774 research outputs found
ASMOOTH: A simple and efficient algorithm for adaptive kernel smoothing of two-dimensional imaging data
An efficient algorithm for adaptive kernel smoothing (AKS) of two-dimensional
imaging data has been developed and implemented using the Interactive Data
Language (IDL). The functional form of the kernel can be varied (top-hat,
Gaussian etc.) to allow different weighting of the event counts registered
within the smoothing region. For each individual pixel the algorithm increases
the smoothing scale until the signal-to-noise ratio (s.n.r.) within the kernel
reaches a preset value. Thus, noise is suppressed very efficiently, while at
the same time real structure, i.e. signal that is locally significant at the
selected s.n.r. level, is preserved on all scales. In particular, extended
features in noise-dominated regions are visually enhanced. The ASMOOTH
algorithm differs from other AKS routines in that it allows a quantitative
assessment of the goodness of the local signal estimation by producing
adaptively smoothed images in which all pixel values share the same
signal-to-noise ratio above the background.
We apply ASMOOTH to both real observational data (an X-ray image of clusters
of galaxies obtained with the Chandra X-ray Observatory) and to a simulated
data set. We find the ASMOOTHed images to be fair representations of the input
data in the sense that the residuals are consistent with pure noise, i.e. they
possess Poissonian variance and a near-Gaussian distribution around a mean of
zero, and are spatially uncorrelated.Comment: 9 pages, 5 figures, to be published in MNRA
Genetic analysis of foot-and-mouth disease virus serotype A of Indian origin and detection of positive selection and recombination in leader protease- and capsid-coding regions
The leader protease (Lpro) and capsid-coding sequences (P1) constitute approximately 3 kb of the foot-and-mouth disease virus (FMDV). We studied the phylogenetic relationship of 46 FMDV serotype A isolates of Indian origin collected during the period 1968-2005 and also eight vaccine strains using the neighbour-joining tree and Bayesian tree methods. The viruses were categorized under three major groups-Asian, Euro-South American and European. The Indian isolates formed a distinct genetic group among the Asian isolates. The Indian isolates were further classified into different genetic subgroups ( < 5% divergence). Post-1995 isolates were divided into two subgroups while a few isolates which originated in the year 2005 from Andhra Pradesh formed a separate group. These isolates were closely related to the isolates of the 1970s. The FMDV isolates seem to undergo reverse mutation or convergent evolution wherein sequences identical to the ancestors are present in the isolates in circulation. The eight vaccine strains included in the study were not related to each other and belonged to different genetic groups. Recombination was detected in the Lpro region in one isolate (A IND 20/82) and in the VP1 coding 1D region in another isolate (A RAJ 21/96). Positive selection was identified at aa positions 23 in the Lpro (P < 0.05; 0.046∗) and at aa 171 in the capsid protein VP1 (P < 0.01; 0.003∗∗)
Chandra Observations of Gas Stripping in the Elliptical Galaxy NGC 4552 in the Virgo Cluster
We use a 54.4 ks Chandra observation to study ram-pressure stripping in
NGC4552 (M89), an elliptical galaxy in the Virgo Cluster. Chandra images in the
0.5-2 keV band show a sharp leading edge in the surface brightness 3.1 kpc
north of the galaxy center, a cool (kT =0.51^{+0.09}_{-0.06} keV) tail with
mean density n_e ~5.4 +/- 1.7 x 10^{-3} cm^{-3} extending ~10 kpc to the south
of the galaxy, and two 3-4 kpc horns of emission extending southward away from
the leading edge. These are all features characteristic of supersonic
ram-pressure stripping of galaxy gas, due to NGC4552's motion through the
surrounding Virgo ICM. Fitting the surface brightness profile and spectra
across the leading edge, we find the galaxy gas inside the edge is cooler (kT =
0.43^{+0.03}_{-0.02} keV) and denser (n_e ~ 0.010 cm^{-3}) than the surrounding
Virgo ICM (kT = 2.2^{+0.7}_{-0.4} keV and n_e = 3.0 +/- 0.3 x 10^{-4} cm^{-3}).
The resulting pressure ratio between the free-streaming ICM and cluster gas at
the stagnation point is ~7.6^{+3.4}_{-2.0} for galaxy gas metallicities of
0.5^{+0.5}_{-0.3} Zsolar, which suggests that NGC4552 is moving supersonically
through the cluster with a velocity v ~ 1680^{+390}_{-220} km/s (Mach
2.2^{+0.5}_{-0.3}) at an angle xi ~ 35 +/- 7 degrees towards us with respect to
the plane of the sky.Comment: 31 pages, 12 figures, ApJ, in press; paper split into 2 parts, Paper
I(sec 1-3) here, added figs and discussion to conform to published version;
Paper II (sec. 4) in astro-ph/060440
Untangling the X-ray Emission From the Sa Galaxy NGC1291 With Chandra
We present a Chandra ACIS-S observation of the nearby bulge-dominated Sa
galaxy NGC1291. The X-ray emission from the bulge resembles the X-ray emission
from a sub-class of elliptical and S0 galaxies with low L_X/L_B luminosity
ratios. The X-ray emission is composed of a central point-like nucleus, ~50
point sources that are most likely low mass X-ray binaries (LMXBs), and diffuse
gas detectable out to a radius of 120" (5.2 kpc). The diffuse gas has a global
temperature of 0.32^{+0.04}_{-0.03} keV and metallicity of 0.06 +/- 0.02 solar,
and both quantities marginally decrease with increasing radius. The hot gas
fills the hole in the HI distribution, and the softening of the spectrum of the
X-ray gas with radius might indicate a thermal coupling of the hot and cold
phases of the interstellar medium as previously suggested. The integrated X-ray
luminosity of the LMXBs, once normalized by the optical luminosity, is a factor
of 1.4 less than in the elliptical galaxy NGC4697 or S0 galaxy NGC1553. The
difference in L_{X,stellar}/L_B between the galaxies appears to be because of a
lack of very bright sources in NGC1291. No sources above 3 x 10^38 ergs/s were
found in NGC1291 when ~7 were expected from scaling from NGC4697 and NGC1553.
The cumulative L_{X,stellar}/L_B value including only sources below 1.0 x 10^38
ergs/s is remarkably similar between NGC1291 and NGC4697, if a recent surface
brightness fluctuation-determined distance is assumed for NGC4697. If this is a
common feature of the LMXB population in early-type systems, it might be used
as a distance indicator. Finally, a bright, variable (1.6-3.1 x 10^39 ergs/s)
source was detected at the optical center of the galaxy. Its spectrum shows
excess soft emission superimposed on a highly absorbed power law component,
similar to what has been found in several other low luminosity AGN (ABRIDGED).Comment: 13 pages in emulateapj5 style with 11 embedded Postscript figures;
minor revisions since last version; accepted by Ap
ROSAT Evidence for Intrinsic Oxygen Absorption in Cooling Flow Galaxies and Groups
Using spatially resolved, deprojected ROSAT PSPC spectra of 10 of the
brightest cooling flow galaxies and groups with low Galactic column densities
we have detected intrinsic absorption over energies ~0.4-0.8 keV in half of the
sample. Since no intrinsic absorption is indicated for energies below ~0.4 keV,
the most reasonable model for the absorber is collisionally ionized gas at
temperatures T=10^{5-6} K with most of the absorption arising from ionized
states of oxygen but with a significant contribution from carbon and nitrogen.
The soft X-ray emission of this warm gas can explain the sub-Galactic column
densities of cold gas inferred within the central regions of most of the
systems. Attributing the absorption to ionized gas reconciles the large columns
of cold H and He inferred from EINSTEIN and ASCA with the lack of such columns
inferred from ROSAT. Within the central ~10-20 kpc, where the constraints are
most secure, the estimated mass of the ionized absorber is consistent with most
(perhaps all) of the matter deposited by a cooling flow over the lifetime of
the flow. Since the warm absorber produces no significant H or He absorption
the large absorber masses are consistent with the negligible atomic and
molecular H inferred from HI and CO observations of cooling flows. It is also
found that if T > ~2x10^5 K then the optical and UV emission implied by the
warm gas does not violate published constraints. Finally, we discuss how the
prediction of warm ionized gas as the product of mass drop-out in these and
other cooling flows can be verified with new CHANDRA and XMM observations.
