Starburst and post-starburst high-redshift protogalaxies

The feedback impact of high energy cosmic rays

¹ Mullard Space Science Laboratory, University College London, Dorking, Surrey RH5 6NT, UK
e-mail: ellis.owen.12@ucl.ac.uk
² Institute of Astronomy, Department of Physics, National Tsing Hua University, Hsinchu, Taiwan (ROC)
³ School of Physics, University of Sydney, Camperdown, NSW 2006, Australia
⁴ School of Physics, Nanjing University, Nanjing 210023, PR China
⁵ Department of Physics and McGill Space Institute, McGill University, 3600 University St., Montreal, QC H3A 2T8, Canada
⁶ Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, Heidelberg 69117, Germany
⁷ Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555, Japan

Received: 1 October 2018
Accepted: 27 April 2019

Abstract

Quenching of star-formation has been identified in many starburst and post-starburst galaxies, indicating burst-like star-formation histories (SFH) in the primordial Universe. Galaxies undergoing violent episodes of star-formation are expected to be rich in high energy cosmic rays (CRs). We have investigated the role of these CRs in such environments, particularly how they could contribute to this burst-like SFH via quenching and feedback. These high energy particles interact with the baryon and radiation fields of their host via hadronic processes to produce secondary leptons. The secondary particles then also interact with ambient radiation fields to generate X-rays through inverse-Compton scattering. In addition, they can thermalise directly with the semi-ionised medium via Coulomb processes. Heating at a rate of ∼10⁻²⁵ erg cm⁻³ s⁻¹ can be attained by Coulomb processes in a star-forming galaxy with one core-collapse SN event per decade, and this is sufficient to cause quenching of star-formation. At high-redshift, a substantial amount of CR secondary electron energy can be diverted into inverse-Compton X-ray emission. This yields an X-ray luminosity of above 10⁴¹ erg s⁻¹ by redshift z = 7 which drives a further heating effect, operating over larger scales. This would be able to halt inflowing cold gas filaments, strangulating subsequent star-formation. We selected a sample of 16 starburst and post-starburst galaxies at 7 ≲ z ≲ 9 and determine the star-formation rates they could have sustained. We applied a model with CR injection, propagation and heating to calculate energy deposition rates in these 16 sources. Our calculations show that CR feedback cannot be neglected as it has the strength to suppress star-formation in these systems. We also show that their currently observed quiescence is consistent with the suffocation of cold inflows, probably by a combination of X-ray and CR heating.