The star formation rates (SFRs) in weak emission line (WEL) galaxies in a volume-limited (0.02~ 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 ± 19 μJy and 0.20 ± 0.05 × 1021 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 ± 0.06 M⊙yr−1, which is much less compared to SFRs (0.5−50 M⊙yr−1) in purely star forming blue ETGs. The SFRs in blue ETGs are found to be correlated with their stellar velocity dispersions (σ) and decreasing gradually beyond σ of ∼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.
A. Paswan, A. Omar
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