arXiv subjects

D. Woods

Publications and source records attributed to D. Woods.

11 recordsLinked to original sources

arXiv2019

Combined Emerging Capabilities for Near-Earth Objects (NEOs)

Assess the joint capabilities of emerging telescopes for near-Earth objects (NEOs) survey and characterization, and what they will add to the current capabilities or replace. NASA telescopes in prime mission, in development, or under study, and requested for this assessment, include: - The Transiting Exoplanet Survey Satellite (TESS) - The James Webb Space Telescope (JWST) - The Wide Field Infrared Survey Telescope (WFIRST) - The Near-Earth Object Camera (NEOCam). Also requested for this assessment is the Large Synoptic Survey Telescope (LSST), an 8.4-meter ground-based telescope in development by the National Science Foundation and Department of Energy (DOE), with the capability to discover and catalogue NEOs.

astro-ph.IM↗

arXiv2014

The Next Generation Virgo Cluster Survey. XV. The photometric redshift estimation for background sources

The Next Generation Virgo Cluster Survey is an optical imaging survey covering 104 deg^2 centered on the Virgo cluster. Currently, the complete survey area has been observed in the u*giz-bands and one third in the r-band. We present the photometric redshift estimation for the NGVS background sources. After a dedicated data reduction, we perform accurate photometry, with special attention to precise color measurements through point spread function-homogenization. We then estimate the photometric redshifts with the Le Phare and BPZ codes. We add a new prior which extends to iAB = 12.5 mag. When using the u*griz-bands, our photometric redshifts for 15.5 \le i \lesssim 23 mag or zphot \lesssim 1 galaxies have a bias |Δz| < 0.02, less than 5% outliers, and a scatter σ_{outl.rej.} and an individual error on zphot that increase with magnitude (from 0.02 to 0.05 and from 0.03 to 0.10, respectively). When using the u*giz-bands over the same magnitude and redshift range, the lack of the r-band increases the uncertainties in the 0.3 \lesssim zphot \lesssim 0.8 range (-0.05 < Δz < -0.02, σ_{outl.rej} ~ 0.06, 10-15% outliers, and zphot.err. ~ 0.15). We also present a joint analysis of the photometric redshift accuracy as a function of redshift and magnitude. We assess the quality of our photometric redshifts by comparison to spectroscopic samples and by verifying that the angular auto- and cross-correlation function w(θ) of the entire NGVS photometric redshift sample across redshift bins is in agreement with the expectations.

astro-ph.GA↗

arXiv2013

Overlap Technique for End-Cap Seals on Cylindrical Magnetic Shields

We present results from studies of the effectiveness of an overlap technique for forming a magnetic seal across a gap at the boundary between a cylindrical magnetic shield and an end-cap. In this technique a thin foil of magnetic material overlaps the two surfaces, thereby spanning the gap across the cylinder and the end-cap, with the magnetic seal then formed by clamping the thin magnetic foil to the surfaces of the cylindrical shield and the end-cap on both sides of the gap. In studies with a prototype 31-cm diameter, 91-cm long, 0.16-cm thick cylindrical magnetic shield and flared end-cap, the magnetic shielding performance of our overlap technique is comparable to that obtained with the conventional method in which the end-cap is placed in direct lapped contact with the cylindrical shield via through bolts or screws.

physics.ins-det↗

arXiv2011

Technique for high axial shielding factor performance of large-scale, thin, open-ended, cylindrical Metglas magnetic shields

Metglas 2705M is a low-cost commercially-available, high-permeability Cobalt-based magnetic alloy, provided as a 5.08-cm wide and 20.3-$μ$m thick ribbon foil. We present an optimized construction technique for single-shell, large-scale (human-size), thin, open-ended cylindrical Metglas magnetic shields. The measured DC axial and transverse magnetic shielding factors of our 0.61-m diameter and 1.83-m long shields in the Earth's magnetic field were 267 and 1500, for material thicknesses of only 122 $μ$m (i.e., 6 foil layers). The axial shielding performance of our single-shell Metglas magnetic shields, obtained without the use of magnetic shaking techniques, is comparable to the performance of significantly thicker, multiple-shell, open-ended Metglas magnetic shields in comparable-magnitude, low-frequency applied external fields reported previously in the literature.

physics.atom-ph↗

arXiv2009

WINGS: a WIde-field nearby Galaxy-cluster survey III. Deep near-infrared photometry of 28 nearby clusters

