| Description |
Compact groups of galaxies represent density enhancements
in the Universe comparable with clusters and are dominated
by early type galaxies that lie in the Green Valley between
the blue and red sequence. Our observations of a sample of
such groups has revealed that 10 percent of our targeted
group members show unusually powerful mid-IR H2 emission
lines relative to PAH emission--suggesting shock-excitation.
Most of these galaxies lie in the optical green valley, and
exhibit specific star formation rates that lie between spirals
and elliptical suggesting that they are a transition population
in which shocks may play a role in their color evolution.
We propose to map key far-IR cooling lines [OI], [CII] and CO
with the PACS and SPIRE spectrometers to both map and
quantify the strength and distribution of shocks to search for
clues about how they might be affected by their environment.
We will also use PACS and SPIRE imaging to constrain dust
SEDs to estimate SFRs and dust/gas masses to explore whether
the shocks may heat the gas above the threshold for star
formation--hence shutting down new star formation.
Alternatively, by comparison with VLA HI maps which show
considerable tidal material in the groups, we will search for
evidence that accretion from tidal streams is responsible
for re-igniting new star formation-thus modifying their optical
colors. This proposal will, for the first time, test whether shocks may play a
transformative role in galaxy evolution. |
