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<R_C<24. We derive joint constraints on Omega_m and sigma_8, by marginalizing over Gamma, Omega_Lambda and the source redshift distribution, using different priors. We obtain a conservative constraint of $\sigma_8=0.45^{+0.09}_{-0.12} \Omega_m^{-0.55}$ (95% confidence). A better constraint is derived when we use Gaussian priors redshift distribution. For this choice of priors, we find $\sigma_8=(0.46^{+0.05}_{-0.07})\Omega_m^{-0.52}$ (95% confidence). Using our setof Gaussian priors, we find that we can place a lower bound on Gamma: Gamma>0.1+0.16\Omega_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)Comment: 9 pages, 6 figures, Accepted for publication in the Astrophysical Journa

The Masses and Shapes of Dark Matter Halos from Galaxy-Galaxy Lensing in the CFHTLS

We present the first galaxy-galaxy weak lensing results using early data from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). These results are based on ~22 sq. deg. of i' data. From this data, we estimate the average velocity dispersion for an L* galaxy at a redshift of 0.3 to be 137 +- 11 km/s, with a virial mass, M_{200}, of 1.1 +- 0.2 \times 10^{12} h^{-1} Msun and a rest frame R-band mass-to-light ratio of 173 +- 34 h Msun/Lsun. We also investigate various possible sources of systematic error in detail. Additionally, we separate our lens sample into two sub-samples, divided by apparent magnitude, thus average redshift. From this early data we do not detect significant evolution in galaxy dark matter halo mass-to-light ratios from a redshift of 0.45 to 0.27. Finally, we test for non-spherical galaxy dark matter halos. Our results favor a dark matter halo with an ellipticity of ~0.3 at the 2-sigma level when averaged over all galaxies. If the sample of foreground lens galaxies is selected to favor ellipticals, the mean halo ellipticity and significance of this result increase.Comment: 12 pages, 11 figures, accepted to ApJ, uses emulateap

Properties of galaxy dark matter halos from weak lensing

We present the results of a study of weak lensing by galaxies based on 45.5 deg$^2$ of $R_C$ band imaging data from the Red-Sequence Cluster Survey (RCS). We present the first weak lensing detection of the flattening of galaxy dark matter halos. We use a simple model in which the ellipticity of the halo is $f$ times the observed ellipticity of the lens. We find a best fit value of $f=0.77^{+0.18}_{-0.21}$, suggesting that the dark matter halos are somewhat rounder than the light distribution. The fact that we detect a significant flattening implies that the halos are well aligned with the light distribution. Given the average ellipticity of the lenses, this implies a halo ellipticity of $=0.33^{+0.07}_{-0.09}$, in fair agreement with results from numerical simulations of CDM. This result provides strong support for the existence of dark matter, as an isotropic lensing signal is excluded with 99.5% confidence. We also study the average mass profile around the lenses, using a maximum likelihood analysis. We consider two models for the halo mass profile: a truncated isothermal sphere (TIS) and an NFW profile. We adopt observationally motivated scaling relations between the lens luminosity and the velocity dispersion and the extent of the halo. The best fit NFW model yields a mass $M_{200}=(8.4\pm0.7\pm0.4)\times 10^{11} h^{-1} M_\odot$ and a scale radius $r_s=16.2^{+3.6}_{-2.9} h^{-1}$ kpc. This value for the scale radius is in excellent agreement with predictions from numerical simulations for a halo of this mass.Comment: Significantly revised version, accepted for publication in ApJ 11 pages, 6 figure

The Phase Space and Stellar Populations of Cluster Galaxies at z ~ 1: Simultaneous Constraints on the Location and Timescale of Satellite Quenching

We investigate the velocity vs. position phase space of z ~ 1 cluster galaxies using a set of 424 spectroscopic redshifts in 9 clusters drawn from the GCLASS survey. Dividing the galaxy population into three categories: quiescent, star-forming, and poststarburst, we find that these populations have distinct distributions in phase space. Most striking are the poststarburst galaxies, which are commonly found at small clustercentric radii with high clustercentric velocities, and appear to trace a coherent ``ring" in phase space. Using several zoom simulations of clusters we show that the coherent distribution of the poststarbursts can be reasonably well-reproduced using a simple quenching scenario. Specifically, the phase space is best reproduced if satellite quenching occurs on a rapid timescale (0.1 < tau_{Q} < 0.5 Gyr) after galaxies make their first passage of R ~ 0.5R_{200}, a process that takes a total time of ~ 1 Gyr after first infall. We compare this quenching timescale to the timescale implied by the stellar populations of the poststarburst galaxies and find that the poststarburst spectra are well-fit by a rapid quenching (tau_{Q} = 0.4^{+0.3}_{-0.4} Gyr) of a typical star-forming galaxy. The similarity between the quenching timescales derived from these independent indicators is a strong consistency check of the quenching model. Given that the model implies satellite quenching is rapid, and occurs well within R_{200}, this would suggest that ram-pressure stripping of either the hot or cold gas component of galaxies are the most plausible candidates for the physical mechanism. The high cold gas consumption rates at z ~ 1 make it difficult to determine if hot or cold gas stripping is dominant; however, measurements of the redshift evolution of the satellite quenching timescale and location may be capable of distinguishing between the two.Comment: 10 pages, 4 figures, submitted to the Ap

