Ruth Gruenwald

Outflows of Very Ionized Gas in the Centers of Seyfert Galaxies: Kinematics and Physical Conditions*

Mid-resolution spectra are used to deduce the size and kinematics of the coronal region in a sample of Seyfert galaxies by means of observations of the [Fe XI], [Fe X], [Fe VII], [Si VI], and [Si VII] lines. These coronal lines (CLs) extend from the unresolved nucleus up to a few tens to a few hundreds of parsecs. The region of the highest ionized ions studied, [Fe XI] and [Fe X], is the least spatially extended and concentrates at the center; intermediate-ionization lines extend from the nucleus up to a few tens to a few hundred parsecs; lower [O III]-like ions are known to extend to the kpc range. 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-1. Moreover, in NGC 1386 and NGC 1068, a double-peaked [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 zero-intensity levels implies gas velocities up to 2000 km s-1. 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.

Temperature Fluctuations and Abundances in H II Galaxies

There is evidence for temperature fluctuations in planetary nebulae and in some Galactic H II regions. If such fluctuations occur in the low-metallicity, extragalactic H II regions used to probe the primordial helium abundance, the derived 4He mass fraction, YP, could be systematically different from the true primordial value. For cooler, mainly high-metallicity H II regions, the derived helium abundance may be nearly unchanged, but the oxygen abundance could have been seriously underestimated. For hotter, mainly low-metallicity H II regions, the oxygen abundance is likely accurate, but the helium abundance could be underestimated. The net effect is to tilt the Y-versus-Z relation, making it flatter and resulting in a higher inferred YP. Although this effect could be large, there are no data that allow us to estimate the size of the temperature fluctuations for the extragalactic H II regions. Therefore, we have explored this effect via Monte Carlo simulations of the data in which the abundances derived from a fiducial data set are modified by ΔT chosen from a distribution with 0 ≤ ΔT ≤ ΔTmax, where ΔTmax is varied from 500 to 4000 K. It is interesting that, although this effect shifts the locations of the H II regions in the Y-versus-O/H plane, it does not introduce any significant additional dispersion.

Molecular Hydrogen in the Ionized Region of Planetary Nebulae

This paper presents an analysis of the concentration of hydrogen molecules inside the ionized region of planetary nebulae (PNs). The equations corresponding to the ionization and chemical equilibria of H, H+, H-, H2, H, and H are coupled with the equations of ionization and thermal balance for a photoionized atomic gas. A total of 40 different reactions related to the formation or destruction of these species are included. The presence of dust is taken into account, since grains act as catalysts for the production of H2 as well as shield the molecules against the stellar ionizing radiation. We analyze the effect of the stellar ionizing continuum as well as of the gas and grain properties on the calculated H2 mass. It is shown that a significant concentration of H2 can survive inside the ionized region of planetary nebulae, mostly in the inner region of the recombination zone. The total H2 to total hydrogen mass ratio inside the ionized region increases with the central star temperature, and, depending on the PN physical conditions, it may be of the order of ~10-6 or even higher. The increase of the recombination zone with stellar temperature can account for such correlation. This may explain why H2 emission is more frequently observed in bipolar PNs (Gatleys rule), since this kind of object typically has hotter stars. Applying our results to the planetary nebula NGC 6720, we obtain an H2 to hydrogen mass ratio similar to the value obtained from the observed H2 line emission.

Temperature of the Central Stars of Planetary Nebulae and the Effect of the Nebular Optical Depth

The effect of the nebula optical depth on the determination of the temperature (T*) of the central stars in planetary nebulae is discussed. Based on photoionization models for planetary nebulae with different optical depths, we show, quantitatively, that the details of the distribution of the H and He II Zanstra temperatures are mainly explained by an optical depth effect; in particular, that the discrepancy is larger for low stellar temperatures. The results also show that for high stellar temperatures the He II Zanstra temperature underestimates the stellar temperature, even for high optical depths. The stellar temperature, as well as the optical depth, can be obtained from a Zanstra temperature ratio (ZR) plot ZR = Tz(He II)/Tz(H) versus Tz(He II). The effects of departures from a blackbody spectrum, as well as of the He abundance in the nebulae, are also discussed. For nebulae of very low optical depth and/or high stellar temperature the distribution ZR versus Tz(He II) only provides lower limits for T*. In order to obtain better values for the optical depth and T*, we propose the use of the line intensity ratio He II/He I versus Tz(He II) diagram.

A NEW GENERATION OF PHOTOIONIZATION CODES: THREE-DIMENSIONAL MODELS. THE BIPOLAR PLANETARY NEBULA IC 4406

A three-dimensional self-consistent photoionization code is developed in order to build more realistic models for asymmetric and/or inhomogeneous photoionized nebulae. With these models the assumption of spherical or plane-parallel symmetry can be dropped and models with various geometries can be treated. The gaseous region is divided into numerous cubic cells. The physical conditions in each cell are obtained taking into account the e†ect of the optical depth and the di†use radiation, which depend on the other cells. In order to compare to observational data, line intensities are calculated for the whole nebula, as well as for regions covered by a given slit. Isophotal maps are also obtained. A model for IC 4406, which is a typical example of bipolar planetary nebula, is presented. The model assumes a torus of dense material around the central star, as suggested by Sahai et al. Its presence is con-rmed by the model, in particular by the shape of the theoretical Ha)(N II) isophotal map. The chemical abundances required to explain the observed line intensities indicate that the chemical proper- ties of this bipolar nebula are not characteristic of type I planetaries. Subject headings: ISM: abundances E planetary nebulae: individual (IC 4406) E radiative transfer

