UV Continuum, Physical Conditions and Filling Factor in Active Galactic Nuclei

The narrow line region of active galaxies is formed by gas clouds surrounded by a diluted gas. Standard one-dimensional photoionization models are usually used to model this region in order to reproduce the observed emission lines. Since the narrow line region is not homogeneous, two major types of models are used: (a) those assuming a homogeneous gas distribution and a filling factor less than unity to mimic the presence of the emitting clouds; (b) those based on a composition of single-cloud models combined in order to obtain the observed spectra. The first method is largely used but may induce to misleading conclusions as shown in this paper. The second one is more appropriate, but requires a large number of observed lines in order to limit the number of single models used. After discussing the case of an extragalactic HII region, for which the ionizing radiation spectrum is better known, we show that 1-D models for the narrow line region with a filling factor less than unit do not properly mimic the clumpiness, but just simulates an overall lower density. Multi-cloud models lead to more reliable results. Both models are tested in this paper, using the emission-line spectra of two well-known Seyfert galaxies, NGC 4151 and NGC 1068. It is shown that ionizing radiation spectra with a blue bump cannot be excluded by multi-cloud models, although excluded by Alexander et al. (1999, 2000)using homogeneous models with a filling factor less than unity.Comment: 23 pages, 7 figures. Accepted for Publication in Ap

Nuclear and Extended Spectra of NGC 1068 - II: Near-Infrared Stellar Population Synthesis

We performed stellar population synthesis on the nuclear and extended regions of NGC 1068 by means of near-infrared spectroscopy to disentangle their spectral energy distribution components. This is the first time that such a technique is applied to the whole 0.8 - 2.4 micron wavelength interval in this galaxy. NGC 1068 is one of the nearest and probably the most studied Seyfert 2 galaxy, becoming an excellent laboratory to study the interaction between black holes, the jets that they can produce and the medium in which they propagate. Our main result is that traces of young stellar population are found at ~ 100 south of the nucleus. The contribution of a power-law continuum in the centre is about 25%, which is expected if the light is scattered from a Seyfert 1 nucleus. We find peaks in the contribution of the featureless continuum about 100 - 150 pc from the nucleus on both sides. They might be associated with regions where the jet encounters dense clouds. Further support to this scenario is given by the peaks of hot dust distribution found around these same regions and the H2 emission line profile, leading us to propose that the peaks might be associate to regions where stars are being formed. Hot dust also has an important contribution to the nuclear region, reinforcing the idea of the presence of a dense, circumnuclear torus in this galaxy. Cold dust appears mostly in the south direction, which supports the view that the southwest emission is behind the plane of the galaxy and is extinguished very likely by dust in the plane. Intermediate age stellar population contributes significantly to the continuum, specially in the inner 200 pc.Comment: 9 pages, 8 figures. Accepted for publication at MNRA

The Evolution of Helium and Hydrogen Ionization Corrections as HII Regions Age

Helium and hydrogen recombination lines observed in low-metallicity, extragalactic, HII regions provide the data used to infer the primordial helium mass fraction, Y_P. In deriving abundances from observations, the correction for unseen neutral helium or hydrogen is usually assumed to be absent; i.e., the ionization correction factor is taken to be unity (icf = 1). In a previous paper (VGS), we revisited the question of the icf, confirming a "reverse" ionization correction: icf < 1. In VGS the icf was calculated using more nearly realistic models of inhomogeneous HII regions, suggesting that the published values of Y_P needed to be reduced by an amount of order 0.003. As star clusters age, their stellar spectra evolve and so, too, will their icfs. Here the evolution of the icf is studied, along with that of two, alternate, measures of the "hardness" of the radiation spectrum. The differences between the icf for radiation-bounded and matter-bounded models are also explored, along with the effect on the icf of the He/H ratio (since He and H compete for some of the same ionizing photons). Particular attention is paid to the amount of doubly-ionized helium predicted, leading us to suggest that observations of, or bounds to, He++ may help to discriminate among models of HII regions ionized by starbursts of different ages and spectra. We apply our analysis to the Izotov & Thuan (IT) data set utilizing the radiation softness parameter, the [OIII]/[OI] ratio, and the presence or absence of He++ to find 0.95 < icf < 0.99. This suggests that the IT estimate of the primordial helium abundance should be reduced by Delta-Y = 0.006 +- 0.002, from 0.244 +- 0.002 to 0.238 +- 0.003.Comment: 27 double-spaced pages, 11 figures, 5 equations; revised to match the version accepted for publication in the Ap

Ionization Corrections For Low-Metallicity H II Regions and the Primordial Helium Abundance

