Complex and Pre-Biotic Molecules in the ISM

CH3CHO

C2H4(OH)2

Ethylene glycol

Héctor G. ArceNSF Astronomy and Astrophysics Postdoctoral Fellow

American Museum of Natural History

We are here to defend funding for Arecibo Observatory

Hayden Planetariuma source of inspiration for NYC youth

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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

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Angel Ramos Foundation Visitor CenterArecibo 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 CEOSEThe 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 underrepresentedin STEM, persons with disabilities, and institutions that serve these populations.

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.”

Closing AO goes against congress’s and NFS’s goal of broadeningthe participation of underrepresented minorities in STEM fields.

Studying molecules 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 providethe essential material that allowed the emergence of life.

Understanding physical and chemical processes in ISM:

CH3CHO

C2H4(OH)2

Formation Mechanisms1) 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.

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Image courtesy of NRAO/AUI

C2H4O

Frequency [GHz]

Spectral line surveys:Schilke et al. (2001); Ziurys & McGonagle (1993) Johansson et al. (1984)

HST image from Luhman et al. (2000)

Hot Cores

Orion Hot Core(the archetypal hot core)

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:QuickTime™ and a

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Hot Corinos(presumed to be similar to hot

cores, but surrounding low-mass protostars)

CH3OCHO(methyl formate)

C2H5CN(ethyl cyanide)

Cazaux et al. (2003)

Looney et al. (2000)

Bottinelli et al. (2007)

Huang et al. (2005)

Example: IRAS 16293-2422in Oph (d ~120pc) CH3OCH3

HCOOCH3

But, hot and dense material is only within 150 AU of source. Transit time of infallingmaterial 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?

2.7mm cont.

Protostellar Outflows

L1157 molecular outflow

Another source of dust heating in star forming regions

Outflows help in the production of Complex Organic (pre-biotic) molecules in the ISM.

Bachiller et al. (2001)

IRAM 30m

90.1 90.2 90.3Rest Frequency [GHz]

0.005

0

CH3OCHOCH3OCHO

HCOOH

C2H5OH?

0.05

0

0.1

135.80 135.75 135.70Rest Frequency [GHz]

CH3CHO

HCOOH

SO234SO

C8H ?

Arce et al., in preparation

Distribution of complex molecules in star forming regions

Is this the real picture?

Image Credit:Bill Saxton, NRAO/AUI/NSF

Arecibo Observatory can helpanswer 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 differentfrequencies help in determining excitation conditions

• Hyperfine splitting more pronounced at lower freq., whichcan be used to derive N, and abundances

Arecibo beam

Cold Molecular Cloudsstudying the pre-collapse stage

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CCS integrated intensity image of TMC1-D from Langer et al. (1995)

DSN beam @ 22GHz

Arecibo beam @ 10GHz

In very cold molecular clouds (T~10K) complex molecules mainly emit low energy transition lines that can only be observed at microwave frequencies.

Arecibo can be important toolin studying chemical evolutionof cores.

Spectral line surveys of molecular clouds

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Kalenskii et al. (2004)MHz

km/sec

• Relatively unexplored spectral band• Unmatched sensitivity • Necessary for cold gas• At lower frequencies there is less “contamination” from other lines from simple molecules

Arecibo Spectral survey of TMC1

Other important Arecibo spectral surveys: • Evolved star IRC+10º 216 (Araya et al. 2003) • Arp 220 galaxy (Minchin et al., in prep.)

Advantages of Arecibo:

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

Polycyclic Aromatic Hydrocarbons (PAH’s)

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• 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 transitionsof four small PAH’s : C12H10, C12H8, C13H10,C10H8. All have lines with GHz.

AO can be used to study distribution ofsmall PAH’s in different ISM environments

Horsehead Nebula a “typical” PDR

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!!