Euclid : Early Release Observations – The star formation history of massive early-type galaxies in the Perseus cluster

The Euclid Early Release Observations (ERO) programme targeted the Perseus galaxy cluster in its central region over 0.7 deg 2 . We combined the exceptional image quality and depth of the ERO-Perseus with FUV and NUV observations from GALEX and AstroSat/UVIT, as well as ugriz H α data from MegaCam at the CFHT, to deliver FUV-to-NIR magnitudes of the 87 brightest galaxies within the Perseus cluster. We reconstructed the star formation history (SFH) of 59 early-type galaxies (ETGs) within the sample, through the spectral energy distribution (SED) fitting code CIGALE and state-of-the-art stellar population (SP) models to reproduce the galactic UV emission from hot, old, low-mass stars (i.e. the UV upturn). In addition, for the six most massive ETGs in Perseus [stellar masses log 10 ( M * / M ⊙ )≥10.3], we analysed their spatially resolved SP and SFH through a radial SED fitting. In agreement with our previous work on Virgo ETGs, we found that (i) the majority of the analysed galaxies needs the presence of a UV upturn component to explain their FUV emission, with average temperatures ⟨ T UV ⟩≃33 800 K; (ii) the ETGs of Perseus have grown their stellar masses quickly, with star formation timescales of τ ≲ 1500 Myr. We found that all ETGs in the sample have formed more than about 30% of their stellar masses at z ≃ 5, up to extreme fractions of ≃100%. At z ≃ 5, the stellar masses of the most massive nearby ETGs, which have present-day stellar masses of log 10 ( M * / M ⊙ )≳10.8, are then found to be comparable to those of the red quiescent galaxies observed by JWST at similar redshifts ( z > 4.6). This study can be extended to ETGs in the 14 000 deg 2 extragalactic sky that will soon be observed by Euclid , in combination with those from other major upcoming surveys (e.g. Rubin /LSST), and UV observations, to ultimately assess whether the massive ETGs that we observe today represent the progeny of the massive high- z JWST red quiescent galaxies.