Publication
Detections and Implications of Radio Emission From E+A Galaxies
Hooper, E. J., Liu, C., van Gorkom, J. & O'Neil, K., 1-Dec-2007, In : Bulletin of the American Astronomical Society. 39, p. 907Research output: Contribution to journal › Article › Academic › peer-review

Galaxies several hundred Myr past a major star formation epoch may show
strong signs of the residual starburst population in the form of Balmer
emission from A-stars superimposed on an older population, the so-called
"E+A" galaxies. Radio emission from such galaxies, absent ongoing star
formation, is expected to be minimal. Indeed, Goto (2004, A&A, 427,
125) did not detect E+A galaxies lacking optical signatures of current
star formation at 21 cm. Any radio emission from these galaxies is
generally assumed to arise from star formation, not AGN, and it is often
used to estimate the current star formation rate independently of
obscuration.
However, the archetypal E+A galaxy G515 (Oegerle et al. 1991, ApJ, 381,
L9; Liu et al. 2007, ApJ, 658, 249) has no detectable [OII] or H-alpha
emisssion, yet it possesses a core radio source and possibly extended
emission. VLA data taken at different epochs show 21 cm continuum fluxes
of 3.0 +/- 0.5, <0.5, and 0.65 +/- 0.09 mJy using the D, B, and A
array configurations, respectively. The latter two values probably
indicate source variability, and hence likely a low-luminosity AGN,
though more data are required for confirmation. The higher D-array flux
could arise from extended radio emission, presumably from extended and
obscured ongoing star formation.
Moreover, G515 is not unique. Nearly half, possibly more, of the radio
detections in a sample of E+A galaxies with little or no detectable
[OII] and H-alpha emission are anomalous, in that they either exhibit
extended emission or nuclear point source variability. Variability is
confirmed in one of the sources. Hence, low level AGN activity is
responsible for the emission in some, possibly a substantial fraction,
of E+A galaxies with detectable radio flux. This is an important
consideration when using post-starburst galaxy radio emission to measure
ongoing obscured star formation.
Original language | English |
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Pages (from-to) | 907 |
Journal | Bulletin of the American Astronomical Society |
Volume | 39 |
Publication status | Published - 1-Dec-2007 |
ID: 25208910