Filamentary Structures in Molecular Cloudsand their connection with Star Formation

E.Schisano1, S.Molinari1, D.Polychroni1, D.Elia1, M.Pestalozzi1, R.Plume2 and other members of Hi-GAL Team

1 Istituto Fisica dello Spazio Interplanetario – Roma – INAF2 Department of Physics & Astronomy - University of Calgary - Canada

Background: Hi-GAL image of l=299°

SPIRE 250 μm

Herschel observations confirmed the presence of filamentary structures withdifferent scales and their association with cores/clumps.

(Molinari et al. 2010, Andre et al. 2010).

What Herschel is saying us

Filaments

Everywhere!

Cores Dist

ribuite

d preferentially

along filaments

detected cores

Second derivative filteringto enanche the structures contrastrespect the diffuse emission

2°x2° maps of theGalactic Planeobserved in the Hi-GAL survey

Filaments are an initial stage of the star formation that is not well studied. Large scale surveys allow a census of such structures to constrain their properties.

Our goal is to use the potentiality of Hi-GAL survey to build up a catalog of filamentary structures on GP maps, for which we determine:

Morphological Properties (length and width) linked to the filament formation process (sweeping/compression of matter, fragmentation etc).

Physical Properties (mass, virial mass per unit length, temperature, column density) mechanisms active in such structures. Comparison with classical filament models (Ostriker et al. 1964, Fiege et al. 2000,2004)

Correlation with the embedded cores (core shapes, core elongation, cores reciprocal distances – scales of filament fragmentation)

1) Filament definition – disentangling from diffuse ISM emission2) Large amount of structures – Need of automatic algorithms

SPIRE 250 μm SPIRE 500 μm

MIPS 24 μm PACS 160 μm

Sample of Hi-GAL tile centered at l = 59°

10'IRDC

HII region (?)

Image processing techniques to develop algorithms able to identify filamentary structures.

Filament: Structure that is concave down along two different principal axes and is almost flat in the other one.

(Aragon-Calvo et al.2007, Bond et al 2010)

Filament identification Algorithm

Elongated cylindrical-like patterns are traced by the lowest eigenvalue (λ

1 << λ

2) and the eigenvectors (A

1,A

2) of the

Hessian matrix computed in each pixel.

Extended not elongated regions are rejected by criteria on the highest eigenvalue and the eigenvectors

Still in development – Work in progress!

Technical Issues:

Noise reduction filtering, better background estimation,sentivity to larger scales (> tens arcmin) structures (ok for Hi-GAL).

Filament

Cores

Filament axis

Example of filament extractionPACS 160 SPIRE 250

SPIRE 500

(very) Preliminary ResultsIntegrating the flux in the identified filamentregions in various band we build the SED of such structures and by greybody fitting wedetermine the physical properties.

Masses around few 10-100 Msun

Temperature hotter than the typical IRDC(~12 K Peretto et al. 2009)

Background determination is still not correcton Herschel maps with intense extended emission (masses underestimated).

Lengths are of few arcminutes (~ tens pc)Widths are ~ 0.8-1.4’ ( ≤ 1 pc) <d> = 2.7 kpc – Russeil et al submitted

We plan to use molecular line data to determine Δv and the virial masses.Currently we have data from 12CO and 13CO (J 1->0), but we are submitting proposalsfor higher transition lines to constrain gasphysical properties.

T = 19.2 KM = 361. M

sun

T = 17.5 KM = 125. M

sun

T = 18.6 KM = 22. M

sun

T = 18.5 KM = 19. M

sun

Supporting Magnetic Field

BindingMagnetic Field

Comparison withClassical modelsFiege et al 2004

Sample of fitted SED

Summary (or... just the beginning)

Herschel maps revealed maps reveal the rich and complex structure of star formationregion with gas and dust arranged in filaments associated with embedded pre/proto-stellar cores.

Filamentary structures, even if spread everywhere, are still not well studied, as well it has to be clarified their precise role in star formation. Simulations with differentprescriptions are able to reproduce qualitatively the observed filamentary patterns, but no systematic study exist yet in literature.

We developed an algorithm to identify cylindrical-like structures on Herschel maps to overcome the difficulties in the definition filaments in an objective way.

We will apply the algorithm to the maps of Galactic plane to build a robust catalog of filaments, for which we will determine morphological and physical properties to be compared with the classical models for such structures.

MIPS 24 μm PACS 70 μm PACS 160 μm

SPIRE 250 μm SPIRE 350 μm SPIRE 500 μm