arXiv subjects

Howard Yee

Publications and source records attributed to Howard Yee.

26 records · Page 2Linked to original sources

arXiv2006

Clusters of Galaxies at 1 < z < 2 : The Spitzer Adaptation of the Red-Sequence Cluster Survey

As the densest galaxy environments in the universe, clusters are vital to our understanding of the role that environment plays in galaxy formation and evolution. Unfortunately, the evolution of high-redshift cluster galaxies is poorly understood because of the ``cluster desert'' that exists at 1 < z < 2. The SpARCS collaboration is currently carrying out a 1-passband (z') imaging survey which, when combined with the pre-existing 50 square degree 3.6 micron Spitzer SWIRE Legacy Survey data, will efficiently detect hundreds of clusters in the cluster desert using an infrared application of the well-proven cluster red-sequence technique. We have already tested this 1-color (z' - [3.6]) approach using a 6 square degree ``pilot patch'' and shown it to be extremely successful at detecting clusters at 1 < z < 2. The clusters discovered in this project will be the first large sample of ``nascent'' galaxy clusters which connect the star-forming proto-cluster regions at z > 2 to the quiescent population at z < 1. The existing seven-passband Spitzer data (3.6, 4.5, 5.8, 8.0, 24, 70, 160 micron) will allow us to make the first measurements of the evolution of the cluster red-sequence, IR luminosity function, and the mid-IR dust-obscured star-formation rate for 1 < z < 2 clusters.

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arXiv2004

Chandra X-ray Observations of Newly Discovered, z ~ 1 Clusters from the Red-Sequence Cluster Survey

Observational studies of cluster evolution over moderate redshift ranges (to z ~ 1) are a powerful tool for constraining cosmological parameters, yet a comprehensive knowledge of the properties of these clusters has been hitherto unattained. Using a highly efficient optical selection technique, the Red-Sequence Cluster Survey (RCS) has unearthed a large sample of high redshift cluster candidates. All six of the clusters from this sample which have been observed with the Chandra X-Ray Observatory were detected in the X-ray. These Chandra follow-up observations (0.64 < z < 1.0) indicate that the clusters are systematically less luminous than their similarly rich, X-ray selected counterparts at lower redshifts, though they are consistent with standard Lx-Tx relationships. Comparisons with X-ray selected samples suggest that the discrepancy may be due in part to systematic differences in the spatial structure of the X-ray emitting gas. Our initial results from Chandra follow-up observations of six RCS clusters are presented, including beta model parameters and spectral information.

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arXiv2003

EXPLORE/OC: A Search for Planetary Transits in the Field of NGC 2660

We present preliminary photometric results of a monitoring study of the open cluster NGC 2660 as part of the EXPLORE/OC project to find planetary transits in Galactic open clusters. Analyzing a total of 21000 stars (3000 stars with photometry to 1% or better) yielded three light curves with low-amplitude signals like those typically expected for transiting hot Jupiters. Although their eclipses are most likely caused by non-planetary companions, our methods and photometric precision illustrate the potential to detect planetary transits around stars in nearby open clusters.

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arXiv2002

Constraints on Omega_m and sigma_8 from weak lensing in RCS fields

We have analysed 53 square degrees of imaging data from the Red-Sequence Cluster Survey (RCS), and measured the excess correlations in the shapes of galaxies on scales out to ~1.5 degrees. We separate the signal into an ``E''- (lensing) and ``B''-mode (systematics), which allows us to study residual systematics. On scales larger than 10 arcminutes, we find no ``B''-mode. On smaller scales we find a small, but significant ``B''-mode. This signal is also present when we select a sample of bright galaxies. These galaxies are rather insensitive to observational distortions, and we therefore conclude that the oberved ``B''-mode is likely to be caused by intrinsic alignments. We therefore limit the cosmic shear analysis to galaxies with 22 0.1+0.16Ω_m$ (95% confidence). Comparison of the RCS results with three other recent cosmic shear measurements shows excellent agreement. The current weak lensing results are also in good agreement with CMB measurements, when we allow the reionization optical depth tau and the spectral index n_s to vary. We present a simple demonstration of how the weak lensing results can be used as a prior in the parameter estimation from CMB measurements to derive constraints on the reionization optical depth tau. (abridged)

