317 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
A Broad Search for Counterrotating Gas and Stars: Evidence for Mergers and Accretion
We measure the frequency of bulk gas-stellar counterrotation in a sample of
67 galaxies drawn from the Nearby Field Galaxy Survey, a broadly representative
survey of the local galaxy population down to M_B-15. We detect 4
counterrotators among 17 E/S0's with extended gas emission (24% +8 -6). In
contrast, we find no clear examples of bulk counterrotation among 38 Sa-Sbc
spirals, although one Sa does show peculiar gas kinematics. This result implies
that, at 95% confidence, no more than 8% of Sa-Sbc spirals are bulk
counterrotators. Among types Sc and later, we identify only one possible
counterrotator, a Magellanic irregular. We use these results together with the
physical properties of the counterrotators to constrain possible origins for
this phenomenon.Comment: 19 pages, 4 figures, AJ, accepte
SIMULTANEOUS ESTIMATION AND METHOD DEVELOPMENT FOR L-CARNITINE AND METFORMIN IN HUMAN PLASMA USING LC-MS/MS
 Objectives: The objective was to develop a robust simultaneous method for quantifying L-Carnitine and metformin using liquid chromatographymass spectrometer (LCMSMS).Methods: LCMSMS method was developed considering its selectivity, sensitivity, and accuracy. Blank correction method was followed as L-Carnitineis found endogenously. Range was selected based on the Normal value for L-Carnitine and maximum concentration for metformin.Results: Rugged simultaneous method using ultra flow LC mass spectrometer for the estimation of L-Carnitine and metformin, in human plasmawith low limit of quantification and upper limit of quantification of 2.289 μg/mL and 33.675 μg/mL for L-Carnitine, 43.483 ng/ml and 639.450 ng/mlfor metformin, respectively, was developed which can be used for therapeutic drug monitoring and as a prognostic tool for Type 2 diabetes mellitus(T2DM). Extraction was optimized using Protein precipitation (PP) in which sample clean-up was simple, and recovery was consistent. Linearity waschecked and found to be within acceptance criteria with 1/×2 as the weighing factor. As L-Carnitine is present endogenously blank correction wascarried by injecting blank six times and calculated for normalization. As the extraction is by simple PP internal standard was not used, and method ismeeting the criteria for validation using LCMSMS.Conclusion: Hence, considering L-Carnitine as the biomarker for T2DM and metformin as the drug for treatment, a simultaneous method wasdeveloped which can be validated as per regulatory requirements and can be verified for the applicability of the method as a therapeutic drugmonitoring and prognostic tool.Keywords: L-Carnitine, Metformin, Type 2 diabetes, Liquid chromatography mass spectrometer
A Quick, Cost-Free Method of Purification of DNA Fragments from Agarose Gel
In this short communication we report a quick, cost-free method of purification of DNA fragments from agarose gel. Unlike those procedures that involve commercial kits, this method uses glass wool or absorbent cotton to filter agarose gel during a quick spinning-down of DNA, thus significantly simplifying the routine practice of many molecular biologists and decreasing the cost
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
Physical Sources of Scatter in the Tully-Fisher Relation
We analyze residuals from the Tully-Fisher relation for the emission-line
galaxies in the Nearby Field Galaxy Survey, a broadly representative survey
designed to fairly sample the variety of galaxy morphologies and environments
in the local universe. For spirals brighter than M_R^i=-18, we find strong
correlations between Tully-Fisher residuals and both B-R color and EW(Halpha).
The extremes of the correlations are populated by Sa galaxies, which show
consistently red colors, and spirals with morphological peculiarities, which
are often blue. If we apply an EW(Halpha)-dependent or B-R color-dependent
correction term to the Tully-Fisher relation, the scatter in the relation no
longer increases from R to B to U but instead drops to a nearly constant level
close to the scatter we expect from measurement errors. We argue that these
results probably reflect correlated offsets in luminosity and color as a
function of star formation history. Broadening the sample in morphology and
luminosity, we find that most non-spirals brighter than M_R^i=-18 follow the
same correlations as do spirals, albeit with greater scatter. However, the
color and EW(Halpha) correlations do not apply to galaxies fainter than
M_R^i=-18 or to emission-line S0 galaxies with anomalous gas kinematics. For
the dwarf galaxy population, the parameters controlling Tully-Fisher residuals
are instead related to the degree of recent disturbance: overluminous dwarfs
have higher rotation curve asymmetries, brighter U-band effective surface
brightnesses, and shorter gas consumption timescales than their underluminous
counterparts. As a result, sample selection strongly affects the measured
faint-end slope of the Tully-Fisher relation. Passively evolving, rotationally
supported galaxies display a break toward steeper slope at low luminosities.Comment: 58 pages including 21 figures, AJ, accepte
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
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