1,722,424 research outputs found
Resolving Clumpy vs. Extended Ly- In Strongly Lensed, High-Redshift Ly- Emitters
Get PDFWe present six strongly gravitationally lensed Ly- Emitters (LAEs) at
with HST narrowband imaging isolating Ly-. Through complex
radiative transfer Ly- encodes information about the spatial
distribution and kinematics of the neutral hydrogen upon which it scatters. We
investigate the galaxy properties and Ly- morphologies of our sample.
Many previous studies of high-redshift LAEs have been limited in Ly-
spatial resolution. In this work we take advantage of high-resolution
Ly- imaging boosted by lensing magnification, allowing us to probe
sub-galactic scales that are otherwise inaccessible at these redshifts. We use
broadband imaging from HST (rest-frame UV) and Spitzer (rest-frame optical) in
SED fitting; providing estimates on the stellar masses (), stellar population ages ( Myr), and amounts of dust
(, statistically consistent with zero). We employ
non-parametric star-formation histories to probe the young stellar-populations
which create Ly-. We also examine the offsets between the Ly-
and stellar continuum, finding small upper limits of offsets ()
consistent with studies of low-redshift LAEs; indicating our galaxies are not
interacting or merging. Finally, we find a bimodality in our sample's
Ly- morphologies: clumpy and extended. We find a suggestive trend: our
LAEs with clumpy Ly- are generally younger than the LAEs with extended
Ly-, suggesting a possible correlation with age.Comment: 17 pages (2 for references), 5 figures, 6 table
GREEN PEA GALAXIES REVEAL SECRETS OF Ly alpha ESCAPE
No full textWe analyze archival Ly alpha spectra of 12 "Green Pea" galaxies observed with the Hubble Space Telescope, model their Ly alpha profiles with radiative transfer models, and explore the dependence of the Ly alpha escape fraction on various properties. Green Pea galaxies are nearby compact starburst galaxies with [O III] lambda 5007 equivalent widths (EWs) of hundreds of angstrom. All 12 Green Pea galaxies in our sample show Ly alpha lines in emission, with an Ly alpha EW distribution similar to high-redshift Ly alpha emitters. Combining the optical and UV spectra of Green Pea galaxies, we estimate their Ly alpha escape fractions and find correlations between Ly alpha escape fraction and kinematic features of Ly alpha profiles. The escape fraction of Ly alpha in these galaxies ranges from 1.4% to 67%. We also find that the Ly alpha escape fraction depends strongly on metallicity and moderately on dust extinction. We compare their high-quality Ly alpha profiles with single H I shell radiative transfer models and find that the Ly alpha escape fraction anticorrelates with the derived H I column densities. Single-shell models fit most Ly alpha profiles well, but not the ones with the. highest escape fractions of Ly alpha. Our results suggest that low H I column density and low metallicity are essential for Ly alpha escape. and make a galaxy an Ly alpha emitter.China Scholarship CouncilNSF
UV & Ly halos of Ly emitters across environments at z=2.84
Get PDFWe present UV and Ly radial surface brightness (SB) profiles of
Ly emitters (LAEs) at detected with the Hyper Suprime-Cam
(HSC) on the Subaru Telescope. The depth of our data, together with the wide
field coverage including a protocluster, enable us to study the dependence of
Ly halos (LAHs) on various galaxy properties, including Mpc-scale
environments. UV and Ly images of 3490 LAEs are extracted, and stacking
the images yields SB sensitivity of
in Ly,
reaching the expected level of optically thick gas illuminated by the UV
background at . Fitting of the two-component exponential function gives
the scale-lengths of and pkpc. Dividing the sample
according to their photometric properties, we find that while the dependence of
halo scale-length on environment outside of the protocluster core is not clear,
LAEs in the central regions of protoclusters appear to have very large LAHs
