arXiv subjects

Masataka Fukugita

Publications and source records attributed to Masataka Fukugita.

At least 19 recordsLinked to original sources

arXiv2022

Physics of star formation history and the luminosity function of galaxies therefrom

We show that the star formation history, the reionization history and the present luminosity function of galaxies are reproduced in a simple gravitational collapse model within the $Λ$CDM regime to almost a quantitative accuracy, when the physical conditions, the Jeans criterion and the cooling process, are taken into account. Taking a reasonable set of the model parameters, the reionisation takes place sharply at around redshift $1+z\simeq 7.5$, and the resulting luminosity function turns off at $L\simeq 10^{10.7}L_\odot$, showing the consistency between the star formation history and the reionisation of the Universe. The model gives the total amount of stars $Ω_\mathrm{star}=0.004$ in units of the critical density compared to the observation $0.0044$ with the recycling factor $1.6$ included. In order to account for the observed star formation rate and the present luminosity function, the star formation efficiency is not halo mass independent but becomes maximum at the halo mass $\simeq 10^{12}M_\odot$ and is suppressed for both smaller and larger mass haloes.

astro-ph.GA↗

arXiv2019

Galaxies and Cluster of Galaxies as Peak Patches of the Density Field

The mass function of galaxies and clusters of galaxies can be derived observationally based on different types of observations. In this study we test if these observations can be combined to a consistent picture which is also in accord with structure formation theory. The galaxy data comprise the optical galaxy luminosity function and the gravitational lensing signature of the galaxies, while the galaxy cluster mass function is derived from the X-ray luminosity distribution of the clusters. We show the results of the comparison in the form of the mass density fraction that is contained in collapsed objects relative to the mean matter density in the Universe. The mass density fraction in groups and clusters of galaxies extrapolated to low masses agrees very well with that of the galaxies: both converge at the low mass limit to a mass fraction of about 28\% if the outer radii of the objects are taken to be $r_{200}$. Most of the matter contained in collapsed objects is found in the mass range $M_{200} \sim 10^{12} - 10^{14} h^{-1}_{70} M_\odot$, while a larger amount of the cosmic matter resides outside of objects with radius $r_{200}$.

astro-ph.GA↗

arXiv2019

Energetics of High-Energy Cosmic Radiations

The luminosity densities of high-energy cosmic radiations are studied to find connections among the various components, including high-energy neutrinos measured with IceCube and gamma rays with the Fermi satellite. Matching the cosmic-ray energy generation rate density in a GeV-TeV range estimated for Milky Way with the ultrahigh-energy component requires a power-law index of the spectrum, $s_{\rm cr}\approx2.1-2.2$, somewhat harder than $s_{\rm cr}\approx2.3-2.4$ for the local index derived from the AMS-02 experiment. The soft GeV-TeV cosmic-ray spectrum extrapolated to higher energies can be compatible with PeV cosmic rays inferred from neutrino measurements, but overshoots the CR luminosity density to explain GeV-TeV gamma rays. The extrapolation from ultrahigh energies with a hard spectrum, on the other hand, can be consistent with both neutrinos and gamma-rays. These point towards either reacceleration of galactic cosmic rays or the presence of extragalactic sources with a hard spectrum. We discuss possible cosmic-ray sources that can be added.

astro-ph.HE↗

arXiv2019

On the nature of the black-body stars

A selection of 17 stars in the Sloan Digital Sky Survey, previously identified as DC class white dwarfs (WDs), has been reported to show spectra very close to blackbody radiation in the wavelength range from ultraviolet to infrared. Due to the absence of lines and other details in their spectra, the surface gravity of these objects has not been previously well constrained and their effective temperatures have been determined by fits to the continuum spectrum using pure helium atmosphere models. We compute model atmospheres with pure helium and H/He mixtures and use Gaia DR2 parallaxes available for 16 out of the 17 selected stars to analyze their physical properties. We find that the atmospheres of the selected stars are very probably contaminated with a trace amount of hydrogen as $-6 \leq \log{N_H/N_{He}} \leq -5.4$. For the 16 stars with Gaia parallaxes, we calculate a mean stellar mass $0.606\pm 0.076\,M_\odot$, which represents typical mass values and surface gravities ($7.8<\log g<8.3$) for WDs.

