Detalles de publicación
PP 06040
First tentative detection of anisotropy in the QSO distribution around nearby edge-on spiral galaxies
IAC
AIMS. To check whether the polar angle distribution of QSOs around nearby spiral
galaxies is isotropic or not.
METHODS. A statistical analysis of the polar angle distribution of large samples
of QSOs from the SDSS survey and Monte Carlo simulations to calculate their significance are carried out.
RESULTS. There is a clear excess of QSOs near the minor axis with respect to
the major axis of nearby edge-on spiral galaxies, significant at a level 3.5-sigma up to angular distances of ~ 3 deg. (or ~1.7 Mpc) from the centre of each galaxy.
The significance is increased to 3.9-sigma with the z>0.5 QSOs, and it reaches
4.8-sigma if we include galaxies whose circles of radius 3 degrees are covered by the
SDSS in more than 98% (instead of 100%) of the area.
CONCLUSIONS. Gravitational lensing in the halo of nearby galaxies or extinction
seem insufficient to explain the observed anisotropic distribution of QSOs. The anisotropic distribution agrees qualitatively with the predictions of Arp's models, which claim that QSOs are ejected by galaxies along the rotation axis, although Arp's prediction give a distance of the QSOs ~3 times smaller than that found here. In any case, a chance fluctuation, although highly improbable, might be a possibility rather than a true anisotropy, and the present results should be corroborated by other groups and samples,
so we prefer to consider it as just a first tentative detection.
galaxies is isotropic or not.
METHODS. A statistical analysis of the polar angle distribution of large samples
of QSOs from the SDSS survey and Monte Carlo simulations to calculate their significance are carried out.
RESULTS. There is a clear excess of QSOs near the minor axis with respect to
the major axis of nearby edge-on spiral galaxies, significant at a level 3.5-sigma up to angular distances of ~ 3 deg. (or ~1.7 Mpc) from the centre of each galaxy.
The significance is increased to 3.9-sigma with the z>0.5 QSOs, and it reaches
4.8-sigma if we include galaxies whose circles of radius 3 degrees are covered by the
SDSS in more than 98% (instead of 100%) of the area.
CONCLUSIONS. Gravitational lensing in the halo of nearby galaxies or extinction
seem insufficient to explain the observed anisotropic distribution of QSOs. The anisotropic distribution agrees qualitatively with the predictions of Arp's models, which claim that QSOs are ejected by galaxies along the rotation axis, although Arp's prediction give a distance of the QSOs ~3 times smaller than that found here. In any case, a chance fluctuation, although highly improbable, might be a possibility rather than a true anisotropy, and the present results should be corroborated by other groups and samples,
so we prefer to consider it as just a first tentative detection.