Work

Burstiness in Low Stellar Mass H α Emitters at z ∼ 2 and z ∼ 4–6 from JWST Medium-band Photometry in GOODS-S

Year: 2025

Type: article

Abstract: We analyze a sample of ∼4500 photometrically selected H α emitter galaxies at redshifts z ∼ 2 and z ∼ 4–6 selected from James Webb Space Telescope Near-Infrared Camera medium-band images in the Great Observatories Origins Deep Survey South. The bulk (80%) of the galaxies in our sample have stellar masses lower than 10 8 M ⊙ , with a median stellar mass of ∼10 7.3 M ⊙ . We derive H α rest-frame equivalent widths (EW 0 H α ), line fluxes, and star formation rates (SFRs) using a robust photometric excess technique tested against spectroscopic measurements, being sensitive to EW 0 H α > 75 Å. Both EW 0 H α and sSFR(H α ) exhibit an anticorrelation with stellar mass. At fixed stellar mass, low-mass galaxies ( M ⋆ < 10 8 M ⊙ ) display a steep increase in sSFR(H α ) with redshift, following a relation sSFR(H α ) ∝ (1 + z ) 2.4 ± 0.3 . In contrast, more massive galaxies ( M ⋆ > 10 8 M ⊙ ) show a significantly flatter evolution, with sSFR(H α ) ∝ (1 + z ) 1.0 ± 0.2 . By comparing the H α and rest-frame UV-derived SFRs, we probe the star formation histories of our galaxies in the past 100 Myr. The fraction of low-mass galaxies with signs of bursty star formation from their SFR(H α )/SFR(UV) is ∼46%. It quickly drops to ∼25% for M ⋆ > 10 8 M ⊙ . This is consistent with the results from sSFR(H α ), showing 72% and 10%, respectively. SFR(H α )/SFR(UV) is a stricter criterion than those based on the galaxy sSFR(H α ), as it only identifies starbursts that are at the initial phases of a bursty star formation episode.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/ae1609