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

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-circle dot residing within (<= R-200c) massive groups and clusters of total host mass M-200c = 10(13-15.2) M-circle dot in TNG100 and TNG300. The model predicts a quenched fraction of similar to 70-90 per cent (on average) for centrals and satellites of mass greater than or similar to 10(10.5) M-circle dot, 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 (less than or similar to 10(10) M-circle dot), on the other hand, are rarely quenched unless they become members of groups (10(13-14) M-circle dot) or clusters (>= 10(14) M-circle dot), where the quenched fraction rises to similar to 80 per cent. Typically, the fraction of low-mass passive galaxies is higher closer to the host centre and for progressively more massive hosts. The population of low-mass satellites accreted more than similar to 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 4-10 billion years ago. For low-mass galaxies (M-stars less than or similar to 10(10-10.5) M-circle dot), 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.

Automated summary

The study using the IllustrisTNG hydrodynamical simulations demonstrates that the quenched fraction remains consistent for galaxies with mass greater than or similar to 10(10.5) M-circle dot across different environments and cosmic time, while low-mass galaxies mainly become quenched after becoming members of groups or clusters. In addition, low-mass satellite galaxies accreted more than approximately 4-6 billion years ago into massive hosts are predominantly passive, suggesting a limit on the time needed for environmental quenching.