astro-ph.SR↗

arXiv2017

Mg II absorbers: metallicity evolution and cloud morphology

Metal abundance and its evolution are studied for Mg II quasar absorption line systems from their weak, unsaturated spectral lines using stacked spectra from the archived data of Sloan Digital Sky Survey. They show an abundance pattern that resembles that of Galactic halo or Small Magellanic Cloud, with metallicity [Z/H] showing an evolution from redshift z=2 to 0.5: metallicity becomes approximately solar or even larger at z~0. We show that the evolution of the metal abundance traces the cumulative amount of the hydrogen fuel consumed in star formation in galaxies. With the aid of a spectroscopic simulation code, we infer the median gas density of the cloud to be roughly 0.3 $\rm cm^{-3}$, with which the elemental abundance in various ionization stages, in particular C I, is consistently explained. This gas density implies that the size of the Mg II clouds is of the order of 0.03 kpc, which suggests that individual Mg II clouds around a galaxy are of a baryonic mass typically $\rm 10^{3} \, M_{\odot}$. This means that Mg II clouds are numerous and `foamy', rather than the large entity that covers a sizable fraction of galaxies with a single cloud.

astro-ph.GA↗

arXiv2017

Black-Body Stars

We report the discovery of stars that show spectra very close to the black-body radiation. We found 17 such stars out of 798,593 stars in the Sloan Digital Sky Survey (SDSS) spectroscopic data archives. We discuss the value of these stars for the calibration of photometry, whatever is the physical nature of these stars. This gives us a chance to examine the accuracy of the zero point of SDSS photometry across various passbands: we conclude that the zero point of SDSS photometric system is internally consistent across its five passbands to the level below 0.01 mag. We may also examine the consistency of the zero-points between UV photometry of Galaxy Evolution Explorer and SDSS, and IR photometry of Wide-field Infrared Survey Explorer against SDSS. These stars can be used as not only photometric but spetrophotometric standard stars. We suggest that these stars showing the featureless black-body like spectrum of the effective temperature of $10000\pm1500$K are consistent with DB white dwarfs with the temperature too low to develop helium absorption features.

astro-ph.SR↗

arXiv2017

The extended ROSAT-ESO Flux-Limited X-ray Galaxy Cluster Survey (REFLEX II) VII The Mass Function of Galaxy Clusters

The mass function of galaxy clusters is a sensitive tracer of the gravitational evolution of the cosmic large-scale structure and serves as an important census of the fraction of matter bound in large structures. We obtain the mass function by fitting the observed cluster X-ray luminosity distribution from the REFLEX galaxy cluster survey to models of cosmological structure formation. We marginalise over uncertainties in the cosmological parameters as well as those of the relevant galaxy cluster scaling relations. The mass function is determined with an uncertainty less than 10% in the mass range 3 x 10^12 to 5 x 10^14 M$_\odot$. For the cumulative mass function we find a slope at the low mass end consistent with a value of -1, while the mass rich end cut-off is milder than a Schechter function with an exponential term exp($- M^δ$) with $δ$ smaller than 1. Changing the Hubble parameter in the range $H_0 = 67 - 73 km s^-1 Mpc^{-1}$ or allowing the total neutrino mass to have a value between 0 - 0.4 eV causes variations less than the uncertainties. We estimate the fraction of mass locked up in galaxy clusters: about 4.4% of the matter in the Universe is bound in clusters (inside $r_200$) with a mass larger than 10^14 M$_\odot$ and 14% to clusters and groups with a mass larger than 10^13 M$_\odot$ at the present Universe. We also discuss the evolution of the galaxy cluster population with redshift. Our results imply that there is hardly any clusters with a mass > 10^15 M$_\odot$ above a redshift of z = 1.

astro-ph.CO↗

arXiv2016

CP violating phase from minimal texture neutrino mass matrix: Test of the phase relevant to leptogenesis

The model of neutrino mass matrix with minimal texture is now tightly constrained by experiment so that it can yield a prediction for the phase of CP violation. This phase is predicted to lie in the range $δ_{CP}=0.77π- 1.24π$. If neutrino oscillation experiment would find the CP violation phase outside this range, this means that the minimal-texture neutrino mass matrix, the element of which is all real, fails and the neutrino mass matrix must be complex, i.e., the phase must be present that is responsible for leptogenesis.

hep-ph↗

arXiv2014

The nature of Damped Lyman-α and MgII absorbers explored with their dust contents

