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

I. Hydrides: the Herschel legacy

HIFI, PACS, SPIRE: 55-600 µm spectroscopy, R=103-107

Beam 20-47’’

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

ISM Cologne

Sweet results from ALMA

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