The Brightest $zgtrsim8$ Galaxies over the COSMOS UltraVISTA Field. (arXiv:1902.10713v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Stefanon_M/0/1/0/all/0/1">Mauro Stefanon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Labbe_I/0/1/0/all/0/1">Ivo Labbé</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bouwens_R/0/1/0/all/0/1">Rychard J. Bouwens</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Oesch_P/0/1/0/all/0/1">Pascal Oesch</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ashby_M/0/1/0/all/0/1">Matthew L. N. Ashby</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Caputi_K/0/1/0/all/0/1">Karina I. Caputi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Franx_M/0/1/0/all/0/1">Marijn Franx</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fynbo_J/0/1/0/all/0/1">Johan P. U. Fynbo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Illingworth_G/0/1/0/all/0/1">Garth D. Illingworth</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fevre_O/0/1/0/all/0/1">Olivier Le Fèvre</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marchesini_D/0/1/0/all/0/1">Danilo Marchesini</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McCracken_H/0/1/0/all/0/1">Henry J. McCracken</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Milvang_Jensen_B/0/1/0/all/0/1">Bo Milvang-Jensen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Muzzin_A/0/1/0/all/0/1">Adam Muzzin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dokkum_P/0/1/0/all/0/1">Pieter van Dokkum</a>
We present 16 new ultrabright $H_{AB}lesssim25$ galaxy candidates at z~8
identified over the COSMOS/UltraVISTA field. The new search takes advantage of
the deepest-available ground-based optical and near-infrared observations,
including the DR3 release of UltraVISTA and full-depth Spitzer/IRAC
observations from the SMUVS and SPLASH programs. Candidates are selected using
Lyman-break color criteria, combined with strict optical non-detection and
SED-fitting criteria, designed to minimize contamination by low-redshift
galaxies and low-mass stars. HST/WFC3 coverage from the DASH program reveals
that one source evident in our ground-based near-IR data has significant
substructure and may actually correspond to 3 separate z~8 objects, resulting
in a total sample of 18 galaxies. The UV-continuum slope $beta$ for the bright
z~8 sample is $beta=-2.2pm0.6$, bluer but still consistent with that of
similarly bright galaxies at z~6 ($beta=-1.55pm0.17$) and z~7
($beta=-1.75pm0.18$). Their typical stellar masses are
10$^{9.1^{+0.5}_{-0.4}}$ $M_{odot}$, with SFRs of
$32^{+44}_{-32}M_{odot}$/year, specific SFR of $4^{+8}_{-4}$ Gyr$^{-1}$,
stellar ages of $sim22^{+69}_{-22}$ Myr, and low dust content
A$_V=0.15^{+0.30}_{-0.15}$ mag. Using this sample we constrain the bright end
of the z~8 UV luminosity function (LF). When combined with recent empty field
LF estimates at similar redshifts, the resulting z~8 LF can be equally well
represented by either a Schechter or a double power-law (DPL) form. Assuming a
Schechter parameterization, the best-fit characteristic magnitude is
$M^*=-20.95^{+0.30}_{-0.35}$ mag with a very steep faint end slope
$alpha=-2.15^{+0.20}_{-0.19}$. These new candidates include amongst the
brightest yet found at these redshifts, 0.5-1.0 magnitude brighter than found
over CANDELS, providing excellent targets for spectroscopic and
longer-wavelength follow-up studies.
We present 16 new ultrabright $H_{AB}lesssim25$ galaxy candidates at z~8
identified over the COSMOS/UltraVISTA field. The new search takes advantage of
the deepest-available ground-based optical and near-infrared observations,
including the DR3 release of UltraVISTA and full-depth Spitzer/IRAC
observations from the SMUVS and SPLASH programs. Candidates are selected using
Lyman-break color criteria, combined with strict optical non-detection and
SED-fitting criteria, designed to minimize contamination by low-redshift
galaxies and low-mass stars. HST/WFC3 coverage from the DASH program reveals
that one source evident in our ground-based near-IR data has significant
substructure and may actually correspond to 3 separate z~8 objects, resulting
in a total sample of 18 galaxies. The UV-continuum slope $beta$ for the bright
z~8 sample is $beta=-2.2pm0.6$, bluer but still consistent with that of
similarly bright galaxies at z~6 ($beta=-1.55pm0.17$) and z~7
($beta=-1.75pm0.18$). Their typical stellar masses are
10$^{9.1^{+0.5}_{-0.4}}$ $M_{odot}$, with SFRs of
$32^{+44}_{-32}M_{odot}$/year, specific SFR of $4^{+8}_{-4}$ Gyr$^{-1}$,
stellar ages of $sim22^{+69}_{-22}$ Myr, and low dust content
A$_V=0.15^{+0.30}_{-0.15}$ mag. Using this sample we constrain the bright end
of the z~8 UV luminosity function (LF). When combined with recent empty field
LF estimates at similar redshifts, the resulting z~8 LF can be equally well
represented by either a Schechter or a double power-law (DPL) form. Assuming a
Schechter parameterization, the best-fit characteristic magnitude is
$M^*=-20.95^{+0.30}_{-0.35}$ mag with a very steep faint end slope
$alpha=-2.15^{+0.20}_{-0.19}$. These new candidates include amongst the
brightest yet found at these redshifts, 0.5-1.0 magnitude brighter than found
over CANDELS, providing excellent targets for spectroscopic and
longer-wavelength follow-up studies.
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