# The Physical and chemical structure of Sagittarius B2 -- IV. Converging filaments in the high-mass cluster forming region Sgr B2(N)

## TL;DR

This study uses high-resolution ALMA observations and a new spectral line stacking method to analyze the small-scale filamentary structure and accretion processes in the high-mass star-forming region Sgr B2(N), revealing high velocity gradients and potential for super stellar cluster formation.

## Contribution

The paper introduces a novel line stacking technique to analyze kinematics in line-rich regions and provides detailed insights into filamentary accretion in Sgr B2(N).

## Key findings

- Eight converging filaments identified with high accretion rates.
- Velocity gradients along filaments are 10-100 times larger than in other regions.
- Potential for Sgr B2(N) to evolve into a super stellar cluster.

## Abstract

We have used an unbiased, spectral line-survey that covers the frequency range from 211 to 275 GHz and was obtained with ALMA (angular resolution of 0.4 arcsec) to study the small-scale structure of the dense gas in Sagittarius B2 (north). Eight filaments are found converging to the central hub and extending for about 0.1 pc. The spatial structure, together with the presence of the massive central region, suggest that these filaments may be associated with accretion processes. In order to derive the kinematic properties of the gas in a chemically line-rich source like Sgr B2(N), we have developed a new tool that stacks all the detected transition lines of any molecular species. This permits to increase the signal-to-noise ratio of our observations and average out line blending effects, which are a common problem in line-rich regions. We derive velocity gradients along the filaments of about 20-100 km s$^{-1}$ pc$^{-1}$, which are 10-100 times larger than those typically found on larger scales (1 pc) in other star-forming regions. The mass accretion rates of individual filaments are about 0.05 M$_\odot$ yr$^{-1}$, which result in a total accretion rate of 0.16 M$_\odot$ yr$^{-1}$. Some filaments harbor dense cores that are likely forming stars and stellar clusters. The stellar content of these dense cores is on the order of 50% of the total mass. We conclude that the cores may merge in the center when already forming stellar clusters but still containing a significant amount of gas, resulting in a "damp" merger. The high density and mass of the central region, combined with the presence of converging filaments with high mass, high accretion rates and embedded dense cores already forming stars, suggest that Sgr B2(N) may have the potential to evolve into a super stellar cluster.