arXiv subjects

Andrew P. Hearin

Publications and source records attributed to Andrew P. Hearin.

41 records · Page 3Linked to original sources

arXiv2012

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.

astro-ph.CO↗

arXiv2011

Testing the Origin of the CMB Large-Angle Correlation Deficit with a Galaxy Imaging Survey

The cosmic microwave background (CMB) temperature distribution measured by the Wilkinson Microwave Anisotropy Probe (WMAP) exhibits anomalously low correlation at large angles. Quantifying the degree to which this feature in the temperature data is in conflict with standard Lambda-CDM cosmology is somewhat ambiguous because of the a posteriori nature of the observation. One physical mechanism that has been proposed as a possible explanation for the deficit in the large-angle temperature correlations is a suppression of primordial power on ~Gpc scales. To distinguish whether the anomaly is a signal of new physics, such as suppressed primordial power, it would be invaluable to perform experimental tests of the authenticity of this signal in data sets which are independent of the WMAP temperature measurements or even other CMB measurements. We explore the possibility of testing models of power suppression with large-scale structure observations, and compare the ability of planned photometric and spectroscopic surveys to constrain the power spectrum. Of the surveys planned for the next decade, a spectroscopic redshift survey such as BigBOSS will have a greater number of radial modes available for study, but we find that this advantage is outweighed by the greater surface density of high-redshift sources that will be observed by photometric surveys such as LSST or Euclid. We also find that the ability to constrain primordial power suppression is insensitive to the precision of the calibration of photometric redshifts. We conclude that very-wide-area imaging surveys have the potential to probe viable models for the missing power but that it will be difficult to use such surveys to conclusively rule out primordial power suppression as the mechanism behind the observed anomaly.

astro-ph.CO↗

arXiv2011

Asymmetric Dark Matter May Alter the Evolution of Low-mass Stars and Brown Dwarfs

We study energy transport by asymmetric dark matter in the interiors of very low-mass stars and brown dwarfs. Our motivation is to explore astrophysical signatures of asymmetric dark matter, which otherwise may not be amenable to conventional indirect dark matter searches. In viable models, the additional cooling of very-low mass stellar cores can alter stellar properties. Asymmetric dark matter with mass 4 < Mx/GeV < 10 and a spin-dependent (spin-independent) cross sections of sigma \sim 10^{-37} cm^2 (sigma \sim 10^{-40} cm^2) can increase the minimum mass of main sequence hydrogen burning, partly determining whether or not the object is a star at all. Similar dark matter candidates reduce the luminosities of low-mass stars and accelerate the cooling of brown dwarfs. Such light dark matter is of particular interest given results from the DAMA, CoGeNT, and CRESST dark matter searches. We discuss possibilities for observing dark matter effects in stars in the solar neighborhood, globular clusters, and, of particular promise, local dwarf galaxies, among other environments, as well as exploiting these effects to constrain dark matter properties.

astro-ph.CO↗

arXiv2010

A General Study of the Influence of Catastrophic Photometric Redshift Errors on Cosmology with Cosmic Shear Tomography

A goal of forthcoming imaging surveys is to use weak gravitational lensing shear measurements to constrain dark energy. We quantify the importance of uncalibrated photometric redshift outliers to the dark energy goals of forthcoming imaging surveys in a manner that does not assume any particular photometric redshift technique or template. In so doing, we provide an approximate blueprint for computing the influence of specific outlier populations on dark energy constraints. We find that outliers whose photo-z distributions are tightly localized about a significantly biased redshift must be controlled to a per-galaxy rate of <~ a few times 10^-3 to insure that systematic errors on dark energy parameters are rendered negligible. In the complementary limit, a subset of imaged galaxies with uncalibrated photometric redshifts distributed over a broad range must be limited to fewer than a per-galaxy error rate of <~ a few times 10^-4. Additionally, we explore the relative importance of calibrating the photo-z's of a core set of relatively well-understood galaxies as compared to the need to identify potential catastrophic photo-z outliers. We discuss the degradation of the statistical constraints on dark energy parameters induced by excising source galaxies at high- and low-photometric redshifts, concluding that removing galaxies with z_phot >~ 2.4 and z_phot <~ 0.3 may mitigate damaging catastrophic redshift outliers at a relatively small (~ 20%) cost in statistical error. In an appendix, we show that forecasts for the degradation in dark energy parameter constraints due to uncertain photometric redshifts depend sensitively on the treatment of the nonlinear matter power spectrum. Previous work using PD96 may have overestimated the photo-z calibration requirements of future surveys.

astro-ph.CO↗

arXiv2009

The Influence of Galaxy Formation Physics on Weak Lensing Tests of General Relativity

Forthcoming projects such as the DES, a JDEM, and LSST, aim to measure weak lensing shear correlations with unprecedented accuracy. Weak lensing observables are sensitive to both the distance-redshift relation and the growth of structure in the Universe. If the cause of accelerated cosmic expansion is dark energy within general relativity (GR), both cosmic distances and structure growth are governed by the properties of dark energy. Consequently, one may use lensing to check for this consistency and test GR. After reviewing the phenomenology of such tests, we address one major challenge to such a program. The evolution of the baryonic component of the Universe is highly uncertain and can influence lensing observables, manifesting as modified structure growth for a fixed cosmic distance scale. Using two proposed methods, we show that one could be led to reject the null hypothesis of GR when it is the true theory if this uncertainty in baryonic processes is neglected. Recent simulations suggest that we can correct for baryonic effects using a parametrized model in which the halo mass-concentration relation is modified. The correction renders biases small compared to statistical uncertainties. We study the ability of future weak lensing surveys to constrain the internal structures of halos and test the null hypothesis of GR simultaneously. Compared to nulling information from small-scales to mitigate sensitivity to baryonic physics, this internal calibration program should provide limits on deviations from GR that are several times more constraining. Specifically, we find that limits on general relativity in the case of internal calibration are degraded by only ~30% or less compared to the case of perfect knowledge of nonlinear structure.

astro-ph.CO↗