Andrew Bunker

Abstract:

ABSTRACT Recent studies of gas kinematics at high redshift have reported discy systems that appear to challenge models of galaxy formation, but it is unclear whether they are representative of the underlying galaxy population. We present the first statistical sample of spatially resolved ionized gas kinematics at high redshift, comprised of 213 H $\alpha$ emitters in GOODS-S and GOODS-N at redshifts $z\approx 3.9\!-\!6.5$, observed with James Webb Space Telescope/NIRCam slitless spectroscopy and imaging from JADES, FRESCO, and CONGRESS. The sample probes two orders of magnitude in stellar mass ($\log (M_{\star }[\mathrm{M}_{\odot }])\approx 8\!-\!10$) and star formation rate ($\text{SFR}\approx 0.3\!-\!100\, \mathrm{M}_{\odot }\, \mathrm{yr}^{-1}$), and is representative down to $\log (M_{\star }[\mathrm{M}_{\odot }])\approx 9$. Using a novel inference tool, geko, we model the grism data to measure morphological and kinematic properties of the ionized gas, as probed by H $\alpha$. Our results are consistent with a decrease of the rotational support $v/\sigma _0$ and increase of the velocity dispersion $\sigma _0$ with redshift, when compared to $z< 3$, with $\sigma _0\approx 100$ km s$^{-1}$ and $v/\sigma _0\approx 1\!-\!2$ at $z\approx 3.9\!-\!6.5$. We study the relations between $\sigma _0$ and $v/\sigma _0$, and different star formation tracers and find a large scatter and diversity, with the most significant correlation between $\sigma _0$ and SFR. We find no evolution of the fraction of rotationally supported systems ($v/\sigma _0>1$) from $z\sim 5.5$ to $z\sim 4.5$, measured at $f=(34\pm 5){{\ \rm per\ cent}}$ in both redshift bins, for galaxies with masses $9<\log (M_{\star }[\mathrm{M}_{\odot }])< 10$. Overall, discs do not dominate the turbulent high-redshift galaxy population in the mass range probed by this work, but they remain a sizeable population. When placed in the context of studies up to cosmic noon, our results are consistent with a needed increase of disc-like systems with cosmic time.

Abstract:

We present the survey design and initial results from the Parallel Ionizing Emissivity (PIE) survey. PIE is a large Hubble Space Telescope survey designed to detect Lyman continuum (LyC) emitting galaxies at 3.1 < z < 3.5 and stack their images in order to measure average LyC escape fractions as a function of galaxy properties. PIE has imaged 37 independent fields in three filters (F336W, F625W, and F814W), of which 18 are observed with a fourth band (F475W) from the accompanying PIE+ program. We use photometric colors to select candidate Lyman break galaxies (LBGs) at 3.1 < z < 3.5, which can be followed up using ground-based spectrographs to confirm their redshifts. Unlike previous surveys, we use many independent fields to remove biases caused by correlated absorption in the intergalactic medium (IGM). In this paper, we describe the survey design, photometric measurements, and the use of mock galaxy samples to optimize our color selection. With three filters, we can select a galaxy sample of which ≈90% are LBGs and over 30% lie in the 3.1 < z < 3.5 range for which we can detect uncontaminated LyC emission in F336W. We also use mock IGM sight lines to measure the expected transmission of the IGM, which will allow us to determine escape fractions from our stacked galaxies. We color-select ≈1400 galaxies, and predict that this includes ≈80 LyC-emitting galaxies and ≈500 that we can use in stacking. Finally, we present the Keck/LRIS spectrum of a galaxy at z ≈ 2.99, demonstrating that we can confirm the redshifts of z ∼ 3 galaxies from the ground.