Complex and Pre-Biotic Molecules in the ISM . CH 3 CHO. Héctor G. Arce NSF Astronomy and Astrophysics Postdoctoral Fellow American Museum of Natural History. C 2 H 4 (OH) 2. Ethylene glycol. We are here to defend funding for Arecibo Observatory.
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Héctor G. Arce
NSF Astronomy and Astrophysics Postdoctoral Fellow
American Museum of Natural History
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)
Angel Ramos Foundation Visitor Center
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
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…”
• 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.”
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.
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.
Dense regions (n~107 cm-3)
and compact (~0.1pc)
that harbor high-mass
Chemically rich region, as evidenced from
spectral line surveys:
Orion Hot Core
(the archetypal hot core)
HST image from Luhman et al. (2000)
Spectral line surveys:
Schilke et al. (2001); Ziurys & McGonagle (1993) Johansson et al. (1984)
Bottinelli et al. (2007)
in r Oph (d ~120pc)
Looney et al. (2000)
Huang et al. (2005)
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)
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
Image Credit:Bill Saxton, NRAO/AUI/NSF
In very cold molecular clouds (T~10K) complex
molecules mainly emit low energy transition
lines that can only be observed at microwave
Arecibo beam @ 10GHz
DSN beam @ 22GHz
Arecibo can be important tool
in studying chemical evolution
CCS integrated intensity image of TMC1-D
from Langer et al. (1995)
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
• 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
Other important Arecibo spectral surveys:
• Evolved star IRC+10º 216 (Araya et al. 2003)
• Arp 220 galaxy (Minchin et al., in prep.)
• 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
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!!