75 research outputs found
First case of strong gravitational lensing by a QSO : SDSS J0013+1523 at z = 0.120
We present the first case of strong gravitational lensing by a QSO : SDSS
J0013+1523, at z = 0.120. The discovery is the result of a systematic search
for emission lines redshifted behind QSOs, among 22298 spectra of the SDSS data
release 7. Apart from the z = 0.120 spectral features of the foreground QSO,
the spectrum of SDSS J0013+1523 also displays the OII and Hbeta emission lines
and the OIII doublet, all at the same redshift, z = 0.640. Using sharp Keck
adaptive optics K-band images obtained using laser guide stars, we unveil two
objects within a radius of 2 arcsec from the QSO. Deep Keck optical
spectroscopy clearly confirms one of these objects at z = 0.640 and shows
traces of the OIII, emission line of the second object, also at z = 0.640. Lens
modeling suggests that they represent two images of the same z = 0.640
emission-line galaxy. Our Keck spectra also allow us to measure the redshift of
an intervening galaxy at z = 0.394, located 3.2 arcsec away from the line of
sight to the QSO. If the z = 0.120 QSO host galaxy is modeled as a singular
isothermal sphere, its mass within the Einstein radius is M_E(r < 1 kpc) =
2.16e10 M_Sun and its velocity dispersion is sigma_SIS = 169 km/s. This is
about 1 sigma away from the velocity dispersion estimated from the width of the
QSO Hbeta emission line, sigma_*(M_BH) = 124 +/- 47 km/s. Deep optical HST
imaging will be necessary to constrain the total radial mass profile of the QSO
host galaxy using the detailed shape of the lensed source. This first case of a
QSO acting as a strong lens on a more distant object opens new directions in
the study of QSO host galaxies.Comment: 6 pages, 5 figures, accepted for publication in A&A Letters. Added
new Keck spectroscop
Periodic ab initio estimates of the dispersive interaction between molecular nitrogen and a monolayer of hexagonal BN
The ab initio determination of the leading long-range term of pairwise additive dispersive interactions, based on the independent analysis of the response properties of the interacting objects, is here considered in the case where these are part of a periodic system. The interaction of a nitrogen molecule with a thin film of hexagonal BN has been chosen as a case study for identifying some of the problems involved, and for proposing techniques for their solution. In order to validate the results so obtained, the interaction energy between N2 and a BN monolayer at different distances has been estimated following a totally different approach, namely by performing post-Hartree–Fock (MP2) supercell calculations using the CRYSTAL+CRYSCOR suite of programs. The results obtained with the two approaches closely agree over a long range, while the limit of validity of the purely dispersive regime can be clearly assessed
Moving beyond Marcuse: gentrification, displacement and the violence of un-homing
Displacement has become one of the most prominent themes in contemporary geographical debates, used to describe processes of dispossession and forced eviction at a diverse range of scales. Given its frequent deployment in studies describing the consequences of gentrification, this paper seeks to better define and conceptualise displacement as a process of un-homing, noting that while gentrification can prompt processes of eviction, expulsion and exclusion operating at different scales and speeds, it always ruptures the connection between people and place. On this basis – and recognising displacement as a form of violence – this paper concludes that the diverse scales and temporalities of displacement need to be better elucidated so that their negative emotional, psychosocial and material impacts can be more fully documented, and resisted
LCAO-LDA calculation of compton profiles in haexagonal BN; Comparison with experiments
The linear-combination-of-atomic-orbitals self-consistent-field process is used with either Hartree-Fock or Kohn-Sham equations in order to calculate average and directional Compton profiles of hexagonal boron nitride. Basis sets and electron correlation effects are discussed and the results are compared with very recent theoretical and experimental data. The reciprocal form factor along the c-axis is also calculated and analysed
A theoretical study of stability, electronic, and optical properties of GeC and SnC
cited By 48International audienceWe present the results of a first principles study on the ordered Ge 0. 50C 0.50 and Sn 0.50C 0.50 cubic alloys. A linear combination of atomic orbitals approach in the framework of density functional theory is employed for total energy calculations in the zincblende phase. A fitting of the energy surface to the equation of state yields the lattice constant of 4.61 and 5.17 Å and the bulk modulus of 181 and 119 GPa for GeC and SnC, respectively. Analysis of band structure suggests a crossover of the nature of the band gap from indirect to direct in going from SiC to GeC to SnC. Although both alloys predicted to be unstable with respect to their elemental components at zero pressure and temperature, GeC appears to become stable at higher pressure. It appears that both the lattice constant and bulk modulus of the ordered alloys do not follow Végard's linear rule, though the calculated dielectric constant of the cubic alloys is approximately the average of the dielectric constant of their elemental components
- …