# Star Formation Efficiencies at Giant Molecular Cloud Scales in the Molecular Disk of the Elliptical Galaxy NGC 5128 (Centaurus A)

## TL;DR

This study uses high-resolution ALMA observations to analyze molecular gas and star formation efficiencies in NGC 5128, revealing similarities to disk galaxies and unique features in the circumnuclear region of an elliptical galaxy.

## Contribution

First detailed high-resolution mapping of molecular gas and star formation in an elliptical galaxy, highlighting differences between core and outer disk star formation efficiencies.

## Key findings

- Global SFE similar to disk galaxies (~0.6 Gyr$^{-1}$)
- Circumnuclear disk has lower SFE (~0.3 Gyr$^{-1}$) than outer disk
- Outer disk contains extended filamentary molecular structures

## Abstract

We present ALMA CO(1-0) observations toward the dust lane of the nearest elliptical and radio galaxy, NGC 5128 (Centaurus A), with high angular resolution ($\sim$ 1 arcsec, or 18 pc), including information from large to small spatial scales and total flux. We find a total molecular gas mass of 1.6$\times$10$^9$ $M_\odot$ and we reveal the presence of filamentary components more extended than previously seen, up to a radius of 4 kpc. We find that the global star formation rate is $\sim$1 \Msol yr$^{-1}$, which yields a star formation efficiency (SFE) of 0.6 Gyr$^{-1}$ (depletion time $\tau =$1.5 Gyr), similar to those in disk galaxies. We show the most detailed view to date (40\,pc resolution) of the relation between molecular gas and star formation within the stellar component of an elliptical galaxy, from several kpc scale to the circumnuclear region close to the powerful radio jet. Although on average the SFEs are similar to those of spiral galaxies, the circumnuclear disk (CND) presents SFEs of 0.3 Gyr$^{-1}$, lower by a factor of 4 than the outer disk. The low SFE in the CND is in contrast to the high SFEs found in the literature for the circumnuclear regions of some nearby disk galaxies with nuclear activity, probably as a result of larger shear motions and longer AGN feedback. The higher SFEs in the outer disk suggests that only central molecular gas or filaments with sufficient density and strong shear motions will remain in $\sim$1 Gyr, which will later result in the compact molecular distributions and low SFEs usually seen in other giant ellipticals with cold gas.