RECENT TOPICS ON ORGANIC MATTERS IN SPACETHROUGH ASTRONOMICAL OBSERVATIONS
Masatoshi OHISHI
Astronomy Data Center, National Astronomical Observatory of Japan,
and the Graduate University for Advanced Studies (SOKENDAI)
2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan.
e-mail: masatoshi.ohishi@nao.ac.jp(Received July 31, 2008; Accepted September 10, 2008)(Abstract)
It is known that more than 140 interstellar andcircumstellar molecules have so far been detected,
mainly by means of the radio astronomy observations.
Many organic molecules are also detected, including
alcohols, ketons, ethers, aldehydes, and others, that are
distributed from dark clouds and hot cores in the giant
molecular clouds. It is believed that most of the organic
molecules in space are synthesized through the grainsurface reactions, and are evaporated from the grainsurface when they are heated up by the UV radiationfrom nearby stars. On the other hand the recent claimon the detection of glycine have raised an important
issue how difficult it is to confirm secure detection of
weak spectra from less abundant organic molecules in
the interstellar molecular cloud.
Recent topics regarding observations of organic
molecules in the interstellar molecular clouds,
including independent observations of glycine by the
45m radio telescope and a detection of amino
acetonitrile (NH2CH2 CN) that is a precursor to glycine.
(Keywords)
Astrochemistry, Astrobiology, Interstellar molecules,
Line identification, Astronomical observations
1. Introduction
In recent years highly sensitive observations on
interstellar molecules have been conducted by, e.g., theGreenbank Telescope (GBT) and the Nobeyama 45m
telescope. Such observations provided lots of new
insights on new species, molecular abundances,
existence of organic species in a wide variety of objects,
and so on. These will be the basis in understanding theinterstellar chemistry.
Remarkable progress was made in observing large,
complex organic species, e.g., glycolaldehyde, thesimplest sugar [1] or glycine, the simplest α-amino acid[2], which may link to the understanding to the originof life in the universe. However some observed spectra
have weak signal intensities and these spectra arecontaminated by other spectra, leading the debates thatsuch observation results are plausible or not.
In this paper I will review several observations onorganic molecules toward cold and dark clouds and star
forming regions, and will discuss what are needed toverify a new identification in this era of crowded
spectra.
2. Molecular Line Survey toward TMC-1
Cold dark interstellar clouds have been extensively
studied as the formation sites of low-mass stars andViva Origino 36 (2008) 51- 54ⓒ 2008 by SSOEL Japanplanetary systems since their identification to theinterstellar molecular clouds in 1970's. A variety of
exotic chemical compounds found in molecular clouds,
especially those containing carbon atoms, attracted
strong interests in connection with the formation ofplanets and the origin of life in the universe. Recent
radio and IR observations towards comets collected
important evidence that comets, 4.6 billion year-old
fossil bodies of the proto-solar-system nebula, keep
molecular composition similar to that in cold darkclouds. Therefore, the chemical evolution in cold darkclouds is basically important as the initial process ofinterstellar matter evolution toward the planets, and,ultimately to life.
Kaifu et al. [3] published a molecular spectral line
survey data toward a dark cloud, the cyanoplyyne peakof Taurus Molecular Cloud-1 (TMC-1), in thefrequency range between 8.8 and 50 GHz (Figure 1),
using the 45-m mm-wave telescope of the Nobeyama
Radio Observatory [4]. They detected 414 lines from
38 molecules. Most of the molecules are linear carbon
chain species and their derivatives, and there are only a
few organic species such as CH3OH, CH3CHO,
HCCCHO and CH2CHCN. More saturated species, e.g.,
C2H5CN and HCOOCH3, were not detected at all.
According to their preliminary analysis [4], these
species generally have less abundance than major linear
carbon chain molecules such as HC3N and CCS, and it
would be possible to conclude that the organic species
are not the main constituent in the cold and dark clouds.
Chemical reactions in dark clouds are not yet fully
understood, and many unknown molecules might besynthesized in dark clouds. It is essential forunderstanding the chemical reactions in dark clouds,

Figure 1. A compressed atlas of the 8.8-50 GHz spectrum toward
TMC-1 (cyanopolyyne peak). The abscissa is the frequency in GHz,and the ordinate is the line intensity expressed in the temperaturescale.

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Viva Origino 36 (2008) 51 - 54
therefore, to make an unbiased frequency survey thatcan detect all molecular lines, including unpredictedlines of unknown molecules.
2. Detection of Organic Species in the Early Stage ofProtostellar Evolution
So far large organic molecules (e.g., HCOOCH3,(CH3)2O and C2H5CN) were observed with highabundances toward the hot cores such as Orion KL, Sgr
B2(N) and W51 e1/e2 where O/B stars are formed. Sgr
B2 is a famous giant molecular cloud near the Galactic
center, and is well-known for the high abundance oflarge organic molecules. There are several hot coresources within the Sgr B2 cloud (e.g., Sgr B2(M) and
Sgr B2(N)), and Sgr B2(N) is known as the position of
the highest abundance of organic molecules. Suchhighly saturated molecules are difficult to be produced
by gas-phase chemical reactions under low-temperature
conditions, and hence the grain surface chemistry isthought to play an important role in their production.
When star formation takes place, the grain mantles areheated up by various activities of newly born stars,
supplying parent molecules, like CH3OH and H2CO,
into the gas phase through evaporation processes.
Subsequent gas-phase reactions under high-temperatureand high-density conditions would produce largeorganic molecules.
Recently detections of large organic species werereported toward the hot corinos in IRAS 16293-2422[5-7]. Further detection of HCOOCH3 toward
NGC1333 IRAS4B [8] and NGC2264 MMS3 [9] werereported. Figure 2 shows the spectrum of HCOOCH3
toward NGC1333 IRAS4B that is a class 0 low-mass
protostar with an estimated age of a few 100 years. Thissuggests that the complex organic molecules appear
from the very early stage of protostellar evolution.
Sakai et al [9] found the HCOOCH3 distribution,
reveald by the Nobeyama Millimeter Array, seems tobe similar to the case of Orion KL Compact Ridge
where the molecular peak is shifted from the dust
continuum peak, and suggests that such distribution
similarity would give a hint to understand the formationof HCOOCH3 in hot corinos and hot cores.
Since other highly saturate organic species, such as
C2H5OH, (CH3)2O and C2H5CN, are observed in hot
cores, it would be necessary to conduct deep
observations on these species toward low-mass
protostars to further understand the formation
mechanism and evaporation conditions of organic
species.

Figure 2. A Spectrum of HCOOCH 3 toward NGC1333 IRAS4B
taken by the Nobeyama 45m Telescope. The abscissa is the radial
velocity with respect to the local standard of rest (LSR), and theordinate is the line intensity expressed in the temperature scale.

The report on the detection of glycolaldehyde [1]toward Sgr B2(N) by the Kitt peak 12m telescope wasan epoch making one, because glycolaldehyde is thesimplest sugar and really a prebiotic molecule.
However the reported spectra had low signal to noise
ratios, and some of them appeared on the shoulders ofother molecular lines. Such a situation had led todebates if the detection was secure. In 2004 Hollis et al[16] made observations of glycolaldehyde by the GBT
in four frequency ranges below 22 GHz, showing datawith sufficient signal to noise ratios. Three transitions
out of four showed absorption features at 63 kms-1
where absorption features from other already known
species appear. The GBT observations made thedetection of glycolaldehyde secure.
On the other hand the cases for propenal andethylene glycol are different. Only two propenal lines
were reported toward Sgr B2(N), and the absorption
features at 63 kms-1 is apparent for only one line. Five
ethylene glycol data were reported, however, they
appeared on the shoulders of other molecular lines.
This situation made difficult to investigate if theintensity distribution was reasonable for species
observed toward Sgr B2(N). Therefore it may beconcluded that the detection of propenal and ethylene
glycol have not yet been confirmed.

3. Recent Reports of Large Organic Species toward
High Mass Star Forming Regions
In the last several years many very large organic
molecules were reported to be detected. This is
primarily because of the powerful observation
performance of the Greenbank Telescope (GBT)
together with improvement of the receiver sensitivities.
These molecules include glycolaldehyde (CH2OHCHO)[1], ethylene glycol ((CH2OH)2) [10], glycine(NH2CH2COOH) [2], propenal (CH2CHCHO) andpropanal (CH3CH2CHO) [11], acetone ((CH3)2CO)[12], cyanoallene (CH2CCHCN) [13], acetamide(CH3CONH2) [14], and cyanoformaldehyde (CNCHO)[15].

4. Interstellar Glycine
The report on the detection of glycine [2], thesimplest α-amino acid, had the similar situation in thatthe signal-to-noise ratios were not so high and many
spectra seemed to be contaminated. They observed 27
frequency bands of glycine conformer I toward Orion
KL, Sgr B2(N) and W51 e1/e2, however, only three ofthem were reported to be observed from three objects.
Intensity analyses by means of the rotation diagram
were made, and the distributions seemed plausible.
However, the derived column densities of glycine forthree sources had similar values, inconsistent with afact that in most cases a column density of a molecule
toward Sgr B2(N) is higher by about two order of-52-

Viva Origino 36 (2008) 51 - 54
magnitudes than those toward Orion KL and W51
e1/e2.
Therefore we made independent observations by the
45m telescope at Nobeyama. Because the glycine
spectra had high possibility of contamination, we
carefully examined our past observed data to find“clean spectrum windows” where no transitions fromother known abundant species may exist.
Figure 3 shows a spectrum observed toward Orion
KL at around 90 GHz. There are transitions of glycine
conformer I at 90043.13 MHz (151,15-141,14, upper
energy = 24.63 cm-1), 90049.71 MHz (150,15-140,14,
upper energy = 24.62 cm-1), and 90056.98 MHz(151,15-140,14, upper energy = 24.63 cm-1). The expected
brightness temperatures for these transitions are around
20 mK when we used the column density and therotation temperature derived by Kuan et al [2]. One
peak coincides with the glycine transition at 90043.13
MHz, and showed expected intensity, however, othertwo are not clearly seen. The line at 90043.13 MHz was
not identified when we investigated available molecularline databases, leaving a possibility that the line could
be identified to the glycine line. However we noticed
that there is another line next to the 90043.13 MHz linewith similar line intensity. Such a “doublet line” could
be due to the internal rotation, and it is well known thatthe molecular abundance of HCOOCH3 toward Orion
KL is so high. We contacted a laboratory molecular
spectroscopist, Dr. Hitoshi Odashima at Toyama
University, asking if he had measured weak lines of
HCOOCH3, and it was revealed that two unassignedlines of HCOOCH3 matched the two lines above.
Therefore it can be concluded that the detection ofinterstellar glycine has not yet been confirmed.

paper observed the Sgr B2(N) with the IRAM 30m
radio telescope in Spain, using 88 millimeter-wave
transitions of amino acetonitrile. A part of reported
spectra is shown in Figure 4. Since it is well known that
Sgr B2(N) shows so many lines from various
interstellar molecules, that have wide line shape, theline contamination is a serious problem when detecting
weak features. It is clearly seen in Figure 4 that theclaimed spectra of amino acetonitrile have low
signal-to-noise ratios, and are often overlapped by otherspectral features.
Thus the authors utilized the IRAM interferometerand the Australian Telescope Compact Array (ATCA)
to pick up signals from very compact sources, andsucceeded to find that the amino acetontrile is confinedwithin a very small (~2 seconds of arc) cores within Sgr
B2(N). A radio interferometer consists of multiple radio
telescopes that are separated with a distance but
connected by data transmission cables. All the received
signals are collected and processed by a correlator to
produce synthesized images. The synthesized images
are equivalent to those observed by a virtually large

5. Detection of Amino acetonitrile in SpaceIn relation with the origin of life, the question if
there are amino acids in the interstellar space has
attracted many researchers. As we have seen, all theattempts to detect the simplest amino acid, glycine,have been unsuccessful. Therefore there would be otherapproaches to study the possible existence of aminoacids through searching for their precursors. As is wellknown the hydrolysis of amino acetonitrle(NH2CH2CN) will produce glycine.
In May 2008 a paper of the detection of amino
acetonitirile was published [17]. The authors of the

Figure 4. Sample spectra of amino acetonitrile (AAN) toward Sgr
B2(N) observed by the IRAM 30m radio telescope, taken from
Figure 1 of the original paper [17]. The lower plot shows in black thespectrum obtained toward Sgr B2(N) in main-beam temperaturescale (K), while the upper plot shows the spectrum toward Sgr
B2(M). The rest frequency axis is labeled in GHz. The lines
identified in the Sgr B2(N) spectrum are labeled in blue. The top redlabel indicates the AAN transition centered in each plot, along withthe energy of its lower level in K. The other AAN lines are labeled inblue only. The green spectrum shows the LTE model containing all
identified molecules, including AAN [17]. The LTE synthetic
spectrum of AAN alone is overlaid in red, and its opacity in dashedviolet. All observed lines which have no counterpart in the green
spectrum are still unidentified in Sgr B2(N).

Figure 3. A Spectrum toward Orion KL at around 90 GHz where the
Glycine (conformer I) transitions exist, that are shown by the verticallines. The abscissa is the frequency in GHz, and the ordinate is theline intensity expressed in the temperature scale. MeF stands for
HCOOCH3.

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Viva Origino 36 (2008) 51 - 54
References

radio telescope with a diameter of the maximum
separation distance between the element telescopes.
Therefore the interferometer can achieve very highspatial resolution. However it is less sensitive toextended sources larger than the field of view of theelement telescope.
The derived column density of aceto aminonitrile is
2.8 1016 cm-2. The volume density of molecularhydrogen is about 1.7 108 cm-3, and a mass of the coreis about 2340 times the solar mass. Therefore an amino
acetonitrile fractional abundance was calculated to be
2.2 10-9, which is relatively high among known
organic interstellar molecules.
The formation of amino acetonitrile itself was also
investigated theoretically [18]. They found that watercan efficiently catalyze a reaction between
methylenimine CH2NH and hydrogen isocyanide HNC
to form amino acetonitrile in the grain mantles at atemperature of 50 K. Methylenimine was detected in
the gas phase toward Sgr B2(N) [19]. An evidence wasfound for both hot, compact and cold, extended
components and derived a column density of 3.3 1017
cm-2 for the compact component, with a source size of
2.7 seconds of arc [19], which is consistent with thatvalue derived by Belloche et al.[17]. This column
density is an order of magnitude larger than the column
density for amino acetonitrile [17], which does not ruleout methylenimine as a precursor of amino acetonitrile.
Since the lines of amino acetonitrile have low
signal-to-noise ratios and are contaminated, it is crucial
to observe other hot core sources to confirm interstellaramino acetonitrile as a direct precursor to glycine.

1.

6. Conclusions
Recent high-sensitivity observations toward
interstellar molecular clouds have revealed several newlarge organic molecules that would be related with theorigin of life. However, it was found that the interstellar
glycine has not been confirmed yet, and the next
generation radio telescopes, such as the ALMA, would
give a clue to search for life-related species. The reportof detection of amino acetonitrile would be very
encouraging to study the origin of life in the Universe.
In any case, careful observations with various pointsof view would be needed toward secure detections ofprebiotic molecules in the interstellar space.
Acknowledgments
This work was supported by the Japan Society for
the Promotion of Science (JSPS) Core to Core Program.
Nobeyama Radio Observatory is an open-use facility
for mm-wave astronomy, being operated under the
National Astronomical Observatory of Japan (NAOJ).

