arXiv subjects

Masahiro Takada

Publications and source records attributed to Masahiro Takada.

At least 127 records · Page 7Linked to original sources

arXiv2017

First results on the cluster galaxy population from the Subaru Hyper Suprime-Cam survey. I. The role of group or cluster environment in star formation quenching from z = 0.2 to 1.1

We utilize the HSC CAMIRA cluster catalog and the photo-$z$ galaxy catalog constructed in the HSC wide field (S16A), covering $\sim$ 174 deg$^{2}$, to study the star formation activity of galaxies in different environments over 0.2 $<$ $z$ $<$ 1.1. We probe galaxies down to $i \sim$ 26, corresponding to a stellar mass limit of log$_{10}$(M$_*$/M$_{\odot}$) $\sim$ 8.2 and $\sim$ 8.6 for star-forming and quiescent populations, respectively, at $z$ $\sim$ 0.2. The existence of the red sequence for low stellar mass galaxies in clusters suggests that the environmental quenching persists to halt the star formation in the low-mass regime. In addition, star-forming galaxies in groups or clusters are systematically biased toward lower values of specific star formation rate by 0.1 -- 0.3 dex with respect to those in the field and the offsets shows no strong redshift evolution over our redshift range, implying a universal slow quenching mechanism acting in the dense environments since $z$ $\sim$ 1.1. Moreover, the environmental quenching dominates the mass quenching in low mass galaxies, and the quenching dominance reverses in high mass ones. The transition mass is greater in clusters than in groups, indicating that the environmental quenching is more effective for massive galaxies in clusters compared to groups.

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arXiv2017

Reconstruction of halo power spectrum from redshift-space galaxy distribution: cylinder-grouping method and halo exclusion effect

The peculiar velocity field measured by redshift-space distortions (RSD) in galaxy surveys provides a unique probe of the growth of large-scale structure. However, systematic effects arise when including satellite galaxies in the clustering analysis. Since satellite galaxies tend to reside in massive halos with a greater halo bias, the inclusion boosts the clustering power. In addition, virial motions of the satellite galaxies cause a significant suppression of the clustering power due to nonlinear RSD effects. We develop a novel method to recover the redshift-space power spectrum of halos from the observed galaxy distribution by minimizing the contamination of satellite galaxies. The cylinder grouping method (CGM) we study effectively excludes satellite galaxies from a galaxy sample. However, we find that this technique produces apparent anisotropies in the reconstructed halo distribution over all the scales which mimic RSD. On small scales, the apparent anisotropic clustering is caused by exclusion of halos within the anisotropic cylinder used by the CGM. On large scales, the misidentification of different halos in the large-scale structures, aligned along the line-of-sight, into the same CGM group, causes the apparent anisotropic clustering via their cross-correlation with the CGM halos. We construct an empirical model for the CGM halo power spectrum, which includes correction terms derived using the CGM window function at small scales as well as the linear matter power spectrum multiplied by a simple anisotropic function at large scales. We apply this model to a mock galaxy catalog at z=0.5, designed to resemble SDSS-III BOSS CMASS galaxies, and find that our model can predict both the monopole and quadrupole power spectra of the host halos up to k<0.5 h/Mpc to within 5%.

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arXiv2016

A New Milky Way Satellite Discovered In The Subaru/Hyper Suprime-Cam Survey

We report the discovery of a new ultra-faint dwarf satellite companion of the Milky Way based on the early survey data from the Hyper Suprime-Cam Subaru Strategic Program. This new satellite, Virgo I, which is located in the constellation of Virgo, has been identified as a statistically significant (5.5 sigma) spatial overdensity of star-like objects with a well-defined main sequence and red giant branch in their color-magnitude diagram. The significance of this overdensity increases to 10.8 sigma when the relevant isochrone filter is adopted for the search. Based on the distribution of the stars around the likely main sequence turn-off at r ~ 24 mag, the distance to Virgo I is estimated as 87 kpc, and its most likely absolute magnitude calculated from a Monte Carlo analysis is M_V = -0.8 +/- 0.9 mag. This stellar system has an extended spatial distribution with a half-light radius of 38 +12/-11 pc, which clearly distinguishes it from a globular cluster with comparable luminosity. Thus, Virgo I is one of the faintest dwarf satellites known and is located beyond the reach of the Sloan Digital Sky Survey. This demonstrates the power of this survey program to identify very faint dwarf satellites. This discovery of VirgoI is based only on about 100 square degrees of data, thus a large number of faint dwarf satellites are likely to exist in the outer halo of the Milky Way.

