Cosmic Origins Spectrograph Research Articles

Multiwavelength campaign on Mrk 509

Aims. To elucidate the location, physical conditions, mass outflow rate, and kinetic luminosity of the outflow from the active nucleus of the Seyfert 1 galaxy Mrk 509, we used coordinated UV and X-ray spectral observations in 2012 to follow up our lengthier campaign conducted in 2009. Methods. We observed Mrk 509 with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) on 2012-09-03 and 2012-10-11 coordinated with X-ray observations using the High Energy Transmission Grating on the Chandra X-ray Observatory. Our far-ultraviolet spectra used grating G140L on COS to cover wavelengths from 920–2000 Å at a resolving power of ∼2000, and gratings G130M and G160M to cover 1160–1750 Å at a resolving power of ∼15, 000. Results. We detect variability in the blueshifted UV absorption lines on timescales spanning 3–12 years. The inferred densities in the absorbing gas are greater than log n cm−3 ∼ 3. For ionization parameters ranging over log U = −1.5 to −0.2, we constrain the distances of the absorbers to be closer than 220 pc to the active nucleus. Conclusions. The impact on the host galaxy appears to be confined to the nuclear region.

The First Metallicity Study of M83 Using the Integrated UV Light of Star Clusters*

Abstract Stellar populations are powerful tools for investigating the evolution of extragalactic environments. We present the first UV integrated-light spectroscopic observations for 15 young star clusters in the starburst M83 with a special focus on metallicity measurements. The data were obtained with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We analyze the data by applying an abundance technique that has previously been used to study an optical set of star clusters. We estimate a central metallicity of [Z] = +0.20 ± 0.15 dex, in agreement with estimates obtained through independent methods, i.e., J band and blue supergiants. We estimate a UV metallicity gradient of −0.041 ± 0.022 dex kpc−1, which is consistent with the optical metallicity gradient of −0.040 ± 0.032 dex kpc−1 for . Combining our stellar metallicities, UV and optical, with those from H ii regions (strong-line abundances based on empirical calibrations), we identify two possible breaks in the gradient of M83 at galactocentric distances of R ∼ 0.5 and 1.0 R 25. If the abundance breaks are genuine, the metallicity gradient of this galaxy follows a steep-shallow-steep trend, a scenario predicted by three-dimensional numerical simulations of disk galaxies. The first break is located near the corotation radius. This first steep gradient may have originated in recent star formation episodes and a relatively young bar (<1 Gyr). In the numerical simulations, the shallow gradient is created by the effects of dilution by outflow, where low-metallicity material is mixed with enriched gas. Finally, the second break and last steep gradient mark the farthest galactocentric distances where the outward flow has penetrated.

Correlation between SFR Surface Density and Thermal Pressure of Ionized Gas in Local Analogs of High-redshift Galaxies

Abstract We explore the relation between the star formation rate surface density (ΣSFR) and the interstellar gas pressure for nearby compact starburst galaxies. The sample consists of 17 green peas and 19 Lyman break analogs (LBAs). Green peas are nearby analogs of Lyα emitters at high redshift and LBAs are nearby analogs of Lyman break galaxies at high redshift. We measure the sizes of green peas using Hubble Space Telescope Cosmic Origins Spectrograph near-UV images with a spatial resolution of ∼0.″05. We estimate the gas thermal pressure in H ii regions by P = N total Tk B ≃ 2n e Tk B . The electron density is derived using the [S ii] doublet at 6716,6731 Å and the temperature is calculated from the [O iii] lines. The correlation is characterized by ΣSFR = . Green peas and LBAs have high ΣSFR up to 1.2 M ⊙ yr−1 kpc−2 and high thermal pressure in the H ii region up to P/k B ∼ 107.2 K cm−3. These values are at the highest end of the range seen in nearby starburst galaxies. The high gas pressure and the correlation are in agreement with those found in star-forming galaxies at z ∼ 2.5. These extreme pressures are shown to be responsible for driving galactic winds in nearby starbursts. These outflows may be crucial in enabling Lyα and Lyman-continuum to escape.

