One-Two Quench: A Double Minor Merger Scenario

Abstract

Using the N-body+Smoothed particle hydrodynamics code, ChaNGa, we identify two merger-driven processes-disk disruption and supermassive black hole (SMBH) feedback-which work together to quench L * galaxies for over 7 Gyr. Specifically, we examine the cessation of star formation in a simulated Milky Way (MW) analog, driven by an interaction with two minor satellites. Both interactions occur within ∼100 Myr of each other, and the satellites both have masses 5 to 20 times smaller than that of their MW-like host galaxy. Using the genetic modification process of Roth et al. ( 2016), we generate a set of four zoom-in, MW-mass galaxies all of which exhibit unique star formation histories due to small changes to their assembly histories. In two of these four cases, the galaxy is quenched by z = 1. Because these are controlled modifications, we are able to isolate the effects of two closely-spaced minor merger events, the relative timing of which determines whether the MW-mass main galaxy quenches. This one-two punch works to: 1. fuel the primary halo's supermassive black hole (SMBH) at its peak accretion rate; and 2. disrupt the cold, gaseous disk of the host galaxy. The end result is that feedback from the SMBH thoroughly and abruptly ends the galaxy's star formation by z ≈ 1. We search for and find a similar quenching event in ROMULUS25, a hydrodynamical (25 Mpc) 3 volume simulation, demonstrating that the mechanism is common enough to occur even in a small sample of MW-mass quenched galaxies at z = 0.

The Impact of Cosmic Rays on Thermal Instability in the Circumgalactic Medium

“…In this work, we analyze cosmological zoom-in simulations of two Milky Way-sized (M vir = 9.9 × 10 11 M at z = 0) galaxies evolved with and without cosmic-ray feedback. The base model, "Patient 0" (P0) has been studied in great detail in Sanchez et al (2019) and Sanchez et al (2020). "Patient 0 with cosmic rays" (P0+CR) uses the same initial conditions and physics as P0 except that it also includes cosmic-ray feedback from supernovae.…”

Interacting galaxies in the IllustrisTNG simulations -- III: (the rarity of) quenching in post-merger galaxies

“…The interaction disrupts the gaseous disk of the galaxy, resulting in a turbulent medium able to remove angular momentum from inflowing material; then, the inflowing material can easily reach the galactic centre to feed the black hole and the subsequent AGN activity contributes significantly to removing the remaining gas from the galaxy (see also Chadayammuri et al 2020). More recently, Sanchez et al (2020) used a similar approach to analyse the impact of minor mergers on the star formation of simulated Milky Way analogues. They find that two small satellites interacting with the host can quench a Milky Way-like galaxy.…”