Spectroscopic Observations of Lyman-Break Galaxies at Redshift ~ 4, 5 and 6 in the GOODS-South Field

We report on observations of Lyman-break galaxies (LBGs) selected from the Great Observatories Origins Deep Survey at mean redshift z~4, 5 and 6, obtained with FORS2 spectrograph at the ESO-VLT.This program has yielded spectroscopic identifications for 114 galaxies of which 51 are at z~4, 31 at z~5, and 32 at z~6. The adopted selection criteria are effective, identifying galaxies at the expected redshift with minimal foreground contamination. Once selection effects are properly accounted for, the rest-frame UV spectra of the higher-redshift LBGs appear to be similar to their counterparts at z~3. As at z~3, LBGs at z~4 and z~5 show Lya both in emission and in absorption; when in absorption, strong interstellar lines and red UV spectra are observed, a fact also measured at z~2 and 3. At z~6, sensitivity issues bias our sample towards galaxies with Lya in emission; nevertheless, these spectra appear to be similar to their lower-redshift counterparts. As in other studies at similar redshifts, we find clear evidence that brighter LBGs tend to have weaker Lya emission lines. At fixed rest-frame UV luminosity, the equivalent width of the Lya emission line is larger at higher redshifts. At all redshifts where the measurements can be reliably made, the redshift of the Lya emission line turns out to be larger than that of the interstellar absorption lines,with a median velocity difference DeltaV~400 km/s at z~4 and 5, consistent with results at lower redshifts. This shows that powerful, large-scale winds are common at high redshift.In general,there is no strong correlation between the morphology of the UV light and the spectroscopic properties. However, galaxies with deep interstellar absorption lines and strong Lya absorption appear to be more diffuse than galaxies with Lya in emission.(abridged)Comment: 58 pages, 19 figures, accepted for publication in The Astrophysical Journa

Automated cross-identifying radio to infrared surveys using the LRPY algorithm: A case study

Cross-identifying complex radio sources with optical or infra red (IR) counterparts in surveys such as the Australia Telescope Large Area Survey (ATLAS) has traditionally been performed manually. However, with new surveys from the Australian Square Kilometre Array Pathfinder detecting many tens of millions of radio sources, such an approach is no longer feasible. This paper presents new software (LRPY - Likelihood Ratio in PYTHON) to automate the process of cross-identifying radio sources with catalogues at other wavelengths. LRPY implements the likelihood ratio (LR) technique with a modification to account for two galaxies contributing to a sole measured radio component. We demonstrate LRPY by applying it to ATLAS DR3 and a Spitzer-based multiwavelength fusion catalogue, identifying 3848 matched sources via our LR-based selection criteria. A subset of 1987 sources have flux density values for all IRAC bands which allow us to use criteria to distinguish between active galactic nuclei (AGNs) and star-forming galaxies (SFG). We find that 936 radio sources (˜47 per cent) meet both of the Lacy and Stern AGN selection criteria. Of the matched sources, 295 have spectroscopic redshifts and we examine the radio to IR flux ratio versus redshift, proposing an AGN selection criterion below the Elvis radio-loud AGN limit for this dataset. Taking the union of all three AGNs selection criteria we identify 956 as AGNs (˜48 per cent). From this dataset, we find a decreasing fraction of AGNs with lower radio flux densities consistent with other results in the literature

Q-LET - Quick Lensing Estimation Tool - An application to SN2003es

Q-LET is a FORTRAN 77 code that enables a quick estimate of the gravitational lensing effects on a point- or an extended source. The user provided input consists of the redshifts, angular positions relative to the source, mass or velocity dispersion estimate and halo type for the lens galaxies. The considered halo types are the Navarro-Frenk-White and the Singular Isothermal Sphere. The code uses the so-called multiple lens-plane method to find the magnification and intrinsic shape of the source. This method takes into account the multiple deflections that may arise when several mass accumulations are situated at different redshifts close to the line-of-sight. The Q-LET code is applied to the recently discovered supernova, SN2003es, which is likely to be of Type Ia as its host galaxy is classified as an elliptical. We find that SN2003es is likely to have been significantly magnified by gravitational lensing and that this should be considered in high-z studies if this SN is to be used to determine the cosmological parameters. Q-LET was motivated by the supernova searches, where lensing can be a problem, but it can also be applied to any simple lens system where a quick estimate is wanted, e.g. the single lens case.Comment: 16 pages, 5 figures. Submitted to JCAP. Software available at http://www.physto.se/~cg/qlet/qlet.ht

Enabling business in resources management Overview

Title from cover. Also available via the InternetAvailable from British Library Document Supply Centre- DSC:02/43426 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Examining the Nature of the Optically Variable, X-ray Undetected GOODS Sources

Deep X-ray surveys using Chandra have found the highest density of AGN on the sky ( ˜ 5000 deg-2) and are thought to be the most efficient means of finding AGN. However, a recent two-epoch variability analysis of the HDF-N found comparable sky densities of sources with variable nuclei, which strongly suggest the presence of an AGN. There is only a small amount of overlap between the optically variable (OV) and X-ray selected AGN, which indicates that the majority of these optically variable selected AGN are underluminous in the X-ray band. In this poster we investigate the nature of the X-ray faint, optically variable GOODS source population. We employ X-ray stacking techniques to measure the average X-ray photometric and spectroscopic properties of these sources. A comparison between the (stacked) X-ray undetected and X-ray detected OV sources shows the hardness ratios of the two populations differ with redshift. The X-ray undetected OV population appears to get harder with redshift, while the hardness ratios of the X-ray detected OV sources remain relatively unchanged. This is consistent with the X-ray undetected OV population being comprised of moderately Compton thick sources (NHI ˜ 2 × 1024 cm-2) where, at higher redshifts, the >10 keV photons that can penetrate this column can be seen in the hard (2-8 keV) X-ray band. In addition, we combine the optical spectra, when available, to look for the presence of high ionization lines that are indicative of AGN. We fail to find high-ionization lines in the stacked optical spectra of the X-ray undetected, optically variable sources, but we do find weak NeIII, NeV, and MgII lines in the stacked X-ray detected, OV population