Large-scale Hydrodynamical Shocks as the Smoking-gun Evidence for a Bar in M31

Abstract

The formation and evolutionary history of M31 are closely related to its dynamical structures, which remain unclear due to its high inclination. Gas kinematics could provide crucial evidence for the existence of a rotating bar in M31. Using the position–velocity diagram of [O III] and H i, we are able to identify clear sharp velocity jump (shock) features with a typical amplitude over 100 km s−1 in the central region of M31 (4.6 kpc × 2.3 kpc, or 20 ′ × 10 ′ ). We also simulate gas morphology and kinematics in barred M31 potentials and find that the bar-induced shocks can produce velocity jumps similar to those in [O III]. The identified shock features in both [O III] and H i are broadly consistent, and they are found mainly on the leading sides of the bar/bulge, following a hallmark pattern expected from the bar-driven gas inflow. Shock features on the far side of the disk are clearer than those on the near side, possibly due to limited data coverage on the near side, as well as to obscuration by the warped gas and dust layers. Further hydrodynamical simulations with more sophisticated physics are desired to fully understand the observed gas features and to better constrain the parameters of the bar in M31.

The CGM2 Survey: Quenching and the Transformation of the Circumgalactic Medium

“…A delay of 0.1-1 Gyr between quenching and a detectable change in the CGM is reasonable. M31 is also known to have a bar, and so could be passive due to internal dynamical effects that are irrelevant for its CGM (Athanassoula & Beaton 2006;Dorman et al 2015;Feng et al 2022).…”

The Complex Structure of the Bulge of M31

“…Opitsch et al (2018) show that kinematics data support a bar in M31, with nontriaxial streaming motions. The presence of a bar is confirmed by Feng et al (2022) in the central 4.6 kpc × 2.3 kpc region of M31. Saglia et al (2018) find that the bar and bulge are similar in age and [α/Fe] maps, but the bar stands out in metallicity, approximately solar, in contrast to the metal-rich bulge.…”

Impacts of Bar-driven Shear and Shocks on Star Formation

“…But exactly where are the velocity gradients enhanced? Previous studies have found that the velocity gradients coincide with the dust lane, i.e., on the leading side of the bar (see, e.g., Zurita et al 2004 andFeng et al 2022 for studies on NGC 1530 and M31, respectively).…”

“…Velocity jumps reaching ∼100−150 km s −1 have been found using Hα, [N II], [S II], H I, and CO (Pence & Blackman 1984;Reynaud & Downes 1998;Laine et al 1999;Mundell & Shone 1999;Weiner et al 2001;Zurita et al 2004), and even up to 200 km s −1 (Zánmar Sánchez et al 2008;Feng et al 2022). Thus, our results are comparable to previous observational studies on the other objects.…”