L. Trouille

An atlas of z = 5.7 and z = 6.5 Lyα emitters

We present an atlas of 88 z~5.7 and 30 z~6.5 Ly alpha emitters obtained from a wide-field narrowband survey. We combined deep narrowband imaging in 120A bandpass filters centered at 8150A and 9140A with deep BVRIz broadband imaging to select high-redshift galaxy candidates over an area of 4180 square arcmin. The goal was to obtain a uniform selection of comparable depth over the 7 targeted fields in the two filters. For the GOODS-N region of the HDF-N field, we also selected candidates using a 120A filter centered at 9210A. We made spectroscopic observations with Keck DEIMOS of nearly all the candidates to obtain the final sample of Ly alpha emitters. At the 3.3A resolution of the DEIMOS observations the asymmetric profile for Ly alpha emission with its steep blue fall-off can be clearly seen in the spectra of nearly all the galaxies. We show that the spectral profiles are surprisingly similar for many of the galaxies and that the composite spectral profiles are nearly identical at z=5.7 and z=6.5. We analyze the distributions of line widths and Ly alpha equivalent widths and find that the lines are marginally narrower at the higher redshift, with median values of 0.77A at z=6.5 and 0.92A at z=5.7. The line widths have a dependence on the Ly alpha luminosity of the form L(L alpha)^(0.3). We compare the surface densities and the luminosity functions at the two redshifts and find that there is a multiplicative factor of 2 decrease in the number density of bright Ly alpha emitters from z=5.7 to z=6.5, while the characteristic luminosity is unchanged.

Measuring the Sources of the Intergalactic Ionizing Flux

We use a wide-field (0.9 deg2) X-ray sample with optical and Galaxy Evolution Explorer (GALEX) ultraviolet observations to measure the contribution of active galactic nuclei (AGNs) to the ionizing flux as a function of redshift. Our analysis shows that the AGN contribution to the metagalactic ionizing background peaks at around z = 2. The measured values of the ionizing background from the AGNs are lower than previous estimates and confirm that ionization from AGNs is insufficient to maintain the observed ionization of the intergalactic medium (IGM) at z > 3. We show that only X-ray sources with broad lines in their optical spectra have detectable ionizing flux and that the ionizing flux seen in an AGN is not correlated with its X-ray color. We also use the GALEX observations of the GOODS-N region to place a 2σ upper limit of 0.008 on the average ionization fraction f ν(700 A)/f ν(1500 A) for 626 UV selected galaxies in the redshift range z = 0.9-1.4. We then use this limit to estimate an upper bound to the galaxy contribution in the redshift range z = 0-5. If the z ~ 1.15 ionization fraction is appropriate for higher-redshift galaxies, then contributions from the galaxy population are also too low to account for the IGM ionization at the highest redshifts (z > 4).

THE OPTX PROJECT. II. HARD X-RAY LUMINOSITY FUNCTIONS OF ACTIVE GALACTIC NUCLEI FOR z ≲ 5

We use the largest, most uniform, and most spectroscopically complete to faint X-ray flux limits Chandra sample to date to construct hard (2-8 keV) rest-frame X-ray luminosity functions (HXLFs) of spectroscopically identified active galactic nuclei (AGNs) to z ~ 5. In addition, we use a new 2-8 keV local sample selected by the very hard (14-195 keV) SWIFT 9-month Burst Alert Telescope survey to construct the local 2-8 keV HXLF. We do maximum likelihood fits of the combined distant plus local sample (as well as of the distant sample alone) over the redshift intervals 0 < z < 1.2, 0 < z < 3, and 0 < z < 5 using a variety of analytic forms, which we compare with the HXLFs. We recommend using our luminosity-dependent density evolution model fits of the combined distant plus local sample over 0 < z < 3 for all the spectroscopically identified sources and for the broad-line AGNs.

The OPTX Project. I. The Flux and Redshift Catalogs for the CLANS, CLASXS, and CDF-N Fields

We present the redshift catalogs for the X-ray sources detected in the Chandra Deep Field North (CDF-N), the Chandra Large Area Synoptic X-ray Survey (CLASXS), and the Chandra Lockman Area North Survey (CLANS). The catalogs for the CDF-N and CLASXS fields include redshifts from previous work, while the redshifts for the CLANS field are all new. For fluxes above 10^-14 ergs cm^-2 s^-1 (2-8 keV) we have redshifts for 76% of the sources. We extend the redshift information for the full sample using photometric redshifts. The goal of the OPTX Project is to use these three surveys, which are among the most spectroscopically complete surveys to date, to analyze the effect of spectral type on the shape and evolution of the X-ray luminosity functions and to compare the optical spectral types with the X-ray spectral properties. We also present the CLANS X-ray catalog. The nine ACIS-I fields cover a solid angle of ~0.6 square degrees and reach fluxes of 7x10^-16 ergs cm^-2 s^-1 (0.5-2 keV) and 3.5x10^-15 ergs cm^-2 s^-1 (2-8 keV). We find a total of 761 X-ray point sources. Additionally, we present the optical and infrared photometric catalog for the CLANS X-ray sources, as well as updated optical and infrared photometric catalogs for the X-ray sources in the CLASXS and CDF-N fields. The CLANS and CLASXS surveys bridge the gap between the ultradeep pencil-beam surveys, such as the CDFs, and the shallower, very large-area surveys. As a result, they probe the X-ray sources that contribute the bulk of the 2-8 keV X-ray background and cover the flux range of the observed break in the logN-logS distribution. We construct differential number counts for each individual field and for the full sample.

