The Triangulum Extended (TREX) Survey: The Stellar Disk Dynamics of M33 as a Function of Stellar Age

• Published in: The Astronomical journal 2022-04, Vol.163 (4), p.166
• Main Authors: Quirk, Amanda C. N., Guhathakurta, Puragra, Gilbert, Karoline M., Chemin, Laurent, Dalcanton, Julianne J., Williams, Benjamin F., Seth, Anil, Patel, Ekta, Fung, Justin T., Tangirala, Pujita, Yusufali, Ibrahim
• Format: Article
• Language: English
• Subjects: Analogs; Andromeda Galaxy; Astronomical models; Astronomy; Disk galaxies; Dispersion; Galaxies; Galaxy evolution; Heating; Helium; Hubble Space Telescope; Kinematics; Main sequence stars; Milky Way; Polls & surveys; Red giant stars; Space telescopes; Spiral galaxies; Stellar age; Velocity
• ISSN: 0004-6256; 1538-3881
• DOI: 10.3847/1538-3881/ac5324

Triangulum (M33) is a low-mass, relatively undisturbed spiral galaxy that offers a new regime in which to test models of dynamical heating. In spite of its proximity, M33's dynamical heating history has not yet been well-constrained. In this work, we present the TREX Survey, the largest stellar spectroscopic survey across the disk of M33. We present the stellar disk kinematics as a function of age to study the past and ongoing dynamical heating of M33. We measure line-of-sight velocities for ∼4500 disk stars. Using a subset, we divide the stars into broad age bins using Hubble Space Telescope and Canada–France–Hawaii Telescope photometric catalogs: massive main-sequence stars and helium-burning stars (∼80 Myr), intermediate-mass asymptotic branch stars (∼1 Gyr), and low-mass red giant branch stars (∼4 Gyr). We compare the stellar disk dynamics to that of the gas using existing H i , CO, and H α kinematics. We find that the disk of M33 has relatively low-velocity dispersion (∼16 km s −1 ), and unlike in the Milky Way and Andromeda galaxies, there is no strong trend in velocity dispersion as a function of stellar age. The youngest disk stars are as dynamically hot as the oldest disk stars and are dynamically hotter than predicted by most M33-like low-mass simulated analogs in Illustris. The velocity dispersion of the young stars is highly structured, with the large velocity dispersion fairly localized. The cause of this high-velocity dispersion is not evident from the observations and simulated analogs presented here.