A. Goldin

THE BOLOCAM LOCKMAN HOLE MILLIMETER-WAVE GALAXY SURVEY: GALAXY CANDIDATES AND NUMBER COUNTS

We present results of a new deep 1.1 mm survey using Bolocam, a millimeter-wavelength bolometer array camera designed for mapping large fields at fast scan rates, without chopping. A map, galaxy candidate list, and derived number counts are presented. This survey encompasses 324 arcmin2 to an rms noise level (filtered for point sources) of ?1:1 mm ’1:4 mJy beam?1 and includes the entire regions surveyed by the published 8 mJy 850 ?m JCMT SCUBA and 1.2 mm IRAM MAMBO surveys. We reduced the data using a custom software pipeline to remove correlated sky and instrument noise via a principal component analysis. Extensive simulations and jackknife tests were performed to confirm the robustness of our source candidates and estimate the effects of false detections, bias, and completeness. In total, 17 source candidates were detected at a significance ?3.0 ?, with six expected false detections. Nine candidates are new detections, while eight candidates have coincident SCUBA 850 ?m and/or MAMBO 1.2 mm detections. From our observed number counts, we estimate the underlying differential number count distribution of submillimeter galaxies and find it to be in general agreement with previous surveys. Modeling the spectral energy distributions of these submillimeter galaxies after observations of dusty nearby galaxies suggests extreme luminosities of L ¼ ð1:0 1:6Þ ; 1013 L? and, if powered by star formation, star formation rates of 500–800 M? yr?1.

Current status of Bolocam: a large-format millimeter-wave bolometer camera

We describe the design and performance of Bolocam, a 144-element, bolometric, millimeter-wave camera. Bolocam is currently in its commissioning stage at the Caltech Submillimeter Observatory. We compare the instrument performance measured at the telescope with a detailed sensitivity model, discuss the factors limiting the current sensitivity, and describe our plans for future improvements intended to increase the mapping speed.

A fluctuation analysis of the Bolocam 1.1 mm Lockman Hole Survey

We perform a fluctuation analysis of the 1.1 mm Bolocam Lockman Hole Survey, which covers 324 arcmin2 to a very uniform point-source-filtered rms noise level of σ 1.4 mJy beam-1. The fluctuation analysis has the significant advantage of using all of the available data, since no extraction of sources is performed: direct comparison is made between the observed pixel flux density distribution [P(D)] and the theoretical distributions for a broad range of power-law number count models, n(S) = n0S-δ. We constrain the number counts in the 1-10 mJy range and derive significantly tighter constraints than in previous work: the power-law index δ = 2.7, while the amplitude is n0 = 1595 mJy-1 , or N(> 1 mJy) = 940 (95% confidence). At flux densities above 4 mJy, where a valid comparison can be made, our results agree extremely well with those derived from the extracted source number counts by Laurent et al.: the best-fitting differential slope is somewhat shallower (δ = 2.7 vs. 3.2), but well within the 68% confidence limit, and the amplitudes (number of sources per square degree) agree to 10%. At 1 mJy, however [the limit of the P(D) analysis], the shallower slope derived here implies a substantially smaller amplitude for the integral number counts than extrapolation from above 4 mJy would predict. Our derived normalization is about 2.5 times smaller than that determined by the Max-Planck Millimeter Bolometer (MAMBO) at 1.2 mm (Greve et al.). However, the uncertainty in the normalization for both data sets is dominated by the systematic (i.e., absolute flux calibration) rather than statistical errors; within these uncertainties, our results are in agreement. Our best-fit amplitude at 1 mJy is also about a factor of 3 below the prediction of Blain et al., but we are in agreement above a few millijanskys. We estimate that about 7% of the 1.1 mm background has been resolved at 1 mJy.

TRANSITION-EDGE SUPERCONDUCTING ANTENNA- COUPLED BOLOMETER

We report test results for a single pixel antenna-coupled bolometric detector. Our device consists of a dual slot microstrip antenna coupled to an Al/Ti/Au voltage-biased transition edge superconducting bolometer (TES). The coupling architecture involves propagating the signal along superconducting microstrip lines and terminating the lines at a normal metal resistor colocated with a TES on a thermally isolated island. The device, which is inherently polarization sensitive, is optimized for 140 GHz band measurements. In the thermal bandwidth of the TES, we measure a noise equivalent power of 2.0 × 10-17 W/√Hz in dark tests that agrees with calculated NEP including only contributions from thermal, Johnson and amplifier noise. We do not measure any excess noise at frequencies between 1 and 200 Hz. We measure a thermal conductance G ~5.5 × 10-11 W/K. We measure a thermal time constant as low as 437μs at 3μV bias when stimulating the TES directly using an LED.

Design of broadband filters and antennas for SAMBA

We present a design for multipixel, multiband submillimeter instrument: SAMBA (Superconducting Antenna-coupled, Multi-frequency, Bolometric Array). SAMBA uses antenna coupled bolometers and microstrip filters. The concept allows for a much more compact, multiband imager compared to a comparable feedhorn-coupled bolometric system. SAMBA incorporates an array of slot antennas, superconducting transmission lines, a wide band multiplexer and superconducting transition edge bolometers. The transition-edge film measures the millimeter-wave power deposited in the resistor that terminates the transmission line.

SAMBA: Superconducting antenna-coupled, multi-frequency, bolometric array

We present a design for a multipixel, multiband (100 GHz, 200 GHz and 400 GHz) submillimeter instrument: SAMBA (Superconducting Antenna-coupled, Multi-frequency, Bolometric Array). SAMBA uses slot antenna coupled bolometers and microstrip filters. The concept allows for a much more compact, multiband imager compared to a comparable feedhorn-coupled bolometric system. SAMBA incorporates an array of slot antennas, superconducting transmission lines, a wide band multiplexer and superconducting transition edge bolometers. The transition-edge film measures the millimeter-wave power deposited in the resistor that terminates the transmission line.

Antenna-coupled TES bolometers for CMB polarimetry

We have developed a completely lithographic antenna-coupled bolometer for CMB polarimetry. The necessary components of a millimeter wave radiometer - a beam forming element, a band defining filter, and the TES detectors - are fabricated on a silicon chip with photolithography. The densely populated antennas allow a very efficient use of the focal plane area. We have fabricated and characterized a series of prototype devices. We find that their properties, including the frequency and angular responses, are in good agreement with the theoretical expectations. The devices are undergoing optimization for upcoming CMB experiments.

Far-infrared/submillimeter imager-polarimeter using distributed antenna-coupled transition edge sensors

We describe a new concept for a detector for the submillimeter and far infrared that uses a distributed hot-electron transition edge sensor (TES) to collect the power from a focal-plane-filling slot antenna array. Because superconducting transmission lines are lossy at frequencies greater than about 1 Thz, the sensors must directly tap the antenna, and therefore must match the antenna impedance (≫ 30 ohms). Each pixel contains many TESs that are all wired in parallel as a single distributed TES, which results in a low impedance that can match to a multiplexed SQUID readout. These detectors are inherently polarization sensitive, with very low cross-polarization, but can also be easily configured to sum both polarizations for imaging applications. The single polarization version can have a very wide bandwidth of greater than 10:1 with a quantum e±ciency greater than 50%. The dual polarization version is narrow band, but can have a higher quantum e±ciency. The use of electron-phonon decoupling obviates the need for micro-machining, making the focal plane much easier to fabricate than with absorber-coupled, geometrically isolated pixels. An array of these detectors would be suitable for an imager for the Single Aperture Far Infrared (SAFIR) observatory. We consider two near-term applications of this technology, a 32 £ 32 element imaging polarimeter for SOFIA and a 3501m camera for the CSO.

Studies of atmospheric noise on Mauna Kea at 143 GHz with Bolocam

We report measurements of the fluctuations in atmospheric emission (atmospheric noise) above Mauna Kea recorded with Bolocam at 143 GHz. These data were collected in November and December of 2003 with Bolocam mounted on the Caltech Submillimeter Observatory (CSO), and span approximately 40 nights. Below ≃ 0.5 Hz, the data time-streams are dominated by the f-δ atmospheric noise in all observing conditions. We were able to successfully model the atmospheric fluctuations using a Kolmogorov-Taylor turbulence model for a thin wind-driven screen in approximately half of our data. Based on this modeling, we developed several algorithms to remove the atmospheric noise, and the best results were achieved when we described the fluctuations using a low-order polynomial in detector position over the 8 arcminute focal plane. However, even with these algorithms, we were not able to reach photon-background-limited instrument photometer (BLIP) performance at frequencies below ≃ 0.5 Hz in any observing conditions. Therefore, we conclude that BLIP performance is not possible from the CSO below ≃ 0.5 Hz for broadband 150 GHz receivers with subtraction of a spatial atmospheric template on scales of several arcminutes.

Integrated focal plane arrays for millimeter-wave astronomy

We are developing focal plane arrays of bolometric detectors for sub-millimeter and millimeter-wave astrophysics. We propose a flexible array architecture using arrays of slot antennae coupled via low-loss superconducting Nb transmission line to microstrip filters and antenna-coupled bolometers. By combining imaging and filtering functions with transmission line, we are able to realize unique structures such as a multi-band polarimeter and a planar, dispersive spectrometer. Micro-strip bolometers have significantly smaller active volume than standard detectors with extended absorbers, and can realize higher sensitivity and speed of response. The integrated array has natural immunity to stray radiation or spectral leaks, and minimizes the suspended mass operating at 0.1 - 0.3 K. We also discuss future space-borne spectroscopy and polarimetry applications.