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: per of pixels 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:

Spatial angular frequency, k [arcmin-1]

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 (Andréet al. 2010;line Könyves 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 formation. 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 histogram 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 taken to be the deconvolved FWHM of the source. These as for Fig. 1. The image has been rotated such that equatorial 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. (2013) using N2H observations,~ and the Distribution of separations from nearest−1 filament crest 2 getfilaments N map value 17 M⊙ pc found by Schmalzl150 et al. (2010) M based/pc on H2 = cores near-infrared extinction measurements. The reason for the discrepancy is not clear, but it is signiﬁcant that all three

Orion B estimates are greater than or equal to the theoretical value −1 of 16 M⊙ pc for an isothermal cylinder in pressure equi-

M = cores 805 pre-★ librium at 10 K (Inutsuka1 & Miyama 1997). This suggests that all of the prestellar cores in L1495 are located in su- cores percritical filaments, in agreement with the HGBS findings in Aquila (Andréet al. 2010; Könyves et al. 2015). We note

that none of the above estimatesline includes the contribution of the extended power-law wings whose inclusion further in- creases the estimated line mass. For example, the line mass per bin per integrated over the full filamentary/M cross section Also of the: B211 −1 filament is 54 M⊙ pc (Palmeirim et al. 2013), and this is −1 consistent with an aperture-basedBresnahan+2018 estimate, ∼ 51 M⊙ pc , obtained from our high-resolutionline,crit column density map by cores dividing the total mass of the filament by its length,( afterCrA) having subtracted the estimated diffuse background.

of Benedettini+2018

(Lupus)

6.2 Relationship to unbound0.1 Könyves+2019 starless cores While the majority of our starless cores are gravitationall (Oriony B) Number unbound and therefore not prestellar,Unbound they nevertheless can provide some important informationLadjelate+2019 relevant to star formation. 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 0.01distribution function0.05 (PDF) of0.1 the gas density produced by

supersonic turbulent flow of isothermal gas is well (Perseus approxi- ) Separation from nearestmated by a lognormal crest form [pc] (Elmegreen & Scalo (2004) and references therein). It is thereforeFiorellino+2019 of interest to plot a his- Könyves et al. 2019, A&A, submittedtogram of estimated density values for the L1495 starless cores, and this histogram is shown in Fig. 8. These (Serpens densities ) André+2010; Könyves+2015are 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 taken to be the deconvolved FWHM of the source. These as for Fig. 1. The image has been rotated such that equatorial 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

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 Strong evidence of a column density transition/ “threshold” for the formation of prestellar cores

Prestellar CFE as a function of background AV In Aquila, ~ 90% of the prestellar cores identiﬁed 15%±5% with Herschel are found above Av ~ 7 ! -2 Σ ~ 150 M pc

Herschel GBS Könyves+2015, A&A Aquila

Core formation efﬁciency [unitless] efﬁciency formation Core 7 Similar to ‘threshold’ for YSOs Background column density [Av units] (Spitzer): CFE(AV) = ΔMcores(AV) / ΔMcloud(AV) Heiderman+2010; Lada+2010; Herschel10years – Madrid – 13 May 2019 - Ph. André Evans+2014

Strong evidence of a column density transition/ “threshold” for the formation of prestellar cores Turbulence-regulated Prestellar CFE as a function of background AV models of SF (εff ~ 1%) cf. Krumholz+2012

Sharp transition 20%±5% around a ﬁducial value Av ~ 7 ! -2 Σ ~ 150 M pc !

M/L ~ 15 M/pc André+2010; Könyves+2015 Interpretation: Critical M/L of nearly Herschel GBS Orion B isothermal cylinders (Ostriker 1964; Inutsuka & Miyama 1997)

Core formation efﬁciency [unitless] efﬁciency formation Core 7 M = 2 c 2/G ~ 16 M /pc Background column density [A units] line, crit s v for T ~ 10 K CFE(AV) = ΔMcores(AV) / ΔMcloud(AV) Könyves+2019, A&A, submitted Herschel10years – Madrid – 13 May 2019 - Ph. André

Most prestellar cores form near the column density “threshold” (in ‘transcritical’ filaments)

Total prestellar core mass as a function of background AV ] ]

