Matt L. Lykins

Atomic Data for S II—Toward Better Diagnostics of Chemical Evolution in High-redshift Galaxies

Absorption-line spectroscopy is a powerful tool used to estimate element abundances in both the nearby and distant universe. The accuracy of the abundances thus derived is naturally limited by the accuracy of the atomic data assumed for the spectral lines. We have recently started a project to perform new extensive atomic data calculations used for optical/UV spectral lines in the plasma modeling code Cloudy using state of the art quantal calculations. Here, we demonstrate our approach by focussing on S II, an ion used to estimate metallicities for Milky Way interstellar clouds as well as distant damped Lyman-alpha (DLA) and sub-DLA absorber galaxies detected in the spectra of quasars and gamma-ray bursts. We report new extensive calculations of a large number of energy levels of S II, and the line strengths of the resulting radiative transitions. Our calculations are based on the configuration interaction approach within a numerical Hartree-Fock framework, and utilize both non-relativistic and quasirelativistic one-electron radial orbitals. The results of these new atomic calculations are then incorporated into Cloudy and applied to a lab plasma, and a typical DLA, for illustrative purposes. The new results imply relatively modest changes (0.04 dex) to the metallicities estimated from S II in past studies. These results will be readily applicable to other studies of S II in the Milky Way and other galaxies.

Radiative cooling in collisionally ionized and photoionized plasmas

We discuss recent improvements in the calculation of the radiative cooling in both collisionally and photo ionized plasmas. We are extending the spectral simulation code Cloudy so that as much as possible of the underlying atomic data is taken from external databases, some created by others, some developed by the Cloudy team. This paper focuses on recent changes in the treatment of many stages of ionization of iron, and discusses its extensions to other elements. The H-like and He-like ions are treated in the iso-electronic approach described previously. Fe II is a special case treated with a large model atom. Here we focus on Fe III through Fe XXIV, ions which are important contributors to the radiative cooling of hot (T 10 5 10 7 K) plasmas and for X-ray spectroscopy. We use the Chianti atomic database to greatly expand the number of transitions in the cooling function. Chianti only includes lines that have atomic data computed by sophisticated methods. This limits the line list to lower excitation, longer wavelength, transitions. We had previously included lines from the Opacity Project database, which tends to include higher energy, shorter wavelength, transitions. These were combined with various forms of the “g-bar” approximation, a highly approximate method of estimating collision rates. For several iron ions the two databases are almost entirely complementary. We adopt a hybrid approach in which we use Chianti where possible, supplemented by lines from the Opacity Project for shorter wavelength transitions. The total cooling including the lightest thirty element differs from some previous calculations by significant amounts.

Stout: Cloudy's Atomic and Molecular Database

We describe a new atomic and molecular database we developed for use in the spectral synthesis code Cloudy. The design of Stout is driven by the data needs of Cloudy, which simulates molecular, atomic, and ionized gas with kinetic temperatures and densities spanning the low-to high-density limits. The radiation field between photon energies 10−8 Ry and 100 MeV is considered, along with all atoms and ions of the lightest 30 elements, and ~102 molecules. For ease of maintenance, the data are stored in a format as close as possible to the original data sources. Few data sources include the full range of data we need. We describe how we fill in the gaps in the data or extrapolate rates beyond their tabulated range. We tabulate data sources both for the atomic spectroscopic parameters and for collision data for the next release of Cloudy. This is not intended as a review of the current status of atomic data, but rather a description of the features of the database which we will build upon.

Expanded Iron UTA Spectra--Probing the Thermal Stability Limits in AGN Clouds

The Fe unresolved transition arrays (UTAs) produce prominent features in the {approx}15-17 A wavelength range in the spectra of active galactic nuclei (AGNs). Here, we present new calculations of the energies and oscillator strengths of inner-shell lines from Fe XIV, Fe XV, and Fe XVI. These are crucial ions since they are dominant at inflection points in the gas thermal stability curve, and UTA excitation followed by autoionization is an important ionization mechanism for these species. We incorporate these, and data reported in previous papers, into the plasma simulation code Cloudy. This updated physics is subsequently employed to reconsider the thermally stable phases in absorbing media in AGNs. We show how the absorption profile of the Fe XIV UTA depends on density, due to the changing populations of levels within the ground configuration.

ATOMIC DATA FOR ZN II: IMPROVING SPECTRAL DIAGNOSTICS OF CHEMICAL EVOLUTION IN HIGH-REDSHIFT GALAXIES

Damped Lyman-alpha (DLA) and sub-DLA absorbers in quasar spectra provide the most sensitive tools for measuring element abundances of distant galaxies. Estimation of abundances from absorption lines depends sensitively on the accuracy of the atomic data used. We have started a project to produce new atomic spectroscopic parameters for optical/UV spectral lines using state-of-the-art computer codes employing very broad configuration interaction basis. Here we report our results for Zn II, an ion used widely in studies of the interstellar medium (ISM) as well as DLA/sub-DLAs. We report new calculations of many energy levels of Zn II, and the line strengths of the resulting radiative transitions. Our calculations use the configuration interaction approach within a numerical Hartree-Fock framework. We use both non-relativistic and quasi-relativistic one-electron radial orbitals. We have incorporated the results of these atomic calculations into the plasma simulation code Cloudy, and applied them to a lab plasma and examples of a DLA and a sub-DLA. Our values of the Zn II {\lambda}{\lambda} 2026, 2062 oscillator strengths are higher than previous values by 0.10 dex. Cloudy calculations for representative absorbers with the revised Zn atomic data imply ionization corrections lower than calculated before by 0.05 dex. The new results imply Zn metallicities should be lower by 0.1 dex for DLAs and by 0.13-0.15 dex for sub-DLAs than in past studies. Our results can be applied to other studies of Zn II in the Galactic and extragalactic ISM.