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arXiv2016

Subaru high-z exploration of low-luminosity quasars (SHELLQs). I. Discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9

We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9. This is the initial result from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the exquisite multiband imaging data produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The candidate selection is performed by combining several photometric approaches including a Bayesian probabilistic algorithm to reject stars and dwarfs. The spectroscopic identification was carried out with the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg2 of the survey footprint. The success rate of our photometric selection is quite high, approaching 100 % at the brighter magnitudes (zAB < 23.5 mag). Our selection also recovered all the known high-z quasars on the HSC images. Among the 15 discovered objects, six are likely quasars, while the other six with interstellar absorption lines and in some cases narrow emission lines are likely bright Lyman-break galaxies. The remaining three objects have weak continua and very strong and narrow Ly alpha lines, which may be excited by ultraviolet light from both young stars and quasars. These results indicate that we are starting to see the steep rise of the luminosity function of z > 6 galaxies, compared with that of quasars, at magnitudes fainter than M1450 ~ -22 mag or zAB ~24 mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing.

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arXiv2016

Prime Focus Spectrograph (PFS) for the Subaru Telescope: Overview, recent progress, and future perspectives

PFS (Prime Focus Spectrograph), a next generation facility instrument on the 8.2-meter Subaru Telescope, is a very wide-field, massively multiplexed, optical and near-infrared spectrograph. Exploiting the Subaru prime focus, 2394 reconfigurable fibers will be distributed over the 1.3 deg field of view. The spectrograph has been designed with 3 arms of blue, red, and near-infrared cameras to simultaneously observe spectra from 380nm to 1260nm in one exposure at a resolution of ~1.6-2.7A. An international collaboration is developing this instrument under the initiative of Kavli IPMU. The project is now going into the construction phase aiming at undertaking system integration in 2017-2018 and subsequently carrying out engineering operations in 2018-2019. This article gives an overview of the instrument, current project status and future paths forward.

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arXiv2016

Separate Universe Consistency Relation and Calibration of Halo Bias

Linear halo bias is the response of dark matter halo number density to a long wavelength fluctuation in the dark matter density. Using abundance matching between separate universe simulations which absorb the latter into a change in the background, we test the consistency relation between the change in a one point function, the halo mass function, and a two point function, the halo-matter cross correlation in the long wavelength limit. We find excellent agreement between the two at the $1-2\%$ level for average halo biases between $1 \lesssim \bar b_1 \lesssim 4$ and no statistically significant deviations at the $4-5\%$ level out to $\bar b_1 \approx 8$. Halo bias inferred assuming instead a universal mass function is significantly different and inaccurate at the 10\% level or more. The separate universe technique provides a way of calibrating linear halo bias efficiently for even highly biased rare halos in the $Λ$CDM model. Observational violation of the consistency relation would indicate new physics, e.g.~in the dark matter, dark energy or primordial non-Gaussianity sectors.

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arXiv2016

Detection of Stacked Filament Lensing Between SDSS Luminous Red Galaxies

We search for the lensing signal of massive filaments between 135,000 pairs of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey. We develop a new estimator that cleanly removes the much larger shear signal of the neighboring LRG halos, relying only on the assumption of spherical symmetry. We consider two models: a thick filament model constructed from ray-tracing simulations for $Λ$CDM model, and a thin filament model which models the filament by a string of halos along the line connecting the two LRGs. We show that the filament lensing signal is in nice agreement with the thick simulation filament, while strongly disfavoring the thin model. The magnitude of the lensing shear due to the filament is below $10^{-4}$. Employing the likelihood ratio test, we find a 4.5$σ$ significance for the detection of the filament lensing signal, corresponding to a null hypothesis fluctuation probability of $3 \times 10^{-6}$. We also carried out several null tests to verify that the residual shear signal from neighboring LRGs and other shear systematics are minimized.

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arXiv2016

Evidence of Halo Assembly Bias in Massive Clusters

We present significant evidence of halo assembly bias for SDSS redMaPPer galaxy clusters in the redshift range $[0.1, 0.33]$. By dividing the 8,648 clusters into two subsamples based on the average member galaxy separation from the cluster center, we first show that the two subsamples have very similar halo mass of $M_{\rm 200m}\simeq 1.9\times 10^{14}~h^{-1}M_\odot$ based on the weak lensing signals at small radii $R<\sim 10~h^{-1}{\rm Mpc}$. However, their halo bias inferred from both the large-scale weak lensing and the projected auto-correlation functions differs by a factor of $\sim$1.5, which is a signature of assembly bias. The same bias hypothesis for the two subsamples is excluded at 2.5$σ$ in the weak lensing and 4.4$σ$ in the auto-correlation data, respectively. This result could bring a significant impact on both galaxy evolution and precision cosmology.

