3249703
Constraining scale-dependent non-Gaussianity with future large-scale structure and the CMB
We forecast combined future constraints from the cosmic microwave background and large-scale structure on the models of primordial non-Gaussianity. We study the gener- alized local model of non-Gaussianity, where the parameter fNL is promoted to a function of scale, and present the principal component analysis applicable to an arbitrary form of fNL(k). We emphasize the complementarity between the CMB and LSS by using Planck, DES and BigBOSS surveys as examples, forecast constraints on the power-law fNL(k) model, and introduce the gure of merit for measurements of scale-dependent non-Gaussianity.
18731427
Joint Minkowski functionals and bispectrum constraints on non-Gaussianity in the cosmic microwave background
Two of the most commonly used tools to constrain the primordial non-Gaussianity are the bispectrum and the Minkowski functionals of cosmic microwave background temperature anisotropies. These two measures of non-Gaussianity in principle provide distinct (though correlated) information, but in the past constraints from them have only been loosely compared and not statistically combined. In this work we evaluate, for the first time, the covariance matrix between the local non-Gaussianity coefficient ${f}_{\mathrm{NL}}$ estimated through the bispectrum and Minkowski functionals. We find that the estimators are positively correlated, with correlation coefficient $r\ensuremath{\simeq}0.3$. Using the WMAP7 data to combine the two measures and accounting for the point-source systematics, we find the combined constraint ${f}_{\mathrm{NL}}=37\ifmmode\pm\else\textpm\fi{}28$, which has a $\ensuremath{\sim}20%$ smaller error than either of the individual constraints.
10108151
First constraints on the running of non-Gaussianity.
We use data from the Wilkinson Microwave Anisotropy probe temperature maps to constrain a scale-dependent generalization of the popular "local" model for primordial non-Gaussianity. In the model where the parameter f(NL) is allowed to run with scale k, f(NL)(k) = f*(NL) (k/k(piv))(n)(fNL), we constrain the running to be n(f)(NL) = 0.30(-1.2)(+1.9) at 95% confidence, marginalized over the amplitude f*(NL). The constraints depend somewhat on the prior probabilities assigned to the two parameters. In the near future, constraints from a combination of Planck and large-scale structure surveys are expected to improve this limit by about an order of magnitude and usefully constrain classes of inflationary models.
54769355
Scale-dependent non-Gaussianity as a generalization of the local model
We generalize the local model of primordial non-Gaussianity by promoting the parameter fNL to a general scale-dependent function fNL(k). We calculate the resulting bispectrum and the eect on the bias of dark matter halos, and thus the extent to which fNL(k) can be measured from the large-scale structure observations. By calculating the principal components of fNL(k), we identify scales where this form of non-Gaussianity is best constrained and estimate the overlap with previously studied local and equilateral non- Gaussian models.
119326960
Difference Image Analysis of Galactic Microlensing. II. Microlensing Events
The MACHO collaboration has been carrying out difference image analysis (DIA) since 1996 with the aim of increasing the sensitivity to the detection of gravitational microlensing. This is a preliminary report on the application of DIA to galactic bulge images in one field. We show how the DIA technique significantly increases the number of detected lensing events, by removing the positional dependence of traditional photometry schemes and lowering the microlensing event detection threshold. This technique, unlike PSF photometry, gives the unblended colors and positions of the microlensing source stars. We present a set of criteria for selecting microlensing events from objects discovered with this technique. The 16 pixel and classical microlensing events discovered with the DIA technique are presented.
