54 research outputs found
The Dark Side of Galaxy Color: evidence from new SDSS measurements of galaxy clustering and lensing
The age matching model has recently been shown to predict correctly the
luminosity L and g-r color of galaxies residing within dark matter halos. The
central tenet of the model is intuitive: older halos tend to host galaxies with
older stellar populations. In this paper, we demonstrate that age matching also
correctly predicts the g-r color trends exhibited in a wide variety of
statistics of the galaxy distribution for stellar mass M* threshold samples. In
particular, we present new measurements of the galaxy two-point correlation
function and the galaxy-galaxy lensing signal as a function of M* and g-r color
from the Sloan Digital Sky Survey, and show that age matching exhibits
remarkable agreement with these and other statistics of low-redshift galaxies.
In so doing, we also demonstrate good agreement between the galaxy-galaxy
lensing observed by SDSS and the signal predicted by abundance matching, a new
success of this model. We describe how age matching is a specific example of a
larger class of Conditional Abundance Matching models (CAM), a theoretical
framework we introduce here for the first time. CAM provides a general
formalism to study correlations at fixed mass between any galaxy property and
any halo property. The striking success of our simple implementation of CAM
provides compelling evidence that this technique has the potential to describe
the same set of data as alternative models, but with a dramatic reduction in
the required number of parameters. CAM achieves this reduction by exploiting
the capability of contemporary N-body simulations to determine dark matter halo
properties other than mass alone, which distinguishes our model from
conventional approaches to the galaxy-halo connection.Comment: references added, minor adjustments to text and notatio
Mind the Gap: Tightening the Mass-Richness Relation with Magnitude Gaps
We investigate the potential to improve optical tracers of cluster mass by
exploiting measurements of the magnitude gap, m12, defined as the difference
between the r-band absolute magnitude of the two brightest cluster members. We
find that in a mock sample of galaxy groups and clusters constructed from the
Bolshoi simulation, the scatter about the mass-richness relation decreases by
15-20% when magnitude gap information is included. A similar trend is evident
in a volume-limited, spectroscopic sample of galaxy groups observed in the
Sloan Digital Sky Survey (SDSS). We find that SDSS groups with small magnitude
gaps are richer than large-gap groups at fixed values of the one-dimensional
velocity dispersion among group members sigma_v, which we use as a mass proxy.
We demonstrate explicitly that m12 contains information about cluster mass that
supplements the information provided by group richness and the luminosity of
the brightest cluster galaxy, L_bcg. In so doing, we show that the luminosities
of the members of a group with richness N are inconsistent with the
distribution of luminosities that results from N random draws from the global
galaxy luminosity function. As the cosmological constraining power of galaxy
clusters is limited by the precision in cluster mass determination, our
findings suggest a new way to improve the cosmological constraints derived from
galaxy clusters.Comment: references adde
Connecting massive galaxies to dark matter halos in BOSS - I. Is galaxy color a stochastic process in high-mass halos?
We use subhalo abundance matching (SHAM) to model the stellar mass function
(SMF) and clustering of the Baryon Oscillation Spectroscopic Survey (BOSS)
"CMASS" sample at . We introduce a novel method which accounts for
the stellar mass incompleteness of CMASS as a function of redshift, and produce
CMASS mock catalogs which include selection effects, reproduce the overall SMF,
the projected two-point correlation function , the CMASS ,
and are made publicly available. We study the effects of assembly bias above
collapse mass in the context of "age matching" and show that these effects are
markedly different compared to the ones explored by Hearin et al. (2013) at
lower stellar masses. We construct two models, one in which galaxy color is
stochastic ("AbM" model) as well as a model which contains assembly bias
effects ("AgM" model). By confronting the redshift dependent clustering of
CMASS with the predictions from our model, we argue that that galaxy colors are
not a stochastic process in high-mass halos. Our results suggest that the
colors of galaxies in high-mass halos are determined by other halo properties
besides halo peak velocity and that assembly bias effects play an important
role in determining the clustering properties of this sample.Comment: 22 pages. Appendix. B added. Matches the version accepted by MNRAS.
