Kavli Affiliate: Linhua Jiang
| First 5 Authors: Shuqi Fu, Fengwu Sun, Linhua Jiang, Xiaojing Lin, Jose M. Diego
| Summary:
We measure H$alpha$ luminosity functions (LFs) at redshifts $z sim 4.5$ and
6.3 using the JWST MAGNIF (Medium-band Astrophysics with the Grism of NIRCam In
Frontier fields) survey. MAGNIF obtained NIRCam grism spectra with the F360M
and F480M filters in four Frontier Fields. We identify 248 H$alpha$ emitters
based on the grism spectra and photometric redshifts from combined HST and JWST
imaging data. The numbers of the H$alpha$ emitters show a large field-to-field
variation, highlighting the necessity of multiple fields to mitigate cosmic
variance. We calculate both observed and dust-corrected H$alpha$ LFs in the
two redshift bins. Thanks to the gravitational lensing, the measured H$alpha$
LFs span three orders of magnitude in luminosity, and the faint-end luminosity
reaches $L_{mathrm{H}alpha} sim 10^{40.3} mathrm{erg} mathrm{s}^{-1}$ at
$z sim 4.5$ and $10^{41.5} mathrm{erg} mathrm{s}^{-1}$ at $z sim 6.3$,
corresponding to star-formation rates (SFRs) of $sim$ 0.1 and 1.7
$mathrm{M}_odot mathrm{yr}^{-1}$. We conclude no or weak redshift evolution
of the faint-end slope of H$alpha$ LF across $zsimeq0.4-6.3$, and the
comparison with the faint-end slopes of UV LF indicates stochastic star
formation history among low-mass H$alpha$ emitters. The derived cosmic SFR
densities are $0.058^{+0.008}_{-0.006} M_odot mathrm{yr}^{-1}
mathrm{Mpc}^{-3}$ at $z sim 4.5$ and $0.025^{+0.009}_{-0.007} M_odot
mathrm{yr}^{-1} mathrm{Mpc}^{-3}$ at $z sim 6.3$. These are approximately
2.2 times higher than previous estimates based on dust-corrected UV LFs, but
consistent with recent measurements from infrared surveys. We discuss
uncertainties in the H$alpha$ LF measurements, including those propagate from
the lens models, cosmic variance, and AGN contribution.
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