Photoionization Model Calculations Research Articles

Origin of Ultraviolet Intermediate-width Emission Lines in Partially Obscured Quasar SDSS J151653.22+190048.2

The quasar SDSS J151653.22+190048.2 (J1516+1900) exhibits very peculiar spectral characters in the observed ultraviolet, optical, and infrared bands: the full widths at half maximum (FWHM) of its optical Hα, Hβ, and infrared Paα and Paβ emission lines are all larger than 5000km/s, and the equivalent widths of these emission lines also approach to those of normal quasars; while the ultraviolet emission lines (Lyβ, OVI, Lyα, NV, SiIV, and CIV) are dominated by intermediate-width emission lines (IELs) with a FWHM of ∼ 1700km/s. This phenomenon can be explained as the effect of partial obscuration: the broad emission lines (BELs) in the ultraviolet waveband are heavily suppressed by the dust extinction, and thus the IELs become prominent; while the dust extinction is not significant in optical and infrared bands, and the IELs can hardly be detected due to the brightness of BELs. Using the IEL width and central supermassive black hole mass MBH∼5.75×108 M⊙ of J1516+1900, and assuming that the intermediate-width emission line region (IELR) is virialized, we estimate the distance of the IEL region to the central black hole is about 1.6pc. On the other side, by combining the photoionization model calculations and observed IELs, we find that the IELR has a density of ∼1012 cm−3, and the ionization parameter of ∼10−0.65, and that its distance to the central region is ∼0.016pc, which is only one percent of the virialized distance. This contradiction can provide an important clue for studying the geometry, physical condition, and origin of the IELRs in active galactic nuclei.

Rapid black hole growth at the dawn of the Universe: a super-Eddington quasar atz = 6.6

We present the analysis of a new near-infrared (NIR) spectrum of a recently discovered $z=6.621$ quasar PSO J006+39 in an attempt to explore the early growth of supermassive black holes (SMBHs). This NIR (rest-frame ultraviolet, UV) spectrum shows blue continuum slope and rich metal emission lines in addition to Ly$\alpha$ line. We utilize the MgII line width and the rest frame luminosity $L_\text{3000\AA}$ to find the mass of SMBH ($M_\text{BH}$) to be $\sim 10^8 M_\odot$, making this one of the lowest mass quasars at high redshift. The power-law slope index ($\alpha_\lambda$) of the continuum emission is $-2.94\pm0.03$, significantly bluer than the slope of $\alpha_\lambda=-7/3$ predicted from standard thin disc models. We fit the spectral energy distribution (SED) using a model which can fit local SMBHs, which includes warm and hot Comptonisation powered by the accretion flow as well as an outer standard disc. The result shows that the very blue slope is probably produced by a small radial ($\sim230$ gravitational radius, $R_\text{g}$) extent of the standard accretion disc. All plausible SED models require that the source is super-Eddington ($L_\text{bol}/L_\text{Edd} \gtrsim 9$), so the apparently small disc may simply be the inner funnel of a puffed up flow, and clearly the SMBH in this quasar is in a rapid growth phase. We also utilize the rest-frame UV emission lines to probe the chemical abundance in the broad line region (BLR) of this quasar. We find that this quasar has super solar metallicity through photoionization model calculations.

DETECTION OF THE INTERMEDIATE-WIDTH EMISSION LINE REGION IN QUASAR OI 287 WITH THE BROAD EMISSION LINE REGION OBSCURED BY THE DUSTY TORUS

