Figure 1.
Estimates of the
relative ages and
metallicities of the
bulges (blue circles)
and disks (red ellipses)
of the S0 galaxies in
the Virgo Cluster. Solid
lines link bulge and
disk stellar populations
from the same galaxy.
The general trend
shows younger, more
metal-rich bulges
relative to their
corresponding disks.
licity values, with stellar indices measured
directly and stellar models used to derive
physical properties. While different models
would provide different absolute values, the
sense of the relationships remains robust,
with younger and more metal-rich stellar
populations in the disks (Figure 1) — the result of recent episodes of star formation in
enriched material.
The cluster environment, too, is likely important in the evolutionary process, which requires a traumatic event to strip the disk gas
(quenching star formation there) and funnel
it toward the galaxy’s center. The rich environments of clusters do provide such opportunities for the progenitor spiral galaxies to
interact with other galaxies and the diffuse
cluster medium. This work, however, is not
sensitive to the possible effects of environmental variations.
Full results are published in Monthly Notices
of the Royal Astronomical Society, 441: 333,
2014, and a preprint is available.
July 2014
Galaxy-wide Outflows Common
Among Quasars
New work shows that galaxy-wide outflows
are common among galaxies that host luminous quasars. The underlying energetic
source of these outflows is unclear, being related either to the accretion onto the central
supermassive black hole or star formation.
Some process to inject mass and energy into
the surroundings does, however, appear to
be an essential aspect of cosmic evolution.
In addition to depositing chemically-enriched material in the halo and larger intergalactic environment, outflows may be a
key link that provides feedback between the
growth of central black holes and star formation, which accounts for the present-day distribution of galaxy properties.
Chris Harrison (Durham University) led the
study, based on observations of 16 luminous
quasars at redshifts z < 0.2. These are all type
2 (i.e., obscured) radio-quiet quasars exhibit-
GeminiFocus
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