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