Suppression of star formation in low-mass galaxies caused by the reionization of their local neighbourhood

Abstract

Photoheating associated with reionization suppressed star formation in low-mass galaxies. Reionization was inhomogeneous, however, affecting different regions at different times. To establish the causal connection between reionization and suppression, we must take this local variation into account. We analyze the results of CoDa ('Cosmic Dawn') I, the first fully-coupled radiation-hydrodynamical simulation of reionization and galaxy formation in the Local Universe, in a volume large enough to model reionization globally but with enough resolving power to follow all atomic-cooling galactic halos in that volume. For every halo identified at a given time, we find the redshift at which the surrounding IGM reionized, along with its instantaneous star formation rate ('SFR') and baryonic gas-to-dark matter ratio (M gas /M dm ). The average SFR per halo with M < 10 9 M was steady in regions not yet reionized, but declined sharply following local reionization. For M > 10 10 M , this SFR continued through local reionization, increasing with time, instead. For 10 9 < M < 10 10 M , the SFR generally increased modestly through reionization, followed by a modest decline. In general, halo SFRs were higher for regions that reionized earlier. A similar pattern was found for M gas /M dm , which declined sharply following local reionization for M < 10 9 M . Local reionization time correlates with local matter overdensity, which determines the local rates of structure formation and ionizing photon consumption. The earliest patches to develop structure and reionize ultimately produced more stars than they needed to finish and maintain their own reionization, exporting their 'surplus' starlight to help reionize regions that developed structure later.

Evolution of dwarf galaxy observable parameters

“…These simulations reproduce stellar-halo mass relations that are consistent with observational data (Munshi et al 2017;Garrison-Kimmel et al 2019). Star formation in the smallest galaxies is truncated by reionization (Efstathiou 1992;Thoul & Weinberg 1996;Dijkstra et al 2004;Hoeft et al 2006;Dawoodbhoy et al 2018;Wheeler et al 2019), but even these galaxies should build up stellar masses M * ∼ 10 3 M before being quenched (Ricotti & Gnedin 2005;Wheeler et al 2015;Munshi et al 2017), although this result is sensitive to the star formation prescription used (Munshi et al 2019). More massive dwarf galaxies have bursty star formation histories (SFHs) (Wheeler et al 2019;Garrison-Kimmel et al 2019), consistent with observations, and are predominantly quenched by stellar feedback (Wang et al 2015), although supernova feedback alone might not be able to quench them completely (Bermejo-Climent et al 2018;Smith et al 2019).…”

“…During the epoch of reionization the average temperature of intergalactic gas rapidly increases up to ∼ 2 × 10 4 K (McQuinn et al 2009), which is above the virial temperature of halos with masses lower than ∼ 10 10 M . Gas accretion in these halos therefore should be shut-off and the star formation rate (SFR) should rapidly decrease (Gnedin 2000;Dawoodbhoy et al 2018;Ivkovich & McCall 2019).…”

How to quench a dwarf galaxy: The impact of inhomogeneous reionization on dwarf galaxies and cosmic filaments

“…Furthermore, it is only recently that the effects of inhomogeneity of reionization can be studied in a full-box cosmological radiation hydrodynamics simulation (e.g. Dawoodbhoy et al 2018).…”

“…Recently, Dawoodbhoy et al (2018) used the CoDa-I simulations (Ocvirk et al 2016) to study how star formation in dwarf galaxies was suppressed by inhomogeneous reionization. They find that in haloes with M vir 10 9 M , the star formation rates rapidly declined following the reionization of the local region.…”

Constraining the intergalactic medium at z ≈ 9.1 using LOFAR Epoch of Reionization observations

“…• Minimum mass of the UV emitting halos (M min ): In the above parametrization of the ionizing efficiency the number of ionizing photons escaping from a halo depends linearly on its mass. However, below a certain minimum mass radiative and mechanical feedback can severely reduce the star formation efficiency (see e.g., Hasegawa & Semelin 2013;Dawoodbhoy et al 2018). We model this by introducing M min as the minimum mass of halos from which ionizing photons escape into the IGM.…”