which could be caused by combined effects of source overlapping and diffuse
Ly emission from cool intergalactic gas permeating the forming
protocluster core irradiated by active members. For the first time, we identify
``UV halos'' around bright LAEs which are probably due to a few lower-mass
satellite galaxies. Through comparison with recent numerical simulations, we
conclude that, while scattered Ly photons from the host galaxies are
dominant, star formation in satellites evidently contributes to LAHs, and that
fluorescent Ly emission may be boosted within protocluster cores at
cosmic noon and/or near bright QSOs.Comment: 29 pages, 20 Figures, Accepted for publication in Ap
Ly Emission at : Clear Ly Equivalent Width Evolution Indicating the Late Cosmic Reionization History
Get PDFWe present the evolution of Ly emission derived from 53 galaxies at
that are identified by multiple JWST/NIRSpec spectroscopy programs
of ERS, GO, DDT, and GTO. These galaxies fall on the star-formation main
sequence and are the typical star-forming galaxies with UV magnitudes of
. We find that 15 out of 53 galaxies show
Ly emission at the levels, and obtain Ly equivalent
width (EW) measurements and stringent upper limits for the 15 and 38
galaxies, respectively. Confirming that Ly velocity offsets and line
widths of our galaxies are comparable with those of low-redshift Ly
emitters, we investigate the redshift evolution of the Ly EW. We find
that Ly EWs statistically decrease towards high redshifts on the
Ly EW vs. plane for various probability distributions of
the uncertainties. We then evaluate neutral hydrogen fractions
with the Ly EW redshift evolution and the cosmic reionization
simulation results on the basis of a Bayesian inference framework, and obtain
, , and at
, , and , respectively. These moderately large
values are consistent with the Planck CMB optical depth measurement and
previous constraints from galaxy and QSO Ly damping wing
absorptions, and strongly indicate a late reionization history. Such a late
reionization history suggests that major sources of reionization would emerge
late and be hosted by moderately massive halos in contrast with the
widely-accepted picture of abundant low-mass objects for the sources of
reionization.Comment: Accepted for publication in Ap
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Constraining The Ly Alpha Escape Fraction With Far- Infrared Observations Of Ly Alpha Emitters
No full textWe study the far-infrared properties of 498 Ly alpha emitters (LAEs) at z = 2.8, 3.1, and 4.5 in the Extended Chandra Deep Field-South, using 250, 350, and 500 mu m data from the Herschel Multi-tiered Extragalactic Survey and 870 mu m data from the LABOCA ECDFS Submillimeter Survey. None of the 126, 280, or 92 LAEs at z = 2.8, 3.1, and 4.5, respectively, are individually detected in the far-infrared data. We use stacking to probe the average emission to deeper flux limits, reaching 1 sigma depths of similar to 0.1 to 0.4 mJy. The LAEs are also undetected at >= 3 sigma in the stacks, although a 2.5 sigma signal is observed at 870 mu m for the z = 2.8 sources. We consider a wide range of far-infrared spectral energy distributions (SEDs), including an M82 and an Sd galaxy template, to determine upper limits on the far-infrared luminosities and far-infrared-derived star formation rates of the LAEs. These star formation rates are then combined with those inferred from the Ly alpha and UV emission to determine lower limits on the LAEs' Lya escape fraction (f(esc)(Ly alpha)). For the Sd SED template, the inferred LAEs fesc(Ly alpha) are greater than or similar to 30% (1 sigma) at z = 2.8, 3.1, and 4.5, which are all significantly higher than the global fesc(Ly alpha) at these redshifts. Thus, if the LAEs fesc(Ly alpha) follows the global evolution, then they have warmer far-infrared SEDs than the Sd galaxy template. The average and M82 SEDs produce lower limits on the LAE fesc(Ly alpha) of similar to 10%-20% (1 sigma), all of which are slightly higher than the global evolution of fesc(Ly alpha), but consistent with it at the 2 sigma-3 sigma level.European Organisation for Astronomical Research in the Southern Hemisphere, Chile 078.F-9028(A), 079.F-9500(A), 080.A-3023(A), 081.F-9500(A)CSA (Canada)NAOC (China)CEA (France)CNES (France)CNRS (France)ASI (Italy)MCINN (Spain)SNSB (Sweden)STFC (UK)UKSA (UK)NASA (USA)Astronom
