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Ly$alpha$ emission is a standard tracer of starburst galaxies at high redshift. However, a number of local Ly$alpha$ emitters (LAEs) are X-ray sources, suggesting a possible origin of Ly$alpha$ photons other than young, hot stars, and which may be active at much later ages relative to the parent starburst. Resolved, nearby LAEs offer the opportunity to discriminate between diffuse X-ray emission arising from supernova-heated gas, high-mass X-ray binaries (HMXBs), or low-luminosity active galactic nuclei (LLAGN). We examine archival X-ray imaging from Chandra and XMM-Newton for 11 galaxies with spatially resolved Ly$alpha$ imaging to determine the luminosity, morphology, and spectral hardness of the X-ray sources. The data are consistent with 9 of the 12, bright Ly$alpha$ sources being driven by luminous, $10^{40}$ erg s$^{-1}$ X-ray sources. Half of the 8 Chandra sources are unresolved. The data suggest that nuclear activity, whether from LLAGN or nuclear starbursts, may play an important role in Ly$alpha$ emission. Our results also suggest a significant link between Ly$alpha$ emission and HMXBs, ULXs, and/or LLAGN, which would imply that Ly$alpha$ may be generated over timescales 1 - 2 orders of magnitude longer than produced by photoionization from OB stars. This highlights a critical need to quantify the relative contributions of different sources across cosmic time, to interpret Ly$alpha$ observations and the resulting properties of distant galaxies.
(abridged) Observing the signature of accretion from the intergalactic medium (IGM) onto galaxies at z~3 requires the detection of faint (L<<L*) galaxies embedded in a filamentary matrix of low-density, metal-poor gas coherent over hundreds of kpc. W
In this work we model the observed evolution in comoving number density of Lyman-alpha blobs (LABs) as a function of redshift, and try to find which mechanism of emission is dominant in LAB. Our model calculates LAB emission both from cooling radiati
The presence of neutral hydrogen in the inter-stellar medium (ISM) and inter-galactic medium (IGM) induces radiative transfer (RT) effects on Ly{alpha} photons which affect the observability of Ly{alpha} emitters (LAEs). We use the GALFORM semi-analy
We use spatially extended measurements of Ly$alpha$ as well as less optically thick emission lines from an $approx$80 kpc Ly$alpha$ nebula at $zapprox1.67$ to assess the role of resonant scattering and to disentangle kinematic signatures from Ly$alph
In this series of lectures, I review our observational understanding of high-$z$ Ly$alpha$ emitters (LAEs) and relevant scientific topics. Since the discovery of LAEs in the late 1990s, more than ten (one) thousand(s) of LAEs have been identified pho