arXiv subjects

Issha Kayo

Publications and source records attributed to Issha Kayo.

At least 55 records · Page 3Linked to original sources

arXiv2007

Discovery of Four Gravitationally Lensed Quasars from the Sloan Digital Sky Survey

We present the discovery of four gravitationally lensed quasars selected from the spectroscopic quasar catalog of the Sloan Digital Sky Survey. We describe imaging and spectroscopic follow-up observations that support the lensing interpretation of the following four quasars: SDSS J0832+0404 (image separation θ=1.98", source redshift z_s=1.115, lens redshift z_l=0.659); SDSS J1216+3529 (θ=1.49", z_s=2.012); SDSS J1322+1052 (θ=2.00", z_s=1.716); and SDSS J1524+4409 (θ=1.67", z_s=1.210, z_l=0.320). Each system has two lensed images. We find that the fainter image component of SDSS J0832+0404 is significantly redder than the brighter component, perhaps because of differential reddening by the lensing galaxy. The lens potential of SDSS J1216+3529 might be complicated by the presence of a secondary galaxy near the main lensing galaxy.

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arXiv2007

The Sloan Digital Sky Survey Quasar Lens Search. II. Statistical Lens Sample from the Third Data Release

We report the first results of our systematic search for strongly lensed quasars using the spectroscopically confirmed quasars in the Sloan Digital Sky Survey (SDSS). Among 46,420 quasars from the SDSS Data Release 3 (~4188 deg^2), we select a subsample of 22,683 quasars that are located at redshifts between 0.6 and 2.2 and are brighter than the Galactic extinction corrected i-band magnitude of 19.1. We identify 220 lens candidates from the quasar subsample, for which we conduct extensive and systematic follow-up observations in optical and near-infrared wavebands, in order to construct a complete lensed quasar sample at image separations between 1'' and 20'' and flux ratios of faint to bright lensed images larger than 10^{-0.5}. We construct a statistical sample of 11 lensed quasars. Ten of these are galaxy-scale lenses with small image separations (~1''-2'') and one is a large separation (15'') system which is produced by a massive cluster of galaxies, representing the first statistical sample of lensed quasars including both galaxy- and cluster-scale lenses. The Data Release 3 spectroscopic quasars contain an additional 11 lensed quasars outside the statistical sample.

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arXiv2007

The Sloan Digital Sky Survey Quasar Lens Search. III. Constraints on Dark Energy from the Third Data Release Quasar Lens Catalog

We present cosmological results from the statistics of lensed quasars in the Sloan Digital Sky Survey (SDSS) Quasar Lens Search. By taking proper account of the selection function, we compute the expected number of quasars lensed by early-type galaxies and their image separation distribution assuming a flat universe, which is then compared with 7 lenses found in the SDSS Data Release 3 to derive constraints on dark energy under strictly controlled criteria. For a cosmological constant model (w=-1) we obtain Ω_Λ=0.74^{+0.11}_{-0.15}(stat.)^{+0.13}_{-0.06}(syst.). Allowing w to be a free parameter we find Ω_M=0.26^{+0.07}_{-0.06}(stat.)^{+0.03}_{-0.05}(syst.) and w=-1.1\pm0.6(stat.)^{+0.3}_{-0.5}(syst.) when combined with the constraint from the measurement of baryon acoustic oscillations in the SDSS luminous red galaxy sample. Our results are in good agreement with earlier lensing constraints obtained using radio lenses, and provide additional confirmation of the presence of dark energy consistent with a cosmological constant, derived independently of type Ia supernovae.

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arXiv2007

A New Quadruply Lensed Quasar: SDSSJ125107.57+293540.5

We report the discovery of a quadruply imaged quasar, SDSSJ125107.57+293540.5, selected from the Sloan Digital Sky Survey. Follow-up imaging reveals that the system consists of four blue point-like components in a typical cusp lens geometry surrounding a central red galaxy. The source redshift is 0.802 and the lens redshift is 0.410. The maximum image separation between the lensed components is 1"79. While the image configuration is well reproduced by standard mass models with reasonable parameter values, the flux ratios predicted by these models differ from the observed ratios in all bands. This is suggestive of small-scale structures in this lens, although the definitive identification of the anomaly requires more accurate photometry and astrometry.

