We present the first results of the KMOS Lens-Amplified Spectroscopic Survey (KLASS), a new ESO Very Large Telescope (VLT) large program, doing multi-object integral field spectroscopy of galaxies ...gravitationally lensed behind seven galaxy clusters selected from the HST Grism Lens-Amplified Survey from Space (GLASS). Using the power of the cluster magnification we are able to reveal the kinematic structure of 25 galaxies at \(0.7 \lesssim z \lesssim 2.3\), in four cluster fields, with stellar masses \(8 \lesssim \log{(M_\star/M_\odot)} \lesssim 11\). This sample includes 5 sources at \(z>1\) with lower stellar masses than in any previous kinematic IFU surveys. Our sample displays a diversity in kinematic structure over this mass and redshift range. The majority of our kinematically resolved sample is rotationally supported, but with a lower ratio of rotational velocity to velocity dispersion than in the local universe, indicating the fraction of dynamically hot disks changes with cosmic time. We find no galaxies with stellar mass \(<3 \times 10^9 M_\odot\) in our sample display regular ordered rotation. Using the enhanced spatial resolution from lensing, we resolve a lower number of dispersion dominated systems compared to field surveys, competitive with findings from surveys using adaptive optics. We find that the KMOS IFUs recover emission line flux from HST grism-selected objects more faithfully than slit spectrographs. With artificial slits we estimate slit spectrographs miss on average 60% of the total flux of emission lines, which decreases rapidly if the emission line is spatially offset from the continuum.
The CIII and CIV rest-frame UV emission lines are powerful probes of the
ionizations states of galaxies. They have furthermore been suggested as
alternatives for spectroscopic redshift confirmation ...of objects at the epoch of
reionization ($z>6$), where the most frequently used redshift indicator,
Ly$\alpha$, is attenuated by the high fraction of neutral hydrogen in the
inter-galactic medium. However, currently only very few confirmations of carbon
UV lines at these high redshifts exist, making it challenging to quantify these
claims. Here, we present the detection of CIV$\lambda\lambda$1548,1551\AA\ in
\HST\ slitless grism spectroscopy obtained by GLASS of a Ly$\alpha$ emitter at
$z=6.11$ multiply imaged by the massive foreground galaxy cluster RXJ2248. The
CIV emission is detected at the 3--5$\sigma$ level in two images of the source,
with marginal detection in two other images. We do not detect significant
CIII$\lambda\lambda$1907,1909\AA\ emission implying an equivalent width
EW$_\textrm{CIII}<20$\AA\ (1$\sigma$) and $\textrm{CIV/CIII}>0.7$ (2$\sigma$).
Combined with limits on the rest-frame UV flux from the HeII$\lambda$1640\AA\
emission line and the OIII$\lambda\lambda$1661,1666\AA\ doublet, we put
constraints on the metallicity and the ionization state of the galaxy. The
estimated line ratios and equivalent widths do not support a scenario where an
AGN is responsible for ionizing the carbon atoms. SED fits including nebular
emission lines imply a source with a mass of log(M/M$_\odot)\sim9$, SFR of
around 10M$_\odot$/yr, and a young stellar population $<50$Myr old. The source
shows a stronger ionizing radiation field than objects with detected CIV
emission at $z<2$ and adds to the growing sample of low-mass
(log(M/M$_\odot)\lesssim9$) galaxies at the epoch of reionization with strong
radiation fields from star formation.
