FUTURE DIRECTIONS IN ULTRAVIOLET SPECTROSCOPY: A Conference Inspired by the Accomplishments of the Far Ultraviolet Spectroscopic Explorer Mission
1135(2009); http://dx.doi.org/10.1063/1.3154080View Description Hide Description
Most of the normal baryonic matter of the Universe at high and at low redshift is found in the space between galaxies. The study of this matter at low redshift has required access to ultraviolet spectroscopic space observatories. HST and FUSE have revealed that at low redshift of the baryons reside in the cool photoionized IGM traced by the Lyman α forest while another might exist in the warm portion of the warm‐hot IGM. Evidence for the warm gas is provided by some of the O VI absorbers, the Ne VIII absorbers and very broad Lyman alpha absorbers. Understanding the physical conditions in these absorbers is important for reliably determining their baryonic content. The low z IGM is likely to play a crucial role in the evolution of the of the baryons found in galaxies.
1135(2009); http://dx.doi.org/10.1063/1.3154092View Description Hide Description
Simulations predict that shocks from large‐scale structure formation and galactic winds have reduced the fraction of baryons in the warm, photoionized phase (the forest) from nearly 100% in the early universe to less than 50% today. Some of the remaining baryons are predicted to lie in the warm‐hot ionized medium (WHIM) phase at but the quantity remains a highly tunable parameter of the models. Modern UV spectrographs have provided unprecedented access to both the forest and potential WHIM tracers at and several independent groups have constructed large catalogs of far‐UV IGM absorbers along AGN sight lines. There is general agreement between the surveys that the warm, photoionized phase makes up of the baryon budget at Another can be accounted for in collapsed structures (stars, galaxies, etc.). However, interpretation of the high‐ion (O VI, etc) absorbers at is more controversial. These species are readily created in the shocks expected to exist in the IGM, but they can also be created by photoionization and thus not represent WHIM material. Given several pieces of observational evidence and theoretical expectations, I argue that most of the observed O VI absorbers represent shocked gas at rather than photoionized gas at and they are consequently valid tracers of the WHIM phase. Under this assumption, enriched gas at can account for of the baryon budget at but this value may increase when bias and incompleteness are taken into account and help close the gap 50% of the “missing” baryons.
1135(2009); http://dx.doi.org/10.1063/1.3154042View Description Hide Description
Over its 8‐year lifetime, the Far Ultraviolet Spectroscopic Explorer observed over 200 hundred active galactic nuclei (AGN). Many of these observations were campaigns dedicated to AGN science, including coordinated observations with other observatories such as Chandra, XMM‐Newton, and the Hubble Space Telescope. However, most observations were part of large samples of nearby AGN that served as background probes of gas in the interstellar medium, the Galactic halo and the local intergalactic medium. These large samples and the dedicated campaigns have broadly advanced our understanding of the far‐ultraviolet continuum of AGN and the ubiquitous outflows of photoionized gas from their active nuclei. The bright, nearby, lower‐luminosity AGN observed with FUSE generally have bluer continua than their higher luminosity counterparts observed with HST, and the spectral shapes are broadly consistent with accretion disk models. More than half of the Type 1 AGN observed with FUSE show blueshifted intrinsic absorption by the O VI doublet, indicative of highly ionized outflows from the central nuclear regions. I will give an overview of these observations, and interpret them in the context of winds from accretion disks and thermally driven winds originating from the obscuring torus, with an eye toward what observational capabilities are needed in the future to understand the role of outflows in the structure and evolution of AGN, and their impact on their environments.
1135(2009); http://dx.doi.org/10.1063/1.3154060View Description Hide Description
We report on the second ever σ detection of a Ne VIII intergalactic absorption system. The system is identified in the FUSE spectrum of 3C 263 at a redshift of The presence of intermediate ionization species such as O III, O IV, N IV and C IV at the same velocity as Ne VIII, confirms that the absorption system is tracing gas at multiple ionization conditions. Unlike the intermediate ions, we find that the Ne VIII in this absorber is inconsistent with having an origin in a cool photoionization gas phase. The more likely source is collisional ionization in a warm shock‐heated phase, in which case the absorber is tracing the WHIM phase of the IGM. Further constraints from H I and O IV are needed to better understand the physical conditions in the warm collisionally ionized gas. The properties of this absorber bear resemblance to the previous detection of Ne VIII reported by Savage et al. (2005).
1135(2009); http://dx.doi.org/10.1063/1.3154068View Description Hide Description
I review some of the findings on the Magellanic System produced by the Far Ultraviolet Spectroscopic Explorer (FUSE) during and after its eight years of service. The Magellanic System with its high‐velocity complexes provides a nearby laboratory that can be used to characterize phenomena that involve interaction between galaxies, infall and outflow of gas and metals in galaxies. These processes are crucial for understanding the evolution of galaxies and the intergalactic medium. Among the FUSE successes I highlight are the coronal gas about the LMC and SMC, and beyond in the Stream, the outflows from these galaxies, the discovery of molecules in the diffuse gas of the Stream and the Bridge, an extremely sub‐solar and sub‐SMC metallicity of the Bridge, and a high‐velocity complex between the Milky Way and the Clouds.
