Search Publications
General relativistic modelling of the negative reverberation X-ray time delays in AGN
Papadakis, I. E.; Emmanoulopoulos, D.; Dovčiak, M. +1 more
We present the first systematic physical modelling of the time-lag spectra between the soft (0.3-1 keV) and the hard (1.5-4 keV) X-ray energy bands, as a function of Fourier frequency, in a sample of 12 active galactic nuclei which have been observed by XMM-Newton. We concentrate particularly on the negative X-ray time-lags (typically seen above 1…
Improved mass and radius constraints for quiescent neutron stars in ω Cen and NGC 6397
Campana, S.; Heinke, C. O.; Cohn, H. N. +8 more
We use Chandra and XMM-Newton observations of the globular clusters ω Cen and NGC 6397 to measure the spectrum of their quiescent neutron stars (NSs), and thus to constrain the allowed ranges of mass and radius for each. We also use Hubble Space Telescope photometry of NGC 6397 to identify a potential optical companion to the quiescent NS, and fin…
CLASH: A Census of Magnified Star-forming Galaxies at z ~ 6-8
Shu, X.; Infante, L.; Zheng, W. +34 more
We utilize 16 band Hubble Space Telescope (HST) observations of 18 lensing clusters obtained as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program to search for z ~ 6-8 galaxies. We report the discovery of 204, 45, and 13 Lyman-break galaxy candidates at z ~ 6, z ~ 7, and z ~ 8, respectively, identifi…
A Herschel [C II] Galactic plane survey. III. [C II] as a tracer of star formation
Goldsmith, P. F.; Langer, W. D.; Pineda, J. L.
Context. The [C ii] 158 µm line is the brightest far-infrared cooling line in galaxies, representing 0.1 to 1% of their far-infrared continuum emission, and is therefore a potentially powerful tracer of star formation activity. The [C ii] line traces different phases of the interstellar medium (ISM), including the diffuse ionized medium, war…
The stellar and dark matter distributions in elliptical galaxies from the ensemble of strong gravitational lenses
Oguri, Masamune; Falco, Emilio E.; Rusu, Cristian E.
We derive the average mass profile of elliptical galaxies from the ensemble of 161 strong gravitational lens systems selected from several surveys, assuming that the mass profile scales with the stellar mass and effective radius of each lensing galaxy. The total mass profile is well fitted by a power law ρ(r) ∝ rγ with best-fitting slop…
Global and Nonglobal Parameters of Horizontal-branch Morphology of Globular Clusters
Milone, A. P.; Marino, A. F.; Sarajedini, A. +10 more
The horizontal-branch (HB) morphology of globular clusters (GCs) is mainly determined by metallicity. However, the fact that GCs with almost the same metallicity exhibit different HB morphologies demonstrates that at least one more parameter is needed to explain the HB morphology. It has been suggested that one of these should be a global paramete…
A VLBI resolution of the Pleiades distance controversy
Stauffer, John R.; Bower, Geoffrey C.; Melis, Carl +2 more
Because of its proximity and its youth, the Pleiades open cluster of stars has been extensively studied and serves as a cornerstone for our understanding of the physical properties of young stars. This role is called into question by the “Pleiades distance controversy,” wherein the cluster distance of 120.2 ± 1.5 parsecs (pc) as measured by the op…
Broadband X-Ray Spectra of the Ultraluminous X-Ray Source Holmberg IX X-1 Observed with NuSTAR, XMM-Newton, and Suzaku
Harrison, F. A.; Ptak, A.; Stern, D. +16 more
We present results from the coordinated broadband X-ray observations of the extreme ultraluminous X-ray source Holmberg IX X-1 performed by NuSTAR, XMM-Newton, and Suzaku in late 2012. These observations provide the first high-quality spectra of Holmberg IX X-1 above 10 keV to date, extending the X-ray coverage of this remarkable source up to ~30 …
NuSTAR and XMM-Newton Observations of Luminous, Heavily Obscured, WISE-selected Quasars at z ~ 2
Harrison, F. A.; Stern, D.; Zhang, W. W. +32 more
We report on a NuSTAR and XMM-Newton program that has observed a sample of three extremely luminous, heavily obscured WISE-selected active galactic nuclei (AGNs) at z ~ 2 across a broad X-ray band (0.1 - 79 keV). The parent sample, selected to be faint or undetected in the WISE 3.4 µm (W1) and 4.6 µm (W2) bands but bright at 12 µ…
Magnetic Helicity, Tilt, and Twist
Pevtsov, Alexei A.; van Driel-Gesztelyi, Lidia; Norton, Aimee A. +2 more
Since its introduction to astro- and solar physics, the concept of helicity has proven to be useful in providing critical insights into physics of various processes from astrophysical dynamos, to magnetic reconnection and eruptive phenomena. Signature of helicity was also detected in many solar features, including orientation of solar active regio…