1. 15/Oct/2010 1 Univ. Minnesota Seminar Interstellar Ices Adwin Boogert IPAC, Caltech, Pasadena Collaborators: Jean Chiar (SETI) Amanda Cook (Ames) Tracy Huard (Maryland) Claudia Knez (Maryland) Klaus Pontoppidan (Caltech) Ewine van Dishoeck (Leiden) Geoff Blake (Caltech) Sandrine Bottinelli (Toulouse) Karin Oberg (Harvard) Leen Decin (Leuven) Xander Tielens (Leiden)

2. 15/Oct/2010 2 Univ. Minnesota Seminar Contents ● Introduction: Formation of Molecules ● Sample Selection and Observations ● Ices in Quiescent Cloud Material Deriving “High Resolution” Extinction Law ● Ices toward YSOs ● Special Case: Ices toward IC 1396 ● Herschel/HIFI Observations of Hot Cores/Corinos ● Conclusions

3. 15/Oct/2010 3 Univ. Minnesota Seminar Introduction: Molecule Formation in Space Gas phase chemistry Ion-neutral reactions orders of magnitude faster than neutral-neutral. Grain surface chemistry freeze out at T<100 K Physisorption, chemisorption, tunneling. Very efficient way to form molecules! In dense clouds much more efficient than gas phase chemistry. “Grain surfaces are the watering holes of astrochemistry where species come to meet and mate.” (Tielens 2005) Thermal processing of ices e.g. acid-base chemistry: NH 3 +HNCO --> NH 4 + + OCN - Energetic processing ices Long exposure to photons or particles can form very complex molecules, incl. amino acids and PAHs.

4. 15/Oct/2010 4 Univ. Minnesota Seminar More realistic: Gas phase chemistry often insufficient to explain observed abundances, and grain surface catalysis required (e.g. Bates & Spitzer ApJ 113, 441, 1951) ● Ices are the main reservoir of volatile species (except H 2 ) Introduction: a Grain in Space

5. 15/Oct/2010 5 Univ. Minnesota Seminar Introduction: the Molecular Universe Molecule formation and destruction takes place in variety of environments with different physical conditions, leading to different chemistries and molecular inventories. Bill Saxton (NRAO/AUI/NSF)

6. 15/Oct/2010 6 Univ. Minnesota Seminar Introduction: Main Questions Astrochemistry Astrochemistry studies molecules anywhere in the universe: how are they formed? how are they destroyed? how complex can they get ? how does molecular composition vary from place to place? use them as tracer of physical conditions (temperature, density)? how are molecules in space related to life as we know it (astrobiology)?

7. 15/Oct/2010 7 Univ. Minnesota Seminar Introduction: Observing Ices (Boogert, Hogerheijde & Blake, ApJ 568,761, 2002) Ices observed by vibrational transitions. Bands broader than gas phase lines. Profile modified by dipole interactions: contains much information!

8. 15/Oct/2010 8 Univ. Minnesota Seminar Introduction: Laboratory Simulations ● Chemical processes occurring in space can be simulated in laboratory at low T (>=10 K) and low pressure. ● Thin films of ice condensed on surface and absorption or reflection spectrum taken. ● Temperature and irradiation by UV light or energetic particles of ice sample can be controlled. ● Astrophysical laboratories: Leiden, Catania, NASA Ames/Goddard, Paris Gerakines et al. A&A 357, 793 (2000)

9. 15/Oct/2010 9 Univ. Minnesota Seminar Introduction: Laboratory Simulations Absorption width, peak position, shape determined by ice composition and temperature (and grain shape) Example: H 2 O:CO 2 :CH 3 OH=1:1:1 heated. Double peak characteristic for pure CO 2 appears after H 2 O crystallization. CO 2 ice heating heating observed toward YSOs

10. 15/Oct/2010 10 Univ. Minnesota Seminar Greenberg et al. ApJ 455, L177 (1995): launched processed ice sample in earth orbit exposing directly to solar radiation (EURECA experiment). Yellow stuff turned brown: highly carbonaceous residue, also including PAH. Complex species formed, some are of biological interest: POM (polyoxymethylene, -(CH 2 -O)n- HMT (hexamethylenetetramine, C 6 H 12 N 4 ) Amino acids (glycine) Urea (H 2 NCONH 2 ) PAHs (polycyclic aromatic hydrocarbons) Introduction: Energetic Processing

11. 15/Oct/2010 11 Univ. Minnesota Seminar H2OH2O CO 2 silicates H2OH2O NH 4 + H2OH2O H2OH2O silicates CO 2 Observing Ices Star-forming dense core Foreground cloud(s) Ices form anywhere T few magn. envelope outflow disk star Background star

