The Specific Angular Momentum of Dense Starless Cores in the Taurus Molecular Cloud

Abstract

In this paper we examine the velocity structure of dense starless cores within the L1495-B218 structure of the Taurus Molecular Cloud (TMC). Here we use maps of velocity with respect to the local standard of rest (𝑣𝑙𝑠𝑟 ) obtained from the Greenbank Telescope (GBT) Ammonia Survey (GAS) (Seo et al. 2015; Friesen et al. 2017). From the gradient of the 𝑣𝑙𝑠𝑟 in these cores, we make estimates of the angular velocity (𝜔) and radius (𝑅) of 12 of the cores designated by Seo et al. (2015) and in turn use these to calculate their specific angular momentum (𝐽/𝑀). We compare the relationship between 𝐽/𝑀 and 𝑅 to similar surveys of cores conducted in ammonia (NH3) to check our measurements and find a similar proportionality of 𝐽/𝑀 ∝ 𝑅1.62±0.19. As chemistry changes with depth in the cores, different molecules trace different radii of the cores, so we make direct comparisons to literature values obtained by Punanova et al. (2018) of different dense gas tracers, to see how ammonia fits into this scheme. In particular we compare our NH3 (1,1) values to those made in N2H+ 1-0, N2D+ 2-1, DCO+ 2-1, and H13CO+ 1-0 in the same cores and found that the 𝐽/𝑀 from NH3 (1,1) most strongly correlates with that of N2D+ 2-1 and DCO+ 2-1, which we found to have Pearson correlation coefficients of 0.93 and 0.92 respectively. The specific angular momentum traced by NH3 (1,1) fits into a sequence where 𝐽/𝑀 decreases with the density of the gas probed by different molecular transitions.