Leonardo Bronfman

The Anisotropy of the microwave background to l = 3500: Mosaic observations with the Cosmic Background Imager

We report measurements of anisotropy in the cosmic microwave background radiation over the multipole range l 200 3500 with the Cosmic Background Imager based on deep observations of three fields. These results confirm the drop in power with increasing l first reported in earlier measurements with this instrument and extend the observations of this decline in power out to l 2000. The decline in power is consistent with the predicted damping of primary anisotropies. At larger multipoles, l 1⁄4 2000 3500, the power is 3.1 greater than standard models for intrinsic microwave background anisotropy in this multipole range and 3.5 greater than zero. This excess power is not consistent with expected levels of residual radio source contamination but, for 8e1, is consistent with predicted levels of a secondary Sunyaev-Zeldovich anisotropy. Further observations are necessary to confirm the level of this excess and, if confirmed, determine its origin. Subject headings: cosmic microwave background — cosmology: observations

Extended mosaic observations with the Cosmic Background Imager

Two years of microwave background observations with the Cosmic Background Imager (CBI) have been combined to give a sensitive, high-resolution angular power spectrum over the range 400 2000 power previously seen with the CBI is reduced. Under the assumption that any signal in excess of the primary anisotropy is due to a secondary Sunyaev-Zeldovich anisotropy in distant galaxy clusters, we use CBI, Arcminute Cosmology Bolometer Array Receiver, and Berkeley-Illinois-Maryland Association array data to place a constraint on the present-day rms mass fluctuation on 8 h-1 Mpc scales, σ8. We present the results of a cosmological parameter analysis on the l < 2000 primary anisotropy data that show significant improvements in the parameters as compared to WMAP alone, and we explore the role of the small-scale cosmic microwave background data in breaking parameter degeneracies.

Cosmological Parameters from Cosmic Background Imager Observations and Comparisons with BOOMERANG, DASI, and MAXIMA

We report on the cosmological parameters derived from observations with the Cosmic Background Imager (CBI), covering 40 deg2 and the multipole range 300 l 3500. The angular scales probed by the CBI correspond to structures that cover the mass range from 1014 to 1017 M?, and the observations reveal, for the first time, the seeds that gave rise to clusters of galaxies. These unique, high-resolution observations also show damping in the power spectrum to l ~ 2000, which we interpret as being due to the finite width of the photon-baryon decoupling region and the viscosity operating at decoupling. Because the observations extend to much higher l, the CBI results provide information complementary to that probed by the BOOMERANG, DASI, MAXIMA, and VSA experiments. When the CBI observations are used in combination with those from COBE-DMR, we find evidence for a flat universe, ?tot = 1.00 (1 ?), a power-law index of primordial fluctuations, ns = 1.08, and densities in cold dark matter, ?cdmh2 = 0.16, and baryons, ?bh2 = 0.023. With the addition of large-scale structure priors the ?cdmh2 value is sharpened to 0.10, and we find ?? = 0.67. In the l < 1000 overlap region with the BOOMERANG, DASI, MAXIMA, and VSA experiments, the agreement between these four experiments is excellent, and we construct optimal power spectra in the CBI bands that demonstrate this agreement. We derive cosmological parameters for the combined cosmic microwave background (CMB) experiments and show that these parameter determinations are stable as we progress from the weak priors using only CMB observations and very broad restrictions on cosmic parameters, through the addition of information from large-scale structure surveys, Hubble parameter determinations, and Type Ia supernova results. The combination of these with CMB observations gives a vacuum energy estimate of ?? = 0.70, a Hubble parameter of h = 0.69 ? 0.04, and a cosmological age of 13.7 ? 0.2 Gyr. As the observations are pushed to higher multipoles, no anomalies relative to standard models appear, and extremely good consistency is found between the cosmological parameters derived for the CBI observations over the range 610 < l < 2000 and observations at lower l.

Polarization Observations with the Cosmic Background Imager

Polarization observations of the cosmic microwave background with the Cosmic Background Imager from September 2002 to May 2004 provide a significant detection of the E-mode polarization and reveal an angular power spectrum of polarized emission showing peaks and valleys that are shifted in phase by half a cycle relative to those of the total intensity spectrum. This key agreement between the phase of the observed polarization spectrum and that predicted on the basis of the total intensity spectrum provides support for the standard model of cosmology, in which dark matter and dark energy are the dominant constituents, the geometry is close to flat, and primordial density fluctuations are predominantly adiabatic with a matter power spectrum commensurate with inflationary cosmological models.

FIRST INTRINSIC ANISOTROPY OBSERVATIONS WITH THE COSMIC BACKGROUND IMAGER

We present the first results of observations of the intrinsic anisotropy of the cosmic microwave background radiation with the Cosmic Background Imager from a site at 5080 m altitude in northern Chile. Our observations show a sharp decrease in Cl in the range l = 400-1500. The broadband amplitudes we have measured are δTband = 58.7 μK for l = 603 and δTband = 29.7 μK for l = 1190, where these are half-power widths in l. Such a decrease in power at high l is one of the fundamental predictions of the standard cosmological model, and these are the first observations which cover a broad enough l range to show this decrease in a single experiment. The Cl we have measured enables us to place limits on the density parameter, Ωtot ≤ 0.4 or Ωtot ≥ 0.7 (90% confidence).

