Detectability of large-scale counter-rotating stellar disks in galaxies with integral-field spectroscopy

• Published in: Astronomy and astrophysics (Berlin) 2021-10, Vol.654, p.A30
• Main Authors: Rubino, M., Pizzella, A., Morelli, L., Coccato, L., Portaluri, E., Debattista, V. P., Corsini, E. M., Dalla Bontà, E.
• Format: Article
• Language: English
• Subjects: Galactic rotation; Galaxies; Kinematics; Large scale structure of the universe; Object recognition; Parameterization; Rotating disks; Separation; Signal to noise ratio; Signatures; Spectroscopy; Stars & galaxies; Stellar kinematics; Stellar rotation; Velocity; Velocity distribution
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202140702

Context. In recent years integral-field spectroscopic surveys have revealed that the presence of kinematically decoupled stellar components is not a rare phenomenon in nearby galaxies. However, complete statistics are still lacking because they depend on the detection limit of these objects. Aims. We investigate the kinematic signatures of two large-scale counter-rotating stellar disks in mock integral-field spectroscopic data to address their detection limits as a function of the galaxy properties and instrumental setup. Methods. We built a set of mock data of two large-scale counter-rotating stellar disks as if they were observed with the Multi Unit Spectroscopic Explorer (MUSE). We accounted for different photometric, kinematic, and stellar population properties of the two counter-rotating components as a function of galaxy inclination. We extracted the stellar kinematics in the wavelength region of the calcium triplet absorption lines by adopting a Gauss-Hermite (GH) parameterization of the line-of-sight velocity distribution (LOSVD). Results. We confirm that the strongest signature of the presence of two counter-rotating stellar disks is the symmetric double peak in the velocity dispersion map, already known as the 2 σ feature. The size, shape, and slope of the 2 σ peak strongly depend on the velocity separation and relative light contribution of the two counter-rotating stellar disks. When the 2 σ peak is difficult to detect due to the low signal-to-noise ratio of the data, the large-scale structure in the h 3 map can be used as a diagnostic for strong and weak counter-rotation. The counter-rotating kinematic signatures become fainter at lower viewing angles as an effect of the smaller projected velocity separation between the two counter-rotating components. We confirm that the observed frequency of 2 σ galaxies represents only a lower limit of the stellar counter-rotation phenomenon. Conclusions. The parameterization with a single GH function does not provide a good description of the LOSVD in the presence of strong counter-rotation. However, using GH parametric solutions is a practical way to reveal the large-scale counter-rotating stellar disks and could be used to detect faint counter-rotating components to improve the statistics of stellar counter-rotation.