Using ALMA to disentangle the Physics of Star Formation in our Galaxy Doug Johnstone: NRC-HIA, U. Victoria 11/13/2018 AAS Calgary 2006

Why the Millimeter/Submillimeter Molecular clouds are cold (T ~ 5-20 K) Even heated dust near stars typically T < 1000 K Dust peak emission at submillimeter SED of dust emission yields dust temperature Longer wavelength emission thin! - column density Molecular lines abundant in millimeter/ submillimeter mm - Ground state CO - traces all but the densest cool gas mm - Ground state N2H+ - traces densest gas Band 3 for ALMA (3mm) - being built in Canada submm - higher energy lines - warmer medium Need an excellent site above much of atmosphere 11/13/2018 AAS Calgary 2006

The Enormous Scales in Star Formation Mass Range Molecular cloud (M ~ 105-6 Msun) Stars (M ~ 0.1 - 10 Msun) Length Scale Molecular cloud (R ~ 1018-19 cm) Star-forming core (R ~ 1016-17 cm) Disk (R ~ 1014-15 cm) Stars (R ~ 1011-12 cm) Additional scale issues Angular momentum Magnetic field strength 11/13/2018 AAS Calgary 2006

Motte, Andre, & Neri 1998 11/13/2018 AAS Calgary 2006

The Angular Resolution Problem Distance 100 pc (low mass) 500 pc (Orion) 2500 pc (high mass) 1” 100 AU 500 AU 2500 AU 0.1” 10 AU 50 AU 250 AU 0.01” 1 AU 5 AU 25 AU 11/13/2018 AAS Calgary 2006

The Need For ALMA Baselines as long as 10 km Angular resolution ~ 0.01” Large collecting area (50-64 12m dishes) Sensitivity to match resolution Excellent sampling of UV plane Superior image fidelity Large bandwidth Multiple lines Sensitive continuum measurements 11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

Antenna Configurations (max) 4 mas @ 950 GHz Site infrastructure (AOS/OSF) + inner array completed 2008 11/13/2018 AAS Calgary 2006

50 Antenna ALMA UV Coverage 11/13/2018 AAS Calgary 2006

Sensitivity after a few hours angular resolution 11/13/2018 AAS Calgary 2006

Problem 1: Turbulence Clouds are not supported by thermal pressure Jeans mass ~ several Msun Support by non-thermal motions Turbulence (possibly mediated by magnetic fields) Turbulence must dissipate Scale of dissipation ~ mean free path For supersonic shocks: d ~ AU (current estimate ~100AU) Large temperature/density variation across shock Resolution is key to observing this scale Desire also to observe diagnostics of warm gas Need to find the energy emitted during dissipation process! ALMA’s higher frequency bands well suited to this problem 11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

Problem 2: The Domain of Gravity Formation of a star requires loss of support Gravity > thermal/non-thermal pressures Quiescent Cores observed (pre-stellar?) Definition: sufficient mass to be bound Di Francesco et al. 2006 PPV chapter Size determined by Jeans length ~ 103 AU Want to probe this region in detail Power-law profile, flattened centres - initial conditions Temperature and/or dust property variations - chemistry Substructure in the core? Multiple density peaks 11/13/2018 AAS Calgary 2006

Problem 2: The Domain of Gravity What can be done with ALMA Dust continuum measurements (0.4 - 3 mm) Temperature and dust properties Molecular line observations CO, N2H+, CS, HCO+ (freeze out, kinematics, infall) Polarization measurements Dust continuum Molecular lines 11/13/2018 AAS Calgary 2006

L1544 90 mm 200 mm 850 mm 1300 mm 11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

B68 C18O Optical Image Dust Emission NICER Extinction Map Radial Density Profile, with Critical Bonnor-Ebert Sphere Fit 11/13/2018 AAS Calgary 2006

Strong B, magnetic support implies: non-tangled (smooth) field lines hourglass morphology 11/13/2018 AAS Calgary 2006 Shu, The Physical Universe (1982)

Problem 2: The Domain of Gravity Massive star formation is a significant problem Distance makes resolution more important If anything the relevant scale is smaller Jeans mass argument Time scale for evolution shorter (cloud and star) Gregarious regions - much more complex Many sources clustered together Internal and external heating sources Need resolution and image fidelity ALMA will be well suited to this problem High angular resolution Excellent image fidelity Large range of molecular tracers (warm and cold gas/dust) 11/13/2018 AAS Calgary 2006

DR 21 Orion 11/13/2018 AAS Calgary 2006

Problem 3: Collapse to Protostar Need to observe the infall motions Optically thin and thick tracers Need to separate the forming components Envelope: temperature, density, chemistry Disk: size, support, chemistry Variety of molecules and molecular lines (+ continuum) Evolution with time Large surveys of protostars Following up on Legacy surveys with Spitzer, Herschel, JCMT etc… 11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

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! 11/13/2018 AAS Calgary 2006

Problem 4: Outflows Outflows and jets are important Determination of local star formation efficiency Removal mechanism for angular momentum May play a role in energizing the cloud May play a role in stopping collapse Interface between the jet and outflow is key The jet is launched from the inner disk The molecular outflow is somehow entrained Observations require resolution/image fidelity Many mol. lines - temperature variation/chemistry 11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

Problem 5: Disks and Planets Everyone is excited by protostellar disks Ubiquitous around young stars Age and environmental diagnostic Significant reservoir of material Chemical processing Planet formation Connection to the Origin of the Solar System Uniqueness of life…. 11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

11/13/2018 AAS Calgary 2006

Problem 6: PDR Physics The interface between atomic and molecular gas Surfaces of molecular clouds Boundary between massive stars and cloud The Orion Bar Outer regions of pre- and proto-stellar envelopes Interesting UV chemistry Strength and hardness of the radiation field Diagnostic of cloud conditions 11/13/2018 AAS Calgary 2006

Problem 7: Chemical Abundances Absorption spectroscopy Probes both gas phase and solids History of the conditions in the ISM Atomic/chemical inventory throughout Galaxy Variations - star formation history/gas mixing… Need bright background continuum sources ALMA’s sensitivity is key 11/13/2018 AAS Calgary 2006

Where to go for more Information North American ALMA Science Centre Located in Charlottesville Excellent web resources (www.cv.nrao.edu/naasc) Talk to someone from the ANASAC We are interested in your needs/concerns Get a copy of the Science with ALMA brochure Lists wavelength coverage, sensitivity, baselines… Visit and look through the ALMA DRSP A sampling of key projects for ALMA Most Importantly: Start thinking about this NOW! 11/13/2018 AAS Calgary 2006