Saying Hallo to M94's Stellar Halo: Investigating the Accretion History of the Largest Pseudobulge Host in the Local Universe
Date
2023-04-01
Journal Title
Journal ISSN
Volume Title
Publisher
ASTROPHYSICAL JOURNAL
Abstract
It is not yet settled how the combination of secular processes and merging gives rise to the bulges and pseudobulges of galaxies. The nearby (D similar to 4.2 Mpc) disk galaxy M94 (NGC 4736) has the largest pseudobulge in the local universe, and offers a unique opportunity for investigating the role of merging in the formation of its pseudobulge. We present a first ever look at M94's stellar halo, which we expect to contain a fossil record of M94's past mergers. Using Subaru's Hyper Suprime-Cam, we resolve and identify red giant branch (RGB) stars in M94's halo, finding two distinct populations. After correcting for completeness through artificial star tests, we can measure the radial profile of each RGB population. The metal-rich RGB stars show an unbroken exponential profile to a radius of 30 kpc that is a clear continuation of M94's outer disk. M94's metal-poor stellar halo is detectable over a wider area and clearly separates from its metal-rich disk. By integrating the halo density profile, we infer a total accreted stellar mass of similar to 2.8 x 10(8) M-circle dot, with a median metallicity of [M/H] = -1.4. This indicates that M94's most-massive past merger was with a galaxy similar to, or less massive than, the Small Magellanic Cloud. Few nearby galaxies have had such a low-mass dominant merger; therefore we suggest that M94's pseudobulge was not significantly impacted by merging.
Description
Keywords
MILKY-WAY, GALAXY FORMATION, STAR-FORMATION, SATELLITE POPULATION, ILLUSTRIS PROJECT, SECULAR EVOLUTION, ANDROMEDA GALAXY, NEUTRAL HYDROGEN, NEARBY GALAXIES, BULGE FORMATION
Citation
Gozman, K., Bell, E. F., Smercina, A., Price, P., Bailin, J., de Jong, R. S., . . . Slater, C. (2023). Saying Hallo to M94's Stellar Halo: Investigating the Accretion History of the Largest Pseudobulge Host in the Local Universe. Astrophysical Journal, 947(1), 14, Article 21. https://doi.org/10.3847/1538-4357/acbe3a