Ionization Parameter Log Research Articles

COSMIC ORIGINS SPECTROGRAPH ANDFUSEOBSERVATIONS OFT∼ 105K GAS IN A NEARBY GALAXY FILAMENT

We present a detection of a broad Ly-alpha absorber (BLA) with a matching O VI line in the nearby universe. The BLA is detected at z = 0.01028 in the high S/N spectrum of Mrk 290 obtained using the Cosmic Origins Spectrograph. The Ly-alpha absorption has two components, with b(HI) = 55 +/- 1 km/s and b(HI) = 33 +/- 1 km/s, separated in velocity by v ~ 115 km/s. The O VI, detected by FUSE at z = 0.01027, has a b(OVI) = 29 +/- 3 km/s and is kinematically well aligned with the broader HI component. The different line widths of the BLA and OVI suggest a temperature of T = 1.4 x 10^5 K in the absorber. The observed line strength ratios and line widths favor an ionization scenario in which both ion-electron collisions and UV photons contribute to the ionization in the gas. Such a model requires a low-metallicity of -1.7 dex, ionization parameter of log U ~ -1.4, a large total hydrogen column density of N(H) ~ 4 x 10^19 cm^-2, and a path length of 400 kpc. The line of sight to Mrk 290 intercepts at the redshift of the absorber, a megaparsec scale filamentary structure extending over 20 deg in the sky, with several luminous galaxies distributed within 1.5 Mpc projected distance from the absorber. The collisionally ionized gas in this absorber is likely tracing a shock-heated gaseous structure, consistent with a few different scenarios for the origin, including an over-dense region of the WHIM in the galaxy filament or highly ionized gas in the extended halo of one of the galaxies in the filament. In general, BLAs with metals provide an efficient means to study T ~ 10^5 - 10^6 K gas in galaxy halos and in the intergalactic medium. A substantial fraction of the baryons "missing" from the present universe is predicted to be in such environments in the form of highly ionized plasma.

PHYSICAL CONDITIONS IN A YOUNG, UNREDDENED, LOW-METALLICITY GALAXY AT HIGH REDSHIFT

Increasingly large samples of galaxies are now being discovered at redshifts z~5-6 and higher. Many of these objects are inferred to be young, low in mass, and relatively unreddened, but detailed analysis of their high quality spectra will not be possible until the advent of future facilities. In this paper we shed light on the physical conditions in a plausibly similar low mass galaxy by presenting the analysis of the rest-frame optical and UV spectra of Q2343-BX418, an L* galaxy at z=2.3 with a very low mass-to-light ratio and unusual properties: BX418 is young (<100 Myr), low mass (M_star ~ 10^9 Msun), low in metallicity (Z ~ 1/6 Zsun), and unreddened (E(B-V)~0.02, UV continuum slope beta=-2.1). We infer a metallicity 12+log(O/H)=7.9 +/- 0.2 from the rest-frame optical emission lines. We also determine the metallicity via the direct, electron temperature method, using the ratio O III] 1661, 1666/[O III] 5007 to determine the electron temperature and finding 12+ log(O/H)=7.8 +/- 0.1. These measurements place BX418 among the most metal-poor galaxies observed in emission at high redshift. The rest-frame UV spectrum contains strong emission from Lya (with rest-frame equivalent width 54 A), He II 1640 (both stellar and nebular), C III] 1907, 1909 and O III] 1661, 1666. The C IV/C III] ratio indicates that the source of ionization is unlikely to be an AGN. Analysis of the He II, O III] and C III] line strengths indicates a very high ionization parameter log U ~ -1, while Lya and the interstellar absorption lines indicate that outflowing gas is highly ionized over a wide range of velocities. It remains to be determined how many of BX418's unique spectral features are due to its global properties, such as low metallicity and dust extinction, and how many are indicative of a short-lived phase in the early evolution of an otherwise normal star-forming galaxy.

EXPLORING THE ORIGIN AND FATE OF THE MAGELLANIC STREAM WITH ULTRAVIOLET AND OPTICAL ABSORPTION

(Abridged) We present an analysis of ionization and metal enrichment in the Magellanic Stream (MS), the nearest gaseous tidal stream, using HST/STIS and FUSE ultraviolet spectroscopy of two background AGN, NGC 7469 and Mrk 335. For NGC 7469, we include optical spectroscopy from VLT/UVES. In both sightlines the MS is detected in low-ion and high-ion absorption. Toward NGC 7469, we measure a MS oxygen abundance [O/H]_MS=[OI/HI]=-1.00+/-0.05(stat)+/-0.08(syst), supporting the view that the Stream originates in the SMC rather than the LMC. We use CLOUDY to model the low-ion phase of the Stream as a photoionized plasma using the observed Si III/Si II and C III/C II ratios. Toward Mrk 335 this yields an ionization parameter log U between -3.45 and -3.15 and a gas density log (n_H/cm^-3) between -2.51 and -2.21. Toward NGC 7469 we derive sub-solar abundance ratios for [Si/O], [Fe/O], and [Al/O], indicating the presence of dust in the MS. The high-ion column densities are too large to be explained by photoionization, but also cannot be explained by a single-temperature collisional-ionization model (equilibrium or non-equilibrium). This suggests the high-ion plasma is multi-phase. Summing over the low-ion and high-ion phases, we derive conservative lower limits on the ratio N(total H II)/N(H I) of >19 toward NGC 7469 and >330 toward Mrk 335, showing that along these two directions the vast majority of the Stream has been ionized. The presence of warm-hot plasma together with the small-scale structure observed at 21 cm provides evidence for an evaporative interaction with the hot Galactic corona. This scenario, predicted by hydrodynamical simulations, suggests that the fate of the MS will be to replenish the Galactic corona with new plasma, rather than to bring neutral fuel to the disk.

Warm absorber and truncated accretion disc in IRAS 05078+1626

X-ray observations of unabsorbed active galactic nuclei provide an opportunity to explore the innermost regions of supermassive black hole accretion discs. Our goal in this paper is to investigate the central environment of a Seyfert 1.5 galaxy IRAS 05078+1626. We studied the time-averaged spectrum obtained with the EPIC and RGS instruments. A power-law continuum (photon index ~ 1.75) dominates the 2-10 keV energy range. A narrow iron K alpha spectral line is clearly seen, presumably originating in a distant torus, but no broad relativistic component was detected. However, the power law and the iron K alpha line alone do not provide a satisfactory fit in the soft X-ray band whose spectrum can be explained by the combination of three components: a) a cold photoelectric absorber with column density ~ 10^(21) cm^(-2). This gas could be located either in outer parts of the accretion disc, at the rim of the torus or farther out in the host galaxy; b) a warm absorber with high ionization parameter (log(xi) ~ 2.2) and column density ~ 10^(24) cm^(-2); c) an ionized reflection where the reflecting gas could be either in the inner wall of a warm absorber cone or in an ionized accretion disc. The first X-ray spectroscopic measurement of IRAS05078+1626 unveils some of the standard ingredients in Seyfert galaxies, such as a power-law primary continuum, modified by reflection from the accretion disc and by the effect of complex, multi-phase obscuration. However, data constrains the accretion disc, if present, not to extend closer than to 60 gravitational radii from the black hole.

First high-resolution detection of a warm absorber in the Broad Line Radio Galaxy 3C 382

Abstract Recent high-resolution measurements suggest that the soft X-ray spectrum of obscured radio galaxies exhibits signatures of photoionized gas (e.g. 3C 445 and 3C 33) similar to those observed in radio-quiet obscured active galactic nuclei. While signatures of warm absorbing gas covering a wide range of temperature and ionization states have been detected in about one-half of the population of nearby type 1 Seyfert galaxies, no traces of warm absorber gas have been reported to date in the high-resolution spectra of broad-line radio galaxies (BLRG). We present here the first detection of a soft X-ray warm absorber in the powerful Fanaroff–Riley type II BLRG 3C 382 using the Reflection Grating Spectrometer on-board XMM–Newton. The absorption gas appears to be highly ionized, with column density of the order of 1022 cm−2, ionization parameter log ξ &amp;gt; 2 erg cm s−1 and outflow velocities of the order of 103 km s−1. The absorption lines may come from regions located outside the torus, however, at distances less than 60 pc. This result may indicate that a plasma ejected at velocities near the speed of light and a photoionized gas with slower outflow velocities can coexist in the same source beyond the broad-line regions.

QUASAR OUTFLOW CONTRIBUTION TO AGN FEEDBACK: OBSERVATIONS OF QSO SDSS J0838+2955

We present a detailed analysis of the Astrophysical Research Consortium 3.5 m telescope spectrum of QSO SDSS J0838+2955. The object shows three broad absorption line (BAL) systems at 22,000, 13,000, and 4900 km s^-1 blueshifted from the systemic redshift of z=2.043. Of particular interest is the lowest velocity system that displays absorption from low-ionization species such as Mg II, Al II, Si II, Si II*, Fe II and Fe II*. Accurate column densities were measured for all transitions in this lowest velocity BAL using an inhomogeneous absorber model. The ratio of column densities of Si II* and Fe II* with respect to their ground states gave an electron number density of log n_e (cm^-3) = 3.75 +/- 0.22 for the outflow. Photoionization modeling with careful regards to chemical abundances and the incident spectral energy distribution predicts an ionization parameter of log U_H = -1.93 +/- 0.21 and a hydrogen column density of log N_H (cm^-2) = 20.80 +/- 0.28. This places the outflow at 3.3+1.5-1.0 kpc from the central AGN. Assuming that the fraction of solid angle subtended by the outflow is 0.2, these values yield a kinetic luminosity of (4.5+3.1-1.8) x 10^45 erg s^-1, which is (1.4+1.1-0.6)% the bolometric luminosity of the QSO itself. Such large kinetic luminosity suggests that QSO outflows are a major contributor to AGN feedback mechanisms.

Exploring the nuclear environment of the NLS1 galaxy Arakelian 564 with XMM-Newton RGS

We present an accurate characterisation of the high-resolution X-ray spectrum of the Narrow Line Seyfert 1 galaxy Arakelian 564 and put it in to context with other objects of its type by making a detailed comparison of their spectra. The best fit to the data identifies five significant emission lines at 18.9, 22.1, 24.7, 29.0 and 33.5A due O VIII Ly alpha, O VII(f), N VII Ly alpha, N VI(i) and C VI Ly alpha respectively. These have an RMS velocity of ~1100km/s and a flow velocity of ~-600km/s, except for the O VII(f) emission line, which has a flow velocity consistent with zero. Two separate emitting regions are identified. Three separate phases of photoionized, X-ray absorbing gas are included in the fit with ionization parameters log xi=-0.86, 0.87, 2.56 and column densities N_H=0.89, 2.41, 6.03*10^20cm^-2 respectively. All three phases show this to be an unusually low velocity outflow (-10pm100km/s) for a narrow line Seyfert 1. We present the hypothesis that the BLR is the source of the NLR and warm absorber, and examine optical and UV images from the XMM-Newton Optical Monitor to relate our findings to the characteristics of the host galaxy.

Physical and kinematical properties of the X-ray absorber in the broad absorption line quasar APM 08279+5255

Context. We have re-analyzed the X-ray spectra of the gravitational lensed high-redshift BAL QSO APM 08279+5255, observed with the XMM−Newton and Chandra observatories. Previous studies (Hasinger et al. 2002, ApJ, 573, L77; Chartas et al. 2002, ApJ, 579, 169) detected unusual, highly-ionized iron absorption features, but differed in their interpretation of these features, regarding the kinematical and ionization structure. Aims. We seek one physical model that can be successfully applied to both observations. Methods. For the first time we have performed detailed photoionization modeling on the X-ray spectrum of APM 08279+5255. Results. The absorbing gas in APM 08279+5255 can be represented by a two-absorbers model with column densities NH(1) ≈ 7 × 10 22 cm −2 , NH(2) ≈ 6 × 10 22 cm −2 , and ionization parameters log ξ(1) ≈ 1. 5a nd logξ(2) ≈ 3, with one of them (the high-ionization component) outflowing at v ≈ 0.18(±0.01)c, carrying large amount of gas out of the system. We find that the Chandra spectrum of APM 08279+5255 requires the same Fe/O ratio overabundance (previously) indicated by the XMM−Newton observation, showing that both absorber components underwent similar chemical evolution and/or have similar origin.

