The Water Maser in MG 0414+0534: The Influence of Gravitational Microlensing

TL;DR

This study models the microlensing effects on water masers in a high-redshift quasar to understand their structure and variability, providing insights into the maser emission regions through numerical simulations.

Contribution

It introduces a high-resolution numerical analysis of microlensed water masers in MG 0414+0534, exploring various models to interpret observed spectral variability.

Findings

Small maser substructure can cause detectable flux and velocity variations within two decades.

Magnification of over 35 occurs in 22% of the time for the smallest maser models.

Observed spectra are consistent with both compact maser spots and smooth extended models.

Abstract

Water masers have been observed in several high redshift active galactic nuclei, including the gravitationally lensed quasar MG 0414+0534. This quasar is lensed into four images, and the water maser is detected in two of them. The broadening of the maser emission line and its velocity offset are consistent with a group of masers associated with a quasar jet. If the maser group is microlensed we can probe its structure and size by observing its microlensing behaviour over time. We present results of a high resolution numerical analysis of microlensing of the maser in MG 0414+0534, using several physically motivated maser models covering a range of sizes and emission profiles. Time-varying spectra of the microlensed maser are generated, displayed, and analysed, and the behaviour of the different models compared. The observed maser line in MG 0414+0534 is consistent with maser spots as in other quasar jets, provided substructure is de-magnified or currently lost in noise; otherwise smooth extended maser models are also candidates to generate the observed spectrum. Using measures of spectral variability we find that if the maser has small substructure of ~ 0.002 pc then a variation of 0.12 mag in flux and 2.0 km/s in velocity centroid of the maser line could be observed within 2 decades. For the smallest maser model in this study a magnification of > 35 is possible 22% of the time, which is of significance in the search for other lensed masers.