-54-

Hollis, J. M., Lovas, F. J. and Jewell, P. R. Interstellar
glycolaldehyde: The first sugar, ApJ (Letter) 540, L107
(2000).
2. Kuan, Y. J., Charnley, S. B., Huang, H. C., Tseng, W. L. andKisiel, Z. Interstellar glycine, ApJ 593, 848 (2003).
3. Kaifu, N., Ohishi, M., Kawaguchi, K., Saito, S., Yamamoto, S.,
Miyaji, T., Miyazawa, K., Ishikawa, S., Noumaru, C., Harasawa,
S., Okuda, M. and Suzuki, H. A 8.8-50GHz complete spectralline survey toward TMC-1 I. Survey data, PASJ 56, 69 (2004).
4. Ohishi, M. and Kaifu, N. Chemical and physical evolution ofdark clouds. Molecular spectral line survey toward TMC-1, J.
Chem. Soc., Faraday Discussion 109, 205 (1998).
5. Cazaux, S., Tielens, A. G. G. M., Ceccarelli, C., Castets, A.,
Wakelam, V., Caux, E., Parise, B. and Teyssier, D. the hot corearound the low-mass protostar IRAS 16293-2422: Scoundrels
Rule!, ApJ (Letter) 593, L51 (2003).
6. Bottinelli, S., Ceccarelli, C., Lefloch, B., Williams, J. P., Castets,
A., Caux, E., Cazaux, S., Maret, S., Parise, B. and Tielens, A. G.
G. M. Complex molecules in the hot core of the low-mass
protostar NGC 1333 IRAS 4A, ApJ 615, 354 (2004).
7. Kuan, Y. J., Huang, H. C., Charnley, S. B., Hirano, N.,
Takakuwa, S., Wilner, D. J., Liu, S. Y., Ohashi, N., Bourke, T.
L., Qi, C. H. and Zhang, Q. Z. Organic molecules in low-mass
protostellar hot cores: Submillimeter imaging of IRAS
16293-2422, ApJ (Letter) 616, L27 (2004).
8. Sakai, N., Sakai, T. and Yamamoto, S. Detection of HCOOCH 3
toward a low-mass protostar, NGC 1333 IRAS 4B, PASJ
(Letter) 58, L15 (2006).
9. Sakai, N., Sakai, T. and Yamamoto, S. Methyl formate in the
NGC 2264 IRS 1 region, ApJ 660, 363 (2007).
10. Hollis, J. M., Lovas, F. J., Jewell, P. R. and Coudert, L. H.
Interstellar antifreeze: ethylene glycol, ApJ (Letter) 571, L59(2002).
11. Hollis, J. M., Jewell, P. R., Lovas, F. J., Remijan, A. J. andMøllendal, H. Green Bank Telescope Detection of new
interstellar aldehydes: propenal and propanal, ApJ (Letter) 610,
L21 (2004).
12. Friedel, D. N., Snyder, L. E., Remijan, A. J. and Turner, B. E.
Detection of interstellar acetone toward the orion-kl hot core,
ApJ (Letter) 632, L95 (2005).
13. Lovas, F. J., Remijan, A. J., Hollis, J. M., Jewell, P. R. and
Snyder, L. E. Hyperfine structure identification of interstellar
cyanoallene toward TMC-1, ApJ (Letter) 637, L37 (2006).
14. Hollis, J. M., Lovas, F. J., Remijan, A. J., Jewell, P. R., Ilyushin,
V. V. and Kleiner, I. Detection of acetamide (CH3CONH2 ): Thelargest interstellar molecule with a peptide bond, ApJ (Letter)
643, L25 (2006).
15. Remijan, A. J., Hollis, J. M., Lovas, F. J., Stork, W. D., Jewell, P.
R. and Meier, D. S. Detection of interstellar cyanoformaldehyde(CNCHO), ApJ (Letter) 675, L85 (2008).
16. Hollis, J. M., Jewell, P. R., Lovas, F. J. and Remijan, A. J. GreenBank telescope observations of interstellar glycolaldehyde:
low-temperature sugar, ApJ (Letter) 613, L45 (2004).
17. Belloche, A., Menten, K. M., Comito, C., Müller, H. S. P.,
Schilke, P., Ott, J., Thorwirth, S. and Hieret, C. Detection ofamino acetonitrile in Sgr B2(N), A&Ap 482, 179 (2008).
18. Koch, D. M., Toubin, C., Peslherbe, G. H. and Hynes, J. T. A
theoretical study of the formation of the aminoacetonitrile
precursor of glycine on icy grain mantles in the interstellar
medium, J. Phys. Chem. C 112(8), 2972 (2008).
19. Nummelin, A., Bergman, P., Hjalmarson, Å., Friberg, P., Irvine,
W. M., Millar, T. J., Ohishi, M. and Saito, S. A three-position
spectral line survey of sagittarius B2 between 218 and 263 GHz.
II. Data analysis, ApJS 128, 213 (2000).