The power spectrum of the Lyman-α Forest at z < 0.5

ABSTRACT We present new measurements of the flux power-spectrum P(k) of the z < 0.5 H i Lyman-α Forest spanning scales $k \sim 0.001\!-\!0.1\, \mathrm{s \, km}^{-1}$. These results were derived from 65 far-ultraviolet quasar spectra (resolution $R \sim 18\, 000$) observed with the Cosmic Origin Spectrograph (COS) on board the Hubble Space Telescope. The analysis required careful masking of all contaminating, coincident absorption from H i and metal–line transitions of the Galactic interstellar medium and intervening absorbers as well as proper treatment of the complex COS line-spread function. From the P(k) measurements, we estimate the H i photoionization rate ($\Gamma _{\rm H\,{\small I}}$) in the z < 0.5 intergalactic medium. Our results confirm most of the previous $\Gamma _{\rm H\,{\small I}}$ estimates. We conclude that previous concerns of a photon underproduction crisis are now resolved by demonstrating that the measured $\Gamma _{\rm H\,{\small I}}$ can be accounted for by ultraviolet emission from quasars alone. In a companion paper, we will present constraints on the thermal state of the z < 0.5 intergalactic medium from the P(k) measurements presented here.

The Near-ultraviolet Continuum Radiation in the Impulsive Phase of HF/GF-type dMe Flares. I. Data

Abstract We present near-UV (NUV) flare spectra from the Hubble Space Telescope (HST)/Cosmic Origins Spectrograph during two moderate-amplitude U-band flares on the dM4e star GJ 1243. These spectra are some of the first accurately flux-calibrated, NUV flare spectra obtained over the impulsive phase in M dwarf flares. We observed these flares with a fleet of nine ground-based telescopes simultaneously, which provided broadband photometry and low-resolution spectra at the Balmer jump. An increase in the broadband continuum occurred with a signal-to-noise ratio >20 in the HST spectra, while numerous Fe ii lines and the Mg ii lines also increased but with smaller flux enhancements than the continuum radiation. These two events produced the most prominent Balmer line radiation and the largest Balmer jumps that have been observed to date in dMe flare spectra. A T = 9000 K blackbody underestimates the NUV continuum flare flux by a factor of two and is a poor approximation to the white light in these types of flare events. Instead, our data suggest that the peak of the specific continuum flux density is constrained to U-band wavelengths near the Balmer series limit. A radiative-hydrodynamic simulation of a very high energy deposition rate averaged over times of impulsive heating and cooling better explains the properties of the λ > 2500 Å flare continuum. These two events sample only one end of the empirical color–color distribution for dMe flares, and more time-resolved flare spectra in the NUV, U band, and optical from 2000 to 4200 Å are needed during more impulsive and/or more energetic flares.

METAL: The Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud Hubble Program. I. Overview and Initial Results

Abstract Metal Evolution, Transport, and Abundance in the LMC (METAL) is a large Cycle 24 program on the Hubble Space Telescope aimed at measuring dust extinction properties and interstellar depletions in the Large Magellanic Cloud (LMC) at half-solar metallicity. The 101-orbit program is composed of Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph spectroscopy toward 33 LMC massive stars between 1150 and 3180 Å and parallel Wide Field Camera 3 imaging in seven near-UV to near-IR filters. The fraction of silicon in the gas phase (depletion) obtained from the spectroscopy decreases with increasing hydrogen column density. Depletion patterns for silicon differ between the Milky Way, LMC, and SMC, with the silicon depletion level offsetting almost exactly the metallicity differences, leading to constant gas-phase abundances in those galaxies for a given hydrogen column density. The silicon depletion correlates linearly with the absolute-to-selective extinction, R V , indicating a link between gas depletion and dust grain size. Extinction maps are derived from the resolved stellar photometry in the parallel imaging, which can be compared to far-IR images from Herschel and Spitzer to estimate the emissivity of dust at LMC metallicity. The full METAL sample of depletions, UV extinction curves, and extinction maps will inform the abundance, size, composition, and optical properties of dust grains in the LMC, comprehensively improve our understanding of dust properties, and improve the accuracy with which dust-based gas masses, star formation rates, and star formation histories in nearby and high-redshift galaxies are estimated. This overview paper describes the goals, design, data reduction, and initial results of the METAL survey.

