Fred Hamann

This paper discusses the detection of P V 1118,1128 and other broad absorption lines (BALs) in archival HST spectra of the low-redshift BALQSO, PG 1254+047. The P V identification is secured by excellent redshift and profile coincidences with the other BALs, such as C IV 1548,1550 and Si IV 1393,1403, and by photoionization calculations showing that other lines near this wavelength, e.g. Fe III 1123, should be much weaker than P V. The observed BAL strengths imply that either 1) there are extreme abundance ratios such as [C/H] >~ +1.0, [Si/H] >~ +1.8 and [P/C] >~ +2.2, or 2) at least some of the lines are much more optically thick than they appear. I argue that the significant presence of P V absorption indicates severe line saturation, which is disguised in the observed (moderate-strength) BALs because the absorber does not fully cover the continuum source(s) along our line(s) of sight. Computed optical depths for all UV resonance lines show that the observed BALs are consistent with solar abundances if 1) the ionization parameter is at least moderately high, log U >~ -0.6, 2) the total hydrogen column density is log N_H(cm-2) >~ 22.0, and 3) the optical depths in strong lines like C IV and O VI 1032,1038 are >~25 and >~80, respectively. These optical depths and column densities are at least an order of magnitude larger than expected from the residual intensities in the BAL troughs, but they are consistent with the large absorbing columns derived from X-ray observations of BALQSOs. The outflowing BALR, at velocities from -15,000 to -27,000 km/s in PG 1254+047, is therefore a strong candidate for the X-ray absorber in BALQSOs

Ne VIII λ774 is an important tracer of the high-ionization gas in QSOs. We examine the Ne VIII emission-line properties using new Hubble Space Telescope (HST)-FOS spectra of four sources, mean spectra derived from two QSO samples in the HST archives, and new photoionization calculations. The results support our previous claim that broad Ne VIII lines are common in QSOs, with an average flux of ~42% of O VI λ1034 and velocity widths that are ~2 to 5 times larger than O VI, C IV λ1549 and other broad lines in the same spectra. The strongest and most reliably measured Ne VIII λ774 lines (in two sources) have FWHM ~14,500 km s^-1. Line profile fits in these cases show that the unusually large widths might be caused by blending with emission from N IV λ765 and O IV λ789. However, standard photoionization calculations indicate that N IV, O IV, and all other lines near this wavelength should be too weak, leaving (very broad) Ne VIII as the only viable identification for the ~774 Å feature. (This conclusion might be avoided if there are large radial velocity dispersions [ 1000 km s^-1] in the emitting region, and the resonant absorption of continuum photons enhances the flux in weaker lines.) The calculations also indicate that the Ne VIII-emitting regions have ionization parameters in the range 5 U 30, total hydrogen column densities of 10²² N_H 3 × 10²³ cm^-2, and an average covering factor of 30% (for solar abundances and a nominal QSO continuum shape). The Ne VIII-emitting region is therefore more extensive, more highly ionized, and has much higher velocities than the rest of the broad emission line region (BELR). This highly ionized BELR component would be a strong X-ray "warm" absorber if it lies along our line of sight to the X-ray continuum source.

This paper discusses the detection of P V 1118,1128 and other broad absorption lines (BALs) in archival HST spectra of the low-redshift BALQSO, PG 1254+047. The P V identification is secured by excellent redshift and profile coincidences with the other BALs, such as C IV 1548,1550 and Si IV 1393,1403, and by photoionization calculations showing that other lines near this wavelength, e.g. Fe III 1123, should be much weaker than P V. The observed BAL strengths imply that either 1) there are extreme abundance ratios such as [C/H] >~ +1.0, [Si/H] >~ +1.8 and [P/C] >~ +2.2, or 2) at least some of the lines are much more optically thick than they appear. I argue that the significant presence of P V absorption indicates severe line saturation, which is disguised in the observed (moderate-strength) BALs because the absorber does not fully cover the continuum source(s) along our line(s) of sight. Computed optical depths for all UV resonance lines show that the observed BALs are consistent with solar abundances if 1) the ionization parameter is at least moderately high, log U >~ -0.6, 2) the total hydrogen column density is log N_H(cm-2) >~ 22.0, and 3) the optical depths in strong lines like C IV and O VI 1032,1038 are >~25 and >~80, respectively. These optical depths and column densities are at least an order of magnitude larger than expected from the residual intensities in the BAL troughs, but they are consistent with the large absorbing columns derived from X-ray observations of BALQSOs. The outflowing BALR, at velocities from -15,000 to -27,000 km/s in PG 1254+047, is therefore a strong candidate for the X-ray absorber in BALQSOs.

