ABSTRACT
We present new observations of 16 bright (r = 19–21) gravitationally lensed galaxies at z ≃ 1–3 selected from the CASSOWARY survey. Included in our sample is the z = 1.42 galaxy CSWA-141, ...one of the brightest known reionization-era analogues at high redshift (g = 20.5), with a large specific star formation rate (31.2 Gyr−1) and an O iii+H β equivalent width (EWO iii + H β = 730 Å) that is nearly identical to the average value expected at z ≃ 7–8. In this paper, we investigate the rest-frame UV nebular line emission in our sample with the goal of understanding the factors that regulate strong C iii emission. Although most of the sources in our sample show weak UV line emission, we find elevated C iii in the spectrum of CSWA-141 (EWC iii = 4.6 ± 1.9 Å) together with detections of other prominent emission lines (O iii, Si iii, Fe ii⋆, Mg ii). We compare the rest-optical line properties of high-redshift galaxies with strong and weak C iii emission, and find that systems with the strongest UV line emission tend to have young stellar populations and nebular gas that is moderately metal-poor and highly ionized, consistent with trends seen at low and high redshift. The brightness of CSWA-141 enables detailed investigation of the extreme emission line galaxies which become common at z > 6. We find that gas traced by the C iii doublet likely probes higher densities than that traced by O ii and S ii. Characterization of the spectrally resolved Mg ii emission line and several low-ionization absorption lines suggests neutral gas around the young stars is likely optically thin, potentially facilitating the escape of ionizing radiation.
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 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 arcmin2. These clusters were selected to be excellent lenses, and we find similar high-redshift sample sizes and magnitude distributions as the Cluster Lensing And Supernova survey with Hubble (CLASH). We discover 257, 57, and eight candidate galaxies at z ∼ 6, 7, and 8 respectively, (322 in total). The observed (lensed) magnitudes of the z ∼ 6 candidates are as bright as AB mag ∼23, making them among the brightest known at these redshifts, comparable with discoveries from 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.
Abstract
We analyze spectra of a gravitationally lensed galaxy, known as the Sunburst Arc, that is leaking ionizing photons, also known as the Lyman continuum (LyC). Magnification from gravitational ...lensing permits the galaxy to be spatially resolved into one region that leaks ionizing photons and several that do not. Rest-frame UV and optical spectra from Magellan target 10 different regions along the lensed Arc, including six multiple images of the LyC leaking region and four regions that do not show LyC emission. The rest-frame optical spectra of the ionizing photon emitting regions reveal a blueshifted (Δ
V
= 27 km s
−1
) broad emission component (FWHM = 327 km s
−1
), comprising 55% of the total O
iii
line flux, in addition to a narrow component (FWHM = 112 km s
−1
), suggesting the presence of strong highly ionized gas outflows. This is consistent with the high-velocity ionized outflow inferred from the rest-frame UV spectra. In contrast, the broad emission component is less prominent in the nonleaking regions, comprising ∼26% of total O
iii
line flux. The high-ionization absorption lines are prominent in both the leaker and the nonleaker, but the low-ionization absorption lines are very weak in the leaker, suggesting that the line-of-sight gas is highly ionized in the leaker. Analyses of stellar wind features reveal that the stellar population of the LyC leaking regions is considerably younger (∼3 Myr) than that of the nonleaking regions (∼12 Myr), emphasizing that stellar feedback from young stars may play an important role in ionizing photon escape.
