1. Submillimetre Observations of Star-Forming Regions: Answers & Questions from Large-Area Mapping Surveys
Doug Johnstone – NRC/HIA & U.Victoria
11/18/2018
SMA Conf 2005

2. Dust Emission vs. Starlight
Submillimetre
optical light
11/18/2018
SMA Conf 2005

3. Recipe for Dust Continuum Analysis
Map submillimetre continuum
Assume optically thin dust emission
Estimate a temperature for the dust
Deduce the column of dust and gas
Identify structures (clumps, filaments)
Compare with physical models
Measure statistical quantities
Reach conclusions (Just So stories?)
11/18/2018
SMA Conf 2005

4. The Ophiuchus Cloud in Visual Light
11/18/2018
SMA Conf 2005

5. The Ophiuchus Cloud in Extinction
Cambresy et al. 1999
11/18/2018
SMA Conf 2005

6. The Ophiuchus Cloud in Millimetre Emission
IRAM mm
0.13 Sq. Degree Map (~1 pc2)
Significant Structure
resolved cores
Coherent regions
Coincident with dense gas tracers
(un)resolved clumps
Located around cores
Motte, Andre, & Neri 1998
11/18/2018
SMA Conf 2005

7. The Ophiuchus Cloud in Millimetre Emission
Found 60 Clumps
Clump Mass F’n
Similar to Stellar MF
Steeper than cloud MF
Possible turn-over near Msun
Motte, Andre, & Neri 1998
11/18/2018
SMA Conf 2005

8. The Ophiuchus Cloud in SubMillimetre
JCMT 850 m
0.25 Sq. Degree Map (~2 pc2)
Filter long spatial scales in data to search for 55 clumps
Separate clumps along minima (Williams et al.)
Measure flux, size, and degree of concentration
Identify with equilibrium structures
Johnstone et al. 2000
11/18/2018
SMA Conf 2005

9. Clump Mass Vs. Radius Relation
Clumps span typical mass range for stars
Most clumps resolved
Sensitivity limited Survey
Most clumps appear stable
Unstable to Collapse
Comparison with CO (Kramer et al. 96)
CO clumps are less dense, require non-thermal support
CO clumps lie below our sensitivity threshold
CO may `freeze-out’ in the dense submillimetre sources
(green lines: resolution & sensitivity limits)
(black lines: isobaric equilibria - unstable only above turn-over)
11/18/2018
SMA Conf 2005

10. Bonnor-Ebert Spheres Static isothermal clouds in equilibrium:
pressure gradients balance gravity
One-dimensional family of models:
Physically - importance of self-gravity
Clump mass versus clump temp.
Observationally – degree of conc.
Peak flux versus mean flux
Three observables (area, flux, conc) yield three physical quantities (mass, temp., external pressure)
Assumes dust temp similar to gas temp
Requires knowledge of opacity ( = 0.01 cm2/gm)
11/18/2018
SMA Conf 2005

11. Physical Conditions in Clumps (Assuming hydrostatic equilibrium)
Pressure at centre of the mol. cloud ~ 107 P/k
Increasing  by 2 lowers T by ~ 2
Adding 50% turbulent pressure lowers T by ~ 2
11/18/2018
SMA Conf 2005

12. Cumulative Mass Spectrum
Warning: Incomplete at low mass!!
m = -1.5
Steep line: ~IMF Shallow line: ~ mol. Clouds
11/18/2018
SMA Conf 2005

13. Thoughts on the Mass Spectrum
Good agreement between sub-mm surveys
Similar results found for Orion B North and South
Motte et al. (Ophiuchus, Orion B), Testi & Sargent (Serpens)
Shape of clump mass function mimics that of stellar IMF
low-mass turn-over may be due to sensitivity
High-mass slope may be somewhat steeper than IMF
Satisfying fits to static, stable, pressure-confined clumps
Low temperatures and stellar-like masses required
High external pressures consistent with depth in mol. Cloud
11/18/2018
SMA Conf 2005

14. Comments on the Stability of Clumps
Are these clumps quasi-static or dynamic?
The clumps may be modeled as hydrostatic entities
Reasonable fit to the physical parameters
Likely end result if the cloud loses support slowly
In a few cases there exist complimentary line data (Friesen, Poster)
Ambi-polar diffusion models predict smallscale clumping
Central region where magnetic support removed
Objects on their way to collapse
Models of turbulent clouds also predict small-scale clumping
Interfaces between waves, not long-lived!
May approximate BE conditions (Ballesteros-Paredes et al 2003)
11/18/2018
SMA Conf 2005

15. Ophiuchus - 3.6, 4.5, 8.0 mm (IRAC) Johnstone et al. (2000)
11/18/2018
SMA Conf 2005
Allen et al. (2005)

16. COMPLETE -> Extinction Maps
(Goodman, Poster)
Extinction derived from 2Mass reddening data (Alves et al.) reveals both the diffuse envelope of the cloud and the dense core regions.
Black contour denotes an Av ~ 5.
11/18/2018
SMA Conf 2005

