Search Publications
Rapid Compton-thick/Compton-thin Transitions in the Seyfert 2 Galaxy NGC 1365
Zezas, A.; Elvis, M.; Baldi, A. +2 more
We present multiple Chandra and XMM-Newton observations of the type 1.8 Seyfert galaxy NGC 1365, which shows the most dramatic X-ray spectral changes observed so far in an active galactic nucleus: the source switched from reflection-dominated to transmission-dominated and back in just 6 weeks. During this time the soft thermal component, arising f…
An Ab Initio Approach to the Solar Coronal Heating Problem
Nordlund, Åke; Gudiksen, Boris Vilhelm
We present an ab initio approach to the solar coronal heating problem by modeling a small part of the solar corona in a computational box using a three-dimensional MHD code including realistic physics. The observed solar granular velocity pattern and its amplitude and vorticity power spectra, as reproduced by a weighted Voronoi tessellation method…
Making the Corona and the Fast Solar Wind: A Self-consistent Simulation for the Low-Frequency Alfvén Waves from the Photosphere to 0.3 AU
Inutsuka, Shu-ichiro; Suzuki, Takeru K.
By performing a one-dimensional magnetohydrodynamic simulation with radiative cooling and thermal conduction, we show that the coronal heating and the fast solar wind acceleration in the coronal holes are natural consequences of the footpoint fluctuations of the magnetic fields at the photosphere. We initially set up a static open flux tube with a…
The Relationship of Hard X-Ray and Optical Line Emission in Low-Redshift Active Galactic Nuclei
Ptak, A.; Heckman, T. M.; Hornschemeier, A. +1 more
In this paper we assess the relationship of the population of active galactic nuclei (AGNs) selected by hard X-rays to the traditional population of AGNs with strong optical emission lines. First, we study the emission-line properties of a new hard-X-ray-selected sample of 47 local AGNs (classified optically as Type 1 and 2 AGNs). We find that the…
The ACS Virgo Cluster Survey. VII. Resolving the Connection between Globular Clusters and Ultracompact Dwarf Galaxies
Djorgovski, S. G.; Jordán, Andrés; Tonry, John L. +10 more
We investigate the connection between globular clusters and ultracompact dwarf galaxies (UCDs) by examining the properties of 10 compact, high-luminosity (-11.8 MV -10.8) objects associated with M87 (NGC 4486, VCC 1316), the cD galaxy in the Virgo Cluster. These objects, most of which were previously classified as M87 globular clusters, were selec…
The ACS Virgo Cluster Survey. X. Half-Light Radii of Globular Clusters in Early-Type Galaxies: Environmental Dependencies and a Standard Ruler for Distance Estimation
Sarazin, Craig L.; Jordán, Andrés; Tonry, John L. +10 more
We have measured half-light radii, rh, for thousands of globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured half-light radii on both the properties of the GCs themselves and their host galaxies reveal…
Infrared Spectral Energy Distributions of Nearby Galaxies
Helou, G.; Roussel, H.; Leitherer, C. +25 more
The Spitzer Infrared Nearby Galaxies Survey (SINGS) is carrying out a comprehensive multiwavelength survey on a sample of 75 nearby galaxies. The 1-850 µm spectral energy distributions (SEDs) are presented using broadband imaging data from Spitzer, 2MASS, ISO, IRAS, and SCUBA. The infrared colors derived from the globally integrated Spitzer …
An Intermediate-Mass Black Hole in the Globular Cluster G1: Improved Significance from New Keck and Hubble Space Telescope Observations
Ho, Luis C.; Gebhardt, Karl; Rich, R. M.
We present dynamical models for the massive globular cluster G1. The goal is to measure or place a significant upper limit on the mass of any central black hole. Whether or not globular clusters contain central massive black holes has important consequences for a variety of studies. We use new kinematic data obtained with Keck and new photometry f…
The Assembly History of Field Spheroidals: Evolution of Mass-to-Light Ratios and Signatures of Recent Star Formation
Treu, Tommaso; van Dokkum, Pieter G.; Coil, Alison +6 more
We present a comprehensive catalog of high signal-to-noise ratio spectra obtained with DEIMOS on the Keck II telescope for a sample of F850LP<22.43 (AB) field spheroidal (E+S0 galaxies; 165) and bulge-dominated disk (61) galaxies in the redshift range 0.2<z<1.2, selected on the basis of visual morphology from the northern field of the Gre…
Relativistic Accretion Disk Models of High-State Black Hole X-Ray Binary Spectra
Hubeny, Ivan; Davis, Shane W.; Turner, Neal J. +1 more
We present calculations of non-LTE, relativistic accretion disk models applicable to the high/soft state of black hole X-ray binaries. We include the effects of thermal Comptonization and bound-free and free-free opacities of all abundant ion species. Taking into account the relativistic propagation of photons from the local disk surface to an obs…