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arXiv2006

Bispectrum and Nonlinear Biasing of Galaxies: Perturbation Analysis, Numerical Simulation and SDSS Galaxy Clustering

We consider nonlinear biasing models of galaxies with particular attention to a correlation between linear and quadratic biasing coefficients, b_1 and b_2. We first derive perturbative expressions for b_1 and b_2 in halo and peak biasing models. Then we compute power spectra and bispectra of dark matter particles and halos using N-body simulation data and of volume-limited subsamples of Sloan Digital Sky Survey (SDSS) galaxies, and determine their b_1 and b_2. We find that the values of those coefficients at linear regimes (k<0.2h/Mpc) are fairly insensitive to the redshift-space distortion and the survey volume shape. The resulting normalized amplitudes of bispectra, Q, for equilateral triangles, are insensitive to the values of b_1 implying that b_2 indeed correlates with b_1. The present results explain the previous finding of Kayo et al. (2004) for the hierarchical relation of three-point correlation functions of SDSS galaxies. While the relations between b_1 and b_2 are quantitatively different for specific biasing models, their approximately similar correlations indicate a fairly generic outcome of the biasing due to the gravity in primordial Gaussian density fields.

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arXiv2006

SDSS J1029+2623: A Gravitationally Lensed Quasar with an Image Separation of 22.5 Arcseconds

We report the discovery of a cluster-scale lensed quasar, SDSS J1029+2623, selected from the Sloan Digital Sky Survey. The lens system exhibits two lensed images of a quasar at z_s=2.197. The image separation of 22.5" makes it the largest separation lensed quasar discovered to date. The similarity of the optical spectra and the radio loudnesses of the two components support the lensing hypothesis. Images of the field show a cluster of galaxies at z_l~0.55 that is responsible for the large image separation. The lensed images and the cluster light center are not collinear, which implies that the lensing cluster has a complex structure.

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arXiv2006

A New Survey for Giant Arcs

We report on the first results of an imaging survey to detect strong gravitational lensing targeting the richest clusters selected from the photometric data of the Sloan Digital Sky Survey (SDSS) with follow-up deep imaging observations from the Wisconsin Indiana Yale NOAO (WIYN) 3.5m telescope and the University of Hawaii 88-inch telescope (UH88). The clusters are selected from an area of 8000 deg^2 using the Red Cluster Sequence technique and span the redshift range 0.1 < z < 0.6, corresponding to a comoving cosmological volume of ~ 2 Gpc^3. Our imaging survey thus targets a volume more than an order of magnitude larger than any previous search. A total of 240 clusters were imaged of which 141 had sub-arcsecond image quality. Our survey has uncovered16 new lensing clusters with definite giant arcs, an additional 12 systems for which the lensing interpretation is very likely, and 9 possible lenses which contain shorter arclets or candidate arcs which are less certain and will require further observations to confirm their lensing origin. The number of new cluster lenses detected in this survey is likely > 30. Among these new systems are several of the most dramatic examples of strong gravitational lensing ever discovered with multiple bright arcs at large angular separation. These will likely become 'poster-child' gravitational lenses similar to Abell 1689 and CL0024+1654. The new lenses discovered in this survey will enable future sysetmatic studies of the statistics of strong lensing and its implications for cosmology and our structure formation paradigm.

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arXiv2006

Discovery of a Gravitationally Lensed Quasar from the Sloan Digital Sky Survey: SDSS J133222.62+034739.9

We report the discovery of the two-image gravitationally lensed quasar SDSS J133222.62+034739.9 (SDSS J1332+0347) with an image separation of Delta_theta=1.14". This system consists of a source quasar at z_s=1.445 and a lens galaxy at z_l=0.191. The agreement of the luminosity, ellipticity and position angle of the lens galaxy with those expected from lens model confirms the lensing hypothesis.

