Related papers: The Extragalactic Ionizing Background at Low Redsh…
We discuss the rest-frame ultraviolet emission line spectra of a large (~100) sample of low luminosity redshift z~3.1 Lyman alpha emitters (LAEs) drawn from a Subaru imaging survey in the SSA22 survey field. Our earlier work based on…
We present a comprehensive analysis of HI absorption around 96 lya emitters (LAEs) at $z\approx3.3$ (median lya luminosity $\approx10^{42}$ erg.s$^{-1}$). These LAEs were identified within 8 MUSE fields, each $1'\times1'$ on the sky and…
Quasar redshifts require the best possible precision and accuracy for a number of applications, such as setting the velocity scale for outflows as well as measuring small-scale quasar-quasar clustering. The most reliable redshift standard…
Blazars are some of the brightest UV and X-ray sources in the sky and are valuable probes of the elusive warm-hot intergalactic medium (WHIM; $T{\simeq} 10^5-10^7$ K). However, many of the brightest blazars$-$called BL Lac objects such as…
Using a sample of nearly half million galaxies, intersected by over 7 million lines of sight from the Sloan Digital Sky Survey Data Release 12, we trace H$\alpha$ + [N{\small II}] emission from a galactocentric projected radius, $r_p$, of 5…
Flux estimates for ionizing radiation escaping from star-forming galaxies with characteristic UV luminosities ($L^{*}_{1500(1+z)}$) derived from GALEX and the VIMOS-VLT Deep Survey, are presented as a function of redshift and assumed escape…
We report the discovery of a high-ionization broad absorption line system at a redshift of z_abs=0.695 in the spectrum of the z_em=1.052 radio-quiet quasar PG 2302+039. Broad absorption with FWHM from 3,000 to 5,000 km/s is detected from C…
The variations in Ly$\alpha$ forest opacity observed at $z>5.3$ between lines of sight to different background quasars are too strong to be caused by fluctuations in the density field alone. The leading hypothesis for the cause of this…
The neutral hydrogen and the ionized helium absorption in the spectra of quasars are unique probes of structure in the early universe. We present Far-Ultraviolet Spectroscopic Explorer observations of the line of sight to the quasar…
In this work, we present new calculations of the observables associated with synthetic metal and HI absorption lines in the spectra of high redshift quasars, inspired by questions and limitations raised in work with a uniform Haardt-Madau…
We discuss observational properties of strong emission-line galaxies at low redshift found by our deep imaging survey for high-redshift Ly alpha emitters. In our surveys, we used the narrowband filter, NB816 (lambda_center=8150A with FWHM =…
We present photoionization calculations for the spatially-extended absorbers observed towards the extended emission line spectrum of two high-redshift radio galaxies: 0943-242 (z=2.922) and 0200+015 (z=2.230), with the aim of reproducing…
Aims: We reanalyse optical spectra of the z=6.7 gamma-ray burst GRB 080913, adding hitherto unpublished spectra, in order to reassess the measurement of the neutral fraction of the IGM at high redshifts. Methods: In the data reduction we…
We calculate the intergalactic photon density as a function of both energy and redshift for 0 < z < 6 for photon energies from .003 eV to the Lyman limit cutoff at 13.6 eV in a Lambda-CDM universe with $\Omega_{\Lambda} = 0.7$ and…
We present results on the X-ray spectrum of the quasar PG 1114+445 from an ASCA observation performed in 1996 June, and a ROSAT observation performed 3 years earlier. We show good agreement between all the datasets can be obtained if the…
Measurements of the mean free path of Lyman-continuum photons in the intergalactic medium during the epoch of reionization can help constrain the nature of the sources as well as sinks of hydrogen-ionizing radiation. A recent approach to…
We present new high-precision measurements of the opacity of the intergalactic and circumgalactic medium (IGM, CGM) at <z>=2.4. Using Voigt profile fits to the full Lyman alpha and Lyman beta forests in 15 high-resolution high-S/N spectra…
A measure of the average depression between Lyman absorption lines in the spectrum of the faint quasar BR1202-0725 ($z_{em}=4.695$) is presented. The relatively high resolution of the spectrum ($\sim 40$ km s$^{-1}$) allows the selection of…
We present an HI 21cm absorption study of a sample of 26 radio-loud active galactic nuclei (AGN) at $0.25 < z < 0.4$ carried out with the Karl G. Jansky Very Large Array. Our aim was to study the rate of incidence of HI in various classes…
A narrowband imaging survey of 276 square minutes of arc was carried out at near infrared wavelengths to search for emission line objects at high redshifts. Most of the fields contained a known quasar or radio galaxy at a redshift that…