Dark Matter in the Central Region of the Spiral Galaxy NGC 4321

TL;DR

This study investigates the central dark matter distribution in galaxy NGC 4321 using ALMA data, finding significant unaccounted mass likely due to dark matter, and evaluates MOND as an alternative explanation, ultimately finding it insufficient.

Contribution

First detailed measurement of central dark matter mass in NGC 4321 using CO observations, challenging MOND's applicability in this context.

Findings

Unaccounted mass of 2.3 x 10^9 M_sun within 0.7 kpc

Dark matter likely causes the unseen mass, not the SMBH

MOND cannot explain the mass discrepancy at this radius

Abstract

We present our results of 12 CO(1-0) transition in the central region of NGC 4321 using the Atacama Large Millimeter and Sub-millimeter Array (ALMA). We found an unaccounted mass of $2.3 \times 10^9 M_{\odot}$ within the central 0.7 kpc of this galaxy. The expected mass of the supermassive black hole (SMBH) in this galaxy is much smaller than the unaccounted mass. The invisible mass is likely caused by dark matter in the central region of the galaxy, indicating a cuspy dark matter profile. We also investigated the Modified Newtonian Dynamics (MOND) as an alternative mechanism to explain the invisible mass. We noted that at the radius of 0.7 kpc of the galaxy, the acceleration is about $1.04 \times 10^-7~cm~s^-2$, which is much larger than the critical acceleration $a_{0} \sim 1.2 \times 10^-8 ~cm~s^-2$ in the MOND theory, suggesting that theory might not be able explain the unseen mass problem in central region of this galaxy.