More Like this

1. Ly $\alpha$ Halo Properties and Dust in the Circumgalactic Medium of z ∼ 2 Star-forming Galaxies

   https://doi.org/10.3847/1538-4357/ad4bd8  

   Song, Zhiyuan; Reddy, Naveen A; Chen, Yuguang; Shapley, Alice E; Rezaee, Saeed; Weldon, Andrew; Fetherolf, Tara; Coil, Alison L; Mobasher, Bahram; Steidel, Charles C (July 2024, The Astrophysical Journal)

   Abstract We present Keck Cosmic Web Imager integral-field unit observations around extended Lyαhalos of 27 typical star-forming galaxies with redshifts 2.0 <z< 3.2 drawn from the MOSFIRE Deep Evolution Field survey. We examine the average Lyαsurface brightness profiles in bins of star formation rate (SFR), stellar mass (M_*), age, stellar continuum reddening, SFR surface density (Σ_SFR), and Σ_SFRnormalized by stellar mass (Σ_sSFR). The scale lengths of the halos correlate with stellar mass, age, and stellar continuum reddening and anticorrelate with SFR, Σ_SFR, and Σ_sSFR. These results are consistent with a scenario in which the down-the-barrel fraction of Lyαemission is modulated by the low-column-density channels in the interstellar medium, and in which the neutral gas covering fraction is related to the physical properties of the galaxies. Specifically, we find that this covering fraction increases with stellar mass, age, andE(B−V) and decreases with SFR, Σ_SFR, and Σ_sSFR. We also find that the resonantly scattered Lyαemission suffers greater attenuation than the (nonresonant) stellar continuum emission, and that the difference in attenuation increases with stellar mass, age, and stellar continuum reddening, and decreases with Σ_sSFR. These results imply that more reddened galaxies have more dust in their circumgalactic medium. 

   more » « less
2. CLASSY VII Lyα Profiles: The Structure and Kinematics of Neutral Gas and Implications for LyC Escape in Reionization-era Analogs*

   https://doi.org/10.3847/1538-4357/aceefd  

   Hu, Weida; Martin, Crystal L.; Gronke, Max; Gazagnes, Simon; Hayes, Matthew; Chisholm, John; Heckman, Timothy; Mingozzi, Matilde; Roy, Namrata; Senchyna, Peter; et al (October 2023, The Astrophysical Journal)

   Abstract Lyαline profiles are a powerful probe of interstellar medium (ISM) structure, outflow speed, and Lyman-continuum escape fraction. In this paper, we present the Lyαline profiles of the Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY, a sample rich in spectroscopic analogs of reionization-era galaxies. A large fraction of the spectra show a complex profile, consisting of a double-peaked Lyαemission profile in the bottom of a damped, Lyαabsorption trough. Such profiles reveal an inhomogeneous ISM. We successfully fit the damped Lyαabsorption and the Lyαemission profiles separately, but with complementary covering factors, a surprising result because this approach requires no Lyαexchange between high-N_Hiand low-N_Hipaths. The combined distribution of column densities is qualitatively similar to the bimodal distributions observed in numerical simulations. We find an inverse relation between Lyαpeak separation and the [Oiii]/[Oii] flux ratio, confirming that the covering fraction of Lyman-continuum-thin sightlines increases as the Lyαpeak separation decreases. We combine measurements of Lyαpeak separation and Lyαred peak asymmetry in a diagnostic diagram, which identifies six Lyman-continuum leakers in the COS Legacy Archive Spectrocopy SurveY (CLASSY) sample. We find a strong correlation between the Lyαtrough velocity and the outflow velocity measured from interstellar absorption lines. We argue that greater vignetting of the blueshifted Lyαpeak, relative to the redshifted peak, is the source of the well-known discrepancy between shell-model parameters and directly measured outflow properties. The CLASSY sample illustrates how scattering of Lyαphotons outside the spectroscopic aperture reshapes Lyαprofiles because the distances to these compact starbursts span a large range. 

   more » « less
3. The Active Galactic Nuclei in the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX). III. A Red Quasar with Extremely High Equivalent Widths Showing Powerful Outflows

   https://doi.org/10.3847/1538-4357/ac9af2  

   Liu, Chenxu; Gebhardt, Karl; Kollatschny, Wolfram; Ciardullo, Robin; Cooper, Erin Mentuch; Davis, Dustin; Farrow, Daniel J.; Finkelstein, Steven L.; Gawiser, Eric; Gronwall, Caryl; et al (November 2022, The Astrophysical Journal)

