Lyα\alpha at Cosmic Dawn with a Simulated Roman Grism Deep Field

The slitless grism on the Nancy Grace Roman Space Telescope will enable deep near-infrared spectroscopy over a wide field of view. We demonstrate Roman's capability to detect Ly$\alpha$ galaxies at $z>7$ using a multi-position-angle (PA) observational strategy. We simulate Roman grism data using a realistic foreground scene from the COSMOS field. We also input fake Ly$\alpha$ galaxies spanning redshift z=7.5-10.5 and a line-flux range of interest. We show how a novel data cube search technique -- CUBGRISM -- originally developed for GALEX can be applied to Roman grism data to produce a Ly$\alpha$ flux-limited sample without the need for continuum detections. We investigate the impact of altering the number of independent PAs and exposure time. A deep Roman grism survey with 25 PAs and a total exposure time of $70$hrs can achieve Ly$\alpha$ line depths comparable to the deepest $z=7$ narrow-band surveys ($L_{{\rm{Ly}}\alpha}\gtrsim10^{43}$erg s$^{-1}$). Assuming a null result, where the opacity of the intergalactic medium (IGM) remains unchanged from $z\sim7$, this level of sensitivity will detect $\sim400$ deg$^{-2}$ Ly$\alpha$ emitters from $z=7.25-8.75$. A decline from this expected number density is the signature of an increasing neutral hydrogen fraction and the onset of reionization. Our simulations indicate that a deep Roman grism survey has the ability to measure the timing and magnitude of this decline, allowing us to infer the ionization state of the IGM and helping us to distinguish between models of reionization.Comment: 11 pages, 7 figures, Submitted to Ap

Probing Patchy Reionization with the Void Probability Function of Lyman-α\alpha Emitters

We probe what constraints for the global ionized hydrogen fraction the Void Probability Function (VPF) clustering can give for the Lyman-Alpha Galaxies in the Epoch of Reionization (LAGER) narrowband survey as a function of area. Neutral hydrogen acts like a fog for Lyman-alpha emission, and measuring the drop in the luminosity function of Lyman-$\alpha$ emitters (LAEs) has been used to constrain the ionization fraction in narrowband surveys. However, the clustering of LAEs is independent from the luminosity function's inherent evolution, and can offer additional constraints for reionization under different models. The VPF measures how likely a given circle is to be empty. It is a volume-averaged clustering statistic that traces the behavior of higher order correlations, and its simplicity offers helpful frameworks for planning surveys. Using the \citet{Jensen2014} simulations of LAEs within various amount of ionized intergalactic medium, we predict the behavior of the VPF in one (301x150.5x30 Mpc$^3$), four (5.44$\times 10^6$ Mpc$^3$), or eight (1.1$\times 10^7$ Mpc$^3$) fields of LAGER imaging. We examine the VPF at 5 and 13 arcminutes, corresponding to the minimum scale implied by the LAE density and the separation of the 2D VPF from random, and the maximum scale from the 8-field 15.5 deg$^2$ LAGER area. We find that even a single DECam field of LAGER (2-3 deg$^2$) could discriminate between mostly neutral vs. ionized. Additionally, we find four fields allows the distinction between 30, 50, and 95 percent ionized; and that eight fields could even distinguish between 30, 50, 73, and 95 percent ionized.Comment: 14 pages, 5 figure

VLA 1.4 GHz Catalogs of the Abell 370 and Abell 2390 Cluster Fields

We present 1.4 GHz catalogs for the cluster fields Abell 370 and Abell 2390 observed with the Very Large Array. These are two of the deepest radio images of cluster fields ever taken. The Abell 370 image covers an area of 40'x40' with a synthesized beam of ~1.7" and a noise level of ~5.7 uJy near field center. The Abell 2390 image covers an area of 34'x34' with a synthesized beam of ~1.4" and a noise level of ~5.6 uJy near field center. We catalog 200 redshifts for the Abell 370 field. We construct differential number counts for the central regions (radius < 16') of both clusters. We find that the faint (S_1.4GHz < 3 mJy) counts of Abell 370 are roughly consistent with the highest blank field number counts, while the faint number counts of Abell 2390 are roughly consistent with the lowest blank field number counts. Our analyses indicate that the number counts are primarily from field radio galaxies. We suggest that the disagreement of our counts can be largely attributed to cosmic variance.Comment: 13 pages, accepted for publication in ApJ

The HETDEX Survey: Emission Line Exploration and Source Classification

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an untargeted spectroscopic survey that aims to measure the expansion rate of the Universe at $z \sim 2.4$ to 1% precision for both $H(z)$ and $D_A(z)$. HETDEX is in the process of mapping in excess of one million Lyman Alpha emitting (LAE) galaxies and a similar number of lower-z galaxies as a tracer of the large-scale structure. The success of the measurement is predicated on the post-observation separation of galaxies with Ly$\alpha$ emission from the lower-$z$ interloping galaxies, primarily [OII], with low contamination and high recovery rates. The Emission Line eXplorer (ELiXer) is the principal classification tool for HETDEX, providing a tunable balance between contamination and completeness as dictated by science needs. By combining multiple selection criteria, ELiXer improves upon the 20 Angstrom rest-frame equivalent width cut commonly used to distinguish LAEs from lower-$z$ [OII] emitting galaxies. Despite a spectral resolving power, R $\sim800$, that cannot resolve the [OII] doublet, we demonstrate the ability to distinguish LAEs from foreground galaxies with 98.1% accuracy. We estimate a contamination rate of Ly$\alpha$ by [OII] of 1.2% and a Ly$\alpha$ recovery rate of 99.1% using the default ELiXer configuration. These rates meet the HETDEX science requirements.Comment: 38 pages, 11 figure

