Are E+A galaxies dusty-starbursts?: VLA 20 cm radio continuum observation^*

Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686, USA e-mail: tomo@jhu.edu

Received: 6 May 2004
Accepted: 19 July 2004

Abstract

E+A galaxies are characterized as a galaxy with strong Balmer absorption lines but without any [OII] or Hα emission lines. The existence of strong Balmer absorption lines means that E+A galaxies have experienced a starburst within the last <1–1.5 Gyr. However, the lack of [OII] or Hα emission lines indicates that E+A galaxies do not have any on-going star formation. Therefore, E+A galaxies are interpreted as a post-starburst galaxy. For more than 20 years, however, it has been a mystery 
why E+A galaxies underwent a starburst then stopped abruptly.
One possible explanation to E+A galaxies is the dusty starburst scenario, where E+A galaxies have on-going star formation, but optical emission lines are invisible due to the heavy obscuration by dust. To test this dusty starburst scenario, we have observed 36 E+A galaxies carefully selected from the Sloan Digital Sky Survey Data Release 1 in 20 cm radio continuum using the VLA. Since the radio emission is not affected by the dust extinction, the star formation rate (SFR) in dusty galaxies can be revealed by the 20 cm continuum. All of our 36 target E+A galaxies are selected to have Hδ equivalent width greater than 6 Å and no detection of [OII] or Hα emission lines within 1σ. These selection criteria are much stronger than previous E+A selections in our attempt to select galaxies in the pure post-starburst phase without any remaining star formation. Except for the two galaxies with a nearby radio source, none of our 34 E+A galaxies are detected in 20 cm continuum to the limits reported in Table [see full text]. The obtained upper limits on the radio estimated SFR suggest that E+A galaxies do not possess strong starburst (>100  yr^-1) hidden by dust extinction for the whole sample while 15 () E+As have lower SFR upper limits of ~15  yr^-1.