353 research outputs found
Keck Spectroscopy of Faint 3<z<7 Lyman Break Galaxies:- II. A High Fraction of Line Emitters at Redshift Six
As Lyman-alpha photons are scattered by neutral hydrogen, a change with
redshift in the Lyman-alpha equivalent width distribution of distant galaxies
offers a promising probe of the degree of ionization in the intergalactic
medium and hence when cosmic reionization ended. This simple test is
complicated by the fact that Lyman-alpha emission can also be affected by the
evolving astrophysical details of the host galaxies. In the first paper in this
series, we demonstrated both a luminosity and redshift dependent trend in the
fraction of Lyman-alpha emitters seen within color-selected Lyman-break
galaxies (LBGs) over the range 3<z<6; lower luminosity galaxies and those at
higher redshift show an increased likelihood of strong emission. Here we
present the results from much deeper 12.5 hour exposures with the Keck DEIMOS
spectrograph focused primarily on LBGs at z~6 which enable us to confirm the
redshift dependence of line emission more robustly and to higher redshift than
was hitherto possible. We find 54+/-11% of faint z~6 LBGs show strong (W_0>25
A) emission, an increase of 1.6x from a similar sample observed at z~4. With a
total sample of 74 z~6 LBGs, we determine the luminosity-dependent Lyman-alpha
equivalent width distribution. Assuming continuity in these trends to the new
population of z~7 sources located with the Hubble WFC3/IR camera, we predict
that unless the neutral fraction rises in the intervening 200 Myr, the success
rate for spectroscopic confirmation using Lyman-alpha emission should be high.Comment: 6 pages, 3 figures, submitted to ApJ
Constraining dust formation in high-redshift young galaxies
Core-collapse supernovae (SNe) are believed to be the first significant
source of dust in the Universe. Such SNe are expected to be the main dust
producers in young high-redshift Lyman emitters (LAEs) given their
young ages, providing an excellent testbed of SN dust formation models during
the early stages of galaxy evolution. We focus on the dust enrichment of a
specific, luminous LAE (Himiko, ) for which a stringent upper
limit of Jy () has recently been obtained from ALMA
continuum observations at 1.2 mm. We predict its submillimetre dust emission
using detailed models that follow SN dust enrichment and destruction and the
equilibrium dust temperature, and obtain a plausible upper limit to the dust
mass produced by a single SN: --0.45 M,
depending on the adopted dust optical properties. These upper limits are
smaller than the dust mass deduced for SN 1987A and that predicted by dust
condensation theories, implying that dust produced in SNe are likely to be
subject to reverse shock destruction before being injected into the
interstellar medium. Finally, we provide a recipe for deriving
from submillimetre observations of young, metal poor objects
wherein condensation in SN ejecta is the dominant dust formation channel.Comment: 10 pages, 3 figures, accepted for publication in MNRA
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