12. 15/Oct/2010 12 Univ. Minnesota Seminar Source Selection Background stars selected using broad-band 2-25 μm colors from c2d catalogs. Extinction determined for many background stars, assuming average, intrinsic stellar colors (“NICE” method). L 1014; A V =2-35; 20” resol; Huard et al. (ApJ 640, 391, 2006)

13. 15/Oct/2010 13 Univ. Minnesota Seminar Ices toward Background Stars YS O Background Star Isolated core L 1014; A V =2-35; Huard et al. 2006, ApJ 640, 391, 2006

14. 15/Oct/2010 14 Univ. Minnesota Seminar Observations ● Initial survey: ● Spitzer legacy program 'From Molecular Cores to Planetary Disks' (c2d; PI N. Evans) ~20h for IRS spectroscopy of ~50 known YSOs and ~15 background stars in clouds and isolated cores ● Follow-up surveys of targets identified in c2d 1-80 mm mapping programs: ● GO2, Boogert et al.: 30 YSOs and 33 BG stars in 26 isolated cores, 29h ● GO4, Knez et al.: ~90 BG stars in Perseus, Lupus, and Serpens, 40h ● GO4+GTO, Huard et al.: ~60 BG stars in 5 isolated cores, ~25h ● Observations motivated by ices, but also by extinction law and dust (silicates) studies, e.g. A K /  9.7 relation. ● Large clouds and isolated cores well-covered ● Some cores observed in dense-grid of background stars, for local studies

15. 15/Oct/2010 15 Univ. Minnesota Seminar Ices toward Background Stars Continuum determination BG stars critical step in analysis. c 2 minimization includes: ● Spectral type: CO overtone (K-band spectra) CO fundamental (5.3 mm/IRS) SiO (8.0 mm/IRS) ● Stellar models (MARC; Decin et al.) ● Extinction laws ● Silicates model ● L-band spectra (H 2 O ice) ● H 2 O ice model ● 1-25 mm photometry CO 2 H2OH2O silicates H2OH2O NH 4 +

16. 15/Oct/2010 16 Univ. Minnesota Seminar ● Broad-band extinction law flattens at 3-10 mm in dense clouds (A V >5 mag).... well fitted by theoretical curve for larger grains (R V ~5.0) Roman-Zuniga et al. ApJ 664, 357 [2007] Lutz et al. A&A 315, L269 [1996] Indebetouw et al. ApJ 619, 931 [2005] Weingartner & Draine ApJ 548, 296 [2001] ● Inclusion 23 mm MIPS point: extinction flat or even increasing toward longer wavelengths. Chapman et al., ApJ 690, 496 [2009] ● Broad-band extinction laws include dust and ice features, while for background stars we need separate continuum-only extinction law...... Ices toward Background Stars Extinction Law

17. 15/Oct/2010 17 Univ. Minnesota Seminar Derive high resolution extinction law, separating features from continuum. Assumptions: ● Spectral type (M1 III) ● Stellar model (Decin et al. ApJS 154, 408, 2004) ● J, H, K extinction is standard power law (e.g. Indebetouw et al.) Ices toward Background Stars Extinction Law

18. 15/Oct/2010 18 Univ. Minnesota Seminar ● 'High' resolution extinction law confirms significant 'continuum' extinction beyond 10 μm ● Much extinction due to features ● Featureless extinction law derived by subtracting laboratory and calculated silicate and ice spectra ● Fits most lines of sights in different isolated cores well. Ices toward Background Stars Extinction Law

19. 15/Oct/2010 19 Univ. Minnesota Seminar Ices toward Background Stars H2OH2O H2OH2O H2OH2O silicates CO 2 ? Red: M1 III model and featureless extinction curve at A K =1.5 magn Green: H 2 O ice and silicate model added

20. 15/Oct/2010 20 Univ. Minnesota Seminar Ices toward Background Stars Using accurate continuum: ● Significant absorption between 5-8 mm not H 2 O ● In small isolated cores and cluster- forming clouds Consequence: ● Responsible species produced prior to star formation, i.e. no YSO processing needed! Questions: ● Which molecules? ● Grain surface or Cosmic Ray induced chemistry? Red is H 2 O ice at 10 K

21. 15/Oct/2010 21 Univ. Minnesota Seminar Ices toward Background Stars 5-8 m m region home to C=C, C=O, C=N stretch and C-H and OH bend modes. Look at other wavelengths to constrain this Allamandola (1984)

22. 15/Oct/2010 22 Univ. Minnesota Seminar Ices toward Background Stars Discovery of solid CH 3 OH in quiescent clouds. CH 3 OH/H 2 O~7% Taurus MC has CH 3 OH/H 2 O < 1% (Chiar et al. ApJ 472, 665, 1996), so formation rates vary with environment.