ChandraLETGS Spectroscopy of the Quasar MR 2251−178 and Its Warm Absorber

We present an analysis of our Chandra Low Energy Transmission Grating Spectrometer (LETGS) observation of the quasar MR 2251–178. The warm absorber of MR 2251–178 is well described by a hydrogen column density NH ≈ 2 × 1021 cm−2 and an ionization parameter log (ξ ) ≈ 0.6. We find in the spectrum weak evidence for narrow absorption lines from carbon and nitrogen which indicate that the ionized material is in outflow. We note changes (in time) of the absorption structure in the band 0.6-1 keV (around the unresolved transition arrays [UTAs] plus the O VII and O VIII K edges) at different periods of the observation. We measure a 0.1-2 keV flux of 2.58 × 10−11 ergs cm−2 s−1. This flux implies that the nuclear source of MR 2251–178 is in a relatively low state. No significant variability is seen in the light curve. We do not find evidence for extra cold material in the line of sight, and set an upper limit of NH ≈ 1.2 × 1020 cm−2. The X-ray spectrum does not appear to show evidence for dusty material, although an upper limit in the neutral carbon and oxygen column densities can only be set to cm−2 and cm−2, respectively.

Unsaturated Low‐Ionization Broad Absorption Lines in the Quasar SDSS J144842.45+042403.1

We present a detailed analysis of the exceptional low-ionization broad absorption line (LoBAL) quasar SDSS J144842.45+042403.1. The C IV absorption trough, which is likely saturated, has a box-shaped bottom at a flux level of 2%-5% of the unabsorbed flux. A large fraction of at least 80% of the C IV and Fe II emission-line fluxes are obliterated by the C IV broad absorption lines (BALs), spanning 3000 km s−1 in velocity. This indicates that the outflow intercepts most of the lines of sight to the continuum source and the broad emission line region (BELR). Therefore, the BAL region (BALR) should be located outside the BELR, and its size is no less than that of the BELR. The Al III and Mg II BAL troughs, which are well resolved, are found to be unsaturated and to show the same velocity structures. Meanwhile, their velocities largely overlap that of the C IV BAL, indicating that the LoBALs and the HiBALs (high-ionization BALs) are closely associated and most likely produced from the same outflow. The column densities of the Mg+ and Al2+ ions in the outflow are measured. Results from an X-ray observation performed with Chandra suggest the presence of intrinsic X-ray absorption with a hydrogen column density of 1022-1023 cm−2. The measured Mg+ and Al2+ column densities can be well reproduced in models with a dimensionless ionization parameter of log U > − 1.5 and a total hydrogen column density of NH = 2.8 × 1022U cm−2. A comparison of models with the observed properties also suggests that the outflow is either very highly ionized (with a high column density) or clumpy.

The Variable Warm Absorber in Circinus X‐1

We observed Circinus X-1 twice during a newly reached low-flux phase near zero orbital phase using the High-Energy Transmission Grating Spectrometer (HETGS) onboard Chandra. In both observations the source did not show the P Cygni lines we observed during the high-flux phases of the source in 2000 and 2001. During the prezero phase the source did not exhibit significant variability but did exhibit an emission-line spectrum rich in H- and He-like lines from high-Z elements such as Si, S, Ar, and Ca. The light curve in the postdip observation showed quiescent and flaring episodes. Only in these flaring episodes was the source luminosity significantly higher than observed during the prezero phase. We analyzed all high-resolution X-ray spectra by fitting photoionization and absorption models from the most recent version of the XSTAR code. The prezero-phase spectrum could be fully modeled with a very hot photoionized plasma with an ionization parameter of log ξ = 3.0, down from log ξ = 4.0 in the high-flux state. The ionization balances we measure from the spectra during the postzero-phase episodes are significantly different. Both episodes feature absorbers with variable high columns, ionization parameters, and luminosity. While cold absorption remains at levels quite similar to that observed in previous years, the new observations show unprecedented levels of variable warm absorption. The line emissivities also indicate that the observed low source luminosity is inconsistent with a static hot accretion disk corona (ADC), an effect that seems common to other near-edge-on ADC sources as well. We conclude that unless there exists some means of coronal heating other than X-rays, the true source luminosity is likely much higher, and we observe obscuration in analogy to the extragalactic Seyfert 2 sources. We discuss possible consequences and relate cold, lukewarm, warm, and hot absorbers to dynamic accretion scenarios.