The galaxy cluster RX J0603.3+4214 at z=0.225 is one of the rarest clusters boasting an extremely large (~2 Mpc) radio-relic. Because of the remarkable morphology of the relic, the cluster is ...nicknamed "Toothbrush Cluster". Although the cluster's underlying mass distribution is one of the critical pieces of information needed to reconstruct the merger scenario responsible for the puzzling radio-relic morphology, its proximity to the Galactic plane b~10 deg has imposed significant observational challenges. We present a high-resolution weak-lensing study of the cluster with Subaru/Suprime Cam and Hubble Space Telescope imaging data. Our mass reconstruction reveals that the cluster is comprised of complicated dark matter substructures closely tracing the galaxy distribution, however in contrast with the relatively simple binary X-ray morphology. Nevertheless, we find that the cluster mass is still dominated by the two most massive clumps aligned north-south with a ~3:1 mass ratio (M_{200}=6.29_{-1.62}^{+2.24} x 10^{14} Msun and 1.98_{-0.74}^{+1.24} x 10^{14} Msun for the northern and southern clumps, respectively). The southern mass peak is ~2' offset toward the south with respect to the corresponding X-ray peak, which has a "bullet"-like morphology pointing south. Comparison of the current weak-lensing result with the X-ray, galaxy, and radio-relic suggests that perhaps the dominant mechanism responsible for the observed relic may be a high-speed collision of the two most massive subclusters, although the peculiarity of the morphology necessitates involvement of additional sub-clusters. Careful numerical simulations should follow in order to obtain more complete understanding of the merger scenario utilizing all existing observations.
MACS0647\(-\)JD is a triply-lensed \(z\sim11\) galaxy originally discovered with the Hubble Space Telescope. Here we report new JWST imaging, which clearly resolves MACS0647\(-\)JD as having two ...components that are either merging galaxies or stellar complexes within a single galaxy. Both are very small, with stellar masses \(\sim10^8\,M_\odot\) and radii \(r<100\,\rm pc\). The brighter larger component "A" is intrinsically very blue (\(\beta\sim-2.6\)), likely due to very recent star formation and no dust, and is spatially extended with an effective radius \(\sim70\,\rm pc\). The smaller component "B" appears redder (\(\beta\sim-2\)), likely because it is older (\(100-200\,\rm Myr\)) with mild dust extinction (\(A_V\sim0.1\,\rm mag\)), and a smaller radius \(\sim20\,\rm pc\). We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be out of phase. With an estimated stellar mass ratio of roughly 2:1 and physical projected separation \(\sim400\,\rm pc\), we may be witnessing a galaxy merger 400 million years after the Big Bang. We also identify a candidate companion galaxy C \(\sim3\,{\rm kpc}\) away, likely destined to merge with galaxies A and B. The combined light from galaxies A+B is magnified by factors of \(\sim\)8, 5, and 2 in three lensed images JD1, 2, and 3 with F356W fluxes \(\sim322\), \(203\), \(86\,\rm nJy\) (AB mag 25.1, 25.6, 26.6). MACS0647\(-\)JD is significantly brighter than other galaxies recently discovered at similar redshifts with JWST. Without magnification, it would have AB mag 27.3 (\(M_{UV}=-20.4\)). With a high confidence level, we obtain a photometric redshift of \(z=10.6\pm0.3\) based on photometry measured in 6 NIRCam filters spanning \(1-5\rm\mu m\), out to \(4300\,Å\) rest-frame. JWST NIRSpec observations planned for January 2023 will deliver a spectroscopic redshift and a more detailed study of the physical properties of MACS0647\(-\)JD.
Using deep Hubble Frontier Fields imaging and slitless spectroscopy from the Grism Lens-Amplified Survey from Space, we analyze 2200 cluster and 1748 field galaxies at \(0.2\leq z\leq0.7\) to ...determine the impact of environment on galaxy size and structure at \(\log M_*/M_\odot>7.8\), an unprecedented limit at these redshifts. Based on simple assumptions-\(r_e=f(M_*)\)-we find no significant differences in half-light radii (\(r_e\)) between equal-mass cluster or field systems. More complex analyses-\(r_e=f(M_*,U-V,n,z,\Sigma\))-reveal local density \((\Sigma\)) to induce only a \(7\% \pm 3\%\) (\(95\%\) confidence) reduction in \(r_e\) beyond what can be accounted for by \(U-V\) color, Sersic index (\(n\)), and redshift (\(z\)) effects.Almost any size difference between galaxies in high- and low-density regions is thus attributable to their different distributions in properties other than environment. Indeed, we find a clear color-\(r_e\) correlation in low-mass passive cluster galaxies (\(\log M_*/M_\odot<9.8\)) such that bluer systems have larger radii, with the bluest having sizes consistent with equal-mass star-forming galaxies. We take this as evidence that large-\(r_e\) low-mass passive cluster galaxies are recently acquired systems that have been environmentally quenched without significant structural transformation (e.g., by ram pressure stripping or starvation).Conversely, \(\sim20\%\) of small-\(r_e\) low-mass passive cluster galaxies appear to have been in place since \(z\sim3\). Given the consistency of the small-\(r_e\) galaxies' stellar surface densities (and even colors) with those of systems more than ten times as massive, our findings suggest that clusters mark places where galaxy evolution is accelerated for an ancient base population spanning most masses, with late-time additions quenched by environment-specific mechanisms are mainly restricted to the lowest masses.