ABSTRACT
Recent observations have revealed the presence of strong C iii emission (EW$_{\rm {C\,{\small III}}}\gt 20$ Å) in z > 6 galaxies, the origin of which remains unclear. In an effort to ...understand the nature of these line emitters, we have initiated a survey targeting C iii emission in gravitationally lensed reionization-era analogues identified in Hubble Space Telescope imaging of clusters from the Reionization Lensing Cluster Survey. Here, we report initial results on four galaxies selected to have low stellar masses (2–8 × 107 M⊙) and J125-band flux excesses indicative of intense O iii + H β emission (EW$_{\rm {O\,{\small III}+H\,\beta }}$ = 500–2000 Å), similar to what has been observed at z > 6. We detect C iii emission in three of the four sources, with the C iii EW reaching values seen in the reionization era (EW$_{\rm {C\,{\small III}}}\simeq 17\!-\!22$ Å) in the two sources with the strongest optical line emission (EW$_{\rm {O\,{\small III}+H\,\beta }}\simeq 2000$ Å). We have obtained a Magellan/FIRE (Folded-port InfraRed Echellette) near-infrared spectrum of the strongest C iii emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense C iii and optical line emission for extremely young (2–3 Myr) and metal-poor (0.06–0.08 Z⊙) stellar populations, as would be expected after a substantial upturn in the star formation rate of a low-mass galaxy. The sources in this survey are among the first for which C iii has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to z > 6 with current facilities, using C iii to measure redshifts of objects with IRAC excesses indicating EW$_{\rm {O\,{\small III}+H\,\beta }}\simeq 2000$ Å, providing a method of spectroscopic confirmation independent of Ly α.
The most distant galaxies known are at z ∼ 10-11, observed 400-500 Myr after the Big Bang. The few z ∼ 10-11 candidates discovered to date have been exceptionally small, barely resolved, if at all, ...by the Hubble Space Telescope. Here we present the discovery of SPT0615-JD1, a fortuitous z ∼ 10 (zphot = ) galaxy candidate stretched into an arc over ∼2 5 by the effects of strong gravitational lensing. Discovered in the Reionization Lensing Cluster Survey (RELICS) Hubble Treasury program and companion S-RELICS Spitzer program, this candidate has a lensed H-band magnitude of 24.6 0.1 AB mag. With a magnification of ∼ 4-7 estimated from our lens models, the delensed intrinsic magnitude is 26.7 0.1 AB mag, and the half-light radius is re < 0.8 kpc, both consistent with other z > 9 candidates. The inferred stellar mass ( ) and star formation rate ( ) indicate that this candidate is a typical star-forming galaxy on the z > 6 SFR-M relation. We note that three independent lens models predict two counter images, at least one of which should be of a similar magnitude to the arc, but these counter images are not yet detected. Counter images would not be expected if the arc were at lower redshift. The relatively large physical size could be due to a merger or accretion event, while the unprecedented lensed size of this z ∼ 10 candidate offers the potential for ALMA and the James Webb Space Telescope to study the geometric and kinematic properties of a galaxy observed 500 Myr after the Big Bang.
Strong gravitational lensing by galaxy clusters magnifies background galaxies, enhancing our ability to discover statistically significant samples of galaxies at , in order to constrain the ...high-redshift galaxy luminosity functions. Here, we present the first five lens models out of the Reionization Lensing Cluster Survey (RELICS) Hubble Treasury Program, based on new HST WFC3/IR and ACS imaging of the clusters RXC J0142.9+4438, Abell 2537, Abell 2163, RXC J2211.7-0349, and ACT-CLJ0102-49151. The derived lensing magnification is essential for estimating the intrinsic properties of high-redshift galaxy candidates, and properly accounting for the survey volume. We report on new spectroscopic redshifts of multiply imaged lensed galaxies behind these clusters, which are used as constraints, and detail our strategy to reduce systematic uncertainties due to lack of spectroscopic information. In addition, we quantify the uncertainty on the lensing magnification due to statistical and systematic errors related to the lens modeling process, and find that in all but one cluster, the magnification is constrained to better than 20% in at least 80% of the field of view, including statistical and systematic uncertainties. The five clusters presented in this paper span the range of masses and redshifts of the clusters in the RELICS program. We find that they exhibit similar strong lensing efficiencies to the clusters targeted by the Hubble Frontier Fields within the WFC3/IR field of view. Outputs of the lens models are made available to the community through the Mikulski Archive for Space Telescopes.
