2,188 research outputs found
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
Analysis of ALOPE data from Superflux
Remote sensing data collected with the airborne lidar oceanographic probing experiment (ALOPE) laser fluorosensor during the Superflux 1 and Superflux 2 experiments were analyzed using two techniques. A qualitative technique which requires no supplementary data provided a near-real-time estimate of relative abundance of the golden-brown and green phytoplankton color groups. Contour plots developed for the later mission are used to demonstrate the utility of this technique. A quantitative technique which requires supplementary data to define the attenuation coefficient provides chlorophyll a concentration by color group. The sum of the golden-brown and green chlorophyll a data yields total chlorophyll a values which may be compared with in situ data. As expected, the golden-brown population was dominant in the Chesapeake Bay and the Bay plume whereas the green population was dominant in shelf waters
Galaxies behind the Galactic plane: First results and perspectives from the VVV Survey
Vista Variables in The Via Lactea (VVV) is an ESO variability survey that is
performing observations in near infrared bands (ZYJHKs) towards the Galactic
bulge and part of the disk with the completeness limits at least 3 mag deeper
than 2MASS. In the present work, we searched in the VVV survey data for
background galaxies near the Galactic plane using ZYJHKs photometry that covers
1.636 square degrees. We identified 204 new galaxy candidates by analyzing
colors, sizes, and visual inspection of multi-band (ZYJHKs) images. The galaxy
candidates colors were also compared with the predicted ones by star counts
models considering a more realistic extinction model at the same completeness
limits observed by VVV. A comparison of the galaxy candidates with the expected
one by Milennium simulations is also presented. Our results increase the number
density of known galaxies behind the Milky Way by more than one order of
magnitude. A catalog with galaxy properties including ellipticity, Petrosian
radii and ZYJHKs magnitudes is provided, as well as comparisons of the results
with other surveys of galaxies towards Galactic plane.Comment: 27 pages, 10 figures, 2 tables; in press at The Astronomical Journa
Binary Galaxies in the Local Supercluster and Its Neighborhood
We report a catalog of 509 pairs identified among 10403 nearby galaxies with
line-of-sight velocities V_LG < 3500 km/s.We selected binary systems in
accordance with two criteria (bounding and temporal), which require the
physical pair of galaxies to have negative total energy and its components to
be located inside the zero-velocity surface. We assume that individual galaxy
masses are proportional to their total K-band luminosities, M = L_K x 6M/L. The
catalog gives the magnitudes and morphological types of galaxies and also the
projected (orbital) masses and pair isolation indices. The component
line-of-sight velocity differences and projected distances of the binary
systems considered have power-law distributions with the median values of 35
km/s and 123 kpc, respectively. The median mass-to-K-band luminosity ratio is
equal to 11 M/L, and its uncertainty is mostly due to the errors of measured
velocities. Our sample of binary systems has a typical density contrast of d
ro/ro_c ~ 500 and a median crossing time of about 3.5 Gyr. We point out the
substantial fraction of binary systems consisting of late-type dwarf galaxies,
where the luminosities of both components are lower than that of the Small
Magellanic Cloud. The median projected distance for 41 such pairs is only 30
kpc, and the median difference of their line-of-sight velocities is equal to 14
km/s which is smaller than the typical error for radial-velocity (30 km/s).
This specific population of gas-rich dwarf binary galaxies such as I Zw 18 may
be at the stage immediately before merging of its components. Such objects,
which are usually lost in flux-limited (and not distance-limited) samples
deserve a thorough study in the HI radio line with high spatial and velocity
resolution.Comment: published in Astrophysical Bulletin, 2008, Vol. 63, No. 4, pp.
