Smith G.P.,University of Birmingham |
Smith G.P.,California Institute of Technology |
Khosroshahi H.G.,Institute for Research in Fundamental Sciences |
Khosroshahi H.G.,Astrophysics Research Institute |
And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010
We study the luminosity gap, Δm12, between the first- and second-ranked galaxies in a sample of 59 massive ( 1015 M) galaxy clusters, using data from the Hale Telescope, the Hubble Space Telescope, Chandra and Spitzer. We find that the Δm12 distribution, p(Δm12), is a declining function of Δm12 to which we fitted a straight line: p(Δm12) -(0.13 ± 0.02)Δm12. The fraction of clusters with 'large' luminosity gaps is p(Δm12≥ 1) = 0.37 ± 0.08, which represents a 3σ excess over that obtained from Monte Carlo simulations of a Schechter function that matches the mean cluster galaxy luminosity function. We also identify four clusters with 'extreme' luminosity gaps, Δm12≥ 2, giving a fraction of More generally, large luminosity gap clusters are relatively homogeneous, with elliptical/discy brightest cluster galaxies (BCGs), cuspy gas density profiles (i.e. strong cool cores), high concentrations and low substructure fractions. In contrast, small luminosity gap clusters are heterogeneous, spanning the full range of boxy/elliptical/discy BCG morphologies, the full range of cool core strengths and dark matter concentrations, and have large substructure fractions. Taken together, these results imply that the amplitude of the luminosity gap is a function of both the formation epoch and the recent infall history of the cluster. 'BCG dominance' is therefore a phase that a cluster may evolve through and is not an evolutionary 'cul-de-sac'. We also compare our results with semi-analytic model predictions based on the Millennium Simulation. None of the models is able to reproduce all of the observational results on Δm12, underlining the inability of the current generation of models to match the empirical properties of BCGs. We identify the strength of active galactic nucleus feedback and the efficiency with which cluster galaxies are replenished after they merge with the BCG in each model as possible causes of these discrepancies. © 2010 The Authors. Journal compilation © 2010 RAS.
Bode M.F.,Astrophysics Research Institute |
Vestrand W.T.,Los Alamos National Laboratory
Proceedings of the International Astronomical Union | Year: 2011
We have entered an era in time-domain astronomy in which the detected rate of explosive transients and important ephemeral states in persistent objects threatens to overwhelm the world's supply of traditional follow-up telescopes. As new, comprehensive time-domain surveys become operational and wide-field multi-messenger observatories come on-line, that problem will become more acute. The goal of this workshop was to foster discussion about how autonomous robotic telescopes and small-aperture conventional telescopes can be employed in the most effective ways to help deal with the coming deluge of scientifically interesting follow-up opportunities. Discussion topics included the role of event brokers, automated event triage, the establishment of cooperative global telescope networks, and real-time coordination of observations at geographically diverse sites. It therefore included brief overviews of the current diverse landscape of telescopes and their interactions, and also considered planned and potential new facilities and operating models. © 2012 International Astronomical Union.
Schwarz G.J.,American Astronomical Society |
Shore S.N.,University of Pisa |
Page K.L.,University of Leicester |
Osborne J.P.,University of Leicester |
And 8 more authors.
Astronomical Journal | Year: 2015
We present the results of an intensive multiwavelength campaign on nova LMC 2012. This nova evolved very rapidly in all observed wavelengths. The time to fall two magnitudes in the V band was only 2 days. In X-rays the super soft phase began 13 ± 5 days after discovery and ended around day 50 after discovery. During the super soft phase, the Swift/XRT and Chandra spectra were consistent with the underlying white dwarf (WD) being very hot, ∼1 MK, and luminous, ∼1038 erg s-1. The UV, optical, and near-IR photometry showed a periodic variation after the initial and rapid fading had ended. Timing analysis revealed a consistent 19.24 ± 0.03 hr period in all UV, optical, and near-IR bands with amplitudes of ∼0.3 mag which we associate with the orbital period of the central binary. No periods were detected in the corresponding X-ray data sets. A moderately high inclination system, i = 60 ± 10, was inferred from the early optical emission lines. The HST/STIS UV spectra were highly unusual with only the N v (1240) line present and superposed on a blue continuum. The lack of emission lines and the observed UV and optical continua from four epochs can be fit with a low mass ejection event, ∼10-6 , from a hot and massive WD near the Chandrasekhar limit. The WD, in turn, significantly illuminated its subgiant companion which provided the bulk of the observed UV/optical continuum emission at the later dates. The inferred extreme WD characteristics and low mass ejection event favor nova LMC 2012 being a recurrent nova of the U Sco subclass. © 2015. The American Astronomical Society. All rights reserved.
