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Investigating star formation burstiness in low-mass galaxies using Helium recombination lines

Presentation #241.37 in the session Evolution of Galaxies — iPoster Session.

Published onJun 29, 2022
Investigating star formation burstiness in low-mass galaxies using Helium recombination lines

Star formation (SF) burstiness refers to the recurrent episodes of rapid, intense star formation in galaxies typically lasting for a few to tens of million years. Bursty star formation is key to understanding galaxy evolution because it plays an important role in the dark matter halo–galaxy connection and is linked to the scaling relation of galaxies. Low-mass galaxies (with stellar mass M* < 109.5 Mʘ) are expected to undergo strong SF bursts: they are more susceptible to feedback effects, as the gases in their shallow gravitational wells can be easily heated and expelled. However, low-mass galaxies haven’t been sufficiently observed beyond our local universe. Here, we present the results from the deep Keck/DEIMOS spectroscopic surveys HALO7D and DEEPwinds. We obtained secure redshifts for ~500 low-mass galaxies at 0.4 < z < 1.0 and detected not only strong emission lines (such as [OII] doublet 3727+3729, [OIII] 5007, and Hβ 4863) but also faint, yet physically important lines ([OIII] 4363, He lines) from a subsample of them. These robust measurements in a large sample of low-mass galaxies make HALO7D and DEEPwinds surveys ideal for analyzing key characteristics of galaxy evolution, such as gas-phase metallicity and star formation. To investigate the SF burstiness in this sample, we search for the faint He I 5876, He I 4471, and He II 4686 lines in the individual and stacked spectra. We then (1) measure the He I/Hβ ratio of the individual and stacked spectra and compare them to starburst models; (2) compare the physical properties of the He I detected galaxies to that of the non–He I detected galaxies; and (3) compare the He I/Hβ ratio to other burstiness indicators (e.g., Hβ/FUV ratio).

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