225 research outputs found
A Search For Star Formation in the Smith Cloud
Motivated by the idea that a subset of HVCs trace dark matter substructure in
the Local Group, we search for signs of star formation in the Smith Cloud, a
nearby ~2x10^6 Msun HVC currently falling into the Milky Way. Using GALEX NUV
and WISE/2MASS NIR photometry, we apply a series of color and apparent
magnitude cuts to isolate candidate O and B stars that are plausibly associated
with the Smith Cloud. We find an excess of stars along the line of sight to the
cloud, but not at a statistically significant level relative to a control
region. The number of stars found in projection on the cloud after removing an
estimate of the contamination by the Milky Way implies an average star
formation rate surface density of 10^(-4.8 +/- 0.3) Msun yr^(-1) kpc^(-2),
assuming the cloud has been forming stars at a constant rate since its first
passage through the Milky Way ~70 Myr ago. This value is consistent with the
star formation rate expected based on the average gas density of the cloud. We
also discuss how the newly discovered star forming galaxy Leo P has very
similar properties to the Smith Cloud, but its young stellar population would
not have been detected at a statistically significant level using our method.
Thus, we cannot yet rule out the idea that the Smith Cloud is really a dwarf
galaxy.Comment: 9 pages, 7 figures, accepted for publication in MNRA
Antibacterial effect of the Indian squid, Loligo duvauceli (d'Orbigny), ink
The ink of the Indian squid Loligo duvauceli (d'Orbigny) was tested for antibacterial activity. The antibacterial effect of bacteria present in the ink gland was also tested. Only one type of bacteria was found to be present in the ink gland of squid and was identified as Photobacterium leiognathi. Among the various forms of ink extracts, the precipitated and freeze-dried ink showed more pronounced antibacterial effect against Gram-negative bacteria, Salmonella, spp. Escherichia coli, Vibrio cholerae, V. parahaemolyticus and Pseudoinonas spp., and a less pronounced effect against Gram-positive bacteria, Staphylococcus spp. and Micrococcus spp., P. leiognathi did not inhibit any of the above bacteria. The antibacterial activity was associated with the compounds of the ink
Ultrasonic and Spectral Studies on Hydrogen Bonded Complexes of Aromatic Aldehydes and N-Methylaniline in n-Hexane
Ultrasonic and UV-spectral studies have been carried out for three ternary systems containing N-methylaniline (NMANI) and three structurally different aromatic aldehydes, benzaldehyde (BA), cinnamaldehyde (CA) and salicylaldehyde(SA) in n-hexane medium at 303.15 K and at atmospheric pressure. Acoustical parameters are computed from the measured values of ultrasonic velocity, density and dynamic viscosity. The variation of acoustical parameters in the concentration range investigated establishes complex formation through intermolecular hydrogen bonding between aldehyde and N-methylaniline. The existence of strong aldehyde-amine interaction is also confirmed through the recorded UV-Visible absorption spectra with Benesi-Hildebrand theory at 303.15 K. The formation constants of the hydrogen bonded complexes are determined by spectroscopic and ultrasonic methods and compared. These values computed by two different methods are comparable and follow similar trend. The trend in the formation constants is discussed based on structures of the component molecules and correlate with computed molecular propertie
The Fueling Diagram: Linking Galaxy Molecular-to-Atomic Gas Ratios to Interactions and Accretion
To assess how external factors such as local interactions and fresh gas
accretion influence the global ISM of galaxies, we analyze the relationship
between recent enhancements of central star formation and total
molecular-to-atomic (H2/HI) gas ratios, using a broad sample of field galaxies
spanning early-to-late type morphologies, stellar masses of 10^(7.2-11.2) Msun,
and diverse stages of evolution. We find that galaxies occupy several loci in a
"fueling diagram" that plots H2/HI vs. mass-corrected blue-centeredness, a
metric tracing the degree to which galaxies have bluer centers than the average
galaxy at their stellar mass. Spiral galaxies show a positive correlation
between H2/HI and mass-corrected blue-centeredness. When combined with previous
results linking mass-corrected blue-centeredness to external perturbations,
this correlation suggests a link between local galaxy interactions and
molecular gas inflow/replenishment. Intriguingly, E/S0 galaxies show a more
complex picture: some follow the same correlation, some are quenched, and a
distinct population of blue-sequence E/S0 galaxies (with masses below key
transitions in gas richness) defines a separate loop in the fueling diagram.
This population appears to be composed of low-mass merger remnants currently in
late- or post-starburst states, in which the burst first consumes the H2 while
the galaxy center keeps getting bluer, then exhausts the H2, at which point the
burst population reddens as it ages. Multiple lines of evidence suggest
connected evolutionary sequences in the fueling diagram. In particular,
tracking total gas-to-stellar mass ratios within the diagram provides evidence
of fresh gas accretion onto low-mass E/S0s emerging from central starbursts.
Drawing on a comprehensive literature search, we suggest that virtually all
galaxies follow the same evolutionary patterns found in our broad sample.Comment: 24 pages, 11 figures (table 4 available at
http://user.physics.unc.edu/~dstark/table4_csv.txt), accepted for publication
in Ap
ECO and RESOLVE: Galaxy Disk Growth in Environmental Context
We study the relationships between galaxy environments and galaxy properties
related to disk (re)growth, considering two highly complete samples that are
approximately baryonic mass limited into the high-mass dwarf galaxy regime, the
Environmental COntext (ECO) catalog (data release herein) and the B-semester
region of the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey. We
quantify galaxy environments using both group identification and smoothed
galaxy density field methods. We use by-eye and quantitative morphological
classifications plus atomic gas content measurements and estimates. We find
that blue early-type (E/S0) galaxies, gas-dominated galaxies, and UV-bright
disk host galaxies all become distinctly more common below group halo mass
~10^11.5 Msun, implying that this low group halo mass regime may be a preferred
regime for significant disk growth activity. We also find that blue early-type
and blue late-type galaxies inhabit environments of similar group halo mass at
fixed baryonic mass, consistent with a scenario in which blue early types can
regrow late-type disks. In fact, we find that the only significant difference
in the typical group halo mass inhabited by different galaxy classes is for
satellite galaxies with different colors, where at fixed baryonic mass red
early and late types have higher typical group halo masses than blue early and
late types. More generally, we argue that the traditional
morphology-environment relation (i.e., that denser environments tend to have
more early types) can be largely attributed to the morphology-galaxy mass
relation for centrals and the color-environment relation for satellites.Comment: 26 pages and 28 figures; v2 contains minor figure and text updates to
match final published version in ApJ; ECO data table release now available at
http://resolve.astro.unc.edu/pages/data.ph
Excess Isentropic Compressibility and Computation of Sound Velocity Internary Liquid Mixtures
A Simple Approach to the Synthesis of Hexagonal-Shaped Silver Nanoplates
This paper deals with the synthesis of hexagonal-shaped silver nanoplates with diameters ranging from 15 to 20 nm along with a smooth nanobulk of 120 nm. These nanoplates were prepared by a kinetically controlled solution growth method using mild reducing agent dextrose, polyvinylpyrrolidone (PVP Mw 40 k Da) as the capping agent and urea as a habit modifier and at a moderate temperature of 50°C. The crystal structure of the highly faceted particles consists mostly of (111) surfaces as revealed by both X-ray diffraction (XRD) studies and transmission electron microscopy (TEM)
Two more disk galaxies with global gas counterrotation
We report a discovery of extended counterrotating gaseous disks in early-type
disk galaxies NGC 2551 and NGC 5631. To find them, we have undertaken complex
spectral observations including integral-field spectroscopy for the central
parts of the galaxies and long-slit deep spectroscopy to probe the external
parts. The line-of-sight velocity fields have been constructed and compared to
the photometric structure of the galaxies. As a result, we have revealed
full-size counterrotating gaseous disks, the one coplanar to the stellar disk
in NGC 2551 and the other inclined to the main stellar disk in NGC 5631. We
suggest that we observe the early stages of minor-merger events which may be
two different stages of the process of lenticular galaxy formation in rather
sparse environments.Comment: 8 pages, 8 EPS figures, accepted for publication in Ap
Synthesis of Silver Nanoparticles Using Curcumin-Cyclodextrins Loaded into Bacterial Cellulose-Based Hydrogels for Wound Dressing Applications.
Chronic wounds are often recalcitrant to treatment because of high microbial bioburden and the problem of microbial resistance. Silver is a broad-spectrum natural antimicrobial agent with wide applications extending to proprietary wound dressings. Recently, silver nanoparticles have attracted attention in wound management. In the current study, the green synthesis of nanoparticles was accomplished using a natural reducing agent, curcumin, which is a natural polyphenolic compound that is well-known as a wound-healing agent. The hydrophobicity of curcumin was overcome by its microencapsulation in cyclodextrins. This study demonstrates the production, characterization of silver nanoparticles using aqueous curcumin:hydroxypropyl-β-cyclodextrin complex and loading them into bacterial cellulose hydrogel with moist wound-healing properties. These silver nanoparticle-loaded bacterial cellulose hydrogels were characterized for wound-management applications. In addition to high cytocompatibility, these novel dressings exhibited antimicrobial activity against three common wound-infecting pathogenic microbes , , and
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