FUSEObservation of the Narrow‐Line Seyfert 1 Galaxy RE 1034+39: Dependence of Broad Emission Line Strengths on the Shape of the Photoionizing Spectrum

We present an analysis from simultaneous FUSE, ASCA, and EUVE observations, as well as a reanalysis of archival HST spectra, from the extreme narrow-line Seyfert 1 Galaxy RE 1034+39 (KUG 1031+398). RE 1034+39 has an unusually hard spectral energy distribution (SED) that peaks in the soft X-rays. Its emission lines are unusual in that they can all be modeled as a Lorentzian centered at the rest wavelength with only a small range in velocity widths. In order to investigate whether the unusual SED influences the emission-line ratios and equivalent widths, we present three complementary types of photoionization analysis. The FUSE spectrum was particularly important because it includes the high-ionization line O VI. First, we use the photoionization code CLOUDY and the SED developed from the coordinated observations to confirm that the emission lines are consistent with observed hard SED. The best model parameters were an ionization parameter log U ≈ -2 and a hydrogen number density log nH = 9.75 (cm-2). Second, we present a locally optimally emitting cloud model. This model produced enhanced O VI as observed, but also yielded far too strong Mg II. Third, we develop a series of semiempirical SEDs, run CLOUDY models, and compare the results with the measured values using a figure of merit (FOM). The FOM minimum indicates SED and gas properties similar to those inferred from the one-zone model using the RE 1034+39 continuum. Furthermore, the FOM increases sharply toward softer continua, indicating that a hard SED is required by the data in the context of a one-zone model.

AChandraHETGS Spectral Study of the Iron K Bandpass in MCG −6‐30‐15: A Narrow View of the Broad Iron Line

We present a high-resolution X-ray spectrum of the iron K bandpass in MCG -6-30-15 based on a 522 ks observation with Chandra's High Energy Transmission Grating Spectrometer (HETGS). The Chandra spectrum is consistent with the presence of a relativistically broadened, highly redshifted iron Kα emission line with a profile similar to previous observations. A number of narrow features are detected above 2 keV, including a narrow Fe Kα emission line and narrow absorption lines from H- and He-like Fe, H-like S, and H-like Si. This absorption is well described by a photoionized plasma with a column density log NH = 23.2 and an ionization parameter log ξ = 3.6, assuming the iron abundance has the solar value and a velocity dispersion parameter b = 100 km s-1. Applying this absorption model to a high-fidelity XMM-Newton EPIC pn spectrum, we find that a broad iron line is still required with emission extending to within 1.9rg of the black hole. If the iron line comes from an accretion disk truncated at the innermost stable circular orbit, this indicates that the black hole must be spinning rapidly with a > 0.95. Ionized absorption models attempting to explain the 3-6 keV spectral curvature without strong gravity predict absorption lines in the 6.4-6.6 keV range that are inconsistent with the Chandra spectrum. The H- and He-like iron absorption lines in the Chandra spectrum are blueshifted by 2.0 × 103 km s-1 compared to the source frame and may originate in a high-velocity, high-ionization component of the warm absorber outflow. This high-ionization component may dominate the energy budget of the outflow and account for a significant fraction of the outflowing mass. Detailed modeling of the warm absorber below 2 keV will be addressed in a later paper, but our results are robust to the broader details of the warm absorber behavior. The difference spectrum between the high- and low-flux states is well described by a power law, in agreement with previous studies.

Hubble Space TelescopeSTIS Ultraviolet Spectral Evidence of Outflow in Extreme Narrow‐Line Seyfert 1 Galaxies. II. Modeling and Interpretation

We present modeling to explore the conditions of the broad-line-emitting gas in two extreme narrow-line Seyfert 1 galaxies, using the observational results described in the first paper of this series. Photoionization modeling using CLOUDY was conducted for the broad blueshifted wind lines and the narrow, symmetric, rest-wavelength-centered disk lines separately. A broad range of physical conditions was explored for the wind component, and a figure of merit was used to quantitatively evaluate the simulation results. Of the three minima in the figure-of-merit parameter space, we favor the solution characterized by an X-ray-weak continuum, elevated abundances, a small column density (log NH ? 21.4), a relatively high ionization parameter (log U ? -1.2 to -0.2), a wide range of densities (log n ? 7-11), and a covering fraction of ~0.15. The presence of low-ionization emission lines implies that the disk component is optically thick to the continuum, and the Si III]/C III] ratio implies a density of 1010-1010.25 cm-3. A low ionization parameter (log U = -3) is inferred for the intermediate-ionization lines, unless the continuum is filtered through the wind before illuminating the intermediate-line-emitting gas, in which case log U = -2.1. The location of the emission regions was inferred from the photoionization modeling and a simple toy dynamical model. A large black hole mass (1.3 ? 108 M?) radiating at 11% of the Eddington luminosity is consistent with the kinematics of both the disk and wind lines, and an emission radius of ~104 RS is inferred for both. We compare these results with previous work and discuss implications.