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arXiv2006

Two New Gravitationally Lensed Double Quasars from the Sloan Digital Sky Survey

We report the discoveries of the two-image gravitationally lensed quasars, SDSS J0746+4403 and SDSS J1406+6126, selected from the Sloan Digital Sky Survey (SDSS). SDSS J0746+4403, which will be included in our lens sample for statistics and cosmology, has a source redshift of z_s=2.00, an estimated lens redshift of z_l~0.3, and an image separation of 1.08". SDSS J1406+6126 has a source redshift of z_s=2.13, a spectroscopically measured lens redshift of z_l=0.27, and an image separation of 1.98". We find that the two quasar images of SDSS J1406+6126 have different intervening MgII absorption strengths, which are suggestive of large variations of absorbers on kpc scales. The positions and fluxes of both the lensed quasar systems are easily reproduced by simple mass models with reasonable parameter values. These objects bring to 18 the number of lensed quasars that have been discovered from the SDSS data.

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arXiv2005

Minkowski Functionals of SDSS galaxies I : Analysis of Excursion Sets

We present a first morphometric investigation of a preliminary sample from the SDSS of 154287 galaxies with apparent magnitude 14.5<m_r<17.5 and redshift 0.001<z<0.4. We measure the Minkowski Functionals, which are a complete set of morphological descriptors. To account for the complicated wedge--like geometry of the present survey data, we construct isodensity contour surfaces from the galaxy positions in redshift space and employ two complementary methods of computing the Minkowski Functionals. We find that the observed Minkowski Functionals for SDSS galaxies are consistent with the prediction of a Lambda--dominated spatially--flat Cold Dark Matter model with random--Gaussian initial conditions, within the cosmic variance estimated from the corresponding mock catalogue. We expect that future releases of the SDSS survey will allow us to distinguish morphological differences in the galaxy distribution with regard to different morphological type and luminosity ranges.

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arXiv2005

Large Scale Clustering of Sloan Digital Sky Survey Quasars: Impact of the Baryon Density and the Cosmological Constant

We report the first result of the clustering analysis of Sloan Digital Sky Survey (SDSS) quasars. We compute the two-point correlation function (2PCF) of SDSS quasars in redshift space at $8h^{-1}{\rm Mpc} < s < 500h^{-1}{\rm Mpc}$, with particular attention to its baryonic signature. Our sample consists of 19986 quasars extracted from the SDSS Data Release 4 (DR4). The redshift range of the sample is $0.72 \le z \le 2.24$ (the mean redshift is $\bar z = 1.46$) and the reddening-corrected $i$-band apparent magnitude range is $15.0 \le m_{i,{\rm rc}} \le 19.1$. Due to the relatively low number density of the quasar sample, the bump in the power spectrum due to the baryon density, $Ω_{\rm b}$, is not clearly visible. The effect of the baryon density is, however, to distort the overall shape of the 2PCF.The degree of distortion makes it an interesting alternate measure of the baryonic signature. Assuming a scale-independent linear bias and the spatially flat universe, i.e., $Ω_{\rm b} + Ω_{\rm d} + Ω_Λ=1$, where $Ω_{\rm d}$ and $Ω_Λ$ denote the density parameters of dark matter and the cosmological constant, we combine the observed quasar 2PCF and the predicted matter 2PCF to put constraints on $Ω_{\rm b}$ and $Ω_Λ$. Our result is fitted as $0.80- 2.8Ω_{\rm b} < Ω_Λ< 0.90 - 1.4Ω_{\rm b}$ at the 2$σ$ confidence level, which is consistent with results from other cosmological observations such as WMAP. (abridged)

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arXiv2004

Modeling peculiar velocities of dark matter halos

We present a simple model that accurately describes various statistical properties of peculiar velocities of dark matter halos. We pay particular attention to the following two effects; first, the evolution of the halo peculiar velocity depends on the local matter density, instead of the global density. Second, dark matter halos are biased tracers of the underlying mass distribution, thus halos tend to be located preferentially at high density regions. For the former, we develop an empirical model calibrated with N-body simulations, while for the latter, we use a conventional halo bias models based on the extended Press-Schechter model combined with an empirical log-normal probability distribution function of the mass density distribution. We find that compared with linear theory, the present model significantly improves the accuracy of predictions of statistical properties of the halo peculiar velocity field including the velocity dispersion, the probability distribution function, and the pairwise velocity dispersion at large separations. Thus our model predictions may be useful in analyzing future observations of the peculiar velocities of galaxy clusters.

