74 research outputs found
MUSE spectroscopy and deep observations of a unique compact JWST target, lensing cluster CLIO
We present the results of a VLT MUSE/FORS2 and Spitzer survey of a unique compact lensing cluster CLIO at z = 0.42, discovered through the GAMA survey using spectroscopic redshifts. Compact and massive clusters such as this are understudied, but provide a unique prospective on dark matter distributions and for finding background lensed high-z galaxies. The CLIO cluster was identified for follow-up observations due to its almost unique combination of high-mass and dark matter halo concentration, as well as having observed lensing arcs from ground-based images. Using dual band optical and infra-red imaging from FORS2 and Spitzer, in combination with MUSE optical spectroscopy we identify 89 cluster members and find background sources out to z = 6.49. We describe the physical state of this cluster, finding a strong correlation between environment and galaxy spectral type. Under the assumption of an NFW profile, we measure the total mass of CLIO to be M200 = (4.49 ± 0.25) × 1014 M⊙. We build and present an initial strong-lensing model for this cluster, and measure a relatively low intracluster light (ICL) fraction of 7.21 ± 1.53 per cent through galaxy profile fitting. Due to its strong potential for lensing background galaxies and its low ICL, the CLIO cluster will be a target for our 110 h James Webb Space Telescope ‘Webb Medium-Deep Field’ (WMDF) GTO program.Publisher PDFPeer reviewe
First insights into the ISM at z > 8 with JWST: possible physical implications of a high [O III] λ4363/[O III] λ5007
© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.We present a detailed analysis of the rest-frame optical emission line ratios for three spectroscopically confirmed galaxies at z > 7.5. The galaxies were identified in the James Webb Space Telescope (JWST) Early Release Observations field SMACS J0723.3 − 7327. By quantitatively comparing Balmer and oxygen line ratios of these galaxies with various low-redshift ‘analogue’ populations (e.g. Green Peas, Blueberries, etc.), we show that no single analogue population captures the diversity of line ratios of all three galaxies observed at z > 7.5. We find that S06355 at z = 7.67 and S10612 at z = 7.66 are similar to local Green Peas and Blueberries. In contrast, S04590 at z = 8.50 appears to be significantly different from the other two galaxies, most resembling extremely low-metallicity systems in the local Universe. Perhaps the most striking spectral feature in S04590 is the curiously high [O III] λ4363/[O III] λ5007 ratio (RO3) of 0.048 (or 0.055 when dust-corrected), implying either extremely high electron temperatures, >3 × 104 K, or gas densities >104 cm−3. Observed line ratios indicate that this galaxy is unlikely to host an AGN. Using photoionization modelling, we show that the inclusion of high-mass X-ray binaries or a high cosmic ray background in addition to a young, low-metallicity stellar population can provide the additional heating necessary to explain the observed high RO3 while remaining consistent with other observed line ratios. Our models represent a first step at accurately characterizing the dominant sources of photoionization and heating at very high redshifts, demonstrating that non-thermal processes may become important as we probe deeper into the Epoch of Reionization.Peer reviewe
Unscrambling the lensed galaxies in JWST images behind SMACS0723
The first deep field images from the James Webb Space Telescope (JWST) of the
galaxy cluster SMACS~J0723.3-7327 reveal a wealth of new lensed images at
uncharted infrared wavelengths, with unprecedented depth and resolution. Here
we securely identify 14 new sets of multiply imaged galaxies totalling 42
images, adding to the five sets of bright and multiply-imaged galaxies already
known from Hubble Space Telescope data. We find examples of arcs crossing
critical curves, allowing detailed community follow-up, such as JWST
spectroscopy for precise redshift determinations, and measurements of the
chemical abundances and of the detailed internal gas dynamics of very distant,
young galaxies. One such arc contains compact knots of magnification
750, and features a microlensed transient. We also detect an Einstein
cross candidate only visible thanks to JWST's superb resolution. Our parametric
lens model is available at
https://www.dropbox.com/sh/gwup2lvks0jsqe5/AAC2RRSKce0aX-lIFCc9vhBXa?dl=0 , and
will be regularly updated using additional spectroscopic redshifts. The model
reproduces the multiple images to better than an rms of ,
and allows for accurate magnification estimates of high-redshift galaxies. The
intracluster light extends beyond the cluster members, exhibiting large-scale
features that suggest a significant past dynamical disturbance. This work
represents a first taste of the enhanced power JWST will have for
lensing-related science.Comment: Submitted to ApJ. 13 pages, 6 figure
PEARLS: Low Stellar Density Galaxies in the El Gordo Cluster Observed with JWST
A full understanding of how unusually large "Ultra Diffuse Galaxies" (UDGs)
fit into our conventional understanding of dwarf galaxies remains elusive,
despite the large number of objects identified locally. A natural extension of
UDG research is the study of similar galaxies at higher redshift to establish
how their properties may evolve over time. However, this has been a challenging
task given how severely systematic effects and cosmological surface brightness
dimming inhibit our ability to study low-surface brightness galaxies at
high-. Here, we present an identification of low stellar surface density
galaxies (LDGs), likely the progenitors of local UDGs, at moderate redshift
with deep near-IR observations of the El Gordo cluster at with JWST.
