Of the over 150 different molecular species detected in the interstellar and circumstellar media, approximately 50 contain 6 or more atoms. These molecules, labeled complex by astronomers if not by chemists, all contain the element carbon and so can be called organic. In the interstellar medium, complex molecules are detected in the denser sources only. Although, with one exception, complex molecules have only been detected in the gas phase, there is strong evidence that they can be formed in ice mantles on interstellar grains. The nature of the gaseous complex species depends dramatically on the source where they are found: in cold, dense regions they tend to be unsaturated (hydrogen-poor) and exotic, whereas in young stellar objects, they tend to be quite saturated (hydrogen-rich) and terrestrial in nature. Based on both their spectra and chemistry, complex molecules are excellent probes of the physical conditions and history of the sources where they reside. Because they are detected in young stellar objects, complex molecules are expected to be common ingredients for new planetary systems. In this review, we discuss both the observation and chemistry of complex molecules in assorted interstellar regions in the Milky Way.

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Complex Organic Interstellar Molecules

Aims. Magnetic fields play a primordial role in the star formation process. The Zeeman effect on the CN radical lines is one of the few methods of measuring magnetic fields in the dense gas of star formation regions. Methods. We report new observations of the Zeeman effect on seven hyperfine CN N = 1−0 lines in the direction of 14 regions of star formation. Results. We have improved the sensitivity of previous detections, and obtained five new detections. Good upper limits are also achieved. The probability distribution of the line-of-sight field intensity, including non-detections, provides a median value of the total field Btot = 0.56 mG while the average density of the medium sampled is n(H2) = 4.5 × 10 5 cm −3 . We show that the CN line probably samples regions similar to those traced by CS and that the magnetic field observed mostly pervades the dense cores. The dense cores are found to be critical to slightly supercritical with a mean mass-to-flux ratio M/Φ ∼ 1 to 4 with respect to critical. Their turbulent and magnetic energies are in approximate equipartition.

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CN Zeeman measurements in star formation regions

We have observed 37 Infrared Dark Clouds (IRDCs), containing a total of 159 clumps, in high-density molecular tracers at 3 mm using the 22 m ATNF Mopra Telescope located in Australia. After determining kinematic distances, we eliminated clumps that are not located in IRDCs and clumps with a separation between them of less than one Mopra beam. Our final sample consists of 92 IRDC clumps. The most commonly detected molecular lines are (detection rates higher than 8%) N2H+, HNC, HN13C, HCO+, H13CO+, HCN, C2H, HC3N, HNCO, and SiO. We investigate the behavior of the different molecular tracers and look for chemical variations as a function of an evolutionary sequence based on Spitzer IRAC and MIPS emission. We find that the molecular tracers behave differently through the evolutionary sequence and some of them can be used to yield useful relative age information. The presence of HNC and N2H+ lines does not depend on the star formation activity. On the other hand, HC3N, HNCO, and SiO are predominantly detected in later stages of evolution. Optical depth calculations show that in IRDC clumps the N2H+ line is optically thin, the C2H line is moderately optically thick, and HNC and HCO+ are optically thick. The HCN hyperfine transitions are blended, and, in addition, show self-absorbed line profiles and extended wing emission. These factors combined prevent the use of HCN hyperfine transitions for the calculation of physical parameters. Total column densities of the different molecules, except C2H, increase with the evolutionary stage of the clumps. Molecular abundances increase with the evolutionary stage for N2H+ and HCO+. The N2H+/HCO+ and N2H+/HNC abundance ratios act as chemical clocks, increasing with the evolution of the clumps.

http://iopscience.iop.org/article/10.1088/0004-637X/756/1/60/pdf

CHEMISTRY IN INFRARED DARK CLOUD CLUMPS: A MOLECULAR LINE SURVEY AT 3 mm

While unbiased surveys observable from ground-based telescopes have previously been obtained towards several high mass protostars, very little exists on low mass protostars. To fill up this gap, we carried out a complete spectral survey of the bands at 3, 2, 1 and 0.8 mm towards the solar type protostar IRAS16293-2422. The observations covered about 200\,GHz and were obtained with the IRAM-30m and JCMT-15m telescopes. Particular attention was devoted to the inter-calibration of the obtained spectra with previous observations. All the lines detected with more than 3 sigma and free from obvious blending effects were fitted with Gaussians to estimate their basic kinematic properties. More than 4000 lines were detected (with sigma \geq 3) and identified, yielding a line density of approximatively 20 lines per GHz, comparable to previous surveys in massive hot cores. The vast majority (~2/3) of the lines are weak and due to complex organic molecules. The analysis of the profiles of more than 1000 lines belonging 70 species firmly establishes the presence of two distinct velocity components, associated with the two objects, A and B, forming the IRAS16293-2422 binary system. In the source A, the line widths of several species increase with the upper level energy of the transition, a behavior compatible with gas infalling towards a ~1 Mo object. The source B, which does not show this effect, might have a much lower central mass of ~0.1 Mo. The difference in the rest velocities of both objects is consistent with the hypothesis that the source B rotates around the source A. This spectral survey, although obtained with single-dish telescope with a low spatial resolution, allows to separate the emission from 2 different components, thanks to the large number of lines detected. The data of the survey are public and can be retrieved on the web site http://www-laog.obs.ujf-grenoble.fr/heberges/timasss.

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TIMASSS: the IRAS 16293-2422 millimeter and submillimeter spectral survey. I. Observations, calibration, and analysis of the line kinematics

Warm Carbon-Chain Chemistry

We have carried out observations toward the W3 complex and G34.3+0.15 using the TRAO 14 m radio telescope to examine in detail the chemical variations occurring while molecular clouds evolve from the prestellar to the H II region phase. Observations include spectral surveys of these objects between 84.7 and 115.6 GHz; mapping observations toward W3(OH) with the emissions of CS (2-1), HCN (1-0), HNC (1-0), and HCO+ (1-0); and mapping of CS (2-1) emission toward W3 IRS 5. Chemical model calculations are used to estimate the age of W3(OH) by comparing with the fractional abundances of detected molecules. We found that G34.3+0.15 and W3(OH) are at a similar evolutionary stage, although large differences in the fractional abundances are found in CH3CN and HC3N. Overall, the properties of the detected species and abundances in three regions support the view that chemistry varies as molecular clouds evolve from a cold, collapsing phase to a high-temperature phase, such as the hot core and H II phase. Chemical model calculations for W3(OH) indicate that the evolutionary age of the cloud is 104-105 yr with temperature in the range 10-60 K.

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A Molecular Line Survey of W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz: Observational Data and Analyses

We present results from a spectral line survey of the young stellar object IRAS 17470-2853, undertaken to examine chemical changes during the evolution from hot molecular cores to ultracompact HII regions. Observations were carried out with the Mopra 22 m radio telescope in the frequency range from 86.1 to 92.1 GHz. A total of 21 lines from 9 molecules were detected. Except for CH3CN they are all simple molecules. We compare the results to the ultracompact HII region G34.3+0.15, where spectral line surveys in the frequency range 80-115 GHz and 330-360 GHz have been performed. While the molecular lines detected are similar, their widths and intensities are somewhat narrower and lower, respectively, in IRAS 17470-2853. The typical line width of ∼ 5k m s −1 indicates relatively quiet or quasi-thermal emission. On the other hand, a significant difference in T ∗

A Spectral Line Survey of IRAS 17470-2853 from 86.1 to 92.1 GHz

A molecular line survey towards the UC H II region G34.3+0.15 from 155.3 to 165.3GHz has been conducted with the TRAO 14-m radio telescope. Combined with our previous observations from 84.7 to 115.6GHz and 123.5 to 155.3GHz (Paper I), the spectral coverage of this survey in G34.3+0.15 now runs from 85 to 165 GHz. From these latest observations, a total of 18 lines from 6 species were detected. These include four new lines corresponding to J = 0, K = 1 transitions of the E-type species, and two new lines corresponding to transitions from and . These 6 new lines are [1(1) - 1(0)E], [2(1) - 2(0)E], [3(1) - 3(0)E], [4(1) - 4(0)E], [14(1, 13) -14(0, 14)] and [18 -17]. We applied a rotation diagram analysis to derive rotation temperatures and column densities from the methanol transitions detected, and combined with NRAO 12-m data from Slysh et al. 1999. Applying a two-component fit, we find a cold component with temperature 13-16K and column density , and a hot component with temperature 64 - 83K and column density . On the other hand, applying just a one-component fit yields temperatures in the 47 -62 K range and column densities from .

A spectral line survey of the ultracompact h ii region g34.3+0.15. ii: 155.3-165.3 ggz

Abstract We have observed the parts of the second quadrant of the Galactic Plane in 13CO(1-0) using the multibeam receiver system installed on the 14 m telescope at Taeduk Radio Astronomy Observatory (TRAO). The first target region A (L=108° to 112°.5) is the part of the 12CO Outer Galactic Plane Survey (OGS; Heyer et al. 1998), and it is for the exact Galactic plane with the latitude range of +1 and -1 degree. A total of 48,000 spectra (about 9 square degrees) were obtained on 50″ grid. Two following regions were also observed; Region B: L = 120° ∼ 121°.7, B = −1° ∼ +1° (38,000 spectra) Region C: L = 130° 132°, B = −1° ∼ +1° (42,000 spectra). Eventually all the regions of the OGS will be covered. The selected velocity resolution is 0.63 km s−1 and the covered velocity is 320 km s−1, from −210 to 110 km s−1. The typical system temperature is ranging from 400 to 800 K, and average sensitivity per channel is 0.17 K. We developed a new reduction method, which effectively deals with a relatively noisy 3-dimensional database. After using simple linear baseline subtraction, we mainly used the IRAF twod.longslit.background task in 3D within some scripts, as well as IRAF tasks dealing with statistics, and a revised FCRAO reduction package, which is working within IRAF as external user's tasks. The collected 13CO database will be manipulated with pre-existing 12CO data to get several physical parameters. As it is located in the second quadrant, the kinematic distances of the individual clouds, which will be identified, can be estimated straightforwardly without any distance ambiguity. In this meeting we present the reduction method, integrated intensity maps, and spatial-velocity maps. We intend to clarify any difference of their characteristics between the clouds in the Outer Galaxy and Inner Galaxy using our data base. The present TRAO receiver system has aged, and thus its performance level degraded. However, we have a plan to renovate our receiver system to a brand new one within the next two years. This will speed up the TOGS project. At present, it costs substantial amount of time to homogeneously reduce the spectra obtained with our present receiver system. To compensate this, we invested more integration time, and developed more advanced reduction methods (see above). A future multibeam array receiver system at the TRAO would be at least 16 beams with most recent mixers (Tsys ∼ 150 K at 110GHz), hopefully.

TRAO 13CO Outer Galaxy Survey

A survey project of TRAO with the fifteen beam array receiver system is presented. A multibeam array receiver system has been purchased from FCRAO, and is being installed on TRAO 14m telescope. The target region of the survey is from ${\iota}

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Hun-Dae Kim

Papers

A Molecular Line Survey of W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz: Observational Data and Analyses

A Spectral Line Survey of IRAS 17470-2853 from 86.1 to 92.1 GHz

A spectral line survey of the ultracompact h ii region g34.3+0.15. ii: 155.3-165.3 ggz

TRAO 13CO Outer Galaxy Survey

The 13 co outer galaxy survey of trao using multibeam array receiver system