Image Flux Ratios of Gravitationally Lensed HS 0810+2554 with High-resolution Infrared Imaging

Terry Jay Jones,Steve Ertel,Philip M Hinz,Liliya L R Williams,Shane Walsh,Ryan Webster,Amali Vaz

doi:10.3847/1538-3881/ab5108

Abstract

Abstract We report near simultaneous imaging using LMIRCam on the LBTI of the quadruply imaged lensed quasar HS 0810+2554 at wavelengths of 2.16, 3.7, and 4.78 μm with a full width at half maximum spatial resolution of 0.″13, 0.″12, and 0.″15 respectively, comparable to Hubble Space Telescope optical imaging. In the z = 1.5 rest frame of the quasar, the observed wavelengths correspond to 0.86, 1.48, and 1.91 μm respectively. The two brightest images in the quad, A and B, are clearly resolved from each other with a separation of 0.″187. The flux ratio of these two images (A/B) trends from 1.79 to 1.23 at wavelengths from 2.16 to 4.78 μm. The trend in flux ratio is consistent with the 2.16 μm flux originating from a small sized accretion disk in the quasar that experiences only microlensing. The excess flux above the contribution from the accretion disk at the two longer wavelengths originates from a larger sized region that experiences no microlensing. A simple model employing multiplicative factors for image B due to stellar microlensing (m) and substructure millilensing (M) is presented. The result is tightly constrained to the product m × M = 1.79. Given the observational errors, the 60% probability contour for this product stretches from m = 2.6, M = 0.69 to m = 1.79, M = 1.0, where the later is consistent with microlensing only.

Highlights

High-resolution N-body simulations of the cold dark matter (CDM) structure formation of the universe predicts that there should be hundreds of dark matter subhalos with mass ∼104–109Me within a massive halo (∼1012Me)
We developed a simple model for the flux from images A and B by making the following assumptions
Flux ratios were computed for all four images in each filter

Summary

Introduction

High-resolution N-body simulations of the cold dark matter (CDM) structure formation of the universe predicts that there should be hundreds of dark matter subhalos with mass ∼104–109Me within a massive halo (∼1012Me). Hsueh et al (2019) use a sample of seven quadruply imaged lensing systems and assuming a CDM cosmology and contribution from low mass halos along the line of sight, they infer an average total mass fraction in substructure that is in rough agreement with the predictions from CDM hydrodynamical simulations. Their result is significantly different when compared to previous studies that did not include line-of-sight halos (Xu et al 2015). Over this wavelength range the flux arises purely from the accretion disk at the shorter wavelength, and from a combination of accretion disk and dusty torus at the two longer wavelengths (e.g., Kobayashi et al 1993; Suganuma et al 2006)

Observations

Analysis

Lensing Model

Findings

Conclusions