   Abstract We report an active galactic nucleus (AGN) with an extremely high equivalent width (EW), EW Ly α +N V,rest ≳921 Å , in the rest frame, at z ∼ 2.24 in the Hobby–Eberly Telescope Dark Energy Experiment Survey (HETDEX), as a representative case of the high-EW AGN population. The continuum level is a nondetection in the HETDEX spectrum; thus the measured EW is a lower limit. The source is detected with significant emission lines (>7 σ ) at Ly α + N v λ 1241, C iv λ 1549, and a moderate emission line (∼4 σ ) at He ii λ 1640 within the wavelength coverage of HETDEX (3500–5500 Å). The r -band magnitude is 24.57 from the Hyper Suprime-Cam-HETDEX joint survey with a detection limit of r = 25.12 at 5 σ . The Ly α emission line spans a clearly resolved region of ∼10″ (85 kpc) in diameter. The Ly α line profile is strongly double peaked. The spectral decomposed blue gas and red gas Ly α emission are separated by ∼1.″2 (10.1 kpc) with a line-of-sight velocity offset of ∼1100 km s −1 . This source is probably an obscured AGN with powerful winds. 

   more » « less
4. Surface Brightness Profile of Lyman-α Halos out to 320 kpc in HETDEX

   https://doi.org/10.3847/1538-4357/ac5cb8  

   Lujan_Niemeyer, Maja; Komatsu, Eiichiro; Byrohl, Chris; Davis, Dustin; Fabricius, Maximilian; Gebhardt, Karl; Hill, Gary J; Wisotzki, Lutz; Bowman, William P; Ciardullo, Robin; et al (April 2022, The Astrophysical Journal)

   Abstract We present the median-stacked Lyman-α (Lyα) surface brightness profiles of 968 spectroscopically selected Lyαemitting galaxies (LAEs) at redshifts 1.9 <z< 3.5 in the early data of the Hobby-Eberly Telescope Dark Energy Experiment. The selected LAEs are high-confidence Lyαdetections with high signal-to-noise ratios observed with good seeing conditions (point-spread function FWHM <1.″4), excluding active galactic nuclei. The Lyαluminosities of the LAEs are 10^42.4–10⁴³erg s⁻¹. We detect faint emission in the median-stacked radial profiles at the level of $(3.6\pm 1.3)\times {10}^{-20}\mathrm{erg}{\mathrm{s}}^{-1}{\mathrm{cm}}^{-2}{\mathrm{arcsec}}^{-2}$from the surrounding Lyαhalos out tor≃ 160 kpc (physical). The shape of the median-stacked radial profile is consistent atr< 80 kpc with that of much fainter LAEs at 3 <z< 4 observed with the Multi Unit Spectroscopic Explorer (MUSE), indicating that the median-stacked Lyαprofiles have similar shapes at redshifts 2 <z< 4 and across a factor of 10 in Lyαluminosity. While we agree with the results from the MUSE sample atr< 80 kpc, we extend the profile over a factor of two in radius. Atr> 80 kpc, our profile is flatter than the MUSE model. The measured profile agrees at most radii with that of galaxies in the Byrohl et al. cosmological radiative transfer simulation atz= 3. This suggests that the surface brightness of a Lyαhalo atr≲ 100 kpc is dominated by resonant scattering of Lyαphotons from star-forming regions in the central galaxy, whereas atr> 100 kpc, it is dominated by photons from galaxies in surrounding dark matter halos. 

   more » « less
5. Radiative Transfer in Lyα Nebulae. I. Modeling a Continuous or Clumpy Spherical Halo with a Central Source

   https://doi.org/10.3847/1538-4357/acac98  

   Chang, Seok-Jun; Yang, Yujin; Seon, Kwang-Il; Zabludoff, Ann; Lee, Hee-Won (March 2023, The Astrophysical Journal)

   Abstract To understand the mechanism behind high- z Ly α nebulae, we simulate the scattering of Ly α in a H i halo about a central Ly α source. For the first time, we consider both smooth and clumpy distributions of halo gas, as well as a range of outflow speeds, total H i column densities, H i spatial concentrations, and central source galaxies (e.g., with Ly α line widths corresponding to those typical of active galactic nucleus or star-forming galaxies). We compute the spatial-frequency diffusion and the polarization of the Ly α photons scattered by atomic hydrogen. Our scattering-only model reproduces the typical size of Ly α nebulae (∼100 kpc) at total column densities N H I ≥ 10 20 cm −2 and predicts a range of positive, flat, and negative polarization radial gradients. We also find two general classes of Ly α nebula morphologies: with and without bright cores. Cores are seen when N H I is low, i.e., when the central source is directly visible, and are associated with a polarization jump, a steep increase in the polarization radial profile just outside the halo center. Of all the parameters tested in our smooth or clumpy medium model, N H I dominates the trends. The radial behaviors of the Ly α surface brightness, spectral line shape, and polarization in the clumpy model with covering factor f c ≳ 5 approach those of the smooth model at the same N H I . A clumpy medium with high N H I and low f c ≲ 2 generates Ly α features via scattering that the smooth model cannot: a bright core, symmetric line profile, and polarization jump. 

   more » « less