Jellyfish galaxies with the IllustrisTNG simulations – I. Gas-stripping phenomena in the full cosmological context

Abstract

We use the IllustrisTNG simulations to study the demographics and properties of jellyfish galaxies in the full cosmological context. By jellyfish galaxies, we mean satellites orbiting in massive groups and clusters that exhibit highly asymmetric distributions of gas and gas tails. In particular, we select TNG100 galaxies at low redshifts (z ≤ 0.6) with stellar mass exceeding 10 9.5 M and with host halo masses in the range 10 13 ≤ M 200c / M ≤ 10 14.6 . Among more than about 6 000 (2 600) galaxies with stars (and some gas), we identify 800 jellyfish galaxies by visually inspecting their gas and stellar mass maps in random projections. Namely, about 31 per cent of cluster satellites are found with signatures of ram-pressure stripping and gaseous tails stemming from their main luminous bodies. This is a lower limit: the random orientation entails a loss of about 30 per cent of galaxies that in an optimal projection would otherwise be identified as jellyfish. Furthermore, jellyfish galaxies are more frequent at intermediate and large cluster-centric distances (r/R 200c 0.25), in more massive hosts and at smaller satellite masses, and they typically orbit supersonically. The gaseous tails usually extend in opposite directions to the galaxy trajectory, with no relation between tail orientation and position of the hosts center. Finally, jellyfish galaxies are late infallers (< 2.5 − 3 Gyrs ago, at z = 0) and the emergence of gaseous tails correlates well with the presence of bow shocks in the intra-cluster medium.

The better half – asymmetric star formation due to ram pressure in the EAGLE simulations

“…These ranges are in agreement with the ones presented in Yun et al (2019) who find that the abundance of jellyfish galaxies peaks at low satellite masses above 10 9.5 [M ] and at r/R 200 > 0.25. The lower resolution limit of the galaxy sample used in Yun et al (2019) is 10 9.5 [M ]. Figure 5 shows that vector normal to the plane that maximizes the SFR differences, in most cases, is well aligned to the velocity vector.…”

“…In observations, the effect of RP has been studied in galaxies that are being gas-stripped in galaxy clusters, identified via their distorted morphologies (Smith et al 2010;McPartland et al 2016). Historically, this identification has been performed via visual inspection of images of cluster members (Poggianti et al 2016;Mc-Partland et al 2016), and in mock images of hydrodynamical simulations (Yun et al 2019). It allows to determine their abundance and dependence with redshift.…”

The Formation History of Subhalos and the Evolution of Satellite Galaxies

“…It should be noted that the infall time distribution of satellite galaxies selected to be found within the virial radius from a more massive host is bimodal as well, even when infall is defined as virial radius crossing. In that case, the bimodality is removed when backsplash satellites are included, i.e those are outside the virial radius at given time (Yun et al 2019;Engler et al 2020. Since the a nf distribution of FA halos is narrow and its peak is always around 1.2, almost independent of z peak , host halo mass, and M peak (Shi et al 2018), we adopt the demarcation value a nf = 1.3 to divide them into FA and SA populations (see Figure 1).…”

“…Gunn & Gott 1972); some satellites even get tidally disrupted (e.g. into intracluster light) before merging with the centrals (Mihos et al 2005;Wetzel & White 2010;Bahé et al 2019); dynamical friction gradually reduces the orbital angular momentum so that the satellites sink towards the halo center (Chandrasekhar 1943a,b,c); ram pressure can remove the hot halo gas reservoir or even the cold gas in the disk of satellites (Gunn & Gott 1972;Ayromlou et al 2019;Yun et al 2019); 'harassment' from neighbouring galaxies can tidally heat the satellite system (Farouki & Shapiro 1981); satellite-satellite mergers can affect both the star formation activity and morphology (Makino & Hut 1997;Wetzel, Cohn & White 2009). However, the importance of these processes in quenching/transforming satellites, and their dependence on various halo properties is still under debate.…”

“…Bahé & McCarthy (2015) showed that ram pressure stripping is the main mechanism that is responsible for satellite quenching in groups and clusters using GIMIC cosmological hydrodynamical simulations. Yun et al (2019) and Jung et al (2018) studied the efficiency of ram pressure in removing the gas content of satellites using TNG100 and HorizonAGN. Joshi et al (in preparation) demonstrates with the TNG50 and TNG100 simulations that group and cluster environments transform galaxies from disc to spheroids, possibly because of tidal shocking.…”