17. Found only 2! Ophiuchus – JCMT 2004 Johnstone,
Di Francesco, & Kirk 2004
In 2003 observed 4 sq. degrees (~30 pc2)
40 hours!
Largest SCUBA map to date (independent pixels)
Expect 100’s of new compact sources
Found only 2!
11/18/2018
SMA Conf 2005

18. Is there a threshold Effect? Where do the clumps reside?
11/18/2018
SMA Conf 2005

19. Is there a threshold Effect? Where is the bulk mass of SCUBA sources?
Does this Av threshold signify the importance of UV photons in maintaining the cloud ionization fraction, coupling the magnetic field to the gas, and preventing collapse (McKee 1989)?
11/18/2018
SMA Conf 2005

20. Significance of these Clumps
Clumps represent ~2% mass of cloud
Clumps represent ~20% mass of core
Clumps live primarily at high (>10) Av
Clumps have stellar IMF-like mass f’n
Embedded stellar clusters have these same properties!
(Lada and Lada 2003)
11/18/2018
SMA Conf 2005

21. Thermal Emission: Perseus
Data from Hatchell et al. (2005) B5
IC348SW
NGC 1333 B1
SCUBA observations of Ophiuchus containing new data
IRAS 03282
L1448
57 objects
Per 6
3.8 sq. degrees; 30 mJy/beam rms
L1455
11/18/2018
SMA Conf 2005
Kirk, Johnstone, & Di Francesco (2005, in prep.)

22. Kirk, Johnstone, & Di Francesco (2005, in prep.)
Thermal Emission + Extinction: Perseus
SCUBA observations of Ophiuchus containing new data
11/18/2018
SMA Conf 2005
Kirk, Johnstone, & Di Francesco (2005, in prep.)

23. Is there a threshold Effect? Where is the bulk mass of SCUBA sources?
Does this Av threshold signify the importance of UV photons in maintaining the cloud ionization fraction, coupling the magnetic field to the gas, and preventing collapse (McKee 1989)?
11/18/2018
SMA Conf 2005
Kirk, Johnstone, & Di Francesco (2005, in prep.)

24. Kirk, Johnstone, & Di Francesco (2005, in prep.)
Triggering by 40 Persei? : Perseus
SCUBA observations of Ophiuchus containing new data
11/18/2018
SMA Conf 2005
Kirk, Johnstone, & Di Francesco (2005, in prep.)

25. Kirk, Johnstone, & Di Francesco (2005, in prep.)
Thermal Emission: Ophiuchus
5.5 sq. degrees; 40 mJy/beam rms
L1709
L1688
L1689N
SCUBA observations of Ophiuchus containing new data
L1712
L1689S
11/18/2018
SMA Conf 2005
Kirk, Johnstone, & Di Francesco (2005, in prep.)

26. Kirk, Johnstone, & Di Francesco (2005, in prep.)
Thermal Emission + Extinction: Ophiuchus
SCUBA observations of Ophiuchus containing new data
11/18/2018
SMA Conf 2005
Kirk, Johnstone, & Di Francesco (2005, in prep.)

27. And the Cosmology Angle?
Large Data Sets Provide Statistical Info
Cloud mass and size distribution - large scales
Clump mass and size distribution - small scales
Clump locations - environment and clustering
Structure - filamentary, ellipticity, direction
Frequency of protostellar stages - Class -I, 0, I, II, III
Polarization Angle - Magnetic Field Orientation
Kinematic Information - CO line shapes. Spatial variation
Any reasonable theory must reproduce these conditions!
(Mac Low & Klessen 2004, Shu 1983, Basu & Ciolek 2004)
11/18/2018
SMA Conf 2005

28. Thermal Emission (2006++)
CO clouds
Imaging at 850 and 450 microns (>100 faster than SCUBA)
Covering 10 sq. deg. to 2mJy (CO clouds) in <100 hrs
Deep, unbiased, structure surveys within molecular clouds
COMPLETE Revisited - COMPLETER
11/18/2018
SMA Conf 2005

29. Gould’s Belt - Nearby Star Formation Sites
SCUBA2 Legacy Project: Mapping all star formation in Gould’s Belt, covering 700 square degrees, and sensitive to every Class O & I protostar and every L1544-like pre-stellar core within 0.5 kpc!
11/18/2018
SMA Conf 2005

30. Thermal Emission (2006++) Polarimetry (>1000 faster than SCUBA)
Should detect magnetic geometry over much of cloud
Important observational constraint for theories/simulations
Further exploration of dust properties
11/18/2018
SMA Conf 2005

31. Thermal Emission (2006++)
Fourier Transform Spectroscopy (>1000 faster than SCUBA)
High spectral resolution - survey strong molecular lines
Low spectral resolution - model SED through submillimetre
Determine dust properties (ß± 0.1) (Friesen et al. 2005)
11/18/2018
SMA Conf 2005

32. The most significant problem for star formation is not forming stars, but rather not forming stars!
11/18/2018
SMA Conf 2005

33. 11/18/2018
SMA Conf 2005