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*

Abstract

The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Br$\gamma$ emission. The ionized hydrogen in combination with the observation of mid-infrared $L$-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. Until now, the question of the origin of these two populations is vague, although all explanations favor migration processes for the individual cluster members. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole Sgr~A* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a non-random distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Based on the photometric analysis, we estimated the individual $H-K$ and $K-L$ colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a Young Stellar Object Class I model. We obtained the position angle from the Keplerian fit results, and additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and mid-infrared domains.