A hydrogen-rich, passive galaxy

Cold gas in the form of neutral hydrogen atoms provides the reservoir for star formation in galaxies from the distant to the nearby Universe. Understanding how it accretes onto galaxies is of crucial importance because fresh supplies of gas fuel the ongoing star-forming. In the most popular version, accretion onto the galaxy occurs along cosmic filaments, and at least in more massive galaxies is heated by shocks in the process; in smaller galaxies the infalling material stays relatively cool. Si