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Astrochemistry:some recent results and future directions
RCW120HerschelA. ZavagnoEwine F. van Dishoeck
Leiden Observatory/MPEThanks to many colleagues for input and discussions
Only a few selected results covered here
From clouds to stars and planets
B. SaxtonNRAO
Specific moleculesfound underspecific conditions
Molecule images:
- Chemistry- Probe of physics
Fantastic facilities for astrochemistry
Herschel
VLT
JWSTE-ELT, TMT, GMT >2024
Spitzer
Keck
Rosetta
SOFIA
ALMA: the astrochemistry machine
ESO/NRAO/NAOJ
NobeyamaIRAM 30m
JCMT CSO APEX
Lots of astrochemistry still based on single-dish dataNOEMA, SMA
Fantastic new experimentsand new groups!
Cavity Ringdown Spectroscopy
UHV surface scienceUV plasma
Crossed beam experiments
Spectroscopy He droplets
Outline
See reviews by Herbst & vD 2009, Caselli & Ceccarelli 2012, Tielens 2013special issue of Chemical Reviews 2013
Hydrides as probe of ISM structure C+ → C → CO transition revisited with
high cosmic ray ionization rates Water and high-J CO: importance of
outflow cavities Complex organic molecules: sweet results
from ALMA
Diffuse and translucent cloudsTesting ion-molecule chemistry
Absorption against bright far-IR continuum
Clouds AV ~few mag All molecules in ground
level→simple analysis Precision astrochemistry
(factor of ~2)
Gerin et al. 2010Gerin et al. 2016, ARA&A
Absorption lines
- HF as tracer of H2 column density because of simple chemistry - Constant H2O/H2 abundance of 5x10-8, consistent with simple models
Neufeld et al. 2010, Sonnetrucker et al. 2010Godard et al. 2012Emprechtinger et al. 2012Flagey et al. 2013
Water o/p=3
Surprise: strong OH+, H2O+
OH+, H2O+ must arise in H2 poor phase (H/H2~10) OH+, H2O+ constrain ζ
Ossenkopf et al., Benz et al., Bruderer et al., Gerin et al., Wyrowski et al., Gupta et al., Schilke et al.,Lis et al. 2010; Neufeld et al. 2012, de Luca et al. 2012, Indriolo et al. 2013, Monje et al. 2013....OH+ detection with APEX Wyrowski et al. 2011
Lis et al.
Ossenkopf et al.Benz et al.
Cosmic ray ionization rates
Indriolo et al. 2015
Red: denser materialassociated withcontinuum source
Chemistry probes lower energyCosmic Rays
First interstellar noble gas molecule!Probe of pure H I gas
Barlow et al. 2013Herschel-SPIRE
Crab nebulaHubble+ Herschel
36ArH+
Schilke et al. 2014Herschel-HIFI Sgr B2
J=1-0
Implies H/H2~104
Large scale hydrosimulations shouldreproduce columnsof ArH+, OH+, ...
Probing H/H2 with hydrides
Neufeld & Wolfire 2016
Test of hydro simulations: reproduce observed columns of these hydrides
II. C+-C-CO transition
Tielens & Hollenbach 1985
N/N2
N2, 14N15N: Li, Heays et al. 2013, 2014CO and isotopologues: Visser et al. 2009
Hollenbach & Tielens 1997
CO vs H2 column density
N(H2) (cm-2)
Obs trends
CH+ + Osuprathermal channel
- At low AV, formation of CH+ through superthermal chemistry of C+ + H2 needs to be invoked to fit observations CO in diffuse clouds
Visser et al. 2009Sheffer et al. 2008
Obs limit
Column densities with NH or AV
⇒Increase in CO/H2 at AV=1-2 mag from 10-7 to 10-4
Exact location and sharpness transition depend on IUV, nH, elemental abundances Presence of PAHs, chemistry details (S), ζ, grain details, geometry….
CO darkgas
vD&Black 1988vD 1990Wolfire et al. 2010
Translucentclouds
CO poor CO rich
Most of gas is in structures close to critical column density
Star-forminggas
P(η)
Schneider et al. 2012,2013Peretto et al. 2012
Probability functionof column densitiesin clouds(based on dust)
C+→ CO
C+-CO-H2 with metallicity
Fraction of molecular gas not traced by CO = f DG increases with decreasingmetallity (provided that cloud size/structure stays the same)
e.g., Pak et al. 1998, Wolfire et al. 2010, Bolatto et al. 2013
Multi-D, coupling with hydro
Lots of recent activity Issues UV radiation field at any point in grid Shielding columns at each point (geometry!) Minimal H2 and CO chemistry Importance of time dependence!
Propagation FIR cooling lines
Glover & MacLow 2007, Dobbs et al. 2008, Glover et al. 2010, Bisbas et al. 2012,Glover & Clark 2012, Offner et al. 2013, Smith et al. 2014, Gong & Ostriker 2016,......
