arXiv subjects

Masataka Fukugita

Publications and source records attributed to Masataka Fukugita.

102 records · Page 6Linked to original sources

arXiv2001

Evolution of the Luminosity Function and Colors of Galaxies in a Lambda-CDM Universe

The luminosity function of galaxies is derived from a cosmological hydrodynamic simulation of a Lambda cold dark matter (CDM) universe with the aid of a stellar population synthesis model. At z=0, the resulting B band luminosity function has a flat faint end slope of α\approx -1.15 with the characteristic luminosity and the normalization in a fair agreement with observations, while the dark matter halo mass function is steep with a slope of α\approx -2. The colour distribution of galaxies also agrees well with local observations. We also discuss the evolution of the luminosity function, and the colour distribution of galaxies from z=0 to 5. A large evolution of the characteristic mass in the stellar mass function due to number evolution is compensated by luminosity evolution; the characteristic luminosity increases only by 0.8 mag from z=0 to 2, and then declines towards higher redshift, while the B band luminosity density continues to increase from z=0 to 5 (but only slowly at z>3).

astro-ph↗

arXiv2001

Galaxy Mass and Luminosity Scaling Laws Determined by Weak Gravitational Lensing

We present new measurements of scaling laws relating the luminosity of galaxies to the amplitude and shape of their dark matter halos. Early imaging and spectroscopic data from the Sloan Digital Sky Survey are used to make weak lensing measurements of the surface mass density contrast Delta Sigma_+ around classes of lens objects. This surface mass density contrast as a function of radius is a measure of the galaxy-mass correlation function (GMCF). Because spectroscopic redshifts are available for all lens objects, the mass and distance scales are well constrained. The GMCF measured around ~31,000 lenses is well fit by a power law of the form Delta Sigma_+ = (2.5+0.7-0.6) (R/1 Mpc)^{-0.8+-0.2} h M_sun pc^-2. We compare this GMCF to galaxy luminosity, type, and environment, and find that it varies strongly with all three. We quantify these variations by comparing the normalization of a fit to the inner 260 h^-1 kpc, M_260, to the galaxy luminosity. While M_260 is not strongly related to luminosity in bluest band u', there is a simple, linear relation between M_260 and luminosity in redder bands (g', r', i', and z'). We test the universality of these mass-to-light scalings by independently measuring them for spiral and elliptical galaxies,and for galaxies in a variety of environments. We find remarkable consistency in these determinations in the red bands, especially i' and z'. This consistency across a wide range of systems suggests that the measured scaling represents an excellent cosmic average, and that the integrated star formation history of galaxies is strongly related to the dark matter environments in which they form.

astro-ph↗

arXiv2001

Galaxy Number Counts from the Sloan Digital Sky Survey Commissioning Data

We present bright galaxy number counts in five broad bands ($u', g', r', i', z'$) from imaging data taken during the commissioning phase of the Sloan Digital Sky Survey (SDSS). The counts are derived from two independent stripes of imaging scans along the Celestial Equator, one each toward the North and the South Galactic cap, covering about 230 and 210 square degrees, respectively. A careful study is made to verify the reliability of the photometric catalog. For galaxies brighter than $r^* = 16$, the catalog produced by automated software is examined against eye inspection of all objects. Statistically meaningful results on the galaxy counts are obtained in the magnitude range $12 \le r^* \le 21$, using a sample of 900,000 galaxies. The counts from the two stripes differ by about 30% at magnitudes brighter than $r^*= 15.5$, consistent with a local $2σ$ fluctuation due to large scale structure in the galaxy distribution. The shape of the number counts-magnitude relation brighter than $r^* = 16$ is well characterized by $N \propto 10^{0.6m}$, the relation expected for a homogeneous galaxy distribution in a ``Euclidean'' universe. In the magnitude range $ 16 < r^* < 21$, the galaxy counts from both stripes agree very well, and follow the prediction of the no-evolution model, although the data do not exclude a small amount of evolution. We use empirically determined color transformations to derive the galaxy number counts in the $B$ and $I_{814}$ bands. We compute the luminosity density of the universe at zero redshift in the five SDSS bands and in the $B$ band. We find ${\cal L}_{B} = 2.4 \pm 0.4 \times 10^8L_\odot h $Mpc$^{-3}$, for a reasonably wide range of parameters of the Schechter luminosity function in the $B$ band.

