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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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Complex and Pre-Biotic Molecules in the ISM

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Complex and Pre-Biotic Molecules in the ISM


Héctor G. Arce

NSF Astronomy and Astrophysics Postdoctoral Fellow

American Museum of Natural History


Ethylene glycol

We are here to defend funding for Arecibo Observatory

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)

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

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 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.”

Studying molecules in ISM


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.


Image courtesy of NRAO/AUI

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.


Hot Cores

Dense regions (n~107 cm-3)

and compact (~0.1pc)

that harbor high-mass

protostars. T~100K

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)


Hot Corinos(presumed to be similar to hot cores, but surrounding low-mass protostars)

2.7mm cont.

Bottinelli et al. (2007)


IRAS 16293-2422

in r Oph (d ~120pc)


Looney et al. (2000)

Huang et al. (2005)


(methyl formate)


(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)

Arce et al.,

in preparation

IRAM 30m

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.

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 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

Arecibo beam

Image Credit:Bill Saxton, NRAO/AUI/NSF

Cold Molecular Cloudsstudying the pre-collapse stage

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

of cores.

CCS integrated intensity image of TMC1-D

from Langer et al. (1995)

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


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


Other important Arecibo spectral surveys:

• Evolved star IRC+10º 216 (Araya et al. 2003)

• Arp 220 galaxy (Minchin et al., in prep.)

Polycyclic Aromatic Hydrocarbons (PAH’s)

• 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!!

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