(Abridged)Comment: 17 pages (5 figures), Accepted for publication in ApJ, expanded
discussion of multiphase spectral models, theoretical implications of warm
gas in cooling flows, and the statistical significance of the oxygen
absorptio
Draft proposal for establishment of CNC centre at NAL
This is a proposal for setting up Computer Numerically Controlled machining facilities at N.A.L. to cater to the increasing requirements for fabrication of complex shaped and intricate/precision components for the aerospace R & D projects of the laboratory for the next 10 - year period. This fairly comprehensive document has been prepared by an
internal technical committee constituted by the Director, after detailed study and discussions and covers the technical and financial aspects for setting up such facilities
X-ray Tail in NGC 7619
We present new observational results of NGC 7619, an elliptical galaxy with a
prominent X-ray tail and a dominant member of the Pegasus group. With Chandra
and XMM-Newton observations, we confirm the presence of a long X-ray tail in
the SW direction; moreover, we identify for the first time a sharp
discontinuity of the X-ray surface brightness in the opposite (NE) side of the
galaxy. The density, temperature and pressure jump at the NE discontinuity
suggest a Mach number ~1, corresponding to a galaxy velocity of ~500 km s-1,
relative to the surrounding hot gas. Spectral analysis of these data shows that
the Iron abundance of the hot gaseous medium is much higher (1-2 solar) near
the center of NGC 7619 and in the tail extending from the core than in the
surrounding regions (< 1/2 solar), indicating that the gas in the tail is
originated from the galaxy. The possible origin of the head-tail structure is
either on-going ram-pressure stripping or sloshing. The morphology of the
structure is more in line with a ram pressure stripping phenomenon, while the
position of NGC 7619 at the center of the Pegasus I group, and its dominance,
would prefer sloshing.Comment: ApJ accepted to appear in the 2008 December 1 issue; Added discussion
on sloshin
The Ionized Gas Kinematics of the LMC-Type Galaxy NGC 1427A in the Fornax Cluster
NGC 1427A is a LMC-like irregular galaxy in the Fornax cluster with an
extended pattern of strong star formation around one of its edges, which is
probably due to some kind of interaction with the cluster environment. We
present H-alpha velocities within NGC 1427A, obtained through long-slit
spectroscopy at seven different positions, chosen to fall on the brightest HII
regions of the galaxy. Due to its location very near the center of the cluster
this object is an excellent candidate to study the effects that the cluster
environment has on gas-rich galaxies embedded in it. The rotation of NGC 1427A
is modeled in two different ways. The global ionized gas kinematics is
reasonably well described by solid-body rotation, although on small scales it
shows a chaotic behaviour. In this simple model, the collision with a smaller
member of the cluster as being responsible for the peculiar morphology of NGC
1427A is very unlikely, since the only candidate intruder falls smoothly into
the general velocity pattern of the main galaxy. In a more elaborate model, for
which we obtain a better solution, this object does not lie in the same plane
of NGC 1427A, in which case we identify it as a satellite bound to the galaxy.
These results are discussed in the context of a normal irregular versus one
interacting with some external agent. Based on several arguments and
quantitative estimates, we argue that the passage through the hot intracluster
gas of the Fornax cluster is a very likely scenario to explain the
morphological properties of NGC 1427A.Comment: 31 pages, LaTeX2e, uses aas2pp4.sty and psfig.sty, including 7
Postscript figures; accepted for publication in ApJ, Vol. 530, February 200
Dust Streamers in the Virgo Galaxy M86 from Ram Pressure Stripping of its Companion VCC 882
The giant elliptical galaxy M86 in Virgo has a ~28 kpc long dust trail inside
its optical halo that points toward the nucleated dwarf elliptical galaxy, VCC
882. The trail seems to be stripped material from the dwarf. Extinction
measurements suggest that the ratio of the total gas mass in the trail to the
blue luminosity of the dwarf is about unity, which is comparable to such ratios
in dwarf irregular galaxies. The ram pressure experienced by the dwarf galaxy
in the hot gaseous halo of M86 was comparable to the internal gravitational
binding energy density of the presumed former gas disk in VCC 882. Published
numerical models of this case are consistent with the overall trail-like
morphology observed here. Three concentrations in the trail may be evidence for
the predicted periodicity of the mass loss. The evaporation time of the trail
is comparable to the trail age obtained from the relative speed of the galaxies
and the trail length. Thus the trail could be continuously formed from stripped
replenished gas if the VCC 882 orbit is bound. However, the high gas mass and
the low expected replenishment rate suggest that this is only the first
stripping event. Implications for the origin of nucleated dwarf ellipticals are
briefly discussed.Comment: 22 pages, 7 figures, Astronomical Journal, August 2000, in pres
Inflationary Baryogenesis
In this letter we explore the possibility of creating the baryon asymmetry of
the universe during inflation and reheating due to the decay of a field
associated with the inflaton. CP violation is attained by assuming that this
field is complex with a phase that varies as the inflaton evolves. We consider
chaotic and natural inflation scenarios. In the former case, the complex
decaying field is the inflaton itself and, in the latter case, the phase of the
complex field is the inflaton. We calculate the asymmetry produced using the
Bogolyubov formalism that relates annihilation and creation operators at late
time to the annihilation and creation operators at early time.Comment: 17 pages, Revte
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