Filamentary Structures in Molecular Clouds and their connection with Star Formation E.Schisano 1, S.Molinari 1, D.Polychroni 1, D.Elia 1, M.Pestalozzi 1, R.Plume 2 and other members of Hi-GAL Team 1 Istituto Fisica dello Spazio Interplanetario – Roma – INAF 2 Department of Physics & Astronomy - University of Calgary - Canada Background: Hi-GAL image of l=299°

Observations show that gas and dust in star forming molecular clouds are arranged in a filamentary pattern. (e.g. Mitchell et al. 2001, Hartmann et al 2002, Hatchell et al. 2005). Most of the numerical simulations predict qualitatively the formation of a complex network of filaments, even with different processes Involved (e.g. Klessen 2001, Bernarjee et al. 2006, Vazques-Semadeni et al. 2007, Heitsch et al. 2008). -) Fragmentation of Magnetical Supported Molecular Cloud -) Gravo-Turbulent formation scenario -) Cloud formation and Thermal fragmentation 1)Not all the scales collapse at the same time (like in the classical gravitationally induced spherical collapse) but some are fasters than others. 2) Cores and stars form in dense filaments where the gravity win against the local internal support. Pre-Herschel

SPIRE 250 μm Herschel observations confirmed the presence of filamentary structures with different scales and their association with cores/clumps. (Molinari et al. 2010, Andre et al. 2010). What Herschel is saying us Filaments Everywhere! Cores Distribuited preferentially along filaments detected cores Second derivative filtering to enanche the structures contrast respect the diffuse emission 2°x2° maps of the Galactic Plane observed 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 emission 2)Large amount of structures – Need of automatic algorithms SPIRE 250 μmSPIRE 500 μm MIPS 24 μmPACS 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 extraction PACS 160SPIRE 250 SPIRE 500

(very) Preliminary Results Integrating the flux in the identified filament regions in various band we build the SED of such structures and by greybody fitting we determine the physical properties. Masses around few M sun Temperature hotter than the typical IRDC (~12 K Peretto et al ) Background determination is still not correct on Herschel maps with intense extended emission ( masses underestimated ). Lengths are of few arcminutes (~ tens pc) Widths are ~ ’ ( ≤ 1 pc) = 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 12 CO and 13 CO (J 1->0), but we are submitting proposals for higher transition lines to constrain gas physical properties. T = 19.2 K M = 361. M sun T = 17.5 K M = 125. M sun T = 18.6 K M = 22. M sun T = 18.5 K M = 19. M sun Supporting Magnetic Field Binding Magnetic Field Comparison with Classical models Fiege et al 2004 Sample of fitted SED

Summary (or... just the beginning) Herschel maps revealed maps reveal the rich and complex structure of star formation region 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 different prescriptions 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 μmPACS 160 μm SPIRE 250 μm SPIRE 350 μmSPIRE 500 μm