Low-ionization Absorption Research Articles

Implications of dramatic broad absorption line variability in the quasar FBQS J1408+3054

We have observed a dramatic change in the spectrum of the formerly heavily absorbed `overlapping-trough' iron low-ionization broad absorption line (FeLoBAL) quasar FBQS J1408+3054. Over a time span of between 0.6 to 5 rest-frame years, the Mg II trough outflowing at 12,000 km/s decreased in equivalent width by a factor of two and the Fe II troughs at the same velocity disappeared. The most likely explanation for the variability is that a structure in the BAL outflow moved out of our line of sight to the ultraviolet continuum emitting region of the quasar's accretion disk. Given the size of that region, this structure must have a transverse velocity of between 2600 km/s and 22,000 km/s. In the context of a simple outflow model, we show that this BAL structure is located between approximately 5800 and 46,000 Schwarzschild radii from the black hole. That distance corresponds to 1.7 to 14 pc, 11 to 88 times farther from the black hole than the H-beta broad-line region. The high velocities and the parsec-scale distance for at least this one FeLoBAL outflow mean that not all FeLoBAL outflows can be associated with galaxy-scale outflows in ultraluminous infrared galaxies transitioning to unobscured quasars. The change of FBQS J1408+3054 from an FeLoBAL to a LoBAL quasar also means that if (some) FeLoBAL quasars have multiwavelength properties which distinguish them from HiBAL quasars, then some LoBAL quasars will share those properties. Finally, we extend previous work on how multiple-epoch spectroscopy of BAL and non-BAL quasars can be used to constrain the average lifetime of BAL episodes (currently >60 rest-frame years at 90% confidence).

HIGH DUST DEPLETION IN TWO INTERVENING QUASAR ABSORPTION LINE SYSTEMS WITH THE 2175 Å EXTINCTION BUMP ATz∼ 1.4

We present the column densities of heavy-elements and dust depletion studies in twostrong Mg~II absorption systems at $z\sim1.4$ displaying the 2175-{\AA} dust extinction feature. Column densities are measured from low-ionization absorption lines using Apparent Optical Depth Method on the Keck/ESI spectra. We find the dust depletion patterns resemble to that of cold diffuse clouds in the Milky Way (MW). The values, [Fe/Zn]$\approx -1.5$ and [Si/Zn]$<-0.67$, are among the highest dust depletion measured for quasar absorption line systems. In another 2175-{\AA} absorber at $z$=1.64 toward the quasar SDSS J160457.50+220300.5, Noterdaeme et al. (2009) reported a similar dust depletion measurement ([Fe/Zn]=$-1.47$ and [Si/Zn]=$-1.07$) and detected C~I and CO absorption lineson its VLT/UVES spectrum. We conclude that heavy dust depletion (i.e. a characteristic of cold dense clouds in MW) is required to produce a pronounced 2175-{\AA} extinction bump.

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.

The nature of proximate damped Lyman α systems★

We present high resolution echelle spectra of 7 proximate damped Lyman alpha (PDLA) systems whose relative velocity separation from the background quasar is Delta V < 3000 km/s. Combining our sample with a further 9 PDLAs from the literature we compare the chemical properties of the proximate systems with a control sample of intervening DLAs. Taken at face value, the sample of 16 PDLAs exhibits a wide range of metallicities, ranging from Z ~ 1/3 Z_sun down to Z ~ 1/1000 Z_sun, including the DLA with the lowest N(SiII)/N(HI) yet reported in the literature. We find several pieces of evidence that indicate enhanced ionization and the presence of a hard ionizing spectrum in PDLAs which lead to properties that contrast with the intervening DLAs, particularly when the N(HI) is low. The abundances of Zn, Si and S in PDLAs with log N(HI) > 21, where ionization corrections are minimized, are systematically higher than the intervening population by a factor of around 3. We also find possible evidence for a higher fraction of NV absorbers amongst the PDLAs, although the statistics are still modest. 6/7 of our echelle sample show high ionization species (SiIV, CIV, OVI or NV) offset by >100 km/s from the main low ion absorption. We analyse fine-structure transitions of CII* and SiII* to constrain the PDLA distance from the QSO. Lower limits range from tens of kpc up to >160 kpc for the most stringent limit. We conclude that (at least some) PDLAs do exhibit different characteristics relative to the intervening population out to 3000 km/s (and possibly beyond). Nonetheless, the PDLAs appear distinct from lower column density associated systems and the inferred QSO-absorber separations mean they are unlikely to be associated with the QSO host. We speculate that the PDLAs preferentially sample more massive galaxies in more highly clustered regions of the high redshift universe.

