Fig 4 - uploaded by Jonas Zmuidzinas
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Mask layout of the QMMIC substrate. Actual size is approximately 2.5x3.8 mm. The InP HEMTs are bonded to the three pads spaced horizontally across the center of the chip. The input is coplanar waveguide on the left, and the output is on the right. There are three bond pads at the top for gate bias, and three across the bottom for drain bias.
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We present a 12CO J ¼ 6-5 map of the nuclear regions of the starburst galaxy M82 at a resolution of 1400 taken at the Caltech Submillimeter Observatory (CSO). Hot spots were found on either side of the dynamical center. We compare our results with a high-resolution 12CO J ¼ 2-1 interferometer map, and present a 12CO J ¼ 6-5/12CO J ¼ 2-1 line ratio map obtained using a novel deconvolution technique. This line ratio is highest at the two J ¼ 6-5 integrated intensity peaks, reaching 0.4 and 0.5 in the northeast and southwest peaks, respectively, and is typically 0.2 elsewhere in the nuclear region. We also present measurements of 12CO J ¼ 4-3, 12CO J ¼ 3-2, and 13CO J ¼ 3-2, and an upper limit for 13CO J ¼ 6-5. We analyze these observations in the context of a two-component large velocity gradient (LVG) excitation model. Likelihood density curves were calculated for each of the model parameters and a variety of related physical quantities for the northeast and southwest peaks based on the measured line intensities and their associated uncertainties. This approach reveals in an unbiased way how well various quantities can be constrained by the CO observa- tions. We find that the beam-averaged 12CO and 13CO column densities, the isotopomer abundance ratio, and the area filling factors are among the best constrained quantities, while the cool component H2 density and pressure are less well constrained. The results of this analysis suggest that the warm gas is less dense than the cool gas, and that over half of the total molecular gas mass in these nuclear regions is warmer than 50 K. Subject headings: galaxies: individual (M82) — galaxies: ISM — galaxies: starburst — submillimeter
New astronomical and remote-sensing instruments require microwave spectrometers with modest spectral res-olution over many gigahertz of instantaneous bandwidth. Applications include millimeter-wave searches for distant objects with poorly known redshifts, submillimeter and far-infrared observations of Doppler-broadened spectral lines from galaxies, and observations of pressure-broadened atmospheric lines. Wide bandwidths and the consequent stability requirements make it difficult to use general-purpose re-ceiver and spectrometer architectures in these applications. We discuss analog auto-and cross-correlation lag spectrometers that are optimized for these observations. Analog correlators obtain their wide bandwidths by a combination of transmission line delays and direct voltage multiplication in transistor or diode mixers. We show results from a new custom transistor multiplier with bandwidth to 25 GHz. Stability becomes increasingly im-portant as bandwidths broaden. We discuss system requirements for single-dish correlation radiometers, which have intrinsic high stability, and present results showing that analog cross-correlators are suitable backends for these receivers.
