90 research outputs found
Structure of the Milky Way stellar halo out to its outer boundary with blue horizontal-branch stars
We present the structure of the Milky Way stellar halo beyond Galactocentric
distances of kpc traced by blue horizontal-branch (BHB) stars, which
are extracted from the survey data in the Hyper Suprime-Cam Subaru Strategic
Program (HSC-SSP). We select BHB candidates based on photometry,
where the -band is on the Paschen series and the colors that involve the
-band are sensitive to surface gravity. About 450 BHB candidates are
identified between kpc and 300 kpc, most of which are beyond the reach
of previous large surveys including the Sloan Digital Sky Survey. We find that
the global structure of the stellar halo in this range has substructures, which
are especially remarkable in the GAMA15H and XMM-LSS fields in the HSC-SSP. We
find that the stellar halo can be fitted to a single power-law density profile
with an index of () with (without) these fields and
its global axial ratio is (). Thus, the stellar halo may be
significantly disturbed and be made in a prolate form by halo substructures,
perhaps associated with the Sagittarius stream in its extension beyond kpc. For a broken power-law model allowing different power-law indices
inside/outside a break radius, we obtain a steep power-law slope of outside a break radius of kpc ( kpc) for the case
with (without) GAMA15H and XMM-LSS. This radius of kpc might be as close
as a halo boundary if there is any, although larger BHB sample is required from
further HSC-SSP survey to increase its statistical significance.Comment: 12 pages, 8 figures, revised version, accepted for publication in
PAS
Plasma ropivacaine concentration after TAP block in a patient with cardiac and renal failure
We report a successful ultrasound-guided transversus abdominis plane (TAP) block as an analgesic option for minor abdominal surgery in a 66-year-old patient with cardiac, respiratory, and renal dysfunction caused by primary systemic amyloidosis. Bilateral TAP blocks with 120 mg (1.8 mg/kg) of ropivacaine provided sufficient intra- and postoperative analgesia for insertion of a continuous ambulatory peritoneal dialysis catheter. However, the plasma concentration of ropivacaine reached a maximum of 2.5 mu g/mL at 15 minutes after the TAP block, a concentration that was potentially neurotoxic. Although apparent signs of local anesthetic systemic toxicity (LAST) such as convulsion or changes in an electrocardiogram were not observed, the patient became drowsy after the TAP block, which might be one of the mild symptoms of LAST. A TAP block by itself can thus be an anesthetic option for patients undergoing minor abdominal surgery. However, cardiac and renal dysfunction might influence the pharmacokinetics of a local anesthetic used, and attention should he paid to the possibility of LAST even with a low dose of a local anesthetic for patients with cardiac and renal failure.ArticleLOCAL AND REGIONAL ANESTHESIA.11:57-60(2018)journal articl
Interparticle normal force in highly porous granular matter during compression
We perform a numerical simulation of compression of a highly porous dust
aggregate of monodisperse spheres. We find that the average interparticle
normal force within the aggregate is inversely proportional to both the filling
factor and the average coordination number, and we also derive this relation
theoretically. Our findings would be applicable for granular matter of
arbitrary structures, as long as the constituent particles are monodisperse
spheres.Comment: 9 pages, 7 figures. Accepted for publication in PR
Searches for New Milky Way Satellites from the First Two Years of Data of the Subaru/Hyper Suprime-Cam Survey: Discovery of Cetus~III
We present the results from a search for new Milky Way (MW) satellites from
the first two years of data from the Hyper Suprime-Cam (HSC) Subaru Strategic
Program (SSP) ~deg and report the discovery of a highly
compelling ultra-faint dwarf galaxy candidate in Cetus. This is the second
ultra-faint dwarf we have discovered after Virgo~I reported in our previous
paper. This satellite, Cetus~III, has been identified as a statistically
significant (10.7) spatial overdensity of star-like objects, which are
selected from a relevant isochrone filter designed for a metal-poor and old
stellar population. This stellar system is located at a heliocentric distance
of 251~kpc with a most likely absolute magnitude of ~mag estimated from a Monte Carlo analysis. Cetus~III is extended with
a half-light radius of ~pc, suggesting that this is a
faint dwarf satellite in the MW located beyond the detection limit of the Sloan
Digital Sky Survey. Further spectroscopic studies are needed to assess the
nature of this stellar system. We also revisit and update the parameters for
Virgo~I finding ~mag and ~pc. Using simulations of -dominated cold dark matter
models, we predict that we should find one or two new MW satellites from ~deg HSC-SSP data, in rough agreement with the discovery rate so far.
The further survey and completion of HSC-SSP over ~deg will
provide robust insights into the missing satellites problem.Comment: 12 pages, 12 figures, accepted for publication in PASJ special issu
Global Properties of M31's Stellar Halo from the SPLASH Survey: III. Measuring the Stellar Velocity Dispersion Profile
We present the velocity dispersion of red giant branch (RGB) stars in M31's
halo, derived by modeling the line of sight velocity distribution of over 5000
stars in 50 fields spread throughout M31's stellar halo. The dataset was
obtained as part of the SPLASH (Spectroscopic and Photometric Landscape of
Andromeda's Stellar Halo) Survey, and covers projected radii of 9 to 175 kpc
from M31's center. All major structural components along the line of sight in
both the Milky Way (MW) and M31 are incorporated in a Gaussian Mixture Model,
including all previously identified M31 tidal debris features in the observed
fields. The probability an individual star is a constituent of M31 or the MW,
based on a set of empirical photometric and spectroscopic diagnostics, is
included as a prior probability in the mixture model. The velocity dispersion
of stars in M31's halo is found to decrease only mildly with projected radius,
from 108 km/s in the innermost radial bin (8.2 to 14.1 kpc) to to 90
km/s at projected radii of to 130 kpc, and can be parameterized with
a power-law of slope . The quoted uncertainty on the power-law
slope reflects only the precision of the method, although other sources of
uncertainty we consider contribute negligibly to the overall error budget.Comment: Submitted to the Astrophysical Journa
Stellar Stream and Halo Structure in the Andromeda Galaxy From a Subaru/Hyper Suprime-Cam Survey
We present wide and deep photometry of the northwest part of the halo of the
Andromeda galaxy (M31) using Hyper Suprime-Cam on the Subaru Telescope. The
survey covers 9.2 deg field in the , , and bands and shows
a clear red giant branch (RGB) of M31's halo stars and a pronounced red clump
(RC) feature. The spatial distribution of RC stars shows a prominent stream
feature, the North Western (NW) Stream, and a diffuse substructure in the south
part of our survey field. We estimate the distances based on the RC method and
obtain = 24.63(random)(systematic) and 24.29(random)(systematic) mag for the NW stream and diffuse
substructure, respectively, implying that the NW Stream is located behind M31,
whereas the diffuse substructure is located in front. We also estimate
line-of-sight distances along the NW Stream and find that the south part of the
stream is 20 kpc closer to us relative to the north part. The distance to
the NW Stream inferred from the isochrone fitting to the color-magnitude
diagram favors the RC-based distance, but the TRGB-based distance estimated for
-selected RGB stars does not agree with it. The surface number density
distribution of RC stars across the NW Stream is found to be approximately
Gaussian with a FWHM of 25 arcmin (5.7 kpc), with a slight skew to the
south-west side. That along the NW Stream shows a complicated structure
including variations in number density and a significant gap in the stream.Comment: 24 pages, 18 figures, accepted for publication in Ap
A New Milky Way Satellite Discovered In The Subaru/Hyper Suprime-Cam Survey
We report the discovery of a new ultra-faint dwarf satellite companion of the
Milky Way based on the early survey data from the Hyper Suprime-Cam Subaru
Strategic Program. This new satellite, Virgo I, which is located in the
constellation of Virgo, has been identified as a statistically significant (5.5
sigma) spatial overdensity of star-like objects with a well-defined main
sequence and red giant branch in their color-magnitude diagram. The
significance of this overdensity increases to 10.8 sigma when the relevant
isochrone filter is adopted for the search. Based on the distribution of the
stars around the likely main sequence turn-off at r ~ 24 mag, the distance to
Virgo I is estimated as 87 kpc, and its most likely absolute magnitude
calculated from a Monte Carlo analysis is M_V = -0.8 +/- 0.9 mag. This stellar
system has an extended spatial distribution with a half-light radius of 38
+12/-11 pc, which clearly distinguishes it from a globular cluster with
comparable luminosity. Thus, Virgo I is one of the faintest dwarf satellites
known and is located beyond the reach of the Sloan Digital Sky Survey. This
demonstrates the power of this survey program to identify very faint dwarf
satellites. This discovery of VirgoI is based only on about 100 square degrees
of data, thus a large number of faint dwarf satellites are likely to exist in
the outer halo of the Milky Way.Comment: typos are corrected, 6 pages, 4 figures, accepted for publication in
Ap
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