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1. CLEAR: High-ionization [Ne v] λ3426 Emission-line Galaxies at 1.4 < z < 2.3

   https://doi.org/10.3847/1538-4357/acc1e6  

   Cleri, Nikko J. ; Yang, Guang ; Papovich, Casey ; Trump, Jonathan R. ; Backhaus, Bren E. ; Estrada-Carpenter, Vicente ; Finkelstein, Steven L. ; Giavalisco, Mauro ; Hutchison, Taylor A. ; Ji, Zhiyuan ; et al ( May 2023 , The Astrophysical Journal)

   We analyze a sample of 25 [Nev] (λ3426) emission-line galaxies at 1.4 <z< 2.3 using Hubble Space Telescope/Wide Field Camera 3 G102 and G141 grism observations from the CANDELS LyαEmission at Reionization (CLEAR) survey. [Nev] emission probes extremely energetic photoionization (creation potential of 97.11 eV) and is often attributed to energetic radiation from active galactic nuclei (AGNs), shocks from supernovae, or an otherwise very hard ionizing spectrum from the stellar continuum. In this work, we use [Nev] in conjunction with other rest-frame UV/optical emission lines ([Oii]λλ3726, 3729, [Neiii]λ3869, Hβ, [Oiii]λλ4959, 5007, Hα+[Nii]λλ6548, 6583, [Sii]λλ6716, 6731), deep (2–7 Ms) X-ray observations (from Chandra), and mid-infrared imaging (from Spitzer) to study the origin of this emission and to place constraints on the nature of the ionizing engine. The majority of the [Nev]-detected galaxies have properties consistent with ionization from AGNs. However, for our [Nev]-selected sample, the X-ray luminosities are consistent with local (z≲ 0.1) X-ray-selected Seyferts, but the [Nev] luminosities are more consistent with those fromz∼ 1 X-ray-selected QSOs. The excess [Nev] emission requires either reduced hard X-rays or a ∼0.1 keV excess. We discuss possible origins of the apparent [Nev] excess, which could be related to the “soft (X-ray) excess” observed in some QSOs and Seyferts and/or be a consequence of a complex/anisotropic geometry for the narrow-line region, combined with absorption from a warm, relativistic wind ejected from the accretion disk. We also consider implications for future studies of extreme high-ionization systems in the epoch of reionization (z≳ 6) with the James Webb Space Telescope.

    

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2. Early Results from GLASS-JWST. VIII. An Extremely Magnified Blue Supergiant Star at Redshift 2.65 in the A2744 Cluster Field

   https://doi.org/10.3847/2041-8213/ac9585  

   Chen, Wenlei ; Kelly, Patrick L. ; Treu, Tommaso ; Wang, Xin ; Roberts-Borsani, Guido ; Keen, Allison ; Windhorst, Rogier A. ; Zhou, Rui ; Bradac, Marusa ; Brammer, Gabriel ; et al ( December 2022 , The Astrophysical Journal Letters)

   We report the discovery of an extremely magnified star at redshiftz= 2.65 in the James Webb Space Telescope (JWST) NIRISS pre-imaging of the A2744 galaxy-cluster field. The star’s background host galaxy lies on a fold caustic of the foreground lens, and the cluster creates a pair of images of the region close to the lensed star. We identified the bright transient in one of the merging images at a distance of ∼0.″15 from the critical curve by subtracting the JWST F115W and F150W imaging from coadditions of archival Hubble Space Telescope (HST) F105W and F125W images and F140W and F160W images, respectively. Since the time delay between the two images should be only hours, the transient must be the microlensing event of an individual star, as opposed to a luminous stellar explosion that would persist for days to months. Analysis of individual exposures suggests that the star’s magnification is not changing rapidly during the observations. From photometry of the point source through the F115W, F150W, and F200W filters, we identify a strong Balmer break, and modeling allows us to constrain the star’s temperature to be approximately 7000–12,000 K.

    

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3. CLEAR: Spatially Resolved Emission Lines and Active Galactic Nuclei at 0.6 < z < 1.3

   https://doi.org/10.3847/1538-4357/aca668  

   Backhaus, Bren E. ; Bridge, Joanna S. ; Trump, Jonathan R. ; Cleri, Nikko J. ; Papovich, Casey ; Simons, Raymond C. ; Momcheva, Ivelina ; Holwerda, Benne W. ; Ji, Zhiyuan ; Jung, Intae ; et al ( January 2023 , The Astrophysical Journal)

