SPIDER: Probing the Early Universe with a Suborbital Polarimeter

We evaluate the ability of SPIDER, a balloon-borne polarimeter, to detect a divergence-free polarization pattern ("B-modes") in the Cosmic Microwave Background (CMB). In the inflationary scenario, the amplitude of this signal is proportional to that of the primordial scalar perturbations through the tensor-to-scalar ratio r. We show that the expected level of systematic error in the SPIDER instrument is significantly below the amplitude of an interesting cosmological signal with r=0.03. We present a scanning strategy that enables us to minimize uncertainty in the reconstruction of the Stokes parameters used to characterize the CMB, while accessing a relatively wide range of angular scales. Evaluating the amplitude of the polarized Galactic emission in the SPIDER field, we conclude that the polarized emission from interstellar dust is as bright or brighter than the cosmological signal at all SPIDER frequencies (90 GHz, 150 GHz, and 280 GHz), a situation similar to that found in the "Southern Hole." We show that two ~20-day flights of the SPIDER instrument can constrain the amplitude of the B-mode signal to r<0.03 (99% CL) even when foreground contamination is taken into account. In the absence of foregrounds, the same limit can be reached after one 20-day flight.Comment: 29 pages, 8 figures, 4 tables; v2: matches published version, flight schedule updated, two typos fixed in Table 2, references and minor clarifications added, results unchange

2022 Upgrade and Improved Low Frequency Camera Sensitivity for CMB Observation at the South Pole

Constraining the Galactic foregrounds with multi-frequency Cosmic Microwave Background (CMB) observations is an essential step towards ultimately reaching the sensitivity to measure primordial gravitational waves (PGWs), the sign of inflation after the Big-Bang that would be imprinted on the CMB. The BICEP Array telescope is a set of multi-frequency cameras designed to constrain the energy scale of inflation through CMB B-mode searches while also controlling the polarized galactic foregrounds. The lowest frequency BICEP Array receiver (BA1) has been observing from the South Pole since 2020 and provides 30 GHz and 40 GHz data to characterize the Galactic synchrotron in our CMB maps. In this paper, we present the design of the BA1 detectors and the full optical characterization of the camera including the on-sky performance at the South Pole. The paper also introduces the design challenges during the first observing season including the effect of out-of-band photons on detectors performance. It also describes the tests done to diagnose that effect and the new upgrade to minimize these photons, as well as installing more dichroic detectors during the 2022 deployment season to improve the BA1 sensitivity. We finally report background noise measurements of the detectors with the goal of having photon noise dominated detectors in both optical channels. BA1 achieves an improvement in mapping speed compared to the previous deployment season.Comment: Proceedings of SPIE Astronomical Telescopes + Instrumentation 2022 (AS22

Detection of B-mode polarization at degree angular scales by BICEP2

We report results from the BICEP2 experiment, a cosmic microwave background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the B-mode power spectrum around ℓ∼80. The telescope comprised a 26 cm aperture all-cold refracting optical system equipped with a focal plane of 512 antenna coupled transition edge sensor 150 GHz bolometers each with temperature sensitivity of ≈300  μKCMB√s . BICEP2 observed from the South Pole for three seasons from 2010 to 2012. A low-foreground region of sky with an effective area of 380 square deg was observed to a depth of 87 nK deg in Stokes Q and U. In this paper we describe the observations, data reduction, maps, simulations, and results. We find an excess of B-mode power over the base lensed-ΛCDM expectation in the range 305σ. Through jackknife tests and simulations based on detailed calibration measurements we show that systematic contamination is much smaller than the observed excess. Cross correlating against WMAP 23 GHz maps we find that Galactic synchrotron makes a negligible contribution to the observed signal. We also examine a number of available models of polarized dust emission and find that at their default parameter values they predict power ∼(5–10)× smaller than the observed excess signal (with no significant cross-correlation with our maps). However, these models are not sufficiently constrained by external public data to exclude the possibility of dust emission bright enough to explain the entire excess signal. Cross correlating BICEP2 against 100 GHz maps from the BICEP1 experiment, the excess signal is confirmed with 3σ significance and its spectral index is found to be consistent with that of the CMB, disfavoring dust at 1.7σ. The observed B-mode power spectrum is well fit by a lensed-ΛCDM+tensor theoretical model with tensor-to-scalar ratio r=0.20 +0.07 −0.05, with r=0 disfavored at 7.0σ. Accounting for the contribution of foreground, dust will shift this value downward by an amount which will be better constrained with upcoming data sets

Design and testing of kinetic inductance detector package for the terahertz intensity mapper

The Terahertz Intensity Mapper (TIM) is designed to probe the star formation history in dust-obscured star-forming galaxies around the peak of cosmic star formation. This will be done via measurements of the redshifted 157.7 μm line of singly ionized carbon ([CII]). TIM employs two R∼250 long-slit grating spectrometers covering 240 to 420 μm. Each is equipped with a focal plane unit containing four wafer-sized subarrays of horn-coupled aluminum kinetic inductance detectors (KIDs). We present the design and performance of a prototype focal plane assembly for one of TIM's KID-based subarrays. The overall detector package must satisfy thermal and mechanical requirements, while maintaining high optical efficiency and a suitable electromagnetic environment for the KIDs. In particular, our design manages to strictly maintain a 50 μm air gap between the array and the horn block. The prototype detector housing in combination with the first flight-like quadrant were tested at 250 mK. A frequency scan using a vector network analyzer shows 823 resonance features, which represents 90% yield, indicating a good performance of our TIM detector wafer and the whole focal plane unit. Initial measurements also showed that many resonances were affected by collisions and/or very shallow transmission dips as a result of a degraded internal quality factor. This is attributed to the presence of an external magnetic field during cooldown. We report on a study of magnetic field dependence of the quality factor of our quadrant array. We implemented a Helmholtz coil to vary the magnetic field at the detectors by (partially) nulling earth's. Our investigation shows that the earth magnetic field can significantly affect our KIDs' performance by degrading the quality factor by a factor of two to five, well below those expected from the operational temperature or optical loading. We find that we can sufficiently recover our detectors' quality factor by tuning the current in the coils to generate a field that matches earth's magnetic field in magnitude to within a few μT. We emphasize that it is impractical to fly a Helmholtz coil on TIM and dynamically "null"earth's. Therefore, it is necessary to employ a properly designed magnetic shield enclosing the TIM focal plane unit. Based on the results presented in this paper, we set a shielding requirement of |B| 3 μT. © 2022 SPIE.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The terahertz intensity mapper: A balloon-borne imaging spectrometer for galaxy evolution

The Terahertz Intensity Mapper (TIM) is a balloon-borne far-infrared imaging spectrometer designed to characterize the star formation history of the universe. In its Antarctic science flight, TIM will map the redshifted 158um line of ionized carbon over the redshift range 0.5-1.7 (lookback times of 5-10 Gyr). TIM will spectroscopically detect ∼100 galaxies, determine the star formation rate history over this time interval through line intensity mapping, and measure the stacked CII emission from galaxies in its well-studied target fields (GOODS-S, SPT Deep Field). TIM consists of a 2-meter telescope feeding two grating spectrometers that that cover 240-420um at R∼250 across a 1.3deg field of view, detected with 7200 kinetic inductance detectors and sampled through a novel RF system-on-chip readout. TIM will serve as an important scientific instrument, accessing wavelengths that cannot easily be studied from the ground, and as a testbed for future FIR space technology. © 2022 SPIE.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The terahertz intensity mapper (TIM): Far-infrared balloon mission for spectroscopic galaxy evolution studies

Understanding the formation and evolution of galaxies over cosmic time is one of the foremost goals of astrophysics and cosmology today. The cosmic star formation rate has undergone a dramatic evolution over the course of the last 14 billion years, and dust obscured star forming galaxies (DSFGs) are a crucial component of this evolution. A variety of important, bright, and unextincted diagnostic lines are present in the far-infrared (FIR) which can provide crucial insight into the physical conditions of galaxy evolution, including the instantaneous star formation rate, the effect of AGN feedback on star formation, the mass function of the stars, metallicities, and the spectrum of their ionizing radiatio

BICEP array cryostat and mount design

International audienceBicep Array is a cosmic microwave background (CMB) polarization experiment that will begin observing at the South Pole in early 2019. This experiment replaces the five Bicep2 style receivers that compose the Keck Array with four larger Bicep3 style receivers observing at six frequencies from 30 to 270GHz. The 95GHz and 150GHz receivers will continue to push the already deep Bicep/Keck CMB maps while the 30/40GHz and 220/270GHz receivers will constrain the synchrotron and galactic dust foregrounds respectively. Here we report on the design and performance of the Bicep Array instruments focusing on the mount and cryostat systems