Day 1035

Friday.  Monday.


1601.01321
SHARP - III: first use of adaptive optics images to constrain cosmology with gravitational lens time delays
Chen, Suyu, et al

Accurate and precise measurements of the Hubble constant are critical for testing the current standard cosmo model and revealing possibly new physics.  With HST imaging, each SL system with measured time delays can allow one to determine the Hubble constant with an uncertainty of ~7%.  Since HST will not last forever, explore AO imaging as an alternative that can provide higher angular resolution than HST imaging but has a less stable PSF due to atmospheric distortion. To make AO imaging useful for time-delay-lens cosmography, develop a method to extract the unknown PSF directly from the imaging of strongly lensed quasars.  In a blind test with two mock data sets created with different PSFs, able to recover the important Cosmo parameters (time-delay distance, external shear, lens mass profile slope, and total Einstein radius).  Analysis of the Keck AO image of the SL system RXJ1131-1231 shows that the important parameters for cosmography agree with those based on HST imaging and modeling within 1-sigma uncertainties.  Most importantly, the constraint on the model time-delay distance by using AO imaging with 0.045" resolution is tighter by ~50% than the constraint of time-delay distance by using HST imaging with 0.09" when a power-law mass distribution for the lens system is adopted.  The PSF reconstruction technique is generic and applicable to data sets that have multiple nearby point sources, enabling scientific studies that require high-precision models of the PSF.


1601.01388
Detection of lensing substructure using ALMA observations of the dusty galaxy SDP.81
Hezveh, Dalal, et al

Study the abundance of substructure in the matter density near galaxies using ALMA SV observations of the SL system SDP.81.  Present a method to measure the abundance of sub haloes around galaxies using interferometric observations of gravitational lenses.  Using simulated ALMA observations, explore the effects of various systematics, including antenna phase errors and source priors, and show how such errors may be measured or marginalized. Apply the formalism to ALMA observations of SDP.81.  Find evidence for the presence of a M=1e8.96±0.12 Msun sub halo near one of the images, with a significance of 6.9sigma in a joint fit to data from bands 6 and 7; the effect of the sub halo is also detected in both bands individually.  Also derive constraints on the abundance of DM sub haloes down to M~2e7Msun, pushing down to the mass regime of the smallest detected satellites in the Local Group, where there are significant discrepancies between the observed population of luminous galaxies and predicted DM sub halos.  Find hints of traditional substructure, warranting further study using the full SDP.81 dataset (including, for example, the spectroscopic imaging of the lensed carbon monoxide emission).  Compare the results of this search to the predictions of LCDM haloes, and find that given current uncertainties in the host halo properties of SDP.81, the measurements of substructure are consistent with theoretical expectations.  Observations of larger samples of gravitational lenses with ALMA should be able to improve the constraints on the abundance of galactic substructure.


1601.01671
SHARP - II: revealing a bias in observational measurements of dark matter substructure with gravitational lens flux ratios
Hush, Fasnacht, et al

Gravitational lens flux-ratio anomalies provide a powerful technique for measuring DM substructure in distant galaxies.  However, before using these flux-ratio anomalies to test galaxy formation models, it is imperative to ascertain that the given anomalies are indeed due to the presence of DM substructure and not due to some other component of the lensing galaxy halo or to propagation effects.  Present the case of CLASS B1555+375, which has a strong radio-wavelength flux-ratio anomaly.  The high-resolution near-IR Kick II AO imaging and archival HST data real the lensing galaxy in this system to have a clear edge-on disc component that crosses directly over the pair of imaging that exhibit the flux-ratio anomaly.  Find simple models that include the disc can reproduce the cm-wavelength flux-ratio anomaly without requiring additional DM substructure.  Although further studies are required, the results suggest the assumption that all flux-ratio anomalies are due to a population of DM sub-haloes may be incorrect, and analyses that do not account for the full complexity of the lens macro-model may overestimate the substructure mass fraction in massive lensing galaxies.