Hydrogen two-photon continuum emission from the Horseshoe filament in NGC 1275

Far ultraviolet emission has been detected from a knot of Ha emission in the Horseshoe filament, far out in the NGC 1275 nebula. The flux detected relative to the brightness of the Ha line in the same spatial region is very close to that expected from Hydrogen twophoton continuum emission in the particle heating model of Ferland et al. (2009) if reddening internal to the filaments is taken into account. We find no need to invoke other sources of far ultraviolet emission such as hot stars or emission lines from CIV in intermediate temperature gas to explain these data.

Implications of coronal line emission in NGC 4696

We announce a new facility in the spectral code CLOUDY that enables tracking the evolution of a cooling parcel of gas with time. For gas cooling from temperatures relevant to galaxy clusters, earlier calculations estimated the [Fe XIV] λ 5303 / [Fe X] λ 6375 luminosity ratio, a critical diagnostic of a cooling plasma, to slightly less th an unity. By contrast, our calculations predict a ratio ∼3. We revisit recent optical coronal line observations alon g the X-ray cool arc around NGC 4696 by Canning et al. (2011), which detected [Fe X] λ 6375, but not [Fe XIV] λ 5303. We show that these observations are not consistent with predictions of cooling flow models. Differential extinction could in principle accoun t for the observations, but it requires extinction levels (AV > 3.625) incompatible with previous observations. The non-detection of [Fe XIV] implies a temperature ceiling of 2.1 million K. Assuming cylindrical geometry and transonic turbulent pressure support, we estimate the gas mass at ∼1 million M⊙. The coronal gas is cooling isochorically. We propose that the coronal gas has not condensed out of the intracluster medium, but instead is the conductive or mixing interface between the X-ray plume and the optical filaments. We present a number of emissi on lines that may be pursued to test this hypothesis and constrain the amount of intermediate temperature gas in the system.

Physical Conditions in Orion's Veil. III. UV Iron Absorption Lines toward θ1B Orionis

We have used archival Space Telescope Imaging Spectrograph (STIS) data in the range 2100-2500 A toward the Trapezium star Θ1 B Orionis (HD 37021) to estimate the Fe column density and other parameters in the neutral Veil of Orion. The Veil lies 1-3 pc in front of the Orion H+ region, it has an estimated volume density of 102.5-3.5 cm–3, and its H° column density has been previously measured via the STIS-observed Lyα line. We find N(Fe)/N(H°) = 4.4 ± 1.3 × 10–7, implying a log depletion of –1.81 ± 0.13 relative to solar. Our estimate of N(Fe) comes from direct integration of the moderate optical depth Fe II λ2249 and λ2260 lines. From this analysis, we are also able to estimate empirically new values for the oscillator strengths of the low optical depth Fe II λ2234 and λ2367 lines. N(Fe)/N(H) in the Veil is consistent with the most recent estimates of this ratio for the main Orion H+ region. Therefore, there is no evidence that significant Fe has been released from grains into the gaseous state in the H+ region via grain destruction processes. The Fe/H ratio in the Veil is also comparable to other Fe/H measurements made in the diffuse interstellar medium for lower density gas. Therefore, the present result suggests that depletion is not strongly correlated with local gas density at least up to n ≈ 103 cm–3. Finally, we have identified several outlying velocity components in some of the Fe II line profiles, components that have been previously identified in optical Ca II and Na I line profiles. These outlying velocity components are probably small concentrations of cold neutral material lying tens of pc or more in front of the Veil and unrelated to it.

Accurate determination of the free–free Gaunt factor – I. Non-relativistic Gaunt factors

Modern spectral synthesis codes need the thermally averaged free-free Gaunt factor dened over a very wide range of parameter space in order to produce an accurate prediction for the spectrum emitted by an ionized plasma. Until now no set of data exists that would meet this need in a fully satisfactory way. We have therefore undertaken to produce a table of very accurate non-relativistic Gaunt factors over a much wider range of parameters than has ever been produced before. We rst produced a table of non-averaged Gaunt factors, covering the parameter space 10 log i = 20 to +10 and 10 logw = 30 to +25. We then continued to produce a table of thermally averaged Gaunt factors covering the parameter space 10 log 2 = 6 to +10 and 10 logu = 16 to +13. Finally we produced a table of the frequency integrated Gaunt factor covering the parameter space 10 log 2 = 6 to +10. All the data presented in this paper are

Radiative Cooling II: Effects of Density and Metallicity

This work follows Lykins et al. discussion of classic plasma cooling function at low density and solar metallicity. Here we focus on how the cooling function changes over a wide range of density (n_H<10^12 cm^(-3)) and metallicity (Z<30Z _sun ). We find that high densities enhance the ionization of elements such as hydrogen and helium until they reach local thermodynamic equilibrium. By charge transfer, the metallicity changes the ionization of hydrogen when it is partially ionized. We describe the total cooling function as a sum of four parts: those due to H&He, the heavy elements, electron-electron bremsstrahlung and grains. For the first 3 parts, we provide a low-density limit cooling function, a density dependence function, and a metallicity dependence function. These functions are given with numerical tables and analytical fit functions. For grain cooling, we only discuss in ISM case. We then obtain a total cooling function that depends on density, metallicity and temperature. As expected, collisional de-excitation suppresses the heavy elements cooling. Finally, we provide a function giving the electron fraction, which can be used to convert the cooling function into a cooling rate.