Abstract. Near-infrared spectroscopy is used to study the kinematics and excitation mechanisms of H 2 and [Fe ] lines in a sample of mostly Seyfert 1 galaxies. The spectral coverage allows simultaneous observation of the JHK bands, thus eliminating the aperture and seeing effects that have usually plagued previous works. The H 2 lines are unresolved in all objects in which they were detected while the [Fe ] lines have widths implying gas velocities of up to 650 km s −1 . This suggests that, very likely, the H 2 and [Fe ] emission does not originate from the same parcel of gas. Molecular H 2 lines were detected in 90% of the sample, including PG objects, indicating detectable amounts of molecular material even in objects with low levels of circumnuclear starburst activity. Analysis of the observations favors thermal excitation mechanisms for the H 2 lines. Indeed, in NGC 3227, Mrk 766, NGC 4051 and NGC 4151, the molecular emission is found to be purely thermal but with heating processes that vary between the objects. Thermal excitation is also confirmed by the rather similar vibrational and rotational temperatures in the objects for which data were available. [Fe ] lines are detected in all of the sample AGN. The [Fe ] 1.254 µm/Paβ ratio is compatible with excitation of the [Fe ] lines by the active nucleus in most Seyfert 1 galaxies, but in Mrk 766 the ratio implies a stellar origin. A correlation between H 2 /Brγ and [Fe ]/Paβ is found for our sample objects supplemented by data from the literature. The correlation of these line ratios is a useful diagnostic tool in the NIR to separate emitting line objects by their level of nuclear activity. X-ray excitation models are able to explain the observed H 2 and part of the [Fe ] emission but fail to explain the observations in Seyfert 2 galaxies. Most likely, a combination of X-ray heating, shocks driven by the radio jet and circumnuclear star formation contributes, in different proportions, to the H 2 and [Fe ] lines observed. In most of our sample objects, the [Fe ] 1.257 µm/1.644 µm ratio is found to be 30% lower than the intrinsic value based on current atomic data. This implies either that the extinction towards the [Fe ]-emitting clouds is very similar in most objects or there are possible inaccuracies in the A-values in the Fe  transitions.

All together indicate a stratification in the ionized gas, usually interpreted in terms of nuclear photoionization as the driving ionization mechanism. However, CL profiles show various peculiarities: they are broader by a factor of 2 than lower ionization lines, the broadening being in terms of asymmetric blue wings, and their centroid position at the nucleus is blueshifted by a few hundred km s À1 . Moreover, in NGC 1386 and NGC 1068, a doublepeaked [Fe vii] line is detected in the nuclear and extended coronal region, this being the first report of this type of profile in CLs in active galactic nuclei. If interpreted as outflow signatures, the total broadening of the lines at zerointensity levels implies gas velocities up to 2000 km s À1. Although the stratification of ions across the coronal region means that photoionization is the main power mechanism, the high velocities deduced from the profiles, the relatively large spatial extension of the emission, and the results from photoionization models indicate that an additional mechanism is at work. We suggest that shocks generated by the outflow could provide the additional required power for line formation.

A B S T R A C TThe radiation temperature±redshift relation for Friedmann±Robertson±Walker geometries is rediscussed in connection with recent observational data based on the fine-structure splitting of atomic and singly ionized carbon lines in quasar absorption-line systems. Indirect measurement of T(z) is one of the most powerful cosmological tests available because it may exclude even the presence of a cosmological constant. Unlike recent claims, we argue that the temperature at high z may be smaller than the standard prediction, thereby opening a window to alternative (big bang) models. By including new ingredients like a phenomenological decaying vacuum energy density and gravitational`adiabatic' photon creation as well as late inflationary models driven by a scalar field, a new temperature law is deduced and its predictions are compared with the standard result.

We calculate theoretical population ratios of the ground fine‐structure levels of some atoms/ions which typically exhibit ultraviolet (UV) lines in the spectra of quasi‐stellar objects (QSO) absorbers redward the Lyα forest: C0, C+, O0, Si+ and Fe+. The most reliable atomic data available are employed and a variety of excitation mechanisms are considered: collisions with several particles in the medium, direct excitation by photons from the cosmic microwave background radiation (CMBR) and fluorescence induced by a UV field present. The theoretical population ratios are compared with the corresponding column density ratios of C i and C ii lines observed in damped Lyα (DLA) and Lyman Limit (LL) systems, collected in the recent literature, to infer their physical conditions. The volumetric density of neutral hydrogen in DLA systems is constrained to be lower than tens of cm−3 (or a few cm−3 in the best cases), and upper limits to the UV radiation field intensities to be about two orders of magnitude bigger than the radiation field of the Galaxy (one order of magnitude in the best cases). Their characteristic sizes are higher than a few pc (tens of pc in the best cases) and lower limits for their total masses vary from 100 to 105 solar masses. For the only LL system in our sample, the electronic density is constrained to be . We suggest that the fine‐structure lines may be used to discriminate between the current accepted picture of the UV extragalactic background as the source of ionization in these systems and a local origin for the ionizing radiation as supported by some authors. We also investigate the validity of the temperature–redshift relation of the CMBR predicted by the standard model and study the case for alternative models.