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Saviane I.,European Southern Observatory | Da Costa G.S.,Australian National University | Held E.V.,National institute for astrophysics | Sommariva V.,National institute for astrophysics | And 3 more authors.
Astronomy and Astrophysics

Well determined radial velocities and abundances are essential for analyzing the properties of the globular cluster system of the Milky Way. However more than 50% of these clusters have no spectroscopic measure of their metallicity. In this context, this work provides new radial velocities and abundances for twenty Milky Way globular clusters which lack or have poorly known values for these quantities. The radial velocities and abundances are derived from spectra obtained at the Ca II triplet using the FORS2 imager and spectrograph at the VLT, calibrated with spectra of red giants in a number of clusters with well determined abundances. For about half of the clusters in our sample we present significant revisions of the existing velocities or abundances, or both. We also confirm the existence of a sizable abundance spread in the globular cluster M 54, which lies at the center of the Sagittarius dwarf galaxy. In addition evidence is provided for the existence of a small intrinsic internal abundance spread (σ[Fe/H] int ≈ 0.11-0.14 dex, similar to that of M 54) in the luminous distant globular cluster NGC 5824. This cluster thus joins the small number of Galactic globular clusters known to possess internal metallicity ([Fe/H]) spreads. © 2012 ESO. Source

Sargent M.T.,Max Planck Institute for Astronomy | Sargent M.T.,ETH Zurich | Carollo C.M.,ETH Zurich | Kampczyk P.,ETH Zurich | And 13 more authors.
Astrophysical Journal Letters

We compare the surface brightness-inclination relation for a sample of COSMOS pure disk galaxies at z 0.7 with an artificially redshifted sample of Sloan Digital Sky Survey (SDSS) disks well matched to the COSMOS sample in terms of rest-frame photometry and morphology, as well as their selection and analysis. The offset between the average surface brightness of face-on and edge-on disks in the redshifted SDSS sample matches that predicted by measurements of the optical depth of galactic disks in the nearby universe. In contrast, large disks at z 0.7 have a virtually flat surface brightness-inclination relation, suggesting that they are more opaque than their local counterparts. This could be explained by either an increased amount of optically thick material in disks at higher redshift or a different spatial distribution of the dust. © 2010 The American Astronomical Society. Source

Massey R.,Durham University | Williams L.,University of Minnesota | Smit R.,Durham University | Swinbank M.,Durham University | And 21 more authors.
Monthly Notices of the Royal Astronomical Society

