Lyman-alpha Forest Tomography from Background Galaxies: The First Megaparsec-Resolution Large-Scale Structure Map at z>2

Abstract

We present the first observations of foreground Lyman-$\alpha$ forest absorption from high-redshift galaxies, targeting 24 star-forming galaxies (SFGs) with $z\sim 2.3-2.8$ within a $5^{\prime }\times 15^{\prime }$ region of the COSMOS field. The transverse sightline separation is $\sim 2h^{-1}\mathrm{Mpc}$ comoving, allowing us to create a tomographic reconstruction of the 3D Ly$\alpha$ forest absorption field over the redshift range $2.20\le z\le 2.45$. The resulting map covers $6h^{-1}\mathrm{Mpc}\times 14h^{-1}\mathrm{Mpc}$ in the transverse plane and $230h^{-1}\mathrm{Mpc}$ along the line-of-sight with a spatial resolution of $\approx 3.5h^{-1}\mathrm{Mpc}$, and is the first high-fidelity map of large-scale structure on $\sim \mathrm{Mpc}$ scales at $z>2$. Our map reveals significant structures with $\gtrsim 10h^{-1}\mathrm{Mpc}$ extent, including several spanning the entire transverse breadth, providing qualitative evidence for the filamentary structures predicted to exist in the high-redshift cosmic web. Simulated reconstructions with the same sightline sampling, spectral resolution, and signal-to-noise ratio recover the salient structures present in the underlying 3D absorption fields. Using data from other surveys, we identified 18 galaxies with known redshifts coeval with our map volume enabling a direct comparison to our tomographic map. This shows that galaxies preferentially occupy high-density regions, in qualitative agreement with the same comparison applied to simulations. Our results establishes the feasibility of the CLAMATO survey, which aims to obtain Ly$\alpha$ forest spectra for $\sim 1000$ SFGs over $\sim 1{\mathrm{deg}}^2$ of the COSMOS field, in order to map out IGM large-scale structure at $⟨z⟩\sim 2.3$ over a large volume $(100h^{-1}\mathrm{Mpc}{)}^3$.

Accepted for publication in Astrophysical Journal Letters; 8 pages and 5 figures

References in corpus (8)

• The Cosmic Evolution Survey (COSMOS) -- Overview
• COSMOS Photometric Redshifts with 30-bands for 2-deg2
• zCOSMOS: A Large VLT/VIMOS redshift survey covering 0 < z < 3 in the COSMOS field
• Baryon Acoustic Oscillations in the Lyα forest of BOSS DR11 quasars
• Baryon Acoustic Oscillations in the Ly-α forest of BOSS quasars
• Multi-Wavelength Constraints on the Cosmic Star Formation History from Spectroscopy: the Rest-Frame UV, H-alpha, and Infrared Luminosity Functions at Redshifts 1.9<z<3.4
• The VIMOS Ultra-Deep Survey: ~10,000 galaxies with spectroscopic redshifts to study galaxy assembly at early epochs 2<z<~6
• IGM Constraints from the SDSS-III/BOSS DR9 Ly-alpha Forest Flux Probability Distribution Function

Cited by in corpus (1)

• IGM Constraints from the SDSS-III/BOSS DR9 Ly-alpha Forest Flux Probability Distribution Function