The Wiener-Filtered COBE DMR Data and Predictions for the Tenerife Experiment

We apply a Wiener filter to the two-year COBE DMR data. The resulting sky map has significantly reduced noise levels compared to the raw data: the most prominent hot and cold spots are significant at the 4-sigma level. Furthermore, the entire covariance matrix of the errors in the filtered sky map is known, and it is therefore possible to make constrained realizations of the microwave sky with the correct a posteriori probability distribution. The filtered DMR sky map is used to make predictions for the Tenerife experiment. Two prominent features are predicted in a region of the sky not yet analyzed by the Tenerife group. The presence of these features is a robust prediction of the standard cosmological paradigm; if these features are not observed, some of our fundamental assumptions must be incorrect.Comment: 15 pages of uuencoded compressed PostScript. A PostScript file including figures is available at ftp://pac2.berkeley.edu/pub/bunn/wienerten

A Fundamental Test of the Nature of Dark Matter

Dark matter may consist of weakly interacting elementary particles or of macroscopic compact objects. We show that the statistics of the gravitational lensing of high redshift supernovae strongly discriminate between these two classes of dark matter candidates. We develop a method of calculating the magnification distribution of supernovae, which can be interpreted in terms of the properties of the lensing objects. With simulated data we show that >~ 50 well measured type Ia supernovae (\Delta m ~ 0.2 mag) at redshifts ~1 can clearly distinguish macroscopic from microscopic dark matter if \Omega_o \simgt 0.2 and all dark matter is in one form or the other.Comment: 8 pages, 2 figures, AASTeX, replaced to conform to the version to be published in ApJL. It is now more clearly written and addresses some possible systematic uncertaintie

A simple theory of bimodal star formation

A model of bimodal star formation is presented, wherein massive stars form in giant molecular clouds (GNC), at a rate regulated by supernovae energy feedback through the interstellar medium, the heat input also ensuring that the initial mass function (IMF) remains skewed towards massive stars. The low mass stars form at a constant rate. The formation of the GMC is governed by the dynamics of the host galaxy through the rotation curve and potential perturbations such as a spiral density wave. The characteristic masses, relative normalizations, and rates of formation of the massive and low mass modes of star formation may be tightly constrained by the requirements of the chemical evolution in the Solar Neighborhood. Good fits were obtained for the age metallicity relation and the metallicity structure of thin disk and spheroid stars only for a narrow range of these parameters

Can the WIMP annihilation boost factor be boosted by the Sommerfeld enhancement?

We demonstrate that the Sommerfeld correction to CDM annihilations can be appreciable if even a small component of the dark matter is extremely cold. Subhalo substructure provides such a possibility given that the smallest clumps are relatively cold and contain even colder substructure due to incomplete phase space mixing. Leptonic channels can be enhanced for plausible models and the solar neighbourhood boost required to account for PAMELA/ATIC data is plausibly obtained, especially in the case of a few TeV mass neutralino for which the Sommerfeld-corrected boost is found to be $\sim10^4-10^5.$ Saturation of the Sommerfeld effect is shown to occur below $\beta\sim 10^{-4},$ thereby constraining the range of contributing substructures to be above $\sim 10^5\rm M_\odot.$ We find that the associated diffuse gamma ray signal from annihilations would exceed EGRET constraints unless the channels annihilating to heavy quarks or to gauge bosons are suppressed. The lepton channel gamma rays are potentially detectable by the FERMI satellite, not from the inner galaxy where substructures are tidally disrupted, but rather as a quasi-isotropic background from the outer halo, unless the outer substructures are much less concentrated than the inner substructures and/or the CDM density profile out to the virial radius steepens significantly.Comment: 8 pages, 5 figures. References added. Replaced to match published versio

Evolution of Supermassive Black Holes from Cosmological Simulations

The correlations between the mass of supermassive black holes and properties of their host galaxies are investigated through cosmological simulations. Black holes grow from seeds of 100 solar masses inserted into density peaks present in the redshift range 12-15. Seeds grow essentially by accreting matter from a nuclear disk and also by coalescences resulting from merger episodes. At z=0, our simulations reproduce the black hole mass function and the correlations of the black hole mass both with stellar velocity dispersion and host dark halo mass. Moreover, the evolution of the black hole mass density derived from the present simulations agrees with that derived from the bolometric luminosity function of quasars, indicating that the average accretion history of seeds is adequately reproduced . However, our simulations are unable to form black holes with masses above $10^9 M_{\odot}$ at $z\sim 6$, whose existence is inferred from the bright quasars detected by the Sloan survey in this redshift range.Comment: Talk given at the International Workshop on Astronomy and Relativistic Astrophysics (IWARA 2009), Maresias, Brazil. to be published in the International Journal of Modern Physics

The Dynamical Evolution of Substructure

The evolution of substructure embedded in non-dissipative dark halos is studied through N-body simulations of isolated systems, both in and out of initial equilibrium, complementing cosmological simulations of the growth of structure. We determine by both analytic calculations and direct analysis of the N-body simulations the relative importance of various dynamical processes acting on the clumps, such as the removal of material by global tides, clump-clump heating, clump-clump merging and dynamical friction. Our comparison between merging and disruption processes implies that spiral galaxies cannot be formed in a proto-system that contains a few large clumps, but can be formed through the accretion of many small clumps; elliptical galaxies form in a more clumpy environment than do spiral galaxies. Our results support the idea that the central cusp in the density profiles of dark halos is the consequence of self-limiting merging of small, dense halos. This implies that the collapse of a system of clumps/substructure is not sufficient to form a cD galaxy, with an extended envelope; plausibly subsequent accretion of large galaxies is required. Persistent streams of material from disrupted clumps can be found in the outer regions of the final system, and at an overdensity of around 0.75, can cover 10% to 30% of the sky.Comment: Accepted for publication in MNRAS. 61 pages, 22 figures; figures 2-7 and 21-22 are separate gif files. Complete paper plus high resolution figures available from http://www.stsci.edu/~mstiavel/Bing_et_al_02.htm

