[en] We describe a new method of combining optical and infrared photometry to select luminous red galaxies (LRGs) at redshifts $z><!--\; >\; -->0.6$. We explore this technique using a combination of optical photometry from CFHTLS and Hubble Space Telescope, infrared photometry from the Wide-Field Infrared Survey Explorer satellite, and spectroscopic or photometric redshifts from the DEEP2 Galaxy Redshift Survey or COSMOS. We present a variety of methods for testing the success of our selection and present methods for optimization given a set of rest-frame color and redshift requirements. We have tested this selection in two different regions of the sky, the COSMOS and Extended Groth Strip (EGS) fields, to reduce the effect of cosmic/sample variance. We have used these methods to assemble large samples of LRGs for two different ancillary programs as a part of the Sloan Digital Sky Survey (SDSS)-III/Baryon Oscillation Spectroscopic Survey. This technique is now being used to select ∼600,000 LRG targets for SDSS-IV/Extended Baryon Oscillation Spectroscopic Survey, which began observations in Fall 2014, and will be adapted for the proposed Dark Energy Spectroscopic Instrument survey. We have found that these methods can select high-redshift LRGs efficiently with minimal stellar contamination; this is extremely difficult to achieve with selections that rely on optical photometry alone.

[en] Many of the cosmological tests to be performed by planned dark energy experiments will require extremely well-characterized photometric redshift measurements. Current estimates for cosmic shear are that the true mean redshift of the objects in each photo-z bin must be known to better than 0.002(1 + z), and the width of the bin must be known to ∼0.003(1 + z) if errors in cosmological measurements are not to be degraded significantly. A conventional approach is to calibrate these photometric redshifts with large sets of spectroscopic redshifts. However, at the depths probed by Stage III surveys (such as DES), let alone Stage IV (LSST, JDEM, and Euclid), existing large redshift samples have all been highly (25%-60%) incomplete, with a strong dependence of success rate on both redshift and galaxy properties. A powerful alternative approach is to exploit the clustering of galaxies to perform photometric redshift calibrations. Measuring the two-point angular cross-correlation between objects in some photometric redshift bin and objects with known spectroscopic redshift, as a function of the spectroscopic z, allows the true redshift distribution of a photometric sample to be reconstructed in detail, even if it includes objects too faint for spectroscopy or if spectroscopic samples are highly incomplete. We test this technique using mock DEEP2 Galaxy Redshift survey light cones constructed from the Millennium Simulation semi-analytic galaxy catalogs. From this realistic test, which incorporates the effects of galaxy bias evolution and cosmic variance, we find that the true redshift distribution of a photometric sample can, in fact, be determined accurately with cross-correlation techniques. We also compare the empirical error in the reconstruction of redshift distributions to previous analytic predictions, finding that additional components must be included in error budgets to match the simulation results. This extra error contribution is small for surveys that sample large areas of sky (>∼10⁰-100⁰), but dominant for ∼1 deg² fields. We conclude by presenting a step-by-step, optimized recipe for reconstructing redshift distributions from cross-correlation information using standard correlation measurements.

[en] The exponential scale length (L _d) of the Milky Way’s (MW’s) disk is a critical parameter for describing the global physical size of our Galaxy, important both for interpreting other Galactic measurements and helping us to understand how our Galaxy fits into extragalactic contexts. Unfortunately, current estimates span a wide range of values and are often statistically incompatible with one another. Here, we perform a Bayesian meta-analysis to determine an improved, aggregate estimate for L _d, utilizing a mixture-model approach to account for the possibility that any one measurement has not properly accounted for all statistical or systematic errors. Within this machinery, we explore a variety of ways of modeling the nature of problematic measurements, and then employ a Bayesian model averaging technique to derive net posterior distributions that incorporate any model-selection uncertainty. Our meta-analysis combines 29 different (15 visible and 14 infrared) photometric measurements of L _d available in the literature; these involve a broad assortment of observational data sets, MW models and assumptions, and methodologies, all tabulated herein. Analyzing the visible and infrared measurements separately yields estimates for L _d of ${2.71}_{-<!--\; ???\; -->0.20}^{+0.22}$ kpc and ${2.51}_{-<!--\; ???\; -->0.13}^{+0.15}$ kpc, respectively, whereas considering them all combined yields 2.64 ± 0.13 kpc. The ratio between the visible and infrared scale lengths determined here is very similar to that measured in external spiral galaxies. We use these results to update the model of the Galactic disk from our previous work, constraining its stellar mass to be ${4.8}_{-<!--\; ???\; -->1.1}^{+1.5}\times <!--\; ??\; -->{10}^{10}$ M _⊙, and the MW’s total stellar mass to be ${5.7}_{-<!--\; ???\; -->1.1}^{+1.5}\times <!--\; ??\; -->{10}^{10}$ M _⊙.

