The Square Kilometre Array (SKA)

Abstract:

The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) has uncovered a population of strongly lensed submillimeter galaxies (SMGs). The Zpectrometer instrument on the Green Bank Telescope (GBT) was used to measure the redshifts and constrain the masses of the cold molecular gas reservoirs for two candidate highredshift lensed sources. We derive CO(1-0) redshifts of z = 3.042 ± 0.001 and z = 2.625 ± 0.001, and measure molecular gas masses of (1-3) ×1010M⊙, corrected for lens amplification and assuming a conversion factor of α = 0.8 M ⊙ (Kkm s-1 pc2)-1. We find typical L(IR)/L'(CO) ratios of 120 ±40 and 140±50L ⊙ (Kkm s-1 pc2)-1, which are consistent with those found for local ultraluminous infrared galaxies (ULIRGs) and other high-redshift SMGs. From analysis of published data, we find no evidence for enhanced L(IR)/L'(CO(1-0)) ratios for the SMG population in comparison to local ULIRGs. The GBT results highlight the power of using the CO lines to derive blind redshifts, which is challenging for the SMGs at optical wavelengths given their high obscuration. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.

Abstract:

The design and preliminary results from testing the performance of a 230GHz unilateral finline SIS mixer, fabricated on a silicon substrate are presented. The mixer will be employed in the single baseline heterodyne interferometer-GUBBINS (220-GHz Ultra-BroadBand INterferometer for S-Z), which aims to measure the null frequency in the Sunyaev-Zel'dovich spectrum at ~227GHz. The mixer is operated in the frequency range of 180GHz~280GHz with an IF bandwidth of 1-13 GHz. An important feature of this mixer is its ultra-wide IF bandwidth, so as to achieve very high brightness sensitivity in the observation of the galaxy clusters in the faint cosmic microwave background radiation. This SIS mixer described is deposited on an 80um silicon substrate with the dielectric constant of 11.9. The incoming RF signal from the feed horn is coupled via the waveguide mode to a unilateral finline, which is tapered to a 2.5um slotline. The signal is coupled from the slotline to the microstrip with the aid of two radial stubs. The employment of a silicon substrates gives a slotline impedance of 36Ω, which is ideal for coupling to the microstrip, where the SIS junction is fabricated. Also, the employment of silicon allows the generation of the trenches around the device so that individual devices can be separated from the batch without dicing. A 2-stage notch was fabricated at the front end of the substrate to match the loaded waveguide to the free space. The capacitance of the SIS junction was tuned out using a wide band circuit consisting of two stubs and a 3-stage Chebyshev transformer. This is followed by a 3-stage RF choke to prevent RF signal from leaking into the IF output port. The mixer chip was fabricated at KOSMA, Cologne using Nb-AlOx-Nb tunnel junction defined with E-beam lithography. The device used in this experiment had a normal resistance of 20Ω, a current density of 14KA/cm2, an area of 1μm2 and an intrinsic capacitance of 75fF. Measurement of the mixer performance was done using a local oscillator which gives sufficient power to pump the mixer in the frequency range 200GHz~260GHz using 12μm beam splitter. Measurement of the mixer sensitivity was done using the hot/cold Y-factor method. Uncorrected noise temperature of 75K was obtained at 208GHz, with 30 K contributed by mismatch to the IF system. Future characterization and improvements of the IF system and the measurement with better-tuned devices will also be reported.

Abstract:

We investigate the behaviour of the accretion discs in the outbursts of the low-mass black hole X-ray binaries (BHXRBs), an overview of which we have presented previously. Almost all of the systems in which there are sufficient observations in the most-disc-dominated states show a variation in the disc luminosity with temperature close to This in turn implies that in these states, the disc radius, Rin, and the colour correction factor, fcol, are almost constant. Deviations away from the T4 law are observed at the beginning and end of the most-disc-dominated states, during the intermediate states. Although these could be explained by an inward motion of the accretion disc, they are more likely to be the result of an increase in the value of fcol as the disc fraction decreases. By comparing the expected and observed disc luminosities, we place approximate limits on the allowed distances and masses of the BHXRB system. In a number of cases, the measured distances and masses of the BHXRB system indicate that it is possible that the black hole may be spinning. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS.