The Infrared-X-ray continuum correlation in Active Galactic Nuclei

The correlation between the soft X-ray and near infrared emission from AGN is analysed using composite models by the code SUMA. We find new evidences for differences in ranges of parameters which characterize the NLR of Seyfert galaxies and LINERs. Results obtained by modelling the Einstein and the ROSAT samples of galaxies are in full agreement. In order to fit the infrared and X-ray continua, an eta factor is defined, which accounts for the emitting area of the cloud. If the infrared emission is due to bremsstrahlung and comes from the same cloud producing the soft X-rays, the eta values obtained from both emissions must be the same. Therefore, if eta_IR < eta_soft-X there must be a strong contribution of soft X-rays from the active centre. From the eta values we expect to identify the objects that could present strong variability. \Comment: 11 pages,13 figures, in press in MNRAS. in press in MNRA

Extended Coronal Emission Lines in Active Galactic Nuclei

VLT and NTT spectra are used to examine the nuclear and extended coronal line emission in a sample of well-known Seyfert 1 and 2 galaxies. The excellent spatial resolution obtained with VLT allowed us to map [SiVI] 1.963 $\mu$m and [SiVII] 2.48 $\mu$m on scales of up to 20 pc. Coronal line emission, extended to distances of $\sim$100 pc, is detected in some of the lines analyzed, particularly in [FeX] 6374\AA, [FeXI] 7891\AA, and [SiVII] 2.48$\mu$m. Most coronal lines are strongly asymmetric towards the blue and broader than low-ionization lines. This result is particularly important for Circinus, where previous observations had failed at detecting larger widths for high-ionization lines. Photoionization models are used to investigate the physical conditions and continuum luminosities necessary to produced the observed coronal emission. We found that an ionization parameter U> 0.10 is necessary to reproduce the observations, although the clouds should be located at distances < 30 pc.Comment: 4 pages, 6 figures, to appear in proceedings of IAU Symposium No. 222, The Interplay Among Black Holes, Stars and ISM in Galacti Nucle

Temperature Fluctuations and Abundances in HII Galaxies

There is evidence for temperature fluctuations in Planetary Nebulae and in Galactic HII regions. If such fluctuations occur in the low-metallicity, extragalactic HII regions used to probe the primordial helium abundance, the derived 4He mass fraction, Y_P, could be systematically different from the true primordial value. For cooler, mainly high-metallicity HII regions the derived helium abundance may be nearly unchanged but the oxygen abundance could have been seriously underestimated. For hotter, mainly low-metallicity HII regions the oxygen abundance is likely accurate but the helium abundance could be underestimated. The net effect is to tilt the Y vs. Z relation, making it flatter and resulting in a higher inferred Y_P. Although this effect could be large, there are no data which allow us to estimate the size of the temperature fluctuations for the extragalactic HII regions. Therefore, we have explored this effect via Monte Carlos in which the abundances derived from a fiducial data set are modified by \Delta-T chosen from a distribution with 0 < \Delta-T < \Delta-T_max where \Delta-T_max is varied from 500K to 4000K. It is interesting that although this effect shifts the locations of the HII regions in Y vs. O/H plane, it does not introduce any significant additional dispersion.Comment: 11 pages, 9 postscript figures; submitted to the Ap