Double dark matter vision: twice the number of compact-source lenses with narrow-line lensing and the WFC3 grism

Abstract

The magnifications of compact-source lenses are extremely sensitive to the presence of low mass dark matter halos along the entire sight line from the source to the observer. Traditionally, the study of dark matter structure in compact-source strong gravitational lenses has been limited to radio-loud systems, as the radio emission is extended and thus unaffected by microlensing which can mimic the signal of dark matter structure. An alternate approach is to measure quasar nuclear-narrow line emission, which is free from microlensing and present in virtually all quasar lenses. In this paper, we double the number of systems which can be used for gravitational lensing analyses by presenting measurements of narrow-line emission from a sample of 8 quadruply imaged quasar lens systems, WGD J0405-3308, HS 0810+2554, RX J0911+0551, SDSS J1330+1810, PS J1606-2333, WFI 2026-4536, WFI 2033-4723 and WGD J2038-4008. We describe our updated grism spectral modelling pipeline, which we use to measure narrow-line fluxes with uncertainties of 2-10%, presented here. We fit the lensed image positions with smooth mass models and demonstrate that these models fail to produce the observed distribution of image fluxes, and have typical deviations larger than those expected from macromodel uncertainties. This discrepancy indicates the presence of perturbations caused by small-scale dark matter structure. The interpretation of this result in terms of dark matter models will be presented in a companion paper.

Tdcosmo

“…We explicitly model the galaxy located behind the main deflector at z = 0.78 as an SIS profile, placing it at an angular position corrected by ∼0.65 arcsec due to foreground lensing effects from the main deflector 5 . Nierenberg et al (2017) measured narrow-line flux ratios for this system (see also Nierenberg et al 2020), and used them to look for substructure near the images. The narrowline flux ratio measurements for this system were also used measure the halo mass function and mass-concentration relation of CDM halos (Gilman et al 2020a,b).…”

Strong lensing signatures of self-interacting dark matter in low-mass halos

“…Because the perturbation by a halo of fixed mass to lensed image depends on the size of the background source (Dobler & Keeton 2006), we must explicitly account for the finite-size background source in the forward model. First, we consider a sample of lenses with measured narrow-line flux ratios (Moustakas & Metcalf 2003;Nierenberg et al 2020). Emission from the nuclear narrow-line region extends out to O (10) pc (Müller-Sánchez et al 2011) from the central engine of the background quasar, washing out contaminating effects of microlensing by stars in the foreground galaxy.…”

Bridging the Gap Between Simply Parametrized and Free-Form Pixelated Models of Galaxy Lenses: The Case of WFI 2033-4723 Quad

“…One of the sets of models we present uses three image flux ratios, obtained from narrow line region of the source quasar, which is unaffected by stellar microlensing (Nierenberg et al 2020;Gilman et al 2020b), and hence probes either ΛCDM substructure, or macro-scale potential of the galaxy, or a combination of the two. The three flux ratios are, f 1 = F B /F A1 = 0.50 ± 0.050, f 2 = F A2 /F A1 = 0.65 ± 0.055, and f 3 = F C /F A1 = 0.53 ± 0.048.…”

“…While in some quads these models could account for flux anomalies, they often resulted in unphysical projected iso-density contour shapes (Biggs et al 2004). The substructure predicted by the Cold Dark Matter Universe model with the Cosmological Constant (ΛCDM), or line of sight (LoS) structure (Gilman et al 2019;Nierenberg et al 2020), and, in some cases, edge-on disks (Hsueh et al 2016) are probably responsible for some, but not all flux anomalies, and there remains a tension between predictions and observations (Xu et al 2015;Hsueh et al 2018).…”