arXiv subjects

J-P. Kneib

Publications and source records attributed to J-P. Kneib.

23 records · Page 2Linked to original sources

arXiv2005

ZEN and the search for high-redshift galaxies

We present the ZEN (z equals nine) survey: a deep, narrow J-band search for proto-galactic Lya emission at redshifts z=9. In the first phase of the survey, dubbed ZEN1, we combine an exceptionally deep image of the Hubble Deep Field South, obtained using a narrow band filter centred on the wavelength 1.187 microns, with existing deep, broad band images covering optical to near infrared wavelengths. Candidate z=9 Lya-emitting galaxies display a significant narrow band excess relative to the Js-band that are undetected at optical wavelengths. We detect no sources consistent with this criterion to the 90% point source flux limit of the NB image, F_NB = 3.28e-18 ergs/s/cm2. The survey selection function indicates that we have sampled a volume of approximately 340 h^{-3} Mpc3 to a Lya emission luminosity of 10e43 h^{-2} ergs/s. When compared to the predicted properties of z=9 galaxies based upon no evolution of observed z=6 Lya-emitting galaxies, the `volume shortfall' of the current survey, i.e. the volume required to detect this putative population, is a factor of at least 8 to 10. We also discuss continuing narrow J-band imaging surveys that will reduce the volume shortfall factor to the point where the no-evolution prediction from z=6 is probed in a meaningful manner.

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arXiv2004

An ISOCAM survey through gravitationally lensing galaxy clusters. II. The properties of infrared galaxies in the A2218 field

We observed the cluster Abell 2218 (z=0.175), with ISOCAM on board the Infrared Space Observatory, using two filters with reference wavelengths of 6.7 and 14.3 microns. We detected 67 extragalactic mid-infrared sources. Using the ``GRASIL'' models of Silva et al. (1998) we have obtained acceptable and well constrained fits to the observed spectral energy distributions (SEDs) of 41 of these sources, for which additional optical/near-infrared magnitudes, and, in some cases, redshifts, were available. We have then determined the total infrared luminosities and star formation rates (SFRs) of these 41 sources, of which 27 are cluster members and 14 are field galaxies at a median redshift z~0.6. The SEDs of most of the ISOCAM cluster members are best fit by models with negligible star formation in the last ~1 Gyr. The 7 faintest cluster members have a slightly higher, but still very mild, star-formation activity. The ISOCAM-selected cluster galaxies appear to be an unbiased subsample of the overall cluster population. If A2218 is undergoing a merger, as suggested by some optical and X-ray analyses, then this merger does not seem to affect the mid-infrared properties of its galaxies. The SEDs of most ISOCAM-selected field sources are best fit by models with significant ongoing (and recent) star formation, resembling those of massive star-forming spirals or (post)starburst galaxies. Their median SFR is 22 solar masses per year. Eight of the 14 field sources are Luminous IR Galaxies. (Abridged)

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arXiv2002

Faint Submillimeter Counts from Deep 850 Micron Observations of the Lensing Clusters A370, A851, and A2390

We present deep 850 micron maps of three massive lensing clusters, A370, A851, and A2390, with well-constrained mass models. Our cluster exposure times are more than 2 to 5 times longer than any other published cluster field observations. We catalog the sources and determine the submillimeter number counts. The counts are best determined in the 0.3 to 2 mJy range where the areas are large enough to provide a significant sample. At 0.3 mJy the cumulative counts are 3.3 (1.3,6.3) 10^4 per square degree, where the upper and lower bounds in the brackets are the 90% confidence range. The surface density at these faint count limits enters the realm of significant overlap with other galaxy populations.The corresponding percentage of the extragalactic background light (EBL) residing in this flux range is about 45-65%, depending on the EBL measurement used. Given that 20-30% of the EBL is resolved at flux densities between 2 and 10 mJy, most of the submillimeter EBL is arising in sources above 0.3 mJy. We also performed a noise analysis to obtain an independent estimate of the counts. The upper bounds on the counts determined from the noise analysis closely match the upper limits obtained from the direct counts. The differential counts from this and other surveys can reasonably be described by the parameterization n(S)=3 10^4/(0.7 + S^3) per square degree per mJy with S in mJy, which also integrates to match the EBL.

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arXiv2001

Detection of an Iron Emission Feature from the Lensed BAL QSO H1413+117 at z=2.56

We present the X-ray energy spectrum of the lensed BAL QSO H1413+117 (the Cloverleaf) at z=2.56 observed with the Chandra X-ray observatory. We detected 293 photons in a 40 ks Advanced CCD Imaging Spectrometer (ACIS-S) observation. The X-ray image consists of four lensed image components, thus the photons are from the lensed QSO itself. The overall spectrum can be described with a power-law function heavily absorbed by neutral matter at a redshift consistent with the QSO redshift. This supports the idea that intrinsic absorption is significant for BAL QSOs. The spectral fit significantly (99% confidence) improves when we include an emission line. The centroid energy and intrinsic width (Gaussian σ) of the line are 6.21 \pm 0.16 keV and 220 ^{+270}_{-130} eV (90% errors), respectively, in the QSO rest frame, assuming the absorbed power-law as the continuum. The equivalent width of the line in the QSO rest frame is 960 ^{+1400}_{-480} eV. We suggest that the large equivalent width, the centroid energy, and the line broadness can be explained by iron K emission arising from X-ray reprocessing in the BAL flow, assuming it has a conical thin-sheet structure.

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arXiv1999

Properties of high-z galaxies as seen through lensing clusters

We discuss the first results obtained on the study of a sample of high-z galaxies (2 < z < 7), using the gravitational amplification effect in the core of lensing clusters. Sources are located close to the critical lines in clusters with well constrained mass distributions, and selected through photometric redshifts, computed on a large wavelength domain, and lens inversion techniques.

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