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arXiv2016

Detection of the Splashback Radius and Halo Assembly bias of Massive Galaxy Clusters

We show that the projected number density profiles of SDSS photometric galaxies around galaxy clusters displays strong evidence for the splashback radius, a sharp halo edge corresponding to the location of the first orbital apocenter of satellite galaxies after their infall. We split the clusters into two subsamples with different mean projected radial distances of their members, $\langle R_{\rm mem}\rangle$, at fixed richness and redshift, and show that the sample with smaller $\langle R_{\rm mem}\rangle$ has a smaller ratio of the splashback radius to the traditional halo boundary $R_{\rm 200m}$, than the subsample with larger $\langle R_{\rm mem}\rangle$, indicative of different mass accretion rates for the two subsamples. The same cluster samples were recently used by Miyatake et al. to show that their large-scale clustering differs despite their similar weak lensing masses, demonstrating strong evidence for halo assembly bias. We expand on this result by presenting a 6.6-$σ$ detection of halo assembly bias using the cluster-photometric galaxy cross-correlations. Our measured splashback radii are smaller, while the strength of the assembly bias signal is stronger, than expectations from N-body simulations based on the $Λ$-dominated, cold dark matter structure formation model. Dynamical friction or cluster-finding systematics such as miscentering or projection effects are not likely to be the sole source of these discrepancies.

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arXiv2015

Detection of universality of dark matter profile from Subaru weak lensing measurements of 50 massive clusters

We develop a novel method of measuring the lensing distortion profiles of clusters with stacking the scaled amplitudes of background galaxy ellipticities as a function of the scaled centric radius according to the NFW prediction of each cluster, based on the assumption that the different clusters in a sample follow the universal NFW profile. First we demonstrate the feasibility of this method using both the analytical NFW model and simulated halos in high-resolution $N$-body simulations. We then apply, as a proof of concept, this method to the Subaru weak lensing data and the XMM/Chandra X-ray observables for a sample of 50 massive clusters in the redshift range $0.15\le z\le 0.3$, where their halo masses range over an order of magnitude. To estimate the NFW parameters of each cluster, we use the halo mass proxy relation of X-ray observables, based on either the hydrostatic equilibrium or the gas mass, and then infer the halo concentration from the model $c(M)$ relation. We evaluate a performance of the NFW scaling analysis by measuring the scatters of 50 cluster lensing profiles relative to the NFW predictions over a range of radii, $0.14\le R/[h^{-1}{\rm Mpc}]\le 2.8$. We found a 4 - 6$σ$ level evidence of the universal NFW profile in 50 clusters, for both the X-ray halo mass proxy relations, although the gas mass appears to be a better proxy of the underlying true mass. By comparing the measurements with the simulations of cluster lensing taking into account the statistical errors of intrinsic galaxy shapes in the Subaru data, we argue that additional halo mass errors or intrinsic scatters of $σ_{\ln M_{500c}}\sim 0.2$ - $0.3$ could reconcile a difference between the measurements and the simulations.

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arXiv2015

Properties of Weak Lensing Clusters Detected on Hyper Suprime-Cam 2.3 Square Degree Field

We present properties of moderately massive clusters of galaxies detected by the newly developed Hyper Suprime-Cam on the Subaru telescope using weak gravitational lensing. Eight peaks exceeding a S/N ratio of 4.5 are identified on the convergence S/N map of a 2.3 square degree field observed during the early commissioning phase of the camera. Multi-color photometric data is used to generate optically selected clusters using the CAMIRA algorithm. The optical cluster positions were correlated with the peak positions from the convergence map. All eight significant peaks have optical counterparts. The velocity dispersion of clusters are evaluated by adopting the Singular Isothemal Sphere (SIS) fit to the tangential shear profiles, yielding virial mass estimates, M500c, of the clusters which range from 2.7x10^13 to 4.4x10^14 solar mass. The number of peaks is considerably larger than the average number expected from LambdaCDM cosmology but this is not extremely unlikely if one takes the large sample variance in the small field into account. We could, however, safely argue that the peak count strongly favours the recent Planck result suggesting high sigma8$value of 0.83. The ratio of stellar mass to the dark matter halo mass shows a clear decline as the halo mass increases. If the gas mass fraction, fg, in halos is universal, as has been suggested in the literature, the observed baryon mass in stars and gas shows a possible deficit compared with the total baryon density estimated from the baryon oscillation peaks in anisotropy of the cosmic microwave background.