Pandey S.B.,University of Michigan |
Swenson C.A.,Pennsylvania State University |
Perley D.A.,University of California at Berkeley |
Guidorzi C.,University of Ferrara |
And 29 more authors.
Astrophysical Journal | Year: 2010
The optical-infrared afterglow of the Large Area Telescope (LAT)-detected long-duration burst, GRB 090902B, has been observed by several instruments. The earliest detection by ROTSE-IIIa occurred 80 minutes after detection by the Gamma-ray Burst Monitor instrument on board the Fermi Gamma-Ray Space Telescope, revealing a bright afterglow and a decay slope suggestive of a reverse shock origin. Subsequent optical-IR observations followed the light curve for 6.5 days. The temporal and spectral behavior at optical-infrared frequencies is consistent with synchrotron fireball model predictions; the cooling break lies between optical and XRT frequencies 1.9 days after the burst. The inferred electron energy index is p = 1.8 ± 0.2, which would however imply an X-ray decay slope flatter than observed. The XRT and LAT data have similar spectral indices and the observed steeper value of the LAT temporal index is marginally consistent with the predicted temporal decay in the radiative regime of the forward shock model. Absence of a jet break during the first 6 days implies a collimation-corrected γ-ray energy E γ > 2.2 × 1052 erg, one of the highest ever seen in a long-duration gamma-ray bursts. More events combiningGeV photon emission with multiwavelength observations will be required to constrain the nature of the central engine powering these energetic explosions and to explore the correlations between energetic quanta and afterglow emission. © 2010. The American Astronomical Society. All rights reserved.
Juan Mateu P.,University of Carabobo |
Mateu C.,National Autonomous University of Mexico |
Gustavo Bruzual A.,National Autonomous University of Mexico |
Gladis Magris C.,Astrophysics Research Institute
Publications of the Astronomical Society of the Pacific | Year: 2015
We explore the ability of four different inverse population synthesis codes to recover the physical properties of galaxies from their spectra by SED fitting. Three codes, DynBaS, TGASPEX, and GASPEX, have been implemented by the authors and are described in detail in the paper. STARLIGHT, the fourth code, is publicly available. DynBaS selects dynamically a different spectral basis to expand the spectrum of each target galaxy, and TGASPEX uses an unconstrained age basis, whereas GASPEX and STARLIGHT use for all fits a fixed spectral basis selected a priori by the code developers. Variable and unconstrained basis reflect the peculiarities of the fitted spectrum and allow for simple and robust solutions to the problem of extracting galaxy parameters from spectral fits. We assemble a Synthetic Spectral Atlas of Galaxies (SSAG),3 comprising 100,000 galaxy spectra corresponding to an equal number of star formation histories based on the recipe of Chen et al.We select a subset of 120 galaxies from SSAG with a color distribution similar to that of local galaxies in the seventh data release (DR7) of the Sloan Digital Sky Survey (SDSS), and produce 30 random noise realizations for each of these spectra. For each spectrum, we recover the mass, mean age, metallicity, internal dust extinction, and velocity dispersion characterizing the dominant stellar population in the problem galaxy. All methods produce almost-perfect fits to the target spectrum, but the recovered physical parameters can differ significantly. Our tests provide a quantitative measure of the accuracy and precision with which these parameters are recovered by each method. From a statistical point of view, all methods yield similar precisions, whereas DynBaS produces solutions with minimal systematic biases in the distributions of residuals for all of these parameters.We caution the reader that the results obtained in our consistency tests represent lower limits to the uncertainties in parameter determination. Our tests compare theoretical galaxy spectra built from the same synthesis models used in the fits. Using different synthesis models and the lack of particular stellar types in the synthesis models but present in real galaxies will increase these errors considerably. Additional sources of error expected to be present in real galaxy spectra are not easy to emulate, and again will result in larger errors © 2015. The Astronomical Society of the Pacific. All rights reserved.