Structure and Fragmentation of a high line-mass filament: Nessie

TL;DR

This study analyzes the fragmentation and star-forming potential of the Nessie high line-mass filament using high-resolution dust extinction mapping, revealing multi-scale fragmentation patterns and star formation rates comparable to nearby giant molecular clouds.

Contribution

It provides the first high-resolution extinction map of Nessie, characterizes its multi-scale fragmentation, and links small-scale structures to star formation potential, comparing observations with theoretical models.

Findings

Nessie has a mean line-mass of ~627 M_sun/pc and is at ~3.5 kpc distance.

Fragmentation occurs at multiple scales with separations near the Jeans length.

Star formation rate is estimated at ~371 M_sun/Myr with a star formation efficiency of 0.017.

Abstract

An increasing number of hundred-parsec scale, high line-mass filaments have been detected in the Galaxy. Their evolutionary path, including fragmentation towards star formation, is virtually unknown. We characterize the fragmentation within the Nessie filament, covering size-scales between $\sim$ 0.1-100 pc. We also connect the small-scale fragments to the star-forming potential of the cloud. We combine near-infrared data from the VVV survey with mid-infrared GLIMPSE data to derive a high-resolution dust extinction map and apply a wavelet decomposition technique on it to analyze the fragmentation characteristics of the cloud, which are compared with predictions from fragmentation models. We compare the detected objects to those identified in $\sim$ 10 times coarser resolution from ATLASGAL data. We present a high-resolution extinction map of Nessie. We estimate the mean line-mass of Nessie to be $\sim$ 627 M$_\odot$/pc and the distance to be $\sim$ 3.5 kpc. We find that Nessie shows fragmentation at multiple size scales. The nearest-neighbour separations of the fragments at all scales are within a factor of 2 of the Jeans' length at that scale. However, the relationship between the mean densities of the fragments and their separations is significantly shallower than expected for Jeans' fragmentation. The relationship is similar to the one predicted for a filament that exhibits a Larson-like scaling between size-scale and velocity dispersion; such a scaling may result from turbulent support. Based on the number of YSOs in Nessie, we estimate that the star formation rate is $\sim$ 371 M$_\odot$/Myr; similar values result if using the number of dense cores, or the amount of dense gas, as the proxy of star formation. The star formation efficiency is 0.017. These numbers indicate that Nessie's star-forming content is comparable to the Solar neighborhood giant molecular clouds like Orion A.