A Full Virial Analysis of the Prestellar Cores in theOphiuchusMolecularCloud

Kate PattleUniversity of Central Lancashire

D. Ward-Thompson, J.M. Kirk,JCMT & Herschel GBS Teams

THE OPHIUCHUS MOLECULAR CLOUD

A nearby region of clustered low- to intermediate-mass star formation (e.g. Wilking et al. 2008)

At a distance of ~138 pc (Mamajek 2008)

Heavily influenced by the nearby Sco OB2 association (Vrba 1977; Loren 1989a,b)

Observed as part of the JCMT Gould Belt Legacy Survey (Ward-Thompson et al. 2007)

Also observed as part of the Herschel Gould Belt Survey (André et al. 2007) and Spitzer Gould Belt Survey (Evans et al. 2009)

Results of this study are presented in:Pattle et al. 2015, MNRAS 450 1094

Ward-Thompson et al. 2007

Figure: Loren, 1989a Towards Sco OB2 Association

THE OPHIUCHUS MOLECULAR CLOUD

JCMT GBS OBSERVATIONS

(Pattle et al. 2015) Yellow stars mark embedded sources from Enoch et al. 2009

JCMT GBS OBSERVATIONS

(Pattle et al. 2015) Yellow stars mark embedded sources from Enoch et al. 2009

JCMT GBS OBSERVATIONS

93 sources were extracted from the SCUBA-2 850μm data using Cutex (Molinari et al. 2011) and were modelled as Gaussian distributions.

Of these 93 sources:

● 46 were classified as protostellar● 47 were classified as starless

● 92 were observed as part of the Herschel GBS (Andre et al. 2010; Ladjalate et al. 2015)

● 70 sources were observed within L1688 region, of which 47 are uniquely associated with a source in the Simpson et al. 2008 SCUBA catalogue

● 23 of the starless cores in L1688 have been observed in both:

12CO/13CO/C18O J=3→2 with HARP (White et al. 2015)

N2H+ J=1→0 with IRAM 30m (André et al. 2007)

SOURCE TEMPERATURES

Source temperatures were determined by SED fitting across 4 bands:

● PACS 160μm● SPIRE 250μm● SCUBA-2 450μm● SCUBA-2 850μm

Herschel data were filtered to remove large-scale structure (Sadavoy et al. 2013)

Data were convolved to the SPIRE 250μm resolution, 18.1”

(Pattle et al. 2015)

STARLESS CORE MASSES

Motte et al. 1998Simpson et al. 2008

Cutex 80% Completeness LimitSCUBA-2 GBS 5σ Sensitivity LimitElmegreen & Falgarone 1996 CO relation

(Patt

le e

t al. 2

015)

Traditional Histogram Fitting:

Maximum Likelihood Estimator:

CORE MASS FUNCTIONS

( )

( )

(Patt

le e

t al. 2

015)

(Patt

le e

t al. 2

015)

DENSE GAS TRACERS

Di Francesco et al. (2007), Protostars & Planets V

DENSE GAS TRACERS

Di Francesco et al. (2007), Protostars & Planets V

N2H+

Traces high-density core material

Significant depletion not expected until densities ~ 106 cm-3

Low abundance: X(N

2H+)=5.2±0.5x10-10

(Pirogov et al. 2003)

DENSE GAS TRACERS

Di Francesco et al. (2007), Protostars & Planets V

C18O

Traces intermediate-density material surrounding core

Traces densities < 105 cm-3

X(C18O)=2.635x10-7

(Frerking 1982; Wilson 1999; Pineda et al. 2010)

CORE MASSES

Dust vs. N2H+ Dust vs. C18O N

2H+ vs. C18O

(Pattle et al. 2015)

CORE MASSES

Dust vs. N2H+ Dust vs. C18O N

2H+ vs. C18O

Some evidence for N2H+ freeze-out at

highest masses

(Pattle et al. 2015)

DISSIPATION OF TURBULENCE

N2H+ non-thermal

linewidths:transonic or mildly supersonic

C18O non-thermal linewidths: substantially supersonic

(Pattle et al. 2015)

VIRIAL STABILITY

GPE of a Gaussian distribution:

GRAVITATIONAL POTENTIAL ENERGY

INTERNAL KINETIC ENERGY

EXTERNAL PRESSURE ENERGY

(Basu 2000)

→

Troland et al. (1996) |B| = 10 μGOH Zeeman Splitting: ρ = 103.2 cm-3

σ ~ 0.57 kms-1}

MAGNETIC ENERGY

VIRIAL STABILITY

(Pattle et al. 2015)

VIRIALLY BOUND

VIRIAL STABILITY

(Pattle et al. 2015)

PR

ES

SU

RE-

CO

NF I

NED

VIRIAL STABILITY

(Pattle et al. 2015)

GR

AV

ITY-

CO

NF I

NED

VIRIAL STABILITY

(Pattle et al. 2015)

GR

AV

ITY-

CO

NF I

NED

VIRIALLY BOUND

VIRIAL STABILITY

(Pattle et al. 2015)(Pattle et al. 2015)

GR

AV

ITY-

CO

NF I

NED

VIRIALLY BOUND

VIRIAL STABILITY

PRESTELLAR

(Pattle et al. 2015)

BONNOR-EBERT STABILITY

Bonnor (1956), Ebert (1955)

(Pattle et al. 2015)

BONNOR-EBERT STABILITY

BONNOR-E

BERT

UNST

ABLE

BE analysis predicts 15 of 23 cores to be collapsing under gravity.

Of these 15, 9 are in fact pressure-confined.

The degree to which cores are virially bound is typically overestimated by the BE model.

(Pattle et al. 2015)

OPH A

Only region with substantially gravitationally bound prestellar cores.

Warmest region in L1688, heated by B stars HD147889 and S1.

One embedded protostar: Class 0 source VLA1623 (André et al 1993)

Star formation appears to be in its early stages.

SCUBA-2 850μm/Herschel 100μm/Spitzer 8μm (Evans et al. 2003)

(Pattle et al. 2015)

OPH BAppears quiescent; cores typically virialised or marginally bound

Cores typically marginally pressure-confined

Coldest region in L1688

4 embedded Class I sources; one driving an outflow (Enoch et al. 2007; White et al. 2015)

Turbulence not being dissipated effectively

(Pattle et al. 2015)

OPH CExtremely quiescent region; less evolved than rest of filament

Cores strongly virially bound and pressure-confined

Effective dissipation of turbulence

No embedded protostars

Possibly at a different line-of-sight distance?

(Pattle et al. 2015)

OPH E & OPH F

Most evolved regions of L1688

Pressure-confined cores

Effective dissipation of turbulence

4 Class I sources in Oph E; 6 in Oph F

Similar temperatures to Oph A, without obvious external heating

(Pattle et al. 2015)

EVOLUTIONARY GRADIENT?

There appears to be an evolutionary gradient from south-west to north-east across L1688

This is consistent with L1688 being influenced by the Sco OB2 association

Also consistent with previous studies (Nutter et al. 2006, Loren 1989)

(Pattle et al. 2015)

CONCLUSIONSThe starless cores identified in SCUBA-2 GBS observations of Ophiuchus:

● Have a mass distribution consistent with the IMF● Are typically bound or virialised, with external pressure being

instrumental in their confinement● Are not well-modelled as critically stable BE spheres.

The properties of the starless cores vary with local environment:

● Temperature depends on local heating● Turbulence appears to be dissipated more effectively in regions

without outflows.

A global evolutionary gradient is seen from south-west to north-east across Ophiuchus.

Thank you for your attention!

For more details, see Pattle et al. 2015, MNRAS 450 1094