[en] We present improved estimates of several global properties of the Milky Way, including its current star formation rate (SFR), the stellar mass contained in its disk and bulge+bar components, as well as its total stellar mass. We do so by combining previous measurements from the literature using a hierarchical Bayesian (HB) statistical method that allows us to account for the possibility that any value may be incorrect or have underestimated errors. We show that this method is robust to a wide variety of assumptions about the nature of problems in individual measurements or error estimates. Ultimately, our analysis yields an SFR for the Galaxy of ${\stackrel{\dot{}<!--\; ??\; -->}{\mathrm{M}}}_{\star <!--\; ???\; -->}=1.65\pm <!--\; ??\; -->0.19{\mathrm{M}}_{\odot <!--\; ???\; -->}\mathrm{y}{\mathrm{r}}^{-<!--\; ???\; -->1}$, assuming a Kroupa initial mass function (IMF). By combining HB methods with Monte Carlo simulations that incorporate the latest estimates of the Galactocentric radius of the Sun, R₀, the exponential scale length of the disk, L_d, and the local surface density of stellar mass, ${\mathrm{\Sigma <!--\; ??\; -->}}_{\star <!--\; ???\; -->}(R_0)$, we show that the mass of the Galactic bulge+bar is ${\mathrm{M}}_{\star <!--\; ???\; -->}^B=0.91\pm <!--\; ??\; -->0.07\times <!--\; ??\; -->{10}^{10}$ ${\mathrm{M}}_{\odot <!--\; ???\; -->}$, the disk mass is ${\mathrm{M}}_{\star <!--\; ???\; -->}^D=5.17\pm <!--\; ??\; -->1.11\times <!--\; ??\; -->{10}^{10}$ ${\mathrm{M}}_{\odot <!--\; ???\; -->}$, and their combination yields a total stellar mass of ${\mathrm{M}}_{\star <!--\; ???\; -->}=6.08\pm <!--\; ??\; -->1.14\times <!--\; ??\; -->{10}^{10}$ ${\mathrm{M}}_{\odot <!--\; ???\; -->}$ (assuming a Kroupa IMF and an exponential disk profile). This analysis is based upon a new compilation of literature bulge mass estimates, normalized to common assumptions about the stellar IMF and Galactic disk properties, presented herein. We additionally find a bulge-to-total mass ratio for the Milky Way of $B/T={0.150}_{-<!--\; ???\; -->0.019}^{+0.028}$ and a specific SFR of ${\stackrel{\dot{}<!--\; ??\; -->}{\mathrm{M}}}_{\star <!--\; ???\; -->}/{\mathrm{M}}_{\star <!--\; ???\; -->}=2.71\pm <!--\; ??\; -->0.59\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->11}$ yr⁻¹.

[en] Cross-correlation techniques provide a promising avenue for calibrating photometric redshifts and determining redshift distributions using spectroscopy which is systematically incomplete (e.g., current deep spectroscopic surveys fail to obtain secure redshifts for 30%-50% or more of the galaxies targeted). In this paper, we improve on the redshift distribution reconstruction methods from our previous work by incorporating full covariance information into our correlation function fits. Correlation function measurements are strongly covariant between angular or spatial bins, and accounting for this in fitting can yield substantial reduction in errors. However, frequently the covariance matrices used in these calculations are determined from a relatively small set (dozens rather than hundreds) of subsamples or mock catalogs, resulting in noisy covariance matrices whose inversion is ill-conditioned and numerically unstable. We present here a method of conditioning the covariance matrix known as ridge regression which results in a more well behaved inversion than other techniques common in large-scale structure studies. We demonstrate that ridge regression significantly improves the determination of correlation function parameters. We then apply these improved techniques to the problem of reconstructing redshift distributions. By incorporating full covariance information, applying ridge regression, and changing the weighting of fields in obtaining average correlation functions, we obtain reductions in the mean redshift distribution reconstruction error of as much as ∼40% compared to previous methods. We provide a description of POWERFIT, an IDL code for performing power-law fits to correlation functions with ridge regression conditioning that we are making publicly available.

[en] As part of the DEEP2 galaxy redshift survey, we analyze absorption line strengths in stacked Keck/DEIMOS spectra of red field galaxies with weak to no emission lines, at redshifts 0.7 ∼< z ∼< 1. Comparison with models of stellar population synthesis shows that red galaxies at z ∼ 0:9 have mean luminosity-weighted ages of the order of only 1 Gyr and at least solar metallicities. These ages cannot be reconciled with a scenario where all stars evolved passively after forming at very high z. Rather, a significant fraction of stars can be no more than 1 Gyr old, which means that some star formation in the stacked populations continued to at least z ∼ 1:2. Furthermore, a comparison of these distant galaxies with a local SDSS sample, using stellar populations synthesis models, shows that the drop in the equivalent width of H(delta) from z ∼ 0:9 to 0.1 is less than predicted by passively evolving models. This admits of two interpretations: either each individual galaxy experiences continuing low-level star formation, or the red-sequence galaxy population from z ∼ 0:9 to 0.1 is continually being added to by new galaxies with younger stars

