First Data Release of the COSMOS Lyα Mapping and Tomography Observations: 3D Lyα Forest Tomography at 2.05 < z < 2.55

Abstract

Faint star-forming galaxies at z∼2-3 can be used as alternative background sources to probe the Lyα forest in addition to quasars, yielding high sightline densities that enable 3D tomographic reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Lyα Mapping And Tomography Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck I telescope. Over an observational footprint of 0.157 deg 2 within the COSMOS field, we used 240 galaxies and quasars at 2.17<z<3.00, with a mean comoving transverse separation of h 2.37 Mpc 1 , as background sources probing the foreground Lyα forest absorption at 2.05<z<2.55. The Lyα forest data was then used to create a Wienerfiltered tomographic reconstruction over a comoving volume of´-h 3.15 10 Mpc 5 3 3 with an effective smoothing scale of h 2.5 Mpc 1. In addition to traditional figures, this map is also presented as a virtual-reality visualization and manipulable interactive figure. We see large overdensities and underdensities that visually agree with the distribution of coeval galaxies from spectroscopic redshift surveys in the same field, including overdensities associated with several recently discovered galaxy protoclusters in the volume. Quantitatively, the map signal-tonoise is » S N 3.4 wiener over a 3 h −1 Mpc top-hat kernel based on the variances estimated from the Wiener filter. This data release includes the redshift catalog, reduced spectra, extracted Lyα forest pixel data, and reconstructed tomographic map of the absorption. These can be downloaded from Zenodo (10.5281/zenodo.1292459).

Three- and two-point spatial correlations of intergalactic medium at z ∼ 2 using projected quasar triplets

“…Therefore a rich insight into the morphological properties of the cosmic web (filaments, sheets, voids and connection between them), but also the large scale ionization and chemical inhomogeneities and their redshift evolution can be gained by simultaneous analysis of Lyα absorption detected along closely spaced sightlines. Virtual experiments performed on simulated data suggest that it is possible to reconstruct a 3D map of the full density field using a dense enough grid of spatially close lines of sight (see, Pichon et al 2001;McDonald 2003;Caucci et al 2008;Lee et al 2018).…”

“…Using a group of background quasars, we can probe different physical processes at different scales: (i) The H i density and velocity fields at the scales of few 100 cKpc may have thermal memory of cosmic reionization in the form of pressure broadening (Peeples et al 2010;Rorai et al 2018); (ii) at the scale of ∼ 1 pMpc we can probe matter clustering around massive galaxies (quasar hosts and intervening metal systems) and various feedback processes connecting gas flows between galaxies and the IGM. At present these scales are best probed using quasar pairs (see for example, Prochaska et al 2013); (iii) at the scales of one to few Mpc, one is probing the cosmic structure of filaments and voids and the effect of radiative feed back from bright persistent objects like quasars (e.g Finley et al 2014;Lee et al 2018); and (iv) the Baryon Acoustic Oscillations (BAO) at ∼100 Mpc probes primordial density fluctuations at very large scales (Ata et al 2018).…”

Searching for the shadows of giants: characterizing protoclusters with line of sight Lyman-α absorption

“…The recent work has been approached from two different directions. The first is Ly-α forest tomography (Lee et al 2014;Stark et al 2015;Lee et al 2018), where the underlying 3-D mass distribution is reconstructed using multiple Ly-α forest spectra in the same patch of sky. Applying insight obtained from a 256 3 h −3 cMpc 3 collisionless dark matter simulation, Lee et al (2016) have used this method to successfully detect a galaxy overdensity at z = 2.44 in the COSMOS field, as well as cosmic voids at z ∼ 2.3 (Krolewski et al 2018).…”

IGM‐Vis: Analyzing Intergalactic and Circumgalactic Medium Absorption Using Quasar Sightlines in a Cosmic Web Context

“…Using multiple sightlines to reveal the spatial structure of absorbing media by sampling several points across the plane of the sky has been employed on a variety of scales. This tomographic approach has been applied to the gas clouds in our own Milky Way [TS12, FWB*14, BFL*17], the halos of other galaxies [BCJ*16,ZCR*16, ROC*, LTL*18], and, on the largest scales, the intergalactic medium of the Cosmic Web [CFP*16, LKW*18]. Within the IGM‐Vis volume, we identified at least four sightlines that exhibit H I absorption signals within a narrow redshift range of one another.…”

“…A researcher may also conduct tomography of foreground structures wherein multiple sightlines pierce the halo of a single foreground galaxy [BCJ*16], galaxy cluster [YP17], or filament [WHF*15]. Alternatively, structures may be identified through absorption alone, as multiple adjacent sightlines might exhibit coherent absorption at a consistent redshift [CFP*16, LKW*18]. IGM‐Vis enables researchers to visually select multiple sightlines within a single filament or galaxy cluster, and encourages the interactive investigation of their absorption properties.…”