Context. This is the third paper of a series devoted to the WIde-field Nearby Galaxy-cluster Survey (WINGS).WINGS is a long term project aimed at gathering wide-field, multiband imaging and spectroscopy of galaxies in a complete sample of 77 X-ray selected nearby clusters (0.04 20deg). The main goal of this project is to establish a local reference sample for evolutionary studies of galaxies and galaxy clusters. Aims. This paper presents the near-infrared (J,K) photometric catalogs of 28 clusters of the WINGS sample and describes the procedures followed to construct them. Methods. The raw data has been reduced at CASU and special care has been devoted to the final coadding, drizzling technique, astrometric solution and magnitude calibration for the WFCAM pipeline processed data. We have constructed the photometric catalogs based on the final calibrated coadded mosaics (0.79 deg2) in J (19 clusters) and K (27 clusters) bands. A customized interactive pipeline has been used to clean the catalogs and to make mock images for photometric errors and completeness estimates. Results. We provide deep near-infrared photometric catalogs (90% complete in detection rate at total magnitudes J =20.5, K =19.4, and in classification rate at J = 19.5 and K = 18.5), giving positions, geometrical parameters, total and aperture magnitudes for all detected sources. For each field we classify the detected sources as stars, galaxies and objects of "unknown" nature.

astro-ph.CO↗

arXiv2009

Normal galaxies in the XMM-Newton fields. X-rays as a star formation indicator

Context: We use the first XMM serendipitous source catalogue (1XMM) to compile a sample of normal X-ray galaxies Aims: We seek to expand the database of X-ray selected normal galaxies at intermediate redshifts and examine the relation between X-ray emission and star formation for late-type systems Methods: The candidates are selected based on their X-ray (soft spectra), X-ray to optical [log(fx/fo)<-2] and optical (extended sources) properties. 44 candidates are found and 35 are spectroscopically observed with the Australian National University's 2.3m telescope to examine their nature. Results: Of the 35 sources observed, 2 are AGN, 11 emission line galaxies, 12 absorption line galaxies, 6 have featureless spectra while 4 are associated with Galactic stars. We combine our emission line sample with earlier works forming the most comprehensive X-ray selected galaxy sample for the study of the X-ray luminosity to the Halpha luminosity - a well-calibrated star-formation indicator - relation. Conclusions: We find that the X-ray luminosity strongly correlates with the Halpha luminosity, suggesting that the X-rays efficiently trace the star-formation.

astro-ph.CO↗

arXiv2005

Science Programs for a 2 m-class Telescope at Dome C, Antarctica: PILOT, the Pathfinder for an International Large Optical Telescope

The cold, dry and stable air above the summits of the Antarctic plateau provides the best ground-based observing conditions from optical to sub-mm wavelengths to be found on the Earth. PILOT is a proposed 2 m telescope, to be built at Dome C in Antarctica, able to exploit these conditions for conducting astronomy at optical and infrared wavelengths. While PILOT is intended as a pathfinder towards the construction of future grand-design facilities, it will also be able to undertake a range of fundamental science investigations in its own right. This paper provides the performance specifications for PILOT, including its instrumentation. It then describes the kinds of science projects that it could best conduct. These range from planetary science to the search for other solar systems, from star formation within the Galaxy to the star formation history of the Universe, and from gravitational lensing caused by exo-planets to that produced by the cosmic web of dark matter. PILOT would be particularly powerful for wide-field imaging at infrared wavelengths, achieving near-diffraction limited performance with simple tip-tilt wavefront correction. PILOT would also be capable of near-diffraction limited performance in the optical wavebands, as well be able to open new wavebands for regular ground based observation; in the mid-IR from 17 to 40 microns and in the sub-mm at 200 microns.

astro-ph↗

arXiv1998

The ROSAT Deep Survey IV. A distant lensing cluster of galaxies with a bright arc

An unusual double-lobed extended X-ray source (RX J105343+5735) is detected in the ROSAT ultra-deep HRI image of the Lockman Hole. The angular size of the source is 1.7 X 0.7 arcmin^2 and its X-ray flux is 2 X 10^-14 erg cm^-2 s^-1. R-band imaging from the Keck telescope revealed a marginal excess of galaxies brighter than R=24.5, but Keck LRIS spectroscopy of 24 objects around the X-ray centroid did not yield a significant number of concordant redshifts. The brightest galaxy close to the centre of the eastern emission peak appears to be a gravitationally lensed arc at z=2.570, suggesting that the X-ray object is associated with the lens, most likely a cluster of galaxies. Based on a comparison of lensing surface mass density, X-ray luminosity, morphology and galaxy magnitudes with clusters of known distance, we argue that RX J105343+5735 is a cluster at a redshift around 1. Future X-ray, ground-based optical/NIR and high resolution HST observations of the system will be able to clarify the nature of the object.