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arXiv2004

Three-point Correlation Functions of SDSS Galaxies in Redshift Space: Morphology, Color, and Luminosity Dependence

We present measurements of the redshift--space three-point correlation function of galaxies in the Sloan Digital Sky Survey (SDSS). For the first time, we analyze the dependence of this statistic on galaxy morphology, color and luminosity. In order to control systematics due to selection effects, we used $r$--band, volume-limited samples of galaxies, constructed from the magnitude-limited SDSS data ($14.5<r<17.5$), and further divided the samples into two morphological types (early and late) or two color populations (red and blue). The three-point correlation function of SDSS galaxies follow the hierarchical relation well and the reduced three-point amplitudes in redshift--space are almost scale-independent ($Q_z=0.5\sim1.0$). In addition, their dependence on the morphology, color and luminosity is not statistically significant. Given the robust morphological, color and luminosity dependences of the two-point correlation function, this implies that galaxy biasing is complex on weakly non-linear to non-linear scales. We show that simple deterministic linear relation with the underlying mass could not explain our measurements on these scales.

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arXiv2004

Cosmological Density Distribution Function from the Ellipsoidal Collapse Model in Real Space

We calculate the one-point probability distribution function (PDF) for cosmic density in non-linear regime of the gravitational evolution. Under the local approximation that the evolution of cosmic fluid fields can be characterized by the Lagrangian local dynamics with finite degrees of freedom, the analytic expressions of PDF are derived taking account of the smoothing effect. The validity and the usefulness of the local approximation are then discussed comparing those results with N-body simulations in a Gaussian initial condition. Adopting the ellipsoidal collapse model (ECM) and the spherical collapse model (SCM) as Lagrangian local dynamics, we found that the PDFs from the local approximation excellently match the simulation results in the case of the cold dark matter initial spectrum. As for the scale-free initial spectra given by $P(k)\propto k^n$, N-body result suffers from spurious numerical effects, which prevent us to give a detailed comparison. Nevertheless, at the quality of N-body data, the model predictions based on the ECM and the SCM quantitatively agree with N-body results in cases with spectral index n<0. For the index n>=0, choice of the Lagrangian local dynamics becomes crucial for an accurate prediction and a more delicate modeling is required, however, we find that the model prediction based on the ECM provides a better approximation to the N-body results of cumulants and PDFs.

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arXiv2003

Properties of host haloes of Lyman-break galaxies and Lyman-alpha Emitters from their number densities and angular clustering

We explore empirical relations between three different populations of high-redshift galaxies and their hosting dark halos employing the halo model approach. Specifically we consider Lyman-break galaxies at z\sim4 and at z\sim5, and Lyman-Alpha emitters at z\simeq 4.86. We adopt a halo occupation function prescription to parameterize the properties of their hosting halos and the efficiency of halo-dependent star formation. We find that the two LBG samples are well described by the halo model with an appropriate HOF. We obtain constraints on properties of their hosting halos. A typical mass of hosting halos for LBGs is 5\times10^{11}h^{-1}M_\odot and the expected number of LBGs per halo is \sim0.5, therefore there is an approximate one-to-one correspondence between halos and LBGs. We also find a sign of the minimum mass of LBG hosting halos decreasing with time. We discuss implications of these findings on the star formation history of LBGs. On the other hand, for LAEs, our simple HOF prescription fails to reproduce simultaneously the observed angular correlation function and the number density. This might imply either that the distribution of LAEs within hosting halos differs from that of dark matter, or that the strong large-scale correlation is due to the existence of an unusual, large overdense region, and so the survey region is not a representative of the z\sim5 universe, the definite answer should wait for a much wider survey of LAEs at high redshifts.