NeVIII 774 is an important tracer of the high-ionization gas in QSOs. We examine the NeVIII emission-line properties using new HST-FOS spectra of four sources, mean spectra derived from two QSO samples in the HST archives, and new photoionization calculations. The results support our previous claim that broad NeVIIIlines are common in QSOs, with an average flux of ~42% of OVI 1034 and velocity widths that are ~2 to 5 times larger than OVI, CIV 1549 and other broad lines in the same spectra. The strongest and most reliably measured NeVIII 774 lines (in two sources) have FWHM ~ 14,500 km/s. Line profile fits in these cases show that the unusually large widths might be caused by blending with emission from NIV 765 and OIV~\lam 789. However, standard photoionization calculations indicate that NIV, OIV and all other lines near this wavelength should be too weak, leaving (very broad) NeVIII as the only viable identification for the ~774 A feature. (This conclusion might be avoided if there are large radial velocity dispersions [>~1000 km/s] in the emitting region and the resonant absorption of continuum photons enhances the flux in weaker lines.) The calculations also indicate that the NeVIII emitting regions have ionization parameters in the range 5 > U > 30, total hydrogen column densities of 10^22 < N_H < 3 x 10^23 cm-2, and an average covering factor of >30% (for solar abundances and a nominal QSO continuum shape). The NeVIII emitting region is therefore more extensive, more highly ionized, and has much higher velocities than the rest of the broad emission line region (BELR). This highly-ionized BELR component would be a strong X-ray ``warm'' absorber if it lies along our line-of-sight to the X-ray continuum source.

We use new UV and optical spectra and an archival Hubble Space Telescope Wide Field Planetary Camera 2 (HST-WFPC2) image to study the z_a ≈ z_e absorber in the z_e ≈ 0.20 QSO PKS 2135-147. The UV spectra, obtained with the Faint Object Spectrograph on HST, show strong z_a ≈ z_e absorption lines of C IV, N V, O VI, Lyα, and Lyβ. The z_a ≈ z_e line profiles are resolved, with deconvolved FWHM of 270-450 km s^-1. The Lyman decrement and the O VI and N V doublet ratios indicate that there are also narrower, optically thick line components, and there is evidence in the C IV and Lyα profiles for two blended components. Lower limits on the total column densities are of order 10¹⁵ cm^-2 for all ions. The ~2:1 ratio of the C IV doublets suggests that the total C IV column density is near the lower limit. If the absorber is photoionized by the QSO and the derived relative columns in C IV and H I are roughly correct, then the metallicity must be at least solar. The location of the z_a ≈ z_e absorber remains uncertain. The line redshifts indicate that the clouds have little radial motion (less than ±200 km s^-1) with respect to the QSO. This small velocity shift could mean that the absorber is outside of the deep gravitational potential of the QSO and the host-galaxy nucleus. Two ~L_* galaxies in a small cluster centered on PKS 2135-147 lie within 36 h^-1 kpc projected distance and have redshifts consistent with causing or contributing to the z_a ≈ z_e lines. The extensive halo of the QSO's host galaxy could also contribute. Calculations show that the QSO is bright enough to photoionize gas up to O VI in the low-density halos of the host and nearby cluster galaxies. Nonetheless, there is indirect evidence for absorption much nearer the QSO, namely (1) the derived high (albeit uncertain) metallicity; (2) the relatively strong N V absorption lines, which might be caused by a higher nitrogen abundance in the metal-rich gas; and (3) strong, lobe-dominated, steep-spectrum radio emission, which is known to correlate with a much higher incidence of (probably intrinsic) z_a ≈ z_e lines. We propose that the C IV/N V/O VI line ratios can be used as a general diagnostic of intrinsic versus intervening absorption, as long as the line saturation effects are understood.

