Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

We present results of a Gemini adaptive optics (AO) imaging program to investigate the host galaxies of typical QSOs at z ∼ 2. Our aim is to study the host galaxies of typical L*QSO QSOs at the epoch of peak QSO and star formation activity. The large database of faint QSOs provided by the Two-Degree Field QSO Redshift Survey allows us to select a sample of QSOs at z = 1.75-2.5 that have nearby (<12″ separation) bright stars suitable for use as AO guide stars. We have observed a sample of nine QSOs. The images of these sources have AO-corrected FWHM of between 0″.11 and 0″.25. We use multiple observations of point-spread function (PSF) calibration star pairs to quantify any uncertainty in the PSF. We then factored these uncertainties into our modeling of the QSO plus host galaxy. In only one case did we convincingly detect a host (2QZ J133311.4+001949, at z = 1.93). This host galaxy has K = 18.5 ± 0.2 mag with a half-light radius Re = 0″.55 ± 0″.1 equivalent to ∼3L*gal, assuming a simple passively evolving model. From detailed simulations of our host galaxy modeling process, we find that for four of our targets we should be sensitive to host galaxies that are equivalent to ∼2L*gal (passively evolved). Our nondetections therefore place tight constraints on the properties of L*QSO QSO host galaxies, which can be no brighter (after allowing for passive evolution) than the host galaxies of L*QSO active galactic nuclei at low redshift, although the QSOs themselves are a factor of ∼50 brighter. This implies that either the fueling efficiency is much greater at high redshift or that more massive black holes are active at high redshift.

Abstract:

Two ground-based experiments have recently independently detected TeV $\gamma$-rays from the direction of the Galactic center. The observations made by the VERITAS and CANGAROO collaborations are unexpected, although not impossible to interpret in terms of astrophysical sources. Here we examine in detail whether the observed $\gamma$-rays may arise from the more exotic alternative of annihilations of dark matter particles clustered in the center of the Galaxy.

Abstract:

We measure the angular power spectrum of radio galaxies in the NRAO VLA Sky Survey (NVSS) using two independent methods: direct spherical harmonic analysis and maximum likelihood estimation. The results are consistent and can be understood using models for the spatial matter power spectrum and for the redshift distribution of radio galaxies at mJy flux-density levels. A good fit to the angular power spectrum can only be achieved if radio galaxies possess high bias with respect to mass fluctuations; by marginalizing over the other parameters of the model we derive a 68% confidence interval 1.53 < b_0 sigma_8 < 1.87, where b_0 is the linear bias factor for radio galaxies and sigma_8 describes the normalization of the matter power spectrum. Our models indicate that the majority of the signal in the NVSS angular power spectrum is generated at low redshifts. Individual redshifts for the NVSS sources are thus required to alleviate projection effects and probe directly the matter power spectrum on large scales.