Search Publications

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…

The physical properties of the Lyα forest at z > 1.5

Cristiani, S.; Giallongo, E.; Carswell, R. F. +2 more

Combining a new, increased data set of eight quasi-stellar objects (QSOs) covering the Lyα forest at redshifts 1.5 > z < 3.6 from VLT/UVES observations with previously published results, we have investigated the properties of the Lyα forest at 1.5 < z <4. With the six QSOs covering the Lyα forest at 1.5 < z < 2.5, we have extende…

Chandra observations of the luminous infrared galaxy NGC 3256

Zezas, A.; Ward, M.; Lira, P. +2 more

We present a detailed analysis of high-resolution Chandra observations of the merger system NGC 3256, the most infrared-luminous galaxy in the nearby universe. The X-ray data show that several discrete sources embedded in complex diffuse emission contribute >~20 per cent of the total emission (L^{tot_{X\sim 8\times 1041\,erg\,s…}}

Mass segregation in young compact star clusters in the Large Magellanic Cloud - II. Mass functions

Mackey, A. D.; de Grijs, R.; Gilmore, G. F. +1 more

We review the complications involved in the conversion of stellar luminosities into masses and apply a range of mass-to-luminosity relations to our Hubble Space Telescope observations of the young Large Magellanic Cloud (LMC) star clusters NGC 1805 and 1818.

Both the radial dependence of the mass function (MF) and the dependence of the cluste…