Distribution of streaming rates into high-redshift galaxies

TL;DR

This study uses cosmological simulations to analyze how streams of gas feed high-redshift galaxies, revealing a consistent accretion pattern, a bimodal distribution of inflow rates, and the impact of feedback mechanisms.

Contribution

It provides a detailed characterization of gas accretion rates and their distribution into high-redshift galaxies, including the effects of feedback and the distinction between smooth inflow and mergers.

Findings

Accretion rates follow predicted mass and redshift dependence.

Distribution of accretion rates fits a sum of two Gaussians.

Strong feedback leads to reaccretion from galactic winds.

Abstract

We study the accretion along streams from the cosmic web into high-redshift massive galaxies using three sets of AMR hydro-cosmological simulations. We find that the streams keep a roughly constant accretion rate as they penetrate into the halo centre. The mean accretion rate follows the mass and redshift dependence predicted for haloes by the EPS approximation, dM / dt is proportional to Mvir^{1.25} (1 + z)^{2.5}. The distribution of the accretion rates can well be described by a sum of two Gaussians, the primary corresponding to "smooth inflow" and the secondary to "mergers". The same functional form was already found for the distributions of specific star formation rates in observations. The mass fraction in the smooth component is 60 - 90 %, insensitive to redshift or halo mass. The simulations with strong feedback show clear signs of reaccretion due to recycling of galactic winds. The mean accretion rate for the mergers is a factor 2 - 3 larger than that of the smooth component. The standard deviation of the accretion rate is 0.2 - 0.3 dex, showing no trend with mass or redshift. For the smooth component it is 0.12 - 0.24 dex.