5,716 research outputs found
Near-IR imaging of moderate redshift galaxy clusters
We have obtained near-IR imaging of 3 moderate-z clusters on the 1.3 m at KPNO with SQIID, a new camera offering wide-field (5.5 arcmin) simultaneous JHK band imaging. Our photometry on a sample of approximately 100 likely member galaxies in one of the clusters, Abell 370 at z = 0.37, shows that we can obtain magnitudes good to 20 percent down to K = 18, considerably below the estimated K* = 16.5 at this redshift. These data indicate that there are no systematic problems in obtaining photometry at faint levels with SQIID. With the development of larger arrays, the field is open to progress. The resulting J, H, and K data for three clusters are combined with previously obtained multiband optical photometry. We present an investigation of the spectral properties and evolution of the dominant cold stellar populations by comparing optical-to-IR colors and color-magnitude diagrams to predictions from population synthesis models and galaxy spectral evolution codes
Distant radio galaxies in the near IR
We are carrying out a program of near IR imaging and spectroscopy of radio galaxies with redshifts of 1.5 and greater. One of its principal goals is to constrain the ages and star formation histories of massive galaxies at early epochs. The radio galaxies are drawn from the survey of 1Jy class sources by McCarthy et al (1989) and McCarthy (1990). The sample contains 18 radio galaxies with redshifts greater than 2 and an additional 10 objects with 1.5 less than z less than 2.0. The redshifts were obtained from long slit spectra with the CTIO 4 m. While the galaxies are quite faint (r approximately = 21-24.5) all have Lyman alpha emission with rest frame equivalent widths of 100 - 1000 A. Multicolor photometry in the g,r,i and J,H,K bands has been obtained with the 2.5-m Du Pont Telescope on Las Campanas and with the Hale 5 m telescope at Palomar. We have recently obtained near IR spectra, using the 4 m telescopes at KPNO and CTIO, of a few objects with the goal of determining the Lyman alpha/H-alpha ratio and hence the reddening
High sensitivity operation of discrete solid state detectors at 4 K
Techniques are described to allow operation of discrete, solid state detectors at 4 K with optimized JFET amplifiers. Three detector types cover the 0.6 to 4 mm spectral range with NEP approximately equal to 10 to the 16th power Hz (-1/2) for two of the types and potential improvement to this performance for the third. Lower NEP's are anticipated at longer infrared wavelengths
Thermal Model Calibration for Minor Planets Observed with Wide-Field Infrared Survey Explorer/Neowise
With the Wide-field Infrared Survey Explorer (WISE), we have observed over 157,000 minor planets. Included in these are a number of near-Earth objects, main-belt asteroids, and irregular satellites which have well measured physical properties (via radar studies and in situ imaging) such as diameters. We have used these objects to validate models of thermal emission and reflected sunlight using the WISE measurements, as well as the color corrections derived in Wright et al. for the four WISE bandpasses as a function of effective temperature. We have used 50 objects with diameters measured by radar or in situ imaging to characterize the systematic errors implicit in using the WISE data with a faceted spherical near-Earth asteroid thermal model (NEATM) to compute diameters and albedos. By using the previously measured diameters and H magnitudes with a spherical NEATM model, we compute the predicted fluxes (after applying the color corrections given in Wright et al.) in each of the four WISE bands and compare them to the measured magnitudes. We find minimum systematic flux errors of 5%-10%, and hence minimum relative diameter and albedo errors of ~10% and ~20%, respectively. Additionally, visible albedos for the objects are computed and compared to the albedos at 3.4 μm and 4.6 μm, which contain a combination of reflected sunlight and thermal emission for most minor planets observed by WISE. Finally, we derive a linear relationship between subsolar temperature and effective temperature, which allows the color corrections given in Wright et al. to be used for minor planets by computing only subsolar temperature instead of a faceted thermophysical model. The thermal models derived in this paper are not intended to supplant previous measurements made using radar or spacecraft imaging; rather, we have used them to characterize the errors that should be expected when computing diameters and albedos of minor planets observed by WISE using a spherical NEATM model
Spitzer Photometry of WISE-Selected Brown Dwarf and Hyper-Luminous Infrared Galaxy Candidates
We present Spitzer 3.6 and 4.5 m photometry and positions for a sample
of 1510 brown dwarf candidates identified by the WISE all-sky survey. Of these,
166 have been spectroscopically classified as objects with spectral types M(1),
L(7), T(146), and Y(12); Sixteen other objects are non-(sub)stellar in nature.
