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

Abstract

E+A galaxies are characterized as a galaxy with strong Balmer absorption lines but without any [OII] or Halpha emission lines. Strong Balmer absorption lines indicate that E+A galaxies have experienced a starburst within the last <1-1.5 Gyr. However, the lack of 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. 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 SDSS DR1 in 20cm radio continuum using the VLA. Since the radio emission is not affected by the dust extinction, the SFR in dusty galaxies can be revealed by the 20 cm continuum. All of our 36 target E+A galaxies are selected to have H\delta EW greater than 6A and no detection of [OII] or Halpha emission lines within 1 sigma. 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 1. The obtained upper limits on the radio estimated SFR suggest that E+A galaxies do not possess strong starburst (> 100 Msun yr^-1) hidden by dust extinction for the whole sample while 15 (z<0.08) E+As have lower SFR upper limits of ~15 Msun yr^-1. (Abridged)