CLEAR: Spatially Resolved Emission Lines and Active Galactic Nuclei at 0.6<z<1.30.6<z<1.3

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 \emph{Hubble Space Telescope} Wide Field Camera 3, taken as part of the CANDELS Ly$\alpha$ Emission at Reionization (CLEAR) survey, to measure ionization profiles and search for low-luminosity active galactic nuclei (AGN). We analyze \OIII\ and \Hb\ emission-line maps, enabling us to spatially resolve the \OIIIHb\ emission-line ratio across the galaxies in the sample. We compare the \OIIIHb\ ratio in galaxy centers and outer annular regions to measure ionization gradients 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 \OIIIHb\ gradients and find that most galaxies are consistent with small or zero gradients, but 6-16\% of galaxies in the sample are likely to host nuclear \OIIIHb\ that is $\sim$0.5~dex higher than in their outer regions. This study is limited by large uncertainties in most of the measured \OIIIHb\ spatial profiles, therefore deeper data, e.g, from deeper \textit{HST}/WFC3 programs or from \textit{JWST}/NIRISS, are needed to more reliably measure the spatially resolved emission-line conditions of individual high-redshift galaxies.Comment: 16 pages, 13 figures, 2 table

CLEAR: The Gas-Phase Metallicity Gradients of Star-Forming Galaxies at 0.6 < z < 2.6

We report on the gas-phase metallicity gradients of a sample of 264 star-forming galaxies at 0.6 < z < 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. The observations include 12-orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Lya Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies (84%) in this sample are consistent with a zero or slightly positive metallicity gradient across the full mass range probed (8.5 < log M_*/M_sun < 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass---consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider---including star-formation rates, sizes, star-formation rate surface densities, and star-formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models.Comment: 19 pages, 10 figures (v2: typo fixed in Figure 10 label); submitted to Ap

CLEAR: Paschen-β\beta Star Formation Rates and Dust Attenuation of Low Redshift Galaxies

We use \Pab\ (1282~nm) observations from the Hubble Space Telescope (\HST) G141 grism to study the star-formation and dust attenuation properties of a sample of 29 low-redshift ($z < 0.287$) galaxies in the CANDELS Ly$\alpha$ Emission at Reionization (CLEAR) survey. We first compare the nebular attenuation from \Pab/\Ha with the stellar attenuation inferred from the spectral energy distribution, finding that the galaxies in our sample are consistent with an average ratio of the continuum attenuation to the nebular gas of 0.44, but with a large amount of excess scatter beyond the observational uncertainties. Much of this scatter is linked to a large variation between the nebular dust attenuation as measured by (space-based) \Pab to (ground-based) \Ha to that from (ground-based) \Ha/\Hb. This implies there are important differences between attenuation measured from grism-based / wide-aperture \Pab fluxes and the ground-based / slit-measured Balmer decrement. We next compare star-formation rates (SFRs) from \Pab to those from dust-corrected UV. We perform a survival analysis to infer a census of \Pab\ emission implied by both detections and non-detections. We find evidence that galaxies with lower stellar mass have more scatter in their ratio of \Pab\ to attenuation-corrected UV SFRs. When considering our \Pab\ detection limits, this observation supports the idea that lower mass galaxies experience "burstier" star-formation histories. Together, these results show that \Pab\ is a valuable tracer of a galaxy's SFR, probing different timescales of star-formation and potentially revealing star-formation that is otherwise missed by UV and optical tracers.Comment: 19 pages, 14 figures, 2 table

CLEAR: High-Ionization [Ne V] λ{\lambda}3426 Emission-line Galaxies at 1.4<z<2.31.4 <z< 2.3