Galaxy cluster Abell 3827 hosts the stellar remnants of four almost equally bright elliptical galaxies within a core of radius 10 kpc. Such corrugation of the stellar distribution is very rare, and suggests recent formation by several simultaneous mergers. We map the distribution of associated dark matter, using new Hubble Space Telescope imaging and Very Large Telescope/Multi-Unit Spectroscopic Explorer integral field spectroscopy of a gravitationally lensed system threaded through the cluster core. We find that each of the central galaxies retains a dark matter halo, but that (at least) one of these is spatially offset from its stars. The best-constrained offset is 1.62+0.47 -0.49 kpc, where the 68 per cent confidence limit includes both statistical error and systematic biases in mass modelling. Such offsets are not seen in field galaxies, but are predicted during the long infall to a cluster, if dark matter self-interactions generate an extra drag force.With such a small physical separation, it is difficult to definitively rule out astrophysical effects operating exclusively in dense cluster core environments - but if interpreted solely as evidence for self-interacting dark matter, this offset implies a crosssection σDM/m ~ (1.7 ± 0.7) × 10-4 cm2 g-1 × (tinfall/109 yr)-2, where tinfall is the infall duration. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Although the popular astronomical event has been observed since the 1800s, its origins had long remained a mystery. It was only discovered relatively recently, compared to other showers such as the Perseids, which were first documented in 36 AD and Leonids, which date back to 902 AD. Then, in 1983, two University of Leicester astronomers—Dr. Simon Green and Dr. John Davies—were studying data from the infrared sensitive telescope on the Infrared Astronomical Satellite, IRAS, and discovered an asteroid with a very unusual orbit. Originally designated 1983 TB, the comet was renamed 3200 Phaethon after the son of Greek Sun god Helios—an appropriate moniker as it orbits closer to the Sun than any other asteroid then known. Shortly after the find, Harvard astronomer Fred Whipple was able to link the newly discovered rocky object, which is about three miles wide, with the Geminid meteors, and the mystifying source of the showers was revealed. Now a Senior Lecturer in Planetary and Space Sciences at the Open University, Dr. Green—a PhD student at the time of Phaethon's discovery—said: "I was a PhD student at Leicester at the time. Professor Jack Meadows, my supervisor, had arranged for me to work on his proposed IRAS Fast Moving Object Survey for my thesis. "The Rutherford Appleton Laboratory near Didcot operated the ground station and did the preliminary analysis of the data to check that everything was working correctly (the complete analysis and catalogues were produced at the Jet Propulsion Laboratory after the mission). "My first task was to write the software to search among all the data rejected from the survey and try to identify potential fast-moving asteroids. It was based on code written by Brian Stewart at RAL to do the rejection." Dr. Green said due to the mounting workload, more help was needed and Dr. Davies joined the team. Dr. Green said: "When we realized that we would need to check the outputs of the code every 12 hours for the planned year of the mission, Jack bid for and obtained funding to employ a postdoc (John). "One or both of John and I were at RAL for almost all the actual 10 months that IRAS operated before running out of liquid helium coolant. "Much of the time we alternated time at RAL and I was the one who was around when Phaethon appeared. "In fact, the previous weekend, on one of the rare times when neither of us could be there, there was another fantastic candidate that we had missed, and I was determined not to miss another—which was the reason why I telephoned Palomar. "We had set up a system to telex observatories (this was pre-email and Internet days), but I didn't want it to be left lying on a desk somewhere. "John and I 'shared' the discoveries we made—several comets including IRAS-Araki-Alcock, which was a naked-eye comet in summer 1983 as it flashed by the Earth, a few asteroids in addition to Phaethon, and the first-ever detection of a cometary dust trail. "The end result of the survey was several papers, including one in Nature, and my PhD thesis." Dr. Green went on to be Comet Halley UK Coordinator and also worked on several space missions including Cassini, Huygens, Stardust and Rosetta. Dr. Davies moved to the Royal Observatory in Edinburgh in 1987 and then relocated to Hawaii in 1993, to join the Joint Astronomy Centre before returning to Edinburgh in 2001. Professor Paul O'Brien, of the University of Leicester Department of Physics and Astronomy, said: "The Geminids are usually the brightest meteor shower of the year, sometimes reaching over 100 per hour. "Finding the source of them was a great achievement and is a good example of how you can make valuable yet unexpected discoveries using spacecraft."

Vulcani B.,University of Padua | Vulcani B.,National institute for astrophysics | Aragon-Salamanca A.,University of Nottingham | Poggianti B.M.,National institute for astrophysics | And 7 more authors.
Astronomy and Astrophysics

We present new spectroscopic observations in a field containing the highest redshift cluster of the ESO Distant Cluster Survey (EDisCS). We measure galaxy redshifts and determine the velocity dispersions of the galaxy structures located in this field. Together with the main cluster Cl 1103.7-1245 (z = 0.9580; δcluslus = 522 ± 111kms-1) we find a secondary structure at z = 0.9830, Cl 1103.7-1245c. We then characterize the galaxy properties in both systems, and find that they contain very different galaxy populations. The cluster Cl 1103.7-1245 hosts a mixture of passive elliptical galaxies and star-forming spirals and irregulars. In the secondary structure Cl 1103.7-1245c all galaxies are lower-mass star-forming irregulars and peculiars. In addition, we compare the galaxy populations in the Cl 1103.7-1245 z = 0.9580 cluster with those in lower redshift EDisCS clusters with similar velocity dispersions. We find that the properties of the galaxies in Cl 1103.7-1245 follow the evolutionary trends found at lower redshifts: the number of cluster members increases with time in line with the expected growth in cluster mass, and the fraction of passive early-type galaxies increases with time while star-forming late types become less dominant. Finally, we find that the mean stellar masses are similar in all clusters, suggesting that massive cluster galaxies were already present at z ∼ 1. © ESO 2012. Source

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