Time-ordered data simulation and map-making for the PIXIE Fourier transform spectrometer

We develop a time-ordered data simulator and map-maker for the proposed PIXIE Fourier transform spectrometer and use them to investigate the impact of polarization leakage, imperfect collimation, elliptical beams, sub-pixel effects, correlated noise and spectrometer mirror jitter on the PIXIE data analysis. We find that PIXIE is robust to all of these effects, with the exception of mirror jitter which could become the dominant source of noise in the experiment if the jitter is not kept significantly below $0.1\mu m\sqrt{s}$. Source code is available at https://github.com/amaurea/pixie.Comment: 27 pages, 15 figures. Accepted for publication in JCA

The Primordial Inflation Explorer (PIXIE)

The Primordial Inflation Explorer is an Explorer-class mission to open new windows on the early universe through measurements of the polarization and absolute frequency spectrum of the cosmic microwave background. PIXIE will measure the gravitational-wave signature of primordial inflation through its distinctive imprint in linear polarization, and characterize the thermal history of the universe through precision measurements of distortions in the blackbody spectrum. PIXIE uses an innovative optical design to achieve background-limited sensitivity in 400 spectral channels spanning over 7 octaves in frequency from 30 GHz to 6 THz (1 cm to 50 micron wavelength). Multi-moded non-imaging optics feed a polarizing Fourier Transform Spectrometer to produce a set of interference fringes, proportional to the difference spectrum between orthogonal linear polarizations from the two input beams. Multiple levels of symmetry and signal modulation combine to reduce systematic errors to negligible levels. PIXIE will map the full sky in Stokes I, Q, and U parameters with angular resolution 2.6 degrees and sensitivity 70 nK per 1degree square pixel. The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r < 10(exp. -3) at 5 standard deviations. The PIXIE mission complements anticipated ground-based polarization measurements such as CMBS4, providing a cosmic-variance-limited determination of the large-scale E-mode signal to measure the optical depth, constrain models of reionization, and provide a firm detection of the neutrino mass (the last unknown parameter in the Standard Model of particle physics). In addition, PIXIE will measure the absolute frequency spectrum to characterize deviations from a blackbody with sensitivity 3 orders of magnitude beyond the seminal COBE/FIRAS limits. The sky cannot be black at this level; the expected results will constrain physical processes ranging from inflation to the nature of the first stars and the physical conditions within the interstellar medium of the Galaxy. We describe the PIXIE instrument and mission architecture required to measure the CMB to the limits imposed by astrophysical foregrounds

The mid-infrared Tully-Fisher relation: Spitzer Surface Photometry

The availability of photometric imaging of several thousand galaxies with the Spitzer Space Telescope enables a mid-infrared calibration of the correlation between luminosity and rotation in spiral galaxies. The most important advantage of the new calibration in the 3.6 micron band, IRAC ch.1, is photometric consistency across the entire sky. Additional advantages are minimal obscuration, observations of flux dominated by old stars, and sensitivity to low surface brightness levels due to favorable backgrounds. Through Spitzer cycle 7 roughly 3000 galaxies had been observed and images of these are available at the Spitzer archive. In cycle 8 a program called Cosmic Flows with Spitzer has been initiated that will increase by 1274 the available sample of spiral galaxies with inclinations greater than 45 degrees from face-on suitable for distance measurements. This paper describes procedures based on the photometry package Archangel that are being employed to analyze both the archival and the new data in a uniform way. We give results for 235 galaxies, our calibrator sample for the Tully-Fisher relation. Galaxy magnitudes are determined with uncertainties held below 0.05 mag for normal spiral systems. A subsequent paper will describe the calibration of the [3.6] luminosity-rotation relation.Comment: Accepted for publication in The Astronomical Journal, 12 pages, 9 figure

Optimal Energy Measurement in Nonlinear Systems: An Application of Differential Geometry

Design of TES microcalorimeters requires a tradeoff between resolution and dynamic range. Often, experimenters will require linearity for the highest energy signals, which requires additional heat capacity be added to the detector. This results in a reduction of low energy resolution in the detector. We derive and demonstrate an algorithm that allows operation far into the nonlinear regime with little loss in spectral resolution. We use a least squares optimal filter that varies with photon energy to accommodate the nonlinearity of the detector and the non-stationarity of the noise. The fitting process we use can be seen as an application of differential geometry. This recognition provides a set of well-developed tools to extend our work to more complex situations. The proper calibration of a nonlinear microcalorimeter requires a source with densely spaced narrow lines. A pulsed laser multi-photon source is used here, and is seen to be a powerful tool for allowing us to develop practical systems with significant detector nonlinearity. The combination of our analysis techniques and the multi-photon laser source create a powerful tool for increasing the performance of future TES microcalorimeters

Dust Emissivity Variations In the Milky Way

Dust properties appear to vary according to the environment in which the dust evolves. Previous observational indications of these variations in the FIR and submm spectral range are scarce and limited to specific regions of the sky. To determine whether these results can be generalised to larger scales, we study the evolution in dust emissivities from the FIR to mm wavelengths, in the atomic and molecular ISM, along the Galactic plane towards the outer Galaxy. We correlate the dust FIR to mm emission with the HI and CO emission. The study is carried out using the DIRBE data from 100 to 240 mic, the Archeops data from 550 mic to 2.1 mm, and the WMAP data at 3.2 mm (W band), in regions with Galactic latitude |b| < 30 deg, over the Galactic longitude range (75 deg < l < 198 deg) observed with Archeops. In all regions studied, the emissivity spectra in both the atomic and molecular phases are steeper in the FIR (beta = 2.4) than in the submm and mm (beta = 1.5). We find significant variations in the spectral shape of the dust emissivity as a function of the dust temperature in the molecular phase. Regions of similar dust temperature in the molecular and atomic gas exhibit similar emissivity spectra. Regions where the dust is significantly colder in the molecular phase show a significant increase in emissivity for the range 100 - 550 mic. This result supports the hypothesis of grain coagulation in these regions, confirming results obtained over small fractions of the sky in previous studies and allowing us to expand these results to the cold molecular environments in general of the outer MW. We note that it is the first time that these effects have been demonstrated by direct measurement of the emissivity, while previous studies were based only on thermal arguments.Comment: 16 pages, 6 figures, accepted in A&