Can Cosmological Accretion be Observed in H-alpha at z~2?

TL;DR

This paper explores whether cosmological gas accretion can be observed via H-alpha emission at redshift around 2, concluding current observations are not yet sensitive enough to detect such accretion signatures.

Contribution

It assesses the feasibility of detecting cosmological accretion through H-alpha emission and compares expected signals with current observational capabilities.

Findings

Accretion energy would need to be much higher than predicted by simulations.

Current observations lack the sensitivity to detect the required surface brightness.

Scaling relations suggest a regime where accretion could be observable, but it is currently out of reach.

Abstract

In previous studies, it has been shown that the large line widths observed in high surface brightness H-alpha emitters at low and high redshifts are likely due to the mechanical energy injected by intense star formation. Here we discuss the possibility that the high surface brightnesses observed are not due to star formation, but due to cosmological gas accretion. We assume that all of the accretion energy is dissipated as shocks from the accreting gas. We show that in order to explain the high surface brightnesses both the mass accretion rate and energy would have to be much higher than expected from simulations or from equating the star formation with the accretion rate. We also investigate scaling relations between the surface brightness expected from accretion and for star formation through mechanical heating and photo-ionization, trying to identify a regime where such accretion may become evident in galaxies. Unfortunately, the surface brightness necessary to detect the gas in optical line emission is about an order of magnitude lower than what has currently been achieved with near-infrared observations of distant galaxies.