Mock galaxy catalog and HOD table are available at
http://www.massivegalaxies.co
General Requirements on Matter Power Spectrum Predictions for Cosmology with Weak Lensing Tomography
Forthcoming projects such as DES, LSST, WFIRST, and Euclid aim to measure
weak lensing shear correlations with unprecedented precision, constraining the
dark energy equation of state at the percent level. Reliance on
photometrically-determined redshifts constitutes a major source of uncertainty
for these surveys. Additionally, interpreting the weak lensing signal requires
a detailed understanding of the nonlinear physics of gravitational collapse. We
present a new analysis of the stringent calibration requirements for weak
lensing analyses of future imaging surveys that addresses both photo-z
uncertainty and errors in the calibration of the matter power spectrum. We find
that when photo-z uncertainty is taken into account the requirements on the
level of precision in the prediction for the matter power spectrum are more
stringent than previously thought. Including degree-scale galaxy clustering
statistics in a joint analysis with weak lensing not only strengthens the
survey's constraining power by ~20%, but can also have a profound impact on the
calibration demands, decreasing the degradation in dark energy constraints with
matter power spectrum uncertainty by a factor of 2-5. Similarly, using galaxy
clustering information significantly relaxes the demands on photo-z
calibration. We compare these calibration requirements to the contemporary
state-of-the-art in photometric redshift estimation and predictions of the
power spectrum and suggest strategies to utilize forthcoming data optimally.Comment: 3 new figures; new section added on multipole-dependence of
calibration requirements; references added; version accepted by JCA
Designing Future Dark Energy Space Missions: II. Photometric Redshift of Space Weak Lensing Optimized Survey
Accurate weak-lensing analysis requires not only accurate measurement of
galaxy shapes but also precise and unbiased measurement of galaxy redshifts.
The photometric redshift technique appears as the only possibility to determine
the redshift of the background galaxies used in the weak-lensing analysis.
Using the photometric redshift quality, simple shape measurement requirements,
and a proper sky model, we explore what could be an optimal weak-lensing dark
energy mission based on FoM calculation. We found that photometric redshifts
reach their best accuracy for the bulk of the faint galaxy population when
filters have a resolution R~3.2. We show that an optimal mission would survey
the sky through 8 filters using 2 cameras (visible and near infrared). Assuming
a 5-year mission duration, a mirror size of 1.5m, a 0.5deg2 FOV with a visible
pixel scale of 0.15", we found that a homogeneous survey reaching IAB=25.6
(10sigma) with a sky coverage of ~11000deg2 maximizes the Weak Lensing FoM. The
effective number density of galaxies then used for WL is ~45gal/arcmin2, at
least a factor of two better than ground based survey. This work demonstrates
that a full account of the observational strategy is required to properly
optimize the instrument parameters to maximize the FoM of the future
weak-lensing space dark energy mission.Comment: 25 pages, 39 figures, accepted in A&
Weak lensing, dark matter and dark energy
Weak gravitational lensing is rapidly becoming one of the principal probes of
dark matter and dark energy in the universe. In this brief review we outline
how weak lensing helps determine the structure of dark matter halos, measure
the expansion rate of the universe, and distinguish between modified gravity
and dark energy explanations for the acceleration of the universe. We also
discuss requirements on the control of systematic errors so that the
systematics do not appreciably degrade the power of weak lensing as a
cosmological probe.Comment: Invited review article for the GRG special issue on gravitational
lensing (P. Jetzer, Y. Mellier and V. Perlick Eds.). V3: subsection on
three-point function and some references added. Matches the published versio
Inference from the small scales of cosmic shear with current and future Dark Energy Survey data
Cosmic shear is sensitive to fluctuations in the cosmological matter density field, including on small physical scales, where matter clustering is affected by baryonic physics in galaxies and galaxy clusters, such as star formation, supernovae feedback and AGN feedback. While muddying any cosmological information that is contained in small scale cosmic shear measurements, this does mean that cosmic shear has the potential to constrain baryonic physics and galaxy formation. We perform an analysis of the Dark Energy Survey (DES) Science Verification (SV) cosmic shear measurements, now extended to smaller scales, and using the Mead et al. 2015 halo model to account for baryonic feedback. While the SV data has limited statistical power, we demonstrate using a simulated likelihood analysis that the final DES data will have the statistical power to differentiate among baryonic feedback scenarios. We also explore some of the difficulties in interpreting the small scales in cosmic shear measurements, presenting estimates of the size of several other systematic effects that make inference from small scales difficult, including uncertainty in the modelling of intrinsic alignment on nonlinear scales, `lensing bias', and shape measurement selection effects. For the latter two, we make use of novel image simulations. While future cosmic shear datasets have the statistical power to constrain baryonic feedback scenarios, there are several systematic effects that require improved treatments, in order to make robust conclusions about baryonic feedback
The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
The Astropy project supports and fosters the development of open-source and openly-developed Python packages that provide commonly-needed functionality to the astronomical community. A key element of the Astropy project is the core package Astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of inter-operable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy project
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