Dark matter, neutron stars and strange quark matter

We show that self-annihilating neutralino WIMP dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star into a strange star. We use an energy estimate for the long-lived strangelet based on the Fermi gas model combined with the MIT bag model to set a new limit on the possible values of the WIMP mass that can be especially relevant for subdominant species of massive neutralinos.Comment: 5 pages, 2 figures, accepted for publication in Phys. Rev. Let

On the Magnitude of Dark Energy Voids and Overdensities

We investigate the clustering of dark energy within matter overdensities and voids. In particular, we derive an analytical expression for the dark energy density perturbations, which is valid both in the linear, quasi-linear and fully non-linear regime of structure formation. We also investigate the possibility of detecting such dark energy clustering through the ISW effect. In the case of uncoupled quintessence models, if the mass of the field is of order the Hubble scale today or smaller, dark energy fluctuations are always small compared to the matter density contrast. Even when the matter perturbations enter the non-linear regime, the dark energy perturbations remain linear. We find that virialised clusters and voids correspond to local overdensities in dark energy, with \delta_{\phi}/(1+w) \sim \Oo(10^{-5}) for voids, \delta_{\phi}/(1+w) \sim \Oo(10^{-4}) for super-voids and \delta_{\phi}/(1+w) \sim \Oo(10^{-5}) for a typical virialised cluster. If voids with radii of $100-300 {\rm Mpc}$ exist within the visible Universe then $\delta_{\phi}$ may be as large as $10^{-3}(1+w)$. Linear overdensities of matter and super-clusters generally correspond to local voids in dark energy; for a typical super-cluster: \delta_{\phi}/(1+w) \sim \Oo(-10^{-5}). The approach taken in this work could be straightforwardly extended to study the clustering of more general dark energy models.Comment: 20 pages, 14 figures. Accepted by the Astrophys.

Galaxy UV-luminosity function and reionization constraints on axion dark matter

If the dark matter (DM) were composed of axions, then structure formation in the Universe would be suppressed below the axion Jeans scale. Using an analytic model for the halo mass function of a mixed DM model with axions and cold dark matter, combined with the abundance-matching technique, we construct the UV-luminosity function. Axions suppress high-$z$ galaxy formation and the UV-luminosity function is truncated at a faintest limiting magnitude. From the UV-luminosity function, we predict the reionization history of the universe and find that axion DM causes reionization to occur at lower redshift. We search for evidence of axions using the Hubble Ultra Deep Field UV-luminosity function in the redshift range $z=6$-$10$, and the optical depth to reionization, $\tau$, as measured from cosmic microwave background polarization. All probes we consider consistently exclude $m_a\lesssim 10^{-23}\text{ eV}$ from contributing more than half of the DM, with our strongest constraint ruling this model out at more than $8\sigma$ significance. In conservative models of reionization a dominant component of DM with $m_a=10^{-22}\text{ eV}$ is in $3\sigma$ tension with the measured value of $\tau$, putting pressure on an axion solution to the cusp-core problem. Tension is reduced to $2\sigma$ for the axion contributing only half of the DM. A future measurement of the UV-luminosity function in the range $z=10$-$13$ by JWST would provide further evidence for or against $m_a=10^{-22}\text{ eV}$. Probing still higher masses of $m_a=10^{-21}\text{ eV}$ will be possible using future measurements of the kinetic Sunyaev-Zel'dovich effect by Advanced ACTPol to constrain the time and duration of reionization.Comment: 17 pages, 8 figures, 2 tables. v2: Minor Changes. References added. Published in MNRA

The Quasar-frame Velocity Distribution of Narrow CIV Absorbers

We report on a survey for narrow (FWHM < 600 km/s) CIV absorption lines in a sample of bright quasars at redshifts $1.8 \le z < 2.25$ in the Sloan Digital Sky Survey. Our main goal is to understand the relationship of narrow CIV absorbers to quasar outflows and, more generally, to quasar environments. We determine velocity zero-points using the broad MgII emission line, and then measure the absorbers' quasar-frame velocity distribution. We examine the distribution of lines arising in quasar outflows by subtracting model fits to the contributions from cosmologically intervening absorbers and absorption due to the quasar host galaxy or cluster environment. We find a substantial number ($\ge 43\pm6$ per cent) of absorbers with REW $> 0.3$ \AA in the velocity range +750 km/s \la v \la +12000 km/s are intrinsic to the AGN outflow. This `outflow fraction' peaks near $v=+2000$ km/s with a value of $f_{outflow} \simeq 0.81 \pm 0.13$. At velocities below $v \approx +2000$ km/s the incidence of outflowing systems drops, possibly due to geometric effects or to the over-ionization of gas that is nearer the accretion disk. Furthermore, we find that outflow-absorbers are on average broader and stronger than cosmologically-intervening systems. Finally, we find that $\sim 14$ per cent of the quasars in our sample exhibit narrow, outflowing CIV absorption with REW $> 0.3$\AA, slightly larger than that for broad absorption line systems.Comment: 11 pages, 9 figures, accepted for publication in MNRA