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arXiv2015

The Weak Lensing Signal and the Clustering of BOSS Galaxies II: Astrophysical and Cosmological Constraints

We perform a joint analysis of the abundance, the clustering and the galaxy-galaxy lensing signal of galaxies measured from Data Release 11 of the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey (SDSS III-BOSS) in our companion paper, Miyatake et al. (2014). The lensing signal was obtained by using the shape catalog of background galaxies from the Canada France Hawaii Telescope Legacy Survey, which was made publicly available by the CFHTLenS collaboration, with an area overlap of about 105 deg$^2$. We analyse the data in the framework of the halo model in order to fit halo occupation parameters and cosmological parameters ($Ω_{\rm m}$ and $σ_8$) to these observables simultaneously, and thus break the degeneracy between galaxy bias and cosmology. Adopting a flat $Λ$CDM cosmology with priors on $Ω_b h^2$, $n_{\rm s}$ and $h$ from the analysis of WMAP 9-year data, we obtain constraints on the stellar mass-halo mass relation of galaxies in our sample. Marginalizing over the halo occupation distribution parameters and a number of other nuisance parameters in our model, we obtain $Ω_{\rm m}=0.310^{+0.019}_{-0.020}$ and $σ_8=0.785^{+0.044}_{-0.044}$ (68% confidence). We demonstrate the robustness of our results with respect to sample selection and a variety of systematics such as the halo off-centering effect and possible incompleteness in our sample. Our constraints are consistent, complementary and competitive with those obtained using other independent probes of these cosmological parameters. The cosmological analysis is the first of its kind to be performed at a redshift as high as $0.53$.

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arXiv2015

The Weak Lensing Signal and the Clustering of BOSS Galaxies I: Measurements

A joint analysis of the clustering of galaxies and their weak gravitational lensing signal is well-suited to simultaneously constrain the galaxy-halo connection as well as the cosmological parameters by breaking the degeneracy between galaxy bias and the amplitude of clustering signal. In a series of two papers, we perform such an analysis at the highest redshift ($z\sim0.53$) in the literature using CMASS galaxies in the Sloan Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Eleventh Data Release (SDSS-III/BOSS DR11) catalog spanning 8300~deg$^2$. In this paper, we present details of the clustering and weak lensing measurements of these galaxies. We define a subsample of 400,916 CMASS galaxies based on their redshifts and stellar mass estimates so that the galaxies constitute an approximately volume-limited and similar population over the redshift range $0.47\le z\le 0.59$. We obtain a signal-to-noise ratio $S/N\simeq 56$ for the galaxy clustering measurement. We also explore the redshift and stellar mass dependence of the clustering signal. For the weak lensing measurement, we use existing deeper imaging data from the CFHTLS with publicly available shape and photometric redshift catalogs from CFHTLenS, but only in a 105~deg$^2$ area which overlaps with BOSS. This restricts the lensing measurement to only 5,084 CMASS galaxies. After careful systematic tests, we find a highly significant detection of the CMASS weak lensing signal, with total $S/N\simeq 26$. These measurements form the basis of the halo occupation distribution and cosmology analysis presented in More et al. (Paper II).

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arXiv2014

Super-Sample Signal

When extracting cosmological information from power spectrum measurements, we must consider the impact of super-sample density fluctuations whose wavelengths are larger than the survey scale. These modes contribute to the mean density fluctuation $δ_b$ in the survey and change the power spectrum in the same way as a change in the cosmological background. They can be simply included in cosmological parameter estimation and forecasts by treating $δ_b$ as an additional cosmological parameter enabling efficient exploration of its impact. To test this approach, we consider here an idealized measurement of the matter power spectrum itself in the $Λ$CDM cosmology though our techniques can readily be extended to more observationally relevant statistics or other parameter spaces. Using sub-volumes of large-volume $N$-body simulations for power spectra measured with respect to either the global or local mean density, we verify that the minimum variance estimator of $δ_b$ is both unbiased and has the predicted variance. Parameter degeneracies arise since the response of the matter power spectrum to $δ_b$ and cosmological parameters share similar properties in changing the growth of structure and dilating the scale of features especially in the local case. For matter power spectrum measurements, these degeneracies can lead in certain cases to substantial error degradation and motivates future studies of specific cosmological observables such as galaxy clustering and weak lensing statistics with these techniques.

