Terahertz Spectroscopy of Molecules in the Interstellar Medium
- Slides: 56
Terahertz Spectroscopy of Molecules in the Interstellar Medium and around Stars – Sure Bets and Challenges Karl M. Menten Max-Planck-Institut für Radioastronomie 64 th Int. Symp. on Molecular Spectroscopy Columbus, OH, June 23, 2009
Complex molecule formation More complex (organic) molecules form on dust grain surfaces: • While a cloud is cold (T ~ 10 K), molecules (e. g. H 2 CO) freeze out or form on grains altogether. More complex molecules form by addition of further H atoms (“hydrogenation”).
Interstellar Ices • Substantial components: H 2 O, CO 2, CH 3 OH • Minor components: HCOOH, CH 4, H 2 CO • [Solid H 2 O, CO] ~ [gaseous H 2 O, CO]
Evaporation • Once the cloud is heated (e. g. by an igniting protostar or an interstellar shock wave), the grain mantles evaporate, releasing large quantities of complex molecules into the gas phase. • more complex species may be formed given the additional heat during warm-up (Herbst, Garrod, Widicus-Weaver…) formation of “hot molecular cores”. • Metals are released into the gas phase by sputtering of grains (“sublimation”). → high Si. O abundance
Hot core chemistry around protostars revp Van Dishoeck & Blake 1998, ARA&A
Chemical Diversity: The W 3(OH) Region dust free-free (Wyrowski et al. 1999)
CSO, 350 μm continuum, Dowell et all. 1999
IRAM 30 m telescope Sgr B 2 -N “Large Molecule Heimat” 3 mm region (80 – 116 GHz) in 500 MHz chunks 4000 – 5000 lines!!!! 10 minutes per spectrum confusion limit (Belloche, Comito, Hieret, Leurini, Menten, Schilke) With ALMA it will be possible to observe that whole spectral range within 10 minutes to confusion limit
C. Hieret, Diploma Thesis, MPIf. R
Amino acetonitrile
Also found in the Sgr B 2(N) Large Molecule Heimat: ethyl formate C 2 H 5 OCHO Close collaboration with the Cologne Laboratory Spectroscopy Group n-propyl cyanide C 3 H 7 CN Belloche et al. 2009
For lines to be thermalized at a certain temperature, the density must be higher than a critical density. If it is lower, the molecular levels are thermalized at the cosmic microwave background temperature (2. 728 K). ij ~ 1010 cm 3 s-1 (D) (GHz) ncrit(cm-3) CO HCO+ 0. 11 3. 89 n x 115. 5 n x 89 103 (low J) few 105 (low J) NH 3 1. 48 24 – 25 few 103
Complex molecules have relatively small rotation constants (heavy), and huge partition functions (that grow with T). They are easiest observable at “lower” frequencies. Optimally, (perhaps) in 30– 150 GHz range
What is the end of the line when it comes to detecting ever more complex molecules? Molecule identification problem much ameliorated by use of interferometers. ALMA and EVLA will help a lot! Talk by Remijan
A pragmatic way to deal with weeds… Talks by de Lucia, Fortman, Medvedev, …
In addition, targeted lab studies of as many species as possible are desirable Talks by de L-H Xu, Müller, Chen, Brauer, Kiesiel, Tudorie, Margoles, Yu, and others
le b a v r e bs o s e l cu e l o m ot h No r( D=1) > revp r( D=1) < revp r( D=1) = f[ , m. D] revp = f(L*) ( D=1) “somewhere” in the far-infrared – submillimeter range
r( D=1) > r(n > ncrit) r( D=1) < r(n > ncrit) = f(mgas, ) r(n = ncrit) “somewhere” in the far-infrared – submillimeter range
You cannot see molecular emission from within the dust photosphere!