The existence of intermediate-width emission line regions (IELRs) in active galactic nuclei has been discussed for over two decades. A consensus, however, is yet to be arrived at due to the lack of convincing evidence for their detection. We present a detailed analysis of the broadband spectrophotometry of the partially obscured quasar OI 287. The ultraviolet intermediate-width emission lines (IELs) are very prominent, in high contrast to the corresponding broad emission lines (BELs) which are heavily suppressed by dust reddening. Assuming that the IELR is virialized, we estimated its distance to the central black hole of $\sim 2.9$ pc, similar to the dust sublimation radius of $\sim 1.3$ pc. Photo-ionization calculations suggest that the IELR has a hydrogen density of $\sim 10^{8.8}-10^{9.4} ~ \rm cm^{-3}$, within the range of values quoted for the dusty torus near the sublimation radius. Both its inferred location and physical conditions suggest that the IELR originates from the inner surface of the dusty torus. In the spectrum of this quasar, we identified only one narrow absorption-line system associated with the dusty material. With the aid of photo-ionization model calculations, we found that the obscuring material might originate from an outer region of the dusty torus. We speculate that the dusty torus, which is exposed to the central ionizing source, may produce IELs through photo-ionization processes, while also obscure BELs as a natural "coronagraph". Such a "coronagraph" could be found in a large number of partially obscured quasars and be a useful tool to study IELRs.

Metallicity of the high-redshift Universe traced by radio galaxies

AbstractWe investigate the metallicity of the narrow line regions (NLRs) of high-z radio galaxies (HzRGs), using new deep optical spectra of 9 HzRGs obtained with FORS2 on VLT and data from the literature. To estimate the metallicity of NLRs we focus on the Civ/Heii and Ciii]/Civ flux ratios. Based on comparison between the observed emission-line flux ratios and the prediction of our photoionization model calculations, we find no significant metallicity evolution in NLRs of HzRGs, up to z ~ 4. We discuss the possibility that massive galaxies had almost completed the major epoch of the star formation in the very high-z universe (z > 5).

Chemical evolution of high-redshift radio galaxies

We present new deep optical spectra of 9 high-z radio galaxies (HzRGs) at z > 2.7 obtained with FORS2 on VLT. These rest-frame ultraviolet spectra are used to infer the metallicity of the narrow-line regions (NLRs) in order to investigate the chemical evolution of galaxies in high-z universe. We focus mainly on the CIV/HeII and CIII]/CIV flux ratios that are sensitive to gas metallicity and ionization parameter. Although the NV emission has been widely used to infer the gas metallicity, it is often too weak to be measured accurately for NLRs. By combining our new spectra with data from the literature, we examine the possible redshift evolution of the NLR metallicity for 57 HzRGs at 1 < z < 4. Based on the comparison between the observed emission-line flux ratios and the results of our photoionization model calculations, we find no significant metallicity evolution in NLRs of HzRGs, up to z ~ 4. Our results imply that massive galaxies had almost completed their chemical evolution at much higher redshift (z > 5). Finally, although we detect strong NV emission lines in 5 HzRGs at z > 2.7, we point out that high NV/HeII ratios are not indicative of high metallicities but correspond to high ionization parameters of gas clouds in NLRs.

Low‐Ionization Emission Regions in Quasars: Gas Properties Probed with Broad Oiand CaiiLines

We have compiled the emission-line fluxes of O I λ8446, O I λ11287, and the near-infrared (IR) Ca II triplet (λ8579) observed in 11 quasars. These lines are considered to emerge from the same gas as do the Fe II lines in the low-ionized portion of the broad emission line region (BELR). The compiled quasars are distributed over wide ranges of redshift (0.06 ⩽ z⩽ 1.08) and of luminosity (–29.8 ⩽ MB ⩽ − 22.1), thus providing a useful sample to investigate the line-emitting gas properties in various quasar environments. The measured line strengths and velocities, as functions of the quasar properties, are analyzed using photoionization model calculations. We found that the flux ratio between the Ca II triplet and O I λ8446 is hardly dependent on the redshift or luminosity, indicating similar gas densities in the emission region from quasar to quasar. On the other hand, a scatter of the O I λ11287/λ8446 ratios appears to imply the diversity of the ionization parameter. These facts invoke a picture of the line-emitting gases in quasars that have similar densities and are located at regions exposed to various ionizing radiation fluxes. The observed O I line widths are found to be remarkably similar over more than 3 orders of magnitude in luminosity, which indicates a kinematically determined location of the emission region and is in clear contrast to the case of H I lines. We also argue about the dust presence in the emission region since the region is suggested to be located near the dust sublimation point at the outer edge of the BELR.

