학술논문
CEERS: Increasing Scatter along the Star-Forming Main Sequence Indicates Early Galaxies Form in Bursts
Document Type
Working Paper
Author
Cole, Justin W.; Papovich, Casey; Finkelstein, Steven L.; Bagley, Micaela B.; Dickinson, Mark; Iyer, Kartheik G.; Yung, L. Y. Aaron; Ciesla, Laure; Amorin, Ricardo O.; Haro, Pablo Arrabal; Bhatawdekar, Rachana; Calabro, Antonello; Cleri, Nikko J.; de la Vega, Alexander; Dekel, Avishai; Endsley, Ryan; Gawiser, Eric; Giavalisco, Mauro; Hathi, Nimish P.; Hirschmann, Michaela; Holwerda, Benne W.; Kartaltepe, Jeyhan S.; Koekemoer, Anton M.; Lucas, Ray A.; Mascia, Sara; Mobasher, Bahram; Perez-Gonzalez, Pablo G.; Rodighiero, Giulia; Ronayne, Kaila; Tachhella, Sandro; Weiner, Benjamin J.; Wilkins, Stephen M.
Source
Subject
Language
Abstract
We present the star-formation-rate -- stellar-mass (SFR-M$_\ast$) relation for galaxies in the CEERS survey at $4.5\leq z\leq 12$. We model the \jwst\ and \hst\ rest-UV and rest-optical photometry of galaxies with flexible star-formation histories (SFHs) using \bagpipes. We consider SFRs averaged from the SFHs over 10~Myr (\sfrten) and 100~Myr (\sfrcen), where the photometry probes SFRs on these timescales, effectively tracing nebular emission lines in the rest-optical (on $\sim10$~Myr timescales) and the UV/optical continuum (on $\sim100$ Myr timescales). We measure the slope, normalization and intrinsic scatter of the SFR-M$_\ast$ relation, taking into account the uncertainty and the covariance of galaxy SFRs and $M_\ast$. From $z\sim 5-9$ there is larger scatter in the $\sfrten-M_\ast$ relation, with $\sigma(\log \sfrcen)=0.4$~dex, compared to the $\sfrcen-M_\ast$ relation, with $\sigma(\log \sfrten)=0.1$~dex. This scatter increases with redshift and increasing stellar mass, at least out to $z\sim 7$. These results can be explained if galaxies at higher redshift experience an increase in star-formation variability and form primarily in short, active periods, followed by a lull in star formation (i.e. ``napping'' phases). We see a significant trend in the ratio $R_\mathrm{SFR}=\log(\sfrten/\sfrcen)$ in which, on average, $R_\mathrm{SFR}$ decreases with increasing stellar mass and increasing redshift. This yields a star-formation ``duty cycle'' of $\sim40\%$ for galaxies with $\log M_\ast/M_\odot\geq 9.3$, at $z\sim5$, declining to $\sim20\%$ at $z\sim9$. Galaxies also experience longer lulls in star formation at higher redshift and at higher stellar mass, such that galaxies transition from periods of higher SFR variability at $z\gtrsim~6$ to smoother SFR evolution at $z\lesssim~4.5$.
Comment: 28 pages, 12 figures, 2 Appendix figures
Comment: 28 pages, 12 figures, 2 Appendix figures