Chemical Diagnostics of Star Forming Regions

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1 School of Physics and Astronomy FACULTY OF MATHEMATICS & PHYSICAL SCIENCES Chemical Diagnostics of Star Forming Regions Paola Caselli N 2 H + (1-0) Di Francesco et al N 2 H + (3-2) Bourke et al. in prep Wilking, Gagne & Allen 2008, Handbook of Star Forming Regions, Vol. II

2 Collaborators Low-mass: Belloche (Bonn), Bourke (CfA), Ceccarelli (Grenoble), Crapsi (Leiden), Di Francesco (Victoria), Emprechtinger (Caltech), Foster (BU), Friesen (NRAO), Goodman (Harvard), Jørgensen (Bonn), Keto (CfA), Mitchell (Leeds), Myers (CfA), Pineda (Harvard), Rushton (Leeds), Schnee (Victoria), Tafalla (Madrid), Vastel (Toulouse), van der Tak (Groningen), Walmsley (Arcetri) Intermediate-mass: Alonso-Albi (Madrid), Ceccarelli (Grenoble), Fuente (Madrid), McCoey (Victoria), Johnstone (Victoria), Plume (Calgary) Massive: Bourke (CfA), Butler (Florida), Fontani (IRAM), Hernandez (Florida), Jimenez-Serra (Leeds), Pillai (Caltech), Tan (Florida), Zhang (CfA)

3 Outline Chemical/physical structure of pre-stellar cores (PSCs) Environmental effects PSCs in isolated and clustered star forming regions Summary/open questions Future directions (PSCs as astrophysical laboratories)

4 N 2 N 2 H + Complex chemical structure in the simplest physical units N 2 takes longer than CO to form (Herbst & Klemperer 1973) CO freeze-out & D-fractionation (Lepp & Dalgarno 1984) Suzuki et al. 1992

5 Deuterium Fractionation at T < 20 K H HD H 2 D + + H K Watson 1974 Millar et al H 2 D + + N 2 N 2 D + + H 2 CO DCO + + H 2 H 2 D + / H 3 + increases if the abundance of gas phase neutral species (in particular CO) decreases (Dalgarno & Lepp 1984; Roberts & Millar 2000).

6 Evidences ortho-h 2 D + of in freeze-out: pre-stellar cores deuterium fractionation The o-h 2 D + line is strong and its emission is extended 5000 AU Only models including all multiply deuterated forms of H 3 + can reproduce these data (Roberts et al. 2003; Walmsley et al. 2004; Aikawa et al. 2005) Vastel et al Caselli et al. 2003, 2008; van der Tak et al o-h 2 D + CSO N 2 H + (1-0) IRAM N 2 D + (2-1) IRAM

7 L1544 Evidences interferometric of freeze-out: observations deuterium fractionation On size scale of ~800 AU: no NH 3 (and N 2 ) freeze-out (see also Hily-Blant et al arxiv: ) 1400 AU N(NH 3 VLA The gas temperature drops to ~6 K in the central 1000 AU The deuterium fractionation is ~0.4 in the central 3000 AU Loss of specific angular momentum towards the small scales N(NH 2 PdBI 700 AU Crapsi, Caselli, Walmsley & Tafalla 2007

8 Evidences Radiative transfer of freeze-out: deuterium Analysis fractionation Static and contracting Bonnor-Ebert sphere Simple CO chemistry (freezeout + photodissociation) Radiative energy balance (+photoelectric heating) Radiative transfer N 2 H + (1-0) ζ ~ 1x10-17 s -1, fluffy grains, n c ~ cm -3 within 500 AU Keto & Caselli 2008, 2010

9 Environmental effects NH 3 and CCS in Perseus cores: CCS almost absent in clustered protoand pre-stellar cores Chemical evolution depends on the environment. Foster et al. 2009

10 Velocity Dispersion Protostellar feedback Protostellar feedback affects the physical conditions of the surrounding cloud (especially in cluster forming regions). Quiscence is soon lost Pineda et al., in prep. Velocity Dispersion

11 Evidences Environmental of freeze-out: effects deuterium fractionation C 17 O(1-0) emission (Caselli et al. 1999) CO hole 0.03 pc dust peak Dust emission in L1544 (Ward-Thompson et al. 1999) 0.01 pc Image: dust emission in ρ Oph A (Di Francesco et al. 2004) Contours: CO depletion factor (Rushton et al., in prep.) See also Friesen et al. 2009!

12 Evidences of freeze-out: deuterium cluster-forming fractionation region N6: starless core in ρ Oph A, the nearest Size (AU) N 2 H + (3-2) BOURKE et al., in prep. N6 L x1500 ~8000 N(N 2 D + )/ N(N 2 H + ) T c (K) 14 7 SMA + JCMT Δv (km/s) N 2 H + (3-2) Δv NT /Δv N 2 H + (3-2) M (M ) Within N 2 H + (3-2)

13 Evidences of freeze-out: Caselli et al., in prep. deuterium fractionation D-fractionation in Infrared Dark Clouds N 2 D + /N 2 H + ~ 0.03 Jimenez-Serra, Caselli, Tan +, in prep.

14 R CHL1157-mm outflow H 2 D O 3 OH SiO = 440 pc, L bol = 8.3 L o 3 B1 B2 Only H 2 O is detected on-source! Water traces hot spots where shocks dump energy into cloud

15 Summary Astrochemical/radiative transfer modeling + observations are needed to identify the right tracer to study the initial conditions of star formation. Environment, protostellar feedback, gas-dust interactions affect chemical/physical evolution difficult to gauge ages and initial conditions. Still puzzling: presence of (N-bearing) gas phase molecules at n H > 10 6 cm -3 (N 2 vs CO) different behavior of NH 2 D and N 2 D + desorption processes Dense and cold material in IRDCs is probably concentrated in small regions (<6 ), filling ~3% of the volume.

16 Future Evidences directions of freeze-out: deuterium fractionation Cosmic-ray ionization rate Metal abundance Grain size distribution H 2 ortho-topara ratio Ice mantle Oxygen abundance

17 Future Evidences directions of freeze-out: deuterium fractionation van Loo, Hartquist, Falle Cazaux, Cuppen Keto, Broderick, Spaans Pineda + Boley, Spaans,Hartquist