Willem H. De Vries

Hubble Space Telescope STIS Observations of the Kinematics of Emission-Line Nebulae in Three Compact Steep-Spectrum Radio Sources

We have obtained Hubble Space Telescope Space Telescope Imaging Spectrograph long-slit spectroscopy of the aligned emission-line nebulae in three compact steep-spectrum radio sources: 3C 67, 277.1, and 303.1. We find systematic offsets (~300–500 km s-1) of the emission-line velocities on one or both sides of the radio sources. We also see evidence for broad lines (FWHM ~ 500 km s-1) and complex emission-line profiles. In 3C 303.1 the data are consistent with multiple components and possibly split lines. The amplitude of the velocity variations is not so large as to exclude gravitationally induced motions. However, the complex kinematics, the lack of a signature of Keplerian rotation, and the association of the velocity variations with the radio lobes are consistent with the motions being driven by the expansion of the radio source. These kinematic signatures are consistent with an interaction between the expanding radio lobe and the emission-line clouds in which the clouds have been accelerated to velocities ~300–500 km s-1. Acceleration of the clouds by the bow shock is plausible given the estimated densities in the clouds and the velocities observed in the much smaller compact symmetric objects and with expansion velocities estimated from spectral aging.

XMM-Newton Detection of X-Ray Emission from the Compact Steep-Spectrum Radio Galaxy 3C 303.1

Using XMM-Newton we detect faint unresolved X-ray emission from the compact steep-spectrum radio galaxy 3C 303.1. We detect a thermal component at kT 0.8 keV, which seems likely to be produced in the interstellar medium (ISM) of the host galaxy. There is evidence for a second component in the spectrum whose nature is currently ambiguous. Plausible hypotheses for the second component include (1) hot gas shocked by the expansion of the radio source, and (2) synchrotron self-Compton emission from the southern radio lobe if the magnetic field is below the equipartition value by a factor of ~3.5.

Space-based telescopes for actionable refinement of ephemeris pathfinder mission

The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information needed to help satellite operators avoid collisions in space by using a network of nano- satellites to determine more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program, two pathfinder cube-satellites (CubeSats) equipped with an optical ima- ging payload are being developed and deployed to demonstrate the main elements of the STARE concept. We first give an overview of the STARE program. The details of the optical imaging payload for the STARE pathfinder CubeSats are then described, followed by a description of the track detection algorithm that will be used on the images it acquires. Finally, simulation results that highlight the effectiveness of the mission are presented.

Intelligent sensor tasking for space collision mitigation

Orbital collisions pose a hazard to space operations. Using a high performance computer modeling and simulation environment for space situational awareness, we explore a new paradigm for improving satellite conjunction analysis by obtaining more precise orbital information only for those objects that pose a collision risk greater than a defined threshold to a specific set of satellites during a specified time interval. In particular, we assess the improvement in the quality of the conjunction analysis that can be achieved using a distributed network of ground-based telescopes.

Optical payload for the STARE pathfinder mission

The Space-based Telescopes for Actionable Refinement of Ephemeris (STARE) program will collect the information needed to help satellite operators avoid collisions in space by using a network of nano-satellites to determine more accurate trajectories for selected space objects orbiting the Earth. In the first phase of the STARE program, two pathfinder cube-satellites (CubeSats) equipped with an optical imaging payload are being developed and deployed to demonstrate the main elements of the STARE concept. In this paper, we first give an overview of the STARE program. We then describe the details of the optical imaging payload for the STARE pathfinder CubeSats, including the optical design and the sensor characterization. Finally, we discuss the track detection algorithm that will be used on the images acquired by the payload.

Bright lights, big city: massive galaxies, giant Ly-α nebulae, and protoclusters

High redshift radio galaxies are great cosmological tools for pinpointing the most massive objects in the early Universe: massive forming galaxies, active super-massive black holes and proto-clusters. We report on deep narrow-band imaging and spectroscopic observations of several z > 2 radio galaxy fields to investigate the nature of giant Ly-α nebulae centered on the galaxies and to search for over-dense regions around them. We discuss the possible implications for our understanding of the formation and evolution of massive galaxies and galaxy clusters.

FOREGROUND PREDICTIONS FOR THE COSMIC MICROWAVE BACKGROUND POWER SPECTRUM FROM MEASUREMENTS OF FAINT INVERTED RADIO SOURCES AT 5 GHz

We present measurements of a population of matched radio sources at 1.4 and 5 GHz down to a flux limit of 1.5 mJy in 7 deg{sup 2} of the NOAO Deep Field South. We find a significant fraction of sources with inverted spectral indices that all have 1.4 GHz fluxes less than 10 mJy and are therefore too faint to have been detected and included in previous radio source count models that are matched at multiple frequencies. Combined with the matched source population at 1.4 and 5 GHz in 1 deg{sup -2} in the ATESP survey, we update models for the 5 GHz differential number counts and distributions of spectral indices in 5 GHz flux bins that can be used to estimate the unresolved point source contribution to the cosmic microwave background temperature anisotropies. We find a shallower logarithmic slope in the 5 GHz differential counts than in previously published models for fluxes {approx}< 100 mJy as well as larger fractions of inverted spectral indices at these fluxes. Because the Planck flux limit for resolved sources is larger than 100 mJy in all channels, our modified number counts yield at most a 10% change in the predicted Poisson contribution tomorexa0» the Planck temperature power spectrum. For a flux cut of 5 mJy with the South Pole Telescope and a flux cut of 20 mJy with the Atacama Cosmology Telescope, we predict a {approx}30% and {approx}10% increase, respectively, in the radio source Poisson power in the lowest frequency channels of each experiment relative to that predicted by previous models.«xa0less

AO Observations of Three Powerful Radio Galaxies

The host galaxies of powerful radio sources are ideal laboratories to study active galactic nuclei (AGN). The galaxies themselves are among the most massive systems in the universe, and are believed to harbor supermassive black holes (SMBH). If large galaxies are formed in a hierarchical way by multiple merger events, radio galaxies at low redshift represent the end-products of this process. However, it is not clear why some of these massive ellipticals have associated radio emission, while others do not. Both are thought to contain SMBHs, with masses proportional to the total luminous mass in the bulge. It either implies every SMBH has recurrent radio-loud phases, and the radio-quiet galaxies happen to be in the low state, or that the radio galaxy nuclei are physically different from radio-quiet ones, i.e. by having a more massive SMBH for a given bulge mass. Here we present the first results from our adaptive optics imaging and spectroscopy pilot program on three nearby powerful radio galaxies. Initiating a larger, more systematic AO survey of radio galaxies (preferentially with Laser Guide Star equipped AO systems) has the potential of furthering our understanding of the physical properties of radio sources, their triggering, and their subsequent evolution.