Colloquium Abstract - Steffes - 2026Mar13

March 13, 2026

11:00am Mountain

Lucy Steffes (University of Arizona)

 

Measuring Velocity Gradients of Intermediate Density Gas in Filament Spines and Prestellar Cores in the Taurus Molecular Cloud

 

Abstract

Understanding how mass flows from large scales in molecular clouds down to small scales in dense cores is one of the outstanding problems of star formation. Ammonia (NH3) traces intermediate to dense gas (>10^3 cm-3) in star forming regions. Using the Green Bank Telescope (GBT) and the Green Bank Ammonia Survey (GAS), NH3 was mapped across the Taurus Molecular Cloud in the (1,1) and (2,2) inversion transitions. 39 dense cores were identified in the L1495-B218 regions from a dendrogram analysis of the NH3 (1,1) emission. Due to the blending of 18 hyperfine transitions of the (1,1) transition of NH3, decomposing multiple velocity components along a single line-of-sight presents challenges for kinematic analysis. Bayesian methods are used to determine the number of velocity components and estimate their model parameters in a statistically rigorous and automated way using Bayes factors computed with a Nested Sampling Monte Carlo routine.
Using filament spines determined from an analysis of dust continuum observations from the Herschel Gould Belt Survey, I project the gradient of the maximum likelihood line-of-sight velocity of the NH3 gas in the parallel and perpendicular directions to the filament spines to measure how gas flows from diffuse regions onto filaments and within filaments into dense cores. Using Nyquist spatial sampling, I examine the cumulative distributions of the magnitude of the velocity gradients, which indicates that lower velocity gradients tend to be more common closer to dust spines, with velocity gradients increasing further away from dust spines. However, we also find high velocity distributions across the regions, suggesting a remaining imprint of the initial turbulence, which has not fully dissipated.
We also examine core rotation, inflows, and line asymmetries to better understand the earliest stages of star formation. This work also includes a comparison with the chemical evolution in the region and an exploration into how the kinematics impact the chemistry. I will present a summary of the gas kinematics measured by analyzing the velocity gradients for the L1495-B218 regions of Taurus.


Local Host: Brian Svoboda

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