3,635 research outputs found
Large-scale variations of the dust optical properties in the Galaxy
We present an analysis of the dust optical properties at large scale, for the
whole galactic anticenter hemisphere. We used the 2MASS Extended Source Catalog
to obtain the total reddening on each galaxy line of sight and we compared this
value to the IRAS 100 microns surface brightness converted to extinction by
Schlegel et al (1998). We performed a careful examination and correction of the
possible systematic effects resulting from foreground star contamination,
redshift contribution and galaxy selection bias. We also evaluated the
contribution of dust temperature variations and interstellar clumpiness to our
method. The correlation of the near-infrared extinction to the far-infrared
optical depth shows a discrepancy for visual extinction greater than 1 mag with
a ratio A_V(FIR) / A_V(gal) = 1.31 +- 0.06. We attribute this result to the
presence of fluffy/composite grains characterized by an enhanced far--infrared
emissivity. Our analysis, applied to half of the sky, provides new insights on
the dust grains nature suggesting fluffy grains are found not only in some very
specific regions but in all directions for which the visual extinction reaches
about 1 mag.Comment: 10 pages, 11 figures, accepted for publication in A&
The Effect of Dust Extinction on the Observed Properties of Galaxies in the Near-Infrared
Galaxies behind the Milky Way suffer size reduction and dimming due to their
obscuration by dust in the disk of our Galaxy. The degree of obscuration is
wavelength dependent. It decreases towards longer wavelengths. Compared to the
optical, the Near InfraRed (NIR) band extinction is only
that of the band. This makes NIR surveys well suited for galaxy surveys
close to the Galactic Plane where extinction is severe.
While Galactic obscuration is less prominent in the NIR it is not negligible.
In this paper we derive empirical relations to correct isophotal radii and
magnitudes of galaxies observed in the NIR for foreground absorption. We
simulate extinction in the , and bands on 64 (unobscured) galaxies
from the 2MASS Large Galaxy Atlas \citep{jarrett}. We propose two methods for
the extinction correction, the first is optimized to provide the most accurate
correction and the second provides a convenient statistical correction that
works adequately in lower extinction regions. The optimized correction utilizes
the galaxy surface brightness, either the disk central surface brightness,
, or the combined disk plus bulge central surface brightness, elliptical
and disk/spiral Hubble types. A detailed comparison between the different
methods and their accuracy is provided.Comment: 9 pages, 8 figures and 8 tables. Accepted by the MNRAS: Accepted 2009
September 18. Received 2009 September 18; in original form 2009 July 1
Water vole (Arvicola amphibius) abundance in grassland habitats of Glasgow
Water vole (Arvicola amphibius) populations have
undergone a serious decline throughout the UK, and
yet a stronghold of these small mammals is found in
the greater Easterhouse area of Glasgow. The water
voles in this location are mostly fossorial, living a
largely subterranean existence in grasslands, rather
than the more typical semi-aquatic lifestyle in
riparian habitats. In this study, we carried out
capture-mark-recapture surveys on water voles at
two sites: Cranhill Park and Tillycairn Drive. We
made a total of 62 captures including retraps, and the
resulting population estimates were 78 individuals
(95% confidence interval 41-197) for Cranhill Park
and 42 individuals (20-141) for Tillycairn Drive.
