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It has been well established in the local universe that galaxy properties differ based on the large-scale environment in which they reside. As luminous Lyαnebulae have been shown to trace overdense environments atz∼ 2–3, comparing the properties of galaxies within Lyαnebulae systems to those in the field can provide insight into how and when locally observed trends between galaxy properties and environment emerged. Six Lyαnebulae were discovered atz∼ 2.3 in a blind search of the GOODS-S extragalactic field, a region also covered by the 3D-HST spectroscopic survey. Utilizing 3D-HST data, we identified 86 galaxies in the vicinity of these nebulae and used statistical tests to compare their physical properties to galaxies elsewhere in the field. Galaxies lying within 320 proper kpc of a Lyαnebula are roughly half a magnitude brighter than those in the field, with higher stellar masses, higher star formation rates, and larger effective radii. Even when considering the effects of sample incompleteness, our study suggests that galaxies in overdensities atz∼ 2.3 traced by Lyαnebulae are being influenced by their environment. Furthermore, Lyα-nebula-associated galaxies lie on the same main sequence of star formation as field galaxies but have a larger proportion of high-mass galaxies, consistent with the idea that galaxy evolution is accelerated in rich environments. Expanded surveys for Lyαnebulae in other deep extragalactic fields and galaxy spectroscopic follow-up with the James Webb Space Telescope (JWST) will better constrain the demographics of Lyα-nebula-associated galaxies.

We investigate the effects of stellar populations and sizes on Lyαescape in 27 spectroscopically confirmed and 35 photometric Lyαemitters (LAEs) atz≈ 2.65 in seven fields of the Boötes region of the NOAO Deep Wide-Field Survey. We use deep HST/WFC3 imaging to supplement ground-based observations and infer key galaxy properties. Compared to typical star-forming galaxies (SFGs) at similar redshifts, the LAEs are less massive (M_⋆≈ 10⁷–10⁹M_⊙), younger (ages ≲1 Gyr), smaller (r_e< 1 kpc), and less dust-attenuated (E(B−V) ≤ 0.26 mag) but have comparable star formation rates (SFRs ≈ 1–100M_⊙yr⁻¹). Some of the LAEs in the sample may be very young galaxies having low nebular metallicities (Z_neb≲ 0.2Z_⊙) and/or high ionization parameters ($\log (\mathrm{U})\gtrsim -2.4$). Motivated by previous studies, we examine the effects of the concentration of star formation and gravitational potential on Lyαescape by computing SFR surface density, Σ_SFR, and specific SFR surface density, Σ_sSFR. For a given Σ_SFR, the Lyαescape fraction is higher for LAEs with lower stellar masses. The LAEs have a higher Σ_sSFR, on average, compared to SFGs. Our results suggest that compact star formation in a low gravitational potential yields conditions amenable to the escape of Lyαphotons. These results have important implications for the physics of Lyαradiative transfer and for the type of galaxies that may contribute significantly to cosmic reionization.

We explore the possibility and practical limitations of using a three-line approach to measure both the slope and normalization of the dust attenuation law in individual galaxies. To do this, we focus on a sample of 11 galaxies with existing ground-based Balmer Hαand Hβmeasurements from slit spectra, plus space-based grism constraints on Paschen-β. When accounting for observational uncertainties, we show that one galaxy has a well-constrained dust-law slope and normalization in the range expected from theoretical arguments; this galaxy therefore provides an example of what may be possible in the future. However, most of the galaxies are best fit by unusually steep or shallow slopes. We then explore whether additional astrophysical effects or observational biases could explain the elevated Paschen-β/Hαratios driving these results. We find that galaxies with high Paschen-β/Hαratios may be explained by slightly sub-unity covering fractions (>97%). Alternatively, differing slit losses for different lines can have a large impact on the results, emphasizing the importance of measuring all three lines with a consistent spectroscopic aperture. We conclude that, while the three-line approach to constraining the shape of the dust attenuation law in individual galaxies is promising, deep observations and a consistent observational strategy will be required to minimize observational biases and to disentangle the astrophysically interesting effect of differing covering fractions. The James Webb Space Telescope will provide more sensitive measurements of Balmer and Paschen lines for galaxies atz≈ 0.3–2, enabling uniform constraints on the optical–infrared dust attenuation law and its intrinsic variation.

Recent wide-field integral-field spectroscopy has revealed the detailed properties of high-redshift Lyαnebulae, most often targeted due to the presence of an active galactic nucleus (AGN). Here, we use VLT/MUSE to resolve the morphology and kinematics of a nebula initially identified due to strong Lyαemission atz∼ 3.2 (LABn06). Our observations reveal a two-lobed Lyαnebula, at least ∼173 pkpc in diameter, with a light-weighted centroid near a mid-infrared source (within ≈17.2 pkpc) that appears to host an obscured AGN. The Lyαemission near the AGN is also coincident in velocity with the kinematic center of the nebula, suggesting that the nebula is both morphologically and kinematically centered on the AGN. Compared to AGN-selected Lyαnebulae, the surface-brightness profile of this nebula follows a typical exponential profile at large radii (>25 pkpc), although at small radii, the profile shows an unusual dip at the location of the AGN. The kinematics and asymmetry are similar to, and the Civand Heiiupper limits are consistent with, other AGN-powered Lyαnebulae. Double-peaked and asymmetric line profiles suggest that Lyαresonant scattering may be important in this nebula. These results support the picture of the AGN being responsible for powering a Lyαnebula that is oriented roughly in the plane of the sky. Further observations will explore whether the central surface-brightness depression is indicative of either an unusual gas or dust distribution or variation in the ionizing output of the AGN over time.