VLBA17B-150

On the nature of M31*

Abstract

We are working on a large project with the High Sensitiviy Array (HSA) to measure the proper motion of the Andromeda galaxy M31 (project BB303) by observing water masers and the continuum nucleus (M31*). Although we achieved a noise of only ~3.5 microJy in our recent HSA observation of M31*, we were surprisingly not able to detect the source. This could be because i) the source is extended, or ii) was in a very low state during our observation. Unfortunately, we did not have any lower resolution VLA observations at the time of the HSA observation. Hence, it is not possible to distinguish between the two cases from our current data. We request a joint HSA and VLA observation of M31* to check whether M31* is resolved, or was just in a very low state. A detection of M31* would be a milestone toward a proper motion measurement which is key in determining the fate of the Local Group of galaxies. A second source within the primary beam (Braun-100) promises an in-beam calibrator or a second astrometric source within M31.

Investigators

Name	Institution
Elke Roediger	Hull, University of
Mark Reid	Center for Astrophysics | Harvard & Smithsonian
Jeremy Darling	Colorado at Boulder, University of
Heino Falcke	Netherlands Institute for Radio Astronomy; Nijmegen, Radboud Universiteit
Laurent Loinard	México, Universidad Nacional Autónoma de
Avi Loeb	Center for Astrophysics | Harvard & Smithsonian
Karl Menten	Max-Planck-Institut für Radioastronomie
Chris Henkel	Max-Planck-Institut für Radioastronomie
Andrea Tarchi	Istituto Nazionale di Astrofisica
Lorant Sjouwerman	National Radio Astronomy Observatory
Andreas Brunthaler *	Max-Planck-Institut für Radioastronomie
GBT Operator	Green Bank Observatory

* indicates the PI