New limits from microlensing on Galactic black holes in the mass range 10 M_⊙ < M < 1000 M_⊙

¹ Laboratoire de Physique des 2 infinis Irène Joliot-Curie, CNRS Université Paris-Saclay, Bât. 100, Faculté des Sciences, 91405 Orsay Cedex, France
e-mail: moniez@lal.in2p3.fr
² IRFU, CEA, Universite de Paris-Saclay, 91191 Gif-sur-Yvette, France
³ Université de Paris, CNRS, Astroparticule et Cosmologie, 75013 Paris, France
⁴ The International Space University, 1 Rue Jean-Dominique Cassini, 67400 Illkirch-Graffenstaden, Germany
⁵ Université de Strasbourg, CNRS, Observatoire Astronomique, CNRS, UMR 7550, 67000 Strasbourg, France
⁶ Sorbonne Université, CNRS/IN2P3, Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), 75005 Paris, France
⁷ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁸ Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, USA
⁹ Sorbonne Universités, UPMC Univ Paris 6 et CNRS, UMR 7095, Institut d’Astrophysique de Paris, IAP, 75014 Paris, France

Received: 27 February 2022
Accepted: 3 June 2022

Abstract

We searched for long-duration microlensing events originating from intermediate-mass black holes (BH) in the halo of the Milky Way, using archival data from the EROS-2 and MACHO photometric surveys towards the Large Magellanic Cloud (LMC). We combined data from these two surveys to create a common database of light curves for 14.1 million objects in the LMC, covering a total duration of 10.6 years, with flux series measured in four wide passbands. We carried out a microlensing search on these light curves, complemented by the light curves of 22.7 million objects, observed only by EROS-2 or only by MACHO, over about 7 years, with flux series measured in only two passbands. A likelihood analysis, taking into account the LMC self-lensing and Milky Way disk contributions, allows us to conclude that compact objects with masses in the range 10 − 100 M_⊙ cannot make up more than ∼15% of a standard halo total mass (at a 95% confidence level). Our analysis sensitivity weakens for heavier objects, although we still rule out the possibility of ∼50% of the halo being made of ∼1000 M_⊙ BHs. Combined with previous EROS results, an upper limit of ∼15% of the total halo mass can be obtained for the contribution of compact halo objects in the mass range 10⁻⁶ − 10² M_⊙.