Constraints on the Epoch of Reionization with Roman Space Telescope and the Void Probability Function of Lyα Emitters

We use large simulations of Ly α emitters with different fractions of ionized intergalactic medium to quantify the clustering of Ly α emitters as measured by the void probability function (VPF), and how it evolves under different ionization scenarios. We quantify how well we might be able to distinguish between these scenarios with a deep spectroscopic survey using the future Nancy Grace Roman Space Telescope. Because Roman will be able to carry out blind spectroscopic surveys of Ly α emitters continuously between 7 3 σ –4 σ at several redshifts between 7 5–8 σ ) across the epoch of reionization, and would yield a detailed history of the reionization of the IGM and its effect on Ly α emitter clustering

Lyα at Cosmic Dawn with a Simulated Roman Grism Deep Field

The slitless grism on the Nancy Grace Roman Space Telescope will enable deep near-infrared spectroscopy over a wide field of view. We demonstrate Roman's capability to detect Ly α galaxies at z > 7 using a multiple position angle (PA) observational strategy. We simulate Roman grism data using a realistic foreground scene from the COSMOS field. We also input fake Ly α galaxies spanning redshift z = 7.5–10.5 and a line-flux range of interest. We show how a novel data-cube search technique—CUBGRISM—originally developed for the Galaxy Evolution Explorer can be applied to Roman grism data to produce a Ly α flux-limited sample without the need for continuum detections. We investigate the impact of altering the number of independent PAs and exposure time. A deep Roman grism survey with 25 PAs and a total exposure time of 70 hr can achieve Ly α line depths comparable to the deepest z = 7 narrowband surveys ( L _Ly _α ≳ 10 ^43 erg s ^−1 ). Assuming a null result, where the opacity of the intergalactic medium (IGM) remains unchanged from z ∼ 7, this level of sensitivity will detect ∼400 deg ^−2 Ly α emitters from z = 7.25 to 8.75. A decline from this expected number density is the signature of an increasing neutral hydrogen fraction and the onset of reionization. Our simulations indicate that a deep Roman grism survey has the ability to measure the timing and magnitude of this decline, allowing us to infer the ionization state of the IGM and helping us to distinguish between models of reionization

Finding Peas in the Early Universe with JWST

The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in characterizing the universe at Cosmic Dawn. We analyze the Near Infrared Spectrograph ERO spectra of three z ∼ 8 galaxies to determine their metallicities, gas temperatures, and ionization. These galaxies offer the first opportunity to understand the physical properties of Epoch-of-Reionization galaxies through detailed rest-optical emission-line spectroscopy. We show that these objects have metal abundances $12+\mathrm{log}[{\rm{O}}/{\rm{H}}]\,\approx$ 6.9–8.3, based on both the T _e method and on a recent calibration of the R _23 metallicity indicator. Since the spectra are some of the earliest science data from JWST, we compare several line ratios with values expected from robust physics, to validate our measurement procedures. We compare the abundances and emission-line ratios to a nearby sample of Green Pea galaxies—a population of nearby emission-line galaxies whose UV properties resemble Epoch-of-Reionization galaxies, and which often have large Lyman continuum escape fractions. The JWST data show striking further similarities between these high-redshift galaxies and nearby Green Peas. The z ∼ 8 galaxies span the metallicity range covered by Green Peas. They also show the compact morphology that is typical of emission-line-dominated galaxies at all redshifts. Based on these similarities with Green Peas, it is likely that these are the first rest-optical spectra of galaxies that are actively driving cosmological reionization

ALMA 1.1mm Observations of a Conservative Sample of High Redshift Massive Quiescent Galaxies in SHELA

We present a sample of 30 massive (log$(M_{\ast}/M_\odot) >11$) $z=3-5$ quiescent galaxies selected from the \textit{Spitzer-}HETDEX Exploratory Large Area (SHELA) Survey and observed at 1.1mm with Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations. These ALMA observations would detect even modest levels of dust-obscured star-formation, on order of $\sim 20 \ M_\odot \textrm{yr}^{-1}$ at $z\sim4$ at a $1\sigma$ level, allowing us to quantify the amount of contamination from dusty star-forming sources in our quiescent sample. Starting with a parent sample of candidate massive quiescent galaxies from the Stevans et al. 2021 v1 SHELA catalog, we use the Bayesian \textsc{Bagpipes} spectral energy distribution fitting code to derive robust stellar masses ($M_*$) and star-formation rates (SFRs) for these sources, and select a conservative sample of 36 candidate massive ($M_* > 10^{11}M_\odot$) quiescent galaxies, with specific SFRs at $>2\sigma$ below the star-forming main sequence at $z\sim4$. Based on ALMA imaging, six of these candidate quiescent galaxies have the presence of significant dust-obscured star-formation, thus were removed from our final sample. This implies a $\sim 17\%$ contamination rate from dusty star-forming galaxies with our selection criteria using the v1 SHELA catalog. This conservatively-selected quiescent galaxy sample at $z=3-5$ will provide excellent targets for future observations to better constrain how massive galaxies can both grow and shut-down their star-formation in a relatively short time period.Comment: 16 pages, 13 figure