THE GALACTIC CENTER CLOUD G2 AND ITS GAS STREAMER

Abstract

We present new, deep near-infrared SINFONI @ VLT integral field spectroscopy\nof the gas cloud G2 in the Galactic Center, from late summer 2013 and spring\n2014. G2 is visible in recombination line emission. The spatially resolved\nkinematic data track the ongoing tidal disruption. As expected for an\nobservation near pericenter passage, roughly half of the gas in 2014 is found\nat the redshifted, pre-pericenter side of the orbit, while the other half is at\nthe post-pericenter, blueshifted side. We also present an orbital solution for\nthe gas cloud G1, which was discovered a decade ago in L'-band images when it\nwas spatially almost coincident with Sgr A*. The orientation of the G1 orbit in\nthe three angles is almost identical to the one of G2, but it has a lower\neccentricity and smaller semi-major axis. We show that the observed astrometric\npositions and radial velocities of G1 are compatible with the G2 orbit,\nassuming that (i) G1 was originally on the G2 orbit preceding G2 by 13 years\nand (ii) a simple drag force acted on it during pericenter passage. Taken\ntogether with the previously described tail of G2, which we detect in\nrecombination line emission and thermal broadband emission, we propose that G2\nmay be a bright knot in a much more extensive gas streamer. This matches purely\ngaseous models for G2, such as a stellar wind clump or the tidal debris from a\npartial disruption of a star.\n