The Virial State of Starless and Prestellar Cores

The Virial State of Starless and Prestellar Cores Yancy Shirley Univ. of Arizona Credit: Herschel Gould Belt Team

The starless core is the fundamental “unit” of star formation capable of forming one star or a bound multiple star system Credit: ESO, Alves

This is NOT a typical starless core… Credit: ESO, Alves

Taurus Molecular Cloud Most (~75%) starless cores are coincident with filamentary structure (Andre’ et al. 2010, HGBT papers) 100% of gravitationally bound prestellar cores lie within filaments (Marsh et al. 2016) Credit: Herschel Gould Belt Team 160 mm, 250/350 mm, 500 mm

Taurus Molecular Cloud These core are not evolving in isolation… CO 1 -0 Mass accretion rate ~10 s Msun/pc/Myr Credit: Herschel Gould Belt Team Palmeirim et al. 2013, Shimajiri et al 2019

Taurus Molecular Cloud What is the dynamical state of starless & prestellar cores in non-isolated environments? Credit: Herschel Gould Belt Team

Taurus Molecular Cloud We will focus on observations of the L 1495 -B 218 region NH 3 (1, 1) Credit: Herschel Gould Belt Team NH 3 map Seo et al. 2015

Taurus Molecular Cloud Also with deuterium fractionation observations o-NH 2 D Gas phase deuteration Credit: Herschel Gould Belt Team Shirley et al. (in prep. )/Ambrose et al. (in prep. ) CH 2 DOH-e 0 Solid phase Seo 39 deuteration

Defining the Starless Core Astro. Dendro NH 3 intensity 500 mm Jimmy Lilly Honors Thesis Astro. Dendro Herschel N(H 2)

Virial Theorem ½ d 2 I/dt 2 = 2 WK + WB – WG – 2 WP – Wram – WD - Wrad WK = Internal Kinetic Energy = ½ M (sv 2)3 D WG = Grav. Potential Energy = ⅗ a GM 2/R WP = External Surface Pressure = 4 p R 3 P 0 500 mm WB = ∫ xi Tij d. Sj - ∫ dij Tij d. V Wram = ∫ r 0 xi vi vj d. Sj WD = ½ d/dt ∫ r 0 r 2 vi d. Si simple approx. If v normal to surface simple approx. P 0 = Weight of filament P 0 = Turbulent r 0 sv 2 ⅙ (B 2 – B 02) R 3 4 p R 3 r 0 v 02 2 R 2 d 2 M/dt 2

NH 3 linewidth NH 3 Linewidth vs. Radius (pc) H. Chen et al. 2019

B Field Strength? Optical/NIR Polarization Bsky ~ 25 – 75 m. G depending on method OH Zeeman Blos ~ 11 +/- 2 m. G Line of sight Chapman et al. 2011 Crutcher & Troland 2000

NH 2 D Detections vs. Non-Detections Virial Parameter X Non-detection • Detection Shirley et al. in prep. Mass

CH 2 DOH Deuterium Fraction Virial Parameter Only B 10 region observed non-detections Ambrose et al. in prep. Deuterium Fraction

Results • Starless cores are the fundamental “unit” of star formation within a turbulent, hierarchical structure. • Their evolution is not isolated from their environment. • There is a correlation between dynamical state (expanded Virial parameter) and the chemical evolution as traced by deuteration • The (preliminary) median fractions for terms in Virial equation are: Turb. only +Filament Weight • 2 W_K 0. 57 0. 32 • 2 W_P 0. 23 0. 59 • W_G 0. 14 0. 07 • W_B 0. 05 0. 02

Additional Slides 500 mm

Hydrostatic vs. Hydrodynamic Collapsing Bonnor-Ebert Sphere similar profile to stable Bonnor-Ebert sphere. Need to probe velocity to differentiate. 40%, 60%, 80% of free-fall time Velocity (km/s) log Density (cm-3) hydrostatic 40%, 60%, 80% of free-fall time Myers 2005 log Radius (pc)