GRB 090426: the environment of a rest-frame 0.35-s gamma-ray burst at a redshift of 2.609

We present the discovery of an absorption-line redshift of z = 2.609 for GRB 090426, establishing the first firm lower limit to a redshift for a gamma-ray burst with an observed duration of <2 s. With a rest-frame burst duration of T_90z = 0.35 s and a detailed examination of the peak energy of the event, we suggest that this is likely (at >90% confidence) a member of the short/hard phenomenological class of GRBs. From analysis of the optical-afterglow spectrum we find that the burst originated along a very low HI column density sightline, with N_HI < 3.2 x 10^19 cm^-2. Our GRB 090426 afterglow spectrum also appears to have weaker low-ionisation absorption (Si II, C II) than ~95% of previous afterglow spectra. Finally, we also report the discovery of a blue, very luminous, star-forming putative host galaxy (~2 L*) at a small angular offset from the location of the optical afterglow. We consider the implications of this unique GRB in the context of burst duration classification and our understanding of GRB progenitor scenarios.

Galaxies at a redshift of ∼0.5 around three closely spaced quasar sightlines

We examine the relationship between galaxies and the intergalactic medium at z < 1 using a group of three closely spaced background QSOs with z_em ~1 observed with the Hubble Space Telescope. Using a new grouping algorithm, we identify groups of galaxies and absorbers across the three QSO sightlines that may be physically linked. There is an excess number of such groups compared to the number we expect from a random distribution of absorbers at a confidence level of 99.9%. The same search is performed with mock spectra generated using a hydrodynamic simulation, and we find the vast majority of such groups arise in dense regions of the simulation. We find that at z<0.5, groups in the simulation generally trace the large-scale filamentary structure as seen in the projected 2-d distribution of the HI column density in a ~30 h^-1 Mpc region. We discover a probable sub-damped Lyman-alpha system at z=0.557 showing strong, low-ionisation metal absorption lines. Previous analyses of absorption across the three sightlines attributed these metal lines to HI. We show that even when the new line identifications are taken into account, evidence remains for planar structures with scales of ~1 Mpc absorbing across the three sightlines. We identify a galaxy at z=0.2272 with associated metal absorption in two sightlines, each 200 kpc away. By constraining the star formation history of the galaxy, we show the gas causing this metal absorption may have been enriched and ejected by the galaxy during a burst of star formation 2 Gyr ago.

METAL-ENRICHED OUTFLOWS IN THE ULTRALUMINOUS INFRARED QUASAR Q1321+058

Quasar outflows may play important role in the evolution of its host galaxy and central black hole, and are most often studied in absorption lines. In this paper, we present a detailed study of multiple outflows in the obscured ultraluminous infrared quasar Q1321+058. The outflows reveal themselves in the complex optical and ultraviolet (UV) emission-line spectrum, with a broad component blueshifted by 1650 km s(-1) and a narrow component by 360 km s(-1), respectively. The higher velocity component shows ever strong N III] (N III]/C III] = 3.8 +/- 0.3 and N III]/C IV = 0.53) and strong Si III] (Si III]/C III] similar or equal to 1), in addition to strong [O III]lambda 5007 and [Ne III]lambda 3869 emission. A comparison of these line ratios with photoionization models suggests an overabundance of N and Si relative to C. The abundance pattern is consistent with a fast chemical enriching process associated with a recent starburst, triggered by a recent galaxy merger. The outflow extends to several tens to hundred parsecs from the quasar, and covers only a very small sky. We find that the outflow with line emitting gas is energetically insufficient to remove the interstellar medium of the host galaxy, but total kinetic energy may be much larger than suggested by the emission lines. The velocity range and the column density suggest that the outflow might be part of the low-ionization broad absorption line region as seen in a small class of quasars. The optical and UV continuum is starlight dominated and can be modeled with a young-aged (1 Myr) plus an intermediate-aged (similar to 0.5-1 Gyr) stellar populations, suggesting a fast building of the stellar mass in the host galaxy, consistent with the starburst-type metal abundances inferred from the high-velocity outflow spectrum. The broadband spectral energy distribution shows that it is an obscured quasar with its bulk emission in the middle infrared. The star formation rate, independently estimated from UV, far-infrared, and emission-line luminosity, is much lower than that is required for the co-evolution of the black hole and its host spheroid.

