Shock-induced Molecular Astrochemistry in Dense Clouds Jeonghee Rho Jeonghee Rho SOFIA Science...
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Transcript of Shock-induced Molecular Astrochemistry in Dense Clouds Jeonghee Rho Jeonghee Rho SOFIA Science...
Shock-induced Molecular Astrochemistry in Dense
Clouds
Jeonghee Rho SOFIA Science Center Universities Space Research Association NASA Ames Research Center, CA Collaborators J. Hewitt (NASA/GSFC), M. Anderson (ESA, ESTEC, Netherland), A.
Tappe (CfA, Harvard Smithsonian), W. T. Reach (SOFIA SMO/NASA Ames), and J. P. Bernard (CNRS, Toulouse)
Interaction with CSM/ISMradiative shock in dense gas
heating, chemistry, dust processing
Massive Stars form in GMC Young adiabatic SNR >8 Msol dies within cloud lifetime
(~40% SNe in the field)expanding in wind cavity
ejecta mixing, dust creation,cosmic ray accel
SNR merges into ISMSuperbubble / Chimney release of cosmic rays
W44, enveloped by a molecular cloudRadiative signatures:• IR-bright => shock cooling in
relatively dense gas (>103 cm-3)• Broad molecular lines (eg. CO 2-1)
Supernova Remnants Interacting with Clouds
Spitzer IRAC color image (Reach, Rho et al. 2006):
Shocked H2 (4.5 μm, green), PAH and dust (8 μm, red)
Reach, Rho, Jarrett (2005)
12CO(2-1), ΔV=40 km/s)
IC 443 : prototype of interacting SNR • Optical, radio are shell-like• X-rays: shell + bright inside• Interaction with clouds: Near-IR H2 image (Burton et al. 1988)
CO broad lines (van Dishoeck et al.)
• 2MASS images: bright K emission (H2) in the southern ridge and J,H emission ([Fe II]) in the northern rim
• H2 lines; 1-0 S(1) in K, 1-0 S(7) in H, 2-1 S(1) in J
(Rho et al. 2001)
[Fe II]
H2
• Spitzer GLIMPSE survey detected 18 IR-bright SNRs
• Colors hint at dominant cooling lines and shock type.
However... Color-typing shows large scatter, even within the same SNR
IR spectroscopy is clearly needed
Supernova Remnants Interacting with Clouds
from Reach et al. 2006
Molecular
Ionic
PAH
Must explain mix of IR lines: H2 S(0)-S(7) [Fe II], [Ne II], [Si II], [S III] PAHs, Dust continuum
• brightest IR clumps in 14 SNRs• long-slit: remove Galactic emission
Hewitt et al. 2009, Andersen et al. (submitted)
Spitzer 5 to 95 μm Spectroscopy
G349.7
Kes 17
IRAC 3-color images
Spitzer IRS SL/LL 5-35μm R~100
Complements IRS mapping 4 SNRs (Neufeld et al.)
• Two H2 components (warm, hot) T(H2)= 320 1150 K OPR = 1.0 3.0● H2 fitting with shock models (Le Bourlot 2002)
VS = 10, 40 km/s nH = 105, 104 cm-3 PS = 1x10-6, 3x10-7 dyne cm-2
over-pressure in warm, dense clumps
Multi-shock fitting:
BEST FIT
H2 Excitation in Kes 69
Rho, Hewitt, Jarrett et al.(in prep.)
