arXiv subjects

Yoshihisa Suzuki

Publications and source records attributed to Yoshihisa Suzuki.

17 recordsLinked to original sources

arXiv2026

Galactic Archaeology with the Subaru `Ōnohi`ula Prime Focus Spectrograph Strategic Program

The recently commissioned Subaru `Ōnohi`ula Prime Focus Spectrograph (PFS) will obtain spectra from nearly 2,400 fibers that cover 1.24 square degrees. The 360 night Subaru Strategic Program for PFS is dedicating approximately one-third of its allocation (130 nights) to study the structure and evolution of galaxies in the Local Group. This Galactic Archaeological survey has three pillars. (1) We will determine whether the mass density profiles of dwarf galaxies are consistent with cusps, as expected for cold dark matter, or cores, as expected from alternative dark matter theories or baryonic feedback. We will deduce the density profiles as a function of radius from modeling of the full line-of-sight velocity and abundance distributions for six dwarf galaxies. Our total sample will consist of 18,000 member stars to beyond the nominal tidal radius of each system. (2) From measurements of the [alpha/Fe] abundance ratio, we will learn the difference in assembly history of the two most massive galaxies in the Local Group: M31 and the Milky Way. We will observe 30,000 member stars over 45 square degrees of M31's halo and outer disk. (3) We will uncover how the most fragile (outer) part of the Milky Way responded to accretion events both in the distant past (such as Gaia-Sausage Enceladus) and in more recent history (such as the Sagittarius dwarf spheroidal galaxy). To support this study, PFS will provide velocities and metallicities--from which, in combination with photometry, we will deduce ages--for tens of thousands of main-sequence stars out to a Galactocentric distance of ~30 kpc.

astro-ph.GA↗

arXiv2026

The Milky Way Tomography with Subaru Hyper Suprime-Cam. II. Global halo structure

We investigate the structure of the Milky Way's stellar halo within 70 kpc of the Sun using a wide-field photometric catalog obtained from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP). We employ a large sample of main-sequence turn-off stars as distance tracers. To robustly derive the structural parameters of the stellar halo, we develop a forward-modeling framework that explicitly accounts for distance uncertainties, the solar position, and the limited sky coverage of the survey. Applying this method to the HSC-SSP catalog, we found that the smooth stellar halo is well described by a double power-law density profile, with inner and outer slope of approximately -3.3 and -4.8, respectively, with a break radius of 17.4 kpc. The outer steep density slope derived in this work supports a picture in which the present-day structure of the Milky Way's stellar halo is influenced by early massive accretion events, consistent with inferences from kinematic substructures such as Gaia Enceladus/Sausage. Ongoing wide-field imaging surveys, including UNIONS and LSST, will provide further constraints on the structure of the stellar halo and key insights into its formation history.

astro-ph.GA↗

arXiv2026

The Milky Way Tomography with Subaru Hyper Suprime-Cam: Implications for the past orbit of the Large Magellanic Cloud

We report the discovery of diffuse stellar substructure in the Milky Way's outer halo toward Boötes, unveiled by deep imaging data of the Subaru/Hyper Suprime-Cam. This substructure is detected as an excess of faint main-sequence stars, at heliocentric distances beyond 30 kpc, extending over at least 100 $\mathrm{deg^2}$. To infer its origin, we compare the projected spatial distribution of these stars to that of simulated tidal debris from the Large Magellanic Cloud (LMC), under the assumptions that the LMC is on either its first or second passage of the Milky Way. We found that the observed overdensity lies in a region of the halo where debris from the LMC is expected if it is on its initial pericentric phase 7-8 Gyr ago, which is predicted in the second-passage model, while the first-passage model is unable to explain the observed substructure. Chemo-kinematical data are required to further constrain its past orbit and to understand the origin of this new halo substructure, as should be obtained in the near future with deep photometric surveys such as UNIONS and LSST, and wide-field spectroscopy such as possible with PFS and DESI.

astro-ph.GA↗

arXiv2026

A Long Stellar Stream in M83: Possible Connection Between XUV Disks and Minor Mergers?

