Lyman alpha Emitting Galaxies in the Nearby Universe

Abstract

The Lya emission line of HI is intrinsically the brightest feature in the spectrum of astrophysical nebulae, making it a very attractive observational tool with which to survey galaxies. Moreover as a UV resonance line, Lya possesses several unique characteristics that make it useful to study the ISM and ionizing stellar population at all cosmic epochs. In this review I present a summary of Lya observations of galaxies in the nearby universe. At UV magnitudes reachable with current facilities, only ~5% of the local galaxy population shows a Lya equivalent width (EW_Lya) that exceeds 20Å. This fraction increases dramatically at higher z, but only in the local universe can we study galaxies in detail and assemble unprecedented multi-wavelength datasets. I discuss many local Lya observations, showing that when galaxies show net Lya emission, they ubiquitously produce large halos of scattered Lya, that dominate the integrated luminosity. We discuss how global EW_Lya and the Lya escape fraction (fescLya) are higher (EW_Lya >~ 20Å and fescLya> 10%) in galaxies that represent the less massive and younger end of the distributions for local objects. This is connected with various properties, such that Lya-emitters have lower metallicities (median value of 12+log(O/H) ~ 8.1) and dust reddening. However, the presence of galactic outflows is also vital to Doppler shift the Lya line out of resonance with the HI, as high EW_Lya is found only among galaxies with winds faster than ~50km/s. The evidence is then assembled into a coherent picture, and the requirement for star formation driven feedback is discussed in the context of an evolutionary sequence where the ISM is accelerated and/or subject to fluid instabilities, which reduce the scattering of Lya. Concluding remarks take the form of perspectives upon the most pressing questions that can be answered by observation.

Invited review article, in press at PASA as part of the series on Lyman alpha emitting galaxies. 27 pages, 12 figures

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Cited by in corpus (32)

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• Near-Infrared Spectroscopy of Galaxies During Reionization: Measuring CIII] in a Galaxy at $\mathbf{z}=7.5$
• From Mirrors to Windows: Lyman-Alpha Radiative Transfer in a Very Clumpy Medium
• The physics of Lyman-alpha escape from disc-like galaxies
• The Diversity of Diffuse Ly$\alpha$ Nebulae around Star-Forming Galaxies at High Redshift
• Ionized gas kinematics and chemical abundances of low-mass star-forming galaxies at $z\sim 3$
• Neutral ISM, Lyman-Alpha and Lyman-continuum in the nearby starburst Haro 11
• The Circumgalactic Medium of Extreme Emission Line Galaxies at z ~ 2: Resolved Spectroscopy and Radiative Transfer Modeling of Spatially Extended Lyman-alpha Emission in the KBSS-KCWI Survey
• MUSE Illuminates Channels for Lyman Continuum Escape in the Halo of SBS 0335-52E
• Spectral Shapes of the Lya Emission from Galaxies. II. the influence of stellar properties and nebular conditions on the emergent Lya profiles
• Effects of Spatial Discretization in Lyman-alpha Line Radiation Transfer Simulations
• The HETDEX Survey: The Ly$\alpha$ Escape Fraction from 3D-HST Emission Line Galaxies at $z\sim 2$
• An investigation of the circumgalactic medium around z~2.2 AGN with ACA and ALMA
• Detection of HI in Emission in the Lyman Alpha Emitting Galaxy Haro 11
• The Lyman Alpha Reference Sample. VIII. Characterizing Lyman-Alpha Scattering in Nearby Galaxies
• Characterizing the Circumgalactic Medium of Quasars at z $\sim$ 2.2 through H$\alpha$ and Ly$\alpha$ Emission
• Deciphering stellar metallicities in the early Universe: Case study of a young galaxy at z = 4.77 in the MUSE eXtremely Deep Field
• Stellar Populations of Lyman-alpha Emitting Galaxies in the HETDEX Survey I: An Analysis of LAEs in the GOODS-N Field
• The Lyman $\alpha$ Reference Sample XIV: Lyman $\alpha$ imaging of 45 low redshift star-forming galaxies and inferences on global emission
• Radio properties of Green Pea galaxies
• Resolved galactic superwinds reconstructed around their host galaxies at z>3
• Lyman-alpha at Cosmic Noon I: Ly-alpha Spectral Type Selection of z ~ 2-3 Lyman Break Galaxies with Broadband Imaging
• Modelling LAEs in the Epoch of Reionization with OBELISK
• SDSS-IV MaNGA: an observational evidence of density bounded region in a Lyman-$\alpha$ emitter
• Impact of Cosmic Variance on the Galaxy-Halo Connection for Lyman-$\alpha$ Emitters
• Influence of turbulence on Lyman-alpha scattering
• Modelling the gas kinematics of an atypical Lyman-alpha emitting compact dwarf galaxy
• Lyman-alpha at Cosmic Noon II: The relationship between kinematics and Lyman-alpha in z~2-3 Lyman Break Galaxies
• Uncertainty-Aware Neural Networks for Fuzzy Dark Matter Model Selection from \texorpdfstring{$x_{\mathrm{HI}}$}{x_HI} Measurements
• Extreme equivalent width-selected low-mass starbursts at $z=4-9$: insights into their role in cosmic reionization