astro-ph↗

arXiv1996

A Weak Gravitational Lensing and X-ray Analysis of Abell 2163

We report on the detection of dark matter in the cluster of galaxies Abell~2163 using the weak gravitational distortion of background galaxies, and an analysis of the cluster X-ray emission. We find that while the qualitative distributions of the cluster light and the dark matter are similar -- shallow and extended, with significant substructure -- the X-ray morphology shows a more regular overall appearance. We interpret the joint lensing and X-ray observations as a signature of a merger event in the cluster. We present new ROSAT/HRI data and reanalyze ROSAT/PSPC data, accounting for the effect of a varying background to determine the best fit parameters in the $β$-model formalism. We combine the surface brightness fits with two determinations of the radial temperature profile to determine the total mass. Although there are slight variations in the total mass determinations introduced by the uncertainties in the $β$-fit, the main contributor to the error arises from the uncertainties in the temperature determinations. Even though the morphologies of the dark matter/light and X-ray gas are quite different, we find that the total mass determined from the X-ray and weak lensing estimates are consistent with each other within the $2σ$ error bars, with the X-ray inferred mass a factor of $\simeq 2$ larger. However, as the lensing mass estimates are differential (the surface density at any point is determined relative to the mean in a control annulus), the shallow, extended nature of the mass profile biases the lensing inferred mass downwards. We estimate the correction for this effect and find very good agreement between the corrected lensing and X-ray results. We determine the gas mass fraction and find $f_g \simeq 0.07h^{-3/2}$ at all radii and a constant mass-to-light ratio of $M/L_V

astro-ph↗

arXiv1996

A Weak Gravitational Lensing Analysis of Abell 2390

We report on the detection of dark matter in the cluster Abell 2390 using the weak gravitational distortion of background galaxies. We find that the cluster light and total mass distributions are quite similar over an angular scale of $\simeq 7^\prime \;(1 \Mpc$). The cluster galaxy and mass distributions are centered on the cluster cD galaxy and exhibit elliptical isocontours in the central $\simeq 2^\prime \; (280 \kpc)$. The major axis of the ellipticity is aligned with the direction defined by the cluster cD and a ``straight arc'' located $\simeq 38^{\prime\prime}$ to the northwest. We determined the radial mass-to-light profile for this cluster and found a constant value of $(320 \pm 90) h\; M_\odot/L_{\odot V}$, which is consistent with other published determinations. We also compared our weak lensing azimuthally averaged radial mass profile with a spherical mass model proposed by the CNOC group on the basis of their detailed dynamical study of the cluster. We find good agreement between the two profiles, although there are weak indications that the CNOC density profile may be falling more steeply for $θ\geq 3^\prime$ $(420\kpc)$.

astro-ph↗

arXiv1995

The Dark Matter, Gas and Galaxy Distributions in Abell 2218: A Weak Gravitational Lensing and X-ray Analysis

We report on the detection of dark matter in the cluster Abell 2218 using the weak gravitational distortion of background galaxies. We find a highly significant, coherent detection of the distortion in the images of the background galaxies. The inferred 2D mass distribution has a peak that is coincident with the optical and X-ray centroid. The qualitative distributions of the cluster light, the X-ray emission and the dark matter are similar and the projected total mass, gas, and light surface densities are consistent with a $r^{-1}$ profile at distance of $r > 180^{\prime\prime}$ from the cluster cD galaxy. Using the weak lensing technique, we determine a lower bound for the total mass in A2218 of $(3.9 \pm 0.7) \times 10^{14}$~h$^{-1}$~M$_\odot$ within a fiducial aperture of radius 0.4~h$^{-1}$Mpc. The associated cluster mass-to-light ratio is $(440 \pm 80)$~h~$M_\odot/L_{\odot B}$. The mass estimated by the weak lensing method is consistent with that inferred from the X-ray data under the assumption of hydrostatic equilibrium and we derive an upper bound for the gas-to-total mass ratio at 400~h$^{-1}$kpc of $M_{gas}/M_{tot} = (0.04 \pm 0.02)$h$^{-3/2}$.

astro-ph↗