The morphological mix of dwarf galaxies in the nearby Universe – Ilin Lazar

This talk, part of the UH Centre for Astrophysics Research (CAR) 2023-2024 seminar series, was presented by Ilin Lazar (UH) on work from his PhD.

Date: 20 March 2024

The morphological mix of dwarf galaxies in the nearby Universe

Abstract: Morphology is a fundamental parameter in observational astrophysics, which is strongly correlated with the evolution of galaxies. Dwarf galaxies dominate the galaxy number density at all epochs and all environments, making them critical to our understanding of galaxy evolution. However, typical dwarfs are too faint to be visible outside the very local Universe in past surveys like the SDSS, which offer large footprints but are relatively shallow. Deep-wide surveys such as LSST and Euclid (which are around 10 magnitudes deeper than the SDSS spectroscopic sample) will detect millions of dwarfs outside the local neighborhood, revolutionizing our understanding of dwarf galaxies. I will present a pilot study for upcoming surveys such as LSST and Euclid on the morphological mix of the dwarf (10^8 M☉ ≲ M⋆ ≲ 10^9.5 M☉) population at z≲0.08 using deep (i ≲ 27.5 mag) unbiased Hyper Suprime-Cam observations in the COSMOS field. We find that ~45 and ~45 per cent of dwarfs exhibit the traditional 'early-type' (elliptical/S0) and 'late-type' (spiral) morphologies, respectively. However, 10 per cent populate a 'featureless' class, that lacks both the central light concentration seen in early-types and any spiral structure - this class is missing in the massive-galaxy regime. Compared to their massive counterparts, dwarf early-types show a much lower incidence of interactions, are significantly less concentrated and share similar rest-frame colours as dwarf late-types. This suggests that the formation histories of dwarf and massive early-types are different, with dwarf early-types being shaped less by interactions and more by secular processes. Finally, we find that it is challenging to cleanly separate early and late-type dwarfs using traditional morphological parameters such as ‘CAS’, M20 and the Gini coefficient (unlike in the massive galaxy regime). I will end with presenting future prospects/plans for dwarf galaxy evolution studies in the era of Euclid and LSST.

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