2 letters:
McConnell et al. 2011
"Two ten-billion-solar-mass black holes at the centres of giant elliptical galaxies"
Paper: here
The authors report on the two new BHs found in the nearby universe, that are now the most massive BHs known to us. They explain their model which they used to infer the mass of these objects and talk about the underlying uncertainty. As a result of their high mass, they are outliers on the Mbh-sigma relation and hence, interesting to the BH-galaxy coevolution question.
Cappellari 2011
"Astrophysics: Monster black holes"
Paper: here
The implication of the above paper on the dry-merger-driven growth scenario for BHs is explored. The author argues that the two outliers on the Mbh-sigma relation could be a result of coalescing BHs, keeping the velocity dispersion on the resultant galaxy the same, but growing the central BH to double its initial mass. A speculative yet interesting insight into the BH-galaxy coevolution.
Comments on paper 1: The two points don't seem very far off the M-sigma relation -- a factor of 10 and 4. So how do these really show something new other than the fact that they're very massive? Figure 3 doesn't really prove that the growth of stars and the black hole wasn't in sync. And, does it really prove that these were Quasars in the beginning past which have not accreted in the recent past?
ReplyDeleteComments on paper 2: It remains unclear how the black hole mass can grow faster than the velocity dispersion of the bulge. If minor mergers provide the offset on the M_BH-sigma relation, then you would still be on the M_BH-luminosity relation, yet these objects lie off both relations. Also, With little gas, is there enough time to let the BH's merge (with little gas, is there enough to provide the dynamical friction required to move the BHs to the center)?