School of Physics and AstronomyFACULTY OF MATHEMATICS & PHYSICAL SCIENCES

Chemical Diagnostics of Star Forming RegionsPaola Caselli

Wilking, Gagne & Allen 2008, Handbook of Star Forming Regions, Vol. II

N2H+(1-0)

Di Francesco et al. 2004

N2H+(3-2) Bourke et al. in prep

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)

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)

Complex chemical structure in thesimplest physical units

N2

N2H+

Suzuki et al. 1992

• N2 takes longer than CO to form(Herbst & Klemperer 1973)

•CO freeze-out & D-fractionation (Lepp & Dalgarno 1984)

H3+ + HD ⇒ H2D+ + H2 + 230 K

H2D+ / H3+ increases if the abundance of gas phase neutral

species (in particular CO) decreases (Dalgarno & Lepp 1984; Roberts & Millar 2000).

Deuterium Fractionation at T < 20 K

N2 → N2D+ + H2H2D+ + CO → DCO+ + H2

Watson 1974Millar et al. 1989

Evidences of freeze-out: deuterium fractionation ortho-H2D+ in pre-stellar cores

o-H2D+

CSO

N2D+(2-1)IRAM

N2H+(1-0)IRAM

Vastel et al. 2006

Caselli et al. 2003, 2008; van der Tak et al. 2005

The o-H2D+ line is strong and its emission is extended 5000 AU Only models includingall multiply deuterated

forms of H3+ can

reproduce these data(Roberts et al. 2003;Walmsley et al. 2004;Aikawa et al. 2005)

Evidences of freeze-out: deuterium fractionation

Crapsi, Caselli, Walmsley & Tafalla 2007

• On size scale of ~800 AU:no NH3 (and N2) freeze-out (see alsoHily-Blant et al. 2010 arXiv:1001.3930)

• The gas temperature drops to ~6 Kin the central 1000 AU

• The deuterium fractionation is ~0.4in the central 3000 AU

• Loss of specific angularmomentum towards the small scales

N(NH3) @ VLA

N(NH2D) @ PdBI

L1544 interferometric observations

700 AU

1400 AU

Evidences of freeze-out: deuterium fractionation Radiative transfer Analysis

Keto & Caselli 2008, 2010

• Static and contractingBonnor-Ebert sphere

• Simple CO chemistry (freeze-out + photodissociation)

• Radiative energy balance(+photoelectric heating)

• Radiative transfer

ζ ~ 1x10-17 s-1, fluffy grains,nc~2×107 cm-3 within 500 AU

N2H+(1-0)

Environmental effects

Foster et al.2009

NH3 and CCS inPerseus cores:

CCS almost absentin clustered proto-

and pre-stellarcores

Chemical evolutiondepends on the

environment.

Pineda et al., in prep.

Protostellarfeedback affectsthe physicalconditions of thesurrounding cloud(especially incluster formingregions).

Quiscence is soonlost…

Velocity Dispersion

Velocity DispersionProtostellar feedback

Evidences of freeze-out: deuterium fractionation Environmental effects

C17O(1-0) emission(Caselli et al. 1999)

CO hole

dust peak

Dust emission in L1544 (Ward-Thompson et al. 1999)

0.01 pc

0.03 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 !

Evidences of freeze-out: deuterium fractionation N6: starless core in ρ Oph A, the nearest cluster-forming region

SMA + JCMT

BOURKE et al., in prep.

0.050.2M (M)Within N2H+(3-2)

0.230.25ΔvNT/ΔvN2H+(3-2)

0.180.25Δv (km/s)N2H+(3-2)

714Tc (K)

0.200.06N(N2D+)/N(N2H+)

~80003000x1500Size (AU)N2H+(3-2)

L1544N6

Evidences of freeze-out: deuterium fractionation D-fractionation in Infrared Dark CloudsCaselli et al., in prep.

Jimenez-Serra, Caselli, Tan +, in prep.

N2D+/N2H+

~ 0.03

3’

Water traces ‘hot spots’ where shocks dump energy into cloud

L1157-mm outflowD = 440 pc, Lbol = 8.3 Lo

B2

B1

R

H2OCH3OH SiO

Only H2O is detected on-source!

Summary • Astrochemical/radiative transfer modeling +observations are needed to identify the righttracer to study the initial conditions of starformation.

• Environment, protostellar feedback, gas-dustinteractions affect chemical/physical evolutiondifficult to gauge ages and initial conditions.

• Still puzzling:• presence of (N-bearing) gas phasemolecules at nH > 106 cm-3 (N2 vs CO)• different behavior of NH2D and N2D+

• desorption processes

Dense and cold material in IRDCs isprobably concentrated in smallregions (<6″), filling ~3% of the volume.

Evidences of freeze-out: deuterium fractionation Future directions

Metalabundance

H2 ortho-to-para ratio

Oxygenabundance

Cosmic-rayionization rate

Grain sizedistribution

Ice mantle

Evidences of freeze-out: deuterium fractionation Future directions

van Loo, Hartquist, Falle Cazaux, Cuppen

Keto, Broderick, Spaans

Pineda + Boley, Spaans,Hartquist