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We present the results of a meeting on numerical simulations of ionized nebulae held at the University of Kentucky in conjunction with the celebration of the 70th birthdays of Profs. Donald Osterbrock and Michael Seaton., Comment: http://adsabs.harvard.edu/abs/1995aelm.conf...83F. The Analysis of Emission Lines, Proc. STScI Symposium May 16--18, 1994, Eds. R.E. Williams & M. Livio, Cambridge University Press, p. 83

Mid-resolution spectra are used to deduce the size and kinematics of the coronal gas in a sample of Seyfert galaxies by means of observations of the [FeXI], [FeX], [FeVII], [SiVI] and [SiVII] lines. These coronal lines (CL) extend from the unresolved nucleus up to a few tens to a few hundreds of parsecs. The region of the highest ionized ions studied, [FeXI] and [FeX], 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 [OIII]-like ions are known to extendin the kpc range. All together indicates 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 two 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 hundreds of km/s. Moreover, in NGC1386 and NGC1068, a double peak [FeVII] line is detected in the nuclear and extended coronal region, this being the first report in of such type of profile in CL 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. 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., Comment: Accepted for publication in the Astrophysical Journal. 40 pages, 15 figures. Minor changes made on the affiliation of one co-author

When analysing HII regions, a possible source of systematic error on empirically derived physical quantities is the limited size of the slit used for the observations. A grid of photoionization models was built through the Aangaba code varying the ionizing radiation spectrum emitted by a stellar cluster, as well as the gas abundance. The calculated line surface brightness was then used to simulate slit observations and to derive empirical parameters using the usual methods described in the literature. Depending on the fraction of the object covered by the slit, the parameters can be different from those obtained from observations of the whole object, an effect that is mainly dependent on the age of the ionizing stellar cluster. The low-ionization forbidden lines are more sensitive to the size of the area covered by the slit than the high-ionization forbidden lines or recombination lines. Regarding the temperature indicator T[OIII], the slit effects are small since this temperature is derived from [OIII] lines. On the other hand, for the abundance indicator R23, which depends also on the [OII] line, the slit effect is slightly higher. Therefore, the systematic error due to slit observations on the O abundance is low, being usually less than 10%, except for HII regions powered by stellar clusters with a relative low number of ionizing photons between 13.6 and 54.4 eV, which create a smaller O++ emitting volume. In this case, the systematic error on the empirical O abundance deduced from slit observations is more than 10% when the covered area is less than 50%., Comment: To be published in MNRAS, accepted in 09/09/2005, 17 pages and 6 figures

We present the first spectroscopic observations in the interval 0.8-4.0 microns, complemented with HST/UV and optical spectroscopy, of the narrow line Seyfert 1 galaxy Mrk766. The NIR spectrum is characterized by permitted lines of HI, HeI, HeII and FeII, and forbidden lines of [SII], [SIII] and [FeII] among others. High ionized species such as [SiIX], [SiX], [SIX] and [MgVII] are also observed. The continuum has a complex shape, with contribution of the central engine, circumnuclear stellar population and dust. This last component is evidenced by the presence of an excess of emission peaking at 2.25 microns, fitted by blackbody function with T_bb=1200K. That temperature is close to the evaporation temperature of graphite grains. As such, it provides strong evidence of hot dust, probably very close to the nucleus. Consistent modeling of the line and broad band continuum spectrum by composite models, which account for the photoionizing flux of the central engine and shocks, shows that the shock velocities are between 100 and 500 km/s, the preshock densities between 100 and 1000 cm^-3 and the radiation fluxes from the active centre between 10^9 and 5x10^12 photons cm^-2 s^-1 eV^-1 at 1 Ryd with spectral indices $\alpha_{UV}$=-1.5 and $\alpha_X$=-0.4. Adopting silicon grains, dust-to-gas ratios are between 10^-{6} and 4x10$^{-4}$ by mass. The emitting clouds are at an average distance of 160 pc from the centre, with high velocity clouds closer and low velocity clouds farther from the centre. The N/H relative abundance could be twice solar. In constrast, Fe is depleted from the gaseous phase by a factor >2. Ratios of calculated to observed line ratios to Hbeta indicate an average contribution of the broad line region to the observed Hbeta of about 40%., Comment: 15 pages, 6 figures. Accepted to MNRAS