The Ly non-detection by JWST NIRSpec of a strong Ly emitter at confirmed by MUSE
Get PDFThe detections of Lyman- () emission in galaxies with
redshifts above 5 are of utmost importance for constraining the cosmic
reionization timeline, yet such detections are usually based on slit
spectroscopy. Here we investigate the significant bias induced by slit
placement on the estimate of escape fraction ( ), by presenting a galaxy (dubbed A2744-z6Lya) at
where its deep JWST NIRSpec prism spectroscopy completely misses the
strong emission detected in the MUSE data. A2744-z6Lya exhibits
a pronounced UV continuum with an extremely steep spectral slope of
, and it has a stellar mass of
, a star-formation rate of
and gas-phase metallicity of
. The observed flux and rest-frame equivalent
width of its Ly from MUSE spectroscopy are and 75\r{A}, equivalent to . However, its Ly non-detection from
JWST NIRSpec gives a 5- upper limit of , in stark contrast to
that derived from MUSE. To explore the reasons for this bias, we perform
spatially resolved stellar population analysis of A2744-z6Lya using the JWST
NIRCam imaging data to construct 2-dimensional maps of SFR, dust extinction and
neutral hydrogen column density. We find that the absence of Ly in the
slit regions probably stems from both the resonance scattering effect of
neutral hydrogen and dust extinction. Through analyzing an extreme case in
detail, this work highlights the important caveat of inferring from slit spectroscopy, particularly when using the
JWST multiplexed NIRSpec microshutter assembly.Comment: 10 pages, 4 figures, 1 tabl
Ciii] emission as an alternative to Ly in the reionization era: the dependence of Ciii] and Ly at from the VANDELS survey
Get PDFThe velocity offset of Ly emission from a galaxy's systemic redshift
is an excellent tracer of conditions that enable the escape of Ly
photons from the galaxy, and potentially hydrogen ionizing Lyman continuum
photons. However at , Ly is often heavily attenuated by the
neutral intergalactic medium. Here we investigate the utility of
Ciii], emission, usually the brightest UV line after
Ly, as a proxy estimating the Ly velocity offset (). To do so, we use analogues of reionization era galaxies
based upon 52 star-forming galaxies with robust Ciii] detections drawn from the
VANDELS survey. Our sample spans a broad UV magnitude range of , with a sample average value of EW(Ciii]) \,{\AA}.
We find a slight increase of EW(Ciii]) with increasing EW(Ly), but find
a large range of EW(Ciii]) 1-13\,{\AA} particularly at EW(Ly)
\,{\AA}. Using the Ciii] line peak as the systemic redshift, we calculate
and recover the previously reported trend of
decreasing with increasing EW(Ly).
Interestingly, we find an anti-correlation between
and EW(Ciii]), which also displays a dependence on the UV absolute magnitude.
We derive a multi-variate fit to obtain using both
EW(Ciii]) and , finding that is more
strongly dependent on EW(Ciii]), with a weaker but non-negligible dependence on
. We find that for a fixed EW(Ciii]), UV-bright Ly
emitting galaxies show smaller values of ,which
suggests that such galaxies may be undergoing more bursty star-formation
compared to the UV-fainter ones, akin to a population of extremely UV-bright
galaxies identified at .Comment: 11 pages, 7 figure
Challenging the LyC-Ly relation: strong Ly emitters without LyC leakage at z 2.3
Get PDFThe escape fraction of LyC ionizing radiation is crucial for
understanding reionization, yet impossible to measure at z 5.3.
