A5007047817- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Astrophysics and Cosmic Phenomena
- Astrophysical Phenomena and Observations
- Cosmology and Gravitation Theories
- Spectroscopy and Laser Applications
- Adaptive optics and wavefront sensing
- Astro and Planetary Science
- Scientific Research and Discoveries
- Pulsars and Gravitational Waves Research
- History and Developments in Astronomy
- Geophysics and Gravity Measurements
- Solar and Space Plasma Dynamics
- Radio Astronomy Observations and Technology
- Phase Equilibria and Thermodynamics
- Atmospheric Ozone and Climate
- Calibration and Measurement Techniques
- CCD and CMOS Imaging Sensors
- Ionosphere and magnetosphere dynamics
- Impact of Light on Environment and Health
- Dark Matter and Cosmic Phenomena
University of Cambridge
2016-2025
National Institute of Astrophysics, Optics and Electronics
2016-2025
Universidad Nacional de La Plata
2024-2025
Institute of Astronomy
2002-2025
University of Hawaii System
2010
European Southern Observatory
2010
Academy of Athens
2010
National Observatory of Athens
2010
Royal Observatory in Greenwich
1993-2008
Observatoire Midi-Pyrénées
2007
An investigation is made of the merits various emission-line intensity ratios for classifying spectra extragalactic objects. It shown empirically that several combinations easily-measured lines can be used to separate objects into one four categories according principal excitation mechanism: normal H II regions, planetary nebulae, photoionized by a power-law continuum, and excited shock-wave heating. A two-dimensional quantitative classification scheme suggested.
We propose to use alternative cosmic tracers measure the dark energy equation of state and matter content Universe [w(z)&Ωm]. Our proposed method consists two components: (a) tracing Hubble relation using HII galaxies which can be detected up very large redshifts, z∼4, as an supernovae type Ia, (b) measuring clustering pattern X‐ray selected AGN at a median redshift ∼1. Each component in itself provide interesting constraints on cosmological parameters, especially under our anticipation that...
view Abstract Citations (1264) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy and Photometry of Elliptical Galaxies. I. New Distance Estimator Dressler, Alan ; Lynden-Bell, Donald Burstein, David Davies, Roger L. Faber, S. M. Terlevich, Roberto Wegner, Gary Kinematic photometric data have been obtained for 97 elliptical galaxies in six rich clusters. These show that ellipticals describe a plane three dimensions which, when viewed...
The pre-galactic (assumed primordial) helium mass fraction YP is determined to be |$0.228\pm0.005\,\text{(s.e.)}\,\text{or}\,{Y}_\text{P}\lt0.242$| with 95 per cent confidence, taking reasonably likely systematic errors into account. This based on INT and AAT observations of emission lines from H II galaxies combined selected data the literature relating extragalactic regions in general, discussed a consistent analysis account known corrections sources error. Maximum-likelihood regressions...
view Abstract Citations (835) References (62) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometry and Spectroscopy of Elliptical Galaxies. V. Galaxy Streaming toward the New Supergalactic Center Lynden-Bell, D. ; Faber, S. M. Burstein, David Davies, Roger L. Dressler, Alan Terlevich, R. J. Wegner, Gary We analyze here dynamics 400 elliptical galaxies our all-sky survey. The motions galaxies, over above Hubble expansion in Cosmic Microwave Background...
We present a simple metallicity estimator based on the logarithmic [N ii] λ6584/Hα ratio, hereafter N2, which we envisage will become very useful for ranking galaxies in sequence from redshift survey-quality data even moderately low spectral resolution.
view Abstract Citations (593) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy and Photometry of Elliptical Galaxies. VI. Sample Selection Data Summary Faber, S. M. ; Wegner, Gary Burstein, David Davies, Roger L. Dressler, Alan Lynden-Bell, D. Terlevich, R. J. Photometric spectroscopic data are presented for a survey the nearest brightest elliptical galaxies. Distances, velocities relative to cosmic rest frame, residual...
Recent observational and theoretical work has shown that, as a consequence of mass loss in the form stellar winds last stages their evolution, massive stars can reach effective temperatures more than 100 000 K, being observed extreme WC or WO Wolf–Rayet stars. This paper examines effect these hot (which authors call Warmers) evolution metal-rich giant H II regions. We show that function age, emission-line spectrum region evolves first into type 2 Seyfert then Liner-type spectrum. suggest...
We present a study of the stellar populations in central ∼200 pc large and homogeneous sample comprising 79 nearby galaxies, most which are Seyfert 2s. The star formation history these nuclei is reconstructed by means state‐of‐the‐art population synthesis modelling their spectra 3500–5200 Å interval. A quasar‐like featureless continuum (FC) added to models account for possible scattered light from hidden active galactic nucleus (AGN). find following. (1) 2 remarkably heterogeneous: young...
We present high signal-to-noise spectroscopic data for 32 selected H II galaxies, most of which have not previously been published. All objects are metal-poor, with gaseous oxygen abundances from ⋍0.05 to ∼0.5 the solar neighborhood value. The nitrogen-to-oxygen abundance ratio has a mean value 0.036, typical and blue compact is uncorrelated abundance, consistent nitrogen being primary origin. Relationships amongst emission-line parameters demonstrate importance temperature ionizing cluster...
