Dr. Boon Kok Tan

Abstract:

We present 12CO J = 3→2 maps of NGC 2976 and NGC 3351 obtained with the James Clerk Maxwell Telescope (JCMT), both early targets of the JCMT Nearby Galaxy Legacy Survey (NGLS). We combine the present observations with 12CO J = 1→0 data and find that the computed 12CO J = 3→2 to 12CO J = 1→0 line ratio (R31) agrees with values measured in other NGLS field galaxies. We compute the MH2 value and find that it is robust against the value of R31 used. Using HI data from The HI Nearby Galaxy Survey, we find a tight correlation between the surface density of H2 and star formation rate density for NGC 3351 when 12CO J = 3→2 data are used. Finally, we compare the 12CO J = 3→2 intensity with the polycyclic aromatic hydrocarbon (PAH) 8 μm surface brightness and find a good correlation in the high surface brightness regions. We extend this study to include all 25 Spitzer Infrared Nearby Galaxies Survey galaxies within the NGLS sample and find a tight correlation at large spatial scales. We suggest that both PAH 8 μm and 12CO J = 3→2 are likely to originate in regions of active star formation. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

Modern ground-based radio-telescopes have stringent requirements on the receiver's feed-horn performance. These include a bandwidth covering a full atmospheric window from good sites (∼ 30%), low cross polarization and high beam circularity. In addition the unprecedented sensitivity required by recent proposed experiments requires large format focal plane arrays consisting of a large number of high performance feeds. While these feeds are straightforward to fabricate at microwave frequencies, the tight tolerances required in the THz region makes the realization of a large format array both expensive and time consuming. In this paper we describe feed designs that can be fabricated cheaply and rapidly without compromising the science requirements within the operating bandwidth. We present simulated and measured far-field beam patterns showing low sidelobe levels, good beam circularity and low cross-polarization levels over a fractional bandwidth of 20%. Having demonstrated the efficacy of our horn designs and fabricating technique experimentally, we have designed, fabricated and tested a prototype focal plane array of 37 hexagonally close packed horns milled in a single block of aluminum. Experimental testing of the radiation patterns of the array feeds demonstrated that they were essentially identical to the patterns of the feeds fabricated individually and that cross coupling between adjacent feeds was negligible. © 2013 IEEE.

Abstract:

In this paper, we describe a simple method for widening the instantaneous frequency (IF) bandwidth of a high frequency superconductor-insulator-superconductor (SIS) mixer. This method requires only a standard PCB technology, without incurring any difficulties or complication in altering the tunnel junction fabrication. It involves the use of a simple multi-stage IF transformer to match the dynamic output impedance of the SIS mixer to a 50 Ω load over a wide IF bandwidth. We use an existing 650 GHz SIS mixer chip as an example to illustrate the methodology of the IF transformer design. In this example, we show how we widen the IF bandwidth of the mixer to operate over 4–12 GHz bandwidth using this simple impedance matching method.