Oct 11, 2018

Eric Bell, University of MI

""How do mergers affect galaxies?""

The stellar parts of large galaxies grow by a combination of star formation in gas that cooled and condensed from the intergalactic medium and the tidal disruption of the stellar bodies of satellite galaxies that merge into the main galaxy. These mergers - while short-lived - may shape a galaxy decisively, but model predictions for the effects of mergers depend on merger parameters and uncertain sub-grid recipes for important physical processes very sensitively. Accordingly, observational measures of the mergers suffered by well-studied local galaxies would be extremely valuable.  

Stellar halos have long been proposed as probes of the merger history of galaxies. Unfortunately, a slew of observational and theoretical limitations have prevented us from being able to quantify merger histories. I will argue that these observational and theoretical issues have now been circumvented. Sensitive studies with HST and other facilities of the individual RGB stars in the stellar halos of external galaxies have revealed that the mass of stellar halos correlates closely with their metallicity. This relationship is in quantitative agreement with models of stellar halo formation and emerges naturally when stellar halos primarily reflect the properties of the single largest satellite that merged with the main galaxy. We calibrate the relationship between the mass of the single largest merger to have affected a galaxy and its stellar halo, and apply it to a modest sample of nearby galaxies with well-studied stellar halos. With this, we explore a range of questions. What is the merger history of the Andromeda galaxy, and how did it shape Andromeda's disk, bulge and satellite system, including the enigmatic M32? Which mergers destroy galactic disks and which mergers leave the final end-product disk-dominated? Is there evidence that bulges are made in mergers?   

Event Details

Oct 11, 2018


4421 Stering Hall

Coffee served at 3:30pm; talk starts at 3:45pm

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