667 research outputs found
Evidence for azimuthal variations of the oxygen abundance gradient tracing the spiral structure of the galaxy HCG91c
Context. The distribution of elements in galaxies forms an important
diagnostic tool to characterize the system's formation and evolution. This tool
is however complex to use in practice, as galaxies are subject to a range of
simultaneous physical processes active from pc to kpc scales. This renders
observations of the full optical extent of galaxies down to sub-kpc scales
essential. Aims. Using the WiFeS integral field spectrograph, we previously
detected abrupt and localized variations in the gas-phase oxygen abundance of
the spiral galaxy HCG91c. Here, we follow-up on these observations to map
HCG91c's disk out to ~2Re at a resolution of 600pc, and characterize the
non-radial variations of the gas-phase oxygen abundance in the system. Methods.
We obtained deep MUSE observations of the target under ~0.6 arcsec seeing
conditions. We perform both a spaxel-based and aperture-based analysis of the
data to map the spatial variations of 12+log(O/H) across the disk of the
galaxy. Results. We confirm the presence of rapid variations of the oxygen
abundance across the entire extent of the galaxy previously detected with
WiFeS, for all azimuths and radii. The variations can be separated in two
categories: a) localized and associated with individual HII regions, and b)
extended over kpc scales, and occurring at the boundaries of the spiral
structures in the galaxy. Conclusions. Our MUSE observations suggest that the
enrichment of the interstellar medium in HGC91c has proceeded preferentially
along spiral structures, and less efficiently across them. Our dataset
highlights the importance of distinguishing individual star-forming regions
down to scales of a few 100pc when using integral field spectrographs to
spatially resolve the distribution of oxygen abundances in a given system, and
accurately characterize azimuthal variations and intrinsic scatter.Comment: 12 pages, 11 figures, accepted for publication in A&A. Supplementary
movie assocociated with Fig. 8 is available (until publication) at:
http://www.sc.eso.org/~fvogt/supp_mat/HCG91c/O_gradient.mp
DETECTION OF DIFFUSE NEUTRAL INTRAGROUP MEDIUM IN HICKSON COMPACT GROUPS
We present new Green Bank Telescope (GBT) 21 cm neutral hydrogen (H I) observations of a complete distance-limited sample of 22 Hickson Compact Groups (HCGs) with at least four true members. We detected an average H I mass of 8 × 109 M (median = 6 × 109 M ), which is significantly larger than previous single-dish measurements. Consequently, the H I deficiencies for these HCGs have been reduced, although not completely eliminated. Spectral comparison of the GBT data with complementary Very Large Array data shows significant H I excess in the GBT spectra. The observed excess is primarily due to the high surface brightness (HSB) sensitivity of the GBT detecting diffuse, low column density H I in these groups. The excess gas forms a faint diffused neutral medium which is an intermediate stage in the evolution of HSB H I tidal debris in the intragroup medium (IGM) before it is fully ionized. The excess gas mass fraction, (M(H I)GBT – M(H I)VLA)/M(H I)GBT, for our complete sample varies from 5% to 81% with an average of 36% (median = 30%). The excess gas mass fraction is highest in slightly H I deficient groups where the tidal debris has had enough time to evolve. We also find the excess gas content increases with the evolutionary phase of the group described in Verdes-Montenegro et al. Theoretical calculations indicate that an H I cloud of radius ≥ 200 pc would survive in an IGM of 2 × 106 K for more than the typical dynamical lifetime of a group. However, smaller clouds get evaporated and assimilated into the hot IGM in a much shorter timescale
Macro and Micro-fungi mediated synthesis of Silver
Silver nanoparticles of size ranging from 1 ∼ 100 nm are petite metallic colloidal particles, with its applications in diagnostics, biomarkers, imaging, cell labeling and drug delivery. Fungus-mediated synthesis of silver nanoparticles is an ecofriendly andgreen process with a comparatively simpler downstream processing. In the presentstudy, the ability of macrofungi and pine stand soil fungi was evaluated for their ability tosynthesize both extracellular as well as intracellular silver nanoparticles. When the macroand microfungi were challenged with 1 mM silver nitrate, colour change of the cell freefiltrates indicated the formation of silver nanoparticles. The presence of silvernanoparticles was confirmed by Surface Plasmon Resonance absorption band in visiblewavelength visualized every 24h upto 72h.Silver nanoparticles are known to possess asharp peak in a range of 400-450 nm and peaks observed at 457nm, 403nm and 414nm bymushroom support their synthesis in comparison to that of 349nm by soil fungi.Transmission Electron Microscopic analysis of the silver nanoparticles revealed thenanorange, dimensions and structural conformation ofbio synthesized nanoparticles.Synergistic study of the synthesized nanoparticles revealed a significant antibacterialactivity against four pathogens viz. MTCC 730 (Escherichia coli), MTCC 1925(Streptococcus pyogenes), MTCC 96 (Staphylococcus aureus) and MTCC 430 (Bacilluscereus).Additionally, the silver nanoparticles inhibited the growth of the yeastpathogen MTCC 183 (Candida albicans) which showed synergistic enhancement inactivity along with flucanazole. The fungal samples were analyzed for phytochemicalconstituents who led to reduction of silver nitrate into nanoparticles. The results obtainedindicated that the experimental voucher fungus are more competent than soil fungi insynthesizing silver nanoparticles and can be used a potent natural antibacterial source forvarious pharmaceutical and textile applications
Galaxy Interactions in Compact Groups II: abundance and kinematic anomalies in HCG 91c
Galaxies in Hickson Compact Group 91 (HCG 91) were observed with the WiFeS
integral field spectrograph as part of our ongoing campaign targeting the
ionized gas physics and kinematics inside star forming members of compact
groups. Here, we report the discovery of HII regions with abundance and
kinematic offsets in the otherwise unremarkable star forming spiral HCG 91c.
