1. Studying Infall
Neal J. Evans II

2. Importance Proving stars form by gravitational collapse
Testing particular theories
Determining timescales

3. Why is it so hard? Troubled history Velocities low Compared to
early claims and sharp criticism
Velocities low
vinf = 1 km/s [(M*/Msun)/(r/1000AU)]0.5
Compared to
turbulence vturb ~ r0.5
rotation on small scales vrot ~ r–1
outflows vflow ~ 1 to 100 km/s

4. Renaissance Discovery of objects in very early stages
Class 0
Class –1 or Pre-Protostellar Cores (PPCs)
Simple models for collapse
Shu 1977 and variations
Systematic predictions of line profiles
Zhou 1992
A credible example: B335
Zhou et al. 1993

5. Objects in Early Stages
Andre 2002

6. Simple Collapse Models
Time Evolution of a Shu, inside-out collapse model.
Initially a 10 K SIS. OH5 dust.
t = 104 to 7 x 105 in 70 steps, dM/dt = 2 x Msun/yr, R* = 3Rsun.
Dust temperature computed with DUSTY (Ivezic and Elitzur 1997)
C. Young

7. Predictions of Line Profiles (Shu models)
HCO+
J =3-2
HCO+
J =4-3
Gregersen et al.
1997

8. The Infall Cartoon
Andre 2002

9. A Credible Example B335 Shu model fits line profiles of CS, H2CO
(Zhou et al.1993)
Improved models by
Choi et al. (1995)

10. Surveys for Infall Signatures
Globules C18O, H2CO 3/12
Wang et al. 1995
Class 0 Cores HCO+ , H13CO+ 6/18
Gregersen et al. 1997
Class 0/I Cores CS, H2CO, N2H+
14/37 CS, 15/47 H2CO
Mardones et al. 1997
Class I Cores HCO+ 8/16
Gregersen et al. 2000

11. Inward Motions in Class –1
Class –1 CS, N2H+ 17/70
Lee et al. 1999
Class –1 HCO+ , H13CO+ 6/17
Gregersen and Evans 2000

12. Getting Quantitative A variety of line profiles
Some blue, some red, some neither
Define BLUE: delta v < –0.25
delta v = (vthick – vthin)/Delta vthin
For a sample, define excess of blue over red
Excess: E = (Nblue – Nred)/Ntot
Surveys: Positive Excess
Systematic tendency for inward motion

13. Does Excess vary with Class?–1 I
0.35
0.31
Based on HCO+ J = 3–2 Gregersen et al. 2000

14. Storm Clouds Interferometers find deviations Chemical Effects
Line profiles on small scales not as predicted
Choi et al. (1999)
Wilner et al. (2000)
Chemical Effects
Depletion can remove infall signature
Rawlings and Yates

15. Inconsistency on Small Scales
Observations with IRAM Array
Resolution about 2.5”
Dotted line shows predicted line
based on standard Shu collapse.
Expect higher velocities than seen.
Spatial pattern also different.
Wilner et al. 2000
ApJ, 544, L69

16. Depletion Can Confuse Infall
Abundance versus
Radius: Different
Chemical Models
Line profiles resulting from different chemical models
Rawling and Yates 2001
HCO+ CS

17. Back to Basics Use dust continuum emission
More robust tracer of n(r)
Modeling with RT yields TD(r)
Gas–Dust energetics yields TK(r)
Use these as constraints
Derive empirical abundances X(r)
Eventually model chemistry/dynamics

18. Dust Emission Images Class –1 L1544 Class 0 B335 Class I CB230
850 micron Emission

19. Results of Modeling Model fits to radial profiles of dust emission:
Bonnor-Ebert sphere fits L1544 (–1)
Power law
(n ~ r–p) fits
B335 (0) and
CB230 (I)
Dust temperature calculated self-consistently.
Beam and chopping simulated.
Evans et al.
2000
Shirley et al.
2002
Young et al.
2002

20. Conclusions for Class –1
Bonnor-Ebert spheres are good fit
Central densities of 105 to 106 cm–3
Unstable if only thermal support
Weather Report for Class –1
Very cold (TD(K) ~ 7 K in center)
Calm (very low turbulence)
Precipitation is expected

21. Molecular Line Studies
Study of PPCs with dust emission models
L1512, L1544, L1689B
Maps of species to probe specific things
C18O, C17O, HCO+, H13CO+, DCO+, N2H+, CCS

22. The PPC is Invisible to Some
Cut in RA: Convert to N(H2) with
standard assumptions
C18O does not peak
C17O slight peak
Optical Depth plus depletion
Color: 850 micron dust continuum
Contours: C18O emission

23. Others See It Green: 850 mic. Red: N2H+ traces PPC Agrees with
predictions of
chemical models
Nitrogen based
and ions less
depleted.
Lee et al. 2002

24. Evidence for Inward Motions
Line profiles of HCO+
Double peaked,
Blue peak stronger
Signature of inward
motion.
Red: Model with
simple dynamics,
depletion model
fits the data.
Lee et al. 2002

25. Results from Molecular Lines
Cold, dense interior causes heavy depletion
Molecular emission affected by
Opacity, depletion, low temperature
Evidence of inward motions
Before central source forms
Plummer model provides reasonable fit
Other models can fit too
Two-layer model (Myers)

26. Two-layer Model for L1544
N2H+ Spectra toward L1544 Spectrum from 30-m shows infall asymmetry. Model fit with inward motions at constant velocity (v~0.15 km/s)
Bourke et al

27. Velocity Increases Inward
N2H+ shows the highest velocities, probes the smallest radii. Evidence of increasing velocity inward.
Bourke et al

28. The Smoking Gun Absorption against a central continuum
Redshifted absorption implies infall
Disk as central source
Seen toward NGC 1333 IRAS 4A
Choi et al. 1999
Di Francesco et al. 2001
Will be easy with ALMA
May be possible in NIR/MIR with high R

29. Inverse P-Cygni Profiles: Cartoon

30. Inverse P-Cygni Profiles: Observed
Inverse P-Cygni profile: absorption against continuum
from disk redshifted due to infall.
Di Francesco et al Ap. J. 562,770

31. Studying the Velocity Field
IRAM 04191
Shift of absorption dip
to red in higher J lines indicates faster infall at smaller r.
Belloche et al. 2002, preprint

32. Velocities in IRAM 04191
Empirical Model of velocity fields in IRAM 04191
Belloche et al. 2002

33. Future Prospects Combined dust and gas analysis
Class –1 and 0, esp. early Class 0
Studies of redshifted absorption
CARMA, ALMA
Detailed studies of velocity fields
On a range of spatial scales
2D, 3D radiative transfer, include rotation
Tests of theoretical models
Infall in regions forming massive stars?

34. Blue Profile in a Massive Region
A Blue profile in HCO+
toward a region with
L = 104 to 105 Lsun.
G. Fuller, hot off the 30 m
HCO+ 1–0