We present the confirmation and characterization of a long stream (S-stream) in the southern part of M83. This feature is revealed using deep wide-field photometric data obtained by the Hyper Suprime-Cam (HSC) mounted on the Subaru Telescope. Using individual red giant branch (RGB) stars, we successfully trace the stream over a large length of $\sim 81$~kpc and a considerable width of $\sim 9$ kpc. With a mean surface brightness of ${\langle μ_{\it V} \rangle} \sim 31.8_{-1.9}^{+1.3}$ mag arcsec$^{-2}$, it is one of the most diffuse extragalactic streams currently known. The mean photometric metallicity of the stream is $\langle[{\rm M/H}]\rangle = -1.23\pm0.02$ dex with a standard deviation of $0.28\pm0.01$ dex, and we estimate the stellar mass to be $(8.5_{-2.8}^{+4.2}) \times 10^6~{\rm M_\odot}$ from the luminosity of RGB stars. Compared to its well-known northern counterpart, the S-stream is slightly more metal-poor, but our large-area RGB map shows compelling evidence that these two features are related, originating from a single low-mass merger event. We identify density variations along the S-stream, which more likely reflect intrinsic density structure within the progenitor rather than the interaction with dark matter subhalos. Similarities between the morphology of the S-stream and some features in the \HI distribution suggest that a minor merger event may have disturbed and redistributed M83's outer \HI gas, leading to triggered star formation and the formation of the XUV disk.

astro-ph.GA↗

arXiv2025

UNIONS: The Ultraviolet Near-Infrared Optical Northern Survey

The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is a "collaboration of collaborations" that is using the Canada-France-Hawai'i Telescope, the Pan-STARRS telescopes, and the Subaru Observatory to obtain $ugriz$ images of a core survey region of 6250 deg$^2$ of the northern sky. The $10σ$ point source depth of the data, as measured within a 2-arcsecond diameter aperture, are $[u,g,r,i,z] = [23.7, 24.5, 24.2, 23.8, 23.3]$\ in AB magnitudes. UNIONS is addressing some of the most fundamental questions in astronomy, including the properties of dark matter, the growth of structure in the Universe from the very smallest galaxies to large-scale structure, and the assembly of the Milky Way. It is set to become the major ground-based legacy survey for the northern hemisphere for the next decade and provides an essential northern complement to the static-sky science of the Vera C. Rubin Observatory's Legacy Survey of Space and Time. UNIONS supports the core science mission of the {\it Euclid} space mission by providing the data necessary in the northern hemisphere for the calibration of the wavelength dependence of the {\it Euclid} point-spread function and derivation of photometric redshifts in the North Galactic Cap. This region contains the highest quality sky for {\it Euclid}, with low backgrounds from the zodiacal light, stellar density, extinction, and emission from Galactic cirrus. Here, we describe the UNIONS survey components, science goals, data products, and the current status of the overall program.

astro-ph.GA↗

arXiv2024

Exploring faint white dwarfs and the luminosity function with Subaru HSC and SDSS in Stripe 82

We present 5,080 white dwarf (WD) candidates selected from stars matching between the multi-band imaging datasets of the Subaru Hyper Suprime-Cam (HSC) Survey and the Sloan Digital Sky Survey (SDSS) in the Stripe82 region covering about 165~deg$^2$. We select WD candidates from the ``reduced proper motion'' diagram by combining the apparent magnitude in the range $i=19$ -- 24 and the proper motion measured from the datasets among a baseline of $\sim$ 14~years. We refine the WD candidates by fitting blackbody and template WD atmosphere models to HSC photometries for each candidate, enabling the estimation of distance and tangential velocity ($v_{\rm t}$). The deep HSC data allow us to identify low-temperature ($<4000$~K) and faint WD candidates down to absolute magnitude, $M_{\rm bol}\simeq 17$. We evaluate the selection function of our WD candidates using a mock catalogue of spatial and kinematic distributions of WDs in the (thin and thick) disc and halo regions based on a Galactic model. We construct samples of disc and halo WD candidates by selecting WDs with tangential velocity, $40<v_{\rm t}/[{\rm km}~{\rm s}^{-1}]<80$ and $200<v_{\rm t}/[{\rm km}~{\rm s}^{-1}]<500$, respectively. The total number densities of the disc and halo WDs are $(9.33 \pm 0.89) \times 10^{-3}$~pc$^{-3}$ and $(6.34 \pm 2.90) \times 10^{-4}$~pc$^{-3}$. Our luminosity functions (LF) extend down to fainter absolute magnitudes compared with previous work. The faint WDs could represent the oldest generation of building blocks over the past $\sim$10 billion years of the assembly history of our Milky Way.

