▪ Abstract Quasar (QSO) elemental abundances provide unique probes of high-redshift star formation and galaxy evolution. There is growing evidence from both the emission and intrinsic absorption lines that QSO environments have roughly solar or higher metallicities out to redshifts >4. The range is not well known, but solar to a few times solar metallicity appears to be typical. There is also evidence for higher metallicities in more luminous objects and for generally enhanced N/C and Fe/α abundances compared with solar ratios. These results identify QSOs with vigorous, high-redshift star formation—consistent with the early evolution of massive galactic nuclei or dense protogalactic clumps. However, the QSOs offer new constraints. For example, (a) most of the enrichment and star formation must occur before the QSOs “turn on” or become observable, on time scales of 1 Gyr at least at the highest redshifts. (b) The tentative result for enhanced Fe/α suggests that the first local star formation began at least...

Elemental Abundances in Quasistellar Objects: Star Formation and Galactic Nuclear Evolution at High Redshifts

Article de synthese traitant des techniques d'observation et de la fonction de luminosite des quasars, ainsi que des associations quasar-galaxie et quasar-quasar

The Space Distribution of Quasars

Most Seyfert 1s show strong Fe II lines in their spectrum having the velocity and width of the broad emission lines. To remove the Fe II contribution in these objects, an accurate template is necessary. We used very high signal-to-noise, medium resolution archive optical spectra of I Zw 1 to build such a template. 
I Zw 1 is a bright narrow-line Seyfert 1 galaxy. As such it is well suited for a detailed analysis of its emission line spectrum. Furthermore it is known to have a very peculiar spectrum with, in addition to the usual broad and narrow line regions, two emission regions emitting broad and blue shifted [O III] lines making it a peculiarly interesting object. While analysing the spectra, we found that the narrow-line region is, unlike the NLR of most Seyfert 1 galaxies, a very low excitation region dominated by both permitted and forbidden Fe II lines. It is very similar to the emission spectrum of a blob in $\eta$ Carinae which is a low temperature (T$_{\rm e}\sim$6 500 K), relatively high density (N$_{\it e}$=10$^{6}$ cm$^{-3}$) cloud. The Fe II lines in this cloud are mainly due to pumping via the stellar continuum radiation field (Verner et al. \cite{verner02}). We did not succeed in modelling the spectrum of the broad-line region, and we suggest that a non radiative heating mechanism increases the temperature in the excited H I region, thus providing the necessary additional excitation of the Fe II lines. For the low-excitation narrow-line region, we are able to settle boundaries to the physical conditions accounting for the forbidden and permitted Fe II lines (10$^{6}$$<$N$_{\rm e}$$<10^{7}$ cm$^{-3}$; 10$^{-6}$$<$U$<10^{-5}$).

/pdf/the-unusual-emission-line-spectrum-of-izw1-3d4qz8oopr.pdf

The unusual emission line spectrum of IZw1

Most Seyfert 1 galaxies show strong Fe II lines in their spectrum having the velocity and width of the broad emission lines. To remove the Fe II contribution in these objects, an accurate template is necessary. We used very high signal-to-noise, medium resolution archive optical spectra of I Zw 1 to build such a template. I Zw 1 is a bright narrow-line Seyfert 1 galaxy. As such it is well suited for a detailed analysis of its emission line spectrum. Furthermore it is known to have a very peculiar spectrum with, in addition to the usual broad and narrow line regions, two emission regions emitting broad and blue shifted (O III) lines making it a peculiarly interesting object. While analysing the spectra, we found that the narrow-line region is, unlike the NLR of most Seyfert 1 galaxies, a very low excitation region dominated by both permitted and forbidden Fe II lines. It is very similar to the emission spectrum of a blob in η Carinae which is a low temperature (Te ∼ 6500 K), relatively high density (Ne = 10 6 cm −3 ) cloud. The Fe II lines in this cloud are mainly due to pumping via the stellar continuum radiation field (Verner et al. 2002). We did not succeed in modelling the spectrum of the broad-line region, and we suggest that a non radiative heating mechanism increases the temperature in the excited H I region, thus providing the necessary additional excitation of the Fe II lines. For the low-excitation narrow-line region, we are able to apply boundaries to the physical conditions accounting for the forbidden and permitted Fe II lines (10 6 < Ne < 10 7 cm −3 ;1 0 −6 < U < 10 −5 ).

/pdf/the-unusual-emission-line-spectrum-of-i-zw-1-45lnhapdm3.pdf

The unusual emission line spectrum of I Zw 1

Deflection of light by gravity was predicted by General Relativity and observationally confirmed in 1919. In the following decades, various aspects of the gravitational lens effect were explored theoretically. Among them were: the possibility of multiple or ring-like images of background sources, the use of lensing as a gravitational telescope on very faint and distant objects, and the possibility of determining Hubble’s constant with lensing. It is only relatively recently, (after the discovery of the first doubly imaged quasar in 1979), that gravitational lensing has became an observational science. Today lensing is a booming part of astrophysics. In addition to multiply-imaged quasars, a number of other aspects of lensing have been discovered: For example, giant luminous arcs, quasar microlensing, Einstein rings, galactic microlensing events, arclets, and weak gravitational lensing. At present, literally hundreds of individual gravitational lens phenomena are known. Although still in its childhood, lensing has established itself as a very useful astrophysical tool with some remarkable successes. It has contributed significant new results in areas as different as the cosmological distance scale, the large scale matter distribution in the universe, mass and mass distribution of galaxy clusters, the physics of quasars, dark matter in galaxy halos, and galaxy structure. Looking at these successes in the recent past we predict an even more luminous future for gravitational lensing.

/pdf/gravitational-lensing-in-astronomy-jqln9jg3t9.pdf

Jean-Pierre Swings

Papers

Quasars and gravitational lenses