Revealing the Milky Way’s Hidden Circumgalactic Medium with the Cosmic Origins Spectrograph Quasar Database for Galactic Absorption Lines

Abstract Every quasar (quasi-stellar object; QSO) spectrum contains absorption-line signatures from the interstellar medium, disk-halo interface, and circumgalactic medium (CGM) of the Milky Way (MW). We analyze Hubble Space Telescope/Cosmic Origins Spectrograph (COS) spectra of 132 QSOs to study the significance and origin of Si iv absorption at km s−1 in the Galactic halo. The gas in the north predominantly falls in at km s−1, whereas in the south, no such pattern is observed. The Si iv column density has an average and a standard deviation of cm−2. At , does not significantly correlate with b, which cannot be explained by a commonly adopted flat-slab geometry. We propose a two-component model to reconstruct the –b distribution: a plane-parallel component to account for the MW’s disk-halo interface and a global component to reproduce the weak dependence on b. We find cm−2 and cm−2 on the basis of Bayesian analyses and block bootstrapping. The global component is most likely to have a Galactic origin, although its exact location is uncertain. If it were associated with the MW’s CGM, we would find for the cool gas at all velocities in the Galactic halo. Our analyses show that there is likely a considerable amount of gas at km s−1 hidden in the MW’s CGM. Along with this work, we make our QSO data set publicly available as the COS Quasar Database for Galactic Absorption Lines (COS-GAL).

Spectroscopic Redshift of the Gamma-Ray Blazar B2 1215+30 from Lyα Emission

Abstract We report on Cosmic Origin Spectrograph observations of the gamma-ray bright blazar B2 1215+30, collected in 2015 November. These observations allow for the confirmation of the source redshift from the detection of a Lyα emission feature at λ ∼ 1374 Å. The emission feature places the source at a redshift of z = 0.1305 ± 0.003, confirming the source’s ground-based spectral measurement. The gamma-ray emission of the source is discussed in the context of the source distance, required for the accurate reconstruction of the intrinsic gamma-ray emission taking the absorption by the extragalactic background light into account. The source distance is found to be low enough that the previously reported detection of an exceptional flaring event from B2 1215+30 in 2014 cannot be used to investigate opacity-specific spectral and variability characteristics introduced by possible ultra-high-energy cosmic-ray propagation.

The Ultraviolet Detection of Diffuse Gas in Galaxy Groups

Abstract A small survey of the UV-absorbing gas in 12 low-z galaxy groups has been conducted using the Cosmic Origins Spectrograph on board the Hubble Space Telescope. Targets were selected from a large, homogeneously selected sample of groups found in the Sloan Digital Sky Survey. A critical selection criterion excluded sight lines that pass close (<1.5 virial radii) to a group galaxy, to ensure absorber association with the group as a whole. Deeper galaxy redshift observations are used both to search for closer galaxies and also to characterize these 1013.5–1014.5 M ⊙ groups, the most massive of which are highly virialized with numerous early-type galaxies (ETGs). This sample also includes two spiral-rich groups, not yet fully virialized. At group-centric impact parameters of 0.3–2 Mpc, these signal-to-noise ratios = 15–30 spectra detected H i absorption in 7 of 12 groups; high (O vi) and low (Si iii) ion metal lines are present in two-thirds of the absorption components. None of the three most highly virialized, ETG-dominated groups are detected in absorption. Covering fractions ≳50% are seen at all impact parameters probed, but do not require large filling factors despite an enormous extent. Unlike halo clouds in individual galaxies, group absorbers have radial velocities that are too low to escape the group potential well without doubt. This suggests that these groups are “closed boxes” for galactic evolution in the current epoch. Evidence is presented that the cool and warm group absorbers are not a pervasive intra-group medium (IGrM), requiring a hotter (T ∼ 106–107 K) IGrM to be present to close the baryon accounting.

