Paspaliaris et al. 2023
Star-forming early-type galaxies and quiescent late-type galaxies in the local Universe
The general consensus is that late-type galaxies (LTGs) undergo intense star-formation activity, while early-type galaxies (ETGs) are mostly inactive. We question this general rule and investigate the existence of star-forming (SF) ETGs and quiescent (Q) LTGs in the local Universe. By computing the physical properties of 2,209 such galaxies in the GAMA survey being morphologically classified and using information on their structural properties as well as the density of their local environment, we seek for understanding the differences from their 'typical' counterparts.
We used the WHAN emission line diagram to separate the galaxies in the sample into star-forming and quiescent, while we also excluded the AGN.
Even a visual inspection of the optical images reveals a strong difference in the appearance of galaxies dominated by different ionisation processes. Q galaxies (top panels) have redder colours compared to their bluer SF counterparts (bottom panels).
We found a large fraction (47%) of the E/S0 types showing ongoing star-formation activity and 8% of Sa-Scds being quiescent. These findings indicate that the place of a galaxy in the SFR-Mstar diagram, does not depend only on its morphology, but mainly on its star-formation activity. The scaling relations of the physical properties of galaxies are also provided in the paper. Surprisingly enough, SF LBS and SF E/S0 galaxies constitute a very similar distribution with the SF Sa-Scds, following the "star-forming main sequence" of galaxies
We also explored the characteristics that make the SF ETGs and Q LTGs differentiate from their 'typical' counterparts. For instance, the local environment is found to affect star-formation activity in galaxies. Denser environments tend to favour the existence of Q galaxies. In the paper you can also found a discussion about the differences in the SEDs and the structural characteristics between Q and SF sources of the same morphologies.
You can find more of this work at the corresponding paper published on the Astronomy & Astrophysics Journal: