Radio continuum detection in blue early-type weak emission line galaxies
  The star formation rates (SFRs) in weak emission line (WEL) galaxies in a
volume-limited ($0.02 < z < 0.05$) sample of blue early-type galaxies (ETGs)
identified from SDSS, are constrained here using 1.4 GHz radio continuum
emission. The direct detection of 1.4 GHz radio continuum emission is made in 8
WEL galaxies and a median stacking is performed on 57 WEL galaxies using VLA
FIRST images. The median stacked 1.4 GHz flux density and luminosity are
estimated as 79 $\pm$ 19 $\mu$Jy and 0.20 $\pm$ 0.05 $\times$ 10$^{21}$ W
Hz$^{-1}$ respectively. The radio far-infrared correlation in 4 WEL galaxies
suggests that the radio continuum emission from WEL galaxies is most likely due
to star formation activities. The median SFR for WEL galaxies is estimated as
0.23 $\pm$ 0.06 M$_{\odot}$yr$^{-1}$, which is much less compared to SFRs ($0.5
- 50$ M$_{\odot}$yr$^{-1}$) in purely star forming blue ETGs. The SFRs in blue
ETGs are found to be correlated with their stellar velocity dispersions
($\sigma$) and decreasing gradually beyond $\sigma$ of $\sim 100$ km s$^{-1}$.
This effect is most likely linked with the growth of black hole and suppression
of star formation via AGN feedback. The color differences between SF and WEL
sub-types of blue ETGs appear to be driven to large extent by the level of
current star formation activities. In a likely scenario of an evolutionary
sequence between sub-types, the observed color distribution in blue ETGs can be
explained best in terms of fast evolution through AGN feedback.