H2 Excitation in G348.5-0.0● Spitzer IRS + near-IR with AAT
● H2 2-1 S(1)/1-0 S(1) Ratio [=X] ~ 7
Shock: X=12-15 (IC 443), UV pumping: X=2-4
=> shock + UV pumping (Chang & Martin 1991)
NIR H2 lines
Para-to-ortho H2 conversion via reactions with atomic-H:
τconv ≈ 3000 yrs [100 cm-3/n(H)] EA/k ~ 4000 K
Ortho-to-Para Ratio in Equilibrium
H2 Excitation: Ortho-to-Para
warm H2: OPR ~ 0.4-3equilibrium: OPRLTE ~ 3
Para-to-ortho H2 conversion via reactions with atomic-H:
τconv ≈ 3000 yrs [100 cm-3/n(H)] EA/k ~ 4000 K
Ortho-to-Para Ratio in Equilibrium
H2 Excitation: Ortho-to-Para
warm H2: OPR ~ 0.4-3equilibrium: OPRLTE ~ 3
OPR < 3 in TH2 = 250-600 K requires τshock < τconv
=> slow C-shocks into cold, quiescent clouds; no significant pre-heating of MC
Kes 69
3C396
G346.6
G348.5
G349.7
Kes 17
Excitation of ionic species: Fe+, Ne+, Ne++, Si+, S++
requires VS >100 km/s, ne ~102-3 cm-3
Ionic emission spatially segregated from H2 along the IRS slit. => multiple shocks
Fast, Dissociative ShocksNeon Line Ratio
Good fits obtained for Dust. TBB = 35-50 K
Relative grain abundances: SNRs MW YVSG/BG 0.23-1.0 0.13 YPAH/BG 0.01-0.2 0.004
=> Processing of grain size distribution by SNR shock
Dust Emission from SNRs
IRS SL/LL
MIPS SED
Dust continuum modeling (DUSTEM, Campiegne et al. 2008, Poster #35) Parameters: Big Grains, Very Small Grains, PAHs, and Radiation Field
0.01-0.2 μm 0.001-0.01μm
line-subtracted spectrum
Milky Way Value
VS > 60 km/sVS < 60 km/s
Sputtering efficient for fast shocks,affecting all grain sizes
Shattering in dense/slow shocks,destroys BGs, but not VSG/PAHs
Observe VSG/BG consistent with shattering, increasing with VS
from Borkowski et al. 1995
Dust Processing by SNR shocks
Dust Heating by SNR shocks
fitted ISRF ~ 20-100
Dust continuum is a significant coolant!
Fit Radiation Field, case B H-recomb. (normalized to ISRF)
Milky Way Value
SNRs have even higher UV radiation from H-recomb (fast shocks, [Fe II])
100 LΘ1 L
Θ
10 4 LΘ
Radiative Cooling: SNR/MCs
G349.7
Kes20A
Kes17
LH2 is ~0.6-6% of LDust in SNR/MCs
[O I] 63μm line detected in 10/14 SNRs, L[OI]/LDust ~ 1-7%What are other coolings?
Fermi γ-ray detections of SNR/MCsMaser SNR subset: interaction, distance, cloud mass, n=105 cm-3
• For π0-decay origin (Drury et al. 1994)
Fγ ~ Mcloud dkpc-2 ωCR
• Given Mcloud, dkpc : determines CR ionization rate ζCR ≈ ωCR ζlocal
• Maser SNRs have ωCR ~ 10-50 enhanced over local density
• Significant ionization, >10-16 s-1
Kes69G16.7
12/24 SNRs detected by Fermi
(Hewitt et al. 2011)
enhances n(H,e)/n(H2) in C-shocks
Fermi image of W44
Far-infrared Spectroscopy
• Abundances of Fe: 99% locked in grains => dust vaporized by shocks• Febry-Perot spectrum of [OI] shows resolved broad line V~100 km/s. • H2O, OH, CO lines are detected <= from warm, dense (105cm-3) gas O + H2 => OH (T>400K) OH + H2 => H2O
Fe IIISO
Reach & Rho 1996
[O I] 63μm
[Fe II] 26μm
Water abundance was smaller than expected relative to OH or CO
Herschel/SOFIA Observations of MSNRs• 18 hours of Herschel
time is granted• 3 brightest molecular
interacting SNRs• What is the post-shock
abundance and excitation of water, hydroxyl, CO and atomic oxygen??
• What mechanism produces the observed non-equilibrium oxygen chemistry?
Hershel: PACS, SPIRE, HIFIComplement with SOFIA: GREAT (1hr)
The violent lives of Supernova Remnants
SNR shocks are a spectacular probe of molecular clouds
Future directions
Non-equilibrium chemistry, driven by enhanced ionization and radiation field?Both collisional and radiative coolingChemistry. Water chemistry. Shock-induced molecule cooling and astrochemical processes• Challenges of molecular astrochemistry modeling
• Multiple shocks, through a multi-phase cloud trace thermal history of the cloud (OPR)
• Radiative cooling: dust continuum, IR lines• Enhanced radiation field ~20-100 x ISRF evidenced
by Dust heating, H2 UV excitation• Grain processing: shattering decreases large grain size • Accelerate cosmic rays yielding up to few % ESN
3 km/s
300km/s
SOFIA Observations of Shocks/PDRs
Molecular lines: CO, OH, H2O
Shock cooling, Ionic lines
Dust Sputtering: Fe, Si
[OI] [CII] velocity and mapping
Shock processed PAHs
Maps of dust processing
GREAT GREAT First Light
April 6, 2011
German REceiver for Astronomy at Teraherz Frequencies (GREAT)
PI: Rolf Güsten, MPIfR in Bonn
M17 (Omega Nebula) CO (J=13-12, green) and [C II] (white) spectra
Velocity (x-axis): from -10 to 50 km/s
GREAT Spectral resolution is between 106 and 108.
