We present the first near-infrared spectroscopic observations of the radio-loud broad absorption line QSO FIRST J155633.8+351758 .
The spectrum is similar to that of a reddened QSO and shows strong emission lines of { H \alpha } and { H \beta } as well as strong \ion Fe2 emission blends near { H \beta } .
The redshift of the object , measured from the { H \alpha } and { H \beta } lines , is z _ { BLR } = 1.5008 \pm 0.0007 , slightly larger than the redshift of z _ { metal } = 1.48 estimated from the broad metal absorption features .
Thus , the broad metal absorption features are blue shifted with respect to the systemic velocity .
The width of the H \alpha emission line ( { FWHM \approx 4100 ~ { } km~ { } s ^ { -1 } } ) is typical of that observed in QSO broad-line regions , but the Balmer decrement ( H \alpha /H \beta \approx 5.8 ) is larger than that of most optically selected QSOs .
Both the Balmer decrement and the slope of the rest-frame UV-optical continuum independently suggest a modest amount of extinction along the line of sight to the broad-line region ( E _ { B - V } \approx 0.5 for SMC-type screen extinction at the redshift of the QSO ) .
The implied gas column density along the line of sight is much less than is implied by the weak X-ray flux of the object , suggesting that either the broad emission and absorption line regions have a low dust-to-gas ratio , or that the rest-frame optical light encounters significantly lower mean column density lines of sight than the X-ray emission .
From the rest-frame UV-optical spectrum , we are able to constrain the stellar mass content of the system ( < 3 \times 10 ^ { 11 } { M _ { \odot } } ) .
Comparing this mass limit with the black hole mass estimated from the bolometric luminosity of the QSO , we find it possible that the ratio of the black hole to stellar mass is comparable to the Magorrian value , which would imply that the Magorrian relation is already in place at z = 1.5 .
However , multiple factors favor a much larger black hole to stellar mass ratio .
This would imply that if the Magorrian relation characterizes the late history of QSOs , and the situation observed for F1556+3517 is typical of the early evolutionary history of QSOs , central black hole masses develop more rapidly than bulge masses .