The optical emission line analysis of this galaxy reveals that at least three
HII regions harbor an oxygen abundance ~0.15 dex lower than expected from their
immediate surroundings and from the abundance gradient present in the inner
regions of HCG 91c. The same star forming regions are also associated with a
small kinematic offset in the form of a lag of 5-10 km/s with respect to the
local circular rotation of the gas. HI observations of HCG 91 from the Very
Large Array and broadband optical images from Pan-STARRS suggest that HCG 91c
is caught early in its interaction with the other members of HCG 91. We discuss
different scenarios to explain the origin of the peculiar star forming regions
detected with WiFeS, and show that evidence point towards infalling and
collapsing extra-planar gas clouds at the disk-halo interface, possibly as a
consequence of long-range gravitational perturbations of HCG 91c from the other
group members. As such, HCG 91c provides evidence that some of the
perturbations possibly associated with the early phase of galaxy evolution in
compact groups impact the star forming disk locally, and on sub-kpc scales.Comment: 25 pages, 21 figures, MNRAS accepted. Until publication of the
article, the interactive component of Figure 4 is available at this URL:
http://www.mso.anu.edu.au/~fvogt/website/misc.htm
A GBT Survey for HI 21 cm Absorption in the Disks and Halos of Low-Redshift Galaxies
We present an HI 21 cm absorption survey with the Green Bank Telescope (GBT)
of galaxy-quasar pairs selected by combining data from the Sloan Digital Sky
Survey (SDSS) and the Faint Images of the Radio Sky at Twenty-Centimeters
(FIRST) survey. Our sample consists of 23 sightlines through 15 low-redshift
foreground galaxy - background quasar pairs with impact parameters ranging from
1.7 kpc up to 86.7 kpc. We detected one absorber in the GBT survey from the
foreground dwarf galaxy, GQ1042+0747, at an impact parameter of 1.7 kpc and
another possible absorber in our follow-up Very Large Array (VLA) imaging of
the nearby foreground galaxy, UGC 7408. Both of the absorbers are narrow (FWHM
of 3.6 and 4.8 km/s), have sub Damped Lyman alpha column densities, and most
likely originate in the disk gas of the foreground galaxies. We also detected H
I emission from three foreground galaxies, including UGC 7408. Although our
sample contains both blue and red galaxies, the two H I absorbers as well as
the H I emissions are associated with blue galaxies. We discuss the physical
conditions in the 21 cm absorbers and some drawbacks of the large GBT beam for
this type of survey.Comment: 15 pages, 6 figures, 3 table
Artisans of Meitei-Pangal/Pangal Community (Muslims) in the Making of Some Bamboo Tools and it’s Implements and Their Role in the Conservation of Bio-Resource in Manipur
Tools and itrsquos implements especially of bamboos have been searched, took photograph and documented their useful aspects. T3he information of artisans in relation with the tool creation by bamboo plants and their view of earning family income in deference with their traditional knowledge have been recorded during a study period (January, 2012 to Nov. 2014). A total of 3 genus 8 bamboo species useful in 5 (five) categories of human affairs i. e. Agriculture amp Horticulture, Fishery, House making, Weaving and Others (household) to make tool amp itrsquos implements has been recorded.nbsp The plants are Dendrocalamus sericious Munro.(Ui), D.longifimbriatus Gamble.(Unan), D.giganteus Munro.(Marubob/Mareebob), B. tulda Roxb. (Saneibi), B. nana Roxb., B. kingiana Gamble (Watangkhoi), B.nutans Wall Ex. Munro.(Oootang) and Melocanna bambusoides Trin. (Moubi).nbsp The plants have been found to be conserved in the villages. It is believed that the long tradition of bamboo plantation has been converted to useful bio-resources of bamboo stalks in the villages
Probing gas and dust in the tidal tail of NGC 5221 with the type Ia supernova iPTF16abc
Context. Type Ia supernovae (SNe Ia) can be used to address numerous
questions in astrophysics and cosmology. Due to their well known spectral and
photometric properties, SNe Ia are well suited to study gas and dust along the
lines-of-sight to the explosions. For example, narrow Na I D and Ca II H&K
absorption lines can be studied easily, because of the well-defined spectral
continuum of SNe Ia around these features. Aims. We study the gas and dust
along the line-of-sight to iPTF16abc, which occurred in an unusual location, in
a tidal arm, 80 kpc from centre of the galaxy NGC 5221. Methods. Using a
time-series of high-resolution spectra, we examine narrow Na I D and Ca II H&K
absorption features for variations in time, which would be indicative for
circumstellar (CS) matter. Furthermore, we take advantage of the well known
photometric properties of SNe Ia to determine reddening due to dust along the
line-of-sight. Results. From the lack of variations in Na I D and Ca II H&K, we
determine that none of the detected absorption features originate from the CS
medium of iPTF16abc. While the Na I D and Ca II H&K absorption is found to be
optically thick, a negligible amount of reddening points to a small column of
interstellar dust. Conclusions. We find that the gas along the line-of-sight to
iPTF16abc is typical of what might be found in the interstellar medium (ISM)
within a galaxy. It suggests that we are observing gas that has been tidally
stripped during an interaction of NGC 5221 with one of its neighbouring
galaxies in the past years. In the future, the gas clouds could
become the locations of star formation. On a longer time scale, the clouds
might diffuse, enriching the circum-galactic medium (CGM) with metals. The gas
profile along the line-of-sight should be useful for future studies of the
dynamics of the galaxy group containing NGC 5221.Comment: 8 pages, 6 figure
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