SUZAKUOBSERVATIONS OF NEAR-RELATIVISTIC OUTFLOWS IN THE BAL QUASAR APM 08279+5255

We present results from three Suzaku observations of the z=3.91 gravitationally lensed broad absorption line quasar APM 08279+5255. We detect strong and broad absorption at rest-frame energies of <2 keV (low-energy) and 7-12 keV (high-energy). The detection of these features confirms the results of previous long-exposure (80-90 ks) Chandra and XMM-Newton observations. The low and high-energy absorption is detected in both the back-illuminated (BI) and front-illuminated (FI) Suzaku XIS spectra (with an F-test significance of >99%). We interpret the low-energy absorption as arising from a low-ionization absorber with log NH~23 and the high-energy absorption as due to lines arising from highly ionized (2.75 < log xi < 4.0; where xi is the ionization parameter) iron in a near-relativistic outflowing wind. Assuming this interpretation we find that the velocities in the outflow range between 0.1c and 0.6c. We constrain the angle between the outflow direction of the X-ray absorber and our line of sight to be <36 degrees. We also detect likely variability of the absorption lines (at the >99.9% and >98% significance levels in the FI and BI spectra, respectively) with a rest-frame time scale of ~1 month. Assuming that the detected high-energy absorption features arise from Fe xxv, we estimate that the fraction of the total bolometric energy injected over the quasar's lifetime into the intergalactic medium in the form of kinetic energy to be >10%.

A COMPREHENSIVE X-RAY SPECTRAL ANALYSIS OF THE SEYFERT 1.5 NGC 3227

We present results of a 100 ks XMM observation of the Seyfert 1.5 NGC 3227. Our best-fit broadband model to the pn spectrum consists of a moderately flat (photon index 1.57) hard X-ray power-law absorbed by cold gas with N_H = 3 * 10^21 cm^-2, plus a strong soft excess, modeled as a steep power law with a photon index of 3.35, absorbed by cold gas with N_H = 9 * 10^20 cm^-2. The soft excess normalization increases by ~20% in ~20 ks, independently of the hard X-ray component, and the UV continuum, tracked via the OM, also shows a strong increasing trend over the observation, consistent with reprocessing of soft X-ray emission. Warm absorber signatures are evident in both the EPIC and RGS; we model two layers, with log(xi) = 1.2 and 2.9 erg cm s^-1, and with similar column densities (~1-2 * 10^21 cm^-2). The outflow velocities relative to systemic of the high- and low-ionization absorbers are estimated to be -(2060(+240,-170)) km/s and -(420(+430,-190)) km/s, respectively. The Fe K alpha line width FWHM is 7000 +/- 1500 km/s; its inferred radius is consistent with the BLR and with the inner radius of the dust reverberation-mapped by Suganuma et al. An emission feature near 6.0 keV is modeled equally well as a narrow redshifted Fe K line, possibly associated with a disk "hot-spot," or as the red wing to a relativistically broadened Fe line profile. Swift-BAT and archival RXTE data suggest at most weak Compton reflection (R <~ 0.5), and a high-energy cutoff near 100 keV. From RXTE monitoring, we find tentative evidence for a significant fraction of the Fe line flux to track continuum variations on time scales < 700 days.

A joint model for the emission and absorption properties of damped Lyα absorption systems

The recently discovered population of ultra-faint extended line emitters can account for the majority of the incidence rate of Damped Lyman Alpha systems (DLAs) at z ~ 3 if the line emission is interpreted as Ly alpha. We show here that a model similar to that proposed by Haehnelt, Steinmetz, & Rauch (2000), which explains the incidence rate and kinematics of DLAs in the context of $\Lambda$CDM models for structure formation, also reproduces the size distribution of the new population of faint Ly alpha emitters for plausible parameters. This lends further support to identification of the emitters with the hitherto elusive population of DLA host galaxies. The observed incidence rate of DLAs together with the observed space density and size distribution of the emitters suggest a duty cycle of ~ 0.2 - 0.4 for the Ly alpha emission from DLA host galaxies. We further show that Ly alpha cooling is expected to contribute little to the Ly alpha emission for the majority of emitters. This leaves centrally concentrated star formation at a rate of a few tenths M_sun/yr, surrounded by extended Ly alpha halos with radii up to 30-50 kpc, as the most plausible explanation for the origin of the emission. Both the luminosity function of Ly alpha emission and the velocity width distribution of low ionization absorption require that galaxies inside Dark Matter (DM) halos with virial velocities < 50 - 70 km/s contribute little to the incidence rate of DLAs at z ~ 3, suggesting that energy and momentum input due to star formation efficiently removes gas from these halos. Galaxies with DM halos with virial velocities of 100 - 150 km/s appear to account for the majority of DLA host galaxies. DLA host galaxies at z ~ 3 should thus become the building blocks of typical present-day galaxies.

