Mark Swinbank, Michael Balogh, Richard Bower, Ann Zabludoff, John Lucey, Sean McGee, Chris Miller, Robert Nichol
We present three dimensional spectroscopy of eleven E+A galaxies, selected
for their strong H-delta absorption but weak (or non-existent) [OII]3727 and
H-alpha emission. This selection suggests that a recent burst of star-formation
was triggered but subsequently abruptly ended. We probe the spatial and
spectral properties of both the young (~1Gyr) and old (few Gyr) stellar
populations. Using the H-delta equivalent widths we estimate that the burst
masses must have been at least 10% by mass (Mburst~10^10Mo), which is also
consistent with the star-formation history inferred from the broad-band SEDs.
On average the A-stars cover ~33% of the galaxy image, extending over
2-15kpc^2, indicating that the characteristic E+A signature is a property of
the galaxy as a whole and not due to a heterogeneous mixture of populations. In
approximately half of the sample, we find that the A-stars, nebular emission,
and continuum emission are not co-located, suggesting that the newest stars are
forming in a different place than those that formed ~1Gyr ago, and that recent
star-formation has occurred in regions distinct from the oldest stellar
populations. At least ten of the galaxies (91%) have dynamics that class them
as "fast rotators" with magnitudes and dynamics comparable to local ellipticals
and S0's. We also find a correlation between the spatial extent of the A-stars
and dynamics such that the fastest rotators tend to have the most compact
A-star populations, providing new constraints on models that aim to explain the
transformation of later type galaxies into early types. Finally, we show that
there are no obvious differences between the line extents and kinematics of E+A
galaxies detected in the radio (AGN) compared to non-radio sources, suggesting
that AGN feedback does not play a dramatic role in defining their properties,
or that its effects are short.
View original:
http://arxiv.org/abs/1110.5638
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