Microlensing towards the Magellanic Clouds and M31: is the quest for MACHOs still open?

TL;DR

Microlensing is a key method for detecting MACHOs as dark matter candidates, with ongoing debates especially for masses between 0.1 and 1 solar mass, and recent focus on pixel lensing towards M31.

Contribution

This paper critically reviews recent microlensing results and emphasizes the pixel lensing analysis of M31 by the PLAN collaboration.

Findings

Constraints exclude MACHOs below 0.1 solar mass

Debate persists for MACHO masses between 0.1 and 1 solar mass

Pixel lensing towards M31 provides new insights

Abstract

Microlensing is the tool of choice for the search and the analysis of compact halo objects ("MACHOs"), a still viable class of dark matter candidates at the galactic scale. Different analyses point towards an agreement in excluding dark matter MACHOs of less than about 0.1 solar mass; it remains however an ongoing debate for values in the mass range (0.1-1) solar mass. The more robust constraints, though not all in agreement, come from the observational campaigns towards the Magellanic Clouds (the LMC and the SMC). The analyses towards the nearby galaxy of M31, in the so called "pixel lensing" regime, have expanded the perspectives in this field of research. In this contribution first we draw a critical view on recent results and then we focus on the pixel lensing analysis towards M31 of the PLAN collaboration.