Polarized near-infrared light of the Dusty S-cluster Object (DSO/G2) at the Galactic Center

Abstract

We investigate an infrared-excess source called G2 or Dusty S-cluster Object (DSO) moving on a highly eccentric orbit around the Galaxy's central black hole, Sgr A*. We use, for the first time, near-infrared polarimetric imaging data to determine the nature and the properties of the DSO, and obtain an improved K_s-band identification of this source in median polarimetry images of different observing years. The source starts to deviate from the stellar confusion in 2008, and it does not show any flux density variability over the years we analyzed it. We measure the polarization degree and angle of the DSO between 2008 and 2012 and conclude, based on the significance analysis on polarization parameters, that it is an intrinsically polarized source (>20%) with a varying polarization angle as it approaches Sgr A* position. DSO shows a near-infrared excess of K_s-L' > 3 that remains compact close to the pericenter of its orbit. Its observed parameters and the significant polarization obtained in this work show that the DSO might be a dust-enshrouded young star, forming a bow shock as it approaches the super massive black hole. The significantly high measured polarization degree indicates that it has a non-spherical geometry and it can be modelled as a combination of a bow shock with a bipolar wind of the star. We use a 3D radiative transfer model that can reproduce the observed properties of the source such as the total flux density and the polarization degree. We obtain that the change of the polarization angle can be due to an intrinsic change in the source structure. Accretion disc precession of the young star in the gravitational field of the black hole can lead to the change of the bipolar outflow and therefore the polarization angle variation. It might also be the result of the source interaction with the ambient medium.

arXiv comment15 pages, 12 figures, Accepted to be published in Astronomy & Astrophysics

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• S62 and S4711: Indications of a population of faint fast moving stars inside the S2 orbit -- S4711 on a 7.6 year orbit around Sgr~A*
• A population of dust-enshrouded objects orbiting the Galactic black hole
• S62 on a 9.9 yr Orbit around SgrA*
• The Keplerian three-body encounter I. Insights on the origin of the S-stars and the G-objects in the Galactic center
• Monitoring dusty sources in the vicinity of Sgr A*
• Nature of the Galactic centre NIR-excess sources. I. What can we learn from the continuum observations of the DSO/G2 source?
• Near- and mid-infrared observations in the inner tenth of a parsec of the Galactic center -- Detection of proper motion of a filament very close to Sgr~A*
• A new bow-shock source with bipolar morphology in the vicinity of Sgr A*
• A binary system in the S cluster close to the supermassive black hole Sagittarius A*
• The apparent tail of the Galactic center object G2/DSO
• First observed interaction of the circumstellar envelope of an S-star with the environment of Sgr A*
• Observation of the apoapsis of S62 in 2019 with NIRC2 and SINFONI
• Polarization simulations of stellar wind bow shock nebulae. I. The case of electron scattering
• Polarization simulations of stellar wind bow shock nebulae. II. The case of dust scattering
• X3: a high-mass Young Stellar Object close to the supermassive black hole Sgr~A*
• Electromagnetic signatures of strong-field gravity from accreting black holes
• 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*
• Continuum polarization reverberation mapping of AGNs
• Closing the gap: Follow-up observations of peculiar dusty objects close to Sgr A* using ERIS