Detection of a spiral lens galaxy and optical variability in the gravitational lens system B1600+434

TL;DR

This study reports the discovery of a spiral lens galaxy and optical variability in the gravitational lens system B1600+434, highlighting dust obscuration effects and potential for cosmological measurements.

Contribution

It presents the first detection of an edge-on spiral galaxy in the lens system and evidence of optical variability, suggesting new avenues for studying lensing and cosmology.

Findings

Detected a spiral galaxy between lensed images with estimated redshift ~0.4

Observed significant colour difference due to dust extinction

Noted flux variability of 0.25 mag over one year

Abstract

The gravitationally lensed quasar B1600+434 (z=1.61, mV=21.6) has been observed at the 2.56m Nordic Optical Telescope (NOT). In this Letter we report the discovery of an edge-on late-type galaxy located between the two lensed components (separation 1\farcs4), close to the fainter image. The galaxy photometry indicates that its redshift is approximately 0.4. We detect a large colour difference between the two images due to significant obscuration of the faint image. The estimated amount of absorption as a function of colour indicates that the extinction may be due to dust in the lensing galaxy. We also present evidence of flux variability in B1600+434 with a detected change of 0.25mag in one year. The theoretically expected time delay is of the order of one month and so the system may be an interesting object for determining the Hubble constant.