Full Text
- View/download PDF