Testing the Relationship Between Bursty Star Formation and Size Fluctuations of Local Dwarf Galaxies

Abstract

Stellar feedback in dwarf galaxies plays a critical role in regulating star formation via galaxy-scale winds. Recent hydrodynamical zoom simulations of dwarf galaxies predict that the periodic outward flow of gas can change the gravitational potential sufficiently to cause radial migration of stars. To test the effect of bursty star formation on stellar migration, we examine star formation observables and sizes of 86 local dwarf galaxies. We find a correlation between the R-band half-light radius (R e ) and far-UV luminosity (L F U V ) for stellar masses below 10 8 M and a weak correlation between the R e and Hα luminosity (L Hα ). We produce mock observations of eight low-mass galaxies from the FIRE-2 cosmological simulations and measure the similarity of the time sequences of R e and a number of star formation indicators with different timescales. Major episodes of R e time sequence align very well with the major episodes of star formation, with a delay of ∼ 50 Myrs. This correlation decreases towards SFR indicators of shorter timescales such that R e is weakly correlated with L F U V (10-100 Myr timescale) and is completely uncorrelated with L Hα (a few Myr timescale), in agreement with the observations. Our findings based on FIRE-2 suggest that the R-band size of a galaxy reacts to star formation variations on a ∼ 50 Myr timescale. With the advent of a new generation of large space telescopes (e.g., JWST), this effect can be examined explicitly in galaxies at higher redshifts where bursty star formation is more prominent.

Observational constraints on stellar feedback in dwarf galaxies

“…[130] show that this is expected if star formation proceeds in repeated impulsive bursts, driving gas outflows that cause stars to slowly migrate outwards. Secondly, the same process drives size-fluctuations that are consistent with current observational constraints [131]. Thirdly, it can explain the existence of 'ultra-diffuse' low surface brightness dwarfs (defined as galaxies with large effective radii, over 1.5 kpc, and low central surface brightnesses, less than µ 0,V ∼ 23.5, [132]) [133,134], though we note that this formation pathway is not without its problems [e.g.…”

The In-situ Origins of Dwarf Stellar Outskirts in FIRE-2

“…This feedback-driven migration has previously been suggested as a formation mechanism for in-situ stellar halos (Stinson et al 2009;Maxwell et al 2012). Star formation feedback-driven size fluctuations have also recently been found via correlations between size and star formation rate in both the FIRE-2 dwarfs and a sample of nearby dwarfs from the Local Volume Legacy Survey (Emami et al 2021).…”

Exploring metallicity-dependent rates of Type Ia supernovae and their impact on galaxy formation

“…For discussion of stellar mass assembly timescales and SFHs in FIRE-2 galaxies, see Garrison-Kimmel et al (2019a), Garrison-Kimmel et al (2019b), Graus et al (2019), Iyer et al (2020), andSantistevan et al (2020). Sparre et al (2017) and Flores Velázquez et al (2021) examined SFRs of FIRE-2 galaxies using different observational tracers, while Emami et al (2021) tested the impact of bursty SFHs on the sizes of FIRE-2 lowmass galaxies. For stellar elemental abundances in FIRE, Ma et al (2016), Escala et al (2018), andHopkins et al (2020) benchmarked both iron and alpha-capture element distributions in high-mass and low-mass galaxies, while Wheeler et al (2019) provided the same for ultra-faint galaxies.…”