Physics
Scientific paper
Oct 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011mnras.417..681l&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 417, Issue 1, pp. 681-688.
Physics
7
Accretion, Accretion Discs, Black Hole Physics, Galaxies: Active, Quasars: General
Scientific paper
The optical-UV continuum of quasars is broadly consistent with the emission from a geometrically thin optically thick accretion disc (AD). The AD produces the ionizing continuum which powers the broad and narrow emission lines. The maximum AD effective temperature is given by ?, where M is the black hole mass, ? the accretion rate and fmax is set by the black hole spin a*. For a low enough value of ?, the AD may become too cold to produce ionizing photons. Such an object will form a lineless quasar. This occurs for a local blackbody (BB) AD with a luminosity Lopt= 1046 erg s-1 for M > 3.6 × 109 M&sun;, when a*= 0, and for M > 1.4 × 1010 M&sun;, when a*= 0.998. Using the AD-based ?, derived from M and Lopt, and the reverberation-based M, derived from Lopt and the Hβ full width at half-maximum, v, gives Teff, max∝L-0.13optv-1.45. Thus, Teff, max is mostly set by v. Quasars with a local BB AD become lineless for v > 8000 km s-1, when a*= 0, and for v > 16 000 km s-1, when a*= 0.998. Higher values of v are required if the AD is hotter than a local BB. The AD becoming non-ionizing may explain why line-emitting quasars with v > 10 000 km s-1 are rare. Weak low-ionization lines may still be present if the X-ray continuum is luminous enough, and such objects may form a population of weak line quasars (WLQ). If correct, such WLQ should show a steeply falling spectral energy distribution (SED) at λ < 1000 Å. Such an SED was observed by Hryniewicz et al. in SDSS J094533.99+100950.1, a WLQ observed down to 570 Å, which is well modelled by a rather cold AD SED. UV spectroscopy of z˜ 1-2 quasars is required to eliminate potential intervening Lyman limit absorption by the intergalactic medium and to explore if the SEDs of lineless quasars and some additional WLQ are also well fitted by a cold AD SED.
Davis Shane W.
Laor Ari
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