科研之友
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摘要
We investigate the role of supermassive black holes in the global context of galaxy evolution by measuring the host galaxy stellar mass HGMF) and the specific accretion rate, that is, lambda(SAR), the distribution SARDF), up to z similar to 2.5 with similar to 1000 X-ray selected AGN from XMM-COSMOS. Using a maximum likelihood approach, we jointly fit the stellar mass function and specific accretion rate distribution function, with the X-ray luminosity function as an additional constraint. Our best-fit model characterizes the SARDF as a double power-law with mass-dependent but redshift-independent break, whose low lambda(SAR) slope flattens with increasing redshift while the normalization increases. This implies that for a given stellar mass, higher lambda(SAR) objects have a peak in their space density at earlier epoch than the lower lambda(SAR) objects, following and mimicking the well-known AGN cosmic downsizing as observed in the AGN luminosity function. The mass function of active galaxies is described by a Schechter function with an almost constant M-star* and a low-mass slope a that flattens with redshift. Compared to the stellar mass function, we find that the HGMF has a similar shape and that up to log(M-star/M-circle dot) similar to 11.5, the ratio of AGN host galaxies to star-forming galaxies is basically constant (similar to 10%). Finally, the comparison of the AGN HGMF for different luminosity and specific accretion rate subclasses with a previously published phenomenological model prediction for the "transient" population, which are galaxies in the process of being mass-quenched, reveals that low-luminosity AGN do not appear to be able to contribute significantly to the quenching and that at least at high masses, that is, M-star > 10(10.7) M-circle dot, feedback from luminous AGN (log L-bol greater than or similar to 46 [erg/s]) may be responsible for the quenching of star formation in the host galaxy.
- 出版日期2016-4
