On The Weak Ly? Emission Line Of The BL Lacertae Objects

Recent studies reveal that the weak Lycx emission line may be a ubiquitous feature of the BL Lacerate objects(BL Lacs).In this dissertation,we present our analysis of intrinsic Ly? emission line of 11 BL Lacerate objects(BL Lacs).The scope of this dissertation is as follows:In chapter 2,we discussed how we selected our research object:11 BL Lac ob-jects in total.We fitted their continua and emission line.In the 11 targets,eight show a clear detection of the intrinsic Lya emission line,among which two were newly detected in this work(FBQS J1217+3007 and 3C 66A).We categorized them as high-frequency peaked BL Lacs,or HBLs(vpeakf ? 1017-18 Hz),low-frequency peaked BL Lacs,or LBLs(vpeak ? 1013-14 Hz),and the intermediate-frequency peaked BL Lacs,or IBLs(vpeak? 1015-16 Hz).We find that most of our targets are either HBLs or IBL(intermediate-frequency peaked BL Lacs)/HBL,with the only exception of a LBL(low-frequency peaked BL Lacs),S5 07 1 6+7 14,We also have found a strong anti-correlation between the line EW of the Ly? emission line and the continuum luminosity at the red-shifted wavelength of the Ly? line,similar to the Baldwin effect discovered in other types of the AGNs.The strong anti-correlation also suggests the beamed jet emission is unlikely the only source of ionization.In chapter 3,we discussed the jet emission of our targets.We can calculate the expected Lya flux with the model in Yuan et al.[1].Assuming the ionizing photons which produce the Ly? emission line only come from the jet emission and the jet emits the ionizing photons isotropically,we can constrain the exact viewing angles of the BLR clouds(relative to the jet)in a very narrow range between?10°-15°.In chapter 4,we discussed the emission come from the accretion disc of our tar-gets.In the previous chapter,we conclude that all the viewing angles of the BLR clouds(relative to the jet)in our target are in a very narrow range between?10°-15°.This conclusion is incompatible with the assumption mentioned above that the jet emits the ionizing photons isotropically.So we must introduce another accretion disc model in Yuan et al.[1]to explain the observed Ly? flux.Assuming the accretion disk provides all the ionizing photons,we can calculate expected Ly? flux with the model in Yuan et al.[1]and the the exact accretion rates by matching the expected Ly? flux with the observed one for all our samples.However,a very likely scenario is that the accretion disk and the jet contribute the ionizing photons together.In this case,the inferred ac-cretion rates above,maybe the upper limits of accretion rates of the central black holes for all our samples.In the last chapter,we made a summary and discussed the further work.