Empirical strong-line oxygen abundance calibrations from galaxies with electron-temperature measurements

Aims. Our aims are to estimate the validity of empirical methods, such as R 23 , R 23 - P, log([N II]/Hα) (N2), log[([O III]/Hβ)/ ([N II]/Hα)] (03N2), and log([S II]/Hα) (S2), and to re-derive (or add) the calibrations of R 23 , N2, 03N2, and S2 indices for oxygen abundances on the basis of a large sample of galaxies with T e -based abundances. Methods. We determined the gas-phase oxygen abundance for a sample of 695 galaxies and H II regions with reliable detections of [O III]4363, using the reliable and direct temperature-sensitive (T e ) method of measuring metallicity. We selected 531 star-forming galaxies from the SDSS-DR4 database with strong emission lines, including [O III]4363 detected at a signal-to-noise ratio higher than 5σ, as well as 164 galaxies and H II regions from the literature with T e measurements. The O/H abundances were derived from a two-zone model for the temperature structure, assuming a relationship between high ionization and low ionization species. Results. We compare our (O/H) Te measurements of the SDSS sample with the abundances obtained by the MPA/JHU group who used multiple strong emission lines and Bayesian techniques (Tremonti et al. 2004). For roughly half of the sample the Bayesian abundances are overestimated ∼0.34 dex, possibly due to the treatment of nitrogen enrichment in the models they used. The R 23 and R 23 - P methods systematically overestimate the O/H abundance by a factor of ∼0.20 dex and ∼0.06 dex, respectively. The N2 index, rather than the 03N2 index, provides more consistent O/H abundances with the T e -method, but with some scatter. The relations of N2, 03N2, and S2 with log(O/H) are consistent with the photoionization model calculations of Kewley & Doptita (2002), but R 23 does not match well. We derive analytical calibrations for O/H from R 23 , N2, 03N2, and S2 indices on the basis of this large sample, including the excitation parameter P as an additional parameter in the N2 calibration. These empirical calibrations are free of the systematic problems inherent in abundance calibrations based on photoionization models. Conclusions. We conclude that the N2, 03N2, and S2 indices are useful indicators for calibrating metallicities of galaxies with 12 + log(O/H) < 8.5 and that the R 23 index works well for the metal-poor galaxies with 12+log(O/H) < 7.9. For the intermediate metallicity range (7.9 < 12 + log(O/H) < 8.4), the R 23 and R 23 - P methods are unreliable for characterizing the O/H abundances.

Long-term optical photometric monitoring of the quasar SDSS J153259.96−003944.1

We report optical Cousins R- and I-band monitoring observations of the high-redshift (z = 4.67) quasi-stellar object (QSO) SDSS J 153259.96-003944.1 which does not show detectable emission lines in its optical spectrum. We show this object varies with a maximum amplitude of ∼0.4 mag over 1 yr and 3 months of monitoring. Combined with two other epochs of photometric data available in the literature, we show the object has gradually faded by ∼0.9 mag during the period 1998 June-2001 April. A linear least-squares fit to all available observations gives a slope of ∼0.35 mag yr -1 which translates to ∼1.9 mag yr -1 in the rest frame of the quasar. Such a variability is higher than that typically seen in QSOs but consistent with that of BL Lacs, suggesting that the optical continuum is Doppler boosted. Alternatively, within photometric errors, the observed light curve is also consistent with the object going through a microlensing event. Photoionization model calculations show the mass of the broad line region to be a few tens of M ○. similar to that of low-luminosity Seyfert galaxies, but ∼2 orders of magnitude less than that of luminous quasars. Further frequent photometric/spectroscopic monitoring is needed to support or refute the different alternatives discussed here about the nature of SDSS J153259.96-003944.1.

