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 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

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 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) C. Young

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 by Choi 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 I 0.35 0.31 Based on HCO+ J = 3–2 Gregersen et al. 2000

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

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

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

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 –1 L1544 Class 0 B335 Class I CB230 850 micron Emission

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

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 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

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

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

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

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

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