114 research outputs found
Molecular dynamics study on structural relaxation of metallic glasses
Abstract. Structural relaxation process in the Zr-Cu metallic glasses is investigated by using molecular dynamics simulations. The enthalpy change in isothermal annealing of the glassy state cannot be fitted by a simple exponential function but obeys a stretched exponential function, which indicates that the relaxation in glassy phase is not a single Debye type process. A close examination of individual atomic motion reveals that the enthalpy relaxation is related to a string-like cooperative motion of atoms. The analysis of the local symmetry around each atom shows that a network of the icosahedral clusters grows in the glassy phases during annealing and it closely relates to the free-volume annihilation in the structural relaxation
The early early type: discovery of a passive galaxy at z=3
We present the discovery of a massive, quiescent galaxy at z=2.99. We have
obtained a HST/WFC3 spectrum of this object and measured its redshift from the
detection of a deep 4000A break consistent with an old population and a high
metallicity. By stellar population modeling of both its grism spectrum and
broad-band photometry, we derive an age of ~0.7 Gyr, implying a formation
redshift of z>4, and a mass >10^11 Msun. Although this passive galaxy is the
most distant confirmed so far, we find that it is slightly less compact than
other z>2 early-types of similar mass, being overall more analogous to those
z~1.6 field early-type galaxies. The discovery of this object shows that
early-type galaxies are detectable to at least z=3 and suggests that the
diversity of structural properties found in z=1.4-2 ellipticals to earlier
epochs could have its origin in a variety of formation histories among their
progenitors.Comment: 6 pages, 4 figures, 1 table. Accepted for publication in The
Astrophysical Journal Letter
WFC3 grism confirmation of the distant cluster Cl J1449+0856 at z=2.00: Quiescent and star-forming galaxy populations
We present deep Hubble Space Telescope Wide Field Camera 3 slitless
spectroscopic observations of the distant cluster Cl J1449+0856. These cover a
single pointing with 18 orbits of G141 spectroscopy and F140W imaging, allowing
us to derive secure redshifts down to m_140~25.5 AB and 3sigma line fluxes of
5*10^(-18) erg/s/cm^2. In particular, we were able to spectroscopically confirm
12 early-type galaxies in the field up to z~3, 6 of which in the cluster core,
which represents the first direct spectroscopic confirmation of passive
galaxies in a z=2 cluster environment. With 140 redshifts in a ~6 arcmin^2
field, we can trace the spatial and redshift galaxy distribution in the cluster
core and background field. We find two strong peaks at z=2.00 and z=2.07, where
only one was seen in our previously published ground-based data. Thanks to the
spectroscopic confirmation of the cluster ETGs, we can now re-evaluate the
redshift of Cl J1449+0856 at z=2.00, rather than z=2.07, with the background
overdensity being revealed to be sparse and "sheet"-like. This presents an
interesting case of chance alignment of two close yet unrelated structures,
each one preferentially selected by different observing strategies. With 6
quiescent or early-type spectroscopic members and 20 star-forming ones, Cl
J1449+0856 is now reliably confirmed to be at z=2.00. The identified members
can now allow for a detailed study of galaxy properties in the densest
environment at z=2.Comment: 12 pages, 13 figure
MOIRCS Deep Survey. X. Evolution of Quiescent Galaxies as a Function of Stellar Mass at 0.5<z<2.5
We study the evolution of quiescent galaxies at 0.5<z<2.5 as a function of
stellar mass, using very deep NIR imaging data taken with the Multi-Object
Infrared Camera and Spectrograph on the Subaru Telescope in the GOODS-North
region. The deep NIR data allow us to construct a stellar mass-limited sample
of quiescent galaxies down to ~10^{10} Msun even at z~2 for the first time. We
selected quiescent galaxies with age/tau>6 by performing SED fitting of the
multi broad-band photometry from the U to Spitzer 5.8um bands with the
population synthesis model of Bruzual & Charlot (2003) where exponentially
decaying star formation histories are assumed. The number density of quiescent
galaxies increases by a factor of ~3 from 1.0<z<1.5 to 0.5<z<1.0, and by a
factor of ~10 from 1.5<z<2.5 to 0.5<z<1.0, while that of star-forming galaxies
with age/tau<4 increases only by factors of ~2 and ~3 in the same redshift
ranges. At 0.5<z<2.5, the low-mass slope of the stellar mass function of
quiescent galaxies is alpha ~ 0 -- 0.6, which is significantly flatter than
those of star-forming galaxies (alpha ~ -1.3 -- -1.5). As a result, the
fraction of quiescent galaxies in the overall galaxy population increases with
stellar mass in the redshift range. The fraction of quiescent galaxies at
10^{11}-10^{11.5} Msun increases from ~20-30% at z~2 to ~40-60% at z~0.75,
while that at 10^{10}-10^{10.5} Msun increases from <~ 5% to ~15% in the same
redshift range. These results could suggest that the quenching of star
formation had been more effective in more massive galaxies at 1<~z<~2. Such a
mass-dependent quenching could explain the rapid increase of the number density
of ~M* galaxies relative to lower-mass galaxies at z >~ 1-1.5.Comment: 12 pages, 7 figures, accepted for publication in PASJ (Subaru special
issue). Updated to accepted versio
MOIRCS Deep Survey. VII: NIR Morphologies of Star-forming Galaxies at Redshift z~1
We investigate rest-frame near-infrared (NIR) morphologies of a sample of 139
galaxies with M_{s} >= 1 x 10^{10} M_{sun} at z=0.8-1.2 in the GOODS-North
field using our deep NIR imaging data (MOIRCS Deep Survey, MODS). We focus on
Luminous Infrared Galaxies (LIRGs), which dominate high star formation rate
(SFR) density at z~1, in the sample identified by cross-correlating with the
Spitzer/MIPS 24um source catalog. We perform two-dimensional light profile
fitting of the z~1 galaxies in the Ks-band (rest-frame J-band) with a single
component Sersic model. We find that at z~1, ~90% of LIRGs have low Sersic
indices (n<2.5, similar to disk-like galaxies) in the Ks-band, and those
disk-like LIRGs consist of ~60% of the whole disk-like sample above M_{s} >= 3
x 10^{10} M_{sun}. The z~1 disk-like LIRGs are comparable or ~20% small at a
maximum in size compared to local disk-like galaxies in the same stellar mass
range. If we examine rest-frame UV-optical morphologies using the HST/ACS
images, the rest-frame B-band sizes of the z~1 disk-like galaxies are
comparable to those of the local disk-like galaxies as reported by previous
studies on size evolution of disk-like galaxies in the rest-frame optical band.
Measuring color gradients (galaxy sizes as a function of wavelength) of the z~1
and local disk-like galaxies, we find that the z~1 disk-like galaxies have 3-5
times steeper color gradient than the local ones. Our results indicate that (i)
more than a half of relatively massive disk-like galaxies at z~1 are in violent
star formation epochs observed as LIRGs, and also (ii) most of those LIRGs are
constructing their fundamental disk structure vigorously. The high SFR density
in the universe at z~1 may be dominated by such star formation in disk region
in massive galaxies.Comment: 16 pages, 15 figures, accepted for publication in PASJ. Catalog data
will be available at http://astr.tohoku.ac.jp/MODS/wiki/index.php soo
Pregabalin- and azithromycin-induced rhabdomyolysis with purpura: An unrecognized interaction: A case report
AbstractIntroductionRhabdomyolysis associated with the use of pregabalin or azithromycin has been demonstrated to be a rare but potentially life-threatening adverse event. Here, we report an extremely rare case of rhabdomyolysis with purpura in a patient who had used pregabalin and azithromycin.Presentation of caseWe present the case of a 75-year-old woman with a history of fibromyalgia who was admitted with mild limb weakness and lower abdominal purpura. She was prescribed pregabalin (75mg, twice daily) for almost 3 months to treat chronic back pain. Her medical history revealed that 3days before admission, she began experiencing acute bronchitis and was treated with a single dose of azithromycin (500mg). She had developed rapid onset severe myalgia, mild whole body edema, muscle weakness leading to gait instability, abdominal purpura and tender purpura on the lower extremities. Laboratory values included a white blood cell count of 25,400/mL and a creatinine phosphokinase (CPK) concentration of 1250 IU/L. Based on these findings and the patient’s clinical history, a diagnosis of pregabalin- and azithromycin-induced rhabdomyolysis was made.DiscussionThe long-term use of pregabalin and the initiation azithromycin therapy followed by a rapid onset of rhabdomyolysis is indicative of a drug interaction between pregabalin and azithromycin.ConclusionWe report an extremely rare case of rhabdomyolysis with purpura caused by a drug interaction between pregabalin and azithromycin. However, the mechanisms of the interactions between azithromycin on the pregabalin are still unknown
MOIRCS Deep Survey V: A Universal Relation for Stellar Mass and Surface Brightness of Galaxies
We present a universal linear correlation between the stellar mass and
surface brightness (SB) of galaxies at 0.3<z<3, using a deep K-band selected
catalog in the GOODS-North region. The correlation has a nearly constant slope,
independent of redshift and color of galaxies in the rest-z frame. Considering
unresolved compact galaxies, the tight correlation gives a lower boundary of SB
for a given stellar mass; lower SB galaxies are prohibited over the boundary.
The universal slope suggests that the stellar mass in galaxies was build up
over their cosmic histories in a similar manner irrelevant to galaxy mass, as
oppose to the scenario that massive galaxies mainly accumulated their stellar
mass by major merging. In contrast, SB shows a strong dependence on redshift
for a given stellar mass. It evolves as (1+z)^(-2.0~-0.8), in addition to
dimming as (1+z)^4 by the cosmological expansion effect. The brightening
depends on galaxy color and stellar mass. The blue population (rest-frame
U-V<0), which is dominated by young and star-forming galaxies, evolves as
~(1+z)^(-0.8 +-0.3) in the rest-V band. On the other hand, the red population
(U-V>0) and the massive galaxies (M_*>10^(10)M_sun) shows stronger brightening,
(1+z)^(-1.5+-0.1). Based on the comparison with galaxy evolution models, we
find that the phenomena are well explained by the pure luminosity evolution of
galaxies out to z~3.Comment: 10 pages, 9 figures. Accepted for publication in Ap
A proto-cluster of massive quiescent galaxies at z=4
We report on discovery of a concentration of massive quiescent galaxies
located at z=4. The concentration is first identified using high-quality
photometric redshifts based on deep, mutli-band data in Subaru/XMM-Newton Deep
Field. Follow-up near-infrared spectroscopic observations with MOSFIRE on Keck
confirm a massive (~10^{11} Msun) quiescent galaxy at z=3.99. Our spectral
energy distribution (SED) analyses reveal that the galaxy experienced an
episode of starburst about 500 Myr prior to the observed epoch, followed by
rapid quenching. As its spectrum is sufficiently good to measure the stellar
velocity dispersion, we infer its dynamical mass and find that it is consistent
with its stellar mass. The galaxy is surrounded by 4 massive (>10^{10} Msun)
quiescent galaxies on a ~1 physical Mpc scale, all of which are consistent with
being located at the same redshift based on high-accuracy spectro-photometric
redshifts. This is likely a (proto-)cluster dominated by quiescent galaxies,
the first of the kind reported at such a high redshift as z=4. Interestingly,
it is in a large-scale structure revealed by spectroscopic redshifts from
VANDELS. Furthermore, it exhibits the red sequence, adding further support to
the physical concentration of the galaxies. We find no such concentration in
the Illustris-TNG300 simulation; it may be that the cluster is such a rare
system that the simulation box is not sufficiently large to reproduce it. The
total halo mass of the quiescent galaxies is ~10^{13} Msun, suggesting that
they form a group-sized halo once they collapse together. We discuss
implications of our findings for the quenching physics and conclude with future
prospects.Comment: 16 pages, 12 figures, submitted to Ap
- …