Aquila Orion B M M mass per bin [ mass per bin [ mass per core core

Total Total 7 10 Total 7 10 Background column density [Av units] Background column density [Av units] Sharp transition around a ﬁducial value Könyves+2019, ! 2 Av ~ 7 Σ ~ 150 M/pc A&A, submitted

! M/L ~ 15 M/pc

Herschel10years – Madrid – 13 May 2019 - Ph. André

A filament paradigm for ~ M" star formation? Schneider & Elmegreen 1979; Larson 1985; Nagasawa 1987; Inutsuka & Miyama 1997; Myers 2009 … Protostars & Planets VI chapter (André, DiFrancesco, Ward-Thompson, Inutsuka, Pudritz, Pineda 2014) 1) Large-scale MHD ‘turbulent’ comp- 2) Gravity fragments the densest ressive flows create ~0.1 pc filaments filaments into prestellar cores 2 M / L > Mline,crit = 2 cs /G

Protostellar Cores

50’ 50’ ~ 2 pc ~ 2 pc

Ward-Thompson + 2010 Miville-Deschênes + 2010 Palmeirim + 2013 André + 2010 Marsh + 2016 Polaris – Herschel/SPIRE 250 µm Taurus B211/3 – Herschel 250 µm Importance of filaments in the ISM of other galaxies?

ALMA detection of pc-scale filaments Long Afilaments characteristic in prestellar inN159W the LMC core formation Responsible for a common efficiencyLinear inb denseresolutionlue gas: filaments~ 1’’ or 0.24red pc @ 50 kpc star formation efficiency in the dense 13 (> 104 cm-3) molecular gas of galaxies? Prestellar CFE as a function of CO(2-1)background A V ] ] 5 pc 15% -1 Galaxies (eg Gao & Galactic clouds Solomon 2004) [yr

unitless ±5% [ dense M 10 pc efﬁciency CMZ (Longmore+2013)

Herschel GBS SFR/ SFE =

formation formation Aquila

7 Mass of dense gas, M [M]

Core dense

Background column density [Av units] Lada+2012 Shimajiri+2017 7 Könyves+2015 Fukui+2015 - see also Saigo, Onishi +2017 Ø Filaments may help to regulate the star formation efficiency in the dense molecular gas of galaxies (e.g. Shimajiri+2017) Herschel10years – Madrid – 13 May 2019 - Ph. André

Filament fragmentation can account for the peak of the prestellar CMF and (possibly) the “base” of the IMF Core Mass Function (CMF) in Aquila Complex logM Δ ~ 450 Jeans mass: N/ CMF prestellar Δ cores 2 MJeans ~ 0.5 M × (T/10 K) -2 -1 × (Σcrit/160 Mpc )

system

per mass bin: per 0.6+/-0.2M IMF (Chabrier 2005) cores of Inutsuka & Miyama 1997

Number André+2014 PPVI; Könyves+2015 Mass (M ) Ø CMF peaks at ~ 0.6 M ≈ Jeans mass in marginally critical filaments Ø CMF peaks at ~ 0.6 M ≈ Jeans mass in marginally critical filaments Ø Close link of the prestellar CMF with the stellar IMF: M★ ~ 0.4×Mcore (see also Motte+1998; Alves+2007) Ø Characteristic (pre)stellar mass may result from filament fragmentation Herschel10years – Madrid – 13 May 2019 - Ph. André

Detailed fragmentation manner of filaments? ALMA 3mm mosaic of the Orion A ISF Some evidence of hierarchical 0.2 pc fragmentation within filaments (e.g. Takahashi+2013; Kainulainen+2013; Teixeira+2016) Two fragmentation modes: - « Cylindrical » mode #$ groups of cores separated by ~ 0.3 pc - « Spherical » Jeans-like mode #$ core spacing < 0.1 pc within groups Two-point correlation function of ALMA dense cores (r) ξ ~ 0.3 pc correlation Surface density of ALMA dense cores 2-pt Kainulainen+2017 Herschel10years – Madrid – 13 May 2019 - Ph. André Radius [kAU]

Role of magnetic fields? Ø Planck polarization data reveal a very organized B field on large ISM scales, ~ perpendicular to dense star-forming filaments, ~ parallel to low-density filaments Ø Suggests that the B field plays a key role in the physics of ISM filaments Taurus Musca/Chamaeleon