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 Nuclei

We discuss the different physical processes contributing to the infrared continuum of AGN, assuming that both photoionization from the active center and shocks ionize and heat the gas and dust contained in an ensemble of clouds surrounding the nucleus. Radiation transfer of primary and secondary radiation throughout a cloud is calculated consistently with collisional processes due to the shock. We consider that the observed continuum corresponds to reprocessed radiation from both dust and gas in the clouds. The model is applied to the continuum of Seyfert galaxies from which best estimate of the nuclear, stellar subtracted, emission is available. The results show that radiation-dominated high velocity clouds are more numerous in Seyfert 1-1.5 whereas shock-dominated low velocity clouds are dominant in Seyfert type 2 in full agreement with the unified model for AGN. In type 2 objects, radiation is partly suppressed by a central dusty medium with a high dust-to-gas ratio. A grid of models is used to provide a phenomenological analysis of the observed infrared spectral energy distribution., Comment: 14 pages, 10 figures. in press in MNRAS

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 MNRAS

We report the detection of the 3.3 mu Polycyclic Aromatic Hydrocarbon (PAH) feature in two Seyfert 1 galaxies - NGC 3227 and Mrk 766, and one QSO - Mrk 478, observed with SpeX at IRTF at a spectral resolution not previously attained for this type of objects. Except for NGC 3227, this is the first time that the 3.3 mu PAH emission is detected in Mrk 766 and Mrk 478. The widths of the emission, reported also for the first time, are rather similar, ranging from 450 A to 550 A. The luminosity of the 3.3 mu PAH emission measured in the QSO Mrk 478 places it at a level similar of that found in starburst and infrared luminous galaxies and implies that this object is having a vigorous burst of star formation. The spatial resolution of the spectra allows us to constrain the location of the star-forming region to the inner 1 Kpc for the QSO and 150 pc for the Seyferts. Our results support the idea that these objects resides in molecular gas-rich galaxies and that their observed infrared excess is primarily due to star formation, as previously indicated by CO and H_2 observations. We also report, for Mrk 1239, the presence of a broad emission feature centred at 3.43 mu, not previosly detected in an extragalactic object and whose origin is not yet clear., Comment: 5 pages, 1 figure. Accepted to MNRAS pink pages

UV, visible, and near-infrared spectroscopy is used to study the transitions of neutral oxygen leading to the emission of broad OI $\lambda$8446, $\lambda$11287 and $\lambda$1304 in Active Galactic Nuclei. From the strength of the former two lines, contrary to the general belief, we found that in six out of seven galaxies, L-beta fluorescence is not the only mechanism responsible for the formation of these three lines. Because OI $\lambda$13165 is almost reduced to noise level, continuum fluorescence is ruled out as an additional excitation mechanism, but the presence of OI $\lambda$7774 in one of the objects suggests that collisional ionization may have an important role in the formation of OI $\lambda$8446. The usefulness of the OI lines as a reliable reddening indicator for the broad line region is discussed. The values of E(B-V) derived from the OI $\lambda 1304/\lambda$8446 ratio agree with those obtained using other reddening indicators. The observations point toward a break in the one-to-one photon relation between OI $\lambda$8446 and OI $\lambda$1304, attributable to several destruction mechanisms that may affect the latter line., Comment: 26 pages, 5 figures. Accepted for publication in ApJ

The multiwavelength emission spectrum and associated velocity field of the Seyfert prototype NGC 4151 is modeled. HST data has impressively revealed the existence of a large range of velocities (100 - 1500 \kms) dominating the emitting clouds in the extended emission line region of the galaxy. Following this observational result, a revision of the photoionization modeling approach applied to NGC 4151 is presented. It is concluded that a mixture of radiation dominated clouds and shock dominated clouds are required to explain the multiwavelength line and continuum spectra of the galaxy., Comment: 16 pages, LaTeX class for Astronomy and Astrophysics (including 3 Tables) + 8 PostScript figures. To appear in "Astronomy and Astrophysics"

