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?
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
Herschel GBS
Celebration – 160/250/500
ESAC Madrid – µm13 Maycomposite
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
Polaris Aquila
2 pc
1deg ~ 4.5pc
Sadavoy + 2014 Ward-Thompson + 2010
5 pc André + 2010
Pezzuto + 2019 Miville-Deschênes + 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)
Number of pixels per bin: ΔN/ΔlogNH2
Column Density PDF for l217-224 field
Column Density PDF for Aquila GMC
PDF on PDF after
filaments subtracting
excl. ‘clumps’ cores
Av ~ 7
Column density, NH2 (cm-2)
Column density, NH2 (cm-2)
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
Number of filaments per bin
0.1 +- 0.05 pc IC5146
Orion B
Aquila
Polaris
Ophiuchus
Distribution of Taurus
Jeans lengths Pipe
~ 5 pc
Distribution of Musca
filament lengths
Example of a filament radial profile
Inner radius 0.1
~ 0.05pc Filament width (FWHM) [pc]
NH2 [cm-2]
D. Arzoumanian+2011 & 2019 (A&A, 621, A42)
Outer radius
0.5pc [but some width variations along each filament: Ysard+2013]
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?
SPIRE 250 µm image of Polaris
Tension with scale-free power spectrum
translucent cloud Panopoulou+2017
Noise-subtracted, deconvolved power
spectrum of Polaris image
P(k) = AISM k-2.69 + P0
Power: P(k) [Jy2/sr]
MJy/sr
4 pc
Miville-Deschênes et al. 2010
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
Power: P(k) [Jy2/sr]
0.1 pc filaments with contrast ~ 50% P(k) = AISM k-2.75 + P0
in SPIRE 250 µm image of Polaris
translucent cloud
Synthetic
filaments
contribution
Spatial angular frequency, k [arcmin-1]
Difference from power-law fit
Residuals: Power-law − Fit
MJy/sr Synthetic
4 pc
4 pc
Conclusion: Observed power spectra
remain consistent with a characteristic Original
filament width ~ 0.1 pc for realistic
filling factors and filament contrasts
Herschel10years – Madrid – 13 May 2019 - Ph. André Spatial angular frequency, k [arcmin-1]
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
Intensity [MJy/sr]
Gaussian fit
350 µm Plummer fit
ArTéMiS
beam
Radius [pc]
Filament width [pc]
Offset along filament crest [arcsec]
W = 0.15 +- 0.05 pc
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 NH2 ~> 7x1021 cm-2
Aquila curvelet NH2 map (cm-2) Σ
1021 1022 Taurus B211/3+L1495
A census of dense cores in the Taurus L1495 cloud
7
Unstable
>
in the range 35 ± 14 M⊙ pc−1 . Our mean value is about
~
a factor of two larger than the value 15 M⊙ pc−1 found
= cores by Hacar et al. (2013) using N2 H+ observations, and the
150 M /pc2
value 17 M⊙ pc−1 found by Schmalzl et al. (2010) based on getfilaments NH2 map
near-infrared extinction measurements. The reason for the
discrepancy is not clear, but it is significant that all three
1
estimates are greater than or equal to the theoretical value
of 16 M⊙ pc−1 for an isothermal cylinder in pressure equi-
librium at 10 K (Inutsuka & Miyama 1997). This suggests
= cores
that all of the prestellar cores in L1495 are located in su-
Mline/Mline,crit
percritical filaments, in agreement with the HGBS findings
in Aquila (André et al. 2010; 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-
creases the estimated line mass. For example, the line mass
Also:
integrated over the full filamentary cross section of the B211
filament is 54 M⊙ pc−1 (Palmeirim et al. 2013), and this is
Bresnahan+2018
consistent with an aperture-based estimate, ∼ 51 M⊙ pc−1 ,
obtained from our high-resolution column density map by
(CrA)
dividing the total mass of the filament by its length, after
having subtracted the estimated diffuse background.
Benedettini+2018
(Lupus)
0.1 starless cores
6.2 Relationship to unboundKönyves+2019
(Orion B)
Unbound
While the majority of our starless cores are gravitationally
unbound and therefore not prestellar, they nevertheless can
provide some important information Ladjelate+2019
relevant to star forma-
tion. For example, they may represent density enhancements
(Oph)
resulting from the interstellar turbulence widely considered
to play a dominant role in the determination of the IMF (see,
for example, Padoan & Nordlund Pezzuto+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 therefore Fiorellino+2019
of interest to plot a his-
togram of estimated density values for the L1495 starless
André+2010; Könyves+2015 cores, and this histogram is shown in Fig. 8. These (Serpens)
densities
…
are mean values, calculated by dividing the mass of each core Figure Marsh al.
