molecular cloud filaments: no evidence for a “characteristic”...
TRANSCRIPT
Molecular Cloud Filaments: No evidence for a “characteristic” width
K. Tassis UCreteI. Psaradaki SRONR. Skalidis UCrete
J. Andrews UCreteP. Goldsmith JPLM. Heyer UMass
PhD studentUniversity of Crete
Gina Panopoulou
G. V. Panopoulou - University of Crete 2
Herschel main results
Taurus B211/B213 Palmeirim+ 2013
1. Filaments are ubiquitous
2. 75% of cores lie on filaments
Aquila: Könyves+ 2015
G. V. Panopoulou - University of Crete 3
Herschel main results
Arzoumanian+ 2011
3. Characteristic width ~0.1 pc
G. V. Panopoulou - University of Crete 4
Herschel main results
BUT: Power spectrum of same data is featureless!
Miville-Deschênes+ 2010
Arzoumanian+ 2011
G. V. Panopoulou - University of Crete 5
Is the power spectrum to blame?
You can not hide a characteristic scale from the power spectrum!
Panopoulou+ 2017
G. V. Panopoulou - University of Crete 6
Can this discrepancy be reproduced?
Artificial scale-free image
FilTER
(Filament Trait-Evaluated Reconstruction)
Panopoulou, Tassis, Goldsmith & Heyer 2014
https://bitbucket.org/ginpan/filter
G. V. Panopoulou - University of Crete 7
Can this discrepancy be reproduced?
Panopoulou+ 2017PS featureless but width measurement produces peaked distribution!
Artificial scale-free image
G. V. Panopoulou - University of Crete 8
Way widths are measured is biased
Sampling a power-law distribution with uncertainties results in a peaked distribution!
Koen & Kondlo 2009
Panopoulou+ 2017
Polaris Flare (Herschel 250 μm)
G. V. Panopoulou - University of Crete 9
Why peaked at 0.1 pc for all clouds?
● width: Gaussian fit within some range
● sensitivity on fitting range (also Smith+2014)
● Similar physical range used leads to similar position of peak for different clouds
Arzoumanian+ 2011
Panopoulou+ 2017
G. V. Panopoulou - University of Crete 10
Why is the peak so narrow?
mean width along filament is reported
Central limit theorem: spread of distribution is error on mean, not range of filament widths
Arzoumanian+ 2011
Individual filaments in literature? (Juvela+2012, Malinen+2012, André+ 2016...)
G. V. Panopoulou - University of Crete 11
What about line emission data?
Panopoulou+ 2014
● Substructure!(Hacar+ 2013, Fernandez-Lopez+ 2014...)
● Taurus 13CO (FCRAO data):filaments unbound!
Range of velocities throughout the filament(Panopoulou+ 2014)
G. V. Panopoulou - University of Crete 12
Panopoulou+ 2014
What about line emission data?
Taurus 13CO filaments in velocity channel maps:
Hint of stochastic origin?
G. V. Panopoulou - University of Crete 13
Filaments from projection effects
Panopoulou+ 2014
Line-of-sight confusion can produce 'filaments'
Cores overlapping in projection?
✔ Observed filament column density profiles identical to those of cores
✔ Fraction of cores 'in' filaments increases with core surface filling factor
✔ Velocity (sub)structure with multiple coherent components
both in observations & simulations: e.g. Juvela+ 2012, Hacar+ 2013, Panopoulou+ 2014, Moeckel & Burkert 2014, Smith+2014, Kirk+2015...
G. V. Panopoulou - University of Crete 14
Conclusions
● Dust emission filaments: “characteristic” width an artifact of the analysis
● Line emission: filaments unbound● An alternative explanation:
Projection effects may be responsible for filamentary appearance
Thank you!