Lance Miller

Abstract:

It is a firm prediction of the concordance cold-dark-matter cosmological model that galaxy clusters occur at the intersection of large-scale structure filaments. The thread-like structure of this 'cosmic web' has been traced by galaxy redshift surveys for decades. More recently, the warm-hot intergalactic medium (a sparse plasma with temperatures of 10 5 kelvin to 10 7 kelvin) residing in low-redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying dark-matter skeleton, which should contain more than half of all matter, has remained elusive, because earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignments of dark and luminous matter. Here we report the detection of a dark-matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft-X-ray emission, and contributes a mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. By combining this result with X-ray observations, we can place an upper limit of 0.09 on the hot gas fraction (the mass of X-ray-emitting gas divided by the total mass) in the filament. © 2012 Macmillan Publishers Limited. All rights reserved.

Abstract:

We have modeled a small sample of Seyfert galaxies that were previously identified as having simple X-ray spectra with little intrinsic absorption. The sources in this sample all contain moderately broad components of FeK-shell emission and are ideal candidates for testing the applicability of a Compton-thick accretion disk wind model to active galactic nucleus (AGN) emission components. Viewing angles through the wind allow the observer to see the absorption signature of the gas, whereas face-on viewing angles allow the observer to see the scattered light from the wind. We find that the FeK emission line profiles are well described with a model of a Compton-thick accretion disk wind of solar abundances, arising tens to hundreds of gravitational radii from the central black hole. Further, the fits require a neutral component of FeKα emission that is too narrow to arise from the inner part of the wind, and likely comes from a more distant reprocessing region. Our study demonstrates that a Compton-thick wind can have a profound effect on the observed X-ray spectrum of an AGN, even when the system is not viewed through the flow. © 2012. The American Astronomical Society. All rights reserved..

Abstract:

We present new Hubble Space Telescope (HST)/Cosmic Origins Spectrograph (COS) observations of the narrow-line Seyfert 1 galaxy NGC4051. These data were obtained as part of a coordinated observing program including X-ray observations with the Chandra/High Energy Transmission Grating (HETG) spectrometer and Suzaku. We detected nine kinematic components of UV absorption, which were previously identified using the HST/Space Telescope Imaging Spectrograph (STIS). None of the absorption components showed evidence for changes in column density or profile within the 10 yr between the STIS and COS observations, which we interpret as evidence of (1) saturation, for the stronger components, or (2) very low densities, i.e., n H < 1 cm-3, for the weaker components. After applying a +200 km s-1 offset to the HETG spectrum, we found that the radial velocities of the UV absorbers lay within the O VII profile. Based on photoionization models, we suggest that, while UV components 2, 5, and 7 produce significant O VII absorption, the bulk of the X-ray absorption detected in the HETG analysis occurs in more highly ionized gas. Moreover, the mass-loss rate is dominated by high-ionization gas which lacks a significant UV footprint. © 2012. The American Astronomical Society. All rights reserved..

Abstract:

X-ray spectra of AGN are complex. X-ray absorption and emission features trace gas covering a wide range of column densities and ionization states. High resolution spectra show the absorbing gas to be outflowing, perhaps in the form of an accretion disk wind. The absorbing complex shapes the form of the X-ray spectrum while X-ray reverberation and absorption changes explain the spectral and timing behaviour of AGN. We discuss recent progress, highlighting some new results and reviewing the implications that can be drawn from the data. © 2012 American Institute of Physics.