Subaru High-Dispersion Spectroscopy of the Narrow-Line Region in the Seyfert Galaxy NGC 4151

We report on a study of the forbidden emission-line spectrum of the nearby Seyfert 1.5 galaxy NGC 4151 based on the high-resolution (R ~ 45,000) optical spectrum obtained using the High Dispersion Spectrograph on the Subaru Telescope. The profile parameters, such as the emission-line widths, velocity shifts from the recession velocity of the host galaxy, and asymmetry indexes, for emission lines, including very faint ones such as [Ar IV] ??4712, 4740 and [Fe VI] ??5631, 5677, are investigated. Statistically significant correlations between the measured profile parameters and the critical densities of transitions are found, while there are no meaningful correlations between the profile parameters and the ionization potentials of ions. By comparing the results with photoionization model calculations, we remark that a simple power-law distribution of the gas density that is independent of the radius from the nucleus cannot explain the observed correlation between the emission-line widths and the critical densities of the transitions. Taking into account the additional dense gas component expected to exist in the innermost area of the narrow-line regions, the observed correlations between the emission-line width and the critical density of the transitions can be understood since high critical density emission lines can arise at such relatively inner regions even if their ionization potentials are low. The observed correlation between the blueshift of the emission lines and the critical densities of the ions is also explained if such dense gas clouds located closer to the nucleus have larger outflowing velocities.

The physical properties of the compact star forming region N88A and its neighbourhood in the SMC

We present optical, near-infrared (NIR) images and spectra of the compact, dusty and complex HII region N88A in the SMC. The data were obtained mainly in the visible with the Boller & Chivens (B&C) spectrograph at the ESO 1.5 m telescope and recently with the infrared spectrometer and array camera (ISAAC) at the VLT, around 2m. The NIR observations identified a region emitting in H 2, both in and around the two major components of N88. Using long-slit spectra obtained in the 3600-10 100 A wavelength range we have re-determined the key physical parameters of electron temperature and densities. The spectral type of the complex exciting source of N88A has been classified as an O6-O8 V, using He and H lines in the visible and NIR, with the HeI 1.7m/2.11m line ratio in the K band spectrum, suggesting that N88A is eectively ionized by a source of type<O7 V. However, from reddening correction and the temperature determined by photoionization model calculations, the ionizing source should also contain a very early type O star. A comparison with a recent photometric study shows that the V magnitude of the exciting source of N88A has previously been overestimated. The chemical abundances of He, O, N, Ne, S, and Ar, from emission-line intensities, are also derived. Abundancies are consistent with the average abundances for SMC HII regions.

Iron Is Not Depleted in High-Ionization Nuclear Emission-Line Regions of Active Galactic Nuclei

In order to examine whether or not high-ionization nuclear emission-line regions (HINERs) in narrow-line regions of active galactic nuclei are dusty, we focus on two high-ionization forbidden emission lines, [Fe VII]6087 and [Ne V]3426. We perform photoionization model calculations to investigate possible dependences of the flux ratio of [Fe VII]6087/[Ne V]3426 on various gas properties, in order to investigate how useful this flux ratio to explore the dust abundances in HINERs. Based on our photoionization model calculations, we show that the observed range of the flux ratio of [Fe VII]6087/[Ne V]3426 is consistent with the dust-free models while that is hard to be explained by the dusty models. This suggests that iron is not depleted at HINERs, which implies that the HINERs are not dusty. This results is consistent with the idea that the HINERs are located closer than the dust-sublimation radius (i.e., inner radius of dusty tori) and thus can be hidden by dusty tori when seen from a edge-on view toward the tori, which has been also suggested by the AGN-type dependence of the visibility of high-ionization emission lines.

Is There an Advection‐dominated Accretion Flow in Radio Galaxies with Double‐peaked Balmer Lines?

