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Observations of the Filament Paradigm for Star Formation: Where Do We Stand?

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Observations of the Filament Paradigm for Star Formation: Where Do We Stand? Observations of the filament paradigm for star formation: Where do we stand? Ph. André CEA - Lab. AIM Paris-Saclay Charlottesville, Oct 10-11, 2014 Filaments 2015 Filaments in Molecular Clouds Munich, March 23-25, 2015 Filaments2018 Herschel 10 years after launch : science and HerschelCelebration GBS – 160/250/500ESAC Madrid – µ13m May composite 2019 image of Taurus B213/B213 (Palmeirim+2013) Polaris Outline Herschel • Introduction: Omnipresence/`Universality’ 250/350/500 µm of filamentary structures in the cold ISM • Results supporting a filament paradigm for star formation • Open issues & future prospects - Role of magnetic fields? With: V. Könyves, D. Arzoumanian, P. Palmeirim, J. Di Francesco, D. Ward-Thompson, S. Pezzuto, J. Kirk, A. Menshchikov, N. Schneider, A. Roy, S. Bontemps, F. Motte, M. Griffin, K. Marsh, N. Peretto, Y. Shimajiri, B. Ladjelate, A. Bracco, N. Cox, P. Didelon, & the Herschel Gould Belt survey Team Herschel10years – Madrid – 13 May 2019 - Ph. André Herschel has revealed the presence of a ‘universal’ filamentary structure in the cold ISM Ophiuchus: L1688 Pipe 2 pc 1.5 pc Peretto+2012 Column density maps available at http://gouldbelt-herschel.cea.fr/archives Perseus Ladjelate + 2019 NGC1333 Aquila Polaris 2 pc 1deg ~ 4.5pc 1deg Sadavoy + 2014 5 pc Ward-Thompson + 2010 Pezzuto + 2019 Miville-Deschênes + 2010 André + 2010 Könyves + 2015 Herschel10years – Madrid – 13 May 2019 - Ph. André Filaments dominate the mass budget of GMCs at high densities Herschel (Hi-GAL) Herschel (HGBS) H2 Column Density PDF for l217-224 field Column Density PDF for Aquila GMC logN Δ N/ Δ PDF on PDF after filaments subtracting excl. ‘clumps’ cores of pixels per bin: of pixels per Av ~ 7 Column density, N (cm-2) Number -2 H2 Column density, NH2 (cm ) Könyves et al. 2015 Schisano et al. 2014 § Below AV ~ 7: ~ 10-20 % of the mass in the form of filaments Arzoumanian et al. 2019 § Above AV ~ 7: > 50-80 % of the mass in the form of filaments Herschel10years – Madrid – 13 May 2019 - Ph. André Nearby filaments have a common inner width ~ 0.1 pc Network of filaments in IC5146 Herschel 500/250 µm Distribution of mean inner widths for ~ 600 nearby (d < 450pc) filaments 0.1 +- 0.05 pc IC5146 Orion B Aquila Polaris Ophiuchus Distribution of Taurus Jeans lengths Pipe ~ 5 pc bin of filaments per Distribution of Musca filament lengths Example of a filament radial profile Number Inner radius 0.1 ~ 0.05pc Filament width (FWHM) [pc] ] -2 D. Arzoumanian+2011 & 2019 (A&A, 621, A42) Outer radius [but some width variations along each filament: Ysard+2013] [cm 0.5pc H2 N Possibly linked to magneto-sonic scale of turbulence? beam background (cf. Padoan+2001; Federrath 2016) Radius [pc] Challenging for numerical simulations (cf. R. Smith+2014; Ntormousi+2016) Herschel10years – Madrid – 13 May 2019 - Ph. André Is a characteristic filament width consistent with the observed power spectrum of cloud images? Tension with scale-free power spectrum SPIRE 250 µm image of Polaris translucent cloud Panopoulou+2017 Noise-subtracted, deconvolved power spectrum of Polaris image -2.69 P(k) = AISM k + P0 /sr] 2 sr / 4 pc MJy Miville-Deschênes et al. 2010 P(k) [Jy Power: -1 Spatial angular frequency, k [arcmin ] Herschel10years – Madrid – 13 May 2019 - Ph. André Simple tests Power spectrum of image A. Roy et al. 2019, arXiv:1903.12608 with synthetic 0.1 pc filaments Injecting a population of synthetic -2.75 /sr] P(k) = AISM k + P0 0.1 pc filaments with contrast ~ 50% 2 in SPIRE 250 µm image of Polaris translucent cloud Synthetic filaments contribution Power: P(k) [Jy Power: Spatial angular frequency, k [arcmin-1] Difference from power-law fit Fit sr − Synthetic / law 4 pc MJy 4 pc Conclusion: Observed power spectra remain consistent with a characteristic : Power- Original filament width ~ 0.1 pc for realistic filling factors and filament contrasts -1 Residuals Herschel10years – Madrid – 13 May 2019 - Ph. André Spatial angular frequency, k [arcmin ] Characteristic filament width ~ 0.1 pc not restricted to the nearby clouds of the Gould Belt NGC6334 main filament: M/L ~ 1000 M/pc Mean radial intensity profile d ~ 1.7 kpc ArTéMiS/APEX Observations + SPIRE Gaussian fit 350 µm /sr] Plummer fit MJy [ ArTéMiS beam Intensity Radius [pc] Offset along filament crest [arcsec] [pc] W = 0.15 +- 0.05 pc width Filament Filament André, Revéret, Könyves+2016 - See Russeil+2013 & Tigé+2017 for Herschel/HOBYS results on NGC6334 +15 ~ 75 - 5 % of prestellar cores form in filaments, above a typical column density N > 7x1021 cm-2 H2 ~ Aquila curvelet N map (cm-2) H Unstable AcensusofdensecoresintheTaurusL1495cloud 7 21 2 22 Σ Taurus B211/3+L1495 10 10 −1 in the range 35 ± 14 M⊙ pc .Ourmeanvalueisabout −1 afactoroftwolargerthanthevalue15 M ⊙>pc found + by Hacar et al. (2013) using N2H observations,~ and the = cores −1 2 getfilaments N map value 17 M⊙ pc found by Schmalzl150 et al. (2010) M based/pc on H2 near-infrared extinction measurements. The reason for the discrepancy is not clear, but it is significant that all three estimates are greater than or M equal to the theoretical value −1 of 16 M⊙ pc for an isothermal1 cylinder in pressure equi- = cores librium at 10 K (Inutsuka & Miyama 1997). This suggests that all of the prestellar cores in L1495 are located in su- percritical filaments, in agreement with the HGBS findings in Aquila (Andr´eet al. 2010;line K¨onyves et al. 2015). We note that none of the above estimates includes the contribution of the extended power-law wings whose inclusion further in- /M creases the estimated line mass. For example, the line mass integrated over the full filamentary cross section Also of the: B211 −1 filament is 54 M⊙ pc (Palmeirim et al. 2013), and this is line,crit −1 consistent with an aperture-basedBresnahan+2018 estimate, ∼ 51 M⊙ pc , obtained from our high-resolution column density map by dividing the total mass of the filament by its length,( afterCrA) having subtracted the estimated diffuse background. Benedettini+2018 (Lupus) 6.2 Relationship to unbound0.1 Könyves+2019 starless cores Unbound While the majority of our starless cores are gravitationall (Oriony B) unbound and therefore not prestellar, they nevertheless can provide some important informationLadjelate+2019 relevant to star forma- tion. For example, they may represent density enhancements resulting from the interstellar turbulence widely conside(Ophred ) to play a dominant role in the determination of the IMF (see, for example, Padoan & NordlundPezzuto+2019 (2002)). The probability distribution function (PDF) of the gas density produced by supersonic turbulent flow of isothermal gas is well (Perseus approxi- ) mated by a lognormal form (Elmegreen & Scalo (2004) and references therein). It is thereforeFiorellino+2019 of interest to plot a his- togram of estimated density values for the L1495 starless André+2010; Könyves+2015cores, and this histogram is shown in Fig. 8. These (Serpens densities ) are mean values, calculated by dividing the mass … of each core FigureMarsh 6. The locations al. of prestellar2016, cores MNRAS (red circles) with re- Herschel10years – Madrid – 13 May 2019 - Ph.by its André total volume, based on the estimated outer radius, spect to filamentary structure, shown with the same field of view as for Fig. 1. The image has been rotated such that equatorial taken to be the deconvolved FWHM of the source. These north is 52◦ anticlockwise from vertical. The filamentary struc- densities also correspond to the n(H2)valueslistedinTable B2 of Appendix B. For consistency, the same completeness ture represents a limited-scale reconstruction, up to a transverse spatial scale of 0.1 pc, obtained using the getfilaments algorithm correction was applied to the starless core histogram as for (Men’shchikov 2013). The greyscale values correspond to the to- the starless CMF in Fig. 5 although, as it turned out, the tal (unfiltered) background line densities within the boundaries correction had negligible effect. It can be seen that, in sharp of the reconstructed features, based on an assumed characteristic contrast to the CMF, the density distribution is accurately filamentary width of 0.1 pc, and are truncated at an upper value −1 lognormal except for a tail at high densities. Note again corresponding to 16 M⊙ pc (100% on the greyscale). As a re- that the difference is not a reflection of incompleteness since sult, the portions in black have a mass per unit length in excess application of the completeness correction discussed in Ap- of the approximate threshold for cylindrical stability. pendix A had no appreciable effect. The variance in log density may provide information on the kinetic energy injection mechanism, the Mach number, pressure-confined clumps5 that probably form the bulk of and the magnetic field (Molina et al. 2012). To compare the unbound core distribution) and assume a mass-radius Fig. 8 with turbulence models, however, it must be borne law of the form M ∝ Rk,thenthecoredensityhistogramof in mind that what we have plotted is essentially a type of mass-weighted PDF, as opposed to the volume-weighted ver- sion usually presented in simulations. More quantitatively, 5 We do not, of course, assume that all cores have the same den- if we make the simplifying assumption that the density is sity. The distribution of core densities would reflect the range of uniform within an individual core (as would be the case for external pressures. ⃝c 2002 RAS, MNRAS 000,1–13 P r Pe P rs r et e se s tl t el e la l lr l a a rc r o cr c oe o rs r e e sf s o fr f om o r r mp m r pi p rm r ia i mr m ai a rl r iy i l l yw y i wt w ih i ti t hn h i i nf n i fl f ia i lm l ae a mn m et e ns n t, t s s , , a a b b oa o vb v eo e v ae a ca c o o lc l uo u ml m nu n m dn d e e nd n se s in i ts t yi y t y t t h h r rt e eh s sr h he o os l lh d do N l dHN 2H 2 N > > H 72 7 >x x 1 1 70 02 x12 1 1 c0 c2 m1 m- 2- c2 m - 2 +15 ~ 75 - 5 % of prestellar cores form in filaments, above a typical column density N > 7x1021 cm-2 H2 ~ Aquila curvelet N map (cm-2) Σ AcensusofdensecoresintheTaurusL1495cloud 7 Unstable Taurus B211/3+L1495 H −1 2 in the range 35 ± 14 M⊙ pc .Ourmeanvalueisabout 21 22 −1 10 afactoroftwolargerthanthevalue1510 M ⊙>pc found + by Hacar et al.
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