We analyze a sample of 25 [Ne V] $\lambda$3426 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 Lyman-$\alpha$ Emission at Reionization (CLEAR) survey. [Ne V] emission probes extremely energetic photoionization (97.11-126.21 eV), and is often attributed to energetic radiation from active galactic nuclei (AGN), shocks from supernova, or an otherwise very hard ionizing spectrum from the stellar continuum. In this work, we use [Ne V] in conjunction with other rest-frame UV/optical emission lines ([O II] $\lambda\lambda$3726,3729, [Ne III] $\lambda$3869, H$\beta$, [O III] $\lambda\lambda$4959,5007, H$\alpha$+[N II] $\lambda\lambda$6548,6583, [S II] $\lambda\lambda$6716,6731), deep (2--7 Ms) X-ray observations (from Chandra), and mid-infrared imaging (from Spitzer) to study the origin of this emission and to place constraints on the nature of the ionizing engine. The majority of the [Ne V]-detected galaxies have properties consistent with ionization from AGN. However, for our [Ne V]-selected sample, the X-ray luminosities are consistent with local ($z\lesssim 0.1$) X-ray-selected Seyferts, but the [Ne V] luminosities are more consistent with those from $z\sim 1$ X-ray-selected QSOs. The excess [Ne V] emission requires either reduced hard X-rays, or a $\sim$0.1 keV excess. We discuss possible origins of the apparent [Ne V] excess, which could be related to the ``soft (X-ray) excess'' observed in some QSOs and Seyferts, and/or be a consequence of a complex/anisotropic geometry for the narrow line region, combined with absorption from a warm, relativistic wind ejected from the accretion disk. We also consider implications for future studies of extreme high-ionization systems in the epoch of reionization ($z \gtrsim 6$) with JWST.Comment: 17 pages + 5 (appendix), 7 figures + 2(appendix

Using [Ne V]/[Ne III] to Understand the Nature of Extreme-Ionization Galaxies

Spectroscopic studies of extreme-ionization galaxies (EIGs) are critical to our understanding of exotic systems throughout cosmic time. These EIGs exhibit spectral features requiring >54.42 eV photons: the energy needed to fully ionize helium into He2+ and emit He II recombination lines. They are likely key contributors to reionization, and they can also probe exotic stellar populations or accretion onto massive black holes. To facilitate the use of EIGs as probes of high ionization, we focus on ratios constructed from strong rest-frame UV/optical emission lines, specifically [O III] 5008, H-beta, [Ne III] 3870, [O II] 3727,3729, and [Ne V] 3427. These lines probe the relative intensity at energies of 35.12, 13.62, 40.96, 13.62 eV, and 97.12, respectively, covering a wider range of ionization than traced by other common rest-frame UV/optical techniques. We use ratios of these lines ([Ne V]/[Ne III] = Ne53 and [Ne III]/[O II]), which are closely separated in wavelength, and mitigates effects of dust attenuation and uncertainties in flux calibration. We make predictions from photoionization models constructed from Cloudy that use a broad range of stellar populations and black hole accretion models to explore the sensitivity of these line ratios to changes in the ionizing spectrum. We compare our models to observations from the Hubble Space Telescope and James Webb Space Telescope of galaxies with strong high-ionization emission lines at z ~ 0, z ~ 2, and z ~ 7. We show that the Ne53 ratio can separate galaxies with ionization from 'normal' stellar populations from those with AGN and even 'exotic' Population III models. We introduce new selection methods to identify galaxies with photoionization driven by Population III stars or intermediate-mass black hole accretion disks that could be identified in upcoming high-redshift spectroscopic surveys.Comment: 16 pages, 5 figures, 1 table. Accepted in Ap

NGDEEP Epoch 1: Spatially Resolved Hα\alpha Observations of Disk and Bulge Growth in Star-Forming Galaxies at z∼z \sim 0.6-2.2 from JWST NIRISS Slitless Spectroscopy

