1,343 research outputs found
A Narrowband Imaging Survey for High Redshift Galaxies in the Near Infrared
A narrowband imaging survey of 276 square minutes of arc was carried out at
near infrared wavelengths to search for emission line objects at high
redshifts. Most of the fields contained a known quasar or radio galaxy at a
redshift that placed one of the strong, restframe optical emission lines
(H-alpha, [O III], H-beta, or [O II]) in the bandpass of the narrowband filter.
The area weighted line flux limit over the entire survey was 3.4x10e-16
erg/cm2/s (3-sigma), while the most sensitive limits reached 1.4x10e-16
erg/cm2/s. Integrating the volume covered by all four optical emission lines in
each image yields a total comoving volume surveyed of 1.4x10e5 cubic
megaparsecs. Considering only H-alpha emission in the K band (2.05 < z < 2.65),
where the survey is most sensitive, the survey covered a comoving volume of
3.0x10e4 cubic megaparsecs to a volume-weighted average star formation rate of
112 M-solar/yr (for Ho = 50 km/s/Mpc, Omega = 1). This is the most extensive
near-infrared survey which is deep enough to have a reasonable chance at
detecting strong line emission from an actively star-forming population of
galaxies, when d against simple models of galaxy formation. One emission line
candidate was identified in this survey, and subsequently confirmed
spectroscopically.Comment: To appear in the Astronomical Journal, November 1996. 23 pages,
including 2 tables and 7 figure
Symmetries In Evolving Space-time and Their Connection To High-frequency Gravity Wave Production
We present how a worm hole bridge from a prior to the present universe allows
us to use symmetry arguments which allow us to generate relic gravity waves,
and also non massless gravitons. The relic gravitons are produced due to
thermal / vacuum energy transferral from a prior universe using a pseudo time
dependent version of the Wheeler De Witt equation as presented by Crowell
(2005)Comment: 10 pages, no figures. AIP conference entry, volume 969 for the STAIF
conference as edited by Mohamed El Genk, as a presented talk at that
conferenc
Laboratory Measurements of Celestial Solids
Our experimental study has focused on laboratory measurements of the low temperature optical properties of a variety of astronomically significant materials in the infrared and mm-wave region of the spectrum. Our far infrared measurements of silicate grains with an open structure have produced a variety of unusual results: (1) the low temperature mass opacity coefficient of small amorphous 2MgO(central dot)SiO2 and MgO(central dot)2SiO2 grains are many times larger than the values previously used for interstellar grain material; (2) all of the amorphous silicate grains studied possess the characteristic temperature dependent signature associated with two level systems in bulk glass; and (3) a smaller but nonzero two level temperature dependence signature is also observed for crystalline particles, its physical origin is unclear. These laboratory measurements yield surprisingly large and variable values for the mm-wave absorption coefficients of small silicate particles similar to interstellar grains, and suggest that the bulk absorptivity of interstellar dust at these long wavelengths will not be well known without such studies. Furthermore, our studies have been useful to better understand the physics of the two level absorption process in amorphous and crystalline grains to gain confidence in the wide applicability of these results
Constraints on the Space Density of Methane Dwarfs and the Substellar Mass Function from a Deep Near-Infrared Survey
We report preliminary results of a deep near-infrared search for
methane-absorbing brown dwarfs; almost five years after the discovery of Gl
229b, there are only a few confirmed examples of this type of object. New J
band, wide-field images, combined with pre-existing R band observations, allow
efficient identification of candidates by their extreme (R-J) colours.
Follow-up measurements with custom filters can then confirm objects with
methane absorption. To date, we have surveyed a total of 11.4 square degrees to
J~20.5 and R~25. Follow-up CH_4 filter observations of promising candidates in
1/4 of these fields have turned up no methane absorbing brown dwarfs. With 90%
confidence, this implies that the space density of objects similar to Gl 229b
is less than 0.012 per cubic parsec. These calculations account for the
vertical structure of the Galaxy, which can be important for sensitive
measurements. Combining published theoretical atmospheric models with our
observations sets an upper limit of alpha <= 0.8 for the exponent of the
initial mass function power law in this domain.Comment: 11 pages + 2 figures To be published in Astrophysical Journal Letter
Making an analogy between a multi chain interaction in charge density wave transport and the use of wavefunctionals to form soliton- anti soliton pairs
A numerical simulation shows that a massive Schwinger model used to formulate
solutions to charge density wave (CDW) transport is insufficient for transport
of soliton- anti soliton pairs through a pinning gap model of CDW transport.
However, a model Hamiltonian with Peierls condensation energy used to couple
adjacent chains (or transverse wave vectors) permits formation of soliton -
anti soliton pairs that could be used to transport CDW through a potential
barrier. There are analogies between this construction and the false vacuum
hypothesis used for showing a necessary and sufficient condition for wave
functionals for formation of soliton - anti soliton pairs. This can be
established by either use of the Bogomol'nyi inequality or through an
experimental artifact resulting through use of the false vacuum hypothesis to
obtain a proportional distance between the soliton - anti soliton pair charge
centersComment: 17 pages, 3 figure
Colliding Particles in Highly Turbulent Flows
We discuss relative velocities and the collision rate of small particles
suspended in a highly turbulent fluid. In the limit where the viscous damping
is very weak, we estimate the relative velocities using the Kolmogorov cascade
principle.Comment: 5 pages, no figures, v2 contains additional result
Improved Si:As BIBIB (Back-Illuminated Blocked-Impurity-Band) hybrid arrays
Results of a program to increase the short wavelength (less than 10 microns) detective quantum efficiency, eta/beta, of Si:As Impurity Band Conduction arrays are presented. The arrays are epitaxially grown Back-Illuminated Blocked (BIB) Impurity-Band (BIBIB) 10x50 detectors bonded to switched-FET multiplexers. It is shown that the 4.7 microns detective quantum efficiency increases proportionately with the thickness of the infrared active layer. A BIB array with a thick active layer, designed for low dark current, exhibits eta/beta = 7 to 9 percent at 4.7 microns for applied bias voltages between 3 and 5 V. The product of quantum efficiency and photoelectric gain, etaG, increases from 0.3 to 2.5 as the voltage increases from 3 to 5 V. Over this voltage range, the dark current increases from 8 to 120 e(-)s(-1) at a device temperature of 4.2 K and is under 70 e(-)s(-1) for all voltages at 2 K. Because of device gain, the effective dark current (equivalent photon rate) is less than 3 e(-)s(-1) under all operating conditions. The effective read noise (equivalent photon noise) is found to be less than 12 electrons under all operating conditions and for integration times between 0.05 and 100 seconds
Optical/IR from ground
Optical/infrared (O/IR) astronomy in the 1990's is reviewed. The following subject areas are included: research environment; science opportunities; technical development of the 1980's and opportunities for the 1990's; and ground-based O/IR astronomy outside the U.S. Recommendations are presented for: (1) large scale programs (Priority 1: a coordinated program for large O/IR telescopes); (2) medium scale programs (Priority 1: a coordinated program for high angular resolution; Priority 2: a new generation of 4-m class telescopes); (3) small scale programs (Priority 1: near-IR and optical all-sky surveys; Priority 2: a National Astrometric Facility); and (4) infrastructure issues (develop, purchase, and distribute optical CCDs and infrared arrays; a program to support large optics technology; a new generation of large filled aperture telescopes; a program to archive and disseminate astronomical databases; and a program for training new instrumentalists
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