PubMed Health⌕ Search

Biomedical subjects

HW Rix

Publications and source records attributed to HW Rix.

2 recordsLinked to original sources
PubMed2000

Evidence for a Black Hole and Accretion Disk in the LINER NGC 4203.

We present spectroscopic observations from the Hubble Space Telescope that reveal for the first time the presence of a broad pedestal of Balmer line emission in the LINER galaxy NGC 4203. The emission-line profile is suggestive of a relativistic accretion disk and is reminiscent of double-peaked transient Balmer emission observed in a handful of other LINERs. The very broad line emission thus constitutes clear qualitative evidence for a black hole, and spatially resolved narrow-line emission in NGC 4203 can be used to constrain its mass, MBH</=6x106 M middle dot in circle, at 99.7% confidence. This value implies a ratio of black hole mass to bulge mass of less, similar7x10-4 in NGC 4203, which is less by a factor of approximately 3-9 than the mean ratio obtained for other galaxies. The availability of an independent constraint on central black hole mass makes NGC 4203 an important testbed for probing the physics of weak active galactic nuclei. Assuming MBH near the detection limit, the ratio of the observed luminosity to the Eddington luminosity is approximately 10-4. This value is consistent with advection-dominated accretion and hence with scenarios in which an ion torus irradiates an outer accretion disk that produces the observed double-peaked line emission. Follow-up observations will make it possible to improve the black hole mass estimate and study variability in the nuclear emission.

Journal Article↗
PubMed2000

Binary Black Hole Mergers from Planet-like Migrations.

If supermassive black holes (BHs) are generically present in galaxy centers, and if galaxies are built up through hierarchical merging, BH binaries are at least temporary features of most galactic bulges. Observations suggest, however, that binary BHs are rare, pointing toward a binary lifetime far shorter than the Hubble time. We show that, almost regardless of the detailed mechanism, all stellar dynamical processes are too slow in reducing the orbital separation once orbital velocities in the binary exceed the virial velocity of the system. We propose that a massive gas disk surrounding a BH binary can effect its merger rapidly, in a scenario analogous to the orbital decay of super-Jovian planets due to a proto-planetary disk. As in the case of planets, gas accretion onto the secondary (here a supermassive BH) is integrally connected with its inward migration. Such accretion would give rise to quasar activity. BH binary mergers could therefore be responsible for many or most quasars.

Journal Article↗