By stacking 8 NIRCAM filters, we are able to achieve an apparent surface
brightness sensitivity of mag arcsec, faint enough to be
complete to the bright end of the LDG population. Our analysis identifies
significant differences between this population and local UDGs, such as their
color and size distributions, which suggest that UDG progenitors are bluer and
more extended at high- than at . This suggests that multiple
mechanisms are responsible for UDG formation and that prolonged transformation
of cluster dwarfs is not a primary UDG formation mechanism at high-.
Furthermore, we find a slight overabundance of LDGs in El Gordo, and, in
contrast to findings in local clusters, our analysis does not show a deficit of
LDGs in the center of El Gordo, implying that tidal destruction of LDGs is
significant between and .Comment: Resubmitted to ApJ after minor revision
JADES: Using NIRCam Photometry to Investigate the Dependence of Stellar Mass Inferences on the IMF in the Early Universe
The detection of numerous and relatively bright galaxies at redshifts z > 9
has prompted new investigations into the star-forming properties of
high-redshift galaxies. Using local forms of the initial mass function (IMF) to
estimate stellar masses of these galaxies from their light output leads to
galaxy masses that are at the limit allowed for the state of the LambdaCDM
Universe at their redshift. We explore how varying the IMF assumed in studies
of galaxies in the early universe changes the inferred values for the stellar
masses of these galaxies. We infer galaxy properties with the SED fitting code
Prospector using varying IMF parameterizations for a sample of 102 galaxies
from the JWST Advanced Deep Extragalactic Survey (JADES) spectroscopically
confirmed to be at z > 6.7, with additional photometry from the JWST
Extragalactic Medium Band Survey (JEMS) for twenty-one galaxies. We demonstrate
that models with stellar masses reduced by a factor of three or more do not
affect the modeled spectral energy distribution (SED).Comment: The Significance statement is required for PNAS submissio
A Strong-Lensing Model for the WMDF JWST/GTO Very Rich Cluster Abell 1489
We present a first strong-lensing model for the galaxy cluster RM
J121218.5+273255.1 (; hereafter RMJ1212; also known as Abell 1489).
This cluster is amongst the top 0.1\% richest clusters in the redMaPPer
catalog; it is significantly detected in X-ray and through the
Sunyaev-Zel'dovich effect in ROSAT and \emph{Planck} data, respectively; and
its optical luminosity distribution implies a very large lens, following
mass-to-light scaling relations. Based on these properties it was chosen for
the Webb Medium Deep Fields (WMDF) JWST/GTO program. In preparation for this
program, RMJ1212 was recently imaged with GMOS on Gemini North and in seven
optical and near-infrared bands with the \emph{Hubble Space Telescope}. We use
these data to map the inner mass distribution of the cluster, uncovering
various sets of multiple images. We also search for high-redshift candidates in
the data, as well as for transient sources. We find over a dozen high-redshift
() candidates based on both photometric redshift and the dropout
technique. No prominent () transients were found in the data
between the two HST visits. Our lensing analysis reveals a relatively large
lens with an effective Einstein radius of
(), in broad agreement with the scaling-relation expectations. RMJ1212
demonstrates that powerful lensing clusters can be selected in a robust and
automated way following the light-traces-mass assumption.Comment: 17 pages, 6 figures, 2 tables; To be submitte
The Galaxies Missed by Hubble and ALMA: The Contribution of Extremely Red Galaxies to the Cosmic Census at 3 < z < 8
Using deep JWST imaging from JADES, JEMS, and SMILES, we characterize optically faint and extremely red galaxies at z > 3 that were previously missing from galaxy census estimates. The data indicate the existence of abundant, dusty, and poststarburst-like galaxies down to 108 M ⊙, below the sensitivity limit of Spitzer and the Atacama Large Millimeter/submillimeter Array (ALMA). Modeling the NIRCam and Hubble Space Telescope (HST) photometry of these red sources can result in extremely high values for both stellar mass and star formation rate (SFR); however, including seven MIRI filters out to 21 μm results in decreased masses (median 0.6 dex for log10(M∗/M⊙) > 10) and SFRs (median 10× for SFR > 100 M ⊙ yr−1). At z > 6, our sample includes a high fraction of “little red dots” (LRDs; NIRCam-selected dust-reddened active galactic nucleus (AGN) candidates). We significantly measure older stellar populations in the LRDs out to rest-frame 3 μm (the stellar bump) and rule out a dominant contribution from hot dust emission, a signature of AGN contamination to stellar population measurements. This allows us to measure their contribution to the cosmic census at z > 3, below the typical detection limits of ALMA (L IR < 1012 L ⊙). We find that these sources, which are overwhelmingly missed by HST and ALMA, could effectively double the obscured fraction of the star formation rate density at 4 < z < 6 compared to some estimates, showing that prior to JWST, the obscured contribution from fainter sources could be underestimated. Finally, we identify five sources with evidence for Balmer breaks and high stellar masses at 5.5 < z < 7.7. While spectroscopy is required to determine their nature, we discuss possible measurement systematics to explore with future data
