# Complex distribution and velocity field of molecular gas in NGC 1316 as revealed by Morita Array of ALMA

## TL;DR

This study uses ALMA to map molecular gas in NGC 1316, revealing complex structures and disturbed kinematics indicative of recent external gas accretion and interaction with nuclear jets.

## Contribution

First detailed kpc-scale molecular gas distribution and velocity field in NGC 1316 using ALMA, highlighting recent external gas accretion and jet interaction effects.

## Key findings

- Molecular gas forms shell, blob, and clumps in the galaxy center.
- Total molecular gas mass is approximately 5.62 x 10^8 solar masses.
- Disturbed velocity field suggests recent external gas accretion (<1 Gyr).

## Abstract

We present the results of $^{12}$CO($J$=1-0) mosaicing observations of the cD galaxy NGC 1316 at kpc-resolution performed with the Morita Array of the Atacama Large Millimeter/submillimeter Array (ALMA). We reveal the detailed distribution of the molecular gas in the central region for the first time: a shell structure in the northwest, a barely resolved blob in the southeast of the center and some clumps between them. The total molecular gas mass obtained with a standard Milky-Way CO-to-H$_2$ conversion factor is $(5.62 \pm 0.53)\times10^8$ M$_\odot$, which is consistent with previous studies. The disturbed velocity field of the molecular gas suggests that the molecular gas is injected very recently ($<1$ Gyr) if it has an external origin and is in the process of settling into a rotating disk. Assuming that a low-mass gas-rich galaxy has accreted, the gas-to-dust ratio and H$_2$-to-HI ratio are unusually low ($\sim 28$) and high ($\sim 5.6$), respectively. To explain these ratios, additional processes should be taken into accounts such as an effective dust formation and conversion from atomic to molecular gas during the interaction. We also discuss the interaction between the nuclear jet and the molecular gas.