Martijn de Kool

Keck HIRES Observations of the QSO FIRST J104459.6+365605: Evidence for a Large-Scale Outflow

This paper presents an analysis of a Keck HIRES spectrum of the QSO FIRST J104459.6+365605, covering the rest wavelength range from 2260 to 2900 A. The line of sight toward the QSO contains two clusters of outflowing clouds that give rise to broad blue-shifted absorption lines. The outflow velocities of the clouds range from -200 to -1200 km s-1 and from -3400 to -5200 km s-1, respectively. The width of the individual absorption lines ranges from 50 to more than 1000 km s-1. The most prominent absorption lines are those of Mg II, Mg I, and Fe II, and Mn II is also present. The low-ionization absorption lines occur at the same velocities as the most saturated Mg II lines, showing that the Fe II, Mg I, and Mg II line-forming regions must be closely associated. Many absorption lines from excited states of Fe II are present, allowing a determination of the population of several low-lying energy levels. The populations of the excited levels are found to be considerably smaller than expected for LTE and imply an electron density in the Fe II line-forming regions of ne ~ 4 × 103 cm-3. Modeling the ionization state of the absorbing gas with this value of the electron density as a constraint, we find that the distance between the Fe II and Mg I line-forming region and the continuum source is ~7 × 102 pc. From the correspondence in velocity between the Fe II, Mg I, and Mg II lines we infer that the Mg II lines must be formed at the same distance. The Mg II absorption fulfills the criteria for broad absorption lines defined by Weymann and coworkers. Therefore, the distance we find between the Mg II line-forming region and the continuum source is surprising, since BALs are generally thought to be formed in outflows at a much smaller distance from the nucleus.

Keck HIRES Spectroscopy of the Fe II Low-Ionization Broad Absorption Line Quasar FBQS 0840+3633: Evidence for Two Outflows on Different Scales*

A Keck echelle spectrum of the quasar FBQS 0840+3633 reveals outflowing gas that gives rise to blueshifted absorption lines of many low-ionization species. The gas covers a range of velocities from -700 to -3500 km s-1, with two main components centered at -900 and -2800 km s-1. The physical conditions in the two main velocity components are found to be significantly different and can be attributed to a difference of a factor of ~100 in the distance from the central continuum source. The low-velocity gas shows absorption lines from excited states with relative strengths that indicate a low density. The level populations of low-lying Ni II, Si II, and Fe II states cannot be explained with a model based on collisional excitation and a single electron density. The lines of Si II provide an upper limit on the electron density of ne < 500 cm-3, and another excitation mechanism must be responsible for the observed excitation of Fe II and Ni II. Assuming that this mechanism is UV fluorescence leads to an estimate of the distance between the low-velocity gas and the active nucleus of ~230 pc. Absorption lines from excited states formed in the high-velocity gas indicate a much higher density. This gas gives rise to Fe III and strong Al III absorption, which indicates that it contains the hydrogen ionization front on our line of sight to the active nucleus. The observed Fe III and Al III column densities and the absence of detectable absorption from the He I 23S state allow us to derive an estimate of the typical distance between the high-velocity gas and the active nucleus of ~1 pc.

THE EFFECTS OF INHOMOGENEOUS ABSORBERS ON THE FORMATION OF INTRINSIC QUASAR ABSORPTION LINES

We investigate the formation of absorption lines in an inhomogeneous medium covering an extended source, in the context of intrinsic quasar (QSO) absorption lines. We first describe a simple formalism to model the effect of having a range of column densities in front of the source. It is shown that if the probability distribution of column densities is a power law with index p, the remaining flux in a line in which the medium is very optically thick scales as τ-(p+1), where τ is the maximum optical depth in front of the source. This power-law behavior appears to give a better description of the observed relation between optical depth and flux near the bottom of strong intrinsic QSO absorption lines than the standard exponential behavior. The formalism provides an alternative to the model that assumes partial homogeneous covering, which is the current standard in the interpretation of intrinsic QSO absorption lines that do not show exponential behavior, and in some respects provides a better fit to the observed line strengths. We show that inhomogeneous covering can lead to an apparent velocity-dependent covering factor if the partial homogeneous covering model is applied to doublet lines. The covering factor derived from a partial homogeneous covering analysis does, however, yield information on the characteristics of the column density distribution, such as the sharpness of the edges and peaks. We apply the inhomogeneous covering formalism to two observed QSO absorption-line systems to demonstrate these effects.

