1,739 research outputs found
A High Galactic Latitude HI 21cm-line Absorption Survey using the GMRT: I. Observations and Spectra
We have used the Giant Meterwave Radio Telescope (GMRT) to measure the
Galactic HI 21-cm line absorption towards 102 extragalactic radio continuum
sources, located at high (|b| >15deg.) Galactic latitudes. The Declination
coverage of the present survey is Decl. ~ -45deg.. With a mean rms optical
depth of ~0.003, this is the most sensitive Galactic HI 21-cm line absorption
survey to date. To supplement the absorption data, we have extracted the HI
21-cm line emission profiles towards these 102 lines of sight from the Leiden
Dwingeloo Survey of Galactic neutral hydrogen. We have carried out a Gaussian
fitting analysis to identify the discrete absorption and emission components in
these profiles. In this paper, we present the spectra and the components. A
subsequent paper will discuss the interpretation of these results.Comment: 46 pages, Accepted for publication in Journal of Astrophysics &
Astronom
Detection of Cold Atomic Clouds in the Magellanic Bridge
We report a detection of cold atomic hydrogen in the Magellanic Bridge using
21-cm absorption spectroscopy toward the radio source B0312-770. With a column
density of N_HI=1.2E20 cm^-2, a maximum absorption optical depth of tau=0.10
and a maximum 21-cm emission brightness temperature of 1.4 K, this line of
sight yields a spin temperature, T_s, between 20 K and 40 K. H I 21-cm
absorption and emission spectroscopy toward 7 other low column density
sightlines on the periphery of the LMC and SMC reveal absorption toward one
additional background radio source behind the SMC with tau=0.03. The data have
typical sensitivities of sigma_tau=0.005 to 0.070 in absorption and
sigma_{T_B}=0.03 K in emission. These data demonstrate the presence of a cold
atomic phase which is probably accompanied by molecular condensations in the
tenuous interstellar medium of the Bridge region. Young OB stars observed in
the Magellanic Bridge could form "in situ" from these cold condensations rather
than migrate from regions of active star formation in the main body of the SMC.
The existence of cold condensations and star formation in the Magellanic Bridge
might be understood as a small scale version of the mechanism that produces
star formation in the tidal tails of interacting galaxies.Comment: 25 pages, uses AASTeX and psfig; Accepted for Publication in the
Astronomical Journa
Galaxies on the Blue Edge
We have successfully constructed a catalog of HI-rich galaxies selected from
the Minnesota Automated Plate Scanner Catalog of the Palomar Observatory Sky
Survey (POSS I) based solely on optical criteria. We identify HI-rich
candidates by selecting the bluest galaxies at a given apparent magnitude,
those galaxies on the "blue edge" of POSS I color-magnitude parameter space.
Subsequent 21-cm observations on the upgraded Arecibo 305m dish detected over
50% of the observed candidates. The detected galaxies are HI-rich with HI
masses comparable to "normal" high surface brightness disk galaxies and they
have gas mass-to-light ratios ranging from 0.1 to 4.8 (in solar units).
Comparison of our candidate galaxies with known low surface brightness galaxies
(hereafter LSBs) shows that they exhibit similar optical and HI properties to
that population. We also show that previously identified LSBs, including
several LSBs with red B-V colors, preferentially occupy the "blue edge" of POSS
I color-magnitude parameter space. Their presence on the "blue edge" appears to
be a selection effect due to differing plate limits in the two POSS I
bandpasses. This suggests the POSS I is a good filter for separating galaxies
on the higher surface brightness end of the LSB population from the general
population of galaxies in the night sky.Comment: 56 pages, 19 figures, to be published in the Astronomical Journal
(July 1, 2002
Power-law random walks
We present some new results about the distribution of a random walk whose
independent steps follow a Gaussian distribution with exponent
. In the case we show that a stochastic
representation of the point reached after steps of the walk can be
expressed explicitly for all . In the case we show that the random
walk can be interpreted as a projection of an isotropic random walk, i.e. a
random walk with fixed length steps and uniformly distributed directions.Comment: 5 pages, 4 figure
Additional symmetries of constrained CKP and BKP hierarchies
The additional symmetries of the constrained CKP (cCKP) and BKP (cBKP)
hierarchies are given by their actions on the Lax operators, and their actions
on the eigenfunction and adjoint eigenfunction are
presented explicitly. Furthermore, we show that acting on the space of the wave
operator, forms new centerless and
-subalgebra of centerless respectively. In
order to define above symmetry flows of the cCKP and cBKP
hierarchies, two vital operators are introduced to revise the additional
symmetry flows of the CKP and BKP hierarchies.Comment: 14 pages, accepted by SCIENCE CHINA Mathematics(2010
Generalized Darboux transformations for the KP equation with self-consistent sources
The KP equation with self-consistent sources (KPESCS) is treated in the
framework of the constrained KP equation. This offers a natural way to obtain
the Lax representation for the KPESCS. Based on the conjugate Lax pairs, we
construct the generalized binary Darboux transformation with arbitrary
functions in time for the KPESCS which, in contrast with the binary Darboux
transformation of the KP equation, provides a non-auto-B\"{a}cklund
transformation between two KPESCSs with different degrees. The formula for
N-times repeated generalized binary Darboux transformation is proposed and
enables us to find the N-soliton solution and lump solution as well as some
other solutions of the KPESCS.Comment: 20 pages, no figure
GMRT Detection of HI 21 cm-line Absorption from the Peculiar Galaxy in Abell 2125
Using the recently completed Giant Meterwave Radio Telescope, we have
detected the HI 21 cm-line absorption from the peculiar galaxy C153 in the
galaxy cluster Abell 2125. The HI absorption is at a redshift of 0.2533, with a
peak optical depth of 0.36. The full width at half minimum of the absorption
line is 100 km/s. The estimated column density of atomic Hydrogen is
0.7e22(Ts/100K) per sq. cm. The HI absorption is redshifted by ~ 400 km/s
compared to the [OIII] emission line from this system. We attribute this to an
in-falling cold gas, or to an out-flowing ionised gas, or to a combination of
both as a consequence of tidal interactions of C153 with either a cluster
galaxy or the cluster potential.Comment: 9 pages, 2 figures, uses jaa.sty (included
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