Deciphering the properties of UV upturn galaxies in the Virgo cluster

TL;DR

This study confirms the presence of UV upturn in Virgo cluster early-type galaxies using SED analysis, revealing that old stellar populations, particularly low-mass evolved stars, are likely responsible for the UV excess.

Contribution

It demonstrates that SED fitting effectively identifies UV upturn galaxies and provides insights into their stellar populations and metallicity, advancing understanding of the phenomenon in galaxy clusters.

Findings

UV upturn confirmed in Virgo ETGs via SED analysis

UV contribution from old, low-mass evolved stars with temperatures 13,000-18,000 K

Higher Mg2 index correlates with UV upturn presence

Abstract

The UV upturn refers to the increase in UV flux at wavelengths shorter than 3000 {\AA} observed in quiescent early-type galaxies (ETGs), which still remains a puzzle. In this study, we aim to identify ETGs showing the UV upturn phenomenon within the Virgo galaxy cluster. We utilized a color-color diagram to identify all potential possible UV upturn galaxies. The Spectral Energy Distributions (SED) of these galaxies were then analyzed using the CIGALE software; we confirmed the presence of UV upturn in galaxies within the Virgo cluster. We found that the SED fitting method is the best tool to visualize and confirm the UV upturn phenomenon in ETGs. Our findings reveal that the population distributions regarding stellar mass and star formation rate properties are similar between UV upturn and red sequence galaxies. We suggest that the UV contribution originates from old stellar populations and can be modeled effectively without a burst model. Moreover, by estimating the temperature of the stellar population responsible for the UV emission, we determined it to be 13,000 K to 18,000 K. These temperature estimates support the notion that the UV upturn likely arises from the contribution of low mass evolved stellar populations (extreme horizontal branch stars). Furthermore, the Mg2 index, a metallicity indicator, in the confirmed upturn galaxies shows higher strength and follows a similar trend to previous studies. This study sheds light on the nature of UV upturn galaxies within the Virgo cluster and provides evidence that low-mass evolved stellar populations are the possible mechanisms driving the UV upturn phenomenon.