Jan/2005Interstellar Ices-I1 Interstellar Ices-2 Ice Inventory Protostellar Environments Energetic Processing? Laboratory Simulations New Spitzer Satellite Results Adwin Boogert California Inst. of Technology

Jan/2005Interstellar Ices-I2 Contents – what else is present in interstellar ices, besides H 2 O and CO? – basic chemistry: Are new molecules formed through energetic processes? – complexity in the 5-10  m region – Ice inventory. Where is NH 3 ? – energetic processing diffuse/dense ISM? – Ions in the ices? – Complex CH 3 OH/CO 2 /CO/H 2 O mixtures

Jan/2005Interstellar Ices-I3 A Grain in Space More realistic: 5

Jan/2005Interstellar Ices-I4 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 a 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) 5

Jan/2005Interstellar Ices-I5 Spitzer Spectroscopy of Ices toward Protostars /SVS 4-5 5

Jan/2005Interstellar Ices-I6 Ice Inventory 6

Jan/2005Interstellar Ices-I7 Ice Inventory 6

Jan/2005Interstellar Ices-I8 Ice Inventory [H 2 O and silicate subtracted!] 6

Jan/2005Interstellar Ices-I9 [H 2 O and silicate subtracted!] Ice Inventory 6

Jan/2005Interstellar Ices-I10 NH 3 /CH 3 OH=4 NH 3 /CH 3 OH<0.5 (SVS 4-5) Ice Inventory 6

Jan/2005Interstellar Ices-I11 'Typical' abundances w.r.t. H 2 O ice Factors of 2 abundance variations between sight- lines are common! Note uncertain NH 3 abundance. Will Spitzer spectra finally establish presence of NH 3 in interstellar ices? Ice Inventory COfew-50% CO % CH 4 2-4% CH 3 OH<8, 30% HCOOH3-8% [NH 3 ]<10, 40% (?) H 2 CO<2, 7% [HCOO-]0.3% OCS<0.05, 0.2% [SO 2 ]<=3% [NH 4 + ]3-12% [OCN - ]<0.2, 7% 6

Jan/2005Interstellar Ices-I12 Evidence for Energetic Processing? ● UV/CR processing simple ices in laboratory produces organic residues ('yellow' stuff). ● Problem: no such complex stuff observed in icy sightlines. Much explained by grain surface chemistry and thermal processing of simple ices. ● Selection effect? ● Low infrared sensitivity? ● Better observe sublimated species (more sensitive)-see lecture Cecilia. Greenberg et al. ApJ 455, L177 (1995): launched processed ice sample in earth orbit exposing directly to solar radiation (EUREKA experiment). Yellow stuff turned brown: highly carbonaceous residue, also including PAH. 7

Jan/2005Interstellar Ices-I13 Evidence for Energetic Processing?  3.4 um absorption feature observed in diffuse ISM (e.g. Galactic Center). Triple peaks due to hydrocarbons (-CH, -CH 2, -CH 3 ).  Little evidence production by UV/CR bombardment of ices: *formed in evolved star envelopes, and injected in ISM *band not polarized as opposed to silicates/ices: not in processed mantle but separate grains *3.4 um band observed in dense clouds, but not triple peaked.NH 3 /H 2 O complex (hydrate)? Pendleton et al. 1994, Adamson et al. 1998, Chiar et al. 1998, Chiar et al

Jan/2005Interstellar Ices-I14  Protostellar luminosity unimportant factor in ice formation and processing Low Mass versus High Mass Protostar Noriega-Crespo et al. ApJS 154, 352 (2004) 7

Jan/2005Interstellar Ices-I15  Major solid state band not firmly identified yet.  Observational constraint: band shifts to red for warmer lines of sight  Condition fulfilled by NH 4 + [Schutte & Khanna A&A 398, 1049, 2003].  Corresponding 3.25 and 3.47  m bands  NH 4 + would require NH 3 as well as thermal- or photo-processing  to be continued... Identification: the 6.85  m band 7

Jan/2005Interstellar Ices-I16 Ions in Ices – NH 4 + roughly has spectral characteristics that fit interstellar 6.85  m band. – NH 4 + easily produced by warming acid/base mixture NH 3 +HNCO – also produces OCN -, which has observed feature at 4.62  m and might account for charge balance; further study needed. – In fact, 4.62 um band attributed to CN-bearing species ('XCN') last 15 years and always considered strongest evidence energetic UV/CR processing. Now less likely. H 2 O:CO 2 :NH 3 :O 2 at different T and mixing ratios H 2 O:N 2 :CH 4 after irradiation:   7

Jan/2005Interstellar Ices-I17 Complex CO 2 /CH 3 OH/H 2 O/CO Ice Mixtures H 2 O:CO 2 :CH 3 OH at different CH 3 OH concentrations. Note CO 2 :CH 3 OH complexes. 8

Jan/2005Interstellar Ices-I18 Complex CO 2 /CH 3 OH/H 2 O/CO Ice Mixtures  Weak wing in 2 Spitzer sources consistent with low CH 3 OH abundance derived from other features  Overall width due to H 2 O:CO 2  Bottom of profile indicates apolar CO/CO 2 component  [Boogert et al. ApJS 154, 359 (2004)] 8

Jan/2005Interstellar Ices-I19 Complex CO 2 /CH 3 OH/H 2 O/CO Ice Mixtures 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. 8

Jan/2005Interstellar Ices-I20 Evolution of Ices as Function of Protostellar Stage No obvious evolution of ice abundances [other than evaporation of volatiles] Effects of heating commonly observed: CO ice band, 6.8  m band, CO 2 ice band 8

Jan/2005Interstellar Ices-I21 Evidence envelope heating: CO 2 crystallization (Boogert et al. 2000; Gerakines et al. 1999) H 2 O crystallization (Smith et al. 1989) gas/solid ratio increases (van Dishoeck et al. 1997) Detailed modelling gas phase mm- wave observations (van der Tak et al. 2000) Solid 13 CO 2 : Ice Processing Massive YSOs 8

Jan/2005Interstellar Ices-I22 Solid 13 CO 2 : Ice Processing Massive YSOs Evidence envelope heating: CO 2 crystallization (Boogert et al. 2000; Gerakines et al. 1999) H 2 O crystallization (Smith et al. 1989) gas/solid ratio increases (van Dishoeck et al. 1997) Detailed modelling gas phase mm- wave observations (van der Tak et al. 2000) 8

Jan/2005Interstellar Ices-I23 Evolution of Ices: Conclusions Ice composition evolution with protostellar phase? No (tentatively), but evaporation of volatiles occurs. What causes composition variations between lines of sight? Ice temperature evolution in low mass protostars? Yes. Profiles 6.8 um and 15 um CO 2 band, apolar CO evaporation, H 2 O crystallization. Also in disks. Ice composition influenced by protostellar mass/luminosity? No observational evidence, except possibly CO 2 : new CO/CO 2 ice phase larger CO 2 ice abundance NH 3 : surprisingly large variations between sightlines (tentative) 8

Jan/2005Interstellar Ices-I24 ISO/SWS+LWS  m spectrum Elias 29 (  Oph) with flared face-on disk model (Boogert et al. 2002, ApJ 570, 708).

Jan/2005Interstellar Ices-I25 Ices abundant toward Elias 29: most luminous (30 Lsun) low mass (1-2 Msun) protostar in  Oph cloud [Before drawing conclusions on ice processing, one needs to locate ices along line of sight] Ices in Low Mass YSOs