Results 11 to 20 of about 24,041 (212)

A Main Sequence for Quasars [PDF]

Frontiers in Astronomy and Space Sciences, 2018
The last 25 years saw a major step forward in the analysis of optical and UV spectroscopic data of large quasar samples. Multivariate statistical approaches have led to the definition of systematic trends in observational properties that are the basis of
Paola Marziani, Deborah Dultzin, Jack W. Sulentic, Ascensión Del Olmo, C. A. Negrete, Mary L. Martínez-Aldama, Mauro D'Onofrio, Edi Bon, Natasa Bon, Giovanna M. Stirpe   +9 more
doaj   +7 more sources

Quantitative susceptibility mapping in magnetically inhomogeneous tissues. [PDF]

Magn Reson Med
Abstract Purpose Conventional quantitative susceptibility mapping (QSM) methods rely on simplified physical models that assume isotropic and homogeneous tissue properties, leading to artifacts and inaccuracies in biological tissues. This study aims to develop and evaluate DEEPOLE, a deep learning–based method that incorporates macroscopically ...
Jochmann T, Salman F, Dwyer MG, Bergsland N, Zivadinov R, Haueisen J, Schweser F.   +6 more
europepmc   +2 more sources

Explainable AI for raising confidence in deep learning-based tumor tracking models. [PDF]

Med Phys
Abstract Background Recently, tumor position monitoring using fluoroscopic images acquired during volumetric modulated arc therapy (VMAT) delivery has become available in a research setting. Accurate tracking during stereotactic body radiotherapy (SBRT), using VMAT, for lung tumors can help to ensure that the tumor is only irradiated when it is inside ...
Grama D, Dahele M, Slotman B, Verbakel WFAR.   +3 more
europepmc   +2 more sources

Quasar Clustering and the Lifetime of Quasars [PDF]

The Astrophysical Journal, 2001
ApJ Accepted (Feb 2001). 30 pages, 8 embedded ps figures, AASTEX5. Added discussion of quasar luminosity evolution. Also available at http://www.ociw.edu/~martini/pubs/
Paul Martini, Paul Martini, David H. Weinberg   +2 more
openaire   +4 more sources

Quasars Probing Quasars. X. The Quasar Pair Spectral Database [PDF]

The Astrophysical Journal Supplement Series, 2018
Abstract The rare close projection of two quasars on the sky provides the opportunity to study the host galaxy environment of a foreground quasar in absorption against the continuum emission of a background quasar. For over a decade the “Quasars probing quasars” series has utilized this technique to further the understanding of galaxy ...
J. Xavier Prochaska, B. Chehade, Stephanie Bartle, M. A. DiPompeo, Joseph R. Findlay, Tom Shanks, Michele Fumagalli, Joseph F. Hennawi, Joseph F. Hennawi, Adam D. Myers, Marie Wingyee Lau, Kate H. R. Rubin   +11 more
openaire   +8 more sources

Binary quasars [PDF]

Monthly Notices of the Royal Astronomical Society, 1999
Quasar pairs are either physically distinct binary quasars or the result of gravitational lensing. The majority of known pairs are in fact lenses, with a few confirmed as binaries, leaving a population of objects that have not yet been successfully classified.
Mortlock, D, Webster, Rachel L, Francis, Paul   +2 more
openaire   +5 more sources

THE PROPERTIES OF QUASAR HOSTS AT THE PEAK OF THE QUASAR ACTIVITY [PDF]

The Astrophysical Journal, 2009
We present near-infrared imaging obtained with ESO VLT/ISAAC of a sample of 16 low luminosity radio-quiet quasars at the epoch around the peak of the quasar activity (2 < z < 3), aimed at investigating their host galaxies. For 11 quasars, we are able to detect the host galaxies and derive their properties, while for the other five quasars, upper ...
Kotilainen J. K., Falomo R., Decarli R., TREVES, ALDO, Uslenghi M., Scarpa R.   +5 more
openaire   +5 more sources

The Reddest Quasars [PDF]

The Astrophysical Journal, 2002
In a survey of quasar candidates selected by matching the FIRST and 2MASS catalogs, we have found two extraordinarily red quasars. FIRST J013435.7-093102 is a 1 Jy source at z=2.216 and has B-K > 10, while FIRST J073820.1+275045 is a 2.5 mJy source at z=1.985 with B-K = 8.4.
Mark Lacy, Mark Lacy, Richard L. White, Michael D. Gregg, Michael D. Gregg, David J. Helfand, Robert H. Becker, Robert H. Becker, Michael S. Brotherton, Eilat Glikman   +9 more
openaire   +3 more sources

A Hubble Diagram for Quasars [PDF]

Frontiers in Astronomy and Space Sciences, 2015
The cosmological model is at present not tested between the redshift of the farthest observed supernovae (z ~ 1.4) and that of the Cosmic Microwave Background (z ~ 1,100). Here we introduce a new method to measure the cosmological parameters: we show that quasars can be used as "standard candles" by employing the non-linear relation between their ...
Guido Risaliti, Guido Risaliti, Elisabeta Lusso, Susanna Bisogni, Susanna Bisogni   +4 more
openaire   +10 more sources

Quasars [PDF]

Symposium - International Astronomical Union, 1994
I review recent results for quasars and discuss how they are related to activity in galaxies. Topics included are studies of quasar host galaxies with HST; searches for quasars in the Hubble Deep Field; evolution of the quasar luminosity function; news highlights from astro-ph; and current observational research problems and their relation to ...
openaire   +3 more sources