astro-ph.GA↗

arXiv2024

The Milky Way Tomography with Subaru Hyper Suprime-Cam. I. Halo substructures

We analyze the photometric data in the Wide layer of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) over $\sim 1,200$ deg$^{2}$ to uncover new halo substructures beyond the distance, $D_{\odot}\sim$ 30 kpc, from the Sun. For this purpose, we develop an isochrone filter for an old, metal-poor stellar system to extract the faint main-sequence stars at a range of distances. With this method, we detect, not only the previously discovered substructures such as the Orphan Stream, but also the new overdensity toward Boötes at about $D_{\odot}\sim$ 60 kpc and the new stream-like feature toward Pisces at around $D_{\odot}\sim$ 60 kpc. It has been suggested that a small-scale overdensity exists in this direction of Pisces (the so-called Pisces Overdensity), but our results show that the overdensity is widely spread with a tidally elongated feature. Combining our results with the ongoing Hyper Suprime-Cam narrow-band survey and the near-future spectroscopic survey with Prime Focus Spectrograph (PFS) will allow us to place strong constraints on the origin of these halo substructures.

astro-ph.GA↗

arXiv2014

Identification of triangular-shaped defects often appeared in hard-sphere crystals grown on a square pattern under gravity by Monte Carlo simulations

In this paper, we have successfully identified the triangular-shaped defect structures with stacking fault tetrahedra. These structure often appeared in hard-sphere (HS) crystals grown on a square pattern under gravity. We have, so far, performed Monte Carlo simulations of the HS crystals under gravity. Single stacking faults as observed previously in the HS crystals grown on a flat wall were not seen in the case of square template. Instead, defect structures with triangular appearance in $xz$- and $yz$- projections were appreciable. We have identified them by looking layer by layer. Those structures are surrounded by stacking faults along face-centered cubic (fcc) {111}. Also, we see isolated vacancies and vacancy-interstitial pairs, and we have found octahedral structures surrounded by stacking faults along fcc {111}.

cond-mat.soft↗

arXiv2014

Gravitational tempering in colloidal epitaxy to reduce defects further

Less-defective colloidal crystals can be used as photonic crystals. To this end, colloidal epitaxy was proposed in 1997 as a method to reduce the stacking defects in the colloidal crystals. In this method, face-centered cubic (fcc) (001) stacking is forced by a template. In fcc (001) stacking, in contract to fcc {111} stacking, the stacking sequence is unique and thus the stacking fault can be avoided. Additionally, in 1997, an effect of gravity that reduces the stacking disorder in hard-sphere (HS) colloidal crystals was found. Recently, we have proposed a gravitational tempering method based on a result of Monte Carlo (MC) simulations using the HS model; after a colloidal crystal is grown in a relatively strong gravitational field, the defects can be reduced by decreasing the gravity strength and maintain for a period of time. Here, we demonstrate this method using MC simulations with a programed gravitation. The dramatic disappearance of defect structures is observed. Gravitational tempering can complement gravitational annealing; some defect structures that accidentally remain after gravitational annealing (keeping the colloidal crystal under gravity of a considerable constant strength) can be erased.

cond-mat.soft↗

arXiv2013

Vanishing linear term in chemical potential difference in volume term of work of critical nucleus formation for phase transition without volume change

A question is given on the form n(μ_β-μ_α) for the volume term of work of formation of critical nucleus. Here, n is the number of molecule undergone the phase transition, μ denotes the chemical potential, α and β represent the parent and nucleating phases, respectively. In this paper we concentrate phase transition without volume change. We have calculated the volume term in terms of the chemical potential difference μ_{re}-μ_{eq}$ for this case. Here, μ_{re} is the chemical potential of the reservoir and μ_{eq} that at the phase transition. We have W_{vol} = -[(κ_β-κ_α)/(2v_{eq}^2)] (μ_{re}-μ_{eq})^2 V_β with κ denoting the isothermal compressibility, v_{eq} being the molecular volume at the phase transition, V_β the volume of the nucleus.

physics.chem-ph↗

arXiv2013

Enlargement of Grains of Silica Colloidal Crystals by Centrifugation in an Inverted-Triangle Internal-Shaped Container

We successfully fabricated large grains of silica colloidal crystals in an inverted-triangle internal-shaped container (inverted-triangle container) by centrifugation. The largest grain in the container was much larger than that in a container which has a flat bottom and constant width (flat-bottomed container). The edged bottom of the inverted-triangle container eliminated the number of the grains, and then the broadened shape of the container effectively widened the grains.

cond-mat.soft↗

arXiv2012

Possibility of Gravitational Tempering in Colloidal Epitaxy to Obtain a Perfect Crystal

We have performed Monte Carlo simulations of hard spheres on a pattern under gravity. We have found that a crystal formed at a moderate gravity strength contains essentially no defects while one formed at a higher strength gravity contains a significant amount of defects. This result suggests the possibility of using gravitational-tempering in a colloidal epitaxy to reduce the number of defects in colloidal crystals. Moreover, we wish to emphasize the possibility to obtain a perfect crystal.