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.

Medium-resolution spectroscopy of FORJ0332−3557: probing the interstellar medium and stellar populations of a lensed Lyman-break galaxy at z = 3.77

We recently reported the discovery of FORJ0332-3557, a lensed Lyman-break galaxy at z=3.77 in a remarkable example of strong galaxy-galaxy gravitational lensing. We present here a medium-resolution rest-frame UV spectrum of the source, which appears to be similar to the well-known Lyman-break galaxy MS1512-cB58 at z=2.73. The spectral energy distribution is consistent with a stellar population of less than 30 Ma, with an extinction of A(V)=0.5 mag and an extinction-corrected star formation rate SFR(UV) of 200-300 Msun/a. The Lyman-alpha line exhibits a damped profile in absorption produced by a column density of about N(HI) = (2.5+_1.0) 10^21 atoms/cm^2, superimposed on an emission line shifted both spatially (0.5 arcsec with respect to the UV continuum source) and in velocity space (+830 km/s with respect to the low-ionisation absorption lines from its interstellar medium), a clear signature of outflows with an expansion velocity of about 270 km/s. A strong emission line from HeII 164.04nm indicates the presence of Wolf-Rayet stars and reinforces the interpretation of a very young starburst. The metallic lines indicate sub-solar abundances of elements Si, Al, and C in the ionised gas phase.

Probing the Ionization Structure of the Narrow‐Line Region in the Seyfert 1 Galaxy NGC 4151

We present a study of the distribution of [O III] λ5007 and [O II] λ3727 emission in the narrow-line region (NLR) of the Seyfert 1 galaxy NGC 4151. While the NLR of NGC 4151 exhibits an overall structure consistent with the unified model of Seyfert galaxies, narrowband [O III] and [O II] images obtained with the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope reveal significant emission from outside the emission-line bicone. The [O III]/[O II] ratios are lower in these regions, consistent with a weaker ionizing flux. We performed a photoionization modeling analysis of the emission-line gas within a series of annuli, centered on the central continuum source, with inner radii from 13 to 90 pc. The gas is ionized by radiation that has been attenuated by a relatively highly ionized absorber (HABS), which completely covers the central source, and a lower ionization absorber (LABS), which has a covering factor ranging from 0 to 1. We found that the [O III]/[O II] ratios are well fit by assuming that, within each segment of an annulus, some fraction of the NLR gas is completely within the shadow of LABS, while the rest is irradiated by the continuum filtered only by HABS. This suggests that the structure of the NLR is due to filtering of the ionizing radiation by ionized gas, consistent with disk-wind models. One possible scenario is that the low-ionization absorbers are dense knots of gas swept up by a wind.

The Suzaku Observation of NGC3516: Complex Absorption and the Broad and Narrow FeK Lines

Abstract We present results from a 150ks Suzaku observation of the Seyfert 1.5 NGC3516 in 2005 October. The source was in a relatively highly absorbed state. Our best-fit model is consistent with the presence of a low-ionization absorber having a column density near 5$\times$10$^{22}$cm$^{-2}$ and covering most of the X-ray continuum source (covering fraction 96-100%). A high-ionization absorbing component, which yields a narrow absorption feature consistent with FeXXVIK, is confirmed. A relativistically broadened FeK$\alpha$ line was required in all fits, even after the complex absorption was taken into account; an additional partial-covering component is an inadequate substitute for the continuum curvature associated with the broad Fe line. A narrow FeK$\alpha$ emission line has a velocity width consistent with the Broad Line Region. The low-ionization absorber may be responsible for producing the narrow FeK$\alpha$ line, though a contribution from additional material out of the line of sight is possible. We include in our model soft band emission lines from He- and H-like ions of N, O, Ne, and Mg, consistent with photo-ionization, though a small contribution from collisionally-ionized emission is possible.

