Prebiological Molecules in the ISM
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Astrobio2010 1
Prebiological Molecules in the
ISM
T. L. Wilson
ALMA
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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 uniqueThis is not the case for some species that are condensed on grains (i.e. PAH’s)
Astrobio2010
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dense (giant) molecular clouds
H 2
T = 10 K
core
n = 10 cm4 -3
embedded stars
protoplanetary disk
hot ionized gas
organic molecules
studied in millimeter-wave and IR
PDR’s
HII region
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5
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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Astrobio2010
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Structure of Some SpeciesThese 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
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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.
Astrobio2010
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1111
Orion KL Spectrum from GroundOrion KL Spectrum from Ground
Astrobio2010
See talk
by Cecile
Favre
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A Typical Set of NumbersIn 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 locatedMeasure all spectral lines from a species with many lines and remove these from the observed spectraFind sources that are more favorable for searches for specific species (i.e. narrower line widths)
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Orion Hot Core
Astrobio2010
See talk
By Cecile
Favre
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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 astronomyEspecially 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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ETH Seminar 16
ALMALocation
Chajntantor Plateau at5000m in northern Chile
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Bilateral ALMA + ALMA Compact Array (in lower right)
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The ALMAFOV is 25”at 1 mm
ALMA ReceiverBands
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Astrobio2010
Sensitivity of ALMA
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Astrobio2010 21
Correlator Set Up: Four IF Bands of 2 GHz Each Can be Analyzed by 32 Filters, 16 in Each Polarization
2 GHz wide IF
Region analyzed by a single spectrometer
Spectrometer has 8192 channels
(we show ½ of the filters)
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ALMA Timeline
CSV starting in a few weeks20 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 capabilityData reduction and Observing Tools for usersALMA Regional Centers to help users in North America, Europe and East Asia