IMPLICATIONS OF THE COSMIC BACKGROUND IMAGER POLARIZATION DATA

We present new measurements of the power spectra of the E mode of cosmic microwave background (CMB) polarization, the temperature T, the cross-correlation of E and T, and upper limits on the B mode from 2.5 yr of dedicated Cosmic Background Imager (CBI) observations. Both raw maps and optimal signal images in the (u, v)-plane and the sky plane show strong detections of the E mode (11.7 σ for the EE power spectrum overall) and no detection of the B mode. The power spectra are used to constrain parameters of the flat tilted adiabatic ΛCDM models: those determined from EE and TE bandpowers agree with those from TT, which is a powerful consistency check. There is little tolerance for shifting polarization peaks from the TT-forecast locations, as measured by the angular sound crossing scale θ = 100/l_s = 1.03 ± 0.02 from EE and TE; compare with 1.044 ± 0.005 with the TT data included. The scope for extra out-of-phase peaks from subdominant isocurvature modes is also curtailed. The EE and TE measurements of CBI, DASI, and BOOMERANG are mutually consistent and, taken together rather than singly, give enhanced leverage for these tests.

SPIRAL STRUCTURE IN THE OUTER GALACTIC DISK. I. THE THIRD GALACTIC QUADRANT

We combine optical and radio observations to trace the spiral structure in the third quadrant of the Milky Way. The optical observations consist of a large sample of young open clusters and associations, whereas the radio observations consist of a surveyofnearbyand distant clouds observedinCO. Boththe optical and radio samples are the largest ones thus far presented in the literature. We use this unique material to analyze the behavior of interstellar extinction and totracethedetailedstructureofthethirdGalacticquadrant(TGQ).Wefindthattheouter(Cygnus)granddesignspiral arm is traced by stellar and CO components, while the Perseus arm is traced solely by CO and is possibly being disrupted by the crossing of the Local (Orion) arm. The Local arm is traced by CO and young stars toward l ¼ 240 � and extends for over 8 kpc along the line of sight reaching the outer arm. Finally, we characterize the Galactic warp and compare the geometries implied by the young stellar and CO components.

Discovery of four new massive and dense cold cores

We report the identification, from a 1.2 mm dust continuum emission survey toward massive star-forming regions, of four strong 1.2 mm sources without counterparts at mid-infrared (Midcourse Space Experiment [MSX]) and far-infrared (IRAS) wavelengths. They have radii in the range 0.2-0.3 pc, dust temperatures ≤17 K, masses in the range 4 × 102-2 × 103 M☉, and densities of ~2 × 105 cm-3. We suggest that these objects are massive and dense cold cores that will eventually collapse to form high-mass stars.

Molecular Outflows and a Mid-Infrared Census of the Massive Star Formation Region Associated with IRAS 18507+0121

We have observed the central region of the infrared-dark cloud filament associated with IRAS 18507+0121 at millimeter wavelengths in CO(J = 1-0), ^(13)CO(J = 1-0), and C^(18)O(J = 1-0) line emission and with Spitzer at mid-infrared wavelengths. Five massive outflows from two cloud cores were discovered. Three outflows are centered on or near an ultracompact (UC) H II region (G34.4+0.23), while the remaining two outflows originate from the millimeter core G34.4+0.23 MM. Modeling of the spectral energy distributions of the mid-infrared sources identified 31 young stellar objects in the filament with a combined stellar mass of ~127 ± 27 M_☉. An additional 22 sources were identified as probable cluster members based on the presence of strong 24 μm emission. The total star formation efficiency in the G34.4 cloud filament is estimated to be ~7%, while the massive and intermediate-mass star formation efficiency in the entire cloud filament is estimated to be roughly 2%. A comparison of the gravitational binding energy with the outflow kinetic energy suggests that the compact core containing G34.4+0.23 MM is being destroyed by its molecular outflows, whereas the outflows associated with the more massive core surrounding the G34.4 UC H II region are not likely to totally disrupt the cloud. In addition, a qualitative evaluation of the region appears to suggest that stars in this region may have formed in two stages: first lower mass stars formed and then, a few Myr later, the more massive stars began to form.

CH3CN Observations toward Southern Massive Star-forming Regions

In an effort to identify very young sites of massive star formation, we have conducted a survey for hot and dense molecular cores toward a sample of 17 southern sources. The sample consists of sources with IRAS color characteristics of ultracompact H II regions for which high-density molecular material had previously been detected. We observed the J = 5-4, 6-5, 8-7, and 12-11 rotational transitions of CH3CN and derived rotation temperatures and column densities using the population-diagram technique. We identify four sources with a high-temperature molecular component (Trot > 90 K) as new candidates for hot molecular cores. We also observed the transitions H35α, CS J = 3-2, and the continuum in the 3, 2 mm bands toward 17 sources, and the 1.3 mm continuum, H41α and 13CO J = 2-1 transitions toward 10 sources. Eight sources show blue and red wings in the CS J = 3-2 line, whereas three sources show wings in the 13CO J = 2-1 spectra, suggestive of molecular outflows. Our continuum and recombination line data show that the 91 GHz continuum emission is dominated by free-free emission from ionized regions, whereas at 147 GHz emission from dust grains contributes significantly.