A spectral atlas of H ii galaxies in the near-infrared

Recent models show that TP-AGB stars should dominate the NIR spectra of populations 0.3 to 2 Gyr old, leaving unique signatures that can be used to detect young/intermediate stellar population in galaxies. However, no homogeneous database of star-forming galaxies is available in the NIR to fully explore these results. With this in mind, we study the NIR spectra of a sample of 23 HII and starburst galaxies, aimed at characterizing the most prominent spectral features and continuum shape in the 0.8-2.4 micron region of these objects. Spectral indices are derived for the relevant absorption lines/bands and a comparison with optical indices of the same sample available in the literature is made. We found no correlation between the optical and the NIR indexes. This is probably due to the differences in aperture between these two sets of data. That result is further supported by the absence or weakness of emission lines in the NIR for a subsample galaxies, while in the optical the emission lines are strong and clear, which means that the ionisation source in many of these galaxies is not nuclear, but circumnuclear or located in hot spots. We detected important signatures predicted for a stellar population dominated by the TP-AGBs, like CN 1.1 micron and CO 2.3 micron. In at least one galaxy (NGC 4102) the CN band at 1.4 micron was detected for the first time. We also detect TiO and ZrO bands that have never been reported before in extragalactic sources. The shape of the continuum emission is found to be strongly correlated to the presence/lack of emission lines. An observational template for the star-forming galaxies is derived to be used as a benchmark of stellar population(s) in starburst galaxies against which to compare near-IR spectroscopy of different types of galaxies, especially those with AGN activity and/or those at high-redshift.

Molecular chemistry and the missing mass problem in planetary nebulae

Context. Detections of molecular lines, mainly from H2 and CO, reveal molecular material in planetary nebulae. Observations of a variety of molecules suggest that the molecular composition in these objects differs from that found in interstellar clouds or in circumstellar envelopes. The success of the models, which are mostly devoted to explain molecular densities in specific planetary nebulae, is still partial however. Aims. The present study aims at identifying the influence of stellar and nebular properties on the molecular composition of planetary nebulae by means of chemical models. A comparison of theoretical results with those derived from the observations may provide clues to the conditions that favor the presence of a particular molecule. Methods. A self-consistent photoionization numerical code was adapted to simulate cold molecular regions beyond the ionized zone. The code was used to obtain a grid of models and the resulting column densities are compared with those inferred from observations. Results. Our models show that the inclusion of an incident flux of X-rays is required to explain the molecular composition derived for planetary nebulae. We also obtain a more accurate relation for the N(CO)/N(H2) ratio in these objects. Molecular masses obtained by previous works in the literature were then recalculated, showing that these masses can be underestimated by up to three orders of magnitude. We conclude that the problem of the missing mass in planetary nebulae can be solved by a more accurate calculation of the molecular mass.

Are He and N Abundances in Type I Planetary Nebulae as High as Empirically Derived

Type I planetary nebulae (PNs) are defined as those with high He and N abundances. These objects present in general bipolar geometries and have high stellar temperatures. In this paper we analyze the empirical methods for abundance determination in order to check if the He and N overabundances in type I PNs are a consequence of a geometrical effect due to the bipolarity or the ionization stratification due to the stellar temperature. For this, we obtain simulated, spherically symmetrical nebulae, as well as bipolar nebulae, using a three-dimensional photoionization code. From the projected emission line intensities for (a) the whole nebula, (b) for a slit crossing the nebula, as well as (c) for different positions in the nebula, we applied the formulae used in the literature to obtain empirical abundances. These empirical abundances are then compared with the adopted ones. We show that empirical abundances depend on the particular line of sight covered by the observation and can simulate an overabundance and/or the presence of abundance gradients of He and N in planetary nebulae with high stellar temperature. The geometrical effects are also discussed. Systematic errors in abundance determinations by empirical methods are higher for the N/H ratio than for N/O. Thus, it seems better to use the N/O value when discussing N-rich objects.

H2 infrared line emission from the ionized region of planetary nebulae

Context. The analysis and interpretation of the H2 line emission from planetary nebulae have been done in the literature by assuming that the molecule survives only in regions where the hydrogen is neutral, as in photodissociation, neutral clumps, or shocked regions. However, there is strong observational and theoretical evidence that at least part of the H2 emission is produced inside the ionized region of these objects. Aims. The aim of the present work is to calculate and analyze the infrared line emission of H2 produced inside the ionized region of planetary nebulae using a one-dimensional photoionization code. Methods. The photoionization code Aangaba was improved in order to calculate the statistical population of the H2 energy levels, as well as the intensity of the H2 infrared emission lines in the physical conditions typical of planetary nebulae. A grid of models was obtained and the results then analyzed and compared with the observational data. Results. We show that the contribution of the ionized region to the H2 line emission can be important, particularly in the case of nebulae with high-temperature central stars. This result explains why H2 emission is more frequently observed in bipolar planetary nebulae (Gatley’s rule), since this kind of object typically has hotter stars. Collisional excitation plays an important role in populating the rovibrational levels of the electronic ground state of H2 molecules. Radiative mechanisms are also important, particularly for the upper vibrational levels. Formation pumping can have minor effects on the line intensities produced by de-excitation from very high rotational levels, especially in dense and dusty environments. We included the effect of the H2 molecule on the thermal equilibrium of the gas, concluding that, in the ionized region, H2 only contributes to the thermal equilibrium in the case of a very high temperature of the central star or a high dust-to-gas ratio, mainly through collisional de-excitation.

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 μm 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 pc south of the nucleus. The contribution of a power-law continuum in the centre is about 25 per cent, 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 H 2 emission-line profile, leading us to propose that the peaks might be associated 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 south-west 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, especially in the inner 200 pc.