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We present the Lya luminosity functions (LFs) derived by our deep Subaru narrowband survey that identifies a total of 3,137 Lya emitters (LAEs) at $z = 2.2$ in five independent blank fields. The sample of these LAEs is the largest, to date, and covers a very wide Lya luminosity range of $\log L_{Ly��} = 41.7-44.4$ erg s$^{-1}$. We determine the Lya LF at $z = 2.2$ with unprecedented accuracies, and obtain the best-fit Schechter parameters of $L^{*}_{Ly��} = 5.29^{+1.67}_{-1.13} \times 10^{42}$ erg s$^{-1}$, $��^{*}_{Ly��} = 6.32^{+3.08}_{-2.31} \times 10^{-4}$ Mpc$^{-3}$, and $��= -1.75^{+0.10}_{-0.09}$ showing a steep faint-end slope. We identify a significant hump at the LF bright end ($\log L_{Ly��} > 43.4$ erg s$^{-1}$). Because all of the LAEs in the bright-end hump have (a) bright counterpart(s) either in the X-ray, UV, or radio data, this bright-end hump is not made by gravitational lensing magnification bias but AGNs. These AGNs allow us to derive the AGN UV LF at $z \sim 2$ down to the faint magnitude limit of $M_{UV} \simeq -22.5$, and to constrain the faint-end slope of AGN UV LF, $��_{AGN}=-1.2 \pm 0.1$, that is flatter than those at $z > 4$. Based on the Lya and UV LFs from our and previous studies, we find the increase of Lya escape fraction $f^{Ly��}_{esc}$ from $z \sim 0$ to $6$ by two orders of magnitude. This large $f^{Ly��}_{esc}$ increase can be explained neither by the evolution of stellar population nor outflow alone, but the evolution of neutral hydrogen HI density in inter-stellar medium that enhances dust attenuation for Lya by resonance scattering. Our uniform expanding shell models suggest that the typical HI column density decreases from $N_{HI} \sim 7 \times 10^{19}$ ($z \sim 0$) to $\sim 1 \times 10^{18}$ cm$^{-2}$ ($z \sim 6$) to explain the large $f^{Ly��}_{esc}$ increase., 18 pages, 10 figures, 5 tables, Accepted for publication in The Astrophysical Journal

We present integral field spectroscopic observations with the Potsdam Multi Aperture Spectrophotometer of all 14 galaxies in the $z\sim 0.1$ Lyman Alpha Reference Sample (LARS). We produce 2D line of sight velocity maps and velocity dispersion maps from the Balmer $��$ (H$��$) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Ly$��$ radiation field. We show our kinematic maps spatially registered onto the Hubble Space Telescope H$��$ and Lyman $��$ (Ly$��$) images. Only for individual galaxies a causal connection between spatially resolved H$��$ kinematics and Ly$��$ photometry can be conjectured. However, no general trend can be established for the whole sample. Furthermore, we compute non-parametric global kinematical statistics -- intrinsic velocity dispersion $��_0$, shearing velocity $v_\mathrm{shear}$, and the $v_\mathrm{shear}/��_0$ ratio -- from our kinematic maps. In general LARS galaxies are characterised by high intrinsic velocity dispersions (54\,km\,s$^{-1}$ median) and low shearing velocities (65\,km\,s$^{-1}$ median). $v_\mathrm{shear}/��_0$ values range from 0.5 to 3.2 with an average of 1.5. Noteworthy, five galaxies of the sample are dispersion dominated systems with $v_\mathrm{shear}/��_0 1$. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Ly$��$ radiation., 26 pages, 15 figures, accepted for publication in A&A

It has been suggested that radiative transfer effects may explain the unusually high equivalent widths (EWs) of the Lya line, observed occasionally from starburst galaxies, especially at high redshifts. If the dust is locked up inside high-density clouds dispersed in an empty intercloud medium, the Lya photons could scatter off of the surfaces of the clouds, effectively having their journey confined to the dustless medium. The continuum radiation, on the other hand, does not scatter, and would thus be subject to absorption inside the clouds. This scenario is routinely invoked when Lya EWs higher than what is expected theoretically are observed, although the ideal conditions under which the results are derived usually are not considered. Here we systematically examine the relevant physical parameters in this idealized framework, testing whether any astrophysically realistic scenarios may lead to such an effect. It is found that although clumpiness indeed facilitates the escape of Lya, it is highly unlikely that any real interstellar media should result in a preferential escape of Lya over continuum radiation. Other possible causes are discussed, and it is concluded that the observed high EWs are more likely to be caused by cooling radiation from cold accretion and/or anisotropic escape of the Lya radiation., Submitted to ApJ. Comments welcome