A catalogue of absorption lines in eight Hubble Space Telescope/STIS E230M 1.0 &lt; z &lt; 1.7 quasar spectra★

We have produced a catalogue of line identifications and equivalent width measurements for all absorption features in eight ultraviolet echelle quasar spectra. These spectra were selected as having the highest signal-to-noise ratio among the Hubble Space Telescope/STIS spectra obtained with the E230M grating. We identify 56 metal-line systems towards the eight quasars, and present plots of detected transitions, aligned in velocity space. We found that about 1/4-1/3 of the features in the Lya forest region, redward of the incidence of the Lyβ forest, are metal lines. High-ionization transitions are common. At the redshift range we study, z < 1.7, we see both O vi and C iv in 88-90 per cent of the metal-line systems for which the spectra cover the expected wavelength. Si III is seen in 58 per cent, while low-ionization absorption in C II, Si II and/or Al II is detected in 50 per cent of the systems for which they are covered. This catalogue will facilitate future studies of the Lya forest and of metal-line systems of various types.

A Census of Intrinsic Narrow Absorption Lines in the Spectra of Quasars at z = 2–4

We use Keck HIRES spectra of 37 optically bright quasars at z = 2-4 to study narrow absorption lines that are intrinsic to the quasars (intrinsic NALs, produced in gas that is physically associated with the quasar central engine). We identify 150 NAL systems, which contain 124 C IV, 12 N V, and 50 Si IV doublets, of which 18 are associated systems (within 5000 km s-1 of the quasar redshift). We use partial coverage analysis to separate intrinsic NALs from NALs produced in cosmologically intervening structures. We find 39 candidate intrinsic systems (28 reliable determinations and 11 that are possibly intrinsic). We estimate that 10%-17% of C IV systems at blueshifts of 5000-70,000 km s-1 relative to quasars are intrinsic. At least 32% of quasars contain one or more intrinsic C IV NALs. Considering N V and Si IV doublets showing partial coverage as well, at least 50% of quasars host intrinsic NALs. This result constrains the solid angle subtended by the absorbers to the background source(s). We identify two families of intrinsic NAL systems, those with strong N V absorption and those with negligible absorption in N V but with partial coverage in the C IV doublet. We discuss the idea that these two families represent different regions or conditions in accretion disk winds. Of the 26 intrinsic C IV NAL systems, 13 have detectable low-ionization absorption lines at similar velocities, suggesting that these are two-phase structures in the wind rather than absorbers in the host galaxy. We also compare possible models for quasar outflows, including radiatively accelerated disk-driven winds, magnetocentrifugally accelerated winds, and pressure-driven winds, and we discuss ways of distinguishing between these models observationally.

Discovery of Probable Relativistic Fe Emission and Absorption in the Cloverleaf Quasar H 1413+117

We present results from Chandra and XMM-Newton observations of the low-ionization broad absorption line (LoBAL) quasar H 1413+117. Our spatial and spectral analysis of a recent deep Chandra observation confirms a microlensing event in a previous Chandra observation performed about 5 years earlier. We present constraints on the structure of the accretion flow in H 1413+117 based on the time-scale of this microlensing event. Our analysis of the combined spectrum of all the images indicates the presence of two emission peaks at rest-frame energies of 5.35 keV and 6.32 keV detected at the > 98% and > 99% confidence levels, respectively. The double peaked Fe emission line is fit well with an accretion-disk line model, however, the best-fitting model parameters are neither well constrained nor unique. Additional observations are required to constrain the model parameters better and to confirm the relativistic interpretation of the double peaked Fe Kalpha line. Another possible interpretation of the Fe emission is fluorescent Fe emission from the back-side of the wind. The spectra of images C and D show significant high-energy broad absorption features that extend up to rest-frame energies of 9 keV and 15 keV respectively. We propose that a likely cause of these differences is significant variability of the outflow on time-scales that are shorter than the time-delays between the images. The Chandra observation of H 1413+117 has made possible for the first time the detection of the inner regions of the accretion disk and/or wind and the high ionization component of the outflowing wind of a LoBAL quasar.

