Search Publications
Searching for dark matter in X-rays: how to check the dark matter origin of a spectral feature
Boyarsky, Alexey; Ruchayskiy, Oleg; Iakubovskyi, Dmytro +3 more
A signal from decaying dark matter (DM) can be unambiguously distinguished from spectral features of astrophysical or instrumental origin by studying its spatial distribution. We demonstrate this approach by examining the recent claim of Loewenstein and Kusenko regarding the possible DM origin of the 2.5 keV line in Chandra observations of the Mil…
MACS J1423.8+2404: gravitational lensing by a massive, relaxed cluster of galaxies at z = 0.54
Kneib, J. -P.; Smith, G. P.; Schrabback, T. +8 more
We present results of a gravitational lensing and optical study of MACS J1423.8+2404 (z = 0.545, MACS J1423), the most relaxed cluster in the high-redshift subsample of clusters discovered in the MAssive Cluster Survey (MACS). Our analysis uses high-resolution images taken with the Hubble Space Telescope in the F555W and F814W passbands, ground-ba…
Stellar winds and mass loss from extreme helium stars
Hamann, W. -R.; Jeffery, C. S.
Extreme helium stars are very rare low-mass supergiants in a late stage of evolution. They are probably contracting to become white dwarfs following a violent phase of evolution which caused them to become hydrogen-deficient giants, possibly R CrB stars. Using the latest generation of models for spherically expanding stellar atmospheres, we set ou…
Offset between dark matter and ordinary matter: evidence from a sample of 38 lensing clusters of galaxies
Zhao, Hongsheng; Shan, Huanyuan; Tao, Charling +3 more
We compile a sample of 38 galaxy clusters which have both X-ray and strong lensing observations, and study for each cluster the projected offset between the dominant component of baryonic matter centre (measured by X-rays) and the gravitational centre (measured by strong lensing). Among the total sample, 45 per cent clusters have offsets >10arc…
The impact of a major cluster merger on galaxy evolution in MACSJ0025.4-1225
Schrabback, T.; Ebeling, H.; Ma, C. -J. +1 more
We present results of an extensive morphological, spectroscopic and photometric study of the galaxy population of MACSJ0025.4-1225 (z = 0.586), a major cluster merger with clear segregation of dark and luminous matter, to examine the impact of mergers on galaxy evolution. Based on 436 galaxy spectra obtained with Keck DEep Imaging Multi-Object Spe…
The X-ray binary analogy to the first AGN quasi-periodic oscillation
Done, Chris; Middleton, Matthew
The narrow line Seyfert 1 galaxy REJ 1034+396 is so far unique amongst active galaxies (AGN) in showing a quasi-periodic oscillation (QPO) in its variability power spectrum. There are multiple types of QPO seen in black hole binary (BHB) systems, so we need to identify which BHB QPO corresponds to the one seen in the AGN. A key hint is the `hot di…
The tidal tails of the ultrafaint globular cluster Palomar 1
Evans, N. W.; Belokurov, V.; Gieles, M. +3 more
Using the optimal filter technique applied to Sloan Digital Sky Survey photometry, we have found extended tails stretching about 1° (or several tens of half-light radii) from either side of the ultrafaint globular cluster Palomar 1. The tails contain roughly as many stars as does the cluster itself. Using deeper Hubble Space Telescope data, we see…
Variability and spectral energy distributions of low-luminosity active galactic nuclei: a simultaneous X-ray/UV look with Swift
Pian, E.; Cucchiara, A.; Pagani, C. +3 more
We have observed four low-luminosity active galactic nuclei (AGNs) classified as type 1 Low-Ionization Nuclear Emission-Line Regions (LINERs) with the X-Ray Telescope (XRT) and the Ultraviolet-Optical Telescope (UVOT) onboard Swift, in an attempt to clarify the main powering mechanism of this class of nearby sources. Among our targets, we detect X…
Stars and dark matter in the spiral gravitational lens 2237+0305
Treu, T.; Koopmans, L. V. E.; Webster, R. L. +1 more
We construct a mass model for the spiral lens galaxy 2237+0305, at redshift zl = 0.04, based on gravitational-lensing constraints, HI rotation, and new stellar-kinematic information, based on data taken with the Echelle Spectrograph and Imager (ESI) spectrograph on the 10-m Keck-II Telescope. High-resolution rotation curves and velocity…
Star formation in the outer filaments of NGC 1275
Fabian, A. C.; Gallagher, J. S.; Conselice, C. J. +5 more
We present photometry of the outer star clusters in NGC 1275, the brightest galaxy in the Perseus cluster. The observations were taken using the Hubble Space Telescope Advanced Camera for Surveys. We focus on two stellar regions in the south and south-east, far from the nucleus of the low-velocity system (~22kpc). These regions of extended star fo…