1135(2009); http://dx.doi.org/10.1063/1.3154078View Description Hide Description
The O VI absorber at detected in the spectrum of the QSO PKS 0312–77 is the strongest discovered so far in the low redshift Universe and is observed near a Lyman limit system (LLS). We present an analysis of these absorbers and their connection to galaxies based on a combination of FUV and NUV spectra of PKS 0312–77 obtained from FUSE and HST/STIS E140M/E230M and optical imaging and spectroscopy of galaxies in the field. Based on O I/H I and a photoionization model, we find a metallicity of 0.25 solar for the LLS, too enriched to be pristine IGM gas. We find that the gas resulting from the merger of a galaxy (impact parameter of 38 kpc) is the likely origin for the LLS. At from the LLS, another absorber is found with a supersolar metallicity. Outflow from this galaxy is likely responsible for this supersolar, fully ionized absorber. The metallicity variation is a possible evidence for poor mixing of metals on galactic structure as observed in the Milky Way halo. The origin of the strong O VI remains more enigmatic with plausible origins including an intragroup medium or a galactic corona.
1135(2009); http://dx.doi.org/10.1063/1.3154079View Description Hide Description
The Far Ultraviolet Spectroscopic Explorer (FUSE) was used to search for emission from the shock interaction of the ejecta of SN 1987A with its circumstellar material. FUSE observations of SN 1987A between 2000 and 2007 did not detect broad O VI emission. However, O VI emission was detected in 2000–2001 with a narrow line width and a heliocentric radial velocity of This places the emitting gas at rest relative to the supernova and is interpreted as emission from unshocked circumstellar gas. This narrow emission had disappeared in 2007 (and possibly earlier) as a result of the advancing shock overtaking the H II region that was flash ionized by the supernova explosion in 1987.
1135(2009); http://dx.doi.org/10.1063/1.3154081View Description Hide Description
We have embarked on a project to characterize the global properties of OVI absorption toward stars in the Large Magellanic Cloud observed with FUSE. OVI ISM absorption in LMC stellar spectra shows a wide range of appearances, depending on the stellar spectral type and luminosity class as well as the presence or absence of galactic or intermediate velocity absorption. We have performed a careful spectral morphology classification of the sight lines, finding 57 useful targets for measuring OVI. We also identified at least nine sight lines for which upper limits can be determined. By grouping the sight lines based on their spatial morphological characteristics (e.g. field sight lines versus targets within emission structures of various kinds), we find a) evidence for a patchy but generally distributed component of OVI, and b) significant evidence for excess OVI from nebular sub‐structures associated with active star formation and superbubbles.
1135(2009); http://dx.doi.org/10.1063/1.3154082View Description Hide Description
We announce the availability of a new online resource through the High Level Science Products program at the Multi‐Mission Archive at Space Telescope (MAST). We have reprocessed the entire far‐ultraviolet database of sight lines toward stars observed with the FUSE satellite in both Magellanic Clouds (187 in the LMC, 100 in the SMC) using the final version of the FUSE calibration pipeline, CalFUSE 3.2. We have made these data and various sight line summary plots and ancillary supporting information available online at the MAST site http://archive.stsci.edu/prepds/fuse_mc. We describe briefly the products available through this web site, and how they can be used to provide a summary assessment of each sight line for use in a wide range of science investigations.
1135(2009); http://dx.doi.org/10.1063/1.3154083View Description Hide Description
Column densities for H I, Al III, Si IV, C IV, and O VI toward 109 stars and 30 extragalactic objects have been assembled in order to study the relative extensions of these species away from the Galactic plane into the Galactic halo. H I and Al III trace the warm neutral and warm ionized medium, respectively, while Si IV, C IV and O VI trace a combination of warm photoionized and collisionally ionized transition temperature plasma. The large object sample allows us to consider and correct for the effects of the sample bias that has affected the results of earlier but smaller surveys of the gas distributions. We find Si IV and C IV have similar exponential scale heights of to 3.6 kpc. The scale height of O VI is marginally smaller with The transition temperature gas is times more extended than the warm ionized medium traced by Al III with and times more extended than the warm neutral medium traced by H I with There is a factor of 2 decrease in the dispersion of the ionic column density ratios for transition temperature gas for lines of sight in the Galactic disk compared to extragalactic lines of sight through the entire halo. The logarithmic dispersions for N(C IV)/N(O VI) and N(Si IV)/N(O VI) are approximately twice that found for N(Si IV)/N(C IV).
