Abstract
Near infrared slitless spectroscopy with the Wide Field Camera 3, onboard the
Hubble Space Telescope, offers a unique opportunity to study low-mass galaxy
populations at high-redshift ($z\sim$1-2). While most high$-z$ surveys are
biased towards massive galaxies, we are able to select sources via their
emission lines that have very-faint continua. We investigate the star formation
rate (SFR)-stellar mass ($M_\star$) relation for about 1000 emission-line
galaxies identified over a wide redshift range of $0.3 z łesssim
2.3$. We use the H$_\alpha$ emission as an accurate SFR indicator and correct
the broadband photometry for the strong nebular contribution to derive accurate
stellar masses down to $M_\star 10^7 M_ødot$. We focus here on a
subsample of galaxies that show extremely strong emission lines (EELGs) with
rest-frame equivalent widths ranging from 200 to 1500 \AA. This population
consists of outliers to the normal SFR-$M_\star$ sequence with much higher
specific SFRs ($> 10$ Gyr$^-1$). While on-sequence galaxies follow a
continuous star formation process, EELGs are thought to be caught during an
extreme burst of star formation that can double their stellar mass in less than
$100$ Myr. The contribution of starbursts to the total star formation density
appears to be larger than what has been reported for more massive galaxies in
previous studies. In the complete mass range $8.2 <$ log($M_\star/M_ødot$)
$< 10$ and a SFR lower completeness limit of about 2 $M_ødot$ yr$^-1$ (10
$M_ødot$ yr$^-1$) at $z\sim1$ ($z 2$), we find that starbursts having
EW$_rest$(H$_\alpha$)$>$ 300, 200, and 100 A contribute up to $\sim13$, 18,
and 34 %, respectively, to the total SFR of emission-line selected sample at
$z\sim1-2$. The comparison with samples of massive galaxies shows an increase
in the contribution of starbursts towards lower masses.
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