Search Publications
The magnetic field and wind confinement of θ1 Orionis C
Donati, J. -F.; Babel, J.; Harries, T. J. +3 more
We report the detection, through spectropolarimetric observations, of a strong dipolar magnetic field of presumably fossil origin at the surface of the very young O star θ1 Ori C. The Stokes V signatures we detect are variable with time, the variations being consistent with rotational modulation. A detailed modelling of our observations…
Measuring the redshift evolution of clustering: the Hubble Deep Field South
Colombi, S.; Matarrese, S.; Fontana, A. +6 more
We present an analysis of the evolution of galaxy clustering in the redshift interval 0<=z<=4.5 in the Hubble Deep Field South (HDF-South). The HST optical data are combined with infrared ISAAC/VLT observations, and photometric redshifts are used for all the galaxies brighter than IAB<=27.5. The clustering signal is obtained in…
New periodic variables from the Hipparcos epoch photometry
Koen, Chris; Eyer, Laurent
Two selection statistics are used to extract new candidate periodic variables from the epoch photometry of the Hipparcos catalogue. The primary selection criterion is a signal-to-noise ratio. The dependence of this statistic on the number of observations is calibrated using about 30000 randomly permuted Hipparcos data sets. A significance level of…
A SAURON study of M32: measuring the intrinsic flattening and the central black hole mass
Copin, Y.; van der Marel, R. P.; de Zeeuw, P. T. +6 more
We present dynamical models of the nearby compact elliptical galaxy M32, using high-quality kinematic measurements, obtained with the integral-field spectrograph SAURON mounted on the William Herschel Telescope on La Palma. We also include STIS data obtained previously by Joseph et al. We find a best-fitting black hole mass of M•= (2.5 …
The internal structure of the lens PG1115+080: breaking degeneracies in the value of the Hubble constant
Treu, T.; Koopmans, L. V. E.
We combine lensing, stellar kinematic and mass-to-light ratio constraints to build a two-component (luminous plus dark) mass model of the early-type lens galaxy in PG1115+080. We find a total mass density profile steeper than r-2, effectively ρ~r-γ' with γ'= 2.35 +/- 0.1 +/- 0.05 (random + systematic). The stellar mass fracti…
Galaxy cores as relics of black hole mergers
van den Bosch, Frank C.; Rest, Armin; Merritt, David +1 more
We investigate the hypothesis that the cores of elliptical galaxies and bulges are created from the binding energy liberated by the coalescence of supermassive binary black holes during galaxy mergers. Assuming that the central density profiles of galaxies were initially steep power laws, ρ ~r -2 , we define the `mass deficit' as the ma…
An empirical calibration of star formation rate estimators
Terlevich, Roberto; Terlevich, Elena; Rosa-González, Daniel
The observational determination of the behaviour of the star formation rate (SFR) with look-back time or redshift has two main weaknesses: (i) the large uncertainty of the dust/extinction corrections, and (ii) that systematic errors may be introduced by the fact that the SFR is estimated using different methods at different redshifts. Most frequen…
How the X-ray spectrum of a narrow-line Seyfert 1 galaxy may be reflection-dominated
Merloni, A.; Iwasawa, K.; Vaughan, S. +3 more
A model for the inner regions of accretion flows is presented where, owing to disc instabilities, cold and dense material is clumped into deep sheets or rings. Surrounding these density enhancements is hot, tenuous gas where coronal dissipation processes occur. We expect this situation to be most relevant when the accretion rate is close to Edding…
Spatially resolved X-ray spectroscopy of the core of the Centaurus cluster
Fabian, A. C.; Sanders, J. S.
We present Chandra data from a 31.7-ks observation of the Centaurus cluster, using the ACIS-S detector. Images of the X-ray emission show a plume-like feature at the centre of the cluster, of extent 60arcsec (20kpc in projection). The feature has the same metallicity as gas at a similar radius, but is cooler. Using adaptive binning, we generate te…
XMM-Newton discovery of a sharp spectral feature at ~ 7 keV in the narrow-line Seyfert 1 galaxy 1H 0707 - 49
Sunyaev, R.; Brandt, W. N.; Iwasawa, K. +6 more
We report the first detection of a sharp spectral feature in a narrow-line Seyfert 1 galaxy. Using XMM-Newton we have observed 1H 0707-495 and find a drop in flux by a factor of more than 2 at a rest-frame energy of ~7 keV without any detectable narrow Fe Kα line emission. The energy of this feature suggests a connection with the neutral iron K ph…