Search Publications
UV bright globular clusters in M87: more evidence for super-He-rich stellar populations?
O'Connell, R. W.; Kaviraj, S.; Yoon, S. -J. +3 more
We study the ultraviolet (UV) and optical properties of 38 massive globular clusters (GCs) in the Virgo elliptical, M87, imaged using the STIS and WFPC2 instruments onboard the Hubble Space Telescope. The majority of these GCs appear extremely bright in the far-UV (FUV) - roughly a magnitude brighter than their Galactic counterparts with similar m…
Kinematics of gas and stars in the circumnuclear star-forming ring of NGC3351
Terlevich, Roberto; Terlevich, Elena; Díaz, Ángeles I. +2 more
We have measured gas and stellar velocity dispersions in five circumnuclear star-forming regions (CNSFRs) and the nucleus of the barred spiral galaxy NGC3351. The stellar dispersions have been obtained from high-resolution spectra of the CaII triplet (CaT) lines at λλ8494, 8542, 8662Å, while the gas velocity dispersions have been measured by Gauss…
XMM-Newton study of 0.012 < z < 0.024 groups - I. Overview of the IGM thermodynamics
Finoguenov, A.; Ponman, T. J.; Osmond, J. P. F. +1 more
We study the thermodynamic properties of the hot gas in a sample of groups in the 0.012-0.024 redshift range, using XMM-Newton observations. We present measurements of temperature, entropy, pressure and iron abundance. Non-parametric fits are used to derive the mean properties of the sample and to study dispersion in the values of entropy and pres…
A survey of the Wolf-Rayet population of the barred, spiral galaxy NGC 1313
Crowther, P. A.; Hadfield, L. J.
We present a VLT/FORS1 survey of Wolf-Rayet (WR) stars in the spiral galaxy NGC 1313. In total, 94 WR candidate sources have been identified from narrow-band imaging. Of these, 82 have been spectroscopically observed, for which WR emission features are confirmed in 70 cases, one of which also exhibits strong nebular He IIλ4686 emission. We also de…
Chandra and XMM-Newton detection of large-scale diffuse X-ray emission from the Sombrero galaxy
Wang, Q. Daniel; Li, Zhiyuan; Hameed, Salman
We present an X-ray study of the massive edge-on Sa galaxy, Sombrero (M 104; NGC 4594), based on XMM-Newton and Chandra observations. A list of 62 XMM-Newton and 175 Chandra discrete X-ray sources is provided, the majority of which are associated with the galaxy. Spectral analysis is carried out for relatively bright individual sources and for an …
Irradiation models for ULXs and fits to optical data
Copperwheat, Christopher; Cropper, Mark; Soria, Roberto +1 more
We have constructed a model which describes the optical emission from ultraluminous X-ray sources (ULXs), and have used it to constrain the parameters of seven ULX systems. Our model assumes a binary nature for ULXs, and accounts for optical emission from an X-ray-irradiated companion star and accretion disc. We apply our model to six different UL…
Evidence for a large fraction of Compton-thick quasars at high redshift
Simpson, Chris; Rawlings, Steve; Almaini, Omar +7 more
Using mid-infrared and radio selection criteria, we pre-select a sample of candidate high-redshift type 2 quasars in the Subaru XMM-Newton Deep Field (SXDF). To filter out starburst contaminants, we use a Bayesian method to fit the spectral energy distributions (SEDs) between 24-µm and the B-band, obtain photometric redshifts, and identify t…
Blending in gravitational microlensing experiments: source confusion and related systematics
Sumi, Takahiro; Mao, Shude; Smith, Martin C. +1 more
Gravitational microlensing surveys target very dense stellar fields in the local group. As a consequence, the microlensed source stars are often blended with nearby unresolved stars. The presence of `blending' is a cause of major uncertainty when determining the lensing properties of events towards the Galactic centre. After demonstrating empirica…
Hubble Space Telescope far-ultraviolet imaging of the jet in 3C273: a common emission component from optical to X-rays
Perlman, Eric S.; Sparks, William B.; Meisenheimer, Klaus +2 more
We present far-ultraviolet (far-UV) observations at ~150 nm of the jet of quasar 3C273 obtained with the Advanced Camera for Surveys (ACS) Solar Blind Channel onboard the Hubble Space Telescope. While the jet morphology is very similar to that in the optical and near-UV, the spectral energy distributions of the jet's subregions show an upturn in ν…
Very deep X-ray observations of the anomalous X-ray pulsar 4U0142+614
Campana, S.; Stella, L.; Parmar, A. N. +8 more
We report on two new XMM-Newton observations of the anomalous X-ray pulsar (AXP) 4U0142+614 performed in 2004 March and July, collecting the most accurate spectrum for this source. Furthermore, we analyse two short archival observations performed in 2002 February and 2003 January in order to study the long-term behaviour of this AXP. 4U0142+614 ap…