astro-ph↗

arXiv2001

Star Formation History and Stellar Metallicity Distribution in a Cold Dark Matter Universe

We study star formation history and stellar metallicity distribution in galaxies in a Lambda cold dark matter universe using a hydrodynamic cosmological simulation. Our model predicts star formation rate declining in time exponentially from an early epoch to the present with the time-scale of 6 Gyr, which is consistent with the empirical Madau plot with modest dust obscuration. Star formation in L^* galaxies continues intermittently to the present also with an exponentially declining rate of a similar time-scale, whereas in small galaxies star formation ceases at an early epoch. The mean age of the extant stars decreases only slowly with increasing redshift, and exceeds 1 Gyr at z=3. Normal galaxies contain stars with a wide range of metallicity and age: stars formed at z<1 have metallicity of 0.1-1.0 Zsun, while old stars take a wide range of values from 10^{-6} Zsun to 3.0 Zsun. The mean metallicity of normal galaxies is in the range 0.1-1.0 Zsun. Dwarf galaxies that contain only old stars have a wide range of mean metallicity (10^{-4}-1.0 Zsun), but on average they are metal deficient compared with normal galaxies.

astro-ph↗

arXiv2001

Weak Lensing Measurements of 42 SDSS/RASS Galaxy Clusters

We present a lensing study of 42 galaxy clusters imaged in Sloan Digital Sky Survey (SDSS) commissioning data. Cluster candidates are selected optically from SDSS imaging data and confirmed for this study by matching to X-ray sources found independently in the ROSAT all sky survey (RASS). Five color SDSS photometry is used to make accurate photometric redshift estimates that are used to rescale and combine the lensing measurements. The mean shear from these clusters is detected to 2 h-1 Mpc at the 7-sigma level, corresponding to a mass within that radius of 4.2 +/- 0.6 x 10^14 h-1 M_sun. The shear profile is well fit by a power law with index -0.9 +/- 0.3, consistent with that of an isothermal density profile. This paper demonstrates our ability to measure ensemble cluster masses from SDSS imaging data.

astro-ph↗

arXiv2000

Cosmology and particle physics

The state of our understanding of cosmology is reviewed from an astrophysical cosmologist point of view with a particular emphasis given to recent observations and their impact. Discussion is then presented on the implications for particle physics.

hep-ph↗

arXiv2000

CMB Observables and Their Cosmological Implications

We show that recent measurements of the power spectrum of cosmic microwave background anisotropies by BOOMERanG and MAXIMA can be characterized by four observables, the position of the first acoustic peak l_1= 206 pm 6, the height of the first peak relative to COBE normalization H_1= 7.6 pm 1.4, the height of the second peak relative to the first H_2 = 0.38 pm 0.04, and the height of the third peak relative to the first H_3 = 0.43 pm 0.07. This phenomenological representation of the measurements complements more detailed likelihood analyses in multidimensional parameter space, clarifying the dependence on prior assumptions and the specific aspects of the data leading to the constraints. We illustrate their use in the flat LCDM family of models, where we find Omega_m h^{3.8} > 0.079 (or nearly equivalently, the age of the universe t_0 < 13-14 Gyr) from l_1 and a baryon density Omega_b h^2 > 0.019, a matter density Omega_m h^2 < 0.42 and tilt n>0.85 from the peak heights (95% CL). With the aid of several external constraints, notably nucleosynthesis, the age of the universe and the cluster abundance and baryon fraction, we construct the allowed region in the (Omega_m,h) plane; it points to high h (0.6< h < 0.9) and moderate Omega_m (0.25 < Omega_m < 0.6).