In order to examine the prediction that the broad-line radio galaxies (BLRGs) with double-peaked Balmer lines harbor an accretion disk characterized by an advection-dominated accretion flow (ADAF) in their nuclei, we investigate narrow emission-line flux ratios of the narrow-line regions which are photoionized by the nuclear continuum radiation. We compile data from the literature and confirm the pioneering work of Eracleous & Halpern that the BLRGs with the double-peaked Balmer emission exhibit larger flux ratios of both [O I]6300/[O III]5007 and [O II]3727/[O III]5007 than the BLRGs without the double-peaked Balmer emission. To examine whether or not these properties are attributed to the difference in the spectral energy distribution (SED) of the ionizing radiation between the BLRGs with and without the double-peaked Balmer emission, we perform photoionization model calculations using two types of input continuum radiation; one has the strong big blue bump which is expected for standard optically-thick accretion disks and another does not exhibit a strong big blue bump as expected for optically-thin ADAFs. We find that the data of the BLRGs with the double-peaked Balmer lines are consistent with the models adopting the SED without a strong big blue bump while the data of the BLRGs without the double-peaked emission lines are well described by the models adopting the SED with a strong big blue bump. On the other hand, the observed differences in the NLR emission is hard to be explain by the difference in the contribution of shocks. These results support the idea that the double-peaked Balmer lines arise at an outer region of an accretion disk which is illuminated by an inner, geometrically-thick ADAF.

Seyfert-Type Dependences of Narrow Emission-Line Ratios and Physical Properties of High-Ionization Nuclear Emission-Line Regions in Seyfert Galaxies

Abstract In order to examine how narrow emission-line flux ratios depend on the Seyfert type, we compiled various narrow emission-line flux ratios of 355 Seyfert galaxies from the literature. We present in this paper that the intensity of the high-ionization emission lines, [Fe VII]$ \lambda6087$, [Fe X]$ \lambda6374$, and [Ne V]$ \lambda3426$, tend to be stronger in Seyfert 1 galaxies than in Seyfert 2 galaxies. In addition to these lines, [O III]$ \lambda4363$ and [Ne III]$ \lambda3869$, whose ionization potentials are not high ($ &amp;lt; 100 \,\mathrm{eV}$), but whose critical densities are significantly high ($ \gtrsim 10^7 \,\mathrm{cm}^{-3}$), also exhibit the same tendency. On the other hand, the emission-line flux ratios among low-ionization emission lines do not show such a tendency. We point out that the most plausible interpretation of these results is that the high-ionization emission lines arise mainly from highly-ionized, dense gas clouds, which are located very close to nuclei, and thus can be hidden by dusty tori. To examine the physical properties of these highly-ionized dense gas clouds, photoionization model calculations were performed. As a result, we find that the hydrogen density and the ionization parameter of these highly-ionized dense gas clouds are constrained to be $ n_\mathrm{H}&amp;gt; 10^6 \,\mathrm{cm}^{-3}$ and $ U &amp;gt; 10^{-2}$, respectively. These lower limits are almost independent both from the metallicity of gas clouds and from the spectral energy distribution of the nuclear ionizing radiation.

The Narrow‐Line Region of Seyfert Galaxies: Narrow‐Line Seyfert 1 Galaxies versus Broad‐Line Seyfert 1 Galaxies

It is known that the spectral energy distribution (SED) of the nuclear radiation of narrow-line Seyfert 1 galaxies (NLS1s) has different shapes with respect to that of ordinary broad-line Seyfert 1 galaxies (BLS1s), particularly in wavelengths of X-ray. This may cause some differences in the ionization degree and the temperature of gas in narrow-line regions (NLRs) between NLS1s and BLS1s. This paper aims to examine whether or not there are such differences in the physical conditions of NLR gas between them. For this purpose, we have compiled the emission-line ratios of 36 NLS1s and 83 BLS1s from the literature. Comparing these two samples, we have found that the line ratios of [O {\sc i}]$\lambda$6300/[O {\sc iii}]$\lambda$5007 and [O {\sc iii}]$\lambda$4363/[O {\sc iii}]$\lambda$5007, which represent the ionization degree and the gas temperature respectively, are statistically indistinguishable between NLS1s and BLS1s. Based on new photoionization model calculations, we show that these results are not inconsistent with the difference of the SED between them. The influence of the difference of SEDs on the highly ionized emission lines is also briefly discussed.

On the Formation of Lithium Emission Lines in Nova Shells

The role of nova outbursts in the galactic lithium production is still controversial. Photoionization model calculations of nova shells are presented in this contribution, aiming to identify the optimal post-outburst phase for detecting lithium emission lines from nova ejecta which may confirm its lithium enhancement. Predictions for the Li I λ6708 Â flux are made as a function of the envelope geometry, its physical parameters and properties of the central ionizing source.