We estimate the abundance of dust in damped Lyman-α absorbers (DLAs) by statistically measuring the excess reddening they induce on their background quasars. We detect systematic reddening behind DLA consistent with the SMC type reddening curve, but it is inconsistent with the Milky Way type reddening. We find that the derived dust-to-gas ratio is, on average, inversely proportional to the column density of neutral hydrogen, implying that the amount of dust is constant, irrespective of the column density of hydrogen. It means that the average metallicity is inversely proportional to the column density of hydrogen, unless the average dust-to-metal ratio varies with the hydrogen column density. This indicates that the prime origin of metals seen in DLAs is not by in situ star formation, with which Z ~ N_{HI}^{0.4} is expected from the empirical star formation law, contrary to our observation. We interpret the metals observed in absorbers being deposited dominantly from nearby galaxies by galactic winds ubiquitous in intergalactic space. When extrapolating the relation between dust-to-gas ratio and HI column density to lower column density, we find a value which is consistent with what is observed for Mg II absorbers.

astro-ph.GA↗

arXiv2013

Properties of Dust Grains Probed with Extinction Curves

Modern data of the extinction curve from the ultraviolet to the near infrared are revisited to study the property of dust grains in the Milky Way (MW) and the Small Magellanic Cloud (SMC). We confirm that the graphite-silicate mixture of grains yields the observed extinction curve with the simple power-law distribution of the grain size but with a cutoff at some maximal size: the parameters are tightly constrained to be $q = 3.5 \pm 0.2$ for the size distribution $a^{-q}$ and the maximum radius $a_{max} = 0.24 \pm 0.05$ um, for both MW and SMC. The abundance of grains, and hence the elemental abundance, is constrained from the reddening versus hydrogen column density, E(B-V)/N_H. If we take the solar elemental abundance as the standard for the MW, >56 % of carbon should be in graphite dust, while it is <40 % in the SMC using its available abundance estimate. This disparity and the relative abundance of C to Si explain the difference of the two curves. We find that 50-60 % of carbon may not necessarily be in graphite but in the amorphous or the glassy phase. Iron may also be in the metallic phase or up to ~80 % in magnetite rather than in silicates, so that the Mg/Fe ratio in astronomical olivine is arbitrary. With these substitutions the parameters of the grain size remain unchanged. The mass density of dust grains relative to hydrogen is $ρ_{dust}/ρ_H = 1/(120 {+10 \atop -16})$ for the MW and $1/(760 {+70 \atop -90}) for the SMC under some abundance constraints. We underline the importance of the wavelength-dependence slope of the extinction curve in the near infrared in constructing the dust model: if $A_λ \propto λ^{-gamma}$ with gamma ~ 1.6, the power-law grain-size model fails, whereas it works if gamma ~ 1.8-2.0.

astro-ph.GA↗

arXiv2012

$θ_{13}$ in Neutrino Mass Matrix with the Minimal Texture

We show that the neutrino mass matrix with the minimal texture leads to the neutrino mass and mixing that are empirically determined, including $θ_{13}$ that is measured recently at a high precision. This mass matrix, where the Majorana nature of the neutrino is essential, only allows the normal hierarchy of the neutrino mass, excluding either inverse mass hierarchy or degenerate mass neutrinos, and hence predicts the effective mass of double beta decay to lie within the range $m_{ee}=3.7-5.6$ eV.

hep-ph↗

arXiv2012

Cosmic dust in MgII absorbers

MgII absorbers induce reddening on background quasars. We measure this effect and infer the cosmic density of dust residing in these systems to be Ω ~ 2e-6, in units of the critical density of the Universe, which is comparable to the amount of dust found in galactic disks or about half the amount inferred to exist outside galaxies. We also estimate the neutral hydrogen abundance in MgII clouds to be Ω ~ 1.5e-4, which is approximately 5% of hydrogen in stars in galaxies. This implies a dust-to-gas mass ratio for MgII clouds of about 1/100, which is similar to the value for normal galaxies. This would support the hypothesis of the outflow origin of MgII clouds, which are intrinsically devoid of stars and hence have no sources of dust. Considerations of the dust abundance imply that the presence of MgII absorbers around galaxies lasts effectively for a few Gyr. High redshift absorbers allow us to measure the rest-frame extinction curve to 900 Angstroms at which the absorption by the Lyman edge dominates over scattering by dust in the extinction opacity.

