Kavli Affiliate: Risa H. Wechsler
| First 5 Authors: Erin Kado-Fong, Marla Geha, Yao-Yuan Mao, Mithi A. C. de los Reyes, Risa H. Wechsler
| Summary:
The redshift-dependent relation between galaxy stellar mass and star
formation rate (the Star-Forming Sequence, or SFS) is a key observational
yardstick for galaxy assembly. We use the SAGAbg-A sample of background
galaxies from the Satellites Around Galactic Analogs (SAGA) Survey to model the
low-redshift evolution of the low-mass SFS. The sample is comprised of 23258
galaxies with H$alpha$-based star formation rates (SFRs) spanning
$6<log_{10}(rm M_star/[M_odot])<10$ and $z<0.21$ ($t<2.5$ Gyr). Although it
is common to bin or stack galaxies at $z lesssim 0.2$ for galaxy population
studies, the difference in lookback time between $z=0$ and $z=0.21$ is
comparable to the time between $z=1$ to $z=2$. We develop a model to account
for both the physical evolution of low-mass SFS and the selection function of
the SAGA survey, allowing us to disentangle redshift evolution from
redshift-dependent selection effects across the SAGAbg-A redshift range. Our
findings indicate significant evolution in the SFS over the last 2.5 Gyr, with
a rising normalization: $langle {rm SFR}({rm M_star=10^{8.5}
M_odot)}rangle(z)=1.24^{+0.25}_{-0.23} {rm z} -1.47^{+0.03}_{-0.03}$. We
also identify the redshift limit at which a static SFS is ruled out at the 95%
confidence level, which is $z=0.05$ based on the precision of the SAGAbg-A
sample. Comparison with cosmological hydrodynamic simulations reveals that some
contemporary simulations under-predict the recent evolution of the low-mass
SFS. This demonstrates that the recent evolution of the low-mass SFS can
provide new constraints on the assembly of the low-mass Universe and highlights
the need for improved models in this regime.
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