A&A 610, A85 (2018) We demonstrate that deep good-seeing VLT/HAWK-I $K_\mathrm{s}$ images
complemented with $g$+$z$-band photometry can yield a sensitivity for weak
lensing studies of massive galaxy ...clusters at redshifts \mbox{$0.7\lesssim z
\lesssim 1.1$}, which is almost identical to the sensitivity of HST/ACS mosaics
of single-orbit depth. Key reasons for this good performance are the excellent
image quality frequently achievable for $K_\mathrm{s}$ imaging from the ground,
a highly effective photometric selection of background galaxies, and a galaxy
ellipticity dispersion that is noticeably lower than for optically observed
high-redshift galaxy samples. Incorporating results from the 3D-HST and
UltraVISTA surveys we also obtained a more accurate calibration of the source
redshift distribution than previously achieved for similar optical weak lensing
data sets. Here we studied the extremely massive galaxy cluster
RCS2$J$232727.7$-$020437 (\mbox{$z=0.699$}), combining deep VLT/\mbox{HAWK-I}
$K_\mathrm{s}$ images (point spread function with a 0\farcs35 full width at
half maximum) with LBT/LBC photometry. The resulting weak lensing mass
reconstruction suggests that the cluster consists of a single overdensity,
which is detected with a peak significance of $10.1\sigma$. We constrained the
cluster mass to \mbox{$M_\mathrm{200c}/(10^{15} \mathrm{M}_\odot)
=2.06^{+0.28}_{-0.26}(\mathrm{stat.})\pm 0.12 (\mathrm{sys.})$} assuming a
spherical Navarro, Frenk \& White model and simulation-based priors on the
concentration, making it one of the most massive galaxy clusters known in the
\mbox{$z\gtrsim 0.7$} Universe. We also cross-checked the HAWK-I measurements
through an analysis of overlapping HST/ACS images, yielding fully consistent
estimates of the lensing signal.
Large surveys of galaxy clusters with the Hubble and Spitzer Space Telescopes, including CLASH and the Frontier Fields, have demonstrated the power of strong gravitational lensing to efficiently ...deliver large samples of high-redshift galaxies. We extend this strategy through a wider, shallower survey named RELICS, the Reionization Lensing Cluster Survey. This survey, described here, was designed primarily to deliver the best and brightest high-redshift candidates from the first billion years after the Big Bang. RELICS observed 41 massive galaxy clusters with Hubble and Spitzer at 0.4-1.7um and 3.0-5.0um, respectively. We selected 21 clusters based on Planck PSZ2 mass estimates and the other 20 based on observed or inferred lensing strength. Our 188-orbit Hubble Treasury Program obtained the first high-resolution near-infrared images of these clusters to efficiently search for lensed high-redshift galaxies. We observed 46 WFC3/IR pointings (~200 arcmin^2) with two orbits divided among four filters (F105W, F125W, F140W, and F160W) and ACS imaging as needed to achieve single-orbit depth in each of three filters (F435W, F606W, and F814W). As previously reported by Salmon et al., we discovered 322 z ~ 6 - 10 candidates, including the brightest known at z ~ 6, and the most distant spatially-resolved lensed arc known at z ~ 10. Spitzer IRAC imaging (945 hours awarded, plus 100 archival) has crucially enabled us to distinguish z ~ 10 candidates from z ~ 2 interlopers. For each cluster, two HST observing epochs were staggered by about a month, enabling us to discover 11 supernovae, including 3 lensed supernovae, which we followed up with 20 orbits from our program. We delivered reduced HST images and catalogs of all clusters to the public via MAST and reduced Spitzer images via IRSA. We have also begun delivering lens models of all clusters, to be completed before the JWST GO call for proposals.
