Quenched fractions in the IllustrisTNG simulations: the roles of AGN feedback, environment, and pre-processing

Abstract

We use the IllustrisTNG hydrodynamical simulations to show how the fractions of quenched galaxies vary across different environments and cosmic time, and to quantify the role AGN feedback and pre-processing play in quenching group and cluster satellites. At z = 0, we select galaxies with M stars = 10 9−12 M residing within ( R 200c ) massive groups and clusters of total host mass M 200c = 10 13−15.2 M in TNG100 and TNG300. The model predicts a quenched fraction of ∼70-90 per cent (on average) for centrals and satellites of mass 10 10.5 M , regardless of host mass, cosmic time (0 z 0.5), cluster-centric distance and time since infall in the z = 0 host. Low-mass central galaxies ( 10 10 M ), on the other hand, are rarely quenched unless they become members of groups (10 13−14 M ) or clusters ( 10 14 M ), where the quenched fraction rises to ∼ 80 per cent. Typically, the fraction of low-mass passive galaxies is higher closer to the host center and for progressively more massive hosts. The population of low-mass satellites accreted more than ∼ 4-6 Gyr ago in massive hosts is almost entirely passive, thus suggesting an upper limit for the time needed for environmental quenching to occur. In fact, about 30 per cent of group and cluster satellites that are quenched at z = 0 were already quenched before falling into their current host, and the bulk of them quenched as early as 4 to 10 billion years ago. For low-mass galaxies (M stars 10 10−10.5 M ), this is due to pre-processing, whereby current satellites may have been members of other hosts, and hence have undergone environmental processes, before falling into their final host, this mechanism being more common and more effective for the purposes of quenching for satellites found today in more massive hosts. On the other hand, massive galaxies quench on their own and because of AGN feedback, regardless of whether they are centrals or satellites.

Anisotropic satellite galaxy quenching modulated by supermassive black hole activity

“…11 shows the number of TNG100 satellites belonging to each group as a function of orientation. It is evident from this figure that, for the specific galaxy and host mass ranges adopted in this work 49 , large-scale structure-sensitive satellites (red and orange symbols) are outnumbered by both star-forming, and particularly, satellites that quenched in their z ∼ 0 host halo, and thus, large-scale effects could only affect a minority of the satellite population.…”

“…8 illustrates how the outcomes of the IllustrisTNG and Illustris cosmological numerical simulations compare. To marginalize over the possible differences in the overall quenching of galaxies between IllustrisTNG and Illustris 49 , also here we subtract the average quiescent fraction of both datasets. Extended Data Figure 6.…”

“…pre-processing or quenching as centrals of a different halo). Satellite infall times have been studied for IllustrisTNG satellites 49 and each satellite can be classified into four different groups: star-forming satellites, satellites quenched in their z ∼ 0 host halo, pre-processed satellites (i.e. quenched as satellites in a different halo), and satellites quenched as centrals of a different halo (before being accreted into their z ∼ 0 host).…”

A MeerKAT view of pre-processing in the Fornax A group

“…Evidence suggests that the group is in the early stage of assembly (Iodice et al 2017;Raj et al 2020) and it is located at the cluster infall distance where pre-processing is thought to occur (Lewis et al 2002;Gómez et al 2003;Verdugo et al 2008;Mahajan et al 2012;Haines et al 2015). The BGG is massive enough to experience efficient pre-processing (Donnari et al 2020) and Raj et al (2020) show that there are signatures of preprocessing in the group, with six of the nine late types having an up-bending (type III) break in their radial light profile. This indicates that the star formation may be halting in the outer disk of galaxies, although it is not yet clear what is driving the decline in star formation.…”

“…Fujita 2004;Mahajan 2013;Roberts & Parker 2017;Cluver et al 2020). In particular, pre-processing is likely to be most efficient in massive (> 10 10.5 M ) galaxies residing in massive (10 13 -10 14 M ) groups (Donnari et al 2020). It has also been shown that pre-processing is responsible for the decrease in star formation activity for late type galaxies at distances between 1 and 3 cluster virial radii (e.g Lewis et al 2002;Gómez et al 2003;Verdugo et al 2008;Mahajan et al 2012;Haines et al 2015).…”