THE OPTX PROJECT. IV. HOW RELIABLE IS [O III] AS A MEASURE OF AGN ACTIVITY?

We compare optical and hard X-ray identifications of active galactic nuclei (AGNs) using a uniformly selected (above a flux limit of f 2-8 keV = 3.5 ? 10?15?erg?cm?2?s?1) and highly optically spectroscopically complete (>80% for f 2-8 keV > 10?14?erg?cm?2?s?1 and >60% below) 2-8?keV sample observed in three Chandra fields (CLANS, CLASXS, and the CDF-N). We find that empirical emission-line ratio diagnostic diagrams misidentify 50% of the X-ray-selected AGNs that can be put on these diagrams as star formers. We confirm that there is a large (two orders of magnitude) dispersion in the ratio of the [O III]?5007 (hereafter [O III]) to hard X-ray luminosities for the non-broad-line AGNs, even after applying reddening corrections to the [O III] luminosities. We find that the dispersion is similar for the broad-line AGNs, where there is not expected to be much X-ray absorption from an obscuring torus around the AGN nor much obscuration from the galaxy along the line of sight if the AGN is aligned with the galaxy. We postulate that the X-ray-selected AGNs that are misidentified by the diagnostic diagrams have low [O III] luminosities due to the complexity of the structure of the narrow-line region, which causes many ionizing photons from the AGN not to be absorbed. This would mean that the [O III] luminosity can only be used to predict the X-ray luminosity to within a factor of ~3 (1?). Despite selection effects, we show that the shapes and normalizations of the [O III] and transformed hard X-ray luminosity functions show reasonable agreement, suggesting that the [O III] samples are not finding substantially more AGNs at low redshifts than hard X-ray samples.

AN EXTREMELY DEEP, WIDE-FIELD NEAR-INFRARED SURVEY: BRIGHT GALAXY COUNTS AND LOCAL LARGE SCALE STRUCTURE

We present a deep, wide-field near-infrared (NIR) survey over five widely separated fields at high Galactic latitude covering a total of ~3 deg2 in J, H, and Ks . The deepest areas of the data (~0.25 deg2) extend to a 5? limiting magnitude of JHKs >24 in the AB magnitude system. Although depth and area vary from field to field, the overall depth and large area of this data set make it one of the deepest wide-field NIR imaging surveys to date. This paper discusses the observations, data reduction, and bright galaxy counts in these fields. We compare the slope of the bright galaxy counts with the Two Micron All Sky Survey and other counts from the literature and explore the relationship between slope and supergalactic latitude. The slope near the supergalactic equator is sub-Euclidean on average, pointing to the possibility of a decreasing average space density of galaxies by ~10%-15% over scales of ~250-350 Mpc. On the contrary, the slope at high supergalactic latitudes is strongly super-Euclidean on average, suggesting an increase in the space density of galaxies as one moves from the voids just above and below the supergalactic plane out to distances of ~250-350 Mpc. These results suggest that local large scale structure could be responsible for large discrepancies in the measured slope between different studies in the past. In addition, the local universe away from the supergalactic plane appears to be underdense by ~25%-100% relative to the space densities of a few hundred megaparsecs distant.

A spectroscopic survey of WISE-selected obscured quasars with the southern african large telescope

We present the results of an optical spectroscopic survey of a sample of 40 candidate obscured quasars identified on the basis of their mid-infrared emission detected by the Wide-Field Infrared Survey Explorer (WISE). Optical spectra for this survey were obtained using the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT). Our sample was selected with WISE colors characteristic of AGNs, as well as red optical to mid-IR colors indicating that the optical/UV AGN continuum is obscured by dust. We obtain secure redshifts for the majority of the objects that comprise our sample (35/40), and find that sources that are bright in the WISE W4 (22

Gravity Spy: Integrating Advanced LIGO Detector Characterization, Machine Learning, and Citizen Science

\mu

Interactive Assessment Tools for Computational Thinking in High School STEM Classrooms

m) band are typically at moderate redshift ( = 0.35

A transient search using combined human and machine classifications

) while sources fainter in W4 are at higher redshifts ( = 0.73