Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

The angular power spectrum of the Cosmic Microwave Background has been measured out to sufficiently small angular scale to encompass a few acoustic oscillations. We use a phenomenological fit to the angular power spectrum to quantify the statistical significance of these oscillations and discuss the cosmological implications of such a finding.

Abstract:

We explore the relative importance of the stellar mass density as compared to the inner dark halo, using the observed gas kinematics throughout the disk of the spiral galaxy NGC 4254 (Messier 99). We perform hydrodynamical simulations of the gas flow for a sequence of gravitational potentials in which we vary the stellar disk contribution to the total potential. This stellar portion of the potential was derived empirically from color corrected K-band photometry reflecting the spiral arms in the stellar mass, while the halo was modelled as an isothermal sphere. The simulated gas density and the gas velocity field are then compared to the observed stellar spiral arm morphology and to the H-alpha gas kinematics. We find that this method is a powerful tool to determine the corotation radius of the spiral pattern and that it can be used to place an upper limit on the mass of the stellar disk. For the case of the galaxy NGC 4254 we find R_cr = 7.5 +/- 1.1 kpc, or R_cr = 2.1 R_exp(K'). We also demonstrate that for a maximal disk the prominent spiral arms of the stellar component over-predict the non-circular gas motions unless an axisymmetric dark halo component contributes significantly (>~ 1/3) to the total potential inside 2.2 K-band exponential disk scale lengths.

Abstract:

We extend the analysis of the MAXIMA-1 cosmic microwave background data to smaller angular scales. MAXIMA, a bolometric balloon-borne experiment, mapped a 124 deg2 region of the sky with 10′ resolution at frequencies of 150, 240, and 410 GHz during its first flight. The original analysis, which covered the multipole range 36 ≤ l ≤ 785 using a 100 deg2 map, is extended to l = 1235 using a subset of the data from three 150 GHz photometers in the fully cross-linked central 60 deg2 of the map. The main improvement over the original analysis is the use of 3′ square pixels in the calculation of the map. The new analysis is consistent with the original for l < 785. For l > 785, where inflationary models predict a third acoustic peak, the new analysis shows power with an amplitude of 56 ± 7 μK at l ≃ 850 in excess to the average power of 42 ± 3 μK in the range 441 < l < 785.

Abstract:

We discuss the cosmological implications of the new constraints on the power spectrum of the cosmic microwave background (CMB) anisotropy derived from a new high-resolution analysis of the MAXIMA-1 measurement. The power spectrum indicates excess power at l ∼ 860 over the average level of power at 411 ≤ l ≤ 785. This excess is statistically significant at the ∼95% confidence level. Its position coincides with that of the third acoustic peak, as predicted by generic inflationary models selected to fit the first acoustic peak as observed in the data. The height of the excess power agrees with the predictions of a family of inflationary models with cosmological parameters that are fixed to fit the CMB data previously provided by BOOMERANG-LDB and MAXIMA-1 experiments. Our results therefore lend support for inflationary models and more generally for the dominance of adiabatic coherent perturbations in the structure formation of the universe. At the same time, they seem to disfavor a large variety of the nonstandard (but inflation-based) models that have been proposed to improve the quality of fits to the CMB data and the consistency with other cosmological observables. Within standard inflationary models, our results combined with the COBE/Differential Microwave Radiometer data give best-fit values and 95% confidence limits for the baryon density, Ωbh2 ≃ 0.033 ± 0.013, and the total density, Ω = 0.9-0.16+0.18. The primordial spectrum slope (ns) and the optical depth to the last scattering surface (τc) are found to be degenerate and to obey the relation ns ≃ (0.99 ± 0.14) + 0.46τc, for τc ≤ 0.5 (all at 95% confidence levels).