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Prebiological
Molecules in the
ISM
T. L. Wilson
ALMA
Astrobio2010
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What are prebiological molecules?
If use Miller-Urey experiment, can consider ammonia,
methane, carbon dioxide, water, etc. are “prebiological”
These are all found in the Interstellar Medium, but at
low concentrations compared to earth
In the following will consider only gas phase species, since
these identifications are rather unique
This is not the case for some species that are condensed on
grains (i.e. PAH’s)
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dense (giant) molecular clouds
organic molecules
H
core
4 -3
n = 10 cm
T = 10 K
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PDR’s
embedded
stars
hot
ionized
gas
HII region
protoplanetary disk
studied in millimeter-wave and IR
Sketch of Protostar Development
All phases are important, but two very relevant stages are Class 0 and and Class II.
These will be addressed in the following talks.
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Number of Species Found
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Structure of Some Species
These are asymmetric
top molecules which have
many transitions in the
millimeter range
in warm sources
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The Ground State of Water Vapor
See talk
by Bill Dent
But not the most sought after:
Glycine (simplest amino acid).
This has not been conclusively found,
so far. Shown on the right are the three
confimers.
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Orion KL Spectrum from Ground
See talk
by Cecile
Favre
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A Typical Set of Numbers
In the 3 mm range, at a frequency of ~100 GHz, the
limit of a fractional abundance of Glycine is reportedly
<10-11 of the abundance of molecular hydrogen. This is
based on a total column density of 5 to 7 1013 cm-2 of
Glycine. The authors comment that the search is
affected by confusion, that is, overlapping spectral lines
of other species.
Can we do better? Yes! Expect the Glycine region to be
small.
The beam size of this search was 30”. With Plateau de
Bure, obtained 3”, or a factor of 100 times better
angular resolution, but the limit to column density was
100 times worse, 1015 cm-2. With ALMA will have at
least 10 times better sensitivity.
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How Can we Do Better?
Improve the angular resolution to pick out regions
where specific species are located
Measure all spectral lines from a species with many
lines and remove these from the observed spectra
Find sources that are more favorable for searches for
specific species (i.e. narrower line widths)
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Orion Hot Core
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See talk
By Cecile
Favre
ALMA: The Future of mm/sub-mm Astronomy
A global project that will revolutionize the field
“a picture is worth a million simulations”
The scientific goals encompass much of astronomy
Especially prominent will be the study of star formation,
interstellar chemistry, and structure of molecular clouds.
In addition will enhance the study of comets, our planets, and
high redshift sources.
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Location
ALMA
Chajntantor
Plateau at
5000m in
northern Chile
ETH Seminar
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Bilateral ALMA + ALMA Compact Array (in lower right)
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The ALMA
FOV is 25”
at 1 mm
ALMA
Receiver
Bands
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Sensitivity of ALMA
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Correlator Set Up: Four IF Bands of 2 GHz Each Can be Analyzed by
32 Filters, 16 in Each Polarization
Region analyzed by a single spectrometer
(we show ½ of
the filters)
2 GHz wide IF
Spectrometer has 8192 channels
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ALMA Timeline
CSV starting in a few weeks
20 months later is the start of Early Science with at least
16 antennas (of the 66 planned)
4 receiver bands (3, 1.3, 0.8 0.6 mm wavelength)
Full spectrometer capability
Data reduction and Observing Tools for users
ALMA Regional Centers to help users in North America,
Europe and East Asia