Strongly lensed [O III] emitters at Cosmic Noon with Roman: Characterizing extreme emission line galaxies on star cluster complex scales (100 pc)

Extreme emission line galaxies (EELGs) are considered the primary contributor to cosmic reionization and are valuable laboratories to study the astrophysics of massive stars. It is strongly expected that Roman's High Latitude Wide Area Survey (HLWAS) will find many strongly gravitationally lensed [O III] emitters at Cosmic Noon (1 < z < 2.8). Roman imaging and grism spectroscopy alone will simultaneously confirm these strong lens systems and probe their interstellar medium (ISM) and stellar properties on small scales ($\lesssim$ 100 pc). Moreover, these observations will synergize with ground-based and space-based follow-up observations of the discovered lensed [O III] emitters in multi-wavelength analyses of their properties (e.g., massive stars and possible escape of ionizing radiation), spatially resolved on the scales of individual star cluster complexes. Only Roman can uniquely sample a large number of lensed [O III] emitters to study the small scale (~ 100 pc) ISM and stellar properties of these extreme emission line galaxies, detailing the key physics of massive stars and the ISM that govern cosmic reionization.Comment: Submitted in response to the call for Roman Telescope CCS white paper

The Cosmic Telescope that Lenses the Sunburst Arc, PSZ1 G311.65-18.48: Strong Gravitational Lensing model and Source Plane Analysis

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. We measure a projected cluster core mass of M(<250 kpc)=2.93+0.01/-0.02x10^14M_sun. The two least-magnified but complete images of the Sunburst Arc's source galaxy are magnified by ~13x, while the LyC clump is magnified by ~4-80x. 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 1x2 kpc, and that it is resolved in three distinct directions in the source plane, 0, 40, and 75 degrees (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.Comment: 31 pages, 14 figures, 4 tables. Submitted to Ap

A Gradual Decline of Star Formation since Cluster In-fall: New Kinematic Insights into Environmental Quenching at 0.3 <z<< z < 1.1

The environments where galaxies reside crucially shape their star formation histories. We investigate a large sample of 1626 cluster galaxies located within 105 galaxy clusters spanning a large range in redshift ($0.26 < z < 1.13)$. The galaxy clusters are massive (M$_{500} \gtrsim 2\times10^{14}$M$_{\odot}$), and are uniformly selected from the SPT and ACT Sunyaev-Zel'dovich (SZ) surveys. With spectra in-hand for thousands of cluster members, we use galaxies' position in projected phase space as a proxy for their in-fall times, which provides a more robust measurement of environment than quantities such as projected cluster-centric radius. We find clear evidence for a gradual age increase of the galaxy's mean stellar populations ($\sim$ 0.71 $\pm$ 0.4 Gyr based on a 4000 $\r{A}$ break, $\rm D_{\rm n}4000$) with the time spent in the cluster environment. This environmental quenching effect is found regardless of galaxy luminosity (faint or bright) and redshift (low-$z$ or high-$z$), although the exact stellar age of galaxies depends on both parameters at fixed environmental effects. Such a systematic increase of $\rm D_{\rm n}4000$ with in-fall proxy would suggest that galaxies that were accreted into hosts earlier were quenched earlier, due to longer exposure to environmental effects such as ram pressure stripping and starvation. Compared to the typical dynamical time scales of $1-3$ Gyr of cluster galaxies, the relatively small age increase ($\sim$ 0.71 $\pm$ 0.4 Gyr) found in our sample galaxies seems to suggest that a slow environmental process such as starvation is the dominant quenching pathway. Our results provide new insights into environmental quenching effects spanning a large range in cosmic time ($\sim 5.2$ Gyr, $z=0.26$--1.13) and demonstrate the power of using a kinematically-derived in-fall time proxy.Comment: 22 pages, 9 figures, 3 tables. Accepted for publication by Ap

Synthesizing Stellar Populations in South Pole Telescope Galaxy Clusters. I. Ages of Quiescent Member Galaxies at 0.3 < z < 1.4