It is shown that the broad permitted and semipermitted emission lines of broad-line region (BLR) radio-quiet active galactic nuclei (AGN) can be generated by strongly radiative (rapidly cooling) supernova remnants expected to occur in central regions early-type galaxies undergoing a starburst. Supernova interacting with circumstellar medium density about |$n\,\sim\,{10}^{7}\,\text{cm}^{-3}$| become while still expanding at several thousand km s–1, miss adiabatic Sedov track. Radiative...
We analyse the correlations between Hβ luminosities, linear diameters and widths of global emission-line profiles giant extragalactic H II regions detached regions. After correction for luminosity evolution, satisfy same luminosity–velocity dispersion relation followed by elliptical galaxies, bulges spiral galaxies globular clusters. also show that correlation size line width is similar to one valid These results strongly suggest are self-gravitating systems, where profile reflect motions in...
The abundance gradient in M 33 is studied on the basis of IPCS and CCD data emission lines selected HII regions, using OII, OIII, SII, SIII wavelength range λλ3700–9600 Å to refine oxygen abundances inner parts as well study behavior S/O.
view Abstract Citations (412) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy and Photometry of Elliptical Galaxies: A Large-Scale Streaming Motion in the Local Universe Dressler, Alan ; Faber, S. M. Burstein, David Davies, Roger L. Lynden-Bell, Donald Terlevich, R. J. Wegner, Gary The authors present results from a study distances velocities elliptical galaxies out to ≡6000 km s-1. Distances are inferred new relation between...
view Abstract Citations (195) References (85) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Evolution of C/O in Dwarf Galaxies from Hubble Space Telescope FOS Observations Garnett, D. R. ; Skillman, E. Dufour, J. Peimbert, M. Torres-Peimbert, S. Terlevich, Shields, G. A. We present UV observations seven H II regions low-luminosity dwarf irregular galaxies and the Magellanic Clouds obtained with Faint Object Spectrograph on (HST) order to measure...
The observational determination of the behaviour star formation rate (SFR) with look-back time or redshift has two main weaknesses: (i) large uncertainty dust/extinction corrections, and (ii) that systematic errors may be introduced by fact SFR is estimated using different methods at redshifts. Most frequently, luminosity Hα emission line, forbidden line [O ii] λ3727 far-ultraviolet continuum are used low-, intermediate- high-redshift galaxies, respectively.
We present the results of a high-resolution UV two-dimensional spectroscopic survey star-forming galaxies observed with Hubble Space Telescope Imaging Spectrograph. Our main aim is to map Lyα profiles learn about gas kinematics and its relation escape photons detect extended emission due scattering in gaseous halos. have combined our data previously obtained spectroscopy on three other galaxies. find that P Cygni profile spatially extended, smooth, spans several kiloparsecs covering region...
The detection of Lyα emission in star-forming galaxies different shapes and intensities (always smaller than predicted for case B recombination) has puzzled the astronomical community more a decade. Here we use two-dimensional calculations to follow evolution superbubbles H ii regions generated by output UV photons from massive stars. We show impact caused star formation ISM look at conditions required detect nuclear region, variety profiles that may be expected as function time.
We demonstrate that the evolution of QSO luminosity density with epoch displays a striking similarity to cosmological field galaxy star formation rate, recently derived from number independent surveys. The at 2800 Å is approximately one-fortieth implied by rate in galaxies throughout past 11 Gyr (z > 4). This suggests substantial fraction may be closely linked process and its cosmic time.
view Abstract Citations (291) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopy and Photometry of Elliptical Galaxies. II. The Spectroscopic Parameters Davies, Roger L. ; Burstein, David Dressler, Alan Faber, S. M. Lynden-Bell, Donald Terlevich, Roberto J. Wegner, Gary Radial velocities, velocity dispersions, Mg line-strength indices are measured for 469 elliptical galaxies using four telescope/detector configurations. data have...
We have re-analysed the relationships between velocity dispersion, line strength and absolute magnitude for normal elliptical galaxies. find that, at fixed magnitude, galaxies with high velocity-dispersions tend to line-strengths those low line-strengths. This implies that are least a two-parameter family. conclusion is based on preliminary sample of 24 which both types measurements available. Well-known apparent scale differences in dispersion various authors shown be due mean line-strength...
Realistic n-body simulations of dynamical evolution open clusters are discussed and compared with observations. Most the models have 1000 bodies initial masses following a power-law mass function slope α = – 2.75 mean 0.5 M⊙. Stellar loss considered in detail. Neutron stars or white dwarfs (depending on stellar mass) generated by instantaneous changes individual masses, when reach end their main sequence life. Close approaches between particles treated two-body regularization technique that...
view Abstract Citations (158) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Violent Star Formation in NGC 2363 Gonzalez-Delgado, Rosa M. ; Perez, Enrique Tenorio-Tagle, Guillermo Vilchez, Jose Terlevich, Elena Roberto Telles, Eduardo Rodriguez-Espinosa, Mas-Hesse, Miguel Garcia-Vargas, Maria Luisa Diaz, Angeles I. Cepa, Jordi Castaneda, Hector We present narrowband H-alpha imaging and long-slit optical near-infrared spectroscopy of the giant...