Star forming filaments: Chemical modeling and synthetic observations!

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1 Star forming filaments: Chemical modeling and synthetic observations Daniel Seifried I. Physikalisches Institut, University of Cologne The 6th Zermatt ISM Symposium , Zermatt Collaborators: Stefanie Walch, Sümeyye Suri, Alvaro Sanchez-Monge, Peter Schilke, Thorsten Balduin

2 Palmeirim et al Observing interstellar filaments Filaments seem to be everywhere: Filamentology? SF takes places in dense cores lining up along filaments pervaded by magnetic fields Recent HERSCHEL observations: typical widths of about 0.1 pc

3 Open questions Filaments are easily reproduced in simulations how would they appear in observation? Here: a set of numerical simulations to tackle some basic questions How universal are filament widths? (e.g. talks by S. Suri & P. Andre on Tuesday) How do widths depend on used tracers (continuum <-> molecular lines)? How does the environment affect chemical composition, widths, and masses?

4 Simulation setup Use FLASH code with resolution of 40 AU ICs of simulating filaments Central density of ~ g/cm -3, T = 15K Without and with magnetic fields Perpendicular and parallel to filaments, strength: 40 mug Turbulent motions with M rms ~ 1 Width ~ 0.1 pc

5 Chemistry network We use KROME ( to model chemical evolution Details of the chemical network 37 species including CO, HCO+, H 2 O, 287 reactions one of the largest chemical networks used to date on-the-fly in 3D-MHD simulations H 2 formation on dust in parametrised form, dust temperature self-consistently from simulation visual extinction AV, H 2 self-shielding, and CO column density self-consistently from simulation

6 Chemistry network

7 Chemistry network

8 Cosmic rays, ISRF, cooling, heating All relevant cooling and heating processes included: metal line cooling, chemical cooling, CO (including isotopes) cooling, dust cooling chemical heating, CR heating, photoelectric effect We investigate impact of varying strengths of the interstellar radiation field and cosmic rays

9 Time evolution Seifried & Walch, 2015 Edge-on collapse, condensations form first at outer edges, gravitational focussing (Pon et al. 11) Fragmentation properties depend on magnetic field configuration and mass of the filaments Filaments get rather narrow (< 0.1 pc) observations

10 Results: chemistry Seifried & Walch, 2015, in prep. In center of the filament AV hydrogen mainly in form of H 2 Carbon almost completely in CO dust temperature decreases consistent with HERSCHEL observations & Clark, Glover et al. 2013

11 Comparison to observations Synthetic line + continuum emission maps with RADMC-3D: 13 CO: J1-0, J2-1 C 18 O: J1-0, J CO: J2-1 continuum emission: 24 µm to 2.6 mm assuming no internal protostellar sources dust temperature directly from simulations Used to calculate column densities, gas temperature, filament masses & widths Here two filaments are considered identical physical structure Different cosmic rate ionisation rate: 1.3 x s -1 & 1 x s -1 Only chemical composition varies

12 Filament masses For continuum emission: SED fit (modified black-body spectrum) For 13 CO 1-0 and C 18 O 1-0: assumption of optically thin gas: skip opacity term All masses well below the actual value (up to a factor of 6) Significant difference between 13 CO and C 18 O masses -> gas optically thick m / Msun

13 Opacity corrected filament masses gas optically thick with τ up to 6 for 13 CO Differences between 13 CO and C 18 O vanish Masses closer to real value, but still too low Impact of cosmic rays on molecular line masses, not dust masses m / Msun higher flux dissociates CO -> lower masses

14 Filament masses Two reasons for uncertainty Conversion from CO to H2 column density: Factor 10 4 assumed value depends on cosmic ray flux Simulations show that it can vary in either direction Conversion from H2 column density to masses: assumption that all hydrogen in molecular form Simulations show that only ~2/3 are in H2 results in underestimation of masses

15 Opacity corrected filament widths width / pc width / pc cosmic ray flux s -1 Similar widths for different lines cosmic ray flux s -1 Comparable with actual 2D-width Higher cosmic ray fluxes cause smaller apparent widths Widths from line emission smaller than widths from dust emission

16 Synthetic polarisation Done with POLARIS ( fully consistent radiation transfer code for dust polarisation Even for easy configuration hard to defer the underlying field structure and we simulators know the 3D structure but observers. More predictions from simulations needed cosmic ray flux s -1

17 Conclusions Large chemical networks in star formation simulations (see also Poster Nr. 86 by Laszlo Szucs) 37 species, ~ 300 reactions (more to follow, e.g. nitrogen chemistry) used on-the-fly in a 3D-MHD simulation (slow-down by a factor of 7) Sophisticated predictions for observations are possible Applied to a collapsing filament Promising physical & chemical results Synthetic dust and CO emission maps Reliable mass estimates (about a factor of two) only with opacity corrected values Cosmic rays influence masses obtained from line emission Filament width determination via intensity affected by optical depth effects Opacity-correction required for reliable widths