23. 15/Oct/2010 23 Univ. Minnesota Seminar Ices toward Background Stars ● CH 3 OH/H 2 O=7% contributes just a bit to 5-8 mm absorption ● Contrasts to early KAO studies attributing most 5-8 mm absorption to H 2 O and CH 3 OH (Tielens et al. ApJ 287, 697 1984): H2OH2O CH 3 OH

24. 15/Oct/2010 24 Univ. Minnesota Seminar Ices toward Background Stars Abundance reproduced by Monte Carlo simulations of H atoms reacting with frozen CO, i.e. at T<16 K (Cuppen et al. A&A 508, 275, 2009) Taurus MC has CH 3 OH/H 2 O<1%. Perhaps lower atomic H/CO ratio? CO and CO 2 only other species identified in background star spectra. When mixed with H 2 O, they have some effect on the 6.0 m m band. Still, not all remaining 5-8 m m absorption explained. Other grain surface chemistry products: H 2 CO, HCOOH, NH 3. See YSO discussion.

25. 15/Oct/2010 25 Univ. Minnesota Seminar Ices toward YSOs ● Continuum determination much tougher problem for YSOs compared to background stars. ● Optical depth spectra were created, using global smooth continuum. ● Same absorption bands as for background stars are seen.

26. 15/Oct/2010 26 Univ. Minnesota Seminar Independent determination HCOOH.... and NH 3 and CH 3 OH columns Ices toward YSOs: 5-8 mm Complex

27. 15/Oct/2010 27 Univ. Minnesota Seminar Ices toward YSOs: 5-8 mm Complex Fair fraction 5-8 μm absorption is complex blend of simple species, formed at the quiescent cloud phase, i.e. prior to star formation CH 3 OH/H 2 O 1-30% HCOOH/H 2 O 3-8% NH 3 /H 2 O 5-10% H 2 CO/H 2 O 6% HCOO - /H 2 O 0.3% [CH 4 /H 2 O 2-4%]

28. 15/Oct/2010 28 Univ. Minnesota Seminar Ices toward YSOs: 6.85 mm Band Toward YSOs, profile 6.85 m m band varies dramatically

29. 15/Oct/2010 29 Univ. Minnesota Seminar Ices toward YSOs: 6.85 mm Band ● YSOs with 'red' 6.85 μm bands have low H 2 O ice abundances, i.e. 'warm' lines of sight. ● For massive YSOs confirmed by warm gas temperatures and ice crystallization ● 6.85 μm band shows evidence of ice processing

30. 15/Oct/2010 30 Univ. Minnesota Seminar Which species.... ●...has absorption band at 6.85 μm that shifts to longer wavelengths when heated? ●...does not survive in diffuse ISM? ●...is less volatile than H 2 O? Ices toward YSOs: 6.85 mm Band

31. 15/Oct/2010 31 Univ. Minnesota Seminar Ices toward YSOs: 6.85 mm Band NH 4 + has spectral characteristics that fit interstellar 6.85 μm band: ● easily produced by 'warming' acid/base mixture NH 3 +HNCO, forming a salt (T~10 K; Raunier et al. A&A 416, 165, 2004) ● Subsequent heating shifts band to longer wavelengths Is HNCO sufficiently available? Alternative formation route: ● UV irradiation H 2 O:CO 2 :NH 3 :O 2 also produces NH 4 + (Schutte & Khanna A&A 398, 1049, 2003). Could Cosmic Rays in dense clouds have same effect? Needs modeling. UV-irradiated heate d

32. 15/Oct/2010 32 Univ. Minnesota Seminar Ices toward YSOs: 6.85 mm Band IC 1396A very different environment. Globule blasted by nearby O-star. May well be more realistic early solar system analog than for example Taurus YSOs. IC 1396A very different environment. Globule blasted by nearby O-star. May well be more realistic early solar system analog than for example Taurus YSOs (Reach et al. 2009, ). Reach et al. 2009, ApJ 690, 683

33. 15/Oct/2010 33 Univ. Minnesota Seminar Ices toward YSOs: 6.85 mm Band Indeed, very 'red' 6.85 μm band AND low H 2 O ice abundance in highly processed globule IC 1396A. Confirms carrier 6.85 μm band affected by processing.