Group-finding with photometric redshifts: The Photo-z Probability Peaks algorithm

We present a galaxy group-finding algorithm, the Photo-z Probability Peaks (P3) algorithm, optimized for locating small galaxy groups using photometric redshift data by searching for peaks in the signal-to-noise of the local overdensity of galaxies in a three-dimensional grid. This method is an improvement over similar two-dimensional matched-filter methods in reducing background contamination through the use of redshift information, allowing it to accurately detect groups at lower richness. We present the results of tests of our algorithm on galaxy catalogues from the Millennium Simulation. Using a minimum S/N of 3 for detected groups, a group aperture size of 0.25 Mpc/h, and assuming photometric redshift accuracy of sigma_z = 0.05 it attains a purity of 84% and detects ~295 groups/deg.^2 with an average group richness of 8.6 members. Assuming photometric redshift accuracy of sigma_z = 0.02, it attains a purity of 97% and detects ~143 groups/deg.^2 with an average group richness of 12.5 members. We also test our algorithm on data available for the COSMOS field and the presently-available fields from the CFHTLS-Wide survey, presenting preliminary results of this analysis.Comment: Accepted for publication by MNRAS, 16 pages, 11 color figure

CFHTLenS: Co-evolution of galaxies and their dark matter haloes

Galaxy-galaxy weak lensing is a direct probe of the mean matter distribution around galaxies. The depth and sky coverage of the CFHT Legacy Survey yield statistically significant galaxy halo mass measurements over a much wider range of stellar masses ($10^{8.75}$ to $10^{11.3} M_{\odot}$) and redshifts ($0.2 < z < 0.8$) than previous weak lensing studies. At redshift $z \sim 0.5$, the stellar-to-halo mass ratio (SHMR) reaches a maximum of $4.0\pm0.2$ percent as a function of halo mass at $\sim 10^{12.25} M_{\odot}$. We find, for the first time from weak lensing alone, evidence for significant evolution in the SHMR: the peak ratio falls as a function of cosmic time from $4.5 \pm 0.3$ percent at $z \sim 0.7$ to $3.4 \pm 0.2$ percent at $z \sim 0.3$, and shifts to lower stellar mass haloes. These evolutionary trends are dominated by red galaxies, and are consistent with a model in which the stellar mass above which star formation is quenched "downsizes" with cosmic time. In contrast, the SHMR of blue, star-forming galaxies is well-fit by a power law that does not evolve with time. This suggests that blue galaxies form stars at a rate that is balanced with their dark matter accretion in such a way that they evolve along the SHMR locus. The redshift dependence of the SHMR can be used to constrain the evolution of the galaxy population over cosmic time.Comment: 18 pages, MNRAS, in pres

Measurement of the bias parameter from weak lensing

We have measured the correlation between the lensing signal induced by (dark) matter and number counts of galaxies on scales ranging from 0.15-3.0 h_{50}^{-1} Mpc (which correspond to aperture radii of 1-15 arcminutes). This provides a direct probe of the scale dependence of the ratio of the classical bias parameter b and the galaxy-mass correlation coefficient r. The results presented here are based on 16 deg^2 of R_C band data taken with the CFHT as part of the Red-Sequence Cluster Survey. We used a sample of lens galaxies with 19.5<R_C<21, and a sample of source galaxies with 21.5<R_C<24. The results are consistent with a scale independent value of b/r, which provides valuable constraints on models of galaxy formation on scales that can only be probed through weak lensing. For the currently favored cosmology (\Omega_m=0.3, \Omega_\Lambda=0.7) we find b/r=1.05^{+0.12}_{-0.10}, similar to what is found on larger scales (~10 h_{50}^{-1} Mpc) from local dynamical estimates. These results support the hypothesis that light traces mass on scales ranging from 0.15 out to ~10 h_{50}^{-1} Mpc. The accuracy of the measurement will improve significantly in the coming years, enabling us to measure both b and r separately as a function of scale.Comment: revised version submitted to ApJ Letters. 4 pages, 2 figure