   We investigate spatially resolved emission-line ratios in a sample of 219 galaxies (0.6 <z< 1.3) detected using the G102 grism on the Hubble Space Telescope Wide Field Camera 3 taken as part of the CANDELS LyαEmission at Reionization survey to measure ionization profiles and search for low-luminosity active galactic nuclei (AGN). We analyze [Oiii] and Hβemission-line maps, enabling us to spatially resolve the [Oiii]/Hβemission-line ratio across the galaxies in the sample. We compare the [Oiii]/Hβratio in galaxy centers and outer annular regions to measure ionization differences and investigate the potential of sources with nuclear ionization to host AGN. We investigate some of the individual galaxies that are candidates to host strong nuclear ionization and find that they often have low stellar mass and are undetected in X-rays, as expected for low-luminosity AGN in low-mass galaxies. We do not find evidence for a significant population of off-nuclear AGN or other clumps of off-nuclear ionization. We model the observed distribution of [Oiii]/Hβspatial profiles and find that most galaxies are consistent with a small or zero difference between their nuclear and off-nuclear line ratios, but 6%–16% of galaxies in the sample are likely to host nuclear [Oiii]/Hβthat is ∼0.5 dex higher than in their outer regions. This study is limited by large uncertainties in most of the measured [Oiii]/Hβspatial profiles; therefore, deeper data, e.g., from deeper HST/WFC3 programs or from JWST/NIRISS, are needed to more reliably measure the spatially resolved emission-line conditions of individual high-redshift galaxies.

    

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4. CLEAR: Emission-line Ratios at Cosmic High Noon

   https://doi.org/10.3847/1538-4357/ac3919  

   Backhaus, Bren E. ; Trump, Jonathan R. ; Cleri, Nikko J. ; Simons, Raymond ; Momcheva, Ivelina ; Papovich, Casey ; Estrada-Carpenter, Vicente ; Finkelstein, Steven L. ; Matharu, Jasleen ; Ji, Zhiyuan ; et al ( February 2022 , The Astrophysical Journal)

   We use Hubble Space Telescope Wide Field Camera 3 G102 and G141 grism spectroscopy to measure rest-frame optical emission-line ratios of 533 galaxies atz∼ 1.5 in the CANDELS LyαEmission at Reionization survey. We compare [Oiii]/Hβversus [Sii]/(Hα+ [Nii]) as an “unVO87” diagram for 461 galaxies and [Oiii]/Hβversus [Neiii]/[Oii] as an “OHNO” diagram for 91 galaxies. The unVO87 diagram does not effectively separate active galactic nuclei (AGN) and [Nev] sources from star-forming galaxies, indicating that the unVO87 properties of star-forming galaxies evolve with redshift and overlap with AGN emission-line signatures atz> 1. The OHNO diagram does effectively separate X-ray AGN and [Nev]-emitting galaxies from the rest of the population. We find that the [Oiii]/Hβline ratios are significantly anticorrelated with stellar mass and significantly correlated with$\log (L_{\mathrm{H}\beta })$, while [Sii]/(Hα+ [Nii]) is significantly anticorrelated with$\log (L_{\mathrm{H}\beta })$. Comparison with MAPPINGS V photoionization models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-star formation rate (SFR) galaxies. We do not find evidence for redshift evolution of the emission-line ratios outside of the correlations with mass and SFR. Our results suggest that the OHNO diagram of [Oiii]/Hβversus [Neiii]/[Oii] will be a useful indicator of AGN content and gas conditions in very high-redshift galaxies to be observed by the James Webb Space Telescope.

    

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5. Brighter and More Massive Galaxies in the Vicinity of Lyα Nebulae

   https://doi.org/10.3847/1538-4357/aca3ac  

   Wells, Natalie K. ; Prescott, Moire K. M. ; Finlator, Kristian M. ( December 2022 , The Astrophysical Journal)

   It has been well established in the local universe that galaxy properties differ based on the large-scale environment in which they reside. As luminous Lyαnebulae have been shown to trace overdense environments atz∼ 2–3, comparing the properties of galaxies within Lyαnebulae systems to those in the field can provide insight into how and when locally observed trends between galaxy properties and environment emerged. Six Lyαnebulae were discovered atz∼ 2.3 in a blind search of the GOODS-S extragalactic field, a region also covered by the 3D-HST spectroscopic survey. Utilizing 3D-HST data, we identified 86 galaxies in the vicinity of these nebulae and used statistical tests to compare their physical properties to galaxies elsewhere in the field. Galaxies lying within 320 proper kpc of a Lyαnebula are roughly half a magnitude brighter than those in the field, with higher stellar masses, higher star formation rates, and larger effective radii. Even when considering the effects of sample incompleteness, our study suggests that galaxies in overdensities atz∼ 2.3 traced by Lyαnebulae are being influenced by their environment. Furthermore, Lyα-nebula-associated galaxies lie on the same main sequence of star formation as field galaxies but have a larger proportion of high-mass galaxies, consistent with the idea that galaxy evolution is accelerated in rich environments. Expanded surveys for Lyαnebulae in other deep extragalactic fields and galaxy spectroscopic follow-up with the James Webb Space Telescope (JWST) will better constrain the demographics of Lyα-nebula-associated galaxies.

    

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