The Transverse Peculiar Velocity of the Q2237+0305 Lens Galaxy and the Mean Mass of Its Stars

TL;DR

This study measures the transverse velocity and average stellar mass of the lens galaxy in Q2237+0305 using 11 years of microlensing data, incorporating stellar motions and Earth's parallax for improved accuracy.

Contribution

It introduces a comprehensive analysis that includes stellar random motions and Earth's parallax, providing new constraints on the lens galaxy's velocity and stellar mass.

Findings

Lower limit on transverse velocity: >338 km/s

Estimated mean stellar mass: 0.12 to 1.94 Msun

Consistent results from different light curve segments

Abstract

Using 11-years of OGLE V-band photometry of Q2237+0305, we measure the transverse velocity of the lens galaxy and the mean mass of its stars. We can do so because, for the first time, we fully include the random motions of the stars in the lens galaxy in the analysis of the light curves. In doing so, we are also able to correctly account for the Earth's parallax motion and the rotation of the lens galaxy, further reducing systematic errors. We measure a lower limit on the transverse speed of the lens galaxy, v_t > 338 km/s (68% confidence) and find a preferred direction to the East. The mean stellar mass estimate including a well-defined velocity prior is 0.12 <= <M/Msun> <= 1.94 at 68% confidence, with a median of 0.52 Msun. We also show for the first time that analyzing subsets of a microlensing light curve, in this case the first and second halves of the OGLE V-band light curve, give mutually consistent physical results.