What can the occult do for you?

TL;DR

This paper discusses using overlapping galaxy pairs observed by Hubble to precisely map dust distribution in galaxies, improving understanding of dust's impact on astronomical measurements.

Contribution

It introduces the STARSMOG program and the use of IFU observations to analyze dust geometry and composition in foreground galaxies.

Findings

High-resolution dust maps in foreground galaxies

Effective extinction curves disentangled from geometry

Insights into dust's wavelength dependence

Abstract

Interstellar dust is still a dominant uncertainty in Astronomy, limiting precision in e.g., cosmological distance estimates and models of how light is re-processed within a galaxy. When a foreground galaxy serendipitously overlaps a more distant one, the latter backlights the dusty structures in the nearer foreground galaxy. Such an overlapping or occulting galaxy pair can be used to measure the distribution of dust in the closest galaxy with great accuracy. The STARSMOG program uses Hubble to map the distribution of dust in foreground galaxies in fine (<100 pc) detail. Integral Field Unit (IFU) observations will map the effective extinction curve, disentangling the role of fine-scale geometry and grain composition on the path of light through a galaxy. The overlapping galaxy technique promises to deliver a clear understanding of the dust in galaxies: geometry, a probability function of dimming as a function of galaxy mass and radius, and its dependence on wavelength.