Complex and Pre-Biotic Molecules in the ISM CH3CHO Héctor G. Arce NSF Astronomy and Astrophysics Postdoctoral Fellow American Museum of Natural History C2H4(OH)2 Ethylene glycol
Hayden Planetariuma source of inspiration for NYC youth Old Hayden Planetarium New (since 2000) Rose Center for Earth and Space and Hayden Planetarium Some scientist that were inspired by Hayden Planetarium: Carl Sagan, Steve Weinberg, Brian Green, Neil deGrasse Tyson (current director of Planetarium)
Arecibo Observatorya source of inspiration to PR youth Angel Ramos Foundation Visitor Center Arecibo Observatory These two facilities provide: • Research opportunities to university students • Expose grade-school students and general public to science • Inspiration for young Puerto Ricans to go into science/engineering career
Congressionally-mandated CEOSE The Committee on Equal Opportunities in Science and Engineering (CEOSE) was established to addressthe problem of diversity in the Science, Technology, Engineering, Math (STEM) workforce in the USA. [see 42 U.S.C. §1885(c) SEC 36(a)]. In latest biennial report the CEOSE indicates: “While there has been some increase in the number of female and minority graduate STEM students, the prevailing numbers of those receiving a Ph.D. are still low…” CEOSE recommends: • That over the next two years NSF assess the outcomes of its programs, investments, and activities with respect to their impact on broadening participation and transforming institutions, and use the results to optimize policies and programs • NSF should ensure that major new initiatives and programs … are created to be fully inclusive, enabling participation in their development,implementation, and funding of persons traditionally underrepresented in STEM, persons with disabilities, and institutions that serve these populations. Closing AO goes against congress’s and NFS’s goal of broadening the participation of underrepresented minorities in STEM fields. Also, in Senior Review: “Astronomy has a proud record of attracting under-represented minorities into science. Any facility closures will likely impact the E/PO component of astronomy and this should be considered along with the science impact.”
Studying molecules in ISM CH3CHO Understanding physical and chemical processes in ISM: • Detection and identification of complex molecules in different environment (e.g., cold clouds, PDRs, diffuse clouds, etc.) provides critical information for understanding the possible formation (and destruction) pathways of these molecules • Constraining chemical models. • Can be used to study evolution of clouds and the star formation process. • Long carbon chain molecules (e.g., PAH’s) play a major role in ISM physics and chemistry Implications to life on Earth: • Some of the complex molecules found in the ISM are large pre-biotic organic molecules, thought to be important to life. • It is possible that chemical processes in the interstellar medium provide the essential material that allowed the emergence of life. C2H4(OH)2
Image courtesy of NRAO/AUI Formation Mechanisms 1) Cold gas-phase processes - in envelopes of evolved stars and dark clouds. These reactions give rise to long carbon chains and ring-structured molecules 2) Grain surface chemistry - atoms accrete into dust grain and react with existing molecules, forming larger molecules. 3) Gas-phase processes in warm gas - icy dust mantles evaporate liberating molecules into gas phase, these molecules then react in the warm gas to form more complex species. C2H4O
Hot Cores Dense regions (n~107 cm-3) and compact (~0.1pc) that harbor high-mass protostars. T~100K Chemically rich region, as evidenced from spectral line surveys: Orion Hot Core (the archetypal hot core) Frequency [GHz] HST image from Luhman et al. (2000) Spectral line surveys: Schilke et al. (2001); Ziurys & McGonagle (1993) Johansson et al. (1984)
HCOOCH3 Hot Corinos(presumed to be similar to hot cores, but surrounding low-mass protostars) 2.7mm cont. Bottinelli et al. (2007) Example: IRAS 16293-2422 in r Oph (d ~120pc) CH3OCH3 Looney et al. (2000) Huang et al. (2005) CH3OCHO (methyl formate) C2H5CN (ethyl cyanide) But, hot and dense material is only within 150 AU of source. Transit time of infalling material thru this region is only ~100 yrs, not enough time to form complex molecules (thought to take ~104 yr to form). Need alternative source: disk?, outflow? Cazaux et al. (2003)
Arce et al., in preparation IRAM 30m Protostellar Outflows Another source of dust heating in star forming regions L1157 molecular outflow Bachiller et al. (2001) Outflows help in the production of Complex Organic (pre-biotic) molecules in the ISM.
Distribution of complex molecules in star forming regions Is this the real picture? Arecibo Observatory can help answer this question: • If complex molecules infall into cold circumstellar envelope (or spread through cloud) will end with T~20K. Low energy transitions for some molecules falls in radio regime. • Detection of more than one transition at very different frequencies help in determining excitation conditions • Hyperfine splitting more pronounced at lower freq., which can be used to derive t, N, and abundances Arecibo beam Image Credit:Bill Saxton, NRAO/AUI/NSF
Cold Molecular Cloudsstudying the pre-collapse stage In very cold molecular clouds (T~10K) complex molecules mainly emit low energy transition lines that can only be observed at microwave frequencies. Arecibo beam @ 10GHz DSN beam @ 22GHz Arecibo can be important tool in studying chemical evolution of cores. CCS integrated intensity image of TMC1-D from Langer et al. (1995)
Spectral line surveys of molecular clouds Arecibo Spectral survey of TMC1 Advantages of Arecibo: Kalenskii et al. (2004) • Relatively unexplored spectral band • Unmatched sensitivity • Necessary for cold gas • At lower frequencies there is less “contamination” from other lines from simple molecules MHz Improvements needed: • Extend frequency to 12 GHz? • Wideband feed (e.g., observe 0.5-12 GHz with only one receiver, instead of ~10) • Broadband backends of at least 1 GHz with narrow channels km/sec Other important Arecibo spectral surveys: • Evolved star IRC+10º 216 (Araya et al. 2003) • Arp 220 galaxy (Minchin et al., in prep.)
Polycyclic Aromatic Hydrocarbons (PAH’s) • Thought to be a main constituent of ISM dust • Efficient particles for the photo-electric effect (e.g., Weingartner & Draine 2001) ---> affect gas heating rate; ionization balance (e.g., Wolfire et al. 2003) • May have impact on formation of H2 (e.g., Habart et al. 2004) • Important role in gas chemistry as they might fragment into smaller carbon clusters and molecules, particularly in PDR’s (e.g., Pety et al. 2005) Thorwirth et al. (2007) report lab measurements of pure rotational transitions of four small PAH’s : C12H10, C12H8, C13H10, C10H8. All have lines with n < 12 GHz. AO can be used to study distribution of small PAH’s in different ISM environments Horsehead Nebula a “typical” PDR
Summary Arecibo Observatory can be an important tool in the study of large complex molecules thought to be crucial to ISM chemistry and emergence of life. AO is of particular importance for the study of large molecules in cold clouds, where most transitions are of low-energy AO can be a powerful tool for conducting spectral line surveys (for studying chemistry of region and discovery of new lines and molecules) if modest improvements in receivers and backends are performed Arecibo is a major source of exposure to science for students and public in PR, inspiring young people to go into science/engineering careers. Closing AO is adverse to Congress and NSF commitment to broaden the participation of underrepresented minorities in science. By the way, two days of IRAQ occupation is more than enough to fund AO for an additional 30 yrs!!