10 pc

Planck intermediate results. XXXV. (2016 J. Soler) Color: N(H) from Planck data @ 5’ resol. (~ 0.2-0.3 pc) Suggests sub-Alfvénic turbulence Drapery: B field lines from Q,U Planck 850 µm @ 10’ on cloud scales F. Boulanger’s group Herschel10years – Madrid – 13 May 2019 - Ph. André

SPICA-POL (« B-BOP ») can unveil the role of magnetic fields in filament evolution and core/star formation See SPICA-POL White Paper Taurus B211 filament (arXiv:1905.03520) Ø Planck pol. resolution (> 10’ or Herschel 250 µm 5 pc > 0.4 pc) insufficient to resolve the + Planck B lines typical ~0.1 pc inner width of filaments. Can be done with SPICA Ø SPICA will provide FIR polarized (Q, U) images with a S/N and Palmeirim dynamic range similar to Herschel +2013 A. Bracco images in I. SPICA resolution Plausible model of the Synthetic polarization maps 0.1 pc B field in the central E.Ntormousi Planck resolution filament

0.5 pc

Herschel10years – Madrid – 13 May 2019 - Ph. André

Filament Formation Herschel 500 m view

Serpens South + N2H Integrated Intensity

Herschel Detection of transverse velocity gradients across filaments: contours Evidence of filament formation within sheet-like structures? CARMA “CLASSy” SF Survey Transverse N H+(1-0) velocity gradient + Coherent motions 2 N2H view inside across massive IRDC 18223 Serpens South sheet-like structure?

Observer

Fernandez-Lopez et al. (2014) ~0.3 km/s difference 4 pc

IRAM NOEMA

Fernandez-Lopez+2014; Dhabal, Mundy+2018 Beuther, Ragan+2015 see also H. Kirk+2013 for Serp-S Herschel10years – Madrid – 13 May 2019 - Ph. André

Evidence of accretion of background material (striations) onto self-gravitating filaments? Ø Striations and sub-filaments are suggestive of accretion flows into the star-forming filaments - Tend to be // to the large-scale B field CO map

Taurus PalmeirimTaurus + 2013 (near-IR)

CO observations from Goldsmith+2008 Estimated mass accretion rate: Palmeirim+2013 M ~ 50 M /pc/Myr Herschel10years – Madrid – 13 May 2019 - Ph. André line Shimajiri+2019a

Velocity-coherent “fibers” in dense molecular filaments: Accretion-generated substructure?

C18O velocity components overlaid on Filtered 250 µm image showing the fine Herschel 250 µm dust continuum image structure of the Taurus B211/3 filament Examples of line spectra in B211/3

(Taurus) C18O(2-1) 1 pc N H+(1-0) striations 2 2 deg

ﬁbers Antenna Temperature [K] Temperature Antenna Obtained with FCRAO obs. Velocity [km/s] getfilaments Hacar, Tafalla+2013 (Men’shchikov 2013) 18’’ resol. Hacar, Tafalla+2013 Ø Bundle of 35 velocity-coherent « fibers » detected in 18 + C O(2-1) and N2H (1-0) and making up the main filament See also Hacar+2018 for Orion Herschel10years – Madrid – 13 May 2019 - Ph. André

Probing the magnetic link between striations and fibers High resolution/dynamic range polarimetric imaging with B-BOP Ø Geometry of the B-field within the (~ 0.1 pc) system of intertwined « fibers » developing inside star-forming filaments and the connection with the striations seen on larger scales SPICA-POL White Paper (arXiv:1905.03520)

striations 2 deg

ﬁbers

Palmeirim + 2013 + Hacar, Tafalla+2013 Hacar+2013 Men’shchikov+2013 18’’ resol. André+2014

Herschel10years – Madrid – 13 May 2019 - Ph. André

Summary and conclusions

Ø Herschel results support a ﬁlamentary paradigm for star formation but many issues remain open and/or strongly debated

Ø The properties of molecular ﬁlaments need to be better understood as they represent the initial conditions of prestellar core formation

Ø Evidence that dense ﬁlaments result from large-scale compressive ﬂows and accretion of matter ~ along B within sheet-like structures.

Ø Magnetic ﬁelds likely play a key role in the formation/evolution/ fragmentation of ﬁlaments but remain poorly constrained

Ø High-resolution polarimetric imaging at far-IR/submm λs from space with SPICA can lead to decisive progress

Herschel10years – Madrid – 13 May 2019 - Ph. André