Velocity-Resolved Line Response of the Emission Lines in the High-Luminosity (Mv ≈ −24) Seyfert 1 Galaxy Fairall 9

AbstractA detailed emission-line decomposition has been made from 15 years of observations with the IUE satellite of the highly variable Seyfert 1 galaxy Fairall 9, allowing us to study the line variability as a function of velocity and continuum brightness. The variability over the different velocity domains of the broad lines has been related to the continuum variability over a large wavelength domain from the X-rays to the infrared. Clear delays were established between the redshifted and blueshifted parts of the lines in Lyα and C IV, with the red sides of the lines responding faster with no delay and the blue sides responding with a delay of some 230 days. The observed spectral variability behavior of the continuum has been used as input for photoionization model calculations and the combined constraints from the models and differences for gas at different velocities define the structure and motions in the BLR.

Density condensations in planetary nebulae and the electron temperature

For planetary nebulae, the electron temperature derived from the [O III] line ratio is usually higher than that obtained from the Balmer discontinuity. This discrepancy is generally explained in terms of temperature fluctuations. It is shown here that the [O III] line ratio could lead to a lower value of the temperature if high-density condensations are present in the gas. An analytical formalism is given for the correction factors for ionic abundances in the presence of such condensations. Illustrative clump filling factors are deduced for several planetary nebulae recently observed by Liu & Danziger. We discuss the effect of dense clumps on the ionic and chemical abundances, partly based on photoionization model calculations. Accurate observations of [O II] 7325/3727 Å and [S II] 4070/6725 Å line ratios provide a diagnostic of the presence of dense clumps.

IUE spectra and optical imaging of the oxygen-rich supernova remnant N132D

We present new optical Charge Coupled Devices (CCD) interference filter imagery and International Ultraviolet Explorer (IUE) spectroscopy for the oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. The optical images show a wealth of structure, and comparison with an archival Einstein High Resolution Imager (HRI) X-ray image shows that a few optical features have X-ray counter-parts, but in general there is little correlation between X-ray and optical features. The IUE spectra at two positions show strong lines of carbon and oxygen, with lines of neon, magnesium, silicon, and helium also present and variable in relative intensities. We use optical data for N132D from Dopita & Tuohy (1984) with our UV observations to compare with shock models (both with and without thermal conduction) and X-ray photoionization model calculations. While none of the model fits is entirely satisfactory, the generally weak UV emission relative to optical disagrees with the general character of shock model predictions and indicates that photoionization is the dominant excitation mechanism for the UV/optical emission. This conclusion is similar to what was found for E0102 - 7219, the oxygen-rich remnant in the Small Magellanic Cloud. We derive rough abundances for the emitting material in N132D, compare to stellar nucleosynthesis models, and discuss the implications for its precursor. A precursor near 20 solar mass is consistent with the data.

CNO abundances and temperature fluctuations in the Orion Nebula

The largest UV-optical data base to date of the Orion Nebula has been assembled, and the CNO abundances their distribution at a statistically significant number of positions to the north and west of the Trapezium and out to a distance of 5 arcmin has been examined. The forbidden O III temperature increases with distance from Theta1 Ori C while the forbidden N II temperature decreases with increasing distance. The density decreases as a function of increasing distance from Theta1 Ori C. The C/H, N/H, O/H, and C/O distributions are constant across the inner 5 arcmin of the northwestern quadrant of the nebula. The empirically determined mean C/H abundance calculated from UV lines is almost a factor of two lower in the number density than earlier estimates. Photoionization model calculations are consistent with a solar abundance for N/H and O/H.

N III line emission in planetary nebulae - Continuum fluorescence

Kastner & Bhatia have recently pointed out that the optical «Bowen» N III emission lines are not produced by Bowen fluorescence in a sample of planetary nebulae. Here I point out that the lines are likely to be excited by direct continuum fluorescence. Photoionization model calculations with an improved treatment of line-continuum fluorescence are presented. The predicted intensity of N III λ4634 is in good agreement with observations