astro-ph.CO↗

arXiv2012

The Sloan Digital Sky Survey Quasar Lens Search. V. Final Catalog from the Seventh Data Release

We present the final statistical sample of lensed quasars from the Sloan Digital Sky Survey (SDSS) Quasar Lens Search (SQLS). The well-defined statistical lens sample consists of 26 lensed quasars brighter than i=19.1 and in the redshift range of 0.6<z<2.2 selected from 50,836 spectroscopically confirmed quasars in the SDSS Data Release 7 (DR7), where we restrict the image separation range to 1"<θ<20" and the i-band magnitude differences in two image lenses to be smaller than 1.25 mag. The SDSS DR7 quasar catalog also contains 36 additional lenses identified with various techniques. In addition to these lensed quasars, we have identified 81 pairs of quasars from follow-up spectroscopy, 26 of which are physically associated binary quasars. The statistical lens sample covers a wide range of image separations, redshifts, and magnitudes, and therefore is suitable for systematic studies of cosmological parameters and surveys of the structure and evolution of galaxies and quasars.

astro-ph.CO↗

arXiv2012

The Sloan Digital Sky Survey Quasar Lens Search. VI. Constraints on Dark Energy and the Evolution of Massive Galaxies

We present a statistical analysis of the final lens sample from the Sloan Digital Sky Survey Quasar Lens Search (SQLS). The number distribution of a complete subsample of 19 lensed quasars selected from 50,836 source quasars is compared with theoretical expectations, with particular attention to the selection function. Assuming that the velocity function of galaxies does not evolve with redshift, the SQLS sample constrains the cosmological constant to Ω_Λ=0.79^{+0.06}_{-0.07}(stat.)^{+0.06}_{-0.06}(syst.) for a flat universe. The dark energy equation of state is found to be consistent with w=-1 when the SQLS is combined with constraints from baryon acoustic oscillation (BAO) measurements or results from the Wilkinson Microwave Anisotropy Probe (WMAP). We also obtain simultaneous constraints on cosmological parameters and redshift evolution of the galaxy velocity function, finding no evidence for redshift evolution at z<1 in any combinations of constraints. For instance, number density evolution quantified as ν_n=d\lnϕ_*/d\ln(1+z) and the velocity dispersion evolution ν_σ=d\lnσ_*/d\ln(1+z) are constrained to ν_n=1.06^{+1.36}_{-1.39}(stat.)^{+0.33}_{-0.64}(syst.) and ν_σ=-0.05^{+0.19}_{-0.16}(stat.)^{+0.03}_{-0.03}(syst.) respectively when the SQLS result is combined with BAO and WMAP for flat models with a cosmological constant. We find that a significant amount of dark energy is preferred even after fully marginalizing over the galaxy evolution parameters. Thus the statistics of lensed quasars robustly confirm the accelerated cosmic expansion.

astro-ph.CO↗

arXiv2011

Milky Way Tomography IV: Dissecting Dust

We use SDSS photometry of 73 million stars to simultaneously obtain best-fit main-sequence stellar energy distribution (SED) and amount of dust extinction along the line of sight towards each star. Using a subsample of 23 million stars with 2MASS photometry, whose addition enables more robust results, we show that SDSS photometry alone is sufficient to break degeneracies between intrinsic stellar color and dust amount when the shape of extinction curve is fixed. When using both SDSS and 2MASS photometry, the ratio of the total to selective absorption, $R_V$, can be determined with an uncertainty of about 0.1 for most stars in high-extinction regions. These fits enable detailed studies of the dust properties and its spatial distribution, and of the stellar spatial distribution at low Galactic latitudes. Our results are in good agreement with the extinction normalization given by the Schlegel et al. (1998, SFD) dust maps at high northern Galactic latitudes, but indicate that the SFD extinction map appears to be consistently overestimated by about 20% in the southern sky, in agreement with Schlafly et al. (2010). The constraints on the shape of the dust extinction curve across the SDSS and 2MASS bandpasses support the models by Fitzpatrick (1999) and Cardelli et al. (1989). For the latter, we find an $R_V=3.0\pm0.1$(random) $\pm0.1$(systematic) over most of the high-latitude sky. At low Galactic latitudes (|b|<5), we demonstrate that the SFD map cannot be reliably used to correct for extinction as most stars are embedded in dust, rather than behind it. We introduce a method for efficient selection of candidate red giant stars in the disk, dubbed "dusty parallax relation", which utilizes a correlation between distance and the extinction along the line of sight. We make these best-fit parameters, as well as all the input SDSS and 2MASS data, publicly available in a user-friendly format.

