Pre-stellar Cores

Pre-stellar Cores

School of Physics and Astronomy FACULTY OF MATHEMATICS & PHYSICAL SCIENCES The chemical interaction of dust and gas in prestellar cores Paola Caselli Collaborators Low-mass: Aikawa (Kobe), Bacmann (LAOG), Belloche (Bonn), Bizzocchi (Lisbon), Bourke (CfA), Ceccarelli (LAOG), Crapsi (Leiden), Di Francesco (Victoria), Emprechtinger (Caltech), Foster (BU), Friesen (NRAO), Goodman (Harvard), Jrgensen (Copenhagen), Keto (CfA), Myers (CfA), Pagani (LERMA), Pineda (Manchester), Schnee (NRAO), Tafalla (Madrid), Vastel (Toulouse), van der Tak (Groningen), Walmsley (Arcetri)

Intermediate-mass: Alonso-Albi (Madrid), Ceccarelli (LAOG), Crimier (Grenoble), Fuente (Madrid), Johnstone (Victoria), Plume (Calgary) Massive: Bourke (CfA), Butler (Florida), Fontani (IRAM), Henshaw (Leeds), Hernandez (Florida), Jimenez-Serra (CfA), Pillai (Caltech), Tan (Florida), Zhang (CfA) Main Uncertainties Cosmic-ray ionization rate (e.g. Keto & Caselli 2008) Elemental abundance (metals) Oxygen chemistry (Herschel !) PAHs abundance (e.g. Wakelam & Herbst 2008) Surface chemistry (e.g. Garrod et al. 2009; Semenov et al. 2010) Dust evolution(e.g. Ormel et al. 2009; Keto & Caselli 2010)

(e.g. Pagani et al. 2009; Troscompt et al. 2009) H2 ortho-to-para ratio Alves et al. 2001 Outline The formation of H2 The chemistry of water CO formation Nitrogen chemistry Molecular freeze-out Deuterium fractionation The Herschel view re Co nte PD R

ce lay er 1. 2. 3. 4. 5. 6. 7. r Bergin & Tafalla 2007 + Di Francesco et al. 2007 1. The formation of H2

H + H H2 on the surface of dust grains (Gould & Salpeter 1963; Hollenbach & Salpeter 1970; Jura 1974; Pirronello et al. 1999; Cazaux & Tielens 2002; Habart et al. 2003; Bergin et al. 2004; Cuppen & Herbst 2005; Cazaux et al. 2008; Cuppen et al. 2010) RH 2 1 = n H v H A ng S H 2 1017 cm-3s-1 Evidences of freeze-out: 2. The chemistry of water deuterium fractionation On the surface of dust grains (e.g. Tielens & Hagen 1982; Cuppen & Herbst 2007; Ioppolo et al. 2008; Cazaux et al. 2010):

Tielens & Hagen 1982 Cuppen & Herbst 2007 Evidences of freeze-out: 2. The chemistry of water deuterium fractionation In the gas phase (e.g. Hollenbach et al. 2009): Desorption (d) from dust surfaces (Hollenbach et al. 2009; Garrod 2008; Cazaux et al. 2010): QuickTime and a

decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. 2. The chemistry of water G0 variations Volume density variations Grain size variations Photodesorption yield variations SWAS + Odin upper limits: x(H2O)gas <10-8 (Bergin & Snell 2002; Klotz et al. 2008) BUT

Line trapping and absorption of the dust continuum challenge the measurement of x(H2O)gas (Poelman et al. 2007) Hollenbach et al. 2009 3. CO formation Sternberg & Dalgarno 1995 CO tCO ~ nC/[n(H2)] ~ 105yr 4. Nitrogen chemistry CO Flower et al. 2006 Hily-Blant et al. 2010 N2

N + H3+ NH+ + H2 N + OH NO + H N + CH CN + H tN2 ~ 106 yr in UV-shielded clouds 5. Molecular freeze-out Freeze-out versus Free-fall t dep = 1 9 1

10 m /T (n ) yr X H 2 n d ad v t 3 1/ 2 7 1/ 2 t ff = yr = 4 10 (n H )

32G Walmsley 1991 van Dishoeck et al. 1993 5. Molecular freeze-out C17O(1-0) emission (Caselli et al. 1999) CO hole dust peak 0.05 ly Dust emission in a pre-stellar core (Ward-Thompson et al. 1999) Molecules

freeze out onto dust grains in the center of prestellar cores Dust grain 5. Molecular freeze-out N2D+(2-1) N2H+(1-0) Dust emission in the pre-stellar core L1544 (Ward-Thompson et al. 1999) See also Bacmann et al. 2002, 2003; Bergin et al. 2002; Lee, Evans et al. 2003 D-fractionation increases

towards the core center (~0.2; Caselli et al. 2002; Crapsi et al. 2004, 2005) 5. Molecular freeze-out 850 m Friesen et al. 2010 N2H+(1-0) 5. Molecular freeze-out On size scale of 800 AU: No NH3 freeze-out at nH ~ 106 cm-3 ! N(NH3) @ VLA 1400 AU