High-Redshift Galaxy Candidates at as Revealed by JWST Observations of WHL0137-08
JWST was designed to peer into the distant universe and study galaxies nearer
the beginning of time than previously. Here we report the discovery of 12
galaxy candidates observed 300-600 Myr after the Big Bang with photometric
redshifts between z ~ 8.5-13 measured using JWST NIRCam imaging of the galaxy
cluster WHL0137 observed in 8 filters spanning 0.8-5.0 m, plus 9 HST
filters spanning 0.4-1.7 m. Three of these candidates are gravitationally
lensed by the foreground galaxy cluster and have magnifications of . The remaining nine candidates are located in a second JWST NIRCam module,
centered ~29' from the cluster center, with expected magnifications of <~
1.1. Our sample of high-redshift candidates have observed F200W AB magnitudes
between 25.9 and 28.1 mag and intrinsic F200W AB magnitudes between 26.4 and
29.7 mag ( = -22.5 to -17). We find the stellar masses of these
galaxies are in the range = 8 - 9, and down to 7.5 for
the lensed galaxies. All are young with mass-weighted ages < 100 Myr, low dust
content < 0.15 mag, and high specific star formation rates sSFR ~10-50
Gyr for most. One z ~ 9 candidate is consistent with an age < 5 Myr and
a sSFR ~250 Gyr, as inferred from a strong F444W excess, implying
[OIII]+H-beta rest-frame equivalent width ~2000 Angstrom, although an older and
redder z~ 10 object is also allowed. Another z~9 candidate ID9356 is lensed
into an arc 2.6" long by the effects of strong gravitational lensing (~8),
and has at least two bright knots of unevenly distributed star formation. This
arc is the most spatially-resolved galaxy at z~9 known to date, revealing
structures ~30 pc across. Follow-up spectroscopy of WHL0137 with JWST/NIRSpec
is planned for later this year, which will validate some of these candidates
and study their physical properties in more detail.Comment: submitted to Ap
JADES: Resolving the Stellar Component and Filamentary Overdense Environment of HST-Dark Submillimeter Galaxy HDF850.1 at
HDF850.1 is the brightest submillimeter galaxy (SMG) in the Hubble Deep
Field. It is known as a heavily dust-obscured star-forming galaxy embedded in
an overdense environment at . With nine-band NIRCam images at 0.8-5.0
m obtained through the JWST Advanced Deep Extragalactic Survey (JADES), we
detect and resolve the rest-frame UV-optical counterpart of HDF850.1, which
splits into two components because of heavy dust obscuration in the center. The
southern component leaks UV and H photons, bringing the galaxy
100 times above the empirical relation between infrared excess and UV
continuum slope (IRX-). The northern component is higher in
dust attenuation and thus fainter in UV and H surface brightness. We
construct a spatially resolved dust attenuation map from the NIRCam images,
well matched with the dust continuum emission obtained through millimeter
interferometry. The whole system hosts a stellar mass of
and star-formation rate of
, placing the galaxy at the
massive end of the star-forming main sequence at this epoch. We further confirm
that HDF850.1 resides in a complex overdense environment at ,
which hosts another luminous SMG at (GN10). The filamentary structures
of the overdensity are characterized by 109 H-emitting galaxies
confirmed through NIRCam slitless spectroscopy at 3.9-5 m, of which only
eight were known before the JWST observations. Given the existence of a similar
galaxy overdensity in the GOODS-S field, our results suggest that % of
the cosmic star formation at occur in protocluster environments.Comment: 44 pages, 16 figures, 2 tables. Resubmitted to ApJ after including
the first-round referee's comment
JWST's PEARLS: Mothra, a new kaiju star at z=2.091 extremely magnified by MACS0416, and implications for dark matter models
We report the discovery of Mothra, an extremely magnified monster star,
likely a binary system of two supergiant stars, in one of the strongly lensed
galaxies behind the galaxy cluster MACS0416. The star is in a galaxy with
spectroscopic redshift in a portion of the galaxy that is parsecs
away from the cluster caustic. The binary star is observed only on the side of
the critical curve with negative parity but has been detectable for at least
eight years, implying the presence of a small lensing perturber.
Microlenses alone cannot explain the earlier observations of this object made
with the Hubble Space Telescope. A larger perturber with a mass of at least
\,\Msun\ offers a more satisfactory explanation. Based on the lack of
perturbation on other nearby sources in the same arc, the maximum mass of the
perturber is \,\Msun, making it the smallest substructure
constrained by lensing above redshift 0.3. The existence of this millilens is
fully consistent with the expectations from the standard cold dark matter
model. On the other hand, the existence of such small substructure in a cluster
environment has implications for other dark matter models. In particular, warm
dark matter models with particle masses below 8.7\,keV are excluded by our
observations. Similarly, axion dark matter models are consistent with the
observations only if the axion mass is in the range .Comment: 26 pages and 27 figure
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