Dwarf Galaxies in the TNG50 Field: connecting their Star-formation Rates with their Environments

TL;DR

This study uses the TNG50 simulation to explore how the star-formation activity of dwarf galaxies relates to their large-scale environments, revealing that most quenched dwarfs are backsplash galaxies near massive halos and identifying a galactic conformity signal.

Contribution

It provides new insights into the environmental factors affecting dwarf galaxy quenching and uncovers a two-halo galactic conformity effect in the context of the TNG50 simulation.

Findings

Most isolated dwarfs remain star-forming.

Quenched dwarfs are mainly backsplash galaxies near large halos.

A galactic conformity signal links quenched dwarfs to quenched massive neighbors.

Abstract

The dwarf galaxies comparable to the LMC and SMC, with stellar masses $7.5 <{\rm log}(M_{\ast}/M_{\odot})<9.5$, are found in a diversity of environments and have long quenching timescales. We need to understand how this phenomenon is connected to the dwarfs' halo properties and their locations in the large-scale structure of the universe. We study the star-formation rates of dwarfs in the TNG50 simulation of the IllustrisTNG project across different environments, focusing on field dwarfs in host halos with virial masses of $9 < {\rm log}(M_{200}/M_{\odot}) < 11.5$, in contrast to dwarf satellites in hosts with ${\rm log}(M_{200}/M_{\odot}) \geq 11.5$. Our field dwarf sample is heterogeneous, consisting of primary (central) galaxies, with smaller numbers of secondaries and dwarf galaxies that are on backsplash orbits around massive galaxies. We study how the quenched fraction and star-formation histories depend on the dwarfs' large-scale environment and find that only $\sim 1\%$ of the most isolated dwarfs are quenched. The vast majority of the quenched field dwarfs are backsplash dwarfs located in the neighborhood of cluster-scale halos. We discover a two-halo galactic conformity signal that arises from the tendency of the quenched dwarfs, particularly the backsplash sample, to have a quenched massive galaxy as a neighbor. We attribute the low quenched fractions of the simulated LMC/SMC analogs in the field to the locations of their low-mass hosts in the sparse large-scale environment, which predominate over the relatively small number of backsplash and quenched primary dwarfs in denser environments.