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arXiv2003

Evolution of Cosmological Density Distribution Function from the Local Collapse Model

We present a general framework to treat the evolution of one-point probability distribution function (PDF) for cosmic density $δ$ and velocity-divergence fields $θ$. In particular, we derive an evolution equation for the one-point PDFs and consider the stochastic nature associated with these quantities. Under the local approximation that the evolution of cosmic fluid fields can be characterized by the Lagrangian local dynamics with finite degrees of freedom, evolution equation for PDFs becomes a closed form and consistent formal solutions are constructed. Adopting this local approximation, we explicitly evaluate the one-point PDFs $P(δ)$ and $P(θ)$ from the spherical and the ellipsoidal collapse models as the representative Lagrangian local dynamics. In a Gaussian initial condition, while the local density PDF from the ellipsoidal model almost coincides with the that of the spherical model, differences between spherical and ellipsoidal collapse model are found in the velocity-divergence PDF. Importantly, the joint PDF of local density, $P(δ,t;δ',t')$, evaluated at the same Lagrangian position but at the different times $t$ and $t'$ from the ellipsoidal collapse model exhibits a large amount of scatter. The mean relation between $δ$ and $δ'$ does fail to match the one-to-one mapping obtained from spherical collapse model. Moreover, the joint PDF $P(δ;θ)$ from the ellipsoidal collapse model shows a similar stochastic feature, both of which are indeed consistent with the recent result from N-body simulations.

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arXiv2002

Non-Gaussian Tails of Cosmological Density Distribution Function from Dark Halo Approach

We present a simple model based on the dark halo approach which provides a useful way to understand key points determining the shape of the non-Gaussian tails of the dark matter one-point probability distribution function(PDF). In particular, using the scale-free models with power-law profile of dark halos, we derive a simple analytic expression for the one-point PDF. It is found that the shape of the PDF changes at the characteristic value of $δ_*$ which is defined by the smoothed density of a halo with the characteristic mass $M_*$ at the epoch. In cold dark matter models with top-hat smoothing filters, the characteristic smoothed density at present time typically takes the value $δ_*\gg 1$ for a small smoothing scale $\rth\sim 1$Mpc$/h$ and conversely $δ_*\ll 1$ for a large smoothing scale $\rth > 10$Mpc$/h$. On the range $δ/δ_*<1$, the shape of the PDF is almost solely determined by the outer slope of halos and scales as a power-law. The resultant non-Gaussian tails of PDF then resemble the log-normal PDFs in that range and show a good agreement with N-body simulations, which can be ascribed to the universality of the outer slope of the halo profile. In contrast, tails of one-point PDF in the range $δ/δ_*>1$ basically follow the steep exponential tails of the halo mass function, which exhibit a strong sensitivity to both the outer slope of the halo profile and the initial power spectrum. Based on these results, the discussion on the PDF of galaxy distribution and the application to the weak lensing statistics are also presented.

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arXiv2002

Three-Dimensional Genus Statistics of Galaxies in the SDSS Early Data Release

We present the first analysis of three-dimensional genus statistics for the SDSS EDR galaxy sample. Due to the complicated survey volume and the selection function, analytic predictions of the genus statistics for this sample are not feasible, therefore we construct extensive mock catalogs from N-body simulations in order to compare the observed data with model predictions. This comparison allows us to evaluate the effects of a variety of observational systematics on the estimated genus for the SDSS sample, including the shape of the survey volume, the redshift distortion effect, and the radial selection function due to the magnitude limit. The observed genus for the SDSS EDR galaxy sample is consistent with that predicted by simulations of a $Λ$-dominated spatially-flat cold dark matter model. Standard ($Ω_0=1$) cold dark matter model predictions do not match the observations. We discuss how future SDSS galaxy samples will yield improved estimates of the genus.

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