Ly <i>α</i> Nebulae in HETDEX: The Largest Statistical Census Bridging Ly <i>α</i> Halos and Blobs across Cosmic Noon

Abstract The Hobby–Eberly Dark Energy Experiment (HETDEX) is an untargeted ∼540 deg 2 spectroscopic survey of Ly α emission in the 1.9 &lt; z &lt; 3.5 Universe. In surface brightness, this survey reaches 1 σ Ly α sensitivities of ∼2–5 × 10 −18 erg s −1 cm <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">arcsec</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> , allowing large samples of extended Ly α nebulae (LAN) to be studied. We selected a sample of 70,691 Ly α -emitting galaxies (LAEs) with an emission-line signal-to-noise ratio greater than 6 and modeled the Ly α emission as a point-source component with an optional exponential envelope. Half (∼47.5%) of the LAE sample (33,612 objects) exhibits significant extended emission and is best fit by the two-component model. The fraction of resolved sources increases with Ly α flux and luminosity. Their isophotal areas range from 10 to 130 arcsec 2 (median 15 arcsec 2 ), with integrated Ly α fluxes from 6 to 2000 × 10 −17 erg s −1 cm −2 (median 20 × 10 −17 erg s −1 cm −2 ). Comparison between point-spread function-weighted and isophotal flux measurements shows that the HETDEX pipeline underestimates the total Ly α flux by ∼30% on average, reflecting the substantial halo contribution in extended sources. Approximately 420 LANs are found per deg 2 over 79.5 deg 2 of noncontiguous sky. About 12% of resolved sources show active galactic nuclei signatures and are bright in Ly α and continuum. The remaining 88% span a wide range of morphologies and often lack continuum counterparts. Exponential scale lengths show no strong correlation with Ly α flux or luminosity (median 11.6 ± 1.9 kpc). Only 2.9% of the full S/N &gt; 6 LAE population with ancillary data have radio counterparts, but 64% of those are found to be extended, with the radio fraction increasing with Ly α size. We present a catalog of all modeled sources, with their positions, redshifts, luminosities, and structural parameters for over 70,000 LAEs consisting of 33,000 spatially extended LAN. The catalog can be found at https://hetdex.org/data-results/ and in the online version of this paper.