The remainder are most likely distant L and T dwarfs lacking spectroscopic
verification, other Y dwarf candidates still awaiting follow-up, and assorted
other objects whose Spitzer photometry reveals them to be background sources.
We present a catalog of Spitzer photometry for all astrophysical sources
identified in these fields and use this catalog to identify 7 fainter (4.5
m 17.0 mag) brown dwarf candidates, which are possibly wide-field
companions to the original WISE sources. To test this hypothesis, we use a
sample of 919 Spitzer observations around WISE-selected high-redshift
hyper-luminous infrared galaxy (HyLIRG) candidates. For this control sample we
find another 6 brown dwarf candidates, suggesting that the 7 companion
candidates are not physically associated. In fact, only one of these 7 Spitzer
brown dwarf candidates has a photometric distance estimate consistent with
being a companion to the WISE brown dwarf candidate. Other than this there is
no evidence for any widely separated ( 20 AU) ultra-cool binaries. As an
adjunct to this paper, we make available a source catalog of 7.33
objects detected in all of these Spitzer follow-up fields for use
by the astronomical community. The complete catalog includes the Spitzer 3.6
and 4.5 m photometry, along with positionally matched and
photometry from USNO-B; , , and photometry from 2MASS; and ,
, , and photometry from the WISE all-sky catalog
Resist, comply or workaround? An examination of different facets of user engagement with information systems
This paper provides a summary of studies of user resistance to Information Technology (IT) and identifies workaround activity as an understudied and distinct, but related, phenomenon. Previous categorizations of resistance have largely failed to address the relationships between the motivations for divergences from procedure and the associated workaround activity. This paper develops a composite model of resistance/workaround derived from two case study sites. We find four key antecedent conditions derived from both positive and negative resistance rationales and identify associations and links to various resultant workaround behaviours and provide supporting Chains of Evidence from two case studies
A z=5.34 Galaxy Pair in the Hubble Deep Field
We present spectrograms of the faint V-drop (V(606) = 28.1, I(814) = 25.6)
galaxy pair HDF3-951.1 and HDF3-951.2 obtained at the Keck II Telescope.
Fernandez-Soto, Lanzetta, & Yahil (1998) derive a photometric redshift of z(ph)
= 5.28 (+0.34,-0.41; 2 sigma) for these galaxies; our integrated spectrograms
show a large and abrupt discontinuity near 7710 (+- 5) Angstroms. This break is
almost certainly due to the Lyman alpha forest as its amplitude (1 - fnu(short)
/ fnu(long) > 0.87; 95% confidence limit) exceeds any discontinuities observed
in stellar or galaxian rest-frame optical spectra. The resulting
absorption-break redshift is z=5.34 (+- 0.01). Optical/near-IR photometry from
the HDF yields an exceptionally red (V(606)-I(814)) color, consistent with this
large break. A more accurate measure of the continuum depression blueward of
Lyman alpha utilizing the imaging photometry yields D(A) = 0.88.
The system as a whole is slightly brighter than L*(1500) relative to the z~3
Lyman break population and the total star formation rate inferred from the UV
continuum is ~22 h(50)^-2 M(sun) yr^-1 (q(0) = 0.5) assuming the absence of
dust extinction. The two individual galaxies are quite small (size scales < 1
h(50)^-1 kpc). Thus these galaxies superficially resemble the Pascarelle etal
(1996) ``building blocks''; if they comprise a gravitationally bound system,
the pair will likely merge in a time scale ~100 Myr.Comment: 18 pages, 4 figures; accepted to A
The Phoenix Deep Survey: Extremely Red Galaxies and Cluster Candidates
We present the results of a study of a sample of 375 Extremely Red Galaxies
(ERGs) in the Phoenix Deep Survey, 273 of which constitute a subsample which is
80% complete to K_s = 18.5 over an area of 1160 arcmin^2. The angular
correlation function for ERGs is estimated, and the association of ERGs with
faint radio sources explored. We find tentative evidence that ERGs and faint
radio sources are associated at z > 0.5. A new overdensity-mapping algorithm
has been used to characterize the ERG distribution, and identify a number of
cluster candidates, including a likely cluster containing ERGs at 0.5 < z < 1.
Our algorithm is also used in an attempt to probe the environments in which
faint radio sources and ERGs are associated. We find limited evidence that the
I - K_s > 4 criterion is more efficient than R - K_s > 5 at selecting dusty
star-forming galaxies, rather than passively evolving ERGs.Comment: 14 emulateapj pages, 15 figures, 1 table, accepted for publication in
Astronomical Journal. A version with full resolution figures is available at
http://www.physics.usyd.edu.au/~asmith/research/ERGpaper.pd
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