Using stellar population synthesis models to infer star formation histories (SFHs), we analyze photometry and spectroscopy of a large sample of quiescent galaxies that are members of Sunyaev–Zel'dovich (SZ)-selected galaxy clusters across a wide range of redshifts. We calculate stellar masses and mass-weighted ages for 837 quiescent cluster members at 0.3 < z < 1.4 using rest-frame optical spectra and the Python-based Prospector framework, from 61 clusters in the SPT-GMOS Spectroscopic Survey (0.3 < z < 0.9) and three clusters in the SPT Hi-z cluster sample (1.25 < z < 1.4). We analyze spectra of subpopulations divided into bins of redshift, stellar mass, cluster mass, and velocity-radius phase-space location, as well as by creating composite spectra of quiescent member galaxies. We find that quiescent galaxies in our data set sample a diversity of SFHs, with a median formation redshift (corresponding to the lookback time from the redshift of observation to when a galaxy forms 50% of its mass, t50) of z = 2.8 ± 0.5, which is similar to or marginally higher than that of massive quiescent field and cluster galaxy studies. We also report median age–stellar mass relations for the full sample (age of the universe at t50 (Gyr) = 2.52 (±0.04)–1.66 (±0.12) log10(M/1011M⊙)) and recover downsizing trends across stellar mass; we find that massive galaxies in our cluster sample form on aggregate ∼0.75 Gyr earlier than lower-mass galaxies. We also find marginally steeper age–mass relations at high redshifts, and report a bigger difference in formation redshifts across stellar mass for fixed environment, relative to formation redshifts across environment for fixed stellar mass

Small Region, Big Impact: Highly Anisotropic Lyman-continuum Escape from a Compact Starburst Region with Extreme Physical Properties

Extreme, young stellar populations are considered the primary contributor to cosmic reionization. However, how Lyman-continuum (LyC) escapes these galaxies remains highly elusive because LyC escape can vary on sub-galactic scales that are technically challenging to observe in LyC emitters. We investigate the Sunburst Arc: a strongly lensed, LyC emitter at $z=2.37$. This galaxy reveals the exceptionally small scale (tens of parsecs) physics of LyC escape thanks to high magnification from strong lensing. Analyzing HST broadband and narrowband imaging, we find that the small ($<$100 pc) LyC leaking region shows distinctly extreme properties: a very blue UV slope ($\beta=-2.9\pm0.1$), high ionization state ([OIII]$\lambda 5007$/[OII]$\lambda 3727=11\pm3$ and [OIII]$\lambda 5007$/H$\beta=6.8\pm0.4$), strong oxygen emission (EW([OIII])$=1095\pm 40 \r{A}$), and high Lyman-$\alpha$ escape fraction ($0.3\pm 0.03$), none of which are found in any non-leaking regions of the galaxy. Moreover, a UV slope comparison with starburst population models indicates that the leaking region's UV emission consists of nearly ``pure'' stellar light with minimal contamination from surrounding nebular continuum emission and dust extinction. These results suggest a highly directional LyC escape such that LyC is produced and escapes from a small, extreme starburst region where the stellar feedback from an ionizing star cluster may create an anisotropic ``pencil beam'' viewing geometry in the surrounding gas. As a result, unabsorbed LyC directly escapes through these perforated hole(s). Importantly, such anisotropic escape processes imply that unfavorable sightline effects are a crucial contributor to the significant scatters between galaxy properties and LyC escape fraction in observations and that strong lensing uniquely reveals the small-scale physics that regulates the ionizing budget of galaxies for reionization.Comment: 17 pages, 5 figures, 3 tables, submitted to ApJ Letters. Comments welcom

SPT-CL J2215−3537: A Massive Starburst at the Center of the Most Distant Relaxed Galaxy Cluster

We present the discovery of the most distant, dynamically relaxed cool core cluster, SPT-CL J2215−3537 (SPT2215), and its central brightest cluster galaxy (BCG) at z = 1.16. Using new X-ray observations, we demonstrate that SPT2215 harbors a strong cool core with a central cooling time of 200 Myr (at 10 kpc) and a maximal intracluster medium cooling rate of 1900 ± 400 M⊙ yr−1. This prodigious cooling may be responsible for fueling the extended, star-forming filaments observed in Hubble Space Telescope imaging. Based on new spectrophotometric data, we detect bright [O ii] emission in the BCG, implying an unobscured star formation rate (SFR) of ${320}_{-140}^{+230}$M⊙ yr−1. The detection of a weak radio source (2.0 ± 0.8 mJy at 0.8 GHz) suggests ongoing feedback from an active galactic nucleus (AGN), though the implied jet power is less than half the cooling luminosity of the hot gas, consistent with cooling overpowering heating. The extreme cooling and SFR of SPT2215 are rare among known cool core clusters, and it is even more remarkable that we observe these at such high redshift, when most clusters are still dynamically disturbed. The high mass of this cluster, coupled with the fact that it is dynamically relaxed with a highly isolated BCG, suggests that it is an exceptionally rare system that must have formed very rapidly in the early universe. Combined with the high SFR, SPT2215 may be a high-z analog of the Phoenix cluster, potentially providing insight into the limits of AGN feedback and star formation in the most massive galaxies

COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens

We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy at z ≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift of z = 5.043, placing it shortly after the end of the “Epoch of Reionization,” and an AB magnitude z AB = 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of the z = 1.001 cluster lens is M(<5.″77)=1.079−0.007+0.023×1013M☉ , significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is 〈μ arc〉 = 76−20+40 , a factor of 2.4−0.7+1.4 greater than previously estimated from ground-based data; the flux-weighted average magnification is 〈μ arc〉 = 92−31+37 . We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to log(M⋆/M⊙)= 9.7 ± 0.3 and SFR = 10.3−4.4+7.0 M ⊙ yr−1, respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy

JWST's TEMPLATES for Star Formation: The First Resolved Gas-Phase Metallicity Maps of Dust-Obscured Star-Forming Galaxies at zz ∼\sim 4

We present the first spatially resolved maps of gas-phase metallicity for dust-obscured star-forming galaxies (DSFGs) at $z$ $\sim$ 4, from the JWST TEMPLATES Early Release Science program, derived from NIRSpec integral field unit spectroscopy of the H$\alpha$ and [NII] emission lines. Empirically derived literature optical line calibrations are used to determine that the sources are highly metal rich, with both appearing to display regions of supersolar metallicity, particularly in SPT2147-50. While we cannot rule out shocks or AGN in these regions, we suggest that the two systems have already undergone significant enrichment as a result of their extremely high star-formation rates. Utilising ALMA rest-frame 380$\mu$m continuum and [CI]($^3$P$_2$-$^3$P$_1$) line maps we compare metallicity and gas-to-dust ratio variations in the two galaxies, finding the two to be anticorrelated on highly resolved spatial scales, consistent with various literature studies of $z$ $\sim$ 0 galaxies. The data are indicative of the enormous potential of JWST to probe the enrichment of the interstellar medium on $\sim$kpc scales in extremely dust-obscured systems at $z$ $\sim$ 4 and beyond.Comment: 12 pages, 5 figures, submitted to Ap

JWST's TEMPLATES for Star Formation: The First Resolved Gas-phase Metallicity Maps of Dust-obscured Star-forming Galaxies at z ∼ 4

We present the first spatially resolved maps of gas-phase metallicity for two dust-obscured star-forming galaxies at z ∼ 4, from the JWST TEMPLATES Early Release Science program, derived from NIRSpec integral field unit spectroscopy of the Hα and [N ii] emission lines. Empirical optical line calibrations are used to determine that the sources are globally enriched to near-solar levels. While one source shows elevated [N ii]/Hα ratios and broad Hα emission consistent with the presence of an active galactic nucleus in a ≳1 kpc region, we argue that both systems have already undergone significant metal enrichment as a result of their extremely high star formation rates. Utilizing Atacama Large Millimeter/submillimeter Array rest-frame 380 μm continuum and [Ci](3P2–3P1) line maps we compare the spatial variation of the metallicity and gas-to-dust ratio in the two galaxies, finding the two properties to be anticorrelated on highly resolved spatial scales, consistent with various literature studies of z ∼ 0 galaxies. The data are indicative of the enormous potential of JWST to probe the enrichment of the interstellar medium on ∼kpc scales in extremely dust-obscured systems at z ∼ 4 and beyond