A transition mass for black holes to show broad emission lines

作者：Chakravorty Susmita^*; Elvis Martin; Ferland Gary

来源：Monthly Notices of the Royal Astronomical Society, 2014, 437(1): 740-747.

DOI：10.1093/mnras/stt1930

• accretion, accretion discs
• black hole physics
• line: formation
• galaxies: active
• quasars: emission lines
• galaxies: Seyfert

Although the supermassive (AGN) and stellar mass (BHBs) black holes have many properties in common, the broad emission lines (BELs) are exclusively signatures of the active galactic nuclei (AGN). Based on the detection of these lines from Sloan Digital Sky Survey (SDSS) data bases, there seems to be no AGN with mass M-BH less than or similar to 10(5) M-circle dot. In this paper, we investigate if such low-mass black holes are really non-existent or they are undetected because the BELs in them are not produced efficiently. Using the ionizing spectral energy distribution for a wide range of black hole mass, 10-10(9) M-circle dot, spanning black hole X-ray binaries (BHBs) to AGN, we calculate the equivalent widths (EWs) of ultraviolet and optical lines Ly alpha 1216 angstrom, H beta 4861 angstrom, CIV 1549 angstrom and MgII 2798 angstrom The LOC (locally optimally emitting cloud) model has been used to describe the broad emission-line region (BELR) for the calculations. We find that the hardening of the SED shape with decreasing mass do not decrease the BEL EWs. However, finite size of the BELR, as measured by the line widths, which is controlled by the mass of the black hole, regulates the production of these emission lines. There seems to be a peak in the EWs of the emission lines for typical AGN black holes of similar to 10(8) M-circle dot, below which the lines become intrinsically fainter with a sharp fall-off below similar to 10(6) M-circle dot. This may be the cause of the absence of low-mass AGN in SDSS.

• 出版日期2014-1