title: Galaxies and Supermassive Black Holes Evolving in a Secular Universe
creator: Cisternas, Mauricio
subject: ddc-520
subject: 520 Astronomy and allied sciences
description: Most massive galaxies host a supermassive black hole (BH), that had most of its mass built up throughout bright periods of vigorous accretion, during which it is referred to as an active galactic nucleus (AGN). In the local universe it has been observed that BH mass (M_BH) follows tight correlations with various properties of the galactic bulge in which it resides. This led to the currently popular co-evolution'' picture, in which most present-day galaxies went through at least one active phase in the past, during which a link between galaxy and BH gets established. However, more robust observational constraints are required on how galaxy and BH related at earlier times, and which mechanism is responsible for triggering these BH growth phases. This thesis studies a large sample of AGN out to z~1 from the COSMOS survey, selected from their X-ray emission and imaged in finest detail with the Hubble Space Telescope, allowing the study of growing BHs together with their host galaxies. We present new constraints on the ratio of BH mass to total galaxy stellar mass (M_*) over the last 7 Gyr for 32 type-1 AGN. We show that the M_BH-M_* ratio at z~0.7 is consistent with the local relation between BH mass and galactic bulge mass. For these galaxies to obey the local relation only a redistribution of disk-to-bulge mass is needed, likely driven by passive secular evolution. We then tackle and answer a 30-year old question: what is the relevance of major mergers and interactions as triggering mechanisms for AGN activity? We visually analyze the morphologies of 140 AGN out to z~1 looking for signatures of recent mergers, and compare them with a control sample of over 1200 matched inactive galaxies. We find that the merger fraction of the AGN host galaxies is statistically identical to the corresponding inactive galaxy population, at roughly 15%. Together with the fact that the majority of the AGN host galaxies are disk-dominated, unlikely relics of a recent major merger, these results are the strongest evidence to date that secular evolution rather than major merging has dominated BH fueling at least since z~1, and that BHs and galaxies have, for the last 7 Gyr, evolved in a secular universe.
date: 2011
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/12761/1/cisternas_thesis.pdf
identifier: DOI:10.11588/heidok.00012761
identifier: urn:nbn:de:bsz:16-opus-127612
identifier:   Cisternas, Mauricio  (2011) Galaxies and Supermassive Black Holes Evolving in a Secular Universe.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/12761/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng