109 research outputs found

    Molecular dynamics study on structural relaxation of metallic glasses

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    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

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    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

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    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

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    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

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    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

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    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

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    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

    Compact, bulge dominated structures of spectroscopically confirmed quiescent galaxies at z~3

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    We study structural properties of spectroscopically confirmed massive quiescent galaxies at z‚Čą3z\approx 3 with one of the first sizeable samples of such sources, made of ten 10.8<log‚Ā°(M‚čÜ/M‚äô)<11.310.8<\log(M_{\star}/M_{\odot})<11.3 galaxies at 2.4<z<3.22.4 < z < 3.2 in the COSMOS field whose redshifts and quiescence are confirmed by HST grism spectroscopy. Although affected by a weak bias toward younger stellar populations, this sample is deemed to be largely representative of the majority of the most massive and thus intrinsically rarest quiescent sources at this cosmic time. We rely on targeted HST/WFC3 observations and fit S\'ersic profiles to the galaxy surface brightness distributions at ‚Čą4000\approx 4000 angstrom restframe. We find typically high S\'ersic indices and axis ratios (medians ‚Čą4.5\approx 4.5 and 0.730.73, respectively) suggesting that, at odds with some previous results, the first massive quiescent galaxies may largely be already bulge-dominated systems. We measure compact galaxy sizes with an average of ‚Čą1.4\approx 1.4kpc at log‚Ā°(M‚čÜ/M‚äô)‚Čą11.2\log(M_{\star}/M_{\odot})\approx 11.2, in good agreement with the extrapolation at the highest masses of previous determinations of the stellar mass - size relation of quiescent galaxies, and of its redshift evolution, from photometrically selected samples at lower and similar redshifts. This work confirms the existence of a population of compact, bulge dominated, massive, quiescent sources at z‚Čą3z\approx 3, providing one of the first statistical estimates of their structural properties, and further constraining the early formation and evolution of the first quiescent galaxies.Comment: 19 pages, 10 figures. Accepted for publication in MNRA
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