34. 15/Oct/2010 34 Univ. Minnesota Seminar Ices toward YSOs ● blend of absorptions by simple species (CH 3 OH, HCOOH, NH 3, H 2 CO, CO 2 ) in addition to H 2 O explains much but not all 5-8 mm absorption. Likely grain surface chemistry products from preceding quiescent cloud phase. ● NH 4 + 'salts' produced by acid-base chemistry at low T, at the quiescent cloud phase. ● signatures of ice heating: sublimation and crystallization ● energetic processing (UV, CR) may be responsible for some absorption in 5-8 μm. Modeling physical conditions (radiation fields, disk inclination, disk/envelope ratio) required. ● Abundance of complex molecules produced on the grains may be too low to be detectable by infrared absorption studies.

35. 15/Oct/2010 35 Univ. Minnesota Seminar Next: Hot Cores/Corinos ● (sub)millimeter-wave gas phase measurements orders of magnitude more sensitive to abundances than IR ice observations ● indirectly trace the ice mantle composition in hot cores/corinos Cazaux et al. 2004

36. 15/Oct/2010 36 Univ. Minnesota Seminar 480-1916 GHz (625-157 mm) Resolving Power /  up to 10 million, or <0.1 km/s (de Graauw et al. A&A 518, 6, 2010) Next: Herschel/HIFI

37. 15/Oct/2010 37 Univ. Minnesota Seminar Next: Herschel/HIFI ● Herschel launched (together with Planck) on 14 May 2009 ● Liquid He will last till end 2012 ● 3 instruments: ● PACS (70, 100, 160 mm photometer and integrated field spectrometer) ● SPIRE (250, 350, 500 mm photometer and fourier transform spectrometer) ● HIFI (480-2000 GHz heterodyne spectroscopy) ● Performance Verification ended October 2009, except HIFI ● HIFI switched to redundant side in January 2010 after LCU failure

38. 15/Oct/2010 38 Univ. Minnesota Seminar Next: Herschel/HIFI DR 21 mass star formation region (Cygnus)

39. 15/Oct/2010 39 Univ. Minnesota Seminar ● CHESS key program (PI C. Ceccarelli) makes full spectral surveys of YSOs at <1 km/s resolution ● Where are the complex molecules? ● Have to be able to separate flowers (amino acid,...) from the weeds (CH 3 OH,...)! Next: Herschel Emprechtinger et al. A&A 521, L28 (2010) H 2 O 1 10 -1 01 557 GHz NGC 6334 I Ceccarelli et al. A&A 521, L22 (2010)

40. 15/Oct/2010 40 Univ. Minnesota Seminar ● Routine Phase observations ongoing ● Results Open Time proposals announced Nov 2010 ● Next Open Time call Feb 2011 ● Data analysis workshop March 2011 ● US astronomers: for questions on proposals, funding, data analysis help, please contact the NASA Herschel Science Center: http://www.herschel.caltech.edu/ Next: Herschel Combined PACS (70, 160 m m) and SPIRE (250, 350, 500 m m) image of Galactic plane.

41. 15/Oct/2010 41 Univ. Minnesota Seminar Conclusions/Future Work ● To first order, same ice features, abundances, and variations thereof for low and high mass YSOs, and background stars. ● 5-8 μm region shows complex absorption from at least 8 different carriers. Much can be explained by simple species (H 2 O, HCOOH, H 2 CO, NH 3, CH 3 OH, CO 2 ), likely grain surface chemistry products. ● Any differences between low and high mass YSOs and background stars explained by thermal processing. ● Identification still issue, especially for 6.85 μm band. 'Salts' are promising, especially NH 4 +. Strongly affected by heating around YSOs. ● “High resolution extinction law” derived from background stars confirms flat law up to at least 25 μm (extinction at 25 mm is half that of 2.2 mm!). ● Sub-millimeter observations of YSOs indirectly trace ice mantle composition: more sensitive searches for complex molecules with Herschel/HIFI underway

42. 15/Oct/2010 42 Univ. Minnesota Seminar Initial results: YSOs (Boogert et al., ApJS 154, 359, 2004); 2 YSOs Background stars (Knez et al., ApJL 635, 145, 2005); 3 BG stars Edge-on disk (Pontoppidan et al., ApJ 622, 463, 2005); 1 YSO Survey papers: I: H2O and the 5-8 m m bands (Boogert et al., ApJ 678, 985, 2008); ~40 YSOs II: CO2 (Pontoppidan et al., ApJ 678, 1005, 2008); ~40 YSOs III: CH4 (Oberg et al., ApJ 678, 1032, 2008); ~40 YSOs IV: NH3 (Bottinelli et al., ApJ 718, 1100, 2010); ~40 YSOs Background Stars behind Isolated Cores (Boogert et al., subm. to ApJ); ~30 BG stars Publications So Far