The Dipole Observed in the COBE DMR Four-Year Data

The largest anisotropy in the cosmic microwave background (CMB) is the $\approx 3$ mK dipole assumed to be due to our velocity with respect to the CMB. Using the four year data set from all six channels of the COBE Differential Microwave Radiometers (DMR), we obtain a best-fit dipole amplitude $3.358 \pm 0.001 \pm 0.023$ mK in the direction $(l,b)=(264\deg.31 \pm 0\deg.04 \pm 0\deg.16, +48\deg.05 \pm 0\deg.02 \pm 0\deg.09)$, where the first uncertainties are statistical and the second include calibration and combined systematic uncertainties. This measurement is consistent with previous DMR and FIRAS resultsComment: New and improved version; to be published in ApJ next mont

Cosmic Mach Number as a Function of Overdensity and Galaxy Age

We carry out an extensive study of the cosmic Mach number (\mach) on scales of R=5, 10 and 20h^-1Mpc using an LCDM hydrodynamical simulation. We particularly put emphasis on the environmental dependence of \mach on overdensity, galaxy mass, and galaxy age. We start by discussing the difference in the resulting \mach according to different definitions of \mach and different methods of calculation. The simulated Mach numbers are slightly lower than the linear theory predictions even when a non-linear power spectrum was used in the calculation, reflecting the non-linear evolution in the simulation. We find that the observed \mach is higher than the simulated mean by more than 2-standard deviations, which suggests either that the Local Group is in a relatively low-density region or that the true value of \Omega_m is ~ 0.2, significantly lower than the simulated value of 0.37. We show from our simulation that the Mach number is a weakly decreasing function of overdensity. We also investigate the correlations between galaxy age, overdensity and \mach for two different samples of galaxies --- DWARFs and GIANTs. Older systems cluster in higher density regions with lower \mach, while younger ones tend to reside in lower density regions with larger \mach, as expected from the hierarchical structure formation scenario. However, for DWARFs, the correlation is weakened by the fact that some of the oldest DWARFs are left over in low-density regions during the structure formation history. For giant systems, one expects blue-selected samples to have higher \mach than red-selected ones. We briefly comment on the effect of the warm dark matter on the expected Mach number.Comment: 43 pages, including 15 figures. Accepted version in ApJ. Included correlation function of different samples of galaxies, and the cumulative number fraction distribution as a fcn. of overdensity. Reorganized figures and added some reference

Measuring the Stellar Masses of z~7 Galaxies with Spitzer Ultrafaint Survey Program (SURFS UP)

We present Spitzer/IRAC observations of nine $z'$-band dropouts highly magnified (2<mu<12) by the Bullet Cluster. We combine archival imaging with our Exploratory program (SURFS UP), which results in a total integration time of ~30 hr per IRAC band. We detect (>3sigma) in both IRAC bands the brightest of these high-redshift galaxies, with [3.6]=23.80+-0.28 mag, [4.5]=23.78+-0.25 mag, and (H-[3.6])=1.17+-0.32 mag. The remaining eight galaxies are undetected to [3.6]~26.4 mag and [4.5]~26.0 mag with stellar masses of ~5x10^7 M_sol. The detected galaxy has an estimated magnification of mu=12+-4, which implies this galaxy has an ultraviolet luminosity of L_1500~0.3 L*_{z=7} --- the lowest luminosity individual source detected in IRAC at z>7. By modeling the broadband photometry, we estimate the galaxy has an intrinsic star-formation rate of SFR~1.3 M_sol/yr and stellar mass of M~2x10^9 M_sol, which gives a specific star-formation rate of sSFR~0.7 Gyr^-1. If this galaxy had sustained this star-formation rate since z~20, it could have formed the observed stellar mass (to within a factor of ~2), we also discuss alternate star-formation histories and argue the exponentially-increasing model is unlikely. Finally, based on the intrinsic star-formation rate, we estimate this galaxy has a likely [C II] flux of = 10^{-17} erg/s/cm2.Comment: Accepted to ApJL. 6 pages, 3 figures, 2 table

A semi-parametric approach to estimate risk functions associated with multi-dimensional exposure profiles: application to smoking and lung cancer

A common characteristic of environmental epidemiology is the multi-dimensional aspect of exposure patterns, frequently reduced to a cumulative exposure for simplicity of analysis. By adopting a flexible Bayesian clustering approach, we explore the risk function linking exposure history to disease. This approach is applied here to study the relationship between different smoking characteristics and lung cancer in the framework of a population based case control study

