Cosmological Signal Research Articles

Root Mean Square Anisotropy in theCOBEDMR Four‐Year Sky Maps

The sky rms is the simplest model-independent characterization of a cosmological anisotropy signal. We show that the rms temperature fluctuations determined from the COBE Differential Microwave Radiometer (DMR) 4 yr sky maps are frequency independent, consistent with the Planckian spectrum expected for the cosmic microwave background signal and therefore with the hypothesis that they are cosmological in origin. The typical rms amplitude is ~35 ± 2 μK at 7° and ~29 ± 1 μK at 10°. An analysis of the rms anisotropy determined from the data in both Galactic and ecliptic coordinates is used to determine the rms quadrupole normalization, Qrms-PS, for a scale-invariant Harrison-Zeldovich power-law model. Corrections are applied for small biases observed in the likelihood analysis. While there are variations depending on the data selection, all results are consistent with a Qrms-PS normalization of ~18 ± 2 μK. This is also shown to be true for a standard cold dark matter model of cosmological anisotropy. The difference in the normalization amplitudes derived when the quadrupole is either included or excluded from the analysis is attributable to contamination of the observed sky quadrupole by foreground Galactic emission.

Molecular Signals from Primordial Clouds at High Redshift

The possibility to detect cosmological signals from the post-recombination Universe is one of the main aims of modern cosmology. In a previous paper we emphasized the role that elastic resonant scattering through LiH molecules can have in dumping primary CBR anisotropies and raising secondary signals. Here we extend our analysis to all the evolutionary stages of a primordial cloud, starting with the linear phase, through the turn-around and to the non linear collapse. We have done calculations for proto-clouds in a CDM scenario and, more generally, for a set of clouds with various masses and various turn-around redshifts, in this case without referring to any particular structure formation scenario. We found that the first phase of collapse, for $t/t_{free-fall}=0.05\div 0.2$ is the best one for simultaneous detection of the first two LiH rotational lines. The observational frequency falls between 30 and 250 GHz and the line width ${\Delta \nu\over \nu}$ is between $10^{-5}$ and $10^{-4}$. As far as we know this is the most favourable process to detect primordial clouds before they start star formation processes.

Hot and Cold Spots in the First Plus Second Year COBE/DMR Maps

Density perturbations at the decoupling epoch produce angular fluctuations in the temperature of the Cosmic Microwave Background (CMB) radiation that may appear as hot and cold spots. Observational data of the CMB includes instrumental noise in addition to the cosmological signal. One would like to determine which of the observed spots are produced by the noise and which correspond to signal. In this work we first present a statistical analysis of the first plus second year COBE/DMR map at 53 GHz that reveals the presence of cosmological signal in the data. The analysis is based on Harrison-Zeldovich Monte Carlo realizations and utilizes a generalized $\chi^2$ statistic. The method is applied to the number of spots and the fraction of the total area that appear above/below a certain value of the dispersion of the noise, including and excluding the quadrupole, giving $Q_{rms-PS}=15^{+3}_{-6}$, $18^{+5}_{-7} \mu K$ and $Q_{rms-PS}=18^{+3}_{-4}$, $21\pm6 \mu K$, at the $95\%$ confidence level, respectively. The data taken by the COBE/DMR experiment during the first two years at three different frequencies (31, 53 and 90 GHz) are used to determine which of the spots observed at 53 GHz appear simultaneously in the other two channels. The significance of those spots is determined by comparison of their area and signal-to-noise with noise Monte Carlo simulations. We point out two cold spots and one hot spot at positions $(l,b)\approx (-99^{\circ},57^{\circ}),(-21^{\circ},-45^{\circ}), (-81^{\circ},-33^{\circ})$ respectively, at the $95 \%$ confidence level.

Interstellar dust spectral index: a balloon-borne experiment

A balloon-borne experiment has been conceived in order to map the sub-millimetric galactic emission at four different wavelengths between 400 μm and 2 mm at an angular scale of 1°. Such measurements will make it possible both to investigate the nature of the interstellar dust and to disentangle the galactic contribution from extragalactic and cosmological signals. A binocular telescope system has been realized by means of two 37 cm of-axis wobbling parabolic mirrors, each one coupled with a two-channel 3He photometer. The first trans-Mediterranean flight is scheduled for summer 1995.

Anisotropy of relic radiation in the RELICT-1 experiment and parameters of grand unification

We discuss new results of the data reduction of the space experiment RELICT-1 (the investigation of the anisotropy of the cosmic microwave background at 37 GHz). The anomalous signal is detected with 99% confidence in a region with an area of about 1 sterad, centered at R.A.=1 h 30 m, Dec=−10° (1=150°, b=−70°). The brightness temperature of the signal is ΔT=−71±43 μK with 90% confidence including systematic errors. The nature of the signal cannot be explained by apparatus effects or by radio emission of known sources, there are reasons to believe that the signal is of cosmological origin. For a model of a cosmological signal with scale invariant spectrum, which is proposed by inflationary theory, we have estimated the quadrupole component to be 6×10 −6< ΔT 2 T <3.3×10 −5 with 90% confidence including systematic errors, some main parameters of grand unification theory, and the nature of the contributors of dark matter in the Universe.

Cosmic rays and cosmological microwave background fluctuations

view Abstract Citations (16) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cosmic Rays and Cosmological Microwave Background Fluctuations Banday, A. J. ; Giler, M. ; Szabelska, B. ; Szabelski, J. ; Wolfendale, A. W. Abstract One of the most important topics in modern cosmology concerns the search for anisotropies in the cosmic microwave background radiation. Searches for these fluctuations have been made in the field of radio astronomy, and tentative claims have been made, specifically at a frequency near to 10 GHz, for fluctuations on a scale of 8^deg^. However, the Galactic synchrotron radiation can mimic or mask a cosmological signal and the present work examines the extent to which the fluctuations in this local component, a component due to cosmic rays, are understood. We conclude that at 10 GHz, although the observed fluctuations are of similar magnitude to those predicted for Galactic synchrotron radiation the actual temperature profiles do not agree. Thus, the nature of the detected fluctuations is not understood, although what can be stated is that there is no evidence to prove the existence of cosmic microwave background anisotropies. A prognosis is made for future searches for CMB fluctuations. Publication: The Astrophysical Journal Pub Date: July 1991 DOI: 10.1086/170204 Bibcode: 1991ApJ...375..432B Keywords: Galactic Cosmic Rays; Relic Radiation; Extragalactic Radio Sources; Milky Way Galaxy; Synchrotron Radiation; Space Radiation; COSMIC BACKGROUND RADIATION; COSMIC RAYS: GENERAL full text sources ADS |

The surface brightness test for the expansion of the universe. II - Radii, surface brightness, and absolute magnitude correlations for nearby E galaxies

view Abstract Citations (50) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Surface Brightness Test for the Expansion of the Universe. II. Radii, Surface Brightness, and Absolute Magnitude Correlations for Nearby E Galaxies Sandage, Allan ; Perelmuter, Jean-Marc Abstract The correlation between absolute magnitude and surface brightness, averaged over a series of areas defined by metric (rather than isophotal) radii, is studied using E galaxies in the Virgo, Fornax, and Coma clusters, and in four additional samples of bright nearby field galaxies. The work is a calibration step in preparation for the Tolman (1 + z)^4^ surface brightness test for the reality of the expansion. As known before, and as is seen in the present data, the average surface brightness is strongly correlated with absolute brightness for giant galaxies. Galaxies brighter than M_B_ ~ -20 have fainter average surface brightness values as the total galaxy luminosity increases. The lack of a constant average surface brightness with changing absolute magnitude for bright E galaxies shows that Hubble's m ~ -5 log r" scaling law is not correct over the first few brightest magnitudes of the E luminosity function. Therefore measurements will be required of the <SB> over a range of M_T_ in distant clusters so as to reduce the <SB> data to "standard conditions" before searching for the Tolman (1 + z)^4^ cosmological test cosmological test signal. The purpose of the present paper is to calibrate the correlation between M_T_ and <SB> using local samples. In the samples studied here the dispersion in the <SB> distributions, after reducing the data to absolute magnitude M_B_ = -22 is ~0.5 mag. This value is smaller than the 1.8 mag Tolman (1 + z)^4^ factor, even at the modest redshift of z = 0.5, showing that the Tolman test is feasible in practice as well as in principle. Publication: The Astrophysical Journal Pub Date: September 1990 DOI: 10.1086/169161 Bibcode: 1990ApJ...361....1S Keywords: Big Bang Cosmology; Brightness; Elliptical Galaxies; Magnitude; Universe; Astronomical Photometry; Galactic Clusters; Radii; Sky Surveys (Astronomy); Astrophysics; COSMOLOGY; GALAXIES: CLUSTERING; GALAXIES: PHOTOMETRY full text sources ADS | data products SIMBAD (463) NED (458) Related Materials (2) Part 1: 1990ApJ...350..481S Part 3: 1991ApJ...370..455S