We study the H$\alpha$ equivalent width, EW(H$\alpha$), maps of 19 galaxies at $0.6 < z < 2.2$ in the Hubble Ultra Deep Field (HUDF) derived from NIRISS slitless spectroscopy as part of the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) Survey. Our galaxies mostly lie on the star-formation main sequence with a stellar mass range of $\mathrm{10^9 - 10^{11} M_\odot}$, and are therefore characteristic of "typical" star-forming galaxies at these redshifts. Leveraging deep HST and JWST broad-band images, spanning 0.4-4 $\mu$m, we perform spatially-resolved fitting of the spectral energy distributions (SEDs) for these galaxies and construct specific star formation rate (sSFR) and stellar-mass-weighted age maps. We compare these to the EW(H$\alpha$) maps with a spatial resolution of $\sim$1 kpc. The pixel-to-pixel EW(H$\alpha$) increases with increasing sSFR and with decreasing age, with the average trend slightly different from the relations derived from integrated fluxes of galaxies from the literature. Quantifying the radial profiles of EW(H$\alpha$), sSFR, and age, the majority (84%) of galaxies show positive EW(H$\alpha$) gradients, positive sSFR gradients, and negative age gradients, in line with the the inside-out quenching scenario. A few galaxies (16%) show inverse (and flat) trends possibly due to merging or starbursts. Comparing the distributions of EW(H$\alpha$) and sSFR to the star formation history models as a function of galactocentric radius, the central region of galaxies (e.g., their bulges) have experienced, at least one, rapid star-formation episodes, which leads to the formation of bulge, while their outer regions (e.g., disks) grow in a more steady-state. These results demonstrate the ability to study resolved star formation in distant galaxies with JWST NIRISS.Comment: 22 pages, 11 figure

CEERS: Diversity of Lyman-Alpha Emitters during the Epoch of Reionization

We analyze rest-frame ultraviolet to optical spectra of three $z\simeq7.47$ - $7.75$ galaxies whose Ly$\alpha$-emission lines were previously detected with Keck/MOSFIRE observations, using the JWST/NIRSpec observations from the Cosmic Evolution Early Release Science (CEERS) survey. From NIRSpec data, we confirm the systemic redshifts of these Ly$\alpha$ emitters, and emission-line ratio diagnostics indicate these galaxies were highly ionized and metal poor. We investigate Ly$\alpha$ line properties, including the line flux, velocity offset, and spatial extension. For the one galaxy where we have both NIRSpec and MOSFIRE measurements, we find a significant offset in their flux measurements ($\sim5\times$ greater in MOSFIRE) and a marginal difference in the velocity shifts. The simplest interpretation is that the Ly$\alpha$ emission is extended and not entirely encompassed by the NIRSpec slit. The cross-dispersion profiles in NIRSpec reveal that Ly$\alpha$ in one galaxy is significantly more extended than the non-resonant emission lines. We also compute the expected sizes of ionized bubbles that can be generated by the Ly$\alpha$ sources, discussing viable scenarios for the creation of sizable ionized bubbles ($>$1 physical Mpc). The source with the highest-ionization condition is possibly capable of ionizing its own bubble, while the other two do not appear to be capable of ionizing such a large region, requiring additional sources of ionizing photons. Therefore, the fact that we detect Ly$\alpha$ from these galaxies suggests diverse scenarios on escape of Ly$\alpha$ during the epoch of reionization. High spectral resolution spectra with JWST/NIRSpec will be extremely useful for constraining the physics of patchy reionization.Comment: Submitted to ApJ (18 pages, 7 figures, 2 tables

CEERS Key Paper VII: Emission Line Ratios from NIRSpec and NIRCam Wide-Field Slitless Spectroscopy at z>2

We use James Webb Space Telescope Near-Infrared Camera Wide Field Slitless Spectroscopy (NIRCam WFSS) and Near-Infrared spectrograph (NIRSpec) in the Cosmic Evolution Early Release survey (CEERS) to measure rest-frame optical emission-line of 155 galaxies at z>2. The blind NIRCam grism observations include a sample of galaxies with bright emission lines that were not observed on the NIRSpec masks. We study the changes of the Ha, [OIII]/Hb, and [NeIII]/[OII] emission lines in terms of redshift by comparing to lower redshift SDSS and CLEAR samples. We find a significant (>3$\sigma$) correlation between [OIII]/Hb with redshift, while [NeIII]/[OII] has a marginal (2$\sigma$) correlation with redshift. We compare [OIII]/Hb and [NeIII]/[OII] to stellar mass and Hb SFR. We find that both emission-line ratios have a correlation with Hb SFR and an anti-correlation with stellar mass across the redshifts 0<z<9. Comparison with MAPPINGS~V models indicates that these trends are consistent with lower metallicity and higher ionization in low-mass and high-SFR galaxies. We additionally compare to IllustriousTNG predictions and find that they effectively describe the highest [OIII]/Hb ratios observed in our sample, without the need to invoke MAPPINGS models with significant shock ionizionation components.Comment: 16 pages, 11 figure