G. T. Laurent

Bolocam Survey for 1.1 mm Dust Continuum Emission in the c2d Legacy Clouds. II. Ophiuchus

We present a large-scale millimeter continuum map of the Ophiuchus molecular cloud. Nearly 11 deg2, including all of the area in the cloud with AV ≥ 3 mag, was mapped at 1.1 mm with Bolocam on the Caltech Submillimeter Observatory (CSO). By design, the map also covers the region mapped in the infrared with the Spitzer Space Telescope. We detect 44 definite sources, and a few likely sources are also seen along a filament in the eastern streamer. The map indicates that dense cores in Ophiuchus are very clustered and often found in filaments within the cloud. Most sources are round, as measured at the half-power point, but elongated when measured at lower contour levels, suggesting spherical sources lying within filaments. The masses, for an assumed dust temperature of 10 K, range from 0.24 to 3.9 M☉, with a mean value of 0.96 M☉. The total mass in distinct cores is 42 M☉, 0.5%-2% of the total cloud mass, and the total mass above 4 σ is about 80 M☉. The mean densities in the cores are quite high, with an average of 1.6 × 106 cm-3, suggesting short free-fall times. The core mass distribution can be fitted with a power law with slope α = 2.1 ± 0.3 for M > 0.5 M☉, similar to that found in other regions, but slightly shallower than that of some determinations of the local IMF. In agreement with previous studies, our survey shows that dense cores account for a very small fraction of the cloud volume and total mass. They are nearly all confined to regions with AV ≥ 9 mag, a lower threshold than found previously.

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.

HerMES: deep galaxy number counts from a P(D) fluctuation analysis of SPIRE Science Demonstration Phase observations

Dusty, star-forming galaxies contribute to a bright, currently unresolved cosmic far-infrared background. Deep Herschel-Spectral and Photometric Imaging Receiver (SPIRE) images designed to detect and characterize the galaxies that comprise this background are highly confused, such that the bulk lies below the classical confusion limit. We analyse three fields from the Herschel Multi-tiered Extragalactic Survey (HerMES) programme in all three SPIRE bands (250, 350 and 500 μm); parametrized galaxy number count models are derived to a depth of ~2 mJy beam^(−1), approximately four times the depth of previous analyses at these wavelengths, using a probability of deflection [P(D)] approach for comparison to theoretical number count models. Our fits account for 64, 60 and 43 per cent of the far-infrared background in the three bands. The number counts are consistent with those based on individually detected SPIRE sources, but generally inconsistent with most galaxy number count models, which generically overpredict the number of bright galaxies and are not as steep as the P(D)-derived number counts. Clear evidence is found for a break in the slope of the differential number counts at low flux densities. Systematic effects in the P(D) analysis are explored. We find that the effects of clustering have a small impact on the data, and the largest identified systematic error arises from uncertainties in the SPIRE beam.

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.

The Bolocam 1.1 mm Lockman Hole Galaxy Survey: SHARC II 350 μm Photometry and Implications for Spectral Models, Dust Temperatures, and Redshift Estimation

We present 350 ?m photometry of all 17 galaxy candidates in the Lockman Hole detected in a 1.1 mm Bolocam survey. Several of the galaxies were previously detected at 850 ?m, at 1.2 mm, in the infrared by Spitzer, and in the radio. Nine of the Bolocam galaxy candidates were detected at 350 ?m, and two new candidates were serendipitously detected at 350 ?m (bringing the total in the literature detected in this way to three). Five of the galaxies have published spectroscopic redshifts, enabling investigation of the implied temperature ranges and a comparison of photometric redshift techniques. For z ? 2.5 thermally emitting galaxies, ? = 350 ?m lies near the spectral energy distribution peak. Thus, luminosities can be measured without extrapolating to the peak from detection wavelengths of ? ? 850 ?m. Characteristically, the galaxy luminosities lie in the range 1.0-1.2 ? 1013 L?, with dust temperatures in the range 40-70 K, depending on the choice of spectral index and wavelength of unit optical depth. The implied dust masses are ? 108 M?. We find that the far-infrared to radio relation for star-forming ULIRGs systematically overpredicts the radio luminosities and overestimates redshifts on the order of ?z ? 1, whereas redshifts based on either submillimeter data alone or the 1.6 ?m stellar bump and PAH features are more accurate.

The Herschel-SPIRE photometer data processing pipeline

We describe the on-board electronics chain and the on-ground data processing pipeline that will operate on data from the Herschel-SPIRE photometer to produce calibrated astronomical products. Data from the three photometer arrays will be conditioned and digitised by on-board electronics and sent to the ground with no further on-board data processing. On the ground, the data pipeline will process the data from point source, jiggle-map, and scan-map observations in a fully automatic manner, producing measured flux densities (for point source observations) or maps. It includes calculation of the bolometer voltages from the raw telemetry, glitch removal, and corrections for various effects including time constants associated with the detectors and electronics, electrical and optical crosstalk, detector temperature drifts, flatfielding, and non-linear response of the bolometers to strong sources. Flux density calibration will be with respect to standard astronomical sources with the planets Uranus and Neptune being adopted as the baseline primary standards. The pipeline will compute estimated values of in-beam flux density for a standard flat νS(ν) source spectrum.

Noise performance of the Herschel-SPIRE bolometers during instrument ground tests.

The flight model of the SPIRE instrument underwent several test campaigns in a test facility at the Rutherford Appleton Laboratory (RAL) in the UK. A final dark campaign, completed in March 2007, provided an environment virtually free from optical radiation. This allowed re-determining the fundamental model parameters of the NTD spider web bolometer detector arrays in the new environment. The tests reported in this paper produced a fairly homogeneous dataset to investigate white noise and 1/f noise at different bias voltages, bias frequencies, and bath temperatures. We find that the white noise performance is in excellent agreement with the model predictions, once we correct the low frequency signal variations that are due to temperature fluctuations of the thermal bath at about 300 mK. The temperature of the thermal bath (detector array base plate) is measured by thermistor pixels that are part of the bolometer arrays. A residual 1/f component beyond those variations is hardly detected. This unexpected stability is very welcome and will positively impact photometer scan maps, the most popular observing mode of SPIRE.

Optical performance characterisation of HERSCHEL/SPIRE

The Spectral and Photometric Imaging Receiver (SPIRE) is one of three scientific instruments on ESAs Herschel Space Observatory. The instrument covers 200 to 670 μm with a three band photometric camera and a two band imaging Fourier Transform Spectrometer (IFTS). In this paper we discuss the performance of the optics of the instrument as determined during the pre-flight instrument testing to date. In particular we concentrate on the response of the instrument to a point source, the comparison between the visible light alignment and the infrared alignment and the effect of the optical performance on the overall instrument sensitivity. We compare the empirical performance of the instrument optics to that expected from elementary diffraction theory.

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.