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arXiv2002

Current status of weak gravitational lensing

Weak gravitational lensing of distant galaxies by foreground structures has proven to be a powerful tool to study the mass distribution in the universe. Nowadays, attention has shifted from clusters of galaxies to the statistical properties of the large scale structures and the halos of (field) galaxies. These applications have become feasible with the advent of panoramic cameras on 4m class telescopes. In this review we will give an overview of recent advances in this fast evolving field of astronomy. We start with a discussion of the recent measurements of weak lensing by large scale structure (``cosmic shear''), which can be used to constrain cosmological parameters. We also show how weak lensing can be used to measure the relation between galaxies and dark matter (galaxy biasing) directly. Another area that benefitted greatly from the current data is the weak lensing by galaxies (galaxy-galaxy lensing). Weak lensing provides a unique probe of the gravitational potential on large scales. Hence, in the context of dark matter, it can provide constrains on the extent and shapes of dark matter halos. Furthermore, it can test alternative theories of gravity (without dark matter). The best constraint comes from the first detection of the anisotropy of the lensing signal around lens galaxies, which suggest that the dark matter halos are flattened. An isotropic signal, as predicted by MOND, is excluded with 99% confidence.

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arXiv2002

Lensing results from the Red-sequence Cluster Survey

We present a variety of weak lensing results based on the ongoing analysis of R_C-band imaging data from the Red-Sequence Cluster Survey (RCS). We briefly discuss the weak lensing signal induced by intervening large scale structure (cosmic shear), and study the properties of the dark matter halos surrounding galaxies with 19.5<R_C<21 (which have a median redshift of z=0.35) using a parametrized mass model for the galaxy mass distribution. This allows us for the first time to constrain the extent of the halos. We find a robust upper limit for the truncation parameter s<470 h^{-1} kpc (99.7% confidence). We also study the biasing properties of these galaxies as a function of scale. We find that both the bias parameter b and the galaxy-mass cross-correlation coefficient r vary with scale (on scales 0.1-6 h^{-1} Mpc). Interestingly, we find that r=0.57^{+0.08}_{-0.07} on scales ~0.5 h^{-1} Mpc.

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arXiv2001

First weak lensing results from the Red-Sequence Cluster Survey

The Red-Sequence Cluster Survey (RCS) is a 100 square degree galaxy cluster survey designed to provide a large sample of optically selected clusters of galaxies with redshifts 0.1 ^{1/2}= 111+-5 km/s. In addition we have constrained for the first time the extent of dark matter halos, and find a robust upper limit for the truncation parameter s<470 h^{-1} kpc (99.7% confidence). A preliminary analysis also excludes a simple ``prediction'' of lensing according to Modified Newtonian Dynamics (MOND) at high confidence.

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arXiv1995

A ROSAT Search for X-ray Emission from Quasar Host Clusters

We report the results of a search for X-ray emission from quasar host clusters at moderate redshift using the {\sl ROSAT} HRI. We detect no emission from the host clusters of 3C~263 (z=0.646) and PKS~2352-34 (z=0.706) to 3$σ$\ limits of 3.26 and 2.86 $\times$10$^{44}$\ ergs~s$^{-1}$ respectively (H$_o$=50, q$_o$=1/2) for clusters with r$_{core}$=125~kpc and T=5~keV. These limits show that these quasar host clusters are not substantially more X-ray luminous than optically or X-ray selected clusters of similar richnesses at z$\gtrsim$0.5. We also report the possible detection of a clump of X-ray emitting gas coincident with the brightest radio lobe of 3C~263. This may be evidence for the existence of a clumpy ICM in the host cluster of 3C~263.

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