arXiv subjects

Keiichi Umetsu

Publications and source records attributed to Keiichi Umetsu.

At least 127 records · Page 7Linked to original sources

arXiv2012

Miscentring in Galaxy Clusters: Dark Matter to Brightest Cluster Galaxy Offsets in 10,000 SDSS Clusters

We characterise the typical offset between the Dark Matter (DM) projected centre and the Brightest Cluster Galaxy (BCG) in 10,000 SDSS clusters. To place constraints on the centre of DM, we use an automated strong-lensing analysis, mass-modelling technique which is based on the well-tested assumption that light traces mass. The cluster galaxies are modelled with a steep power-law, and the DM component is obtained by smoothing the galaxy distribution fitting a low-order 2D polynomial (via spline interpolation), while probing a whole range of polynomial degrees and galaxy power laws. We find that the offsets between the BCG and the peak of the smoothed light map representing the DM, Δ, are distributed equally around zero with no preferred direction, and are well described by a log-normal distribution with =-1.895^{+0.003}_{-0.004}, and σ=0.501\pm0.004 (95% confidence levels), or =0.564\pm0.005, and σ=0.475\pm0.007. Some of the offsets originate in prior misidentifications of the BCG or other bright cluster members by the cluster finding algorithm, whose level we make an additional effort to assess, finding that ~10% of the clusters in the probed catalogue are likely to be misidentified, contributing to higher-end offsets in general agreement with previous studies. Our results constitute the first statistically-significant high-resolution distributions of DM-to-BCG offsets obtained in an observational analysis, and importantly show that there exists such a typical non-zero offset in the probed catalogue. The offsets show a weak positive correlation with redshift, so that higher separations are generally found for higher-z clusters in agreement with the hierarchical growth of structure, which in turn could help characterise the merger, relaxation and evolution history of clusters, in future studies. [ABRIDGED]

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arXiv2012

Cluster Mass Profiles from a Bayesian Analysis of Weak Lensing Distortion and Magnification Measurements: Applications to Subaru Data

We directly construct model-independent mass profiles of galaxy clusters from combined weak-lensing distortion and magnification measurements within a Bayesian statistical framework,which allows for a full parameter-space extraction of the underlying signal. This method applies to the full range of radius outside the Einstein radius, and recovers the absolute mass normalization. We apply our method to deep Subaru imaging of five high-mass (>10^{15}M_{sun}) clusters, A1689, A1703, A370, Cl0024+17, and RXJ1347-11, to obtain accurate profiles to beyond the virial radius (r_{vir}). For each cluster the lens distortion and magnification data are shown to be consistent with each other, and the total signal-to-noise ratio of the combined measurements ranges from 13 to 24 per cluster. We form a model-independent mass profile from stacking the clusters, which is detected at 37σ out to R ~ 1.7r_{vir}. The projected logarithmic slope steepens from -1.01 \pm 0.09 at R ~ 0.1r_{vir} to -1.92 \pm 0.51 at R ~ 0.9r_{vir}. We also derive for each cluster inner strong-lensing based mass profiles from deep HST/ACS observations, which we show overlap well with the outer Subaru-based profiles and together are well described by a generalized form of the Navarro-Frenk-White profile, except for the ongoing merger RXJ1347-11, with modest variations in the central cusp slope (-dlnρ/dlnr < 0.9). The improvement here from adding the magnification measurements is significant, ~30% in terms of cluster mass profile measurements, compared with the lensing distortion signal.

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arXiv2012

CLASH: Mass Distribution in and around MACS J1206.2-0847 from a Full Cluster Lensing Analysis

We derive an accurate mass distribution of the galaxy cluster MACS J1206.2-0847 (z=0.439) from a combined weak-lensing distortion, magnification, and strong-lensing analysis of wide-field Subaru BVRIz' imaging and our recent 16-band Hubble Space Telescope observations taken as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) program. We find good agreement in the regions of overlap between several weak and strong lensing mass reconstructions using a wide variety of modeling methods, ensuring consistency. The Subaru data reveal the presence of a surrounding large scale structure with the major axis running approximately north-west south-east (NW-SE), aligned with the cluster and its brightest galaxy shapes, showing elongation with a \sim 2:1 axis ratio in the plane of the sky. Our full-lensing mass profile exhibits a shallow profile slope dlnΣ/dlnR\sim -1 at cluster outskirts (R>1Mpc/h), whereas the mass distribution excluding the NW-SE excess regions steepens further out, well described by the Navarro-Frenk-White form. Assuming a spherical halo, we obtain a virial mass M_{vir}=(1.1\pm 0.2\pm 0.1)\times 10^{15} M_{sun}/h and a halo concentration c_{vir} = 6.9\pm 1.0\pm 1.2 (\sim 5.7 when the central 50kpc/h is excluded), which falls in the range 4< <7 of average c(M,z) predictions for relaxed clusters from recent Lambda cold dark matter simulations. Our full lensing results are found to be in agreement with X-ray mass measurements where the data overlap, and when combined with Chandra gas mass measurements, yield a cumulative gas mass fraction of 13.7^{+4.5}_{-3.0}% at 0.7Mpc/h (\approx 1.7r_{2500}), a typical value observed for high mass clusters.

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arXiv2012

A highly magnified candidate for a young galaxy seen when the Universe was 500 Myrs old

The early Universe at redshift z\sim6-11 marks the reionization of the intergalactic medium, following the formation of the first generation of stars. However, those young galaxies at a cosmic age of \lesssim 500 million years (Myr, at z \gtrsim 10) remain largely unexplored as they are at or beyond the sensitivity limits of current large telescopes. Gravitational lensing by galaxy clusters enables the detection of high-redshift galaxies that are fainter than what otherwise could be found in the deepest images of the sky. We report the discovery of an object found in the multi-band observations of the cluster MACS1149+22 that has a high probability of being a gravitationally magnified object from the early universe. The object is firmly detected (12 sigma) in the two reddest bands of HST/WFC3, and not detected below 1.2 μm, matching the characteristics of z\sim9 objects. We derive a robust photometric redshift of z = 9.6 \pm 0.2, corresponding to a cosmic age of 490 \pm 15Myr (i.e., 3.6% of the age of the Universe). The large number of bands used to derive the redshift estimate make it one of the most accurate estimates ever obtained for such a distant object. The significant magnification by cluster lensing (a factor of \sim15) allows us to analyze the object's ultra-violet and optical luminosity in its rest-frame, thus enabling us to constrain on its stellar mass, star-formation rate and age. If the galaxy is indeed at such a large redshift, then its age is less than 200 Myr (at the 95% confidence level), implying a formation redshift of zf \lesssim 14. The object is the first z>9 candidate that is bright enough for detailed spectroscopic studies with JWST, demonstrating the unique potential of galaxy cluster fields for finding highly magnified, intrinsically faint galaxies at the highest redshifts.

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arXiv2012

The Universal Einstein Radius Distribution from 10,000 SDSS Clusters

We present results from strong-lens modelling of 10,000 SDSS clusters, to establish the universal distribution of Einstein radii. Detailed lensing analyses have shown that the inner mass distribution of clusters can be accurately modelled by assuming light traces mass, successfully uncovering large numbers of multiple-images. Approximate critical curves and the effective Einstein radius of each cluster can therefore be readily calculated, from the distribution of member galaxies and scaled by their luminosities. We use a subsample of 10 well-studied clusters covered by both SDSS and HST to calibrate and test this method, and show that an accurate determination of the Einstein radius and mass can be achieved by this approach "blindly", in an automated way, and without requiring multiple images as input. We present the results of the first 10,000 clusters analysed in the range $0.1 =0.73^{+0.02}_{-0.03}$, $σ=0.316^{+0.004}_{-0.002}$, and with higher abundance of large $θ_{e}$ clusters than predicted by $Λ$CDM. We visually inspect each of the clusters with $θ_{e}>40 \arcsec$ ($z_{s}=2$) and find that $\sim20%$ are boosted by various projection effects detailed here, remaining with $\sim40$ real giant-lens candidates, with a maximum of $θ_{e}=69\pm12 \arcsec$ ($z_{s}=2$) for the most massive candidate, in agreement with semi-analytic calculations. The results of this work should be verified further when an extended calibration sample is available.