Detection of nitrogen gas in the β Pictoris circumstellar disc

Context. The gas composition of the debris disc surrounding β Pictoris is rich in carbon and oxygen relative to solar abundances. Two possible scenarios have been proposed to explain this enrichment. The preferential production scenario suggests that the produced gas may be naturally rich in carbon and oxygen, while the alternative preferential depletion scenario states that the enrichment has evolved to the current state from a gas with solar-like abundances. In the latter case, the radiation pressure from the star expels the gas outwards, leaving behind species that are less sensitive to stellar radiation such as C and O. Nitrogen is not sensitive to radiation pressure either as a result of its low oscillator strength, which would make it also overabundant under the preferential depletion scenario. The abundance of nitrogen in the disc may therefore provide clues to why C and O are overabundant. Aims. We aim to measure the nitrogen column density in the direction of β Pictoris (including contributions by the interstellar medium and circumstellar disc), and use this information to distinguish these different scenarios to explain the C and O overabundance. Methods. Using far-UV spectroscopic data collected by the Hubble Space Telescope’s Cosmic Origins Spectrograph (COS) instrument, we analysed the spectrum and characterised the NI triplet by modelling the absorption lines. Results. We measure the nitrogen column density in the direction of β Pictoris for the first time, and find it to be log(NNI/1 cm2) = 14.9 ± 0.7. The nitrogen gas is found to be consistent with solar abundances and Halley dust. We also measure an upper limit for the column density of MnII in the disc at log(NMnII/1 cm2)CS = 12.7+0.1 and calculate the column density of SIII** in the disc to be log(NSIII★★/1 cm2)CSX = 14.2 ± 0.1. Both results are in good agreement with previous studies. Conclusions. The solar nitrogen abundance supports the preferential production hypothesis, in which the composition of gas in β Pictoris is the result of photodesorption from icy grains that are rich in C and O or collisional vaporisation of C- and O-rich dust in the disc. It does not support the hypothesis that C and O are overabundant because C and O are insensitive to radiation pressure, which would cause them to accumulate in the disc.

Characterizing circumgalactic gas around massive ellipticals atz∼ 0.4 – II. Physical properties and elemental abundances

We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d<160 kpc of luminous red galaxies (LRGs). The sample comprises 16 intermediate-redshift (z=0.21-0.55) LRGs of stellar mass M_star>1e11 M_sun. Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full HI Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually-matched components, we show that cool gas (T~1e4 K) density and metallicity can vary by more than a factor of ten in in an LRG halo. Specifically, metal-poor absorbing components with <1/10 solar metallicity are seen in 50% of the LRG halos, while gas with solar and super-solar metallicity is also common. These results indicate a complex multiphase structure and poor chemical mixing in these quiescent halos. We calculate the total surface mass density of cool gas, \Sigma_cool, by applying the estimated ionization fraction corrections to the observed HI column densities. The radial profile of \Sigma_cool is best-described by a projected Einasto profile of slope \alpha=1 and scale radius r_s=48 kpc. We find that typical LRGs at z~0.4 contain cool gas mass of M_cool= (1-2) x1e10 M_sun at d<160 kpc (or as much as 4x1e10 M_sun at d<500 kpc), comparable to the cool CGM mass of star-forming galaxies. Furthermore, we show that high-ionization OVI and low-ionization absorption species exhibit distinct velocity profiles, highlighting their different physical origins. We discuss the implications of our findings for the origin and fate of cool gas in LRG halos.

HST/COS observations of the newly discovered obscuring outflow in NGC 3783

Aims.To understand the nature of transient obscuring outflows in active galactic nuclei, we use simultaneous multiwavelength observations withXMM-Newton, NuSTAR, theHubbleSpace Telescope (HST), and the Max Planck Gesellschaft/European Southern Observatory (ESO) 2.2 m telescope triggered by soft X-ray absorption detected bySwift.Methods.We obtained ultraviolet spectra on 2016-12-12 and 2016-12-21 using the Cosmic Origins Spectrograph (COS) on HST simultaneously with X-ray spectra obtained withXMM-NewtonandNuSTAR. We modeled the ultraviolet spectra to measure the strength and variability of the absorption, and used photoionization models to obtain its physical characteristics.Results.We find new components of broad, blue-shifted absorption associated with Lyα, N V, Si IV, and C IVin our COS spectra. The absorption extends from near-zero velocities in the rest-frame of the host galaxy to −6200 km s−1. These features appear for the first time in NGC 3783 at the same time as heavy soft X-ray absorption seen in theXMM-NewtonX-ray spectra. The X-ray absorption has a column density of ∼1023cm−2, and it partially covers the X-ray continuum source. Combining the X-ray column densities with the UV spectral observations yields an ionization parameter for the obscuring gas of logξ= 1.84−0.2+0.4erg cm s−1. Despite the high intensity of the UV continuum in NGC 3783,F(1470 Å) = 8 × 10−14erg cm−2s−1Å−1&gt;, the well known narrow UV absorption lines are deeper than in earlier observations in unobscured states, and low ionization states such as C IIIappear, indicating that the narrow-line gas is more distant from the nucleus and is being shadowed by the gas producing the obscuration. Despite the high continuum flux levels in our observations of NGC 3783, moderate velocities in the UV broad line profiles have substantially diminished.Conclusions.We suggest that a collapse of the broad line region has led to the outburst and triggered the obscuring event.

