The SAMI Galaxy Survey: The relationship between galaxy rotation and the motion of neighbours

Yifan Mai, Sam P. Vaughan, Scott M. Croom, Jesse van de Sande, Stefania Barsanti, Joss Bland-Hawthorn, Sarah Brough, Julia J. Bryant, Matthew Colless, Michael Goodwin, Brent Groves, Iraklis S. Konstantopoulos, Jon S. Lawrence, Nuria P. F. Lorente, Samuel N. Richards

Submitted on 8 July 2022


Using data from the SAMI Galaxy Survey, we investigate the correlation between the projected stellar kinematic spin vector of 1397 SAMI galaxies and the line-of-sight motion of their neighbouring galaxies. We calculate the luminosity-weighted mean velocity difference between SAMI galaxies and their neighbours in the direction perpendicular to the SAMI galaxies angular momentum axes. The luminosity-weighted mean velocity offsets between SAMI and neighbours, which indicates the signal of coherence between the rotation of the SAMI galaxies and the motion of neighbours, is 9.0 ± 5.4 km s1 (1.7 σ) for neighbours within 1 Mpc. In a large-scale analysis, we find that the average velocity offsets increase for neighbours out to 2 Mpc. However, the velocities are consistent with zero or negative for neighbours outside 3 Mpc. The negative signals for neighbours at distance around 10 Mpc are also significant at 2 σ level, which indicate that the positive signals within 2 Mpc might come from the variance of large-scale structure. We also calculate average velocities of different subsamples, including galaxies in different regions of the sky, galaxies with different stellar masses, galaxy type, λRe and inclination. Although low-mass, high-mass, early-type and low-spin galaxies subsamples show 2 - 3 σ signal of coherence for the neighbours within 2 Mpc, the results for different inclination subsamples and large-scale results suggest that the 2σ signals might result from coincidental scatter or variance of large-scale structure. Overall, the modest evidence of coherence signals for neighbouring galaxies within 2 Mpc needs to be confirmed by larger samples of observations and simulation studies.


Comment: 14 pages, 9 figures, accepted for publication in MNRAS

Subject: Astrophysics - Astrophysics of Galaxies