87 research outputs found
Turbulence in the Harassed Galaxy NGC 4254
Galaxy harassment is an important mechanism for the morphological evolution
of galaxies in clusters. The spiral galaxy NGC 4254 in the Virgo cluster is
believed to be a harassed galaxy. We have analyzed the power spectrum of HI
emission fluctuations from NGC 4254 to investigate whether it carries any
imprint of galaxy harassment. The power spectrum, as determined using the 16
central channels which contain most of the HI emission, is found to be well
fitted by a power law with at
length-scales to . This is similar to
other normal spiral galaxies which have a slope of and is
interpreted as arising from two dimensional turbulence at length-scales larger
than the galaxy's scale-height. NGC 4254 is hence yet another example of a
spiral galaxy that exhibits scale-invariant density fluctuations out to
length-scales comparable to the diameter of the HI disk. While a large variety
of possible energy sources like proto-stellar winds, supernovae, shocks, etc.
have been proposed to produce turbulence, it is still to be seen whether these
are effective on length-scales comparable to that of the entire HI disk. On
separately analyzing the HI power spectrum in different parts of NGC 4254, we
find that the outer parts have a different slope ()
compared to the central part of the galaxy (). Such a
change in slope is not seen in other, undisturbed galaxies. We suggest that, in
addition to changing the overall morphology, galaxy harassment also effects the
fine scale structure of the ISM, causing the power spectrum to have a steeper
slope in the outer parts.Comment: 6 figures, 1 table, accepted for publication in MNRAS letter
The Scale Height of NGC 1058 Measured from its HI Power Spectrum
We have measured the HI power spectrum of the nearly face-on spiral galaxy
NGC 1058 from radio-interferometric observations using a visibility based
estimator. The power spectrum is well fitted by two different power laws
, one with at small length-scales
and another with
at large length-scales . We interpret this change in the slope of the power spectrum as a
transition from 3D turbulence at small length-scales to 2D turbulence in the
plane of the galaxy's disk at large length-scales. We use the observed break in
the power spectrum to estimate the galaxy's scale-height, which we find to be pc.Comment: Accepted for publication in Mon. Not. of Royal Astron. Soc. Letter
A slow bar in the dwarf irregular galaxy NGC 3741
Using the Tremaine-Weinberg method, we measure the speed of the HI bar seen
in the disk of NGC 3741. NGC 3741 is an extremely gas rich galaxy with an
{H\,{\sc i}} disk which extends to about 8.3 times its Holmberg radius. It is
also highly dark matter-dominated. Our calculated value of the pattern speed
is 17.1 3.4 km . We also
find the ratio of the co-rotation radius to the bar semi-major axis to be (1.6
0.3), indicating a slow bar. This is consistent with bar models in which
dynamical friction results in a slow bar in dark matter dominated galaxies.Comment: 7 pages, 4 figures, 2 tables Accepted for publlication in MNRA
A study on neonatal hyperbilirubinemia due to ABO incompatibility in sick newborn care unit, Telangana
Background: Hyperbilirubinemia is one of the most common clinical signs encountered in neonates which if untreated is potentially neurotoxic. The neonates at higher risk of jaundice should be identified at birth and kept under enhanced surveillance for occurrence and progression of jaundice and promptly intervened. Aim: This study aims to study and analyze the neonatal hyperbilirubinemia in the babies born to O positive mother. Subjects and Methods: A prospective observational cohort study of healthy term neonates born to O positive mothers with clinical jaundice was conducted in a sick newborn care unit (SNCU) attached to a tertiary level government maternity hospital. SPSS version 19 was used for statistical analysis. Descriptive statistics such as mean, median, standard deviation, and Chi-square test were calculated. p<0.05 was taken as statistically significant. Results: A total of 100 babies, born to O positive mothers brought to SNCU with clinical jaundice of <120 h of age, were studied. 72 babies had ABO incompatibility, of which 52 (72%) babies required phototherapy and 1 (1.3%) required exchange transfusion. There was no significant difference in the severity and outcome in both O-A and O-B incompatibility, although O-B incompatibility was more (65%). Conclusion: Blood group of mother should always be noted and babies born to O positive mothers must be followed for early identification and prompt intervention
A search for HI in some peculiar faint dwarf galaxies
We present a deep Giant Metrewave Radio Telescope (GMRT) search for HI 21 cm
emission from three dwarf galaxies, viz. POX 186, SC 24 and KKR 25. Based, in
part, on previous single dish HI observations, these galaxies have been
classified as a BCD, a dwarf irregular and a transition galaxy respectively.
However, in conflict with previous single dish detections, we do not detect HI
in SC 24 or KKR 25. We suggest that the previous single dish measurements were
probably confused with the local galactic emission. In the case of POX 186, we
confirm the previous non detection of HI but with substantially improved limits
on its HI mass. Our derived upper limits on the HI mass of SC 24 and KKR 25 are
similar to the typical HI mass limit for dwarf spheroidal galaxies, whereas in
the case of POX 186, we find that its gas content is somewhat smaller than is
typical of BCD galaxies.Comment: Accepted for publication in MNRA
Thick gas discs in faint dwarf galaxies
We determine the intrinsic axial ratio distribution of the 'gas' disks of
extremely faint M_B > -14.5 dwarf irregular galaxies. We start with the
measured (beam corrected) distribution of apparent axial ratios in the HI 21cm
images of dwarf irregular galaxies observed as part of the Faint Irregular
Galaxy GMRT Survey (FIGGS). Assuming that the disks can be approximated as
oblate spheroids, the intrinsic axial ratio distribution can be obtained from
the observed apparent axial ratio distribution. We use a couple of methods to
do this, and our final results are based on using Lucy's deconvolution
algorithm. This method is constrained to produce physically plausible
distributions, and also has the added advantage of allowing for observational
errors to be accounted for. While one might a priori expect that gas disks
would be thin (because collisions between gas clouds would cause them to
quickly settle down to a thin disk), we find that the HI disks of faint dwarf
irregulars are quite thick, with mean axial ratio ~ 0.6. While this is
substantially larger than the typical value of ~ 0.2 for the 'stellar' disks of
large spiral galaxies, it is consistent with the much larger ratio of velocity
dispersion to rotational velocity (sigma/v_c) in dwarf galaxy HI disks as
compared to that in spiral galaxies. Our findings have implications for studies
of the mass distribution in and the Tully - Fisher relation for faint dwarf
irregular galaxies, where it is often assumed that the gas is in a thin disk.Comment: 5 pages, 4 figures. Minor changes in revised version. The definitive
version is available at http://www.blackwell-synergy.com
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