Search

Lyman-alpha-emitting galaxies (LAEs) are typically young, low-mass, star-forming galaxies with little extinction from interstellar dust. Their low dust attenuation allows their Ly α emission to shine brightly in spectroscopic and photometric observations, providing an observational window into the high-redshift Universe. Narrowband surveys reveal large, uniform samples of LAEs at specific redshifts that probe large-scale structure and the temporal evolution of galaxy properties. The One-hundred-deg ^2 DECam Imaging in Narrowbands (ODIN) utilizes three custom-made narrowband filters on the Dark Energy Camera (DECam) to discover LAEs at three equally spaced periods in cosmological history. In this paper, we introduce the hybrid-weighted double-broadband continuum estimation technique, which yields improved estimation of Ly α equivalent widths. Using this method, we discover 6032, 5691, and 4066 LAE candidates at z = 2.4, 3.1, and 4.5 in the extended COSMOS field (∼9 deg ^2 ). We find that [O ii ] emitters are a minimal contaminant in our LAE samples, but that interloping Green Pea–like [O iii ] emitters are important for our redshift 4.5 sample. We introduce an innovative method for identifying [O ii ] and [O iii ] emitters via a combination of narrowband excess and galaxy colors, enabling their study as separate classes of objects. We present scaled median stacked spectral energy distributions for each galaxy sample, revealing the overall success of our selection methods. We also calculate rest-frame Ly α equivalent widths for our LAE samples and find that the EW distributions are best fit by exponential functions with scale lengths of w _0 = 53 ± 1, 65 ± 1, and 59 ± 1 Å, respectively.

We describe the survey design and science goals for One-hundred-deg ^2 DECam Imaging in Narrowbands (ODIN), a NOIRLab survey using the Dark Energy Camera (DECam) to obtain deep (AB ∼ 25.7) narrowband images over an unprecedented area of sky. The three custom-built narrowband filters, N 419, N 501, and N 673, have central wavelengths of 419, 501, and 673 nm and respective FWHM of 7.5, 7.6, and 10.0 nm, corresponding to Ly α at z = 2.4, 3.1, and 4.5 and cosmic times of 2.8, 2.1, and 1.4 Gyr, respectively. When combined with even deeper, public broadband data from the Hyper Suprime-Cam, DECam, and in the future, the Legacy Survey of Space and Time, the ODIN narrowband images will enable the selection of over 100,000 Ly α -emitting (LAE) galaxies at these epochs. ODIN-selected LAEs will identify protoclusters as galaxy overdensities, and the deep narrowband images enable detection of highly extended Ly α blobs (LABs). Primary science goals include measuring the clustering strength and dark matter halo connection of LAEs, LABs, and protoclusters, and their respective relationship to filaments in the cosmic web. The three epochs allow for the redshift evolution of these properties to be determined during the period known as Cosmic Noon, where star formation was at its peak. The narrowband filter wavelengths are designed to enable interloper rejection and further scientific studies by revealing [O ii ] and [O iii ] at z = 0.34, Ly α and He ii 1640 at z = 3.1, and Lyman continuum plus Ly α at z = 4.5. Ancillary science includes similar studies of the lower-redshift emission-line galaxy samples and investigations of nearby star-forming galaxies resolved into numerous [O iii ] and [S ii ] emitting regions.

We present the first publicly released catalog of sources obtained from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). HETDEX is an integral field spectroscopic survey designed to measure the Hubble expansion parameter and angular diameter distance at 1.88 < z < 3.52 by using the spatial distribution of more than a million Ly α -emitting galaxies over a total target area of 540 deg ^2 . The catalog comes from contiguous fiber spectra coverage of 25 deg ^2 of sky from 2017 January through 2020 June, where object detection is performed through two complementary detection methods: one designed to search for line emission and the other a search for continuum emission. The HETDEX public release catalog is dominated by emission-line galaxies and includes 51,863 Ly α -emitting galaxy (LAE) identifications and 123,891 [O ii ]-emitting galaxies at z < 0.5. Also included in the catalog are 37,916 stars, 5274 low-redshift ( z < 0.5) galaxies without emission lines, and 4976 active galactic nuclei. The catalog provides sky coordinates, redshifts, line identifications, classification information, line fluxes, [O ii ] and Ly α line luminosities where applicable, and spectra for all identified sources processed by the HETDEX detection pipeline. Extensive testing demonstrates that HETDEX redshifts agree to within Δ z < 0.02, 96.1% of the time to those in external spectroscopic catalogs. We measure the photometric counterpart fraction in deep ancillary Hyper Suprime-Cam imaging and find that only 55.5% of the LAE sample has an r -band continuum counterpart down to a limiting magnitude of r ∼ 26.2 mag (AB) indicating that an LAE search of similar sensitivity to HETDEX with photometric preselection would miss nearly half of the HETDEX LAE catalog sample. Data access and details about the catalog can be found online at http://hetdex.org/ . A copy of the catalogs presented in this work (Version 3.2) is available to download at Zenodo doi:10.5281/zenodo.7448504.