Jellyfish galaxy candidates in MACS J0717.5+3745 and 39 other clusters of the DAFT/FADA and CLASH surveys
Authors: Durret F. , Chiche S. , Lobo C. , Jauzac M. 
Published: February 2021

Context. Galaxies in clusters undergo several phenomena, such as RPS and tidal interactions, that can trigger or quench their star formation and, in some cases, lead to galaxies acquiring unusual shapes and long tails – some become jellyfish.
Aims. We searched for jellyfish galaxy candidates in a sample of 40 clusters from the DAFT/FADA and CLASH surveys covering the redshift range 0.2 < z < 0.9. In MACS J0717.5+3745 (MACS0717), our large spatial coverage and abundant sampling of spectroscopic redshifts allowed us to pursue a detailed analysis of jellyfish galaxy candidates in this cluster and its extended filament.
Methods. We retrieved galaxy spectroscopic redshifts in the NASA Extragalactic Database for galaxies in all the clusters of our sample (except for MACS0717 for which we had an extensive catalogue), looked at the Hubble Space Telescope ACS images of these objects (mainly the F606W and F814W bands), and classified them as a function of their likeliness to be jellyfish galaxies. We give catalogues of jellyfish galaxy candidates with positions, redshifts, magnitudes, and projected distance to their respective cluster centre. For MACS0717, an eight-magnitude optical and infrared catalogue covering the entire region allowed us to compute the best stellar population fits with LePhare through the GAZPAR interface. For the 31 jellyfish candidates in the other clusters belonging to the CLASH survey, we extracted up to 17 magnitudes available in the CLASH catalogues to fit their spectral energy distribution in the same way.
Results. We found 81 jellyfish galaxy candidates in the extended region around MACS0717 as well as 97 in 22 other clusters. Jellyfish galaxy candidates in MACS0717 tend to avoid the densest regions of the cluster, while this does not appear to be the case in the other clusters. The best fit templates found by LePhare show that star formation is occurring. Stellar masses are in the range 109 − 1011 M⊙, and the star formation rates (SFRs) are in the 10−1 − 60 M⊙ yr−1 range for MACS0717 and in the 10−1 − 10 M⊙ yr−1 range for the other sample. Specific star formation rates (sSFRs) are notably higher in MACS0717, with more than half of the sample having values larger than 10−9 yr−1, while in the other clusters, most galaxies have sSFR < 10−10 yr−1. Stellar populations appear younger in MACS0717 (more than half have an age smaller than 1.5 × 109 yrs), and, following mid-infrared criteria, two galaxies may contain an active galactic nucleus. In a SFR versus stellar mass diagram, jellyfish galaxy candidates appear to have somewhat larger SFRs than “non-jellyfish star-forming” galaxies. For MACS0717, the mean sSFR of the 79 jellyfish galaxy candidates is 3.2 times larger than that of star-forming non-jellyfish galaxies (selected with log(sSFR)  ≥   − 11).
Conclusions. Our jellyfish galaxy candidates are star-forming objects, with young ages and blue colours. Based on several arguments, the jellyfish candidates identified in MACS0717 seem to have fallen rather recently into the cluster. A very rough estimate of the proportions of jellyfish galaxies in the studied clusters is about 10%; this number does not seem to vary strongly with the cluster relaxation state, though this result must be confirmed with more data. Our sample of 97 galaxies in 22 clusters represents the basis of future works.