Highly ionized plasma in the Large Magellanic Cloud: evidence for outflows and a possible galactic wind

Based on an analysis of the interstellar highly ionised species C IV, Si IV, N V, and O VI observed in the FUSE and HST/STIS E140M spectra of four hot stars in the Large Magellanic Cloud (LMC), we find evidence for a hot LMC halo fed by energetic outflows from the LMC disk and even possibly an LMC galactic wind. Signatures for such outflows are the intermediate and high-velocity components (v_LSR>100 km/s) relative to the LMC disk observed in the high- and low-ion absorption profiles. The stellar environments produce strong, narrow (T<20,000 K) components of C IV and Si IV associated with the LMC disk; in particular they are likely signatures of H II regions and expanding shells. Broad components are observed in the profiles of C IV, Si IV, and O VI with their widths implying hot, collisionally ionised gas at temperatures of a few times 100,000 K. There is a striking similarity in the O VI/C IV ratios for the broad LMC and high-velocity components, suggesting much of the material at v_LSR>100 km/s is associated with the LMC. The velocity of the high-velocity component is large enough to escape altogether the LMC, polluting the intergalactic space between the LMC and the Milky Way. The observed high-ion ratios of the broad LMC and high-velocity components are consistent with those produced in conductive interfaces; such models are also favored by the apparent kinematically coupling between the high and the weakly ionised species.

Lyα emission in high-redshift galaxies

Context. A significant fraction of the high-redshift galaxies show st rong Lyα emission lines. For redshifts z> 5, most known galaxies belong to this class. However, so far not much is known about the physical structure and nature of these objects. Aims. Our aim is to analyse the Lyα emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the Lyα profile and the line strength. Methods. VLT/FORS spectra with a resolution of R≈ 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented. The observed Lyα profiles are compared with theoretical models. Results. The Lyα lines range from pure absorption (EW = -17 A) to strong emission (EW = 153 A). Most Lyα emission lines show an asymmetric profile, and three galaxies have a double-peaked profile. Both types of profiles can be explained by a uniform mo del consisting of an expanding shell of neutral and ionised hydrogen around a compact starburst region. The broad, blueshifted, low-ionisation interstellar absorption lines indicate a galaxy-scale outflow of the ISM. The strengths of these lines are found to be determined in part by the velocity dispersion of the outflowing medium. We find star-formation r ates of these galaxies ranging from S FRUV = 1.2 to 63.2 M⊙yr −1 uncorrected for dust absorption. Conclusions. The Lyα emission strength of our target galaxies is found to be deter mined by the amount of dust and the kinematics of the outflowing material.

Simultaneous Ultraviolet and X‐Ray Observations of the Seyfert Galaxy NGC 4151. II. Physical Conditions in the UV Absorbers

We present a detailed analysis, including photoionization modeling, of the intrinsic absorption in the Seyfert 1 galaxy NGC 4151 using ultraviolet (UV) spectra from the Hubble Space Telescope Space Telescope Imaging Spectrograph and the Far Ultraviolet Spectrographic Explorer obtained 2002 May as part of a set of contemporaneous observations that included Chandra High Energy Transmission Grating Spectrometer spectra. In our analysis of the Chandra spectra, we determined that the X-ray absorption was dominated by two components: a high-ionization absorber, revealed by the presence of H-like and He-like lines of Mg, Si, and S, and a lower ionization absorber, in which inner shell absorption lines from lower ionization species of these elements formed. We identified the latter as the source of the saturated UV lines of O VI, C IV, and N V associated with the absorption feature at a radial velocity of ~-500 km s-1, which we referred to as component D+E. In the present work, we have derived tighter constrains on the line-of-sight covering factors, densities, and radial distances of the absorbers. We confirm the presence of the three subcomponents of D+E described in our previous paper, with line-of-sight covering factors (Clos) ranging from ~0.5 to 0.9, and find evidence for a fourth component, D+Ed, characterized by low ionization and a Clos ~ 0.2. The complexity of the UV absorption in NGC 4151 may be a consequence of the fact that we are viewing the black hole/accretion disk system at a relatively high inclination and, therefore, may be detecting the densest part of the flow. Our deconvolution of the underlying C IV emission indicates that D+E must lie outside the intermediate line region (ILR), hence at a radial distance of ~0.1 pc. We find that the equivalent widths (EWs) of the low-ionization lines associated with D+E varied over the period from 1999 July to 2002 May. Although over part of this time, the variations were correlated with changes in the UV continuum, the drop in the EWs of these lines between 2001 April and 2002 May are suggestive of bulk motion of gas out of our line of sight. Over this period, Clos for the low-ionization absorption lines dropped from ~0.7 to ~0.2. If these lines from these two epochs arose in the same subcomponent, the transverse velocity of the gas is ≈2100 km s-1. This is similar to the constraint on transverse velocity derived from the drop in the X-ray absorbing column between 2000 March and 2002 May. Transverse velocities of this order are consistent with an origin in a rotating disk, at the roughly radial distance we derived for D+E. As we suggested in our previous study, it is likely that the absorption arises in a disk-driven wind.