CO
[C II][C I]
Galaxy-scale simulations
Smith et al. 2014
-fDG=0.42 MW galaxy vs ~0.3 observed GOTC+ (Pineda et al. 2013)- fDG much higher for lower surface density
Turbulent cloud exposed to high cosmic ray rateζ= 1 10 100 1000x Galactic
Bisbas et al.2015, 2017Glover & Clark 2016
H2
H
CO
C
C+
disappears
stays!
increases
10x10pc cloud
[C I] as tracer of H2
H2
H
C
C+
CO
Most of star-forming galaxies at z~2 may be at ζ’=100
Bisbas et al.2017
Temperature dependence CO
Related to O + H+ → O+ + H reaction ∆E=226 K
100 K
50 K
20 KBisbas et al. 2017Bialy & Sternberg 2016
III. Water and high-J COWater In Star-forming regions with Herschel
~70 papers, initial summary in van Dishoeck et al. 2011, PASPBergin & van Dishoeck 2012, van Dishoeck et al. 2013, Chem. Rev. , 2014, PPVI
Ringberg, January 2013
~80 sourcesLow to highmass
Doubled withOT
www.strw.leidenuniv.nl/WISH
Bulk of water is formed on grains
Based on laboratory data Cuppen et al. 2010
Ice formation starts in clouds with AV> 1 mag
Movie posted at www.strw.leidenuniv.nl/WISH
Water in low-mass protostars
Kristensen, et al. 2010, 2012Mottram et al. 2014, 2017
outflow
Absorption in outer envelope
NGC 1333p-H2Oground-state Line: 1 THz
L~20 LSunD~750 lyr
Broad lines: outflow dominates, even for H218O
Outflows, jets → Shocks
Nisini et al. 2010, 2014
Water traces ‘hot spots’ where shocks dump energy into cloud
Hot H2O, OH in low-mass protostars
COH2OOH
Herczeg et al. 2012
All lines assigned to 4 species, from levels up to several thousand K
NGC1333IRAS4BPACSSpectral scan(continuumsubtracted)
L=4.4 LSund=235 pc
Importance of outflow cavity
Hot coreCompact (~200 AU) regionwhere H2O ice evaporates
OutflowsExtended emission alongoutflow; H2O enhanced in shock
0.05
pc
~ 1’
Dominates Herschel emissionDominates ALMA H218O emission
Spitzer image from Velusamy et al. (2007)
Models: Visser et al. 2012Observations: Karska et al. 2013, 2015
OH/H2O higher than expected from shock models → UV irradiated shocks (M. Kaufman 2017)
UV-irradiated outflow cavity walls: ‘feedback’
Herczeg et al. 2012Goicoechea et al. 2012Manoj et al. 2013: HOPSGreen et al. 2013: DIGIT
Universal CO ladders
IV. Complex organic molecules
Full inventory with Herschel, IRAM, .... Complex molecules found at all stages: in pre-stellar cores,
protostars, shocks, disks Pre-stellar cores: Bacmann et al. 2012, Vastel et al. 2014
Shocks: Arce et al. 2008, Codella et al.
Disks: CH3CN Öberg et al. 2015; CH3OH Walsh et al. 2016 ALMA
New era with ALMA ALMA can image each line Sensitivity to more complex species Sensitivity to solar-mass protostars, not just Orion-like
Detection of branched molecules‘branching out’
Such side chains are characteristics of amino acidsBelloche et al. 2014EMOCA survey
First chiral molecule!
McGuire, Carroll, Blake et al. 2016Science June 14 Note: not yet possible to measure
left/right ratio, need polarized lightGBT, ATCA
IRAS16293-2422
The ALMA PILS surveyO
phiu
chus
d=1
25 p
c lo
w-m
ass s
tar-
form
ing
regi
on
NASA/WISE
60 AU
IRAS 16293-2422 low-mass protobinary starALMA: 0.4-3 mm
Protostellar Interferometric Line Survey (PILS)
Source BFace-on disk
Source AInclined diskPineda et al. 2012
Oya et al. 2016
Jes Jørgensen
Detection of ‘sugar’ near solar-mass protostar
ALMAIRAS16293 B
Jørgensen et al. 12
Complex molecules found on solar system scales!(orbit of Uranus, 25 AU)
Previous limit
150AU Band 9, 0.2’’
6 glycolaldehyde lines in Band 6 and 7 lines in Band 9 identified; Tex=300 K
IRAS16293d=125 pc
Glycolaldehyde discovery(Jørgensen+ 2012)
Full spectral survey of IRAS 16293–2422
Jørgensen et al. 2016
IRAS 16293-2422Glycolaldehyde and ethylene glycol confirmed
Jørgensen et al. 2016Other sources:
Lykke et al. 2015, Coutens et al. 2015,Taquet et al. 2015, Rivilla et al. 2016,
de Simone et al. 2017
Band 9 image: 0.5’’ source size
B
Baryshev et al. 2015
- EG/GA ~1 vs 5-15 high mass protostars(but range of values)
- Ratio consistent with lab experiments- Very high deuteration
Sweet spot
Increasing complexity
• Examples: detections of acetone, propanal and ethylene oxide –previously only seen toward SgrB2(N) and selected hot cores.
• Isomers important tests for chemical models/lab. experiments. For example, observed ratios between these isomer pairs not well-reproduced in models (Garrod+ 2013; Occhiogrosso+ 2014). Physics or chemistry?
Lykke et al. 2016
Scenario complex molecules formation
0th generation: cold ices: CO → CH3OH + ?1st generation: warm ices, radicals mobile: more complex organics2nd generation: high-T gas-phase chemistry
Herbst & vDARA&A 2009
Visser et al. 2009
Conclusions• New insight on H/H2 from hydrides• CO vs C or C+ as tracer of H2
• Star formation and feedback– H2O, hydrides as tracers of shocks, UV– Snowlines (CO, H2O)→ temperature– COM story still unfolding → hot core,
young disks– Quantitative vs qualitative information
• Future: imaging physical components: ALMA, JWST