Search Publications
Challenging times: a re-analysis of NGC 5408 X-1
Done, C.; Roberts, T. P.; Middleton, M. J. +1 more
The ultraluminous X-ray source, NGC 5408 X-1, is one of only three such objects to show a quasi-periodic oscillation (QPO) in its power spectrum. Previous analysis of this signal identified it with the well-studied type-C low-frequency QPO (LFQPO) seen in black hole binaries (BHBs), implying an intermediate mass black hole (IMBH). However, in BHBs…
The peculiar horizontal branch of NGC 2808
Dalessandro, E.; Salaris, M.; Sabbi, E. +5 more
We present an accurate analysis of the peculiar horizontal branch (HB) of the massive Galactic globular cluster NGC 2808, based on high-resolution far-UV and optical images of the central region of the cluster obtained with the Hubble Space Telescope. We confirm the multimodal distribution of stars along the HB: four sub-populations separated by g…
Spectral classification of O2-3.5 If*/WN5-7 stars
Walborn, Nolan R.; Crowther, Paul A.
An updated classification scheme for transition O2-3.5 If*/WN5-7 stars is presented, following recent revisions to the spectral classifications for O and WN stars. We propose that O2-3.5 If*, O2-3.5 If*/WN5-7 and WN5-7 stars may be discriminated using the morphology of Hβ to trace increasing wind density as follows: purely in absorption for O2-3.5…
Constraining the role of star cluster mergers in nuclear cluster formation: simulations confront integral-field data
Quinn, Thomas R.; Cappellari, Michele; Seth, Anil +2 more
We present observations and dynamical models of the stellar nuclear clusters (NCs) at the centres of NGC 4244 and M33. We then compare these to an extensive set of simulations testing the importance of purely stellar dynamical mergers on the formation and growth of NCs. Mergers of star clusters are able to produce a wide variety of observed proper…
On the origin of radio loudness in active galactic nuclei and its relationship with the properties of the central supermassive black hole
Marconi, Alessandro; Chiaberge, Marco
We investigate the relationship between the mass of central supermassive black holes (SMBHs) and the radio loudness of active galactic nuclei (AGNs). We use the most recent calibrations to derive 'virial' BH masses for samples of radio-loud quasi-stellar objects (QSOs) for which relatively small masses (MBH < 108 M⊙
Spatially resolved optical integral field unit spectroscopy of the inner superwind of NGC 253
Smith, L. J.; Gallagher, J. S., III; Westmoquette, M. S.
We present optical integral field unit (IFU) observations (VLT/VIMOS-IFU and WIYN/SparsePak), and associated archival deep Hα imaging (MPG/ESO 2.2 m WFI), of the nearby starburst galaxy NGC 253. With VIMOS we observed the nuclear region and southern superwind outflow in detail with five pointings, and with the WIYN/SparsePak IFU we observed two pa…
Morphological properties of z∼ 0.5 absorption-selected galaxies: the role of galaxy inclination
Kacprzak, Glenn G.; Steidel, Charles C.; Churchill, Christopher W. +2 more
We have used Galaxy IMage 2D (GIM2D) to quantify the morphological properties of 40 intermediate-redshift Mg II absorption-selected galaxies [0.03 ≤ Wr(2796) ≤ 2.9 Å], imaged with WFPC-2/Hubble Space Telescope (HST), and compared them to the halo gas properties measured from HIRES/Keck and UVES/VLT quasar spectra. We find that as the qu…
Weak lensing from space: first cosmological constraints from three-point shear statistics
Schrabback, Tim; Hilbert, Stefan; van Waerbeke, Ludovic +3 more
We use weak lensing data from the Hubble Space Telescope COSMOS survey to measure the second- and third-order moments of the cosmic shear field, estimated from about 450 000 galaxies with average redshift ?.
We measure two- and three-point shear statistics using a tree-code, dividing the signal in E, B and mixed components. We present a detec…Negative X-ray reverberation time delays from MCG-6-30-15 and Mrk 766
Papadakis, I. E.; Emmanoulopoulos, D.; McHardy, I. M.
We present an X-ray time lag analysis, as a function of Fourier frequency, for MCG-6-30-15 and Mrk 766 using long-term XMM-Newton light curves in the 0.5-1.5 and the 2-4 keV energy bands, together with some physical modelling of the corresponding time lag spectra. Both the time lag spectra of MCG-6-30-15 and Mrk 766 show negative values (i.e. soft…
A deep probe of the galaxy stellar mass functions at z∼ 1-3 with the GOODS NICMOS Survey
Conselice, Christopher J.; Bluck, Asa F. L.; Mortlock, Alice +4 more
We use a sample of 8298 galaxies observed as part of the Hubble Space Telescope (HST) H160-band GOODS NICMOS Survey (GNS) to construct the galaxy stellar mass function both as a function of redshift and as stellar mass up to z= 3.5. Our mass functions are constructed within the redshift range z= 1-3.5 and consist of galaxies with stella…