Subject: z2p5 notes #5 Date: Mon, 30 Mar 1998 15:48:34 +0100 From: Bob Fosbury Organization: ST-ECF To: Andrea Cimatti , Bob Fosbury , Bob Goodrich , Joel Vernet , Marshall Cohen , Montse Villar , Sperello di Serego Alighieri Dear Bob, Thanks for the note about the NV in BALQs. I read it over the weekend - but I've only just printed out your BALQ paper and have not read it yet... >From what you describe in the note, it seems to me that the differences between the BAL and our RG phenomena are both in spatial scale and in velocity range. The BAL processes happen on ~ the scale of the BLR and occupy ranges in velocity which are large enough to allow migration of photons from one line to another (Ly-a -> NV). The radio galaxy light is coming from scales of tens of kpc and much of the gas, at least in the outer regions, is rather quiescent: there is some calm water between Ly-a and NV - probably quite a lot in a given spatial region. To first order, neither NV nor CIV are much affected by transfer effects and, given the similar ionization levels of the objects, the ratio is predominantly dependent on the N/C abundance ratio (we can check that with the models - Montse). So this ratio, I believe, is telling us about the properties - star formation history - of the gas which is being illuminated by the quasar. On discussion with Alvio Renzini here, it appears that a nitrogen enrichment following a starburst can remain for some 30-300 Myr - after which the abundance ratios tend towards more solar values. This may partly coincide with the time during which the AGN is alive and illuminating the gas and so there may be some natural selection of objects with high nitrogen. Our crude scenario is that some event - like a tidal interaction - may trigger a period of intense star formation (over an extended region) and the building of an AGN. Both the lifetime of the AGN and the period of enhanced nitrogen can be rather short (<10^8 years) and, depending at what phase we see the object, we see different amounts of dust and nitrogen. The dust and nitrogen are naturally correlated in this picture. Regards, Bob... -- R A E Fosbury (Bob) Space Telescope - European Coordinating Facility rfosbury@eso.org, http://ecf.hq.eso.org/~rfosbury/ Tel:+49 89 320 06 235 (o) +49 89 609 9650 (h) Fax:+49 89 320 06 480