The Galactic Center cloud G2 and its gas streamer

TL;DR

This study provides detailed near-infrared spectroscopic observations of the G2 gas cloud near the Galactic Center, revealing its tidal disruption, orbital dynamics, and possible connection to a larger gas streamer, supporting gaseous models.

Contribution

It offers new deep spectroscopic data of G2, an orbital analysis of G1, and proposes G2 as part of an extensive gas streamer, advancing understanding of gas dynamics near the Galactic Center.

Findings

G2 is undergoing tidal disruption near pericenter.

G1's orbit is similar to G2's but with lower eccentricity.

G2 may be a bright knot in a larger gas streamer.

Abstract

We present new, deep near-infrared SINFONI @ VLT integral field spectroscopy of the gas cloud G2 in the Galactic Center, from late summer 2013 and spring 2014. G2 is visible in recombination line emission. The spatially resolved kinematic data track the ongoing tidal disruption. As expected for an observation near pericenter passage, roughly half of the gas in 2014 is found at the redshifted, pre-pericenter side of the orbit, while the other half is at the post-pericenter, blueshifted side. We also present an orbital solution for the gas cloud G1, which was discovered a decade ago in L'-band images when it was spatially almost coincident with Sgr A*. The orientation of the G1 orbit in the three angles is almost identical to the one of G2, but it has a lower eccentricity and smaller semi-major axis. We show that the observed astrometric positions and radial velocities of G1 are compatible with the G2 orbit, assuming that (i) G1 was originally on the G2 orbit preceding G2 by 13 years and (ii) a simple drag force acted on it during pericenter passage. Taken together with the previously described tail of G2, which we detect in recombination line emission and thermal broadband emission, we propose that G2 may be a bright knot in a much more extensive gas streamer. This matches purely gaseous models for G2, such as a stellar wind clump or the tidal debris from a partial disruption of a star.