Upper Limit on Brackett-gamma Emission from the Immediate Accretion Flow onto the Galactic Black Hole

Abstract

We present the first observational constraint on the Br-gamma recombination line emission associated with the supermassive black hole at the center of our Galaxy, known as Sgr A*. By combining 13 years of data with the Adaptive Optics fed integral field spectrograph OSIRIS at the W. M. Keck Observatory obtained as part of the Galactic Center Orbits Initiative, we extract the near-infrared spectrum within ~0.2'' of the black hole and we derive an upper limit on the Br-gamma flux. The aperture was set to match the size of the disk-like structure that was recently reported based on millimeter-wave ALMA observations of the hydrogen recombination line, H30-alpha. Our stringent upper limit is at least a factor of 80 (and up to a factor of 245) below what would be expected from the ALMA measurements and strongly constrains possible interpretation of emission from this highly under-luminous supermassive black hole.

arXiv commentAccepted by ApJ

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• Tracing the Milky Way's Vestigial Nuclear Jet
• A binary system in the S cluster close to the supermassive black hole Sagittarius A*
• Observation of the apoapsis of S62 in 2019 with NIRC2 and SINFONI
• The formation and stability of a cold disc made out of stellar winds in the Galactic Centre
• Candidate Young Stellar Objects in the S-cluster: The Kinematic Analysis of a Sub-population of the Low-mass G-objects close to Sgr A*
• High Energy Emission from the Galactic Center
• Revisiting the Evolutionary Status of Massive Stars at the central parsec of the Milky Way