ChandraHigh‐Resolution Spectroscopy of the Absorption‐Line Features in the Low‐Mass X‐Ray Binary GX 13+1

We present the results of high-resolution spectroscopy of absorption-line features of highly ionized ions in the X-ray spectra of GX 13+1 with the Chandra HETGS. We have resolved Kabsorption lines of hydrogen-like Fe, Mn, Cr, Ca, Ar, S, Si, and Mg ions and helium-like Fe ions. Applying the Voigt profile to these spectral features, we find that the plasma responsible for the absorption lines has a significant blueshift of 460 � 70 km s � 1 , indicating an outflow velocity of � 400 km s � 1 corrected for the proper motion, with a line-of-sight velocity dispersion of 490 þ110 � 140 km s � 1 . The plasma is photoionized with an ionization parameter of log� ' 4:1 4:7. The inferred mass outflow rate is 0:7 ; 10 18 gs � 1 or higher, comparable to the mass accretion rate (10 18 gs � 1 ) estimated from the continuum spectrum. This indicates that the mass outflow plays a significant role to determine the whole dynamics of the accretion disk. We consider a simplified radiation-driven disk wind model for the origin of the outflow. Our observations are explained by the wind originating from radii of � 10 10 -10 11 cm with a density k10 13 cm � 3 . Subject headings: stars: individual (GX 13+1) — X-rays: binaries — X-rays: stars

The X-ray nebula around the type 2 Seyfert galaxy NGC 4388

We report on X-ray emission from the type 2 Seyfert galaxy NGC 4388 observed with the Chandra X-ray Observatory. A hard X-ray peak is found at the position of the active nucleus suggested by optical and radio observations. Extended soft X-ray emission correlates well with the ionization cone found in optical-line emission. A large soft X-ray extension is found up to 16 kpc (and possibly 30 kpc) to the north of the galaxy. Photoionized gas with low ionization parameters (log ξ ≤ 0.4) appears to be the likely explanation for this emission. The same ionized gas clouds could be responsible for the optical [O III] emission. Fe Ka line emission from cold material is found to be extended by a few kpc.

Evidence of a high-velocity ionized outflow in a second narrow-line quasar PG 0844+349

Following the discovery of X-ray absorption in a high-velocity outflow from the bright quasar PG 1211 + 143 we have searched for similar features in XMM–Newton archival data of a second (high accretion rate) quasar PG 0844+349. Evidence is found for several faint absorption lines in both the EPIC and RGS spectra, whose most likely identification with resonance transitions in H-like Fe, S and Ne implies an origin in highly ionized matter with an outflow velocity of order ∼0.2c. The line equivalent widths require a line-of-sight column density of NH∼ 4 × 1023 cm−2, at an ionization parameter of log ξ∼ 3.7. Assuming a radial outflow being driven by radiation pressure from the inner accretion disc, as suggested previously for PG 1211 + 143, the flow in PG 0844+349 is also likely to be optically thick, in this case within ∼25 Schwarzschild radii. Our analysis suggests that a high-velocity, highly ionized outflow is likely to be a significant component in the mass and energy budgets of active galactic nuclei accreting at or above the Eddington rate.

A two-component ionized reflection model of MCG-6-30-15

Ionized reflection has often been considered as the explanation for the unusual Fe Kα variability observed in MCG‐6-30-15. In this paper, we test this model using a 325-ks observation of MCG‐6-30-15 by XMM‐Newton and BeppoSAX. The data are fitted between 2.5 and 80 keV with the constant-density models of Ross & Fabian. The best-fitting ionized reflection model requires the Fe Kα line to be split into two reprocessing events: one from the inner disc to build up the red wing, and the other from the outer accretion disc to fit the blue horn. The implied geometry is a disc that becomes strongly warped or flared at large radii. A good fit was obtained with a solar abundance of iron and a reflection fraction (R) of unity for the inner reflector. The combination of the two reflection spectra can appear to have R > 2 as required by the BeppoSAX data. The inner reflector has an ionization parameter of log ξ = 3.8, but the outer one is neutral with an inner radius of ∼70 gravitational radii (r g), corresponding to a