The Ly alpha Reference Sample (LARS) is a substantial program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the detailed astrophysics of the visibility and strength of the Ly alpha line of neutral hydrogen. Ly alpha is the dominant spectral line in use for characterizing high-redshift (z) galaxies. This paper presents an overview of the survey, its selection function, and HST imaging observations. The sample was selected from the combined GALEX+Sloan Digital Sky Survey catalog at z = 0.028-0.19, in order to allow Ly alpha to be captured with combinations of long-pass filters in the Solar Blind Channel (SBC) of the Advanced Camera for Surveys (ACS) onboard HST. In addition, LARS utilizes H alpha and H beta narrowband and u, b, i broadband imaging with ACS and the Wide Field Camera 3 (WFC3). In order to study galaxies in which large numbers of Ly alpha photons are produced (whether or not they escape), we demanded an H alpha equivalent width W(H alpha) >= 100 angstrom. The final sample of 14 galaxies covers far-UV (FUV, lambda similar to 1500 angstrom) luminosities that overlap with those of high-z Ly alpha emitters (LAEs) and Lyman break galaxies (LBGs), making LARS a valid comparison sample. We present the reduction steps used to obtain the Ly alpha images, including our LARS eXtraction software (LaXs), which utilizes pixel-by-pixel spectral synthesis fitting of the energy distribution to determine and subtract the continuum at Ly alpha. We demonstrate that the use of SBC long-pass-filter combinations increase the signal-to-noise ratio by an order of magnitude compared to the nominal Ly alpha filter available in SBC. To exemplify the science potential of LARS, we also present some first results for a single galaxy, Mrk 259 (LARS #1). This irregular galaxy shows bright and extended (indicative of resonance scattering) but strongly asymmetric Ly alpha emission. Spectroscopy from the Cosmic Origins Spectrograph on board HST centered on the brightest UV knot shows a moderate outflow in the neutral interstellar medium (probed by low ionization stage absorption features) and Ly alpha emission with an asymmetric profile. Radiative transfer modeling is able to reproduce the essential features of the Ly alpha line profile and confirms the presence of an outflow. From the integrated photometry we measure an Ly alpha luminosity of L-Ly alpha= 1.3x10(42) erg s(-1) an equivalent width W(Ly alpha) = 45 angstrom and an FUV absolute magnitude M-FUV = -19.2 (AB). Mrk 259 would hence be detectable in high-z Ly alpha and LBG surveys. The total Ly alpha escape fraction is 12%. This number is higher than the low-z average, but similar to that at z > 4, demonstrating that LARS provides a valid comparison sample for high-z galaxy studies.

We present high-resolution far-UV spectroscopy of the 14 galaxies of the Ly alpha Reference Sample; a sample of strongly star-forming galaxies at low redshifts (0.028 < z < 0.18). We compare the derived properties to global properties derived from multi-band imaging and 21 cm H I interferometry and single-dish observations, as well as archival optical SDSS spectra. Besides the Ly alpha line, the spectra contain a number of metal absorption features allowing us to probe the kinematics of the neutral ISM and evaluate the optical depth and and covering fraction of the neutral medium as a function of line of sight velocity. Furthermore, we show how this, in combination with the precise determination of systemic velocity and good Ly alpha spectra, can be used to distinguish a model in which separate clumps together fully cover the background source, from the "picket fence" model named by Heckman et al. We find that no one single effect dominates in governing Ly alpha radiative transfer and escape. Ly alpha escape in our sample coincides with a maximum velocity-binned covering fraction of less than or similar to 0.9 and bulk outflow velocities of greater than or similar to 50 km s(-1), although a number of galaxies show these characteristics and yet little or no Ly alpha escape. We find that Ly alpha peak velocities, where available, are not consistent with a strong backscattered component, but rather with a simpler model of an intrinsic emission line overlaid by a blueshifted absorption profile from the outflowing wind. Finally, we find a strong anticorrelation between H alpha equivalent width and maximum velocity-binned covering factor, and propose a heuristic explanatory model.