Helium and hydrogen recombination lines observed in low-metallicity, extragalactic H II regions provide the data used to infer the primordial helium mass fraction, Y_P. The ionization corrections for unseen neutral helium (or hydrogen) are usually assumed to be absent; i.e., the ionization correction factor is taken to be unity (icf = 1). In this paper we revisit the question of the icf for H II regions ionized by clusters of young, hot, metal-poor stars. Our key result is that for the H II regions used in the determination of Y_P, there is a ``reverse'' ionization correction: icf < 1. We explore the effect on the icf of more realistic inhomogeneous H II region models and find that for those regions ionized by young stars, with ``hard'' radiation spectra, the icf is reduced further below unity. In Monte Carlos using H II region data from the literature (Izotov and Thuan 1998) we estimate a reduction in the published value of Y_P of order 0.003, which is roughly twice as large as the quoted statistical error in the Y_P determination.Comment: 23 pages, 2 postscript figures; ApJ accepted; minor change

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

3-D Photoionization Structure and Distances of Planetary Nebulae II. Menzel 1

We present the results of a spatio-kinematic study of the planetary nebula Menzel 1 using spectro-photometric mapping and a 3-D photoionization code. We create several 2-D emission line images from our long-slit spectra, and use these to derive the line fluxes for 15 lines, the Halpha/Hbeta extinction map, and the [SII] line ratio density map of the nebula. We use our photoionization code constrained by these data to derive the three-dimensional nebular structure and ionizing star parameters of Menzel 1 by simultaneously fitting the integrated line intensities, the density map, and the observed morphologies in several lines, as well as the velocity structure. Using theoretical evolutionary tracks of intermediate and low mass stars, we derive a mass for the central star of 0.63+-0.05 Msolar. We also derive a distance of 1050+_150 pc to Menzel 1.Comment: To be published in ApJ of 10th February 2005. 12 figure

An analysis of views about supported reduction or discontinuation of antipsychotic treatment among people with schizophrenia and other psychotic disorders

BACKGROUND: Antipsychotic medication can reduce psychotic symptoms and risk of relapse in people with schizophrenia and related disorders, but it is not always effective and adverse effects can be significant. We know little of patients' views about continuing or discontinuing antipsychotic treatment. AIMS: To explore the views of people with schizophrenia and other psychotic disorders about continuing their antipsychotic medication or attempting to reduce or discontinue this medication with clinical support. METHODS: We collected quantitative and qualitative data by conducting semi-structured interviews in London, UK. Factors predicting a desire to discontinue medication were explored. Content analysis of qualitative data was undertaken. RESULTS: We interviewed 269 participants. 33% (95% CI, 27 to 39%) were content with taking long-term antipsychotic medication. Others reported they took it reluctantly (19%), accepted it on a temporary basis (24%) or actively disliked it (18%). 31% (95% CI, 25 to 37%) said they would like to try to stop medication with professional support, and 45% (95% CI, 39 to 51%) wanted the opportunity to reduce medication. People who wanted to discontinue had more negative attitudes towards the medication but were otherwise similar to other participants. Wanting to stop or reduce medication was motivated mainly by adverse effects and health concerns. Professional support was identified as potentially helpful to achieve reduction. CONCLUSIONS: This large study reveals that patients are commonly unhappy about the idea of taking antipsychotics on a continuing or life-long basis. Professional support for people who want to try to reduce or stop medication is valued

Nuclear and Extended Spectra of NGC 1068 - I: Hints from Near-Infrared Spectroscopy

We report the first simultaneous zJHK spectroscopy on the archetypical Seyfert 2 Galaxy NGC 1068 covering the wavelength region 0.9 to 2.4 micron. The slit, aligned in the NS direction and centred in the optical nucleus, maps a region 300 pc in radius at sub-arcsec resolution, with a spectral resolving power of 360 km s^-1. This configuration allow us to study the physical properties of the nuclear gas including that of the north side of the ionization cone, map the strong excess of continuum emission in the K-band and attributed to dust and study the variations, both in flux and profile, in the emission lines. Our results show that (1) Mid- to low-ionization emission lines are splitted into two components, whose relative strengths vary with the position along the slit and seem to be correlated with the jet. (2) The coronal lines are single-peaked and are detected only in the central few hundred of parsecs from the nucleus. (3) The absorption lines indicate the presence of intermediate age stellar population, which might be a significant contributor to the continuum in the NIR spectra. (4) Through some simple photoionization models we find photoionization as the main mechanism powering the emitting gas. (5) Calculations using stellar features point to a mass concentration inside the 100 - 200 pc of about 10^10 solar masses.Comment: 19 Pages, 14 figures. Accepted for publication in MNRA