Abstract
ABSTRACT Low-surface-brightness galaxies (LSBGs) – defined as systems that are fainter than the surface-brightness limits of past wide-area surveys – form the overwhelming majority of galaxies in the dwarf regime (M⋆ < 109 M⊙). Using NewHorizon, a high-resolution cosmological simulation, we study the origin of LSBGs and explain why LSBGs at similar stellar mass show the large observed spread in surface brightness. NewHorizon galaxies populate a well-defined locus in the surface brightness–stellar mass plane, with a spread of ∼3 mag arcsec−2, in agreement with deep Sloan Digital Sky Survey (SDSS) Stripe 82 data. Galaxies with fainter surface brightnesses today are born in regions of higher dark matter density. This results in faster gas accretion and more intense star formation at early epochs. The stronger resultant supernova feedback flattens gas profiles at a faster rate, which, in turn, creates shallower stellar profiles (i.e. more diffuse systems) more rapidly. As star formation declines towards late epochs ( z < 1), the larger tidal perturbations and ram pressure experienced by these systems (due to their denser local environments) accelerate the divergence in surface brightness, by increasing their effective radii and reducing star formation, respectively. A small minority of dwarfs depart from the main locus towards high surface brightnesses, making them detectable in past wide surveys (e.g. standard-depth SDSS images). These systems have anomalously high star formation rates, triggered by recent fly-by or merger-driven starbursts. We note that objects considered extreme or anomalous at the depth of current data sets, e.g. ‘ultra-diffuse galaxies’, actually dominate the predicted dwarf population and will be routinely visible in future surveys like the Legacy Survey of Space and Time (LSST).
Highlights
1 INTRODUCTION Our statistical understanding of galaxy evolution is fundamentally driven by objects that are brighter than the surface brightness limits of wide-area surveys
We showed that galaxies that lower locus galaxies are those that experience an earlier phase of more intense star formation
Our statistical comprehension of galaxy evolution is driven by objects that are brighter than the surface brightness limits of wide-area surveys
Summary
Our statistical understanding of galaxy evolution is fundamentally driven by objects that are brighter than the surface brightness limits of wide-area surveys. Both theory (Martin et al 2019; Kulier et al 2019) and observational work using small, deep surveys (e.g. McGaugh et al 1995; Bothun et al 1997; Dalcanton et al 1997) indicate that most galaxies are, fainter than the surface brightness limits of past wide-area surveys These LSBGs are a heterogeneous population, ranging from massive, diffuse disks to all dwarf galaxies at cosmological distances. Martin et al (2019) have performed a comprehensive study of the formation of relatively massive LSBGs, using the Horizon-AGN cosmological simulation (Kaviraj et al 2017) They showed that, in the stellar mass range M★ > 109 M , the formation of LSBGs and their eventual divergence from their high surface brightness counterparts, is triggered by a period of more intense star formation activity in the early (z > 2) Universe.
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