1135(2009); http://dx.doi.org/10.1063/1.3154084View Description Hide Description
We present Far Ultraviolet Spectroscopic Explorer (FUSE) measurements and photoionization analysis of UV absorption in the 3 observations of the low‐z Seyfert 1 object IRAS F22456‐5125. These 5 distinct, narrow absorbers span a significant range in velocity ( to ) and ionization (Lyman series, C III, N III, and O VI). We find that the object shows little evidence for corresponding X‐ray absorption, and shows variability in the continuum flux of the object (by a factor of 6) the timescale covered by the FUSE observations.
In the coming HST cycle we will observe this object and 5 other low‐z quasars and Seyfert galaxies with the Cosmic Origins Spectrograph (COS) as part of a systematic effort to determine the chemical abundances of AGN. These objects show strong C III absorption, which leads us to believe that these targets are good candidates to search for C 1173 Å. This will provide us with both the density and the distance to the absorbers for several objects, which therefore yield the kinetic luminosity for the outflows.
1135(2009); http://dx.doi.org/10.1063/1.3154085View Description Hide Description
FUSE Spectra of the nuclear region of NGC 1068 find strong OVI emission consisting of a pair of narrow and broad components. There is a gradient in the velocity field for the narrow O VI component of from southwest of the nucleus to northeast. A similar pattern is also observed with the broad O VI component, with a gradient of These results are consistent with the HST/STIS findings and suggest a biconical structure in which the velocity field is mainly radial outflow.
1135(2009); http://dx.doi.org/10.1063/1.3154086View Description Hide Description
Highly‐ionized high‐velocity clouds have been studied for the last decade. Some lines of reasoning have suggested an extragalactic origin for these clouds, placing them near the outskirts of the Milky Way or Local Group, and some models have explored the possibility that they may be associated with dark matter minihalos. We have observed highly‐ionized HVCs toward the inner Galaxy globular cluster Messier 5 that appear to have a Galactic origin. We present FUSE and STIS observations of the post‐AGB star ZNG 1 in M 5 ( ). Absorption is seen in O VI, C IV, Si IV, and lower ionization species at LSR velocities near and Photoionization models and path length arguments rule out the possibility that this gas is circumstellar. The metallicity of these HVCs is the highest of any known HVC. Given the metallicity and distance constraints, we conclude that these HVCs have a Galactic origin. We hypothesize that these HVCs are part of a large‐scale circulation and may be related to a Galactic nuclear wind. A full description of this work can be found in Zech et al. (2008, ApJ, 679, 460).
1135(2009); http://dx.doi.org/10.1063/1.3154087View Description Hide Description
We present recent results on highly ionized gas in Galactic High‐Velocity Clouds (HVCs), originally surveyed in O VI , In a new FUSE /HST survey of Si II/III/IV (Shull et al. 2009) toward 37 AGN, we detected Si III (λ 1206.500 Å) absorption with a sky coverage fraction (61 HVCs along 30 of 37 high‐latitude sight lines). The Si III (λ 1206.500 Å) line is typically 4–5 times stronger than O VI (λ 1031.926 Å). The mean HVC colum density of perhaps of low‐metallicity ionized gas in the low halo. Recent determinations of HVC distances allow us to estimate a total reservoir of Estimates of infall velocities indicate an infall rate of around comparable to the replenishment rate for star formation in the disk. HVCs appear to be sheathed by intermediate‐temperature gas detectable in Si III and Si IV, as well as hotter gas seen in O VI and other high ions. To prepare for HST observations of 10 HVC‐selected sight lines with the Cosmic Origins Spectrograph (COS), we compile FUSE /STIS spectra of these ions, plus Fe III, C III, C IV, and S IV. Better constraints on the physical properties of HVC envelopes and careful treatment of HVC kinematics and infall rates should come from high‐quality (S/N ) COS data.
1135(2009); http://dx.doi.org/10.1063/1.3154088View Description Hide Description
Analyses of spectra obtained with the Far Ultraviolet Spectrograph Explorer (FUSE) satellite, together with spectra from the Copernicus, Hubble Space Telescope (HST) , and Interstellar Medium Absorption Profile Spectrograph (IMAPS) instruments reveal a very wide range in the observed deuterium/hydrogen (D/H) ratios for interstellar gas in the Galactic disk beyond the Local Bubble. For gas located beyond the Local Bubble but within several hundred parsecs, the observed D/H ratios differ by a factor of 4–5. A critically important question is what value or values of D/H in the local region of our Galaxy should be compared with chemical evolution models of the Galaxy and with the primordial deuterium abundance. Linsky et al. [Astrophys. J. 647, 1106 (2006)] argued that spatial variations in the depletion of deuterium onto dust grains can explain these local variations in the observed gas‐phase D/H ratios. In this provacative introduction to the deuterium session, I ask six questions concerning analysis techniques and proposed results from the FUSE D/H program in the hope that the speakers and participants in this conference will give serious thought to the robustness of our present understanding of this important topic. In particular, is the deuterium depletion model valid? Is it only part of the explanation?
1135(2009); http://dx.doi.org/10.1063/1.3154089View Description Hide Description
During its lifetime, FUSE produced a broad array of exciