Mark A. Lim

Degree-scale anisotropy in the cosmic microwave background: SP94 results

We present results from two observations of the cosmic microwave background (CMB) performed from the South Pole during the 1993-1994 austral summer. Each observation employed a 3 deg peak-to-peak sinusoidal, single-difference chop and consisted of a 20 deg x 1 deg strip on the sky. The first observation used a receiver which operates in three channels between 38 and 45 GHz (Q-band) with a full width half maximum (FWHM) beam which varies from 1 deg to 1.15 deg. The second observation overlapped the first observation and used a receiver which operates in four channels between 26 and 36 GHz (Ka-band) with a FWHM beam which varies from 1.5 deg to 1.7 deg. Significant correlated structure is observed in all channels for each observation. The spectrum of the structure is consistent with a CMB spectrum and is formally inconsistent with diffuse synchrotron and free-free emission at the 5 sigma level. The amplitude of the structure is inconsistent with 20 K interstellar dust; however, the data do not discriminate against flat or inverted spectrum point sources. The root mean square amplitude (+/- 1 sigma) of the combined (Ka + Q) data is Delta T(sub rms) = 41.2(sup +15.5, sub -6.7) micro-K for an average window function which has a peak value of 0.97 at l = 68 and drops to e(exp -0.5) of the peak value at l = 36 and l = 106. A band power estimate of the CMB power spectrum, C(sub l), gives average value of (C(sub l)l(l + 1)/(2 pi))(sub B) = 1.77(sup +1.58, sub -0.54) x 10(exp -10).

MAX 4 and MAX 5 Cosmic Microwave Background Anisotropy Measurement Constraints on Open and Flat-Λ Cold Dark Matter Cosmogonies

We account for experimental and observational uncertainties in likelihood analyses of cosmic microwave background (CMB) anisotropy data from the MAX 4 and MAX 5 experiments. These analyses use CMB anisotropy spectra predicted in open and spatially flat Λ cold dark matter cosmogonies. Among the models considered, the combined MAX data set is most consistent with the CMB anisotropy shape in Ω0 ~ 0.1-0.2 open models and less so with that in old (t0 15-16 Gyr, i.e., low-h), high baryon density (ΩB 0.0175 h-2), low-density (Ω0 ~ 0.2-0.4), flat-Λ models. The MAX data alone do not rule out any of the models we consider at the 2 σ level. Model normalizations deduced from the combined MAX data are consistent with those drawn from the UCSB South Pole 1994 data, except for the flat bandpower model for which MAX favors a higher normalization. The combined MAX data normalization for open models with Ω0 ~ 0.1-0.2 is higher than the upper 2 σ value of the DMR normalization. The combined MAX data normalization for old (low-h), high baryon density, low-density flat-Λ models is below the lower 2 σ value of the DMR normalization. Open models with Ω0 ~ 0.4-0.5 are not far from the shape most favored by the MAX data, and for these models, the MAX and DMR normalizations overlap. The MAX and DMR normalizations also overlap for Ω0 = 1 and some higher h, lower ΩB, low-density flat-Λ models.

Measurements of anisotropy in the cosmic microwave background radiation at 0.5 deg angular scales near the star gamma ursae minoris

We present results from a four-frequency observation of a 6 deg x 0.6 deg strip of the sky centered near the star Gamma Ursae Minoris (GUM) during the fourth flight of the Millimeter-wave Anistropy experiment(MAX). The observation was made with a 1.4 deg peak-to-peak sinusoidal chop in all bands. The FWHM beam sizes were 0.55 deg +/- 0.05 deg at 3.5 per cm and 0.75 deg +/- 0.05 deg at 6, 9, and 14 per cm. During this observation significant correlated structure was observed at 3.5, 6 and 9 per cm with amplitudes similar to those observed in the GUM region during the second and third fligts of MAX. The frequency spectrum is consistent with cosmic microwave background (CMB) and inconsistent with thermal emission from interstellar dust. The extrapolated amplitudes of synchrotron and free-free emission are too small to account for the amplitude of the observed structure, If all of the structure is attributed to CMB anisotropy with a Gaussian autocorrelation function and a coherence angle of 25 min, then the most probable values of delta T/TCMB in the 3.5, 6 and 9 per cm bads are (4.3 +2.7/-1.6) x 10-5, 2.8 (+4.3/-1/1) x 10-5, and 3.5 (+3.0/-1.6) x 10-5 (95% confidence upper and lower limits), respectively.