Circumgalactic Gas at Its Extreme: Tidal Gas Streams around the Whale Galaxy NGC 4631 Explored with HST/COS

Abstract We present a detailed analysis of the absorption properties of one of the tidal gas streams around the “Whale” galaxy NGC 4631 in the direction of the quasar 2MASS J12421031+3214268. Our study is based on ultraviolet spectral data obtained with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope (HST) and 21cm-data from the HALOGAS project and the Green Bank Telescope (GBT). We detect strong H i Lyα absorption in the velocity range +550 to +800 km s−1 related to gas from a NGC 4631 tidal stream known as Spur 2. We measure a column density of log (N(H i/cm−2)) = 18.68 ± 0.15, indicating that the quasar sightline traces the outer boundary of Spur 2 as seen in the 21 cm data. Metal absorption in Spur 2 is detected in the lines of O i, C ii, Si ii, and Si iii in a complex absorption pattern that reflects the multiphase nature of the gas. We find that the average neutral gas fraction in Spur 2 toward 2MASS J12421031+3214268 is only 14%. This implies that ionized gas dominates the total mass of Spur 2, which then may comprise more than 109 M ☉. No significant depletion of Si is observed, showing that Spur 2 does not contain significant amounts of dust. From the measured O i/H i column density ratio, we determine an α abundance in Spur 2 of solar ([α/H] = −0.90±0.16), which is substantially lower than what is observed in the NGC 4631 disk. The low metallicity and low dust content suggest that Spur 2 represents metal-deficient gas stripped off a gas-rich satellite galaxy during a recent encounter with NGC 4631.

The COS CGM Compendium. I. Survey Design and Initial Results

Abstract We present a neutral hydrogen-selected absorption-line survey of gas with H i column densities at using the Cosmic Origins Spectrograph on the Hubble Space Telescope. Our main aim is to determine the metallicity distribution of these absorbers. Our sample consists of 224 absorbers selected on the basis of their H i absorption strength. Here we discuss the properties of our survey and the immediate empirical results. We find singly and doubly ionized metal species, and H i typically have similar velocity profiles, implying they probe gas in the same or similar environments. The ionic ratios (e.g., / , / ) indicate that the gas in these absorbers is largely ionized, and the ionization conditions are quite comparable across the sampled range. The Doppler parameters of the H i imply K on average, consistent with the gas being photoionized. The Mg ii column densities span &gt;2 orders of magnitude at any given , indicating a wide range of metallicities (from solar to &lt;1/100 solar). In the range of , there is a gap in the distribution corresponding to gas with ∼10% solar metallicity, consistent with the gap seen in the previously identified bimodal metallicity distribution in this column density regime. Less than 3% of the absorbers in our sample show no detectable metal absorption, implying that truly pristine gas at is uncommon. We find [Fe ii/Mg ii] , and since α-enhancement can affect this ratio, dust depletion is extremely mild.

The z = 0.54 LoBAL Quasar SDSS J085053.12+445122.5. I. Spectral Synthesis Analysis Reveals a Massive Outflow∗

Abstract We introduce SimBAL, a novel spectral-synthesis procedure that uses grids of ionic column densities generated by the photoionization code Cloudy and a Bayesian model calibration to forward-model broad absorption-line quasar (BALQ) spectra. We used SimBAL to analyze the Hubble Space Telescope Cosmic Origins Spectrograph (COS) spectrum of the low-redshift BALQ SDSS J085053.12+445122.5. SimBAL analysis yielded velocity-resolved information about the physical conditions of the absorbing gas. We found that the ionization parameter and column density increase, and the covering fraction decreases, as a function of velocity. The log column density is 22.9 (22.4) (cm−2) for solar (Z = 3 Z ⊙) metallicity. The outflow lies 1–3 pc from the central engine, consistent with the estimated location of the torus. The mass outflow rate is 17–28 M ⊙ yr−1, the momentum flux is consistent with L Bol/c, and the ratio of the kinematic to bolometric luminosity is 0.8%–0.9%. The outflow velocity is similar to the escape velocity at the absorber’s location, and force multiplier analysis indicates that part of the outflow could originate in resonance-line driving. The location near the torus suggests that dust scattering may play a role in the acceleration, although the lack of reddening in this UV-selected object indicates a relatively dust-free line of sight. The low accretion rate (0.06L Edd) and compact outflow suggests that SDSS J0850+4451 might be a quasar past its era of feedback, although since its mass outflow is about eight times the accretion rate, the wind is likely integral to the accretion physics of the central engine.

FUV line emission, gas kinematics, and discovery of [Fe XXI] λ1354.1 in the sightline toward a filament in M87

We present new Hubble Space Telescope – Cosmic Origins Spectrograph (HST-COS) G130M spectroscopy which we have obtained for a sightline toward a filament projected 1.9 kpc from the nucleus of M87, near the edge of the inner radio lobe to the east of the nucleus. The combination of the sensitivity of COS and the proximity of M87 allows us to study the structure of this filament in unparalleled detail. We propose that the filament is composed of many cold clumps, each surrounded by an FUV-emitting boundary layer, with the filament having a radius rc ~ 10 pc and the clumps filling the cylinder with a low volume filling factor. The observed velocity dispersion in emission lines from the filament results from the random motions of these clumps within the filament. We have measured fluxes and kinematics for emission lines of Lyα, C II λ1335, and N V λ1238, finding vr = 147 ± 2 km s−1, 138 ± 18 km s−1, and 148−16+14 km s−1 relative to M87, and line broadenings σr = 171 ± 2 km s−1, 189−11+12 km s−1, and 128−17+23 km s−1 respectively. We associate these three lines, as well as archival measurements of Hα, C IV λ1549, and He II λ1640, with a multitemperature boundary layer around clumps which are moving with supersonic random motions in the filament. This boundary layer is a significant coolant of the hot gas. We show that the [C II] λ158 μm flux observed by Herschel-PACS from this region implies the existence of a massive cold (T ~ 103 K) component in the filament which contains significantly more mass (M ~ 8000 M⊙ within our r ≈ 100 pc sightline) than the FUV-emitting boundary layer. It has about the same bulk velocity and velocity dispersion as the boundary layer. We also detect [Fe XXI] λ1354 in emission at 4−5σ. This line is emitted from 1 keV (T ≈ 107 K) plasma, and we use it to measure the bulk radial velocity vr = −92−22+34 km s−1 and velocity dispersion σr = 69−27+79 km s−1 of the plasma at this temperature. In contrast to the intermediate-temperature FUV lines, [Fe XXI] is blueshifted relative to M87 and matches the bulk velocity of a nearby filament to the south. We hypothesize that this line arises from the approaching face of the radio bubble expanding through this sightline, while the filament lies on the receding side of the bubble. A byproduct of our observations is the detection of absorption from interstellar gas in our Galaxy, observed in C II λ1335 and Lyα.

Revisiting the Iron Abundance in the Hyper Iron-poor Star HE 1327–2326 with UV COS/HST Data*

Abstract We present a new iron abundance analysis of the hyper metal-poor star HE 1327−2326, based on Fe ii lines detected in its UV spectral range for the first time. In a Cosmic Origins Spectrograph (COS) spectrum, five new Fe ii lines could be measured. A Si i line was also detected for the first time. We determine a 1D local thermodynamic equilibrium (LTE) Fe ii abundance of [Fe ii/H] = −5.99 ± 0.25. We also investigate departures from LTE for both Fe i and Fe ii lines. Guided by 3D non-LTE (NLTE) analyses of other well-studied metal-poor stars, we identify potential “residual” 3D effects in HE 1327−2326 arising from the absence of full 3D NLTE Fe calculations. Accordingly, we employ measurements of 10 weak Fe i lines previously detected in an optical spectrum of HE 1327−2326, as no Fe i lines are detectable in our UV spectrum. Following our previous work, we adopt the 1D NLTE Fe i abundance of = −5.20 ± 0.12 for HE 1327−2326. Adopting a value based on the optical Fe i rather than UV lines was heavily informed by our extensive investigation of model atmosphere and radiative transfer effects on different lines across the entire UV–optical wavelength range. An iron abundance of = −5.20 ± 0.12 is only 0.2 dex higher than what was used in previous studies. Accordingly, no previous conclusions regarding the nature of the star are affected.

