Properties of interstellar filaments as derived from Herschel Gould Belt observations

Transcription

1 Properties of interstellar filaments as derived from Herschel Gould Belt observations Doris Arzoumanian PhD student at CEA Saclay, France with Ph. André, V. Könyves, N. Schneider, N. Peretto, A. Men shchikov, P. Didelon, P. Palmeirim Herschel Gould Belt and SPIRE/SAG 3 consortia D. Arzoumanian et al 2011 IC5146 Herschel Composite image Red: SPIRE 500 m and 350 m Green: SPIRE 250 m and PACS 160 m Blue: PACS 70 m

2 The filamentary structure of molecular clouds as seen by the Herschel Gould Belt survey Survey of nearby molecular clouds < 0.5 kpc Sensitivity and resolution: detection of structures down to 0.1Av and 0.02pc What are the properties of the filaments? Aquila Polaris André et al., Bontemps et al., Könyves et al., Men shchikov et al.,ward-thompson et al. 2010

3 Curvelet component of the column density maps Decomposition of the maps on curvelets and wavelets (Starck et al. 2003) Enhances the contrast of the filamentary structure Courtesy Pierre Didelon IC5146 Aquila Arzoumanian et al Polaris André et al., Bontemps et al., Könyves et al Men shchikov et al.,ward-thompson et al. 2010

4 Skeletons of the filamentary networks Traced with the DisPerSE algorithm IC5146 (Sousbie 2011) Aquila Arzoumanian et al.2011 Polaris André et al., Bontemps et al., Könyves et al Men shchikov et al.,ward-thompson et al. 2010

5 Properties of a filament radial column density profile perpendicular to the filament axis Taurus filament N H2 [cm-2] Flat radius 0.047pc N H2 [cm -2 ]! Outer radius 0.5pc beam background M line = 50 M sun /pc Radius [pc]! Plummer-like density profile:!(r) =! c / [1 + (r/r flat ) 2 ] p/2 best fit for! " r 2 not! " r 4 as for isothermal filaments in hydrostatic equilibrium (Ostriker 1964) R flat ~ 0.05 pc Diameter of flat inner plateau (width ) ~ 0.1 pc Palmeirim, André, Arzoumanian et al Cf. Pedro Palmeirim s poster

6 Distribution of widths for 227 filaments in 6 regions from the Gould Belt Survey Characteristic width of ~ 0.1 pc Distances From 130pc to 460pc Resolutions from 0.02pc to 0.04pc Number of filaments per bin! Arzoumanian et al bbbbbbbbbbbbb Distances bb IC pc Aquila 260pc Polaris 150pc Pipe 145pc Ophiuchus 140pc Taurus Distances 130pc 460pc 260pc 145pc Jeans lengths [# J ~ c s2 /(G$)] 150pc 130pc 1.4 pc 0.1 Filament width (FWHM) [pc]! Median value ( )pc 0.003pc < Jeans length < 1.4pc

7 Filament width vs. Column density Filament M line in unit of M line,cirt = 2c s2 /G ~20 M sun /pc for T=12K Filament width (FWHM) [pc]! Jeans length [# J ~ c s2 /(G$)] ~ 0.1 pc Central column density N H2 [cm -2 ]! Updated version of Figure 7 from Arzoumanian et al. 2011

8 The characteristic width of the filaments corresponds to the sonic scale of the ISM Log (Velocity Dispersion)! [km/s]! Linewidth-Size relation in clouds (Larson 1981) 0.1 pc Sonic scale % V (L) L 0.5 Log (Size) haha [pc]! 0.2 km/s sound speed Simulations of turbulent fragmentation Padoan, Juvela et al The 0.1 pc is the typical thickness of shock-compressed structures/filaments in the turbulent fragmentation scenario

9 Two regimes: Low density vs. dense, self gravitating filaments Filament M line in unit of M line,cirt = 2c s2 /G ~20 M sun /pc for T=12K Filament width (FWHM) [pc]! Subcritical filaments (unbound) Av~8 Supercritical filaments (gravitationally unstable) bbbbbbbbbbbbb bb limit of gravitational instability Jeans length [# J ~ c s2 /(G$)] ~ 0.1 pc Central column density N H2 [cm -2 ]!

10 Arzoumanian et al in prep. Subcritical filaments C 18 O(1-0) N H2 (cm -2 ) Follow up IRAM 30m observations velocity dispersion of filaments with Ph. André, N. Peretto, V. Könyves, P. Didelon, P. Palmeirim N H2 [cm-2] N 2 H + (1-0) 9.9x10 21 cm -2 NT = 0.2 km/s 1.1x10 22 cm -2 NT = 0.1 km/s 2.1x10 23 cm -2 NT = 0.6 km/s N 2 H + (1-0) N 2 H + (1-0) Aquila Herschel Gould Belt survey Supercritical filaments Doris Arzoumanian From atoms to pebbles - Grenoble, Tuesday 20 March x10 22 cm -2 NT = 0.3 km/s

11 Total velocity dispersion of the filaments Total Velocity Dispersion [km/s]! C s (10K)=0.2km/s (Schneider et al. 2010,Henneman et al. 2012) (Peretto et al. 2006) Central column density N H2 [cm -2 ]! M line ~ 0 x W fil M line,cirt = 2c s2 /G Arzoumanian et al in prep.

12 Conclusions Filaments share a characteristic width ~ 0.1 pc Observations consistent with the turbulent fragmentation scenario of filament formation D. Arzoumanian et al 2011 Two regimes: subcritical unbound filaments and supercritical gravitationally unstable filaments Evolution of the velocity dispersion and the mass per unit length of supercritical filaments D. Arzoumanian et al in prep Thank you for your attention