Recently, studies have focused on calibrating indirect indicators of
at z 0.3, finding that Ly is closely linked to
it. What is still unclear is whether the LyC - Ly relation evolves with
redshift, and if Ly is truly applicable as an indicator
during the reionization epoch. In this study, we investigate seven gravitationally lensed galaxies from the BELLS
GALLERY survey at z 2.3. Our targets have rest-frame Ly
equivalent widths ranging from 10 \r{A} to 100 \r{A} and low dust content
(), both indicative of high LyC escape.
Surprisingly, direct estimates of using Hubble Space Telescope
imaging with F275W and F225W reveal that our targets are not LyC emitters, with
absolute 6.5% at 3 significance (with two
sources having absolute (3) 10% and
16%). The low , coupled with the high Ly
escape fraction and equivalent width could potentially be attributed to the
redshift evolution of the neutral hydrogen column density and dust content. Our
results challenge previous studies based on local samples, suggesting that the
extrapolation of z ~ 0 Ly-based LyC indirect estimators into the
reionization epoch might not be correct.Comment: 19 Pages, 8 Figures. Submitted to Ap
Construction of the Damped Ly Absorber Catalog for DESI DR2 Ly BAO
No full textInternational audienceWe present the Damped Ly Toolkit for automated detection and characterization of Damped Ly absorbers (DLA) in quasar spectra. Our method uses quasar spectral templates with and without absorption from intervening DLAs to reconstruct observed quasar forest regions. The best-fitting model determines whether a DLA is present while estimating the redshift and HI column density. With an optimized quality cut on detection significance (), the technique achieves an estimated 72% purity and 71% completeness when evaluated on simulated spectra with S/N that are free of broad absorption lines (BAL). We provide a catalog containing candidate DLAs from the DLA Toolkit detected in DESI DR1 quasar spectra, of which 21,719 were found in S/N spectra with predicted and detection significance . We compare the Damped Ly Toolkit to two alternative DLA finders based on a convolutional neural network (CNN) and Gaussian process (GP) models. We present a strategy for combining these three techniques to produce a high-fidelity DLA catalog from DESI DR2 for the Ly forest baryon acoustic oscillation measurement. The combined catalog contains 41,152 candidate DLAs with from quasar spectra with S/N. We estimate this sample to be approximately 76% pure and 71% complete when BAL quasars are excluded
On the origin of metallicity in ly alpha forest systems
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We investigate the hypothesis that Ly alpha absorption lines arise in two populations of halos---minihalos of small circular velocity (Vc <~ 55 km s-1), in which star formation and metal production are inhibited by photoionization of the UV background radiation, and large galactic halos (55 <~ Vc <~ 250 km s-1) that contain stars and metals. Based on the model of Ly alpha -absorbing gas confined in both populations of halos, we attempt to explain the recent observations of (1) associations of visible galaxies with Ly alpha lines at low redshifts z <~ 1 and (2) metal lines associated with a nonnegligible fraction of low H I column density Ly alpha lines at z ~ 3. For galactic halos, we find that photoionized gas clouds confined in the pressure of ambient hot gas can produce Ly alpha absorption for H I column densities as low as 1014 cm-2 and that the impact parameter of a sight line for such absorptions matches well with the observed radius of the gaseous envelope of a typical luminous galaxy. Using the Press-Schechter prescription for the mass function of halos, we also show that the fraction of Ly alpha lines with associated metal lines can be understood in terms of the fraction of Ly alpha absorbers associated with galactic halos. In particular, the reported fraction of ~0.5--0.75 at z ~ 3 is reproduced when the boundary value of Vc to separate minihalos or galactic halos is 40--60 km s-1, which is consistent with the theoretical prediction of galaxy formation under photoionization. The average metallicity of both Ly alpha forest and damped Ly alpha systems at z ~ 3 is explained in terms of the model of halo-formation history combined with the age-metallicity relationship of Galactic halo stars. Possible methods to test this hypothesis and alternative scenarios are also discussed
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