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arXiv2012

Bolocam Observations of Two Unconfirmed Galaxy Cluster Candidates from the Planck Early SZ Sample

We present Bolocam observations of two galaxy cluster candidates reported as unconfirmed in the Planck early Sunyaev-Zel'dovich (eSZ) sample, PLCKESZ G115.71+17.52 and PLCKESZ G189.84-37.24. We observed each of these candidates with Bolocam at 140 GHz from the Caltech Submm Observatory in October 2011. The resulting images have white noise levels of ~30 μKCMB-arcmin in their central regions. We find a significant SZ decrement towards PLCKESZ G115.71. This decrement has a false detection probability of 5.3\times10-5, and we therefore confirm PLCKESZ G115.71 as a cluster. The maximum SZ decrement towards PLCKESZ G189.84 corresponds to a false detection probability of 0.027, and it therefore remains as an unconfirmed cluster candidate. In order to make our SZ-derived results more robust, we have also analyzed data from the Wide-field Infrared Survey Explorer (WISE) at the location of each cluster candidate. We find an overdensity of WISE sources consistent with other clusters in the eSZ at the location of PLCKESZ G115.71, providing further evidence that it is a cluster. We do not find a significant overdensity of WISE sources at the location of PLCKESZ G189.84.

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arXiv2012

CLASH: Precise New Constraints on the Mass Profile of Abell 2261

We precisely constrain the inner mass profile of Abell 2261 (z=0.225) for the first time and determine this cluster is not "over-concentrated" as found previously, implying a formation time in agreement with ΛCDM expectations. These results are based on strong lensing analyses of new 16-band HST imaging obtained as part of the Cluster Lensing and Supernova survey with Hubble (CLASH). Combining this with revised weak lensing analyses of Subaru wide field imaging with 5-band Subaru + KPNO photometry, we place tight new constraints on the halo virial mass M_vir = 2.2\pm0.2\times10^15 M\odot/h70 (within r \approx 3 Mpc/h70) and concentration c = 6.2 \pm 0.3 when assuming a spherical halo. This agrees broadly with average c(M,z) predictions from recent ΛCDM simulations which span 5 <~ <~ 8. Our most significant systematic uncertainty is halo elongation along the line of sight. To estimate this, we also derive a mass profile based on archival Chandra X-ray observations and find it to be ~35% lower than our lensing-derived profile at r2500 ~ 600 kpc. Agreement can be achieved by a halo elongated with a ~2:1 axis ratio along our line of sight. For this elongated halo model, we find M_vir = 1.7\pm0.2\times10^15 M\odot/h70 and c_vir = 4.6\pm0.2, placing rough lower limits on these values. The need for halo elongation can be partially obviated by non-thermal pressure support and, perhaps entirely, by systematic errors in the X-ray mass measurements. We estimate the effect of background structures based on MMT/Hectospec spectroscopic redshifts and find these tend to lower Mvir further by ~7% and increase cvir by ~5%.

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arXiv2012

Cluster Lensing And Supernova survey with Hubble (CLASH): An Overview

The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit multi-cycle treasury program to use the gravitational lensing properties of 25 galaxy clusters to accurately constrain their mass distributions. The survey, described in detail in this paper, will definitively establish the degree of concentration of dark matter in the cluster cores, a key prediction of CDM. The CLASH cluster sample is larger and less biased than current samples of space-based imaging studies of clusters to similar depth, as we have minimized lensing-based selection that favors systems with overly dense cores. Specifically, twenty CLASH clusters are solely X-ray selected. The X-ray selected clusters are massive (kT > 5 keV; 5 - 30 x 10^14 M_solar) and, in most cases, dynamically relaxed. Five additional clusters are included for their lensing strength (Einstein radii > 35 arcsec at z_source = 2) to further quantify the lensing bias on concentration, to yield high resolution dark matter maps, and to optimize the likelihood of finding highly magnified high-redshift (z > 7) galaxies. The high magnification, in some cases, provides angular resolutions unobtainable with any current UVOIR facility and can yield z > 7 candidates bright enough for spectroscopic follow-up. A total of 16 broadband filters, spanning the near-UV to near-IR, are employed for each 20-orbit campaign on each cluster. These data are used to measure precise (sigma_phz < 0.02(1+z)) photometric redshifts for dozens of newly discovered multiply-lensed images per cluster. Observations of each cluster are spread over 8 epochs to enable a search, primarily in the parallel fields, for Type Ia supernovae at z > 1 to improve constraints on the time dependence of the dark energy equation of state and the evolution of such supernovae in an epoch when the universe is matter dominated.

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arXiv2011

Star Formation and AGN activity in Galaxies classified using the 1.6 μm Bump and PAH features at $z = 0.4-2$

We have studied the star-formation and AGN activity of massive galaxies in the redshift range $z=0.4-2$, which are detected in a deep survey field using the AKARI InfraRed (IR) astronomical satellite and {\em Subaru} telescope toward the North Ecliptic Pole (NEP). The AKARI/IRC Mid-InfraRed (MIR) multiband photometry is used to trace their star-forming activities with the Polycyclic-Aromatic Hydrocarbon (PAH) emissions, which is also used to distinguish star-forming populations from AGN dominated ones and to estimate the Star Formation Rate (SFR) derived from their total emitting IR (TIR) luminosities. In combination with analyses of their stellar components, we have studied the MIR SED features of star-forming and AGN-harboring galaxies.

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arXiv2011

Cluster-Cluster Lensing and the Case of Abell 383

Extensive surveys of galaxy clusters motivate us to assess the likelihood of cluster-cluster lensing (CCL), namely, gravitational-lensing of a background cluster by a foreground cluster. We briefly describe the characteristics of CCLs in optical, X-ray and SZ measurements, and calculate their predicted numbers for $Λ$CDM parameters and a viable range of cluster mass functions and their uncertainties. The predicted number of CCLs in the strong-lensing regime varies from several ($<10$) to as high as a few dozen, depending mainly on whether lensing triaxiality bias is accounted for, through the c-M relation. A much larger number is predicted when taking into account also CCL in the weak-lensing regime. In addition to few previously suggested CCLs, we report a detection of a possible CCL in A383, where background candidate high-$z$ structures are magnified, as seen in deep Subaru observations.

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arXiv2011

Weak and strong lensing analysis of the triaxial matter distribution of A1689

Halos formed in the standard Lambda cold dark matter framework should follow an universal mass density profile and fit a well defined mass-concentration relation. Lensing analyses of clusters with a large Einstein radius seem to contradict this scenario, with the massive cluster Abell 1689 being often claimed as a notable example of a highly over-concentrated halo. Shape and orientation biases in lensing studies might be at the basis of this disagreement between theory and observations. We developed a method for a full three-dimensional analysis of strong and weak lensing data. Surface density maps estimated from lensing are de-projected to infer the actual triaxial structure of the cluster, whose mass distribution is approximated as an ellipsoidal Navarro-Frenk-White halo with arbitrary orientation. Inversion is performed under competing a priori assumptions, integrated in the method thanks to Bayesian statistics. We applied the method to A1689. Whatever the considered priors on shape and orientation, both weak and strong lensing analyses found the halo to be slightly over-concentrated but still consistent with theoretical predictions. We found some evidence for a mildly triaxial lens (minor to major axis ratio ~ 0.5 +- 0.2) with the major axis orientated along the line of sight. Exploiting priors from N-body simulations, we found mass M_{200} = (1.3 +- 0.4)x 10^{15}M_Sun and concentration c_{200} =10+-3 for the weak lensing analysis of Subaru data, M_{200} = (1.7 +- 0.3)x 10^{15}M_Sun and c_{200} =6.1+-0.9 for the strong lensing analysis of multiple image systems, and M_{200} = (1.3 +- 0.2)\times 10^{15}M_Sun and c_{200} =7.3+-0.8 for the combined weak plus strong analysis.

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arXiv2011

A Precise Cluster Mass Profile Averaged from the Highest-Quality Lensing Data

We outline our methods for obtaining high precision mass profiles, combining independent weak-lensing distortion, magnification, and strong-lensing measurements. For massive clusters the strong and weak lensing regimes contribute equal logarithmic coverage of the radial profile. The utility of high-quality data is limited by the cosmic noise from large scale structure along the line of sight. This noise is overcome when stacking clusters, as too are the effects of cluster asphericity and substructure, permitting a stringent test of theoretical models. We derive a mean radial mass profile of four similar mass clusters of high-quality HST and Subaru images, in the range R=40kpc/h to 2800kpc/h, where the inner radial boundary is sufficiently large to avoid smoothing from miscentering effects. The stacked mass profile is detected at 58-sigma significance over the entire radial range, with the contribution from the cosmic noise included. We show that the projected mass profile has a continuously steepening gradient out to beyond the virial radius, in remarkably good agreement with the standard Navarro-Frenk-White form predicted for the family of CDM-dominated halos in gravitational equilibrium. The central slope is constrained to lie in the range, -dlnρ/dln{r}=0.89^{+0.27}_{-0.39}. The mean concentration is c_{vir}=7.68^{+0.42}_{-0.40} (at a mean virial mass 1.54^{+0.11}_{-0.10}\times 10^{15} M_{sun}/h), which is high for relaxed, high-mass clusters, but consistent with LCDM when a sizable projection bias estimated from N-body simulations is considered. This possible tension will be more definitively explored with new cluster surveys, such as CLASH, LoCuSS, Subaru HSC, and XXM-XXL, to construct the c-M relation over a wider mass range.

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arXiv2011

Triaxiality and non-thermal gas pressure in Abell 1689

Clusters of galaxies are uniquely important cosmological probes of the evolution of the large scale structure, whose diagnostic power depends quite significantly on the ability to reliably determine their masses. Clusters are typically modeled as spherical systems whose intracluster gas is in strict hydrostatic equilibrium (i.e., the equilibrium gas pressure is provided entirely by thermal pressure), with the gravitational field dominated by dark matter, assumptions that are only rough approximations. In fact, numerical simulations indicate that galaxy clusters are typically triaxial, rather than spherical, and that turbulent gas motions (induced during hierarchical merger events) provide an appreciable pressure component. Extending our previous work, we present results of a joint analysis of X-ray, weak and strong lensing measurements of Abell 1689. The quality of the data allows us to determine both the triaxial shape of the cluster and the level of non-thermal pressure that is required if the intracluster gas is in hydrostatic equilibrium. We find that the dark matter axis ratios are 1.24 +/- 0.13 and 2.02 +/- 0.01 on the plane of the sky and along the line of sight, respectively, and that about 20% of the pressure is non-thermal. Our treatment demonstrates that the dynamical properties of clusters can be determined in a (mostly) bias-free way, enhancing the use of clusters as more precise cosmological probes.

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arXiv2011

LoCuSS: Subaru Weak Lensing Study of 30 Galaxy Clusters

(Abridged) We use Subaru data to conduct a detailed weak-lensing study of the dark matter distribution in a sample of 30 X-ray luminous galaxy clusters at 0.15<z<0.3. A weak-lensing signal is detected at high statistical significance in each cluster, the total detection S/N ranging from 5 to 13. In this paper we concentrate on fitting spherical models to the tangential distortion profiles of the clusters. When the models are fitted to the clusters individually, we are unable to discriminate statistically between SIS and NFW models. However when the tangential distortion profiles of the individual clusters are combined, and models fitted to the stacked profile, the SIS model is rejected at 6- and 11-sigma, respectively, for low- and high-mass bins. We also use the individual cluster NFW model fits to investigate the relationship between cluster mass (M_vir) and concentration (c_vir), finding an anti-correlation of c_vir and M_vir. The best-fit c_vir-M_vir relation is: c_vir(M_vir) propto M_vir^{-alpha} with alpha=0.41+/-0.19 -- i.e. a non-zero slope is detected at 2sigma significance. We then investigate the optimal radius within which to measure cluster mass, finding that the typical fractional errors are improved to sigma(M_Delta)/M_Delta ~ 0.1-0.2 for cluster masses at higher over-densities Delta=500-2000, from 0.2-0.3 for the virial over-density (~110). Further comparisons between mass measurements based on spherical model fitting and the model-independent aperture mass method reveal that the 2D aperture mass enclosed within a cylinder of a given aperture radius is systematically greater than the 3D spherical mass obtained from NFW model fitting: M_2D/M_3D= 1.34 and 1.40 for Delta=500 and 110, respectively. The amplitude of this effect agrees well with that predicted by integrating the NFW model along the line-of-sight.

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arXiv2011

A Weak Lensing Detection of the Cosmological Distance-Redshift Relation Behind Three Massive Clusters

The amplitude of weak lensing should increase with source distance, rising steeply behind a lens and saturating at high redshift, providing a model-independent means of measuring cosmic geometry. We measure the amplitude of weak lensing with redshift for three massive clusters, A370 (z=0.375), ZwCl0024+17 (z=0.395) and RXJ1347-11 (z=0.451), using deep, three-colour Subaru imaging. We define the depth of lensed populations with reference to the COSMOS and GOODS fields, providing a consistency check of photo-z estimates over a wide range of redshift and magnitude. The predicted distance-redshift relation is followed well for the deepest dataset, A370, for a wide range of cosmologies, and is consistent with less accurate data for the other two clusters. Scaling this result to a new survey of ~25 massive clusters should provide a useful cosmological constraint on w, complementing existing techniques, with distance measurements covering the untested redshift range, 1<z<5.

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arXiv2010

1.2 Meter Shielded Cassegrain Antenna for Close-Packed Radio Interferometer

Interferometric millimeter observations of the cosmic microwave background and clusters of galaxies with arcmin resolutions require antenna arrays with short spacings. Having all antennas co-mounted on a single steerable platform sets limits to the overall weight. A 25 kg lightweight novel carbon-fiber design for a 1.2 m diameter Cassegrain antenna is presented. The finite element analysis predicts excellent structural behavior under gravity, wind and thermal load. The primary and secondary mirror surfaces are aluminum coated with a thin TiO$_2$ top layer for protection. A low beam sidelobe level is achieved with a Gaussian feed illumination pattern with edge taper, designed based on feedhorn antenna simulations and verified in a far field beam pattern measurement. A shielding baffle reduces inter-antenna coupling to below $\sim$ -135 dB. The overall antenna efficiency, including a series of efficiency factors, is estimated to be around 60%, with major losses coming from the feed spillover and secondary blocking. With this new antenna, a detection rate of about 50 clusters per year is anticipated in a 13-element array operation.

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arXiv2010

Contamination of the Central Sunyaev--Zel'dovich Decrements in AMiBA Galaxy Cluster Observations

We investigate the contamination of the Sunyaev--Zel'dovich (SZ) effect for six galaxy clusters, A1689, A1995, A2142, A2163, A2261, and A2390, observed by the Y. T. Lee Array for Microwave Background Anisotropy during 2007. With the range of baselines used, we find that the largest effect (of order 13%-50% of the central SZ flux density) comes from primary anisotropies in the cosmic microwave background and exceeds the thermal noise in all six cases. Contamination from discrete radio sources is estimated to be at a level of (3%-60%) of the central SZ flux density. We use the statistics of these contaminating sources to estimate and correct the errors in the measured SZ effects of these clusters.

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arXiv2010

Constraining Intra-cluster Gas Models with AMiBA13

Clusters of galaxies have been used extensively to determine cosmological parameters. A major difficulty in making best use of Sunyaev-Zel'dovich (SZ) and X-ray observations of clusters for cosmology is that using X-ray observations it is difficult to measure the temperature distribution and therefore determine the density distribution in individual clusters of galaxies out to the virial radius. Observations with the new generation of SZ instruments are a promising alternative approach. We use clusters of galaxies drawn from high-resolution adaptive mesh refinement (AMR) cosmological simulations to study how well we should be able to constrain the large-scale distribution of the intra-cluster gas (ICG) in individual massive relaxed clusters using AMiBA in its configuration with 13 1.2-m diameter dishes (AMiBA13) along with X-ray observations. We show that non-isothermal beta models provide a good description of the ICG in our simulated relaxed clusters. We use simulated X-ray observations to estimate the quality of constraints on the distribution of gas density, and simulated SZ visibilities (AMiBA13 observations) for constraints on the large-scale temperature distribution of the ICG. We find that AMiBA13 visibilities should constrain the scale radius of the temperature distribution to about 50% accuracy. We conclude that the upgraded AMiBA, AMiBA13, should be a powerful instrument to constrain the large-scale distribution of the ICG.

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