Complex and PreBiotic Molecules in the ISM

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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
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We are here to defend funding for Arecibo
Observatory
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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)
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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
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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 congresss and NFSs 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.
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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., PAHs) 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
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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
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Hot Cores
Dense regions (n107 cm-3) and compact (0.1pc)
that harbor high-mass protostars. T100K
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)
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Hot Corinos(presumed to be similar to hot cores,
but surrounding low-mass protostars)
HCOOCH3
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)
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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.
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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 T20K. 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 CreditBill Saxton, NRAO/AUI/NSF
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Cold Molecular Cloudsstudying the pre-collapse
stage
In very cold molecular clouds (T10K) complex
molecules mainly emit low energy transition
lines that can only be observed at microwave
frequencies.
Arecibo beam _at_ 10GHz
DSN beam _at_ 22GHz
Arecibo can be important tool in studying
chemical evolution of cores.
CCS integrated intensity image of TMC1-D from
Langer et al. (1995)
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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 IRC10º 216 (Araya et al. 2003)
Arp 220 galaxy (Minchin et al., in prep.)
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Polycyclic Aromatic Hydrocarbons (PAHs)
Thought to be a main constituent of ISM dust
Efficient particles for the photo-electric effect
(e.g., Weingartner Draine 2001) ---gt
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 PDRs (e.g., Pety et
al. 2005)
Thorwirth et al. (2007) report lab measurements
of pure rotational transitions of four small
PAHs C12H10, C12H8, C13H10, C10H8. All have
lines with n lt 12 GHz. AO can be used to study
distribution of small PAHs in different ISM
environments
Horsehead Nebula a typical PDR
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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!!
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