We present detailed optical, near-infrared, and radio observations of the X-ray flash XRF 050416a obtained with Palomar and Siding Springs Observatories, as well as the HST and VLA, placing this event among the best-studied X-ray flashes to date. In addition, we present an optical spectrum from Keck LRIS from which we measure the redshift of the burst, z = 0.6528. At this redshift the isotropic-equivalent prompt energy release was about 10(51) ergs, and using a standard afterglow synchrotron model, we find that the blast wave kinetic energy is a factor of 10 larger, EK,(iso) approximate to 10(52) ergs. The lack of an observed jet break to t similar to 20 days indicates that the opening angle is theta(j) greater than or similar to 7 degrees and the total beaming-corrected relativistic energy is greater than or similar to 10(50) ergs. We further show that the burst produced a strong radio flare at t similar to 40 days accompanied by an observed flattening in the X-ray band, which we attribute to an abrupt circumburst density jump or an episode of energy injection (from either a refreshed shock or off-axis ejecta). Late-time observations with HST show evidence for an associated supernova with peak optical luminosity roughly comparable to that of SN 1998bw. Next, we show that the host galaxy of XRF 050416a is actively forming stars at a rate of at least 2 M-circle dot yr(-1) with a luminosity of L-B approximate to 0.5L* and metallicity of Z similar to 0.2-0.8 Z(circle dot). Finally, we discuss the nature of XRF 050416a in the context of short-hard GRBs and under the framework of off-axis and dirty fireball models for X-ray flashes.

We carry out cosmological chemodynamical simulations with different strengths of supernova ( SN) feedback and study how galactic winds from star-forming galaxies affect the features of hydrogen ( Hi) and metal ( C IV and O VI) absorption systems in the intergalactic medium at high redshift. We find that the outflows tend to escape to low-density regions, and hardly affect the dense filaments visible in H I absorption. As a result, the strength of H I absorption near galaxies is not reduced by galactic winds, but even slightly increases. We also find that a lack of H I absorption for lines of sight ( LOSs) close to galaxies, as found by Adelberger et al., can be created by hot gas around the galaxies induced by accretion shock heating. In contrast to HI, metal absorption systems are sensitive to the presence of winds. The models without feedback can produce the strong C IV and O VI absorption lines in LOSs within 50 kpc from galaxies, while strong SN feedback is capable of creating strong C IV and O vi lines out to about twice that distance. We also analyze the mean transmissivity of H I, C IV, and O VI within 1 h(-1) Mpc from star-forming galaxies. The probability distribution of the transmissivity of H I is independent of the strength of SN feedback, but strong feedback produces LOSs with lower transmissivity of metal lines. In addition, strong feedback can produce strong O VI lines even in cases where H I absorption is weak. We conclude that O VI is probably the best tracer for galactic winds at high redshift.

We have conducted a long-slit search for low surface brightness Ly alpha emitters at redshift 2: 67 < z < 3.75. A 92 hr long exposure with the ESO VLT FORS2 instrument down to a 1 sigma surface brightness detection limit of 8 x 10(-20) erg cm(-2) s(-1) arcsec(-2) per arcsec(2) aperture yielded a sample of 27 single line emitters with fluxes of a few x 10(-18) erg s(-1) cm(-2). We present arguments that most objects are indeed Ly alpha. The large comoving number density, 3 x 10(-2) h(70)(3) Mpc(-3), the large covering factor, dN/dz similar to 0.2-1, and the often extended Ly alpha emission suggest that the emitters can be identified with the elusive host population of damped Ly alpha systems (DLAS) and high column density Lyman limit systems (LLS). A small inferred star formation rate, perhaps supplemented by cooling radiation, appears to energetically dominate the Ly alpha emission, and is consistent with the low metallicity, low dust content, and theoretically inferred low masses of DLAS, and with the relative lack of success of earlier searches for their optical counterparts. Some of the line profiles show evidence for radiative transfer in galactic outflows. Stacking surface brightness profiles, we find emission out to at least 4 ''. The centrally concentrated emission of most objects appears to light up the outskirts of the emitters (where LLS arise) down to a column density where the conversion from UV to Ly alpha photon becomes inefficient. DLAS, high column density LLS, and the emitter population discovered in this survey appear to be different observational manifestations of the same low-mass, protogalactic building blocks of present-day L-* galaxies.

As the topics of study of Ly alpha emitters evolve, new selection methods are being developed to find these high redshift galaxies. In this proceedings, three new methods are presented, based on large integral field unit spectrographs, ultradeep slit spectroscopy and serendipitous discoveries. (C) 2009 Elsevier B.V. All rights reserved.

