Scientific Results in Press

Dust emission from the lensed Lyman break galaxy cB58

Baker, A.J.(¹), Lutz, D.(¹), Genzel, R.(¹), Tacconi, L.J.(¹) and Lehnert, M.D.(¹),
(¹)Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany

Abstract:
We detect 1.2 mm continuum emission from dust in the gravitationally lensed Lyman break galaxy MS 1512+36-cB58. Our detected flux is surprisingly low: relative to local starburst galaxies, cB58 appears to produce somewhat less far-IR emission than its UV reddening predicts. After comparing several different estimates of the source's dust content, we conclude that the apparent discrepancy is most likely related to uncertainty in its UV spectral slope. Alternate scenarios to account for a far-IR ``deficit'' which rely on a high dust temperature or differential magnification are less satisfactory. Our result underscores one of the risks inherent in characterizing the cosmic star formation history from rest-UV data alone.

Appeared in: A&A, 372, L37

Cometary molecular clouds around RNO6.
On-going star formation near the double cluster h and $\chi$ Persei

R. Bachiller(¹), A. Fuente(¹), and M.S.N. Kumar(¹)
(¹)IGN Observatorio Astronómico Nacional, Apartado 1143, E-28800 Alcalá de Henares, Spain

Abstract:
We present molecular line observations of the star-forming cloud around RNO6 along with a newly discovered nearby molecular cloud that we name RNO6NW. Both clouds display striking similarities in their cometary structures and overall kinematics. By using ¹³CO line observations, we estimate that these clouds have similar sizes ($\sim$4.5pc) and masses ($\sim$200 M$_\odot$).
Both molecular clouds RNO6 and RNO6NW are active in star formation. From new high resolution near-IR narrowband images, we confirm that RNO6 hosts an embedded IR cluster that includes a Herbig Be star. A conspicuous H₂ filament is found to delineate the dense cometary head of the globule. RNO6NW hosts at least two IR sources and a bipolar molecular outflow of $\sim$0.9pc of length and $\sim$0.5M$_\odot$ of mass.
We show that the cometary structure of both clouds has been created by the UV radiation from numerous OB stars lying $\sim$1.5^$^\circ$ to the north. Such OB stars are associated with the double cluster h and $\chi$Persei, and are probably members of the PerOB1 association. Thus star formation inside these clouds has been very likely triggered by the Radiation Driven Implosion (RDI) mechanism. From comparison to RDI theoretical models, we find that the similar kinematics and morphology of both clouds is well explained if they are at a re-expansion phase. Triggered sequential star formation also explains the observed spatial distribution of the members of the near-IR cluster inside the RNO6 cloud, and the morphology of the H₂ filament. We conclude that the RNO6 and RNO6NW clouds are high-mass counterparts to the cometary globules of smaller masses which have been studied up to now. Thus our observations demonstrate that the RDI mechanism can produce, not only low mass stars in small globules, but also intermediate mass stars and clusters in massive clouds.

E-mail contact: bachiller@oan.es. Preprints can be obtained at http://www.oan.es/preprints/bachiller.ps.gz

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Accepted by Astronomy & Astrophysics

A search for radio supernovae and supernova remnants in the region of NGC1569's super star clusters

A. Greve(¹), A. Tarchi(²),(³), S. Hüttemeister(⁴),(⁵), R. de Grijs(⁶), J.M. van der Hulst(⁷), S.T. Garrington(⁸)and N. Neininger(²)
(¹)Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d`Hères, France, (²)Astronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany, (³)Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany, (⁴)Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstr. 150, D-44780 Bochum, Germany, (⁵)Onsala Space Observatory, S-43920 Onsala, Sweden, (⁶)Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK, (⁷)Kapteyn Astronomical Instituut, Postbus 800, 9700 AV Groningen, The Netherlands, (⁸)Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield Cheshire SK11 9DL, UK

Abstract:
We have used MERLIN, at 1.4 and 5 GHz, to search for radio supernovae (RSNe) and supernova remnants (SNRs) in the unobscured irregular dwarf galaxy NGC1569, and in particular in the region of its super star clusters (SSCs) A and B. Throughout NGC1569 we find some 5 RSNe and SNRs but the SSCs and their immediate surroundings are largely devoid of non-thermal radio sources. Even though many massive stars in the SSCs are expected to have exploded already, when compared with M82 and its many SSCs the absence of RSNe and SNRs in and near A and B may seem plausible on statistical arguments. The absence of RSNe and SNRs in and near A and B may, however, also be due to a violent and turbulent outflow of stellar winds and supernova ejected material, which does not provide a quiescent environment for the development of SNRs within and near the SSCs.

Accepted by Astronomy & Astrophysics

Design and characterization of 225-370 GHz DSB and 247-360 GHz SSB waveguide SIS mixers

A. Navarrini(¹), D. Billon-Pierron(¹), I. Peron(¹), B. Lazareff(¹)
(¹)Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d`Hères, France

Abstract:
We report on the design and characterization of two full height waveguide SIS mixers for astronomical applications: a Double Side Band (DSB) fixed-tuned mixer covering the 225-370 GHz band, and a tunable Single Side Band (SSB) mixer covering the 247-360 GHz frequency range. The lowest DSB receiver noise temperatures we have measured are 37 K at 320 GHz for the DSB mixer, and 63 K at 350 GHz for the SSB mixer. The measured image gain rejection of the SSB mixer is around -15 dB over most of the frequency range. The ${\rm\approx 50~\%}$bandwidth of the DSB mixer is, to our knowledge, the widest ever reported.
Both mixers use similar chips that integrate a parallel tuning inductor with a radial microstrip stub to compensate for the junction capacitance of 75 fF (junction size ${\rm 1~\mu m^2}$). The junction is mounted on a ${\rm 80 ~\mu m}$ thick quartz that stretches only part way across the waveguide. In the SSB mixer the image rejection is achieved by using a mechanically rugged noncontacting backshort with a circular cross-section that can be moved inside a circular waveguide. A stability criterion for intrinsically DSB and SSB mixers under typical operating conditions has been derived. The receiver design has been optimised in order to guarantee a low mixer noise temperature while maintaining adequate gain and stable operation over the whole frequency band of interest.

To be published in: Proceedings of the 26th. International Conference on Infrared and Millimeter Waves, Toulouse, France, 10/09/2001-14/09/2001.