astro-ph.GA↗

arXiv2011

Matter Distribution around Galaxies

We explore the mass distribution of material associated with galaxies from the observation of gravitational weak lensing for the galaxy mass correlation function with the aid of $N$-body simulations of dark matter. The latter is employed to unfold various contributions that contribute to the integrated line of sight mass density. We conclude that galaxies have no definite edges of the matter distribution, extending to the middle to neighbouring galaxies with the density profile roughly $r^{-2.4}$ beyond the virial radius. The mass distributed beyond the virial radius (gravitationally bound radius) explains the gap seen in the mass density estimates, the global value $Ω_m\sim 0.27$ and typically $Ω_{\rm gal} \sim 0.15$ from the luminosity density multiplied by the mass to light ratio. We suggest to use a physical method of gravitational lensing to characterise galaxy samples rather than characterise them with photometric means.

astro-ph.CO↗

arXiv2011

Supernovae in the Subaru Deep Field: the rate and delay-time distribution of type Ia supernovae out to redshift 2

The type Ia supernova (SN Ia) rate, when compared to the cosmic star formation history (SFH), can be used to derive the delay-time distribution (DTD) of SNe Ia, which can distinguish among progenitor models. We present the results of a SN survey in the Subaru Deep Field (SDF). Over a period of 3 years, we have observed the SDF on 4 independent epochs with Suprime-Cam on the Subaru 8.2-m telescope, with 2 nights of exposure per epoch, in the R, i', and z' bands. We have discovered 150 SNe out to redshift z~2. Using 11 photometric bands from the observer-frame far-ultraviolet to the near-infrared, we derive photometric redshifts for the SN host galaxies (for 24 we also have spectroscopic redshifts). This information is combined with the SN photometry to determine the type and redshift distribution of the SN sample. Our final sample includes 28 SNe Ia in the range 1.0<z<1.5 and 10 in the range 1.5<z<2.0. Our SN Ia rate measurements are consistent with those derived from the HST/GOODS sample, but the overall uncertainty of our 1.5<z<2.0 measurement is a factor of 2 smaller, of 35-50%. We find that the SN Ia rate evolution levels off at 1.0<z<2.0, but shows no sign of declining. Combining our SN Ia rate measurements and those from the literature, and comparing to a wide range of possible SFHs, the best-fit DTD is a power law of the form Psi(t) ~ t^beta, with beta = -1.1 +/- 0.1 (statistical) +/- 0.17 (systematic). This result is consistent with other recent DTD measurements at various redshifts and environments, and is in agreement with a generic prediction of the double-degenerate progenitor scenario for SNe Ia. By combining the contribution to iron production from core-collapse SNe, based on the wide range of SFHs, with that from SNe Ia, calculated with the best-fit DTD, we predict that the mean present-day cosmic iron abundance is in the range Z(Fe) = (0.09-0.37) Z(Fe,Sun) (abridged).

astro-ph.CO↗

arXiv2011

Microwave Emission from the Edgeworth-Kuiper Belt and the Asteroid Belt Constrained from WMAP

Objects in the Edgeworth-Kuiper belt and the main asteroid belt should emit microwaves that may give rise to extra anisotropy signals in the multipole of the cosmic microwave background (CMB) experiment. Constraints are derived from the absence of positive detection of such anisotropies for ell < 50, giving the total mass of Edgeworth-Kuiper belt objects to be smaller than 0.2 earth mass. This limit is consistent with the mass extrapolated from the observable population with the size of a > 15 km, assuming that the small-object population follows the power law in size dN/da ~ a^{-q} with the canonical index expected for collisional equilibrium, q ~ 3.5, with which 23% of the mass is ascribed to objects smaller than are observationally accessible down to grains. A similar argument applied to the main asteroid belt indicates that the grain population should not increase faster than q ~ 3.6 towards smaller radii, if it follows the power law continued to observed asteroids with larger radii. It is underlined that both cases are at or only slightly above the limit that can be physically significant, implying the importance of tightening further the CMB anisotropy limit, which may be attained with the observation at higher radio frequencies.

astro-ph.CO↗