Studying Infall

Neal J. Evans II

Importance

• Proving stars form by gravitational collapse

• Testing particular theories

• Determining timescales

Why is it so hard?

• Troubled history– 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

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

Objects in Early Stages

Andre 2002

Simple Collapse Models

C. Young

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 10-6 Msun/yr, R* = 3Rsun.Dust temperature computed with DUSTY (Ivezic and Elitzur 1997)

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Predictions of Line Profiles(Shu models)

HCO+

J =3-2

HCO+

J =4-3

Gregersen et al.1997

The Infall Cartoon

Andre 2002

A Credible Example

B335 Shu model fits line profiles of CS, H2CO(Zhou et al.1993)Improved models byChoi et al. (1995)

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

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

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

Does Excess vary with Class?

–1 0 I

0.35 0.31 0.31

Based on HCO+ J = 3–2 Gregersen et al. 2000

Storm Clouds

• Interferometers find deviations– 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

Inconsistency on Small Scales

Wilner et al. 2000ApJ, 544, L69

Observations with IRAM ArrayResolution about 2.5”Dotted line shows predicted linebased on standard Shu collapse.Expect higher velocities than seen.Spatial pattern also different.

Depletion Can Confuse Infall

Abundance versusRadius: Different Chemical Models

HCO+ CS

Rawling and Yates 2001

Line profiles resulting from different chemical models

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

Dust Emission Images

Class –1L1544

Class 0B335

Class ICB230

850 micron Emission

Results of Modeling

Evans et al. 2000

Shirley et al. 2002

Young et al. 2002

Model fits to radial profiles of dust emission: Bonnor-Ebert sphere fits L1544 (–1)Power law (n ~ r–p) fitsB335 (0) and CB230 (I)

Dust temperature calculated self-consistently.Beam and chopping simulated.

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

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

The PPC is Invisible to Some

Color: 850 micron dust continuumContours: C18O emission

Cut in RA: Convert to N(H2) with standard assumptions

C18O does not peak C17O slight peakOptical Depth plus depletion

Others See It

Green: 850 mic.Red: N2H+

traces PPC

Agrees withpredictions ofchemical models

Nitrogen basedand ions lessdepleted.

Lee et al. 2002

Evidence for Inward Motions

Lee et al. 2002

Line profiles of HCO+

Double peaked,Blue peak strongerSignature of inwardmotion.

Red: Model withsimple dynamics,depletion modelfits the data.

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)

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. 2002

Velocity Increases Inward

N2H+ shows the highest velocities, probes the smallest radii. Evidence of increasing velocity inward.

Bourke et al. 2002

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

Inverse P-Cygni Profiles: Cartoon

Inverse P-Cygni Profiles: Observed

Inverse P-Cygni profile: absorption against continuum from disk redshifted due to infall. Di Francesco et al.

2001 Ap. J. 562,770

Studying the Velocity Field

IRAM 04191Shift of absorption dipto red in higher J lines indicates faster infall at smaller r.

Belloche et al. 2002, preprint

Velocities in IRAM 04191

Belloche et al. 2002

Empirical Model of velocity fields in IRAM 04191

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?

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