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Arxiv: Burstiness in low stellar-mass Ha emitters at z~2 and z~4-6 from JWST medium band photometry in GOODS-S Published: 10/30/2024 7:34:07 PM Updated: 10/30/2024 7:34:07 PM

Paper abstract: We analyze a sample of 4500 photometrically-selected Ha emitter galaxies atredshifts z~2 and z~4-6 selected from James Webb Space Telescope (JWST)Near-Infrared Camera (NIRCam) medium-band images in the Great ObservatoriesOrigins Deep Survey South (GOODS-S). The bulk (80%) of the galaxies in oursample have stellar masses lower than 10^8 Msun, with a median stellar mass of~10^7.3 Msun. We derive Ha rest-frame equivalent widths ( EW0(Ha) ), linefluxes, and star formation rates using a robust photometric excess techniquetested against spectroscopic measurements, being sensitive to EW0(Ha) > 75 A.Both EW0(Ha) and sSFR(Ha) anti-correlate with stellar mass, and at fixedstellar mass, show a steep increasing trend with redshift sSFR(Ha) ~(1+z)^2.55. By comparing the Ha and rest-frame UV-derived SFRs, we probe thestar formation histories (SFHs) of our galaxies in the past 100 Myr. Thefraction of low-mass galaxies (M < 10^8 Msun) with signs of bursty starformation from their SFR(Ha)/SFR(UV) is ~ 50 %. It quickly drops to ~ 25 % forM > 10^8 Msun. This is consistent with the results from sSFR(Ha), showing 80%and 17%, respectively. SFR(Ha)/SFR(UV) is a stricter criterion than those basedon the galaxy sSFR(Ha), as it only identifies the strongest starbursts, theones at the initial phases of a bursty star-formation episode.