The Kinematics and Physical Conditions of the Ionized Gas in Markarian 509. I.ChandraHigh Energy Grating Spectroscopy

We observed the Seyfert 1 galaxy Mrk 509 for ~59 ks with the Chandra high-energy transmission gratings, simultaneously with HST/STIS and RXTE. Here we present a detailed analysis of the soft X-ray spectrum observed with Chandra. We measure strong absorption lines from He-like Ne and Mg and from H-like N, O, and Ne. Weaker absorption lines may also be present. The lines are unresolved except for Ne X Lyα (λ12.134) and Ne IX 1s2-1s2p (λ13.447), which appear to be marginally resolved. The profiles are blueshifted with respect to the systemic velocity of Mrk 509, indicating an outflow of ~-200 km s-1. There is also a hint that the profiles may have a velocity component near systemic. The soft X-ray spectrum can be described in remarkable detail with a simple, single-zone photoionized absorber having an equivalent neutral hydrogen column density of 2.06 × 1021cm-2 and an ionization parameter of log ξ = 1.76 (or log U = 0.27). Although the photoionized gas almost certainly is comprised of matter in more than one ionization state and may consist of several kinematic components, data with better spectral resolution and signal-to-noise ratio would be required to justify a more complex model. The UV data, on the other hand, have a velocity resolution of ~10 km s-1 and can easily detect eight kinematic components, covering roughly the same velocities as the X-ray absorption profiles. Even though the X-ray and UV absorbers share the same velocity space, the UV absorbers have a much smaller column density and ionization state. We show that models of the X-ray data do not predict significant UV absorption and are therefore consistent with the UV data. Finally, we do not detect any soft X-ray emission lines.

Far Ultraviolet Spectroscopic Explorerand Space Telescope Imaging Spectrograph Observations of Intervening OviAbsorption Line Systems in the Spectrum of PG 0953+415

We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope Imaging Spectrograph (STIS) observations of the intergalactic medium toward the bright QSO PG 0953+415 (zem = 0.239). The FUSE spectra extend from 905 to 1187 A and have a resolution of 25 km s-1, while the STIS spectra cover 1150-1730 A and have a resolution of 7 km s-1. Additional STIS observations at 30 km s-1 are obtained in selected wavelength ranges. An O VI system at z = 0.06807 is detected in H I Lyα, Lyβ, Lyγ, O VI λλ1031.93, 1037.62, N V λλ1238.82, 1242.80, C IV λλ1548.20, 1550.77, and C III λ977.02. The observed column densities can be modeled as a low-density intervening gas with a metallicity of 0.4 times solar in photoionization equilibrium with the ionizing extragalactic background radiation. The best fit is achieved with an ionization parameter, log U = -1.35, which implies nH ~ 10-5 cm-3 and a path length of ~80 kpc through the absorbing gas. H I Lyα absorption at z = 0.14232 spans a velocity range of 410 km s-1 with the strongest components near 0 and 80 km s-1 in the z = 0.14232 rest frame. In this system, O VI λλ1031.93, 1037.62 absorption is strong near 0 km s-1 and not detected at 80 km s-1. C III λ977.02 absorption is marginally detected at 80 km s-1 but is not detected at 0 km s-1. The observations place constraints on the properties of the z = 0.14232 system but do not discriminate between collisional ionization in hot gas versus photoionization in a very low density medium with an ionization parameter log U > -0.74. The z = 0.06807 and 0.14232 O VI systems occur at redshifts where there are peaks in the number density of intervening galaxies along the line of sight determined from WIYN redshift measurements of galaxies in the ~1° field centered on PG 0953+415. We combine our observations of PG 0953+415 with those for other QSOs to update the estimate of the low-redshift number density of intervening O VI systems. Over a total unobscured redshift path of Δz = 0.43, we detect six O VI systems with rest-frame equivalent widths of the O VI λ1031.93 line exceeding 50 mA, yielding dN/dz = 14 for z = 0.09. This implies a low-redshift value of the baryonic contribution to the closure density of the O VI systems of Ωb(O VI) > 0.002 h, assuming that the average metallicity in the O VI systems is 0.1 solar.