Sgr B 2 In molecules: • (almost) only absorption • only simple species (hydrides, C-chains) • from extended envelope, not from hot core Goicoechea & Cernichao 2004
Why does ISO not see hot core molecules in Sgr B 2? http: //www. ph 1. uni-koeln. de/cgi-bin/cdmsinfo? file=e 032504. cat
Why did ISO not see hot core molecules inis. Sgr B 2? th t bu ! effect • dust photosphere/critical densityo, sphere to s n i k unclear n i h oked t ’t e lo n o • beam dilution? I d ld b u o h s. Herschel ISO 80” (150 m) 20” (300 m) • spectral dilution? ISO LWS Herschel Grating Fabry-Perot max 300 10000 300000
Herschel Mission Overview • ESA Cornerstone Far-IR / Submillimeter mission • Three instruments (PI led efforts) – HIFI - Heterodyne Instrument for the Far-Infrared • 480 -1250 GHz and 1410 -1910 GHz, l/Dl up to 107 • 625 -240 µm and 213 -157 µm, Dv > 30 m/s – SPIRE - Spectral and Photometric Imaging Receiver • 200 -670 µm, simultaneous 3 color imaging photometry • Broadband spectroscopy, 2 arrays, l/Dl ~ 20 - 1000 – PACS - Photodetector Array Camera and Spectrometer • 60 -210 µm 3 -color (2 simultaneous) imaging photometry • Broadband spectroscopy, 2 arrays, l/Dl ~ 1000 • 3. 5 m telescope, ~80 K optics (at L 2); WFE ~6 µm • Size: 7. 5 m x 4 m ; Mass: 3200 kg ; Power: 1 k. W • Absolute / Relative Pointing: 3 / 0. 3 arc-second • Ariane-5 launch May 2009 from French Guyana • Transit to ES-L 2: ~5 months
M 51 Herschel PACS “sneak preview” 160, 100, and 70 μm 2009 June 19 Extensive Herschel guaranteed and open time spectroscopy key programmes Talk by John Pearson
Stratospheric Observatory for Infrared Astronomy (SOFIA)
Talks by Bob Gehrz
Some new species Herschel/SOFIA might find…
3 - 3 C 4 5 or C 4 H 7? Cernicharo et al. 2002
IRC+10216 ISO/LWS Cernicharo et al. 1996
IRC+10216 ISO/SWS Cernicharo et al. 1999
VY CMa ISO/LWS Polehampton et al. 2009
The Big Question: Will dust photosphere or critical density barrier prohibit studies of hot, very dense regions at farinfrared wavelengths? Far-reaching consequences on the scientific program for Herschel and the case for far-infrarede… l g n a space interferometry, and ALMA. g n wi e i v e Not only for high-mass star-forming regions, but h t f o n also, e. g. , for the inner regions io of ultraluminous t s ueaccretion disks/tori. q infrared galaxies ande. AGN a b y a It m
Protostars AD 1982 Willner et al. 1982
The Willner et al. protostars became a bonanza for spectroscopists when ISO came and even before
ISO SWS spectra of hot water ( 2 bending mode) Tex 250 K, 5 10 -6 < X(H 2 O) < 6 10 -5 Boonman & van Dishoeck 2003 Also gas phase SO 2, CO 2: Keane et al. 2001, Boonman et al. 2003
A&A (2006)
T ~ 100 K [H 2 CO/H 2] ~ 10 -7
Submm emission indicates ~20 times lower abundance than IR absorption, but similar temperature
CRIRES/ESO VLT
R ~ 3000 over 5 – 27 μm range
The chemistry around high-mass protostars and in the regions in which they form is remarkably heterogeneous and many observations are still poorly understood. Yet many more systematic observations are needed. Possibly dramatic changes in the chemistry occur during the short-lived contraction and initial burning phases. High resolution radio, (sub)mm, and IR observations and lab spectroscopy are needed to get the “full picture”.
ly d d n e e i d r e f r- ne e s tly u ) n r e e g r m o nu n o tio r t s ida A ( l o s n co
Molecular astronomy is at the verge of a new, grand age of discovery made possible by Herschel, SOFIA, ALMA, and the EVLA at (sub)mm to radio wavelengths along with high resolution nearinfrared spectrometers on large optical telescopes The new opportunities will only be fully exploitable by a large-scale laboratory effort in all these wavelength ranges
Light Hydrides • Optical absorption from CH and CH+ important probe of diffuse interstellar clouds (1937 – 1941, Dunham; Swings & Rosenfeld, Mc. Kellar; Douglas & Herzberg) • Potentially important coolants of the densest regions of the ISM Goldsmith & Langer 1978
T = 70 K
- Terahertz spectroscopy principles and applications
- Interstellar medium ppt
- Interstellar medium
- High-resolution terahertz
- Organic molecules vs inorganic molecules
- What is cold media
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- Diffuse interstellar bands
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- Diffuse interstellar bands
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