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arXiv2014

An optimal survey geometry of weak lensing survey: minimizing super-sample covariance

Upcoming wide-area weak lensing surveys are expensive both in time and cost and require an optimal survey design in order to attain maximum scientific returns from a fixed amount of available telescope time. The super-sample covariance (SSC), which arises from unobservable modes that are larger than the survey size, significantly degrades the statistical precision of weak lensing power spectrum measurement even for a wide-area survey. Using the 1000 mock realizations of the log-normal model, which approximates the weak lensing field for a $Λ$-dominated cold dark matter model, we study an optimal survey geometry to minimize the impact of SSC contamination. For a continuous survey geometry with a fixed survey area, a more elongated geometry such as a rectangular shape of 1:400 side-length ratio reduces the SSC effect and allows for a factor 2 improvement in the cumulative signal-to-noise ratio ($S/N$) of power spectrum measurement up to $\ell_{\rm max}\simeq $ a few $10^3$, compared to compact geometries such as squares or circles. When we allow the survey geometry to be disconnected but with a fixed total area, assuming $1\times 1$ sq. degrees patches as the fundamental building blocks of survey footprints, the best strategy is to locate the patches with $\sim 15$ degrees separation. This separation angle corresponds to the scale at which the two-point correlation function has a negative minimum. The best configuration allows for a factor 100 gain in the effective area coverage as well as a factor 2.5 improvement in the $S/N$ at high multipoles, yielding a much wider coverage of multipoles than in the compact geometry.

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arXiv2014

Statistical challenges in weak lensing cosmology

Cosmological weak lensing is the powerful probe of cosmology. Here we address one of the most fundamental, statistical questions inherent in weak lensing cosmology: whether or not we can recover the initial Gaussian information content of large-scale structure by combining the weak lensing observables, here focused on the weak lensing power spectrum and bispectrum. To address this question we fully take into account correlations between the power spectra of different multipoles and the bispectra of different triangle configurations, measured from a finite area survey. In particular we show that super-survey modes whose length scale is larger than or comparable with the survey size cause significant sample variance in the weak lensing correlations via the mode-coupling with sub-survey modes due to nonlinear gravitational clustering -- the so-called super-sample variance. In this paper we discuss the origin of the super-sample variance and then study the information content inherent in the weak lensing correlation functions up to three-point level.

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arXiv2014

Joint likelihood function of cluster counts and $n$-point correlation functions: Improving their power through including halo sample variance

Naive estimates of the statistics of large scale structure and weak lensing power spectrum measurements that include only Gaussian errors exaggerate their scientific impact. Non-linear evolution and finite volume effects are both significant sources of non-Gaussian covariance that reduce the ability of power spectrum measurements to constrain cosmological parameters. Using a halo model formalism, we derive an intuitive understanding of the various contributions to the covariance and show that our analytical treatment agrees with simulations. This approach enables an approximate derivation of a joint likelihood for the cluster number counts, the weak lensing power spectrum and the bispectrum. We show that this likelihood is a good description of the ray-tracing simulation. Since all of these observables are sensitive to the same finite volume effects and contain information about the non-linear evolution, a combined analysis recovers much of the "lost" information and obviates the non-Gaussian covariance. For upcoming weak lensing surveys, we estimate that a joint analysis of power spectrum, number counts and bispectrum will produce an improvement of about $30-40\%$ in determinations of the matter density and the scalar amplitude. This improvement is equivalent to doubling the survey area.

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arXiv2014

Super-Sample Covariance in Simulations

Using separate universe simulations, we accurately quantify super-sample covariance (SSC), the typically dominant sampling error for matter power spectrum estimators in a finite volume, which arises from the presence of super survey modes. By quantifying the power spectrum response to a background mode, this approach automatically captures the separate effects of beat coupling in the quasilinear regime, halo sample variance in the nonlinear regime and a new dilation effect which changes scales in the power spectrum coherently across the survey volume, including the baryon acoustic oscillation scale. It models these effects at typically the few percent level or better with a handful of small volume simulations for any survey geometry compared with directly using many thousands of survey volumes in a suite of large volume simulations. The stochasticity of the response is sufficiently small that in the quasilinear regime, SSC can be alternately included by fitting the mean density in the volume with these fixed templates in parameter estimation. We also test the halo model prescription and find agreement typically at better than the 10% level for the response.

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