Intrinsic Absorption in the QSO FIRST J121442.3+280329

This paper presents an analysis of a Keck HIRES spectrum of the QSO FIRST J121442.3+280329, covering the rest wavelength range from 2300 to 3500 A. The line of sight toward this quasar (QSO) contains an outflow giving rise to many blueshifted absorption lines. The outflow consists of material with a continuous range of velocities from -1200 to -2800 km s-1. Significant substructure is present in the absorption line profiles. The spectrum is dominated by absorption lines of Mg II and the singly ionized iron group elements Fe II, Cr II, and Mn II, including absorption lines from excited levels with energies above 30,000 cm-1 (~4 eV).We derive constraints on the physical conditions in the outflow by fitting a model to the observed spectrum that simultaneously optimizes the values for the column densities of all species, the excitation temperature, the shape of the unabsorbed continuum, and the covering factor. By comparing these constraints with ionization models, we conclude that the ionization parameter, density, and column density of the outflow is characterized by -2.0 < log U < -0.7, 7.5 < log nH < 9.5, and 21.4 < log NH < 22.2. These values place the absorbing outflow at a distance between 1 and 30 pc from the QSO core.

Thermal Evolution of the Envelope of SN 1987A

We model the heating and cooling processes in the hydrogen- and helium-rich zones of the envelope of SN 1987A from t = 200 to 1200 days after outburst and use these results to calculate the light curves of the most prominent emission lines. For the first 600 days, heating and cooling processes are in equilibrium. The main heating mechanism is direct heat deposition by nonthermal electrons, and the main cooling mechanism is collisional excitation of trace elements such as Ca II, Fe II, and C I, followed by the emission of a line photon. After 600 days adiabatic cooling becomes important, and the cooling and heating rates are no longer in equilibrium. Dust, formed in the Fe/Co/Ni zone after t ~ 400 days, plays an important role in the formation of the emission lines. It both modifies the internal UV radiation field that excites the ions and reduces the escaping line fluxes by extinction. The pseudocontinuum opacity in the envelope due to the many absorption lines of metals, which we model crudely by a simple power law, is also important for the emerging spectrum. Our results for the temperature evolution do not depend strongly on our assumptions. We find that the temperatures of the hydrogen and helium zones evolve from T ? 6000 K at t = 200 days to T ? 1000 K at t = 1200 days. The ionized fraction of hydrogen evolves from xH ? 6 ? 10-3 at t = 200 days to xH ? 3 ? 10-4 at t = 1200 days. With abundances determined from observations of the circumstellar ring, the model can account for the light curves of most strong emission lines of H I, He I, Ca II, and Fe II, but some discrepancies remain. Especially interesting is the H? light curve, which exhibits a clear plateau when H? is still optically thick, but Pa? is already optically thin. In all our models this phase appears to occur later than in the observations. For t 800 days, the infrared emission lines of Fe II are produced mainly by primordial iron in the H/He envelope, not by newly synthesized iron. The fluxes of C I and O I lines that our model predicts are much higher than observed, and they may require a significant adjustment in abundance or mass of the different composition zones to make them agree with observations. Our models also indicate that the total helium mass in the core of the remnant (v < 2500 km s-1) must lie in the range 2-5 M?. The hydrogen mass in the core is less well constrained, because the hydrogen line strength does not vary much as long as most of the nonthermal energy is deposited in hydrogen. The ratio of the fluxes of the Br? and the He I 2.058 ?m lines is slightly more sensitive, and it indicates a helium mass-to-hydrogen mass ratio ~ 1:2.