From these figures we estimated a population
density of water voles, which appeared to be higher
than other reports from the UK. Despite the
difficulties of sampling in urban environments that
resulted in relatively low capture rates, our data
suggest that the greater Easterhouse area of Glasgow
holds water voles at relatively high population
densities. These results will inform future
conservation in the City of Glasgow and surrounding
areas, as well as raise awareness of important water
vole populations in urban environments
On How to Extend the NIR Tully-Fisher Relation to be Truly All-Sky
Dust extinction and stellar confusion by the Milky Way reduce the efficiency
of detecting galaxies at low Galactic latitudes, creating the so-called Zone of
Avoidance. This stands as a stumbling block in charting the distribution of
galaxies and cosmic flow fields, and therewith our understanding of the local
dynamics in the Universe (CMB dipole, convergence radius of bulk flows). For
instance, ZoA galaxies are generally excluded from the whole-sky Tully-Fisher
Surveys () even if catalogued. We show here that by
fine-tuning the near-infrared TF relation, there is no reason not to extend
peculiar velocity surveys deeper into the ZoA. Accurate axial ratios ()
are crucial to both the TF sample selection and the resulting TF distances. We
simulate the effect of dust extinction on the geometrical properties of
galaxies. As expected, galaxies appear rounder with increasing obscuration
level, even affecting existing TF samples. We derive correction models and
demonstrate that we can reliably reproduce the intrinsic axial ratio from the
observed value up to extinction level of about mag (
mag), we also recover a fair fraction of galaxies that otherwise would fall out
of an uncorrected inclination limited galaxy sample. We present a
re-calibration of the 2MTF relation in the NIR , , and -bands for
isophotal rather than total magnitudes, using their same calibration sample.
Both TF relations exhibit similar scatter at high Galactic latitudes. However,
the isophotal TF relation results in a significant improvement in the scatter
for galaxies in the ZoA, and low surface brightness galaxies in general,
because isophotal apertures are more robust in the face of significant stellar
confusion.Comment: 12 pages, 10 figures, 4 tables, accepted for publication in MNRA
Galaxy peculiar velocities in the Zone of Avoidance
Dust extinction and stellar confusion of the Milky Way hinder the detection
of galaxies at low Galactic latitude, creating the so-called Zone of Avoidance
(ZoA). This has hampered our understanding of the local dynamics, cosmic flow
fields and the origin of the Cosmic Microwave Background dipole. The ZoA () is also excluded from the "whole-sky" Two Micron All-Sky Survey
(2MASS) Redshift Survey (2MRS) and 2MASS Tully-Fisher Survey (2MTF). The latter
aims to provide distances and peculiar velocities for all bright inclined 2MASS
galaxies with \leq 11\hbox{.\!\!^{\rm m}}25. Correspondingly,
knowledge about the density distribution in the ZoA remains limited to
statistical interpolations. To improve on this bias we pursued two different
surveys to fill in the southern and northern ZoA. These data will allow a
direct measurement of galaxy peculiar velocities. In this paper we will present
a newly derived optimized Tully-Fisher (TF) relation that allow accurate
measures of galaxy distances and peculiar velocities for dust-obscured
galaxies. We discuss further corrections for magnitudes and biases and present
some preliminary results on flow fields in the southern ZoA.Comment: 6 pages, 3 figures, to appear in Proceedings of SAIP2013, the 58th
Annual Conference of the South African Institute of Physics, edited by Roelf
Botha and Thulani Jili (SAIP and University of Zululand, 2014). ISBN:
978-0-620-62819-
Dye laser remote sensing of marine plankton
Dye laser, emitting four wavelengths sequentially in time, has been incorporated into helicopter-borne lidar flight package, for performing studies of laser-induced fluorescence of chlorophyll A in algae. Data obtained by multicolor lidar technique can provide water-resource management with rapid-access wide-area coverage of the impact of various environmental factors for any body of water
Absorption heating-cooling system
An improved heating or cooling system based on absorption principles is disclosed and claimed herein. A closed system is provided with a refrigerant-absorbent solution where separation of the refrigerant-absorbent is accomplished by a semi-permeable membrane. The refrigerant-absorbent solution at its normal concentration is pumped under pressure to a membrane separation unit where the refrigerant is selectively passed through a membrane separator in some proportion while a remaining absorbent enriched refrigerant-absorbent solution is rejected. The membrane separated refrigerant is then circulated through a heat exchange leg of the system for heating and/or cooling of affected areas depending upon the particular treatment of the refrigerant. At the end of the heat exchange leg, the refrigerant is fed to an absorber where it is recombined with the absorbent enriched solution to reconstitute the original refrigerant-absorbent solution which is then recirculated by the pump and the cycle is repeated. The apparatus and process of heat transfer systems utilizing the present membrane separation are claimed
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