We use new UV and optical spectra and an archival HST-WFPC2 image to study the z_a~z_e absorber in the z_e = 0.20 QSO PKS 2135-147. The UV spectra, obtained with HST-FOS, show strong z_a~z_e absorption lines of C IV, N V, O VI, Ly-alpha and Ly-beta. The z_a~z_e line profiles are resolved, with deconvolved FWHM of 270 to 450 km/s. Lower limits on the total column densities are of order 10^15 cm-2 for all ions. If the absorber is photoionized by the QSO and the derived relative columns in C IV and H I are roughly correct, then the metallicity must be at least solar. The location of the z_a~z_e absorber remains uncertain. Two ~L_* galaxies in a small cluster centered on PKS 2135-147 lie within 36h^{-1} kpc projected distance and have redshifts consistent with causing or contributing to the z_a~z_e lines. The extensive halo of the QSO's host galaxy could also contribute. Calculations show that the QSO is bright enough to photoionize gas up to O VI in the low-density halos of the host and nearby cluster galaxies. Nonetheless, there is indirect evidence for absorption much nearer the QSO, namely (1) the derived high (albeit uncertain) metallicity, (2) the relatively strong N V absorption lines, which might be caused by a higher nitrogen abundance in the metal-rich gas, and (3) strong, lobe-dominated steep-spectrum radio emission, which is known to correlate with a much higher incidence of (probably intrinsic) z_a~z_e lines. We propose that the CIV/NV/OVI line ratios can be used as a general diagnostic of intrinsic versus intervening absorption, as long as the line saturation effects are understood.

This paper provides a general reference for deriving the ionizations and metal abundances for absorption-line clouds in photoionization equilibrium with a QSO spectrum. The results include a quantitative assessment of the theoretical uncertainties and firm lower limits on the metallicities when no ionization constraints are available. The calculations applied to the best available column densities for QSO intrinsic absorbers support previous studies; there is strong evidence for super-solar metallicities in broad absorption line (BAL) and at least some ``associated'' (z_a~z_e) absorption regions. Even in cases where the level of ionization is unknown (for example, when only H I and C IV lines are measured), firm lower limits on the metal abundances (C/H) imply Z ~> Z_o for typical BALs and some z_a~z_e absorbers. These results support the independent evidence for high metallicities in QSO broad emission-line regions. I argue that high gas-phase abundances, up to ~10 Z_o, can be expected in QSOs due to the normal enrichment by stars in the cores of young, massive (~> 10^11 M_o) galaxies. The measured column densities indicate that the gas is usually optically thin in the continuum out to energies above at least the CIV and NV ionization edges (i.e. >100 eV). The column density ratios often require a range of ionization states in the same absorber, and neighboring (blended or adjacent) systems can have ionization parameters that differ by more than an order of magnitude. These result, and the overall levels of ionization, are not consistent with single-zone models of the UV line and X-ray continuum (``warm'') absorbers.

This paper provides a general reference for deriving the ionizations and metal abundances for absorption-line clouds in photoionization equilibrium with a QSO spectrum. The results include a quantitative assessment of the theoretical uncertainties and firm lower limits on the metallicities when no ionization constraints are available. The calculations applied to the best available column densities for QSO intrinsic absorbers support previous studies; there is strong evidence for super-solar metallicities in broad absorption line (BAL) and at least some "associated" (z_a ≈ z_e) absorption regions. Even in cases where the level of ionization is unknown (e.g., when only H I and C IV lines are measured), firm lower limits on the metal abundances (C/H) imply Z Z_☉ for typical BALs and some z_a ≈ z_e absorbers. These results support the independent evidence for high metallicities in QSO broad emission line regions. I argue that high gas-phase abundances, up to ~10 Z_☉, can be expected in QSOs because of the normal enrichment by stars in the cores of young, massive ( 10¹¹ M_☉) galaxies. The measured column densities in intrinsic absorbers also indicate that the gas is usually optically thin in the H I Lyman continuum out to energies above at least the C IV and N V ionization edges (i.e., 100 eV). The column density ratios often require a range of ionization states in the same absorber. Neighboring z_a ≈ z_e systems (having similar redshifts and often blended spectroscopically) also usually require different ionizations or metal abundances. If the abundances are similar in neighboring systems, their ionization parameters must sometimes differ by more than an order of magnitude, requiring a significant range of densities and/or distances from the ionizing QSO. These results, and the overall levels of ionization, are not consistent with single-zone models of the UV line and X-ray continuum ("warm") absorbers.