Karl M. Menten

ATLASGAL - The APEX Telescope Large Area Survey of the Galaxy at 870 microns

Context. Thanks to its excellent 5100 m high site in Chajnantor, the Atacama Pathfinder Experiment (APEX) systematically explore s the southern sky at submillimeter wavelengths, both in continuum and in spectral line emission. Studying continuum emission from interstellar dust is essential to locate the highest densit y regions in the interstellar medium, and to derive their masses, column densities, density structures, and larger scale morpholog ies. In particular, the early stages of (massive) star forma tion are still quite mysterious: only small samples of high-mass proto-stellar or young stellar objects have been studied in detail so far. Aims. Our goal is to produce a large scale, systematic database of massive pre- and proto-stellar clumps in the Galaxy, in order to better understand how and under what conditions star formation takes place. Only a systematic survey of the Galactic Plane can provide the statistical basis for unbiased studies. A well characteriz ed sample of Galactic star-forming sites will deliver an evolutionary sequence and a mass function of high-mass star-forming clumps. Such a systematic survey at submillimeter wavelengths also represents a pioneering work in preparation for Herschel and ALMA. Methods. The APEX telescope is ideally located to observe the inner Milky Way. The recently commissioned Large APEX Bolometer Camera (LABOCA) is a 295-element bolometer array observing at 870 µm, with a beam of 19. ′′ 2. Taking advantage of its large field of view (11. ′ 4) and excellent sensitivity, we have started an unbiased survey of the whole Galactic Plane accessible to APEX, with a typical noise level of 50‐70 mJy/beam: the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). Results. As a first step, we have covered ∼95 deg 2 of the Galactic Plane. These data reveal∼6000 compact sources brighter than 0.25 Jy, or 63 sources per square degree, as well as extended structures, many of them filamentary. About two thirds of the c ompact sources have no bright infrared counterpart, and some of them are likely to correspond to the precursors of (high-mass) proto-stars or proto-clusters. Other compact sources harbor hot cores, compact Hii regions or young embedded clusters, thus tracing more evolved stages after star formation has occurred. Assuming a typical distance of 5 kpc, most sources are clumps smaller than 1 pc with masses from a few 10 to a few 100 M⊙. In this first introductory paper, we show preliminary resul ts from these ongoing observations, and discuss the mid- and long-term perspectives of the survey.

Herschel Survey of Galactic OH+, H2O+, and H3O+: Probing the Molecular Hydrogen Fraction and Cosmic-Ray Ionization Rate

In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen-bearing ions OH+, H2O+, and H3O+ begins with the ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H2. Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray ionization rate of atomic hydrogen (ζH) and molecular hydrogen fraction (f_H_2). We present observations targeting transitions of OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources. Both OH+ and H2O+ are detected in absorption in multiple velocity components along every sight line, but H3O+ is only detected along 7 sight lines. From the molecular abundances we compute f_H_2 in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0.042 ± 0.018. This confirms previous findings that OH+ and H2O+ primarily reside in gas with low H2 fractions. We also infer ζH throughout our sample, and find a lognormal distribution with mean log (ζH) = –15.75 (ζH = 1.78 × 10–16 s–1) and standard deviation 0.29 for gas within the Galactic disk, but outside of the Galactic center. This is in good agreement with the mean and distribution of cosmic-ray ionization rates previously inferred from H_3^+ observations. Ionization rates in the Galactic center tend to be 10-100 times larger than found in the Galactic disk, also in accord with prior studies.

DIGGING INTO NGC 6334 I(N): MULTIWAVELENGTH IMAGING OF A MASSIVE PROTOSTELLAR CLUSTER

We present a high-resolution, multi-wavelength study of the massive protostellar cluster NGC 6334 I(N) that combines new spectral line data from the Submillimeter Array (SMA) and VLA with a re-analysis of archival VLA continuum data, Two Micron All Sky Survey and Spitzer images. As shown previously, the brightest 1.3 mm source SMA1 contains substructure at subarcsecond resolution, and we report the first detection of SMA1b at 3.6 cm along with a new spatial component at 7 mm (SMA1d). We find SMA1 (aggregate of sources a, b, c, and d) and SMA4 to be comprised of free-free and dust components, while SMA6 shows only dust emission. Our 15 resolution 1.3 mm molecular line images reveal substantial hot-core line emission toward SMA1 and to a lesser degree SMA2. We find CH3OH rotation temperatures of 165 ± 9 K and 145 ± 12 K for SMA1 and SMA2, respectively. We estimate a diameter of 1400 AU for the SMA1 hot-core emission, encompassing both SMA1b and SMA1d, and speculate that these sources comprise a 800 AU separation binary that may explain the previously suggested precession of the outflow emanating from the SMA1 region. Compact line emission from SMA4 is weak, and none is seen toward SMA6. The LSR velocities of SMA1, SMA2, and SMA4 all differ by 1-2 km s–1. Outflow activity from SMA1, SMA2, SMA4, and SMA6 is observed in several molecules including SiO(5-4) and IRAC 4.5 μm emission; 24 μm emission from SMA4 is also detected. Eleven water maser groups are detected, eight of which coincide with SMA1, SMA2, SMA4, and SMA6, while two others are associated with the Sandell source SM2. We also detect a total of 83 Class I CH3OH 44 GHz maser spots which likely result from the combined activity of many outflows. Our observations paint the portrait of multiple young hot cores in a protocluster prior to the stage where its members become visible in the near-infrared.

The distribution of the 6(2)-6(1) and 5(2)-5(1) E-type methanol masers in OMC-1

The 6 2 -6 1 and 5 2 -5 1 E transitions of CH 3 OH have been mapped toward the Orion-KL region with an angular resolution of 3″ and a frequency resolution of 12 kHz (=0.15 km/s). There are at least 16 masers of flux density greater than 3 Jy. These are distributed in a 40″ long crescent shaped region, extending from NW to SE around the hot core. The radial velocities and positions of some of these masers agree with a peak of the 8 0 -7 1 A transition of CH 3 OH, near 95 GHz

VLBI observations of 12 GHz methanol masers

VLBI observations of 12.1-GHz emission from interstellar methanol toward three star-formation regions, obtained with the Haystack 37-m, NRAO 43-m, and NRL 25-m antennas on April 9, 1988, are reported. Data on W3(OH), NGC 7538, and Cep A are presented in tables, graphs, and contour maps and characterized in detail. All three of the regions are found to contain both compact continuum emission and individual OH maser spots. The spots in W3(OH) have sizes less than 7 x 10 to the 13th cm and temperatures in excess of 2 x 10 to the 10th K. 24 references.

High-resolution VLA observations of the W3(OH) methanol masers

VLA observations of the 9(2)-10(1) A(+) transition of methanol (CH3OH) with 0.08-arcsec resolution toward W3(OH) are presented. The emission arises from at least eight regions situated on a crescent-shaped arc which is aligned in approximately the N-S direction in front of the compact H II region. The angular sizes of the individual regions are less tha 0.04 arcsec, the brightness temperature of the most intense region is at least 10 to the 7th K. A VLBI experiment gave no fringes, implying a lower limit of 0.003 arcsec on the angular size or an upper limit of 2 X 10 to the 9th K on the brightness temperature of the strongest feature. There is a close resmeblance between the spatial distribution of the CH3OH and OH maser emission. It is concluded that the conditions required for maser action of both species must be closely related. 16 references.

Parallaxes and proper motions of interstellar masers toward the Cygnus X star-forming complex

K. L. J. Rygl∗a, A. Brunthalerb, A. Sannab, K. M. Mentenb, M. J. Reidc, H. J. van Langevelded, f , M. Honmae, K. J. E. Torstensson f ,d, and K. Fujisawag aIstituto di Astrofisica e Planetologia Spaziali (INAF-IAPS), Via del fosso del cavaliere 100, 00133 Roma, Italy b Max-Planck-Institut für Radiostronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany c Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA d Joint Institute for VLBI in Europe (JIVE), Postbus 2, 7990 AA Dwingeloo, the Netherlands e Mizusawa VLBI Observatory, National Astronomical Observatory of Japan (NAOJ), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan f Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, the Netherlands gFaculty of Science, Yamaguchi University, 1677-1 Yoshida, Yamaguchi 753-8512, Japan E-mail: kazi.rygl@inaf.it

Mapping the Milky Way structure with methanol and water masers

We review recent VLBA and VERA results in measuring trigonometric parallaxes of methanol and water maser sources. The derived source distances are typically accurate to 5-10%, and in a few cases even better. Proper motions are measured with typical uncertainties of a few kilometer per second. The VLBA data observed so far allow one to precisely locate portions of the Perseus Arm, the Local Spur and Carina-Sagittarius Arm. VERA and VLBA observations support the presence of an Outer Arm extending from the 2nd to the 3rd quadrant of the Milky Way. Derived peculiar motions suggest that the observed maser sources orbit slower than the Galaxy spins.

Triennial Report, International Astronomical Union, Division VI/Commission 34/Working Group Astrochemistry

The study of molecules in space, known as astrochemistry or molecular astrophysics, is a rapidly growing field. Molecules exist in a wide range of environments in both gaseous and solid form, from our own solar system to the distant early universe. To astronomers, molecules are indispensable and unique probes of the physical conditions and dynamics of regions in which they are detected, especially the interstellar medium. In particular, the many stages of both low-mass and high-mass star formation are better understood today thanks to the analysis of molecular observations. Molecules can also yield a global picture of the past and present of sources. Moreover, molecules affect their environment by contributing to the heating and cooling processes that occur.

Division VI / Commission 34 / Working Group Astrochemistry

The study of molecules in space, known as astrochemistry or molecular astrophysics, is a rapidly growing field. Molecules exist in a wide range of environments in both gaseous and solid form, from our own solar system to the distant early universe. To astronomers, molecules are indispensable and unique probes of the physical conditions and dynamics of regions in which they are detected, especially the interstellar medium. In particular, the many stages of both low-mass and high-mass star formation are better understood today thanks to the analysis of molecular observations. Molecules can also yield a global picture of the past and present of sources. Moreover, molecules affect their environment by contributing to the heating and cooling processes that occur.