We present the results of Magellan/MMIRS and Keck/NIRSPEC spectroscopy for five Ly alpha emitters (LAEs) at z similar or equal to 2.2 for which high-resolution FUV spectra from Magellan/MagE are available. We detect nebular emission lines including H alpha on the individual basis and low-ionization interstellar (LIS) absorption lines in a stacked FUV spectrum, and measure average offset velocities of the Ly alpha line, Delta v(Ly alpha), and LIS absorption lines, Delta v(abs), with respect to the systemic velocity defined by the nebular lines. For a sample of eight z similar to 2-3 LAEs without active galactic nucleus from our study and the literature, we obtain Delta v(Ly alpha) = 175 +/- 35 km s(-1), which is significantly smaller than that of Lyman-break Galaxies (LBGs), Delta v(Ly alpha) similar or equal to 400 km s(-1). The stacked FUV spectrum gives Delta v(abs) = -179 +/- 73 km s(-1), comparable to that of LBGs. These positive Delta v(Ly alpha) and negative Delta v(abs) suggest that LAEs also have outflows. In contrast to LBGs, however, the LAEs' Delta v(Ly alpha) is as small as |Delta v(abs)|, suggesting low neutral hydrogen column densities. Such a low column density with a small number of resonant scattering may cause the observed strong Ly alpha emission of LAEs. We find an anti-correlation between Ly alpha equivalent width (EW) and Delta v(Ly alpha) in a compilation of LAE and LBG samples. Although its physical origin is not clear, this anti-correlation result appears to challenge the hypothesis that a strong outflow, by means of a reduced number of resonant scattering, produces a large EW. If LAEs at z > 6 have similarly small Delta v(Ly alpha) values, constraints on the reionization history derived from the Ly alpha transmissivity may need to be revised.

We present a statistical study of velocities of Ly alpha, interstellar (IS) absorption, and nebular lines and gas covering fraction for Ly alpha emitters (LAEs) at z similar or equal to 2. We make a sample of 22 LAEs with a large Ly alpha equivalent width (EW) of greater than or similar to 50 angstrom based on our deep Keck/Low Resolution Imaging Spectrometer (LRIS) observations, in conjunction with spectroscopic data from the Subaru/Fiber Multi Object Spectrograph program and the literature. We estimate the average velocity offset of Ly alpha from a systemic redshift determined with nebular lines to be Delta upsilon(Ly alpha) = 234 +/- 9 km s(-1). Using a Kolmogorov-Smirnov test, we confirm the previous claim of Hashimoto et al. that the average Delta upsilon(Ly alpha) of LAEs is smaller than that of Lyman break galaxies (LBGs). Our LRIS data successfully identify blueshifted multiple IS absorption lines in the UV continua of four LAEs on an individual basis. The average velocity offset of IS absorption lines from a systemic redshift is Delta upsilon(IS) = 204 +/- 27 km s(-1), indicating LAEs' gas outflow with a velocity comparable to typical LBGs. Thus, the ratio R-IS(Ly alpha) = Delta upsilon(Ly alpha)/Delta upsilon(IS) of LAEs is around unity, suggestive of low impacts on Ly alpha transmission by resonant scattering of neutral hydrogen in the IS medium. We find an anti-correlation between Ly alpha EW and the covering fraction, f(c), estimated from the depth of absorption lines, where f(c) is an indicator of average neutral hydrogen column density, N-HI. The results of our study support the idea that N-HI is a key quantity determining Ly alpha emissivity.

We present the discovery of two z > 6 quasars, selected as i-band dropouts in the Very Large Telescope Survey Telescope ATLAS survey. Our first quasar has redshift, z = 6.31 +/- 0.03, z-band magnitude, z(AB) = 19.63 +/- 0.08 and rest frame 1450 angstrom absolute magnitude, M-1450 = -27.8 +/- 0.2, making it the joint second most luminous quasar known at z > 6. The second quasar has z = 6.02 +/- 0.03, z(AB) = 19.54 +/- 0.08 and M-1450 = -27.0 +/- 0.1. We also recover a z = 5.86 quasar discovered by Venemans et al., in preparation. To select our quasars, we use a new 3D colour space, combining the ATLAS optical colours with mid-infrared data from the Wide-field Infrared Survey Explorer. We use i(AB) - z(AB) colour to exclude main-sequence stars, galaxies and lower redshift quasars, W1 - W2 to exclude L dwarfs and z(AB) - W2 to exclude T dwarfs. A restrictive set of colour cuts returns only our three high redshift quasars and no contaminants, albeit with a sample completeness of similar to 50 per cent. We discuss how our 3D colour space can be used to reject the majority of contaminants from samples of bright 5.7 < z < 6.3 quasars, replacing follow-up near-infrared photometry, whilst retaining high completeness.

We present the results of an Ly alpha profile analysis of 12 Ly alpha emitters (LAEs) at z similar to 2.2 with high-resolution Ly alpha spectra. We find that all 12 objects have an Ly alpha profile with the main peak redward of the systemic redshift defined by nebular lines, and five have a weak, secondary peak blueward of the systemic redshift (blue bump). The average velocity offset of the red main peak (the blue bump, if any) with respect to the systemic redshift is Delta nu(Ly alpha,r) = 174 +/- 19 km s(-1) (Delta nu(Ly alpha,b) = -316 +/- 45 km s(-1)), which is smaller than (comparable to) that of Lyman break galaxies (LBGs). The outflow velocities inferred from metal absorption lines in three individual and one stacked spectra are comparable to those of LBGs. The uniform expanding shell model constructed by Verhamme et al. reproduces not only the Ly alpha profiles but also other observed quantities, including the outflow velocity and the FWHM. of nebular lines for the non-blue-bump objects. On the other hand, the model predicts too high FWHMs of nebular lines for the blue bump objects, although this discrepancy may disappear if we introduce additional Ly alpha photons produced by gravitational cooling. We show that the small D nu(Ly alpha,r) values of our sample can be explained by low neutral. hydrogen column densities of log(N-H (I)) = 18.9 cm(-2) on average. This value is more than one order of magnitude lower than those of LBGs but is consistent with recent findings that LAEs have high ionization parameters and low H (I) gas masses. This result suggests that low N-H (I) values, giving reduced numbers of resonant scattering of Ly alpha photons, are the key to the strong Ly alpha emission of LAEs.