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Prebiological Molecules in the

ISM

T. L. Wilson

ALMA

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)

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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

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.

Number of Species Found

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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

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 GroundOrion KL Spectrum from Ground

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See talk

by Cecile

Favre

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

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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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

2 GHz wide IF

Region analyzed by a single spectrometer

Spectrometer has 8192 channels

(we show ½ of the filters)

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