We obtained 0.8-2.4 micron spectra at a resolution of 320 km/s of four narrow-line Seyfert 1 galaxies in order to study the near-infrared properties of these objects. We focus on the analysis of the FeII emission in that region and the kinematics of the low-ionization broad lines. We found that the 1 micron FeII lines (9997 A, 10501 A, 10863 A and 11126 A) are the strongest FeII lines in the observed interval. For the first time, primary cascade lines of FeII arising from the decay of upper levels pumped by Ly-alpha fluorescence are resolved and identified in active galactic nuclei. Excitation mechanisms leading to the emission of the 1 micron FeII features are discussed. A combination of Ly-alpha fluorescence and collisional excitation are found to be the main contributors. The flux ratio between near-IR FeII lines varies from object to object, in contrast to what is observed in the optical region. A good correlation between the 1 micron and optical FeII emission is found. This suggests that the upper z4Fo and z4Do levels from which the bulk of the optical lines descend are mainly populated by the transitions leading to the 1 micron lines. The width and profile shape of FeII 11127, CaII 8642 and OI 8446 are very similar but significantly narrower than Pa-beta, giving strong observational support to the hypothesis that the region where FeII, CaII and OI are produced are co-spatial, interrelated kinematically and most probably located in the outermost portion of the BLR., Comment: Accepted for publication in ApJ - 35 pages

A grid of models for starburst spectra is presented and compared with power-law models which represent AGNs. The models are composite, i.e., they account for the radiation from the starburst and for the shocks created by super-winds. Some interesting fit of models to observations are also discussed. In particular, it is found that [OIII]/Hb ~can reach values as high as for the AGN when the emitting clouds are close to the starburst region. Moreover CIV lines can be high even if SiIV lines are relatively low. It is found that for some line ratios, which have similar values for starburst and AGN models, the width of the lines can distinguish between the two types., Comment: grpaper.tex + 10 tables PostScript + 9 figures PostScript Accepted for publication in ApJS

We calculate theoretical population ratios of the ground fine-structure levels of some atoms/ions which typically exhibit UV lines in the spectra of QSO absorbers redward the Ly-alpha forest: C0, C+, O0, Si+ and Fe+. The most reliable atomic data available is employed and a variety of excitation mechanisms 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 confronted with the corresponding column density ratios of C I and C II lines observed in damped Ly-alpha (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 the UV radiation field intensity must be lower than two orders of magnitude 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 10^0 to 10^5 solar masses. For the only LL system in our sample, the electronic density is constrained to be n_e<0.15 cm^-3. We suggest that the fine-structure lines may be used to discriminate between the current accepted picture of the UV extragalatic background as the source of ionization in these systems against 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., Comment: 16 pages, 12 figures

We describe a Fortran 90 program to calculate population ratios of atomic levels. The program solves the equations of statistical equilibrium considering all possible bound-bound processes: spontaneous, collisional or radiation induced (the later either directly or by fluorescence). There is no limit on the number of levels or in the number of processes that may be taken into account. The program may find a wide range of applicability in astronomical problems, such as interpreting fine-structure absorption lines or collisionally excited emission lines (such as coronal emission lines) in the spectra of several objects, and also in calculating the cooling rates due to collisional excitation., Comment: 23 pages, no figures. Submitted to Computer Physics Communications. Code available at http://www.iagusp.usp.br/~alexsilv/popratio

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., Comment: 24 pages, 4 figures; to appear in ApJ, Nov 2000

A grid of composite models for the narrow line region of active galaxies, which consistently account for both the effect of a photoionizing radiation from the active center and of a shock front, is presented. Theoretical results, calculated with the SUMA code, are given for different values of shock velocities, preshock densities, geometrical thickness of the clouds, and, particularly, for the ionizing radiation intensity in a large range. The input parameters are chosen within the ranges indicated by previous fits of several observed emission-line and continuum spectra from active galaxies. Shock velocities from 100 \kms ~to 1500 \kms ~and preshock densities from 100 \cm3 to 1000 \cm3 are considered. The line intensities of the most important ultraviolet, optical and infrared transitions are obtained and are listed in several tables., Comment: 14 pages Latex + 2 Postscript tables + 1 Postscript figures

