Transforming gas-rich low-mass disky galaxies into ultra-diffuse galaxies by ram pressure

TL;DR

This study identifies low-mass, gas-rich disky galaxies in clusters with signs of ram pressure stripping and recent star formation, suggesting they evolve into ultra-diffuse galaxies over billions of years.

Contribution

It provides observational evidence linking ram pressure stripping to the formation of ultra-diffuse galaxies from disky progenitors in galaxy clusters.

Findings

11 low-mass galaxies with large radii and recent star formation identified

Deep spectroscopy shows rotating stellar discs with high dark matter content

Passive evolution could transform most of these galaxies into ultra-diffuse galaxies within 10 Gyr

Abstract

Faint extended elliptically-shaped ultra-diffuse galaxies and slightly brighter and more compact dwarf elliptical and lenticular stellar systems are common in galaxy clusters. Their poorly constrained evolutionary paths can be studied by identifying young ultra-diffuse galaxy and dwarf elliptical analogs populated with bright, massive stars. Using data mining we identified 11 such low-mass ($2\times10^8<M_*<2\times10^9 M_{\odot}$) galaxies with large half-light radii ($2.0<r_e<5$ kpc) and recently quenched star formation in the Coma and Abell 2147 galaxy clusters. All galaxies happen to have ram-pressure-stripped tails with signs of current or recent star formation. Deep spectroscopic observations revealed rotating stellar discs containing 70-95% dark matter by mass. A large fraction of the disc stars (10-60%) formed in intense star bursts 180-970 Myr ago, probably triggered by ram pressure. Observed global gradients of stellar age corroborate this scenario. Passive evolution in the next 10 Gyr will transform 9 of the 11 galaxies into ultra-diffuse galaxies. If we assume a constant rate of galaxy infall, 44$\pm$16% of the most luminous present-day ultra-diffuse galaxies in Coma must have formed via ram pressure stripping of disky progenitors.