Strong gravitational lensing by clusters of galaxies probes the mass distribution at the core of each cluster and magnifies the universe behind it. MACS J0417.5−1154 at z = 0.443 is one of the most ...massive clusters known based on weak lensing, X-ray, and Sunyaev-Zel'dovich analyses. Here we compute a strong lens model of MACS J0417 based on Hubble Space Telescope imaging observations collected, in part, by the Reionization Lensing Cluster Survey (RELICS), and recently reported spectroscopic redshifts from the MUSE instrument on the Very Large Telescope (VLT). We measure an Einstein radius of at z = 9 and a mass projected within 200 kpc of M . Using this model, we measure a ratio between the mass attributed to cluster-member galaxy halos and the main cluster halo of order 1:100. We assess the probability to detect magnified high-redshift galaxies in the field of this cluster, both for comparison with RELICS HST results and as a prediction for the James Webb Space Telescope (JWST) Guaranteed Time Observations upcoming for this cluster. Our lensing analysis indicates that this cluster has similar lensing strength to other clusters in the RELICS program. Our lensing analysis predicts a detection of at least a few z ∼ 6-8 galaxies behind this cluster, at odds with a recent analysis that yielded no such candidates in this field. Reliable strong lensing models are crucial for accurately predicting the intrinsic properties of lensed galaxies. As part of the RELICS program, our strong lensing model produced with the Lenstool parametric method is publicly available through the Mikulski Archive for Space Telescopes.
Abstract
We present a strong-lensing analysis of the cluster PSZ1 G311.65−18.48, based on Hubble Space Telescope imaging, archival VLT/MUSE spectroscopy, and Chandra X-ray data. This cool-core ...cluster (
z
= 0.443) lenses the brightest lensed galaxy known, dubbed the “Sunburst Arc” (
z
= 2.3703), a Lyman continuum (LyC) emitting galaxy multiply imaged 12 times. We identify in this field 14 additional strongly lensed galaxies to constrain a strong-lens model and report secure spectroscopic redshifts of four of them. We measure a projected cluster core mass of
M
(<250 kpc) =
2.93
−
0.02
+
0.01
×
10
14
M
⊙
. The two least magnified but complete images of the Sunburst Arc’s source galaxy are magnified by ∼13×, while the LyC clump is magnified by ∼4–80×. We present time delay predictions and conclusive evidence that a discrepant clump in the Sunburst Arc, previously claimed to be a transient, is not variable, thus strengthening the hypothesis that it results from an exceptionally high magnification. A source plane reconstruction and analysis of the Sunburst Arc finds its physical size to be 1 × 2 kpc and that it is resolved in three distinct directions in the source plane, 0°, 40°, and 75° (east of north). We place an upper limit of
r
≲ 50 pc on the source plane size of unresolved clumps and
r
≲ 32 pc for the LyC clump. Finally, we report that the Sunburst Arc is likely in a system of two or more galaxies separated by ≲6 kpc in projection. Their interaction may drive star formation and could play a role in the mechanism responsible for the leaking LyC radiation.
Recent studies have revealed detections of UV metal emission lines (CIII, OIII, CIV) in three of the first galaxies observed at z>6, providing the first spectroscopic insight into the nature of early ...star forming galaxies. The equivalent widths (EWs) of these lines are more than an order of magnitude stronger than what is typical at lower redshifts, potentially indicating significant differences in the ionizing spectrum of galaxies in the reionization era. The origin of the high ionization lines remains unclear, likely requiring either a low metallicity stellar population or AGN. However owing to the limited number of z>6 sources with deep spectroscopy and limited number of analogs at lower redshifts, it has proven difficult to generalize and interpret the initial results. In the first part of my thesis, I have undertaken a comprehensive Keck, LBT and VLT spectroscopic campaign to characterize the EW distribution of UV metal lines at z>6. My results present new constraints on the fraction of strong CIII and CIV emitting galaxies at z>6 and indicate that ionizing spectrum from stellar population at z>6 could be significantly harder than systems at a lower redshift. In the second part of my thesis, I have developed a new strategy to identify and characterize analogs of the strong UV metal line emitters at lower redshift. This has resulted in a new sample of extreme CIII emitters at z~2. Using spectroscopic tools, I have shown that large equivalent width CIII emission lines tend to be those with moderately low gas-phase oxygen abundance, low stellar metallicity, large ionization parameter, and very little dust extinction. My results will guide surveys with current and future facilities (Spitzer, JWST, WFIRST) providing optimal strategy to target UV metal lines in the reionization epoch.
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