Friday, 6 March 2009

Weak velocity dispersion evolution

from Cenarro & Trujillo,

We know massive quiescent galaxies evolve strongly in size and
surface density from z=2 to the present. But what about in velocity
dispersion? Here the authors use a stacked spectrum of 13 early-type
galaxies at z~1.6 (total exposure time of 480 hours) from the GMASS
survey. By fitting templates to this stacked spectrum, they derive a
velocity dispersion of 240 km/s at z=1.6, in contrast to the local
value of about 180 km/s. This (shown in the bottom panel) is much
weaker than the size evolution over the same interval (top panel),
but agrees well with models of the sigma evolution via merging
(Hopkins et al 2008; shaded region) and disagrees with the AGN
feedback scenario of Fan et al. (2008; solid line). The authors
attribute the weak evolution to the changing role of dark matter in
galaxies' potential wells: at high redshift the central potential is
dominated by baryons, and at low redshifts it's dominated by dark

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