299-34
A Massive Spiral Galaxy in the Zone of Avoidance
We report the discovery of a very HI-massive disk galaxy, HIZOA J0836-43, at
a velocity of v_hel = 10689 km/s, corresponding to a distance of 148 Mpc
(assuming H_0=75 km/s/Mpc). It was found during the course of a systematic HI
survey of the southern Zone of Avoidance (|b| < 5 deg) with the multibeam
system at the 64m Parkes radio telescope. Follow-up observations with the
Australia Telescope Compact Array (ATCA) reveal an extended HI disk. We derive
an HI mass of 7.5 x 10^10 Msun. Using the HI radius, we estimate a total
dynamical mass of 1.4 x 10^12 Msun, similar to the most massive known disk
galaxies such as Malin 1. HIZOA J0836-43 lies deep in the Zone of Avoidance (l,
b = 262.48 deg, -1.64 deg) where the optical extinction is very high, A_B =
9.8. However, in the near-infrared wavebands, where the extinction is
considerably lower, HIZOA J0836-43 is clearly detected by both DENIS and 2MASS.
Deep AAT near-infrared (Ks and H-band) images show that HIZOA J0836-43 is an
inclined disk galaxy with a prominent bulge (scale length 2.5 arcsec or 1.7
kpc), and an extended disk (scale length 7 arcsec or 4.7 kpc) which can be
traced along the major axis out to a radius of 20 arcsec or 13.4 kpc (at 20
mag/arcsec^2 in Ks). The HI disk is much more extended, having a radius of 66
kpc at 1 Msun/pc^2. Detections in the radio continuum at 1.4 GHz and at 60
micron (IRAS) are consistent with HIZOA J0836-43 forming stars at a rate of ~35
Msun/yr. We compare the properties of HIZOA J0836-43 with those of the most
HI-massive galaxies currently known, UGC 4288, UGC 1752 and Malin 1, all of
which are classified as giant low surface brightness galaxies.Comment: Accepted for publication in MNRAS, 17 pages, 11 figures, 7 tables,
version with high-resolution figures available at:
http://frodo.as.arizona.edu/~jdonley/massive
Global anisotropy of arrival directions of ultra-high-energy cosmic rays: capabilities of space-based detectors
Planned space-based ultra-high-energy cosmic-ray detectors (TUS, JEM-EUSO and
S-EUSO) are best suited for searches of global anisotropies in the distribution
of arrival directions of cosmic-ray particles because they will be able to
observe the full sky with a single instrument. We calculate quantitatively the
strength of anisotropies associated with two models of the origin of the
highest-energy particles: the extragalactic model (sources follow the
distribution of galaxies in the Universe) and the superheavy dark-matter model
(sources follow the distribution of dark matter in the Galactic halo). Based on
the expected exposure of the experiments, we estimate the optimal strategy for
efficient search of these effects.Comment: 19 pages, 7 figures, iopart style. v.2: discussion of the effect of
the cosmic magnetic fields added; other minor changes. Simulated UHECR
skymaps available at http://livni.inr.ac.ru/UHECRskymaps
The First Supernova Explosions: Energetics, Feedback, and Chemical Enrichment
We perform three-dimensional smoothed particle hydrodynamics simulations in a
realistic cosmological setting to investigate the expansion, feedback, and
chemical enrichment properties of a 200 M_sun pair-instability supernova in the
high-redshift universe. We find that the SN remnant propagates for a Hubble
time at z = 20 to a final mass-weighted mean shock radius of 2.5 kpc (proper),
roughly half the size of the HII region, and in this process sweeps up a total
gas mass of 2.5*10^5 M_sun. The morphology of the shock becomes highly
anisotropic once it leaves the host halo and encounters filaments and
neighboring minihalos, while the bulk of the shock propagates into the voids of
the intergalactic medium. The SN entirely disrupts the host halo and terminates
further star formation for at least 200 Myr, while in our specific case it
exerts positive mechanical feedback on neighboring minihalos by
shock-compressing their cores. In contrast, we do not observe secondary star
formation in the dense shell via gravitational fragmentation, due to the
previous photoheating by the progenitor star. We find that cooling by metal
lines is unimportant for the entire evolution of the SN remnant, while the
metal-enriched, interior bubble expands adiabatically into the cavities created
by the shock, and ultimately into the voids with a maximum extent similar to
the final mass-weighted mean shock radius. Finally, we conclude that dark
matter halos of at least M_vir > 10^8 M_sun must be assembled to recollect all
components of the swept-up gas.Comment: 16 pages, 14 figures, published in Ap
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