We use a 3D photoionization modeling tool to study the morpho-kinematic properties of the Planetary Nebula (PN) NGC 3132. We show that it is possible to reproduce the low resolution observations (spectra and images) with an ellipsoidal shell. However, high resolution observations, as those showing a density variation along the nebula and the [O III]5007 velocity profiles, definitively rule out this description. We show that a bipolar Diabolo shape with a 40 degres rotation of the symmetry axis relative to the line of sight successfully reproduces the observed images, as well as the high resolution observations., Comment: 9 pages, 7 figures, accepted in ApJ main serie

This paper aims to understand the continuum of Seyfert 2 galaxies. By fitting the single galaxies in the sample of Heckman et al. (1995) with composite models (shock+ photoionization from the active center), we show that five main components characterize the SED of the continuum. Shocks play an important role since they produce a high temperature zone where soft X-rays are emitted. We show that in the optical-UV range, the slope of the NLR emission reproduces the observed values, and may be the main component of the featureless continuum. The presence of star forming regions cannot be excluded in the circumnuclear region of various Seyfert galaxies. An attempt is made to find their fingerprints in the observed AGN spectra. Finally, it is demonstrated that multi-cloud models are necessary to interpret the spectra of single objects, even in the global investigation of a sample of galaxies., Comment: 26 pages, LaTeX (including 5 Tables) + 17 PostScript figures. To appear in "The Astrophysical Journal"

We present a new modeling tool for planetary nebulae, based on 3D photoionization calculations. Our goal is to show that all the information provided by observations, regarding kinematics and morphology, have to be consistently accounted for, in order to get a real insight of the object. Only 3D simulations offer this possibility. From models for two theoretical PNe, we show that the enhancement in the equatorial zone observed in several PNe is not necessarily due to a density gradient, as usually interpreted. It is also shown that asymmetric velocity profiles often observed (e.g., Gesicki et al. 1998) can be easily reproduced. Observations providing a better insight on the morphology of the PN are discussed., Comment: 10 pages, 9 figures, accepted in ApJ Main Serie

We present a new modeling tool for planetary nebulae (PNe), based on 3D photoionization calculations. From models for two theoretical PNe, we show that the enhancement in the equatorial zone observed in several PNe is not necessarily due to a density gradient, as usually interpreted. We study the morpho-kinematic properties of the PN NGC 3132 and show that a bipolar Diabolo shape successfully reproduces the observed images, as well as the high resolution observations., Comment: 4 pages, 6 figures, to appear in ``Asymmetrical Planetary Nebulae II: from Origins to Microstructures,'' ASP Conference Series, J.H. Kastner, N. Soker, & S.A. Rappaport, eds

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 changes

A multi-cloud model is presented which explains the soft X-ray excess in NGC 4051 and, consistently, the optical line spectrum and the SED of the continuum. The clouds are heated and ionized by the photoionizing flux from the active center and by shocks. Diffuse radiation, partly absorbed throughout the clouds, nicely fits the bump in the soft X-ray domain, while bremsstrahlung radiation from the gaseous clouds contribute to the fit of the continuum SED. Debris of high density fragmented clouds are necessary to explain the absorption oxygen throats observed at 0.87 keV and 0.74 keV. The debris are heated by shocks of about 200-300 km/s. Low velocity (100 km/s)-density (100 cm-3) clouds contribute to the line and continuum spectra, as well as high velocity (1000 km/s)-density (8000 cm-3) clouds which are revealed by the FWHM of the line profiles. The SED in the IR is explained by reradiation of dust, however, the dust-to-gas ratio is not particularly high. Radio emission is well fitted by synchrotron radiation created at the shock front by Fermi mechanism., Comment: 19 pages + 3 figures PostScript

Simultaneous modeling of the line and continuum emission from the nuclear region of the Circinus galaxy is presented. Composite models which include the combined effect of shocks and photoionization from the active center and from the circumnuclear star forming region are considered. The effects of dust reradiation, bremsstrahlung from the gas and synchrotron radiation are treated consistently. The proposed model accounts for two important observational features. First, the high obscuration of Circinus central source is produced by high velocity and dense clouds with characteristic high dust-to-gas ratios. Their large velocities, up to 1500 km\s, place them very close to the active center. Second, the derived size of the line emitting region is well in agreement with the observed limits for the coronal and narrow line region of Circinus., Comment: 36 pages, LaTex (including 4 Tables and 9 figures), $$ removed from Abstract To appear in "The Astrophysical Journal"