18048767
The Impact of the Astro2010 Recommendations on Variable Star Science
The next decade of survey astronomy has the potential to transform our knowledge of variable stars. Stellar variability underpins our knowledge of the cosmological distance ladder, and provides direct tests of stellar formation and evolution theory. Variable stars can also be used to probe the fundamental physics of gravity and degenerate material in ways that are otherwise impossible in the laboratory. The computational and engineering advances of the past decade have made large-scale, time-domain surveys an immediate reality. Some surveys proposed for the next decade promise to gather more data than in the prior cumulative history of astronomy. The actual implementation of these surveys will have broad implications for the types of science that will be enabled. We examine the design considerations for an optimal time-domain photometric survey dedicated to variable star science, including: observing cadence, wavelength coverage, photometric and astrometric accuracy, single-epoch and cumulative depth, overall sky coverage, and data access by the broader astronomical community. The best surveys must combine aspects from each of these considerations to fully realize the potential for the next decade of time-domain science.
3487686
FIRST-YEAR SLOAN DIGITAL SKY SURVEY-II (SDSS-II) SUPERNOVA RESULTS: CONSTRAINTS ON NONSTANDARD COSMOLOGICAL MODELS
We use the new Type Ia supernovae discovered by the Sloan Digital Sky Survey-II supernova survey, together with additional supernova data sets as well as observations of the cosmic microwave background and baryon acoustic oscillations to constrain cosmological models. This complements the standard cosmology analysis presented by Kessler et al. in that we discuss and rank a number of the most popular nonstandard cosmology scenarios. When this combined data set is analyzed using the MLCS2k2 light-curve fitter, we find that more exotic models for cosmic acceleration provide a better fit to the data than the ΛCDM model. For example, the flat Dvali-Gabadadze-Porrati model is ranked higher by our information-criteria (IC) tests than the standard model with a flat universe and a cosmological constant. When the supernova data set is instead analyzed using the SALT-II light-curve fitter, the standard cosmological-constant model fares best. This investigation of how sensitive cosmological model selection is to assumptions about, and within, the light-curve fitters thereby highlights the need for an improved understanding of these unresolved systematic effects. Our investigation also includes inhomogeneous Lemaitre-Tolman-Bondi (LTB) models. While our LTB models can be made to fit the supernova data as well as any other model, the extra parameters they require are not supported by our IC analysis. Finally, we explore more model-independent ways to investigate the cosmic expansion based on this new data set.
17253852
Time Variability of Quasars: the Structure Function Variance
Significant progress in the description of quasar variability has been recently made by employing SDSS and POSS data. Common to most studies is a fundamental assumption that photometric observations at two epochs for a large number of quasars will reveal the same statistical properties as well‐sampled light curves for individual objects. We critically test this assumption using light curves for a sample of ∼2,600 spectroscopically confirmed quasars observed about 50 times on average over 8 years by the SDSS stripe 82 survey. We find that the dependence of the mean structure function computed for individual quasars on luminosity, rest‐frame wavelength and time is qualitatively and quantitatively similar to the behavior of the structure function derived from two‐epoch observations of a much larger sample. We also reproduce the result that the variability properties of radio and X‐ray selected subsamples are different. However, the scatter of the variability structure function for fixed values of luminosity,...
118058418
Transit Timing Observations of the Extrasolar Hot‐Neptune Planet GL 436 b
Gliese 436 is an M dwarf with a mass of 0.45 M⊙ and hosts the extrasolar planet GL 436 b [3, 6, 7, 2], which is currently the least massive transiting planet with a mass of ∼23.17 M⊕ [10], and the only planet known to transit an M dwarf. GL 436 b represents the first transiting detection of the class of extrasolar planets known as “Hot Neptunes” that have masses within a few times that of Neptune’s mass (∼17 M⊕) and orbital semimajor axis <0.1 AU about the host star. Unlike most other known transiting extrasolar planets, GL 436 b has a high eccentricity (e∼0.16). This brings to light a new parameter space for habitability zones of extrasolar planets with host star masses much smaller than typical stars of roughly a solar mass. This unique system is an ideal candidate for orbital perturbation and transit‐time variation (TTV) studies to detect smaller, possibly Earth‐mass planets in the system. In April 2008 we began a long‐term intensive campaign to obtain complete high‐precision light curves using the Apa...