Efficient Scan mapping capability.
GREAT
OB (yellow) stars, [CII] (green) contours on VLA image (ionizing flux). Inserted CO (J=13-12) image with [CII] contours.
[CII] is ionized gas at the boundary of dense warm CO.
(Perez-Beaupuits, Güsten, and GREAT team, in preparation)
Lee et al. 1996
VLA image
[CII] image
CO (13-12) contours
GREAT
OB (yellow) stars, [CII] (green) contours on VLA image (ionizing flux). Inserted CO (J=13-12) image with [CII] contours.
[CII] is ionized gas at the boundary of dense warm CO.
(Perez-Beaupuits, Güsten, and GREAT team, in preparation)
Lee et al. 1996
VLA image
[CII] image
CO (13-12) contours
Comparison between Herschel and SOFIA far-IR instrumentsPACS
specFIFI-LS HIFI GREAT PACS
imagerHAWC
Wavelength range (μm)
55-210 42-110,110-220
157-213, 240-625
60, 110-125, 156-165, 200-240
55-210 53, 89, 115, 216
Field of View
47’’x47’’ 30’’x30’’60’’x60’’
Single pixel
Single pixel (7 pixels in future)
47’’x47’’ 27’’x72’’, 42’’x112’’, 72’’x192’’,96’’x256’’
Pixel size 9’’ 6’’, 12’’ 13’’, 39’’ 20’’ 9’’ 2.3’’,3.5’’, 6’’, 8’’
Sensitivity 2-5x10-18
Wm-2
100-250mJy
Similar to PACSspec within a factor of 3-5, but efficient mapping
A few to 100 mK
Similar to HIFI with a factor of 2-8, but efficient mapping
2-5x10-18
Wm-2
100-250mJy
60-120mJy
SpectralResolution
2600-5400 (55-72μm)900-3000
1000-5000
1000-107 106-108 2600-5400 (55-72μm)900-3000
None
Current Schedule• GREAT Short Science Flights: April 2011 • FORCAST Basic Science Flights: May to June 2011• GREAT Basic Science Flights: July and September 2011• FLITECAM Verification flights: Aug 2011
Draft AO for 2nd Generation Instruments• Draft AO: http://soma.larc.nasa.gov/SOFIA/sofiapbtelecon_agenda.html• Anticipated proposal announcement: Mid- 2011 (it is coming soon)• Asilomar meeting proceedingshttp://www.sofia.usra.edu/Science/workshops/asilomar.html
Next Science Proposal Call • Fall to Winter 2011, 300 hours observing time: open internationally• FORCAST(w/grism), GREAT, FLITECAM and HIPO are scheduled to be included.• Data Analysis funding is available for US Investigators
W44, enveloped by a molecular cloudRadiative signatures:• IR-bright => shock cooling in
relatively dense gas (>103 cm-3)• Broad molecular lines (eg. CO 2-1)• OH(1720 MHz) Masers (Hewitt et al. 2008, 2010)
Catalog of SNR/MCs (Jiang et al. 2009)• 34 confirmed (24 w/Masers)• 11 probable• 19 possible
64 of 274 Galactic SNRs (~23%) expect ~40% of SNe in field
Supernova Remnants Interacting with Clouds
20cm Radio
Recent Spitzer IR surveys have made the largest contribution(Reach et al. 2006; Hewitt, Rho et al. 2009; Anderson, Rho et al. 2011)
• Spitzer GLIMPSE survey detected 18 IR-bright SNRs
• Colors hint at dominant cooling lines and shock type.
Supernova Remnants Interacting with Clouds
from Reach et al. 2006
Shocks into multi-phase Molecular Clouds
(Chevalier 1999, Cox et al. 1999, Reach et al. 2005)
How to reconcile different IR lines? multiple shocks in a multi-phase medium
What about dust emission?
Dense Clump
Atomic Gas
Dust Heating by SNR shocks
Collisional Heating dominatesthrough collisions with electrons Hcoll ≈ 5.4E-18 a2 ne T3/2 [erg/s]
Radiative Heating dominatesthrough H recomb. emission
[Fe II] emitting gas: ne~100-1000 cm-3, T=5-10x103 K
Above assumes radiative field is = ISRF
SNRs have even higher UV radiation from H-recomb (fast shocks, [Fe II])
Maser-emitting SNRsYoung SNR