We present a lens model for the cluster SPT-CLJ0615\(-\)5746, which is the highest redshift (\(z=0.972\)) system in the Reionization of Lensing Clusters Survey (RELICS), making it the highest ...redshift cluster for which a full strong lens model is published. We identify three systems of multiply-imaged lensed galaxies, two of which we spectroscopically confirm at \(z=1.358\) and \(z=4.013\), which we use as constraints for the model. We find a foreground structure at \(z\sim0.4\), which we include as a second cluster-sized halo in one of our models; however two different statistical tests find the best-fit model consists of one cluster-sized halo combined with three individually optimized galaxy-sized halos, as well as contributions from the cluster galaxies themselves. We find the total projected mass density within \(r=26.7"\) (the region where the strong lensing constraints exist) to be \(M=2.51^{+0.15}_{-0.09}\times 10^{14}\)~M\(_{\odot}\). If we extrapolate out to \(r_{500}\), our projected mass density is consistent with the mass inferred from weak lensing and from the Sunyaev-Zel'dovich effect (\(M\sim10^{15}\)~M\(_{\odot}\)). This cluster is lensing a previously reported \(z\sim10\) galaxy, which, if spectroscopically confirmed, will be the highest-redshift strongly lensed galaxy known.
The gravitationally lensed star WHL0137-LS, nicknamed Earendel, was identified with a photometric redshift \(z_{phot} = 6.2 \pm 0.1\) based on images taken with the Hubble Space Telescope. Here we ...present James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam) images of Earendel in 8 filters spanning 0.8--5.0\(\mu\)m. In these higher resolution images, Earendel remains a single unresolved point source on the lensing critical curve, increasing the lower limit on the lensing magnification to \(\mu > 4000\) and restricting the source plane radius further to \(r < 0.02\) pc, or \(\sim 4000\) AU. These new observations strengthen the conclusion that Earendel is best explained by an individual star or multiple star system, and support the previous photometric redshift estimate. Fitting grids of stellar spectra to our photometry yields a stellar temperature of \(T_{\mathrm{eff}} \simeq 13000\)--16000 K assuming the light is dominated by a single star. The delensed bolometric luminosity in this case ranges from \(\log(L) = 5.8\)--6.6 \(L_{\odot}\), which is in the range where one expects luminous blue variable stars. Follow-up observations, including JWST NIRSpec scheduled for late 2022, are needed to further unravel the nature of this object, which presents a unique opportunity to study massive stars in the first billion years of the universe.
Massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. We present here ...the z ~ 6 - 8 candidate high-redshift galaxies from the Reionization Lensing Cluster Survey (RELICS), a Hubble and Spitzer Space Telescope survey of 41 massive galaxy clusters spanning an area of ~200 arcmin^2. These clusters were selected to be excellent lenses and we find similar high-redshift sample sizes and magnitude distributions as CLASH. We discover 321 candidate galaxies with photometric redshifts between z ~ 6 to z ~ 8, including extremely bright objects with H-band magnitudes of m_AB ~ 23 mag. As a sample, the observed (lensed) magnitudes of these galaxies are among the brightest known at z> 6, comparable to much wider, blank-field surveys. RELICS demonstrates the efficiency of using strong gravitational lenses to produce high-redshift samples in the epoch of reionization. These brightly observed galaxies are excellent targets for follow-up study with current and future observatories, including the James Webb Space Telescope.