Spectroscopic Analysis of H I Absorption Line Systems in 40 HIRES Quasars

We list and analyze H I absorption lines at redshifts 2 < z < 4 with column density (12 < log(N_HI) < 19) in 40 high-resolutional (FWHM = 8.0 km/s) quasar spectra obtained with the Keck+HIRES. We de-blend and fit all H I lines within 1,000 km/s of 86 strong H I lines whose column densities are log(N_HI/[cm^-2]) > 15. Unlike most prior studies, we use not only Lya but also all visible higher Lyman series lines to improve the fitting accuracy. This reveals components near to higher column density systems that can not be seen in Lya. We list the Voigt profile fits to the 1339 H I components that we found. We examined physical properties of H I lines after separating them into several sub-samples according to their velocity separation from the quasars, their redshift, column density and the S/N ratio of the spectrum. We found two interesting trends for lines with 12 < log(N_HI) < 15 which are within 200-1000 km/s of systems with log(N_HI) > 15. First, their column density distribution becomes steeper, meaning relatively fewer high column density lines, at z < 2.9. Second, their column density distribution also becomes steeper and their line width becomes broader by about 2-3 km/s when they are within 5,000 km/s of their quasar.Comment: 32 pages, 14 figures, accepted for publication in the Astronomical Journal. A complete version with all tables and figures is available at http://www.astro.psu.edu/users/misawa/pub/Paper/40hires.ps.g

Cosmological parameters sigma_8, the baryon density, and the UV background intensity from a calibrated measurement of H I Lyman-alpha absorption at z = 1.9

We identify a concordant model for the intergalactic medium (IGM) at redshift z=1.9 that uses popular values for cosmological and astrophysical parameters and accounts for all baryons with an uncertainty of 6%. We have measured the amount of absorption, DA, in the Ly-alpha forest at redshift 1.9 in spectra of 77 QSO from the Kast spectrograph. We calibrated the continuum fits with realistic artificial spectra, and we found that averaged over all 77 QSOs the mean continuum level is within 1-2% of the correct value. Absorption from all lines in the Ly-alpha forest at z=1.9 removes DA=15.1 +/- 0.7% of the flux between 1070 and 1170 (rest) Angstroms. This is the first measurement using many QSOs at this z, and the first calibrated measurement at any redshift. Metal lines absorb 2.3 +/- 0.5%, and LLS absorb 1.0 +/- 0.4% leaving 11.8 +/- 1.0% from the lower density bulk of the IGM. Averaging over Delta z=0.1 or 154 Mpc, the dispersion is 6.1 +/- 0.3% including LLS and metal lines, or 3.9 (+0.5, -0.7)% for the lower density IGM alone, consistent with the usual description of large scale structure. LLS and metal lines are major contributors to the variation in the mean flux, and they make the flux field significantly non-Gaussian. We find that a hydrodynamic simulation on a 1024 cubed grid in a 75.7 Mpc box reproduces the observed DA from the low density IGM with parameters values H_o=71 km/s/Mpc, Omega_Lambda=0.73, Omega_m=0.27, Omega_b=0.044, sigma_8=0.9 and a UV background that has an ionization rate that is 1.08 +/- 0.08 times the prediction by Madau, Haardt & Rees (1999).Comment: Submitted to Ap

Wigner Crystalline Edges in nu < 1 Quantum Dots

We investigate the edge reconstruction phenomenon believed to occur in quantum dots in the quantum Hall regime when the filling fraction is nu < 1. Our approach involves the examination of large dots (< 40 electrons) using a partial diagonalization technique in which the occupancies of the deep interior orbitals are frozen. To interpret the results of this calculation, we evaluate the overlap between the diagonalized ground state and a set of trial wavefunctions which we call projected necklace (PN) states. A PN state is simply the angular momentum projection of a maximum density droplet surrounded by a ring of localized electrons. Our calculations reveal that PN states have up to 99% overlap with the diagonalized ground states, and are lower in energy than the states identified in Chamon and Wen's study of the edge reconstruction.Comment: 8 pages, 8 figures, to be published in Phys. Rev.

The Age of the Oldest Stars in the Local Galactic Disk From Hipparcos Parallaxes of G and K Subgiants

We review the history of the discovery of field subgiant stars and their importance in the age dating of the Galactic disk. We use the cataloged data from the Hipparcos satellite in this latter capacity. Based on Hipparcos parallaxes accurate to 10% or better, the absolute magnitude of the lower envelope of the nearly horizontal subgiant sequence for field stars in the H-R diagram for B-V colors between 0.85 and 1.05 is measured to be M_V = 4.03 +/- 0.06. The age of the field stars in the solar neighborhood is found to be 7.9 +/- 0.7 Gyr by fitting the theoretical isochrones for [Fe/H] = +0.37 to the lower envelope of the Hipparcos subgiants. The same grid of isochrones yields ages, in turn, of 4.0 +/- 0.2 Gyr, 6.2 +/- 0.5 Gyr, and 7.5 to 10 Gyr for the old Galactic clusters M67, NGC188, and NGC6791. The ages of both the Galactic disk in the solar neighborhood and of NGC6791 are, nevertheless, likely between 3 and 5 Gyr younger than the oldest halo globular clusters, which have ages of 13.5 Gyr. The most significant results are (1) the supermetallicity of the oldest local disk stars, and (2) the large age difference between the most metal-poor component of the halo and the thick and thin disk in the solar neighborhood. These facts are undoubtedly related and pose again the problem of the proper scenario for the timing of events in the formation of the halo and the Galactic disk in the solar neighborhood. [Abstract Abridged]Comment: 44 pages, 12 Figures; accepted for publication in PASP; high resolution versions of Figures 1, 2, 6 and 9 available at http://bubba.ucdavis.edu/~lubin/Sandage