249 research outputs found
First performance of the gems + gmos system. Part1. Imaging
During the commissioning of the Gemini MCAO System (GeMS), we had the
opportunity to obtain data with the Gemini Multi-Object Spectrograph (GMOS),
the most utilised instrument at Gemini South Observatory, in March and May
2012. Several globular clusters were observed in imaging mode that allowed us
to study the performance of this new and untested combination. GMOS is a
visible instrument, hence pushing MCAO toward the visible.We report here on the
results with the GMOS instruments, derive photometric performance in term of
Full Width Half Maximum (FWHM) and throughput. In most of the cases, we
obtained an improvement factor of at least 2 against the natural seeing. This
result also depends on the Natural Guide Star constellation selected for the
observations and we then study the impact of the guide star selection on the
FWHM performance.We also derive a first astrometric analysis showing that the
GeMS+GMOS system provide an absolute astrometric precision better than 8mas and
a relative astrometric precision lower than 50 mas.Comment: 13 pages, 11 figures, accepted for publication in MNRAS on March 23rd
201
First Results from the Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) Survey: Cosmological Reionization at z ~ 7
We present the first results from the ongoing LAGER project (Lyman Alpha
Galaxies in the Epoch of Reionization), which is the largest narrowband survey
for 7 galaxies to date. Using a specially built narrowband filter
NB964 for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m
Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in
the 3 deg COSMOS field. We have identified 23 Lyman Alpha Emitter (LAE)
candidates at = 6.9 in the central 2-deg region, where DECam and public
COSMOS multi-band images exist. The resulting luminosity function can be
described as a Schechter function modified by a significant excess at the
bright end (4 galaxies with 10 erg
s). The number density at 10 erg
s is little changed from z= 6.6, while at fainter it is
substantially reduced. Overall, we see a fourfold reduction in Ly
luminosity density from = 5.7 to 6.9. Combined with a more modest evolution
of the continuum UV luminosity density, this suggests a factor of
suppression of Ly by radiative transfer through the 7
intergalactic medium (IGM). It indicates an IGM neutral fraction
0.4--0.6 (assuming Ly velocity offsets of 100-200 km s).
The changing shape of the Ly luminosity function between and supports the hypothesis of ionized bubbles in a patchy
reionization at 7.Comment: 7 pages, 3 figures (updated), 2 tables (updated), Accepted for
publication in ApJ Letter
A narrow-band search for Ly alpha emitting galaxies at z = 8.8
Aims: The first star forming galaxies in the early universe should be copious
Ly alpha emitters, and may play a significant role in ionizing the
intergalactic medium (IGM). It has been proposed that the luminosity function
of Lya emitting galaxies beyond z~6 may be used to constrain the neutral
fraction of the IGM during this epoch. In this work we report on a search for
Ly alpha emitters at redshift 8.8.
Methods: We performed a narrow band imaging programme using ISAAC at the ESO
VLT. Seven fields, covering a total area of 31sq. arcmin and for which optical
and broad band infra-red images have been obtained in the GOODS survey, were
imaged to a limiting flux (respectively luminosity) of ~ 1.3 x 10^{-17}
ergs.s^{-1}.cm^{-2} (respectively ~ 1.3 x 10^{43} ergs.s^{-1} in a narrow band
filter centered in a region of low OH sky emission at 1.19 micron. Candidate
Lyman alpha emitters are objects that are detected in the ISAAC NB images and
undetected in the visible broad band images.
Results: No z=8.8 Ly alpha emitting galaxies were detected to a limit
approaching recent estimates of the luminosity function at z ~ 6. Our results
do suggest, however, that detections or substantial constraints could be
achieved by this method in the near future with larger field instruments
planned for various telescopes.Comment: 7 pages, accepted for publication in A&
First results from Faint Infrared Grism Survey (FIGS): first simultaneous detection of Lyman-alpha emission and Lyman break from a galaxy at z=7.51
Galaxies at high redshifts provide a valuable tool to study cosmic dawn, and
therefore it is crucial to reliably identify these galaxies. Here, we present
an unambiguous and first simultaneous detection of both the Lyman-alpha
emission and the Lyman break from a z = 7.512+/- 0.004 galaxy, observed in the
Faint Infrared Grism Survey (FIGS). These spectra, taken with G102 grism on
Hubble Space Telescope (HST), show a significant emission line detection (6
sigma) in multiple observational position angles (PA), with total integrated
Ly{\alpha} line flux of 1.06+/- 0.12 e10-17erg s-1cm-2. The line flux is nearly
a factor of four higher than the previous MOSFIRE spectroscopic observations of
faint Ly{\alpha} emission at {\lambda} = 1.0347{\mu}m, yielding z = 7.5078+/-
0.0004. This is consistent with other recent observations implying that
ground-based near-infrared spectroscopy underestimates total emission line
fluxes, and if confirmed, can have strong implications for reionization studies
that are based on ground-based Lyman-{\alpha} measurements. A 4-{\sigma}
detection of the NV line in one PA also suggests a weak Active Galactic Nucleus
(AGN), potentially making this source the highest-redshift AGN yet found. Thus,
this observation from the Hubble Space Telescope clearly demonstrates the
sensitivity of the FIGS survey, and the capability of grism spectroscopy to
study the epoch of reionization.Comment: Published in ApJL; matches published versio
First Spectroscopic Confirmations of z ~ 7.0 Lya Emitting Galaxies in the LAGER Survey
Narrowband imaging is a highly successful approach for finding large numbers
of high redshift Lya emitting galaxies (LAEs) up to z~6.6. However, at z>~7
there are as yet only 3 narrowband selected LAEs with spectroscopic
confirmations (two at z~6.9-7.0, one at z~7.3), which hinders extensive studies
on cosmic reionization and galaxy evolution at this key epoch. We have selected
23 candidate z~6.9 LAEs in COSMOS field with the large area narrowband survey
LAGER (Lyman-Alpha Galaxies at the End of Reionization). In this work we
present spectroscopic followup observations of 12 candidates using IMACS on
Magellan. For 9 of these, the observations are sufficiently deep to detect the
expected lines. Lya emission lines are identified in six sources (yielding a
success rate of 2/3), including 3 luminous LAEs with Lya luminosities of L(Lya)
~ 10^{43.5} erg/s, the highest among known spectroscopically confirmed galaxies
at >~7.0. This triples the sample size of spectroscopically confirmed
narrowband selected LAEs at z>~7, and confirms the bright end bump in the Lya
luminosity function we previously derived based on the photometric sample,
supporting a patchy reionization scenario. Two luminous LAEs appear physically
linked with projected distance of 1.1 pMpc and velocity difference of ~ 170
km/s. They likely sit in a common ionized bubble produced by themselves or with
close neighbors, which reduces the IGM attenuation of Lya. A tentative narrow
NV1240 line is seen in one source, hinting at activity of a central
massive black hole with metal rich line emitting gas.Comment: 6 pages, 3 figures, 2 tables, accepted by ApJ
Probing the first galaxies with the SKA
Observations of anisotropies in the brightness temperature of the 21 cm line
of neutral hydrogen from the period before reionization would shed light on the
dawn of the first stars and galaxies. In this paper, we use large-scale
semi-numerical simulations to analyse the imprint on the 21 cm signal of
spatial fluctuations in the Lyman-alpha flux arising from the clustering of the
first galaxies. We show that an experiment such as the Square Kilometer Array
(SKA) can probe this signal at the onset of reionization, giving us important
information about the UV emission spectra of the first stars and characterizing
their host galaxies. SKA-pathfinders with ~ 10% of the full collecting area
should be capable of making a statistical detection of the 21 cm power spectrum
at redshifts z 67 MHz). We then show
that the SKA should be able to measure the three dimensional power spectrum as
a function of the angle with the line of sight and discuss the use of the
redshift space distortions as a way to separate out the different components of
the 21 cm power spectrum. We demonstrate that, at least on large scales where
the Lyman-alpha fluctuations are linear, they can be used as a model
independent way to extract the power spectra due to these Lyman-alpha
fluctuations.Comment: 13 pages, 17 figures. New version to match version accepted by A&A.
Improved discussions on the Lyman-alpha simulation, adiabatic cooling
fluctuations, the Fisher matrix approach and the Poisson term calculation.
New version of the code available at: http://www.SimFast21.or
FIGS -- Faint Infrared Grism Survey: Description and Data Reduction
The Faint Infrared Grism Survey (FIGS) is a deep Hubble Space Telescope (HST)
WFC3/IR (Wide Field Camera 3 Infrared) slitless spectroscopic survey of four
deep fields. Two fields are located in the Great Observatories Origins Deep
Survey-North (GOODS-N) area and two fields are located in the Great
Observatories Origins Deep Survey-South (GOODS-S) area. One of the southern
fields selected is the Hubble Ultra Deep Field. Each of these four fields were
observed using the WFC3/G102 grism (0.8-1.15 continuous coverage)
with a total exposure time of 40 orbits (~ 100 kilo-seconds) per field. This
reaches a 3 sigma continuum depth of ~26 AB magnitudes and probes emission
lines to . This paper details the four
FIGS fields and the overall observational strategy of the project. A detailed
description of the Simulation Based Extraction (SBE) method used to extract and
combine over 10000 spectra of over 2000 distinct sources brighter than
m_F105W=26.5 mag is provided. High fidelity simulations of the observations is
shown to significantly improve the background subtraction process, the spectral
contamination estimates, and the final flux calibration. This allows for the
combination of multiple spectra to produce a final high quality, deep,
1D-spectra for each object in the survey.Comment: 21 Pages. 17 Figures. To appear in Ap
Onset of Cosmic Reionization: Evidence of An Ionized Bubble Merely 680 Myrs after the Big Bang
While most of the inter-galactic medium (IGM) today is permeated by ionized
hydrogen, it was largely filled with neutral hydrogen for the first 700 million
years after the Big Bang. The process that ionized the IGM (cosmic
reionization) is expected to be spatially inhomogeneous, with fainter galaxies
playing a significant role. However, we still have only a few direct
constraints on the reionization process. Here we report the first spectroscopic
confirmation of two galaxies and very likely a third galaxy in a group
(hereafter EGS77) at redshift z = 7.7, merely 680 Myrs after the Big Bang. The
physical separation among the three members is < 0.7 Mpc. We estimate the
radius of ionized bubble of the brightest galaxy to be about 1.02 Mpc, and show
that the individual ionized bubbles formed by all three galaxies likely overlap
significantly, forming a large yet localized ionized region, which leads to the
spatial inhomogeneity in the reionization process. It is striking that two of
three galaxies in EGS77 are quite faint in the continuum, thanks to our
selection of reionizing sources using their Lyman-alpha line emission. Indeed,
one is the faintest spectroscopically confirmed galaxy yet discovered at such
high redshifts. Our observations provide direct constraints in the process of
cosmic reionization, and allow us to investigate the properties of sources
responsible for reionizing the universe.Comment: Submitted after addressing referee's comment
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