6. The locations 2016,coresMNRAS
of prestellar (red circles) with re-
Herschel10years – Madrid – 13 May 2019 - Ph. André spect to filamentary structure, shown with the same field of view
by its total volume, based on the estimated outer radius,
taken to be the deconvolved FWHM of the source. These as for Fig. 1. The image has been rotated such that equatorial
densities also correspond to the n(H2 ) values listed in Table north is 52◦ anticlockwise from vertical. The filamentary struc-
ture represents a limited-scale reconstruction, up to a transverse
+15
~ 75 - 5
% of prestellar cores form in filaments,
above a typical column density NH2 ~> 7x1021 cm-2
Aquila curvelet NH2 map (cm-2) Σ Taurus B211/3+L1495
A census of dense cores in the Taurus L1495 cloud
7
1021 1022 >
Unstable
in the range 35 ± 14 M⊙ pc−1 . Our mean value is about
~
Distribution of separations from nearest filament crest
a factor of two larger than the value 15 M⊙ pc−1 found
by Hacar et al. (2013) using N2 H+ observations, and the
getfilaments NH2 map
= cores 150 M /pc2
value 17 M⊙ pc−1 found by Schmalzl et al. (2010) based on
near-infrared extinction measurements. The reason for the
Orion B discrepancy is not clear, but it is significant that all three
estimates are greater than or equal to the theoretical value
805 pre-★ of 16 M⊙ pc−1 for an isothermal cylinder in pressure equi- = cores
1
librium at 10 K (Inutsuka & Miyama 1997). This suggests
that all of the prestellar cores in L1495 are located in su-
cores
Number of cores per bin
percritical filaments, in agreement with the HGBS findings
Mline/Mline,crit
in Aquila (André et al. 2010; 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-
creases the estimated line mass. For example, the line mass
Also:
integrated over the full filamentary cross section of the B211
filament is 54 M⊙ pc−1 (Palmeirim et al. 2013), and this is
Bresnahan+2018
consistent with an aperture-based estimate, ∼ 51 M⊙ pc−1 ,
obtained from our high-resolution column density map by
(CrA)
dividing the total mass of the filament by its length, after
having subtracted the estimated diffuse background.
Benedettini+2018
(Lupus)
6.2 Relationship to unboundKönyves+2019
0.1 starless cores(Orion B)
While the majority of our starless cores are gravitationally
unbound and therefore not prestellar, they nevertheless can
Unbound
provide some important information Ladjelate+2019
relevant to star forma-
tion. For example, they may represent density enhancements
(Oph)
resulting from the interstellar turbulence widely considered
to play a dominant role in the determination of the IMF (see,
for example, Padoan & Nordlund Pezzuto+2019
(2002)). The probability
0.01 0.05
distribution function (PDF) of0.1
the gas density produced by
supersonic turbulent flow of isothermal gas is well (Perseus)
approxi-
Separation from nearest crest
mated by a lognormal form [pc]
(Elmegreen & Scalo (2004) and
references therein). It is therefore Fiorellino+2019
of interest to plot a his-
Könyves et al. 2019, A&A, submitted togram of estimated density values for the L1495 starless
cores, and this histogram is shown in Fig. 8. These (Serpens)
densities
André+2010; Könyves+2015 …
are mean values, calculated by dividing the mass of each core Figure Marsh al.
6. The locations 2016,coresMNRAS
of prestellar (red circles) with re-
Herschel10years – Madrid – 13 May 2019 - Ph. André spect to filamentary structure, shown with the same field of view
by its total volume, based on the estimated outer radius,
taken to be the deconvolved FWHM of the source. These as for Fig. 1. The image has been rotated such that equatorial
densities also correspond to the n(H2 ) values listed in Table north is 52◦ anticlockwise from vertical. The filamentary struc-
ture represents a limited-scale reconstruction, up to a transverseStrong 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
Core formation efficiency [unitless]
cores identified
15%±5% with Herschel
are found above
Av ~ 7 !
Σ ~ 150 M pc-2
Herschel GBS Könyves+2015, A&A
Aquila
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+2014Strong 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
Core formation efficiency [unitless]
Sharp transition
20%±5% around a fiducial
value Av ~ 7 !