The gas temperature drops to ~6 K in the central 1000 AU ( 4 larger dust emissivity; Keto & Caselli 2008) The deuterium fractionation is ~0.4 in the central 3000 AU (larger than in N2H+; see also Pillai et al. 2006, Fontani et al. 2008; Busqet et al. 2010) Loss of specific angular momentum towards the small scales Crapsi, Caselli, Walmsley & Tafalla 2007 N(NH2D) @ PdBI 700 AU 6. Deuterium fractionation H + HD H2D + H2 + 230 K

+ 3 + H2D+ + Watson 1974 Millar et al. 1989 N2 N2D+ + H2 CO DCO+ + H2 H2D+ / H3+ increases when Tkin < 20 K + when the abundance of gas phase neutral species (in particular CO and O) decreases (Dalgarno & Lepp 1984; Roberts & Millar 2000). Evidences of freeze-out:

6. Deuterium fractionation deuterium fractionation The H2D+ and N2D+ lines trace the same region (size ~ 5000 AU) Only models including all multiply deuterated forms of H3+ can reproduce these data (Roberts et al. 2003; Walmsley et al. 2004; Aikawa et al. 2005) Caselli et al. 2003, 2008 Vastel et al. 2006 o-H2D+ CSO

N2H+(1-0) IRAM N2D+(2-1) IRAM Evidences of freeze-out: 6. Deuterium fractionation deuterium fractionation The ortho-to-para ratio: Caselli et al. 2008 Flower, Pineau des Forts, Walmsley 2004 L429

L694-2 L1544 L183 TMC-1C L1517B B68 L1521F B1 OphD NGC1333 DCO+ See also Pagani et al. 2009

16293E NGC2264G Sipil et al. 2010 Evidences of freeze-out: 7. The Herschel view deuterium fractionation QuickTime and a decompressor are needed to see this picture. Casellietetal. al.2010, 2010,submitted

in press Caselli 1.3 mm continuum map from Ward-Thompson et al. (1999) Evidences of freeze-out: 7. The Herschel view deuterium fractionation QuickTime and a decompressor are needed to see this picture. Caselli et al. 2010 Evidences of freeze-out: 7. The Herschel

view deuterium fractionation x(o-H2O) ~ 210-10 within the central ~7000 AU ~ 510-9 at larger radii Peak (very similar to what found by van der Tak et al. 2010 in high-mass star forming regions) Using Keto & Caselli (2010) RT models: abundance ~ 10-8 at ~0.1 pc from center Evidences of freeze-out: 7. The Herschel view deuterium fractionation Evidences Summaryof freeze-out: deuterium fractionation 1. Prestellar cores (PCSs) are the earliest phases (initial

conditions) of star/planet formation. Ideal laboratories. 2. Severe (> 90%) freeze-out of CO (CS, H2CO, CH3OH) at densities above a few 104 cm-3. 3. N2H+ starts to freeze-out at nH > 105 cm-3. 4. No clear evidence of NH3 freeze-out at large nH (Herschel needed!), as well as CN, HCN and HNC. 5. N2D+ and deuterated ammonia peak toward the coldest and densest zones (tfreeze < 1000 yr) (ALMA). 6. H2D+ is spatially coincident with N2D+ (i.e. it does not trace molecular holes). D2H+ observations needed. 7. PSCs H2O abundances are low (~10-10) within cores (steep gradients?). Chemical models need revision. Evidences of freeze-out: Whats next? deuterium fractionation 1. WISH GT: Higher sensitivity spectrum toward L1544 2. Herschel OT1: High sensitivity water spectra toward

TMC-1, L1689B, and L183 (30 h HIFI, Aikawa, Caselli, Tafalla et al.): Test intra-cloud variations of H2O abundance in the Taurus molecular cloud Compare the Taurus abundance with that of other clouds with different physical conditions. Link physical conditions with H2O observations to understand chemical processes. Evidences of freeze-out: Whats next? PSC propertiesfractionation in cluster forming regions deuterium Oph A seen in 850 m (color scale), N2H+(4-3) (green contours) and ortho-H2D+(101-110) (blue

contours). QuickTime and a decompressor are needed to see this picture. Di Francesco et al., in prep. With Herschel/HIFI (Di Francesco, Caselli, Jrgensen +): ortho-NH3(11-00), N2H+(6-5) H2O(110-101) para-D2H+(110-111) ortho-D2H+(111-000) Evidences of freeze-out: Whats next?

PSCs in high-mass star forming regions deuterium fractionation QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. 3 MJy Sr-1 g cm-2 Spitzer IRAC 8mmmMass Surface Densit (Butler & Tan 2009; Peretto & Fuller 2 Evidences

of freeze-out: Whats next? PSCs in high-mass star forming regions deuterium fractionation Multilayer spectroscopy of 8/24/70m-dark pre-star-cluster clumps in IRDCs (31 h, HIFI+PACS; Caselli, Tan, Beltran et al.) A. Dense cores and their molecular envelopes: HIFI simultaneous observations of ortho-H2O(110-101) and orthoNH3(11-00) + N2H+(6-5). B. The atomic layer: [CII] 158m maps with HIFI. C. The extinction low + [OI]63m: PACS imaging spectroscopy between 51 and 73m

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