astro-ph↗

arXiv2000

Discovery of a Close Pair of z = 4.25 Quasars from the Sloan Digital Sky Survey

We report the discovery of a pair of z = 4.25 quasars with a separation of 33 arcseconds. The brighter of the two objects was identified as a high-redshift quasar candidate from Sloan Digital Sky Survey multicolor imaging data, and the redshift was measured from a spectrum obtained with the Hobby-Eberly Telescope. The slit orientation of this observation {\it by chance} included another quasar, approximately one magnitude fainter and having the same redshift as the target. This is the third serendipitous discovery of a z > 4 quasar. The differences in the relative strengths and profiles of the emission lines suggest that this is a quasar pair and not a gravitational lens. The two objects are likely to be physically associated; the projected physical separation is approximately 210 $h_{50}^{-1}$ kpc and the redshifts are identical to $\approx$ 0.01, implying a radial physical separation of 950 $h_{50}^{-1}$ kpc or less. The existence of this pair is strong circumstantial evidence that $z \sim 4$ quasars are clustered.

astro-ph↗

arXiv2000

The Global Cosmological Parameters

This lecture note presents a survey of the current status of the determination of the three cosmological parameters, the Hubble constant, the mass density paramater and the cosmological constant, to the closing date of the end of November 1999.

astro-ph↗

arXiv1999

Limits on Neutrino Mass from Cosmic Structure Formation

We consider the effect of three species of neutrinos with nearly degenerate mass on the cosmic structure formation in a low matter-density universe within a hierarchical clustering scenario with a flat initial perturbation spectrum. The matching condition for fluctuation powers at the COBE scale and at the cluster scale leads to a strong upper limit on neutrino mass. For a flat universe with matter density parameter Omega=0.3, we obtain m_nu<0.6eV for the Hubble constant H_0<80km/s/Mpc. Allowing for the more generous parameter space limited by Omega<0.4, H_0<80km/s/Mpc and age t_0>11.5Gyr, the limit is 0.9eV.

hep-ph↗

arXiv1999

A Study of the B-V Colour Temperature Relation

We attempt to construct a B-V colour temperature relation for stars in the least model dependent way employing the best modern data. The fit we obtained with the form Teff = Teff((B-V)0,[Fe/H],log g) is well constrained and a number of tests show the consistency of the procedures for the fit. Our relation covers from F0 to K5 stars with metallicity [Fe/H] = -1.5 to +0.3 for both dwarfs and giants. The residual of the fit is 66 K, which is consistent with what are expected from the quality of the present data. Metallicity and surface gravity effects are well separated from the colour dependence. Dwarfs and giants match well in a single family of fit, differing only in log g. The fit also detects the Galactic extinction correction for nearby stars with the amount E(B-V) = 0.26 +/-0.03 mag/kpc. Taking the newly obtained relation as a reference we examine a number of B-V colour temperature relations and atmosphere models available in the literature. We show the presence of a systematic error in the colour temperature relation from synthetic calculations of model atmospheres; the systematic error across K0 to K5 dwarfs is 0.04-0.05 mag in B-V, which means 0.25-0.3 mag in Mv for the K star range. We also argue for the error in the temperature scale used in currently popular stellar population synthesis models; synthetic colours from these models are somewhat too blue for aged elliptical galaxies. We derive the colour index of the sun (B-V)sun = 0.627 +/-0.018, and discuss that redder colours (e.g., 0.66-0.67) often quoted in the literature are incompatible with the colour-temperature relation.

astro-ph↗

arXiv1994

Galaxy Mergers and Gravitational Lens Statistics

We investigate the impact of hierarchical galaxy merging on the statistics of gravitational lensing of distant sources. Since no definite theoretical predictions for the merging history of luminous galaxies exist, we adopt a parametrized prescription, which allows us to adjust the expected number of pieces comprising a typical present galaxy at z=0.65. The existence of global parameter relations for elliptical galaxies and constraints on the evolution of the phase space density in dissipationless mergers, allow us to limit the possible evolution of galaxy lens properties under merging. We draw two lessons from implementing this lens evolution into statistical lens calculations: (1) The total optical depth to multiple imaging (e.g. of quasars) is quite insensitive to merging. (2) Merging leads to a smaller mean separation of observed multiple images. Because merging does not reduce drastically the expected lensing frequency it cannot make $λ$-dominated cosmologies compatible with the existing lensing observations. A comparison with the data from the HST Snapshot Survey shows that models with little or no evolution of the lens population are statistically favored over strong merging scenarios. The specific merging scenario proposed by Toomre (1977) can be rejected (95\% level) by such a comparison. Some versions of the scenario proposed by Broadhurst, Ellis \& Glazebrook (1992), are statistically acceptable.

astro-ph↗