Σ ~ 150 M pc-2 !
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)
7
Mline, crit = 2 cs2/G ~ 16 M /pc
Background column density [Av units]
for T ~ 10 K
CFE(AV) = ΔMcores(AV) / ΔMcloud(AV)
Könyves+2019, A&A, submitted
Herschel10years – Madrid – 13 May 2019 - Ph. AndréMost prestellar cores form near the column density
“threshold” (in ‘transcritical’ filaments)
Total prestellar core mass as a function of background AV
Total core mass per bin [M ]
Total core mass per bin [M ]
Aquila Orion B
7 10 7 10
Background column density [Av units] Background column density [Av units]
Sharp transition around
a fiducial value Könyves+2019,
Av ~ 7 ! Σ ~ 150 M /pc2 A&A, submitted
! M/L ~ 15 M /pc
Herschel10years – Madrid – 13 May 2019 - Ph. AndréA 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
M / L > Mline,crit = 2 cs2 /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 µmImportance of filaments in the ISM of other galaxies?
ALMA detection of pc-scale filaments
Long Afilaments inprestellar
characteristic N159W
in the LMC core formation Responsible for a common
efficiency inblue
Linear dense gas filaments
resolution: ~ 1’’ or 0.24
redpc @ 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 AV
Core formation efficiency [unitless]
SFE = SFR/Mdense [yr-1]
5 pc Galaxies (eg Gao &
15% Galactic clouds Solomon 2004)
±5%
10 pc
CMZ
(Longmore+2013)
Herschel GBS
Aquila
7 Mass of dense gas, Mdense [M ]
Background column density [Av units] Lada+2012 Shimajiri+2017
Fukui+2015 - see also Saigo, Onishi +2017
Könyves+2015
7
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. AndréFilament fragmentation can account for the peak of the
prestellar CMF and (possibly) the “base” of the IMF
Number of cores per mass bin: ΔN/ΔlogM
Core Mass Function (CMF) in Aquila Complex
~ 450
CMF prestellar
Jeans mass:
cores MJeans ~ 0.5 M × (T/10 K)2
× (Σcrit/160 M pc-2)-1
system 0.6+/-0.2M
IMF
(Chabrier 2005)
Inutsuka & Miyama 1997
Mass (M ) André+2014 PPVI; Könyves+2015
Ø
Ø CMF peaks at ~ 0.6 M ≈ Jeans mass in marginally critical filaments
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. AndréDetailed 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
2-pt correlation ξ(r)
~ 0.3 pc
Surface density of
ALMA dense cores
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
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
Herschel10years – Madrid – 13 May 2019 - Ph. André
F. Boulanger’s groupSPICA-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
B field in the central 0.1 pc E.Ntormousi Planck resolution
filament
0.5 pc
Herschel10years – Madrid – 13 May 2019 - Ph. AndréDetection of transverse velocity gradients across filaments:
Evidence of filament formation within sheet-like structures?
CARMA “CLASSy” SF Survey Transverse +
N2H+ view
Coherent motions N2H (1-0) velocity gradient
inside across massive IRDC 18223
Serpens South sheet-like structure?
Observer
(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. AndréEvidence 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 Taurus
Palmeirim
+ 2013
(near-IR)
CO observations from Goldsmith+2008 Estimated mass accretion rate:
Palmeirim+2013
Herschel10years – Madrid – 13 May 2019 - Ph. André
Mline ~ 50 M /pc/Myr Shimajiri+2019aVelocity-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
Antenna Temperature [K]
(Taurus)
C18O(2-1)
1 pc
2 deg
N2H+(1-0)
striations
fibers
Obtained with
FCRAO obs.
getfilaments
Velocity [km/s]
Hacar, Tafalla+2013 (Men’shchikov 2013)
18’’ resol.
Hacar, Tafalla+2013
Ø Bundle of 35 velocity-coherent « fibers » detected in
C18O(2-1) and N2H+(1-0) and making up the main filament See also Hacar+2018 for Orion
Herschel10years – Madrid – 13 May 2019 - Ph. AndréProbing 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)
2 deg
striations
fibers
Palmeirim
+ 2013
+ Hacar, Tafalla+2013
Hacar+2013 Men’shchikov+2013
18’’ resol. André+2014
Herschel10years – Madrid – 13 May 2019 - Ph. AndréSummary 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
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