[en] We measure the evolution in the virial mass-to-light ratio(M₂₀₀/L_B) and virial-to-stellar mass ratio (M₂₀₀/M*) for isolated ∼;L*galaxies between z∼;1 and z∼;0 by combining data from the DEEP2 Galaxy Redshift Survey and the Sloan Digital Sky Survey. Utilizing the motions of satellite galaxies around isolated galaxies, we measure line-of-sight velocity dispersions and derive dark matter halo virial masses for these host galaxies. At both epochs the velocity dispersion of satellites correlates with host galaxy stellar mass, with sigma prop M*(0.4±0.1),while the relation between satellite velocity dispersion and host galaxy B-band luminosity may grow somewhat shallower, from sigma prop L_B(0.6±0.1) at z∼;1 to sigma proportional to L_B(0.4±0.1) at z∼;0. The evolution in M₂₀₀/M* from z∼;1 to z∼;0 displays a bimodality, insofar as host galaxies with stellar mass below M*∼;1011 h-11M_Sub maintain a constant ratio (the intrinsic increase is constrained to a factor of1.1+-0.5) while host galaxies above this mass experience a factor of3.3+-2.2 increase in their virial-to-stellar mass ratio. This result can be easily understood if galaxies below this stellar mass scale continue to form stars while star formation in galaxies above this scale is quenched and the dark matter halos of galaxies both above and below this scale grow in accordance with LCDM cosmological simulations. Host galaxies that are red in U - B color have larger satellite dispersions and hence reside on average in more massive halos than blue galaxies at both z∼;1 and z∼;0. The satellite population of host galaxies varies little between these epochs; the only significant difference is that satellites at z∼;1 tend to be comparatively fainter (by ∼;0.15 magnitudes in the mean) relative to their host luminosity than satellites at z ∼; 0.The redshift and host galaxy stellar mass dependence of M₂₀₀/M* agrees qualitatively with the Millennium Run semi-analytic model of galaxy formation

[en] We perform a cross-correlation analysis of microwave data from the Wilkinson Microwave Anisotropy Probe and photometric quasars from the Sloan Digital Sky Survey, testing for the Sunyaev-Zeldovich (SZ) effect from quasars. A statistically significant (2.5σ) temperature decrement exists in the 41 GHz microwave band. A two-component fit to the cross-correlation spectrum incorporating both dust emission and SZ yields a best-fit y parameter of (7.0 ± 3.4) x 10^-7. A similar cross-correlation analysis with the luminous red galaxy sample from Sloan gives a best-fit y parameter of (5.3 ± 2.5) x 10^-7. We discuss the possible physical origin of these signals, which is likely a combination of SZ effects from quasars and galaxy clusters. Both the Planck Surveyor satellite and the current ground-based arcminute-resolution microwave experiments will detect this signal with a higher statistical significance.

[en] We report on the results of a visual search for galaxy-scale strong gravitational lenses over 650 arcmin² of HST/ACS (F606W and F814W) imaging in the DEEP2-Extended Groth Strip (EGS). In addition to a previously-known Einstein Cross also found by our search (the 'Cross', HSTJ141735+52264, z_lens = 0.8106, z_source = 3.40), we identify two new strong galaxy-galaxy lenses with multiple extended arcs. The first, HSTJ141820+52361 (the 'Dewdrop'; z_lens = 0.5798), lenses two distinct extended sources into two pairs of arcs (z_source = 0.9818), while the second, HSTJ141833+52435 (the 'Anchor'; z_lens = 0.4625), produces a single pair of arcs (z_lens not yet known). Four less convincing arc/counter-arc and two-image lens candidates are also found and presented for completeness. Lenses are found in a both underdense and overdense local environments, as characterized by a robust measure, 1+(delta)₃, a normalized density that uses the distance to the third nearest neighbor. All three definite lenses are fit reasonably well by simple singular isothermal ellipsoid models including external shear, giving χ_ν² values close to unity. These shears are much greater than those implied by a simple consideration of the three-dimensional convergence and shear from galaxies along the line of sight, where each galaxy is approximated by a singular isothermal sphere halo truncated at 200 h^-1 kpc. This shows how a realistic treatment of galaxies and the large scale structure they are embedded in is necessary, and that simply characterizing the very-local environment may be insufficient

[en] Upcoming imaging surveys such as the Large Synoptic Survey Telescope will repeatedly scan large areas of sky and have the potential to yield million-supernova catalogs. Type Ia supernovae are excellent standard candles and will provide distance measures that suffice to detect mean pairwise velocities of their host galaxies. We show that when combining these distance measures with photometric redshifts for either the supernovae or their host galaxies, the mean pairwise velocities of the host galaxies will provide a dark energy probe which is competitive with other widely discussed methods. Adding information from this test to type Ia supernova photometric luminosity distances from the same experiment, plus the cosmic microwave background power spectrum from the Planck satellite, improves the Dark Energy Task Force figure of merit by a factor of 1.8. Pairwise velocity measurements require no additional observational effort beyond that required to perform the traditional supernova luminosity distance test, but may provide complementary constraints on dark energy parameters and the nature of gravity. Incorporating additional spectroscopic redshift follow-up observations could provide important dark energy constraints from pairwise velocities alone. Mean pairwise velocities are much less sensitive to systematic redshift errors than the luminosity distance test or weak lensing techniques, and also are only mildly affected by systematic evolution of supernova luminosity.