cond-mat.soft↗

arXiv2012

Monte Carlo simulation of defects in hard-sphere crystal grown on a square pattern

Monte Carlo simulations of hard-sphere (HS) crystal grown on a square patterned wall under gravity have been performed. While previous simulations were performed with step-wise controlled gravity, in the present simulations constant gravity has been applied from the first. In the case in which a flat wall is used as the bottom wall, if a large gravity is suddenly applied, the system does polycrystallize. On the other hand, in the present simulations, despite the sudden application of gravity, the system has not polycrystallize. Crystalline nucleation on the square pattern and successive crystal growth upward are suggested to overcome the homogeneous nucleation inside and result in. Defect disappearance, which has been essentially the same as that for the case with step-wise controlled gravity, has also observed for the present case. The characteristic of the square patterned bottom wall simulation with a large horizontal system size has been existence of triangular defects suggesting stacking tetrahedra.

cond-mat.soft↗

arXiv2012

Gravitational Annealing of Colloidal Crystals

A silica colloidal crystal obtained by centrifugation at 9 G for 2 days in water was annealed by additional stronger centrifugation at 50 G for 5 days. The number of the striations observed in the colloidal crystal under crossed polarized light decreased at some parts in a growth container after additional centrifugation, while the number alse increase at the other parts. The decrease probably shows the shrinkage of the stacking disorders under high gravity, while the increase probably shows the production of new stacking disorder.

cond-mat.soft↗

arXiv2010

Interplay between elastic fields due to gravity and a partial dislocation for a hard-sphere crystal coherently grown under gravity: driving force for defect disappearance

We previously observed that an intrinsic staking fault shrunk through a glide of a Shockley partial dislocation terminating its lower end in a hard-sphere crystal under gravity coherently grown in <001> by Monte Carlo simulations [Mori et al., Molec. Phys. 105, 1377 (2007)]; it was an answer to a one-decade long standing question why the stacking disorder in colloidal crystals reduced under gravity [Zhu et al., Nature 387, 883 (1997)]. Here, we present an elastic energy calculation; in addition to the self-energy of the partial dislocation [Mori et al., Prog. Theor. Phys. Suppl. 178, 33 (2009)] we calculate the cross-coupling term between elastic field due to gravity and that due to a Shockley partial dislocation. The cross term is a increasing function of the linear dimension R over which the elastic field expands, showing that a driving force arises for the partial dislocation moving toward the upper boundary of a grain.

cond-mat.soft↗

arXiv2009

Disappearance of a Stacking Fault in Hard-Sphere Crystals under Gravity

In the first part of this paper, a review is given on the mechanism for the disappearance of an intrinsic stacking fault in a hard-sphere (HS) crystal under gravity, which we recently discovered by Monte Carlo (MC) simulations [A. Mori et al., J. Chem. Phys., 124 (2006), 17450; Mol. Phys. 105 (2007), 1377]. We have observed, in the case of fcc (001) stacking, that the intrinsic stacking fault running along an oblique direction shrunk through the gliding of a Shockley partial dislocation at the lower end of the stacking fault. In order to address the shortcomings and approximations of previous simulations, such as the use of periodic boundary condition (PBC) and the fact that the fcc (001) stacking had been realized by the stress from the small PBC box, we present an elastic strain energy calculation for an infinite system and a MC simulation result for HSs in a pyramidal pit under gravity. In particular, the geometry of the latter has already been tested experimentally [S. Matsuo et al., Appl. Phys. Lett., 82 (2003), 4283]. The advantage of using a pyramidal pit as a template as well as the feasibility of the mechanism we describe is demonstrated.

cond-mat.soft↗

arXiv2007

Shrinking stacking fault through glide of the Shockley partial dislocation in hard-sphere crystal under gravity

Disappearance of a stacking fault in the hard-sphere crystal under gravity, such as reported by Zhu et al. [Nature 387 (1997) 883], has successfully been demonstrated by Monte Carlo simulations. We previously found that a less ordered (or defective) crystal formed above a bottom ordered crystal under stepwise controlled gravity [Mori et al. J. Chem. Phys. 124 (2006) 174507]. A defect in the upper defective region has been identified with a stacking fault for the (001) growth. We have looked at the shrinking of a stacking fault mediated by the motion of the Shockley partial dislocation; the Shockley partial dislocation terminating the lower end of the stacking fault glides. In addition, the presence of crystal strain, which cooperates with gravity to reduce stacking faults, has been observed.

cond-mat.soft↗