A Galaxy Redshift Survey Near HST/COS AGN Sight Lines

Abstract To establish the connection between galaxies and UV-detected absorption systems in the local universe, a deep (g ≤ 20) and wide (∼20′ radius) galaxy redshift survey is presented around 47 sight lines to UV-bright AGNs observed by the Cosmic Origins Spectrograph (COS). Specific COS science team papers have used this survey to connect absorbers to galaxies, groups of galaxies, and large-scale structures, including voids. Here we present the technical details of the survey and the basic measurements required for its use, including redshifts for individual galaxies and uncertainties determined collectively by spectral class (emission-line, absorption-line, and composite spectra) and completeness for each sight line as a function of impact parameter and magnitude. For most of these sight lines, the design criteria of &gt;90% completeness over a &gt;1 Mpc region down to ≲0.1 L* luminosities at z ≤ 0.1 allows a plausible association between low-z absorbers and individual galaxies. Lyα covering fractions are computed to approximate the star-forming and passive galaxy populations using the spectral classes above. In agreement with previous results, the covering fraction of star-forming galaxies with L ≥ 0.3 L* is consistent with unity inside one virial radius and declines slowly to &gt;50% at four virial radii. On the other hand, passive galaxies have lower covering fractions (∼60%) and a shallower decline with impact parameter, suggesting that their gaseous halos are patchy but have a larger scale-length than star-forming galaxies. All spectra obtained by this project are made available electronically for individual measurement and use.

Probing the Southern Fermi Bubble in Ultraviolet Absorption Using Distant AGNs

Abstract The Fermi Bubbles are two giant gamma-ray emitting lobes extending 55° above and below the Galactic center. While the Northern Bubble has been extensively studied in ultraviolet (UV) absorption, little is known about the gas kinematics of the southern Bubble. We use UV absorption-line spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to probe the southern Fermi Bubble using a sample of 17 background AGNs projected behind or near the Bubble. We measure the incidence of high-velocity clouds (HVC), finding that 4 out of 6 sightlines passing through the Bubble show HVC absorption, versus 6 out of 11 passing outside. We find strong evidence that the maximum absolute LSR velocity of the HVC components decreases as a function of galactic latitude within the Bubble, for both blueshifted and redshifted components, as expected for a decelerating outflow. We explore whether the column density ratios Si iv/Si iii, Si iv/Si ii, and Si iii/Si ii correlate with the absolute galactic latitude within the Bubble. These results demonstrate the use of UV absorption-line spectroscopy to characterize the kinematics and ionization conditions of embedded clouds in the Galactic center outflow.

Low-redshift Lyman continuum leaking galaxies with high [O iii]/[O ii] ratios

We present observations with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope of five star-forming galaxies at redshifts z in the range 0.2993-0.4317 and with high emission-line flux ratios O32=[OIII]5007/[OII]3727 ~ 8-27 aiming to detect the Lyman continuum (LyC) emission. We detect LyC emission in all galaxies with the escape fractions fesc(LyC) in a range of 2-72 per cent. A narrow Ly-alpha emission line with two peaks in four galaxies and with three peaks in one object is seen in medium-resolution COS spectra with a velocity separation between the peaks Vsep varying from ~153 km/s to ~345 km/s. We find a general increase of the LyC escape fraction with increasing O32 and decreasing stellar mass M*, but with a large scatter of fesc(LyC). A tight anti-correlation is found between fesc(LyC) and Vsep making Vsep a good parameter for the indirect determination of the LyC escape fraction. We argue that one possible source driving the escape of ionizing radiation is stellar winds and radiation from hot massive stars.