Near Infrared Extragalactic Background

We searched for the near infrared extragalactic background light (IREBL) in the data from the Near Infrared Spectrometer (NIRS) on the Infrared Telescope in Space (IRTS). After subtracting the contribution of faint stars and zodiacal component based on the model, significant isotropic emission is detected whose in-band flux amounts to ∼ 30 nWm-2sr-1. This brightness is consistent with upper limits of COBE/DIRBE, but is much brighter than the integrated light of faint galaxies at the H and K bands. A significant fluctuation of the skybrigh tness was also detected that can not be explained bykno wn foreground emission components. 2- point correlation analysis indicates that the fluctuation has a characteristic spatial frequencyat 1 ∼ 2 × 102 arcmin. These results indicate that the detected isotropic emission is cosmological in origin, and is new observational evidence for the study of the formation and evolution of galaxies.

A Spin-Modulated Telescope to Make Two-Dimensional Cosmic Microwave Background Maps

We describe the HEMT Advanced Cosmic Microwave Explorer (HACME), a balloon-borne experiment designed to measure subdegree-scale cosmic microwave background anisotropy over hundreds of deg2, using a unique two-dimensional scanning strategy. A spinning flat mirror that is canted relative to its spin axis modulates the direction of beam response in a nearly elliptical path on the sky. The experiment was successfully flown in 1996 February, achieving near laboratory performance for several hours at float altitude. A map free of instrumental systematic effects is produced for a 3.5 hr observation of 630 deg2, resulting in a flat-band power upper limit of l(l + 1)Cl/(2π)0.5 < 77 μK at l = 38 (95% confidence). The experiment design, flight operations, and data, including atmospheric effects and noise performance, are discussed.

COSMIC MICROWAVE BACKGROUND MAPS FROM THE HACME EXPERIMENT

We present cosmic microwave background (CMB) maps from the Santa Barbara HACME balloon experiment (Staren et al.), covering about 1150 square degrees split between two regions in the northern sky, near the stars c Ursae Minoris and a Leonis, respectively. The FWHM of the beam is in D0i.77 three frequency bands centered on 39, 41, and 43 GHz. The results demonstrate that the thoroughly interconnected scan strategy employed allows efficient removal of 1/f-noise and slightly variable scan- synchronous oUsets. The maps display no striping, and the noise correlations are found to be virtually isotropic, decaying on an angular scale D1i. The noise performance of the experiment resulted in an upper limit on CMB anisotropy. However, our results demonstrate that atmospheric contamination and other systematics resulting from the circular scanning strategy can be accurately controlled and bode well for the planned follow-up experiments BEAST and ACE, since they show that even with the overly cautious assumption that 1/f-noise and oUsets will be as dominant as for HACME, the problems they pose can be readily overcome with the mapmaking algorithm discussed. Our prewhitened notch-—lter algorithm for destriping and oUset removal is proving useful also for other balloon- and ground-based experiments whose scan strategies involve substantial interleaving, e.g., Boomerang. Subject headings: balloonscosmic microwave backgroundcosmology: observations On-line material: color —gures

Anisotropy measurements of the cosmic microwave background

The cosmic microwave background (CMB) is one of only a few physically observable remnants of the early Universe. Studies of the spectrum, polarization and spatial distribution of the CMB can potentially lead to a detailed understanding of the processes that took place in the early Universe. Many of the outstanding cosmological questions regarding the age, contents, future, and large scale dynamics of the universe are addressed in these studies. In particular, measurements of the spatial anisotropy of the CMB are a very effective method for testing and constraining models of cosmic structure formation.