NGDEEP: Anchoring the $0.5<z<3.5$ Star-Forming Main Sequence at Low Stellar Masses with Ultradeep JWST/NIRISS WFSS

Abstract

Here we present deep JWST/NIRISS wide-field slitless spectroscopy (WFSS) that covers $\mathrm{H}\alpha$ and $\mathrm{H}\beta$ for galaxies at $0.5<z<3.5$ in the NGDEEP survey. The NGDEEP NIRISS observations detect emission line fluxes from galaxies in the Hubble Ultra Deep Field to ${\mathrm{m}}_{F150W}\lesssim$ 28 mag, enabling studies of star-formation based on $\mathrm{H}\alpha$ (or $\mathrm{H}\beta$, if necessary) in low-mass galaxies with $\log ({\mathrm{M}}_{\ast }/{\mathrm{M}}_{\odot })\gtrsim 7$ at z = 0.5 and $\log ({\mathrm{M}}_{\ast }/{\mathrm{M}}_{\odot })\gtrsim 8$ at z = 3.5. For 284 NGDEEP galaxies with $>3\sigma$ detections of $\mathrm{H}\alpha$ or $\mathrm{H}\beta$, we determine dust-corrected star-formation rates, $\mathrm{SF}{\mathrm{R}}_{\mathrm{H}\alpha }$, via flux measurements of these Balmer lines and compare them to the galaxies' stellar masses to investigate the properties of the star-forming main sequence (SFMS) on short, $\sim 10$~Myr timescales across three redshift bins. When we contrast the intrinsic scatter in the $\mathrm{H}\alpha$--based SFMS to that of a SFMS comprised of UV--based SFRs, which trace star formation within the past $\sim 100$~Myr, we find that the \Ha--based SFMS's intrinsic scatter ($\approx 0.35-0.5$~dex over $0.5<z<3.5$) is $\approx 0.2-0.4$~dex higher than the UV--based SFMS's intrinsic scatter at $z<2.5$. We argue that brief ($\lesssim 10$~Myr) bursts of star formation likely account for this disparity in SFMS scatter. Theoretical predictions from the FIRE simulations underestimate the scatter we observe in the $\mathrm{H}\alpha$--based SFMS at $1.5<z<2.5$ and $\log ({\mathrm{M}}_{\ast }/{\mathrm{M}}_{\odot })<9$ by up to $\approx 0.25$~dex, which suggests that low-mass galaxies have burstier star-formation histories than expected on $\lesssim 10$~Myr timescales.

arXiv commentSubmitted for publication in ApJL