Challenges for the Study of Hot Cores with ALMA: NGC 6334I Crystal Brogan (NRAO/North American ALMA Science Center) Collaborators: Todd Hunter (NRAO) Remy Indebetouw (UVa/NRAO), Ken (Taco) Young (CfA), Karl Menten (MPIfR), Henrik Beuther (MPIfA) From Data Cubes to Science: Advanced Tools for ALMA, Koln Oct. 5 2009
The NGC6334 Star Forming Complex 25 = 15 pc SCUBA 850 µm I(N) I GLIMPSE 3.6 µm 4.5 µm 8.0 µm Distance ~ 1.7 kpc NGC 6334 I luminosity 3x105 L, I(N) two orders of magnitude less Based on IR, I(N) is probably less evolved than I 2
NGC6334I 1.3mm SMA Continuum: Warm Dust Resolution: 10,000 AU 0. 8 x 0. 4 1400 x 700 AU NGC 6334 I Peak Velocity (km/s) 6 = 10,000 AU CO(2-1) 3.6 cm continuum (ionized gas) + H2O masers 1.3 mm 3.6 cm 6.7 GHz methanol masers (Norris et al. 1993) 3
Hot Cores around Massive Protostars Van Dishoeck & Blake (1998) 1 = 10 16 cm (1,000 AU) at 1kpc Dust grain ice mantles melt High temperature combined with newly liberated atoms and molecules drive copious organic chemistry Can only be observed at small spatial scales (beam dilution) 4
Now That s a Hot Core! Brogan et al. in prep. Line-to-continuum ratio: 18% at 225 GHz 14% at 340 GHz 30% of lines in both bands are unidentified Similar to SgrB2 except notable weakness of Sulfur bearing molecules 5
Line Comparison: SMA1 SMA2 SMA4 1.3 mm Remarkable chemical variation between SMA1 and SMA2, only 4000 AU apart Why is SMA 4 line-free? Is it in a pre-hot core stage? 6
Line Emission Probes Physical Conditions CH 3 CN K Lines of the same J lie close together in frequency J J=(12-11) As K increases so does the temperature of the transition High dipole moment means only excited at high density (> 10 5 cm -3 ) K Chen et al. (2006) 7
CH 3 CN Integrated Intensity Velocity CH 3 13 CN Zooming in on SMA1 and SMA2: Morphology vs. line excitation temperature suggests central heating But isotopologue reveals that low transitions are also very optically thick CH 3 CN (K=2): τ SMA1 =90 τ SMA2 =50 For both sources T b (K=2) =80 K Probably requires 2-temp model, uniqueness? SMA1 shows consistent SE/NW velocity gradient 8
Blended Various organic species Note widely different distributions and kinematics 9
SMA1 Velocity Gradient = Disk(ish) Rotation? H 2 O masers ΔV= 21 km/s CH 3 CN (k=8) ΔV= 10 km/s IF we assume Keplerian rotation and the full velocity width, the enclosed mass is ~ 20-40 M T dust (K) M gas (M ) SMA1 85-150 45-13 For this range of T dust the dust optical depth is 0.5 1 at 1.3mm! 10
Kinematics from 850 µm Lines (our highest resolution) In 850 μm data: No lines peak on SMA1 or SMA2 continuum peak continuum opacity is simply too high Beam 0.5 x 0.3 (850 x 510 AU) 11
Dust emission from NGC 6334 I (Beam 0.8 x 0.4 ) It is crucial to observe with high spectral resolution to remove the lines! α +2.7 1.3 mm 870 µm α +3.4 10,000 AU α +1.9 α -0.3 Higher frequency = increased Flux ν 2 to 4 Dust emissivity β = α - 2 thick thin Result: Optical depth or composition of dust varies from source to source. For T dust =125 K, τ dust ~ 1 at 870 μm 12
Summary and Conclusions High resolution observations of protoclusters reveal: Multiple dust cores with separations of ~ 1,000-10,000 AU Confusion is severe and relative velocities between protocluster members can mimic rotation at low angular resolution A range of evolutionary states The copious line emission is a powerful probe of the physical conditions: NGC6334I Kinematics; Temperature; Mass; Chemistry Inner disk regions subject to absorption from high continuum opacity longer wavelengths the key for innermost regions ALMA will improve resolution and spectral sensitivity ~25x EVLA essential to probe optically thick inner disk regions Herschel & Sofia: far-ir SEDs Need simultaneous of analysis of: Chemistry, Kinematics, 3-d line radiative transfer including continuum opacity! Desperately need better tools to make sense of massive YSOs 13
Extra slides 14
More Complex Molecules Trace Hot Spots and working surfaces CO(3 2) 15
How Do Observations Compare with Theory? Resolution 0.5 x 0.3 (850 x 510 AU) Represents current state of the art: morphology appears more complex than simple disk Recent simulations suggest that massive accretion disks will NOT be axisymmetric, and may show spiral arm structure Morphology will be complex ALMA simulation of spiral disk at 0.5 kpc in CH 3 CN (K=0) (Krumholtz, Klein, & McKee 2007) 16