Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Fengwu Sun, Eiichi Egami, Nor Pirzkal, Marcia Rieke, Stefi Baum
| Summary:
We present a sample of four emission-line galaxies at $z=6.11-6.35$ that were
serendipitously discovered using the commissioning data for the JWST/NIRCam
wide-field slitless spectroscopy (WFSS) mode. One of them (at $z=6.11$) has
been reported previously while the others are new discoveries. These sources
are selected by the secure detections of both [O III] $lambda$5007 and
H$alpha$ lines with other fainter lines tentatively detected in some cases
(e.g., [O II] $lambda$3727, [O III] $lambda$4959 and [N II] $lambda$6583).
In the [O III]/H$beta$ – [N II]/H$alpha$ Baldwin-Phillips-Terlevich diagram,
these galaxies occupy the same parameter space as that of $zsim2$ star-forming
galaxies, indicating that they have been enriched rapidly to sub-solar
metallicities ($sim$0.6 $Z_{odot}$), similar to galaxies with comparable
stellar masses at much lower redshifts. The detection of strong H$alpha$ lines
suggests a higher ionizing photon production efficiency within galaxies in the
early Universe. We find brightening of the [O III] $lambda$5007 line
luminosity function (LF) from $z=3$ to 6, and no or weak redshift evolution of
the H$alpha$ line LF from $z=2$ to 6. Both LFs are under-predicted at $zsim6$
by a factor of $sim$10 in certain cosmological simulations. This further
indicates a global Ly$alpha$ photon escape fraction of 5-7% at $zsim6$, much
lower than previous estimates through the comparison of the UV-derived
star-formation rate density and Ly$alpha$ luminosity density. Our sample
recovers $88^{+164}_{-57}$% of $z=6.0-6.6$ galaxies in the survey volume with
stellar masses greater than $5times10^8$ $M_{odot}$, suggesting the ubiquity
of strong H$alpha$ and [O III] line emitters in the Epoch of Reionization,
which will be further uncovered in the era of JWST.
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