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TIME DELAY ANALYSIS OF THE LENSED QUASAR SDSS J1001+5027
Aghamousa, Amir,Shafieloo, Arman American Astronomical Society 2017 The Astrophysical journal Vol.834 No.1
<P>We modify. the algorithm we proposed. in Aghamousa & Shafieloo for. the. time delay. estimation of. strongly lensed systems incorporating the. weighted cross-correlation and weighted summation of correlation coefficients. We show the high performance of this algorithm by applying it to. Time Delay Challenge (TDC1) simulated data. We apply then our proposed method to. the light curves of the lensed quasar SDSS J1001+5027. since this system has been well studied by other groups, to compare our results with their findings. In this work we propose a new estimator, the 'mirror' estimator, along with a list of criteria for reliability testing of the estimation. Our mirror estimator results are. -117.1(-3.7)(+7.1) and -117.1(-8.8)(+7.2) using simple Monte Carlo simulations and simulated light curves provided by Rathna Kumar et al., respectively. Although the. TDC1 simulations do not reflect the properties of the. SDSS J1001+5027 light curves, using these simulations results in a. smaller uncertainty, which shows that the. higher quality observations can lead to a. substantially more precise time delay estimation. Our time delay estimation is in agreement with the. findings of the other groups for this strongly lensed system, and the difference in the size of the error bars reflects the importance of appropriate light curve simulations.</P>
PROBING BULK FLOW WITH NEARBY SNe Ia DATA
Appleby, Stephen,Shafieloo, Arman,Johnson, Andrew IOP Publishing 2015 The Astrophysical journal Vol.801 No.2
<P>We test the isotropy of the local universe using low-redshift supernova data from various catalogs and the nonparametric method of smoothed residuals. Using a recently developed catalog that combines supernova data from various surveys, we show that the isotropic hypothesis of a universe with zero velocity perturbation can be rejected with moderate significance, with p-value similar to 0.07 out to redshift z < 0.045. We estimate the direction of maximal anisotropy on the sky for various preexisting catalogs and show that it remains relatively unaffected by the light-curve fitting procedure. However, the recovered direction is biased by the underlying distribution of data points on the sky. We estimate both the uncertainty and bias in the direction by creating mock data containing a randomly oriented bulk flow and using our method to reconstruct its direction. After correcting for this bias effect, we infer the direction of maximum anisotropy as (b, l) = (20 degrees, 276 degrees) +/- (12 degrees, 29 degrees) in galactic coordinates. Finally, we compare the anisotropic signal in the data to mock realizations in which large-scale velocity perturbations are consistently accounted for at the level of linear perturbation theory. We show that including the effect of the velocity perturbation in our mock catalogs degrades the significance of the anisotropy considerably, with p-value increasing to similar to 0.29. One can conclude from our analysis that there is a moderate deviation from isotropy in the supernova data, but the signal is consistent with a large-scale bulk velocity expected within Lambda CDM.</P>
Aghamousa, Amir,Shafieloo, Arman IOP Publishing 2015 The Astrophysical journal Vol.804 No.1
<P>The observable time delays between multiple images of strong lensing systems with time variable sources can provide us with some valuable information for probing the expansion history of the universe. Estimating these time delays can be very challenging due to complexities in the observed data caused by seasonal gaps, various noises, and systematics such as unknown microlensing effects. In this paper, we introduce a novel approach for estimating the time delays for strong lensing systems, implementing various statistical methods of data analysis including the smoothing and cross-correlation methods. The method we introduce in this paper has recently been used in the TDC0 and TDC1 Strong Lens Time Delay Challenges and has shown its power in providing reliable and precise estimates of time delays dealing with data with different complexities.</P>
Growth of perturbations in nonlocal gravity with non- ΛCDM background
Park, Sohyun,Shafieloo, Arman American Physical Society 2017 Physical Review D Vol.95 No.6
<P>We reanalyze the nonlocal gravity model of Deser and Woodard, which was proposed to account for the current phase of cosmic acceleration. We show that the growth of perturbations predicted by this nonlocal gravity model when its background evolution is fixed by some particular non-Lambda-cold-dark-matter (Lambda CDM) models can be substantially lower than when its background is fixed by Lambda CDM. This can be seen when we consider the background expansion by a dark energy model with a slightly less negative equation of state with respect to cosmological constant. Our results hint towards a fact that the choice of the background expansion can play a crucial role in how this nonlocal gravity model can fit the growth history data. While the growth data might show better consistency to general relativity (GR) models (among the background models we studied so far), it seems the nonlocal gravity model studied in this work is able to show comparable consistency to the growth data as well. Showing this consistency can be considered as a significant result since this model can stand as a distinguishable alternative to the standard model of cosmology.</P>
Model independent expansion history from supernovae: Cosmology versus systematics
L’Huillier, Benjamin,Shafieloo, Arman,Linder, Eric V,Kim, Alex G Oxford University Press 2019 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.485 No.2
<B>Abstract</B><P>We examine the Pantheon supernovae distance data compilation in a model independent analysis to test the validity of cosmic history reconstructions beyond the concordance ΛCDM cosmology. Strong deviations are allowed by the data at z ≳ 1 in the reconstructed Hubble parameter, Om diagnostic, and dark energy equation of state. We explore three interpretations: 1) possibility of the true cosmology being far from ΛCDM, 2) supernovae property evolution, and 3) survey selection effects. The strong (and theoretically problematic) deviations at z ≳ 1 vanish and good consistency with ΛCDM is found with a simple Malmquist-like linear correction. The adjusted data is robust against the model independent iterative smoothing reconstruction. However, we caution that while by eye the original deviation from ΛCDM is striking, χ2 tests do not show the extra linear correction parameter is statistically significant, and a model-independent Gaussian Process regression does not find significant evidence for the need for correction at high-redshifts.</P>