Effects of helium sedimentation on late star formation in galaxy clusters

TL;DR

This paper investigates how helium sedimentation in galaxy clusters influences star formation in central galaxies, finding negligible effects in smaller clusters and potentially significant effects in the largest clusters.

Contribution

It presents a 1D numerical simulation of helium sedimentation and assesses its impact on star formation across different cluster masses.

Findings

Helium sedimentation effects are negligible in clusters with mass < 10^{14} M_sun.

Effects are mild (below factor 2) in clusters with mass between 10^{14} and 10^{15} M_sun.

Helium sedimentation can significantly enhance star formation in clusters with mass > 10^{15} M_sun.

Abstract

We discuss how helium sedimentation in galaxy clusters can affect the history of star formation in the central cluster galaxy. As helium sediments, the gas density in the inner regions of the cluster increases and there is also a non-trivial, radially dependent redistribution of the atomic nuclei and electrons. As a result, the cooling rate in the center increases and this can enhance star formation. On the other hand, there is a slow contraction of the intracluster gas, which may induce gravitational heating and therefore has an opposite effect on star formation. In this work we present these effects and aim to estimate their relevance. For this we have performed a 1-dimensional numerical simulation of helium sedimentation and applied it to a simple semi-analytical model of star formation. We find that for clusters with a halo mass $M_{\rm halo} \lesssim 10^{14} M_{\rm sun}$, helium sedimentation effects on the star formation rate are negligible, even under idealized conditions. In the intermediate range, $10^{14} M_{\rm sun} \lesssim M_{\rm halo} \lesssim 10^{15} M_{\rm sun}$, the effects are at most mild, below a factor ~ 2 in the isothermal model we consider, even for idealized conditions. For clusters with a halo mass $M_{\rm halo} \gtrsim 10^{15} M_{\rm sun}$, helium sedimentation effects can potentially be very important and renew star formation activity in the central galaxy.