Planet Hunters. V. A Confirmed Jupiter-Size Planet in the Habitable Zone and 42 Planet Candidates from the Kepler Archive Data

We report the latest Planet Hunter results, including PH2 b, a Jupiter-size (R_PL = 10.12 \pm 0.56 R_E) planet orbiting in the habitable zone of a solar-type star. PH2 b was elevated from candidate status when a series of false positive tests yielded a 99.9% confidence level that transit events detected around the star KIC 12735740 had a planetary origin. Planet Hunter volunteers have also discovered 42 new planet candidates in the Kepler public archive data, of which 33 have at least three transits recorded. Most of these transit candidates have orbital periods longer than 100 days and 20 are potentially located in the habitable zones of their host stars. Nine candidates were detected with only two transit events and the prospective periods are longer than 400 days. The photometric models suggest that these objects have radii that range between Neptune to Jupiter. These detections nearly double the number of gas giant planet candidates orbiting at habitable zone distances. We conducted spectroscopic observations for nine of the brighter targets to improve the stellar parameters and we obtained adaptive optics imaging for four of the stars to search for blended background or foreground stars that could confuse our photometric modeling. We present an iterative analysis method to derive the stellar and planet properties and uncertainties by combining the available spectroscopic parameters, stellar evolution models, and transiting light curve parameters, weighted by the measurement errors. Planet Hunters is a citizen science project that crowd-sources the assessment of NASA Kepler light curves. The discovery of these 43 planet candidates demonstrates the success of citizen scientists at identifying planet candidates, even in longer period orbits with only two or three transit events.Comment: 35 pages, 11 figures, 6 tables, accepted and published on ApJ ApJ, 776, 1

A measurement of weak lensing by large scale structure in RCS fields

We have analysed ~24 square degrees of R_C-band imaging data from the Red-Sequence Cluster Survey (RCS), and measured the excess correlations between galaxy ellipticities on scales ranging from 1 to 30 arcminutes. We have used data from two different telescopes: ~16.4 square degrees of CFHT data and ~7.6 square degrees of CTIO 4-meter data, distributed over 13 widely separated patches. For the first time, a direct comparison can be made of the lensing signal measured using different instruments, which provides an important test of the weak lensing analysis itself. The measurements obtained from the two telescopes agree well. For the lensing analysis we use galaxies down to a limiting magnitude of R_C=24, for which the redshift distribution is known relatively well. This allows us to constrain some cosmological parameters. For the currently favored $\Lambda$CDM model $(\Omega_m=0.3, \Omega_\Lambda=0.7, \Gamma=0.21)$ we obtain $\sigma_8=0.81^{+0.14}_{-0.19}$ (95% confidence), in agreement with the results from Van Waerbeke et al. (2001) which used fainter galaxies (and consequently higher redshift galaxies). The good agreement between these two very different weak lensing studies demonstrates that weak lensing is a useful tool in observational cosmology.Comment: accepted for publication in the Astrophysical Journal 11 pages, 12 figure

Annotation of two large contiguous regions from the Haemonchus contortus genome using RNA-seq and comparative analysis with Caenorhabditis elegans

The genomes of numerous parasitic nematodes are currently being sequenced, but their complexity and size, together with high levels of intra-specific sequence variation and a lack of reference genomes, makes their assembly and annotation a challenging task. Haemonchus contortus is an economically significant parasite of livestock that is widely used for basic research as well as for vaccine development and drug discovery. It is one of many medically and economically important parasites within the strongylid nematode group. This group of parasites has the closest phylogenetic relationship with the model organism Caenorhabditis elegans, making comparative analysis a potentially powerful tool for genome annotation and functional studies. To investigate this hypothesis, we sequenced two contiguous fragments from the H. contortus genome and undertook detailed annotation and comparative analysis with C. elegans. The adult H. contortus transcriptome was sequenced using an Illumina platform and RNA-seq was used to annotate a 409 kb overlapping BAC tiling path relating to the X chromosome and a 181 kb BAC insert relating to chromosome I. In total, 40 genes and 12 putative transposable elements were identified. 97.5% of the annotated genes had detectable homologues in C. elegans of which 60% had putative orthologues, significantly higher than previous analyses based on EST analysis. Gene density appears to be less in H. contortus than in C. elegans, with annotated H. contortus genes being an average of two-to-three times larger than their putative C. elegans orthologues due to a greater intron number and size. Synteny appears high but gene order is generally poorly conserved, although areas of conserved microsynteny are apparent. C. elegans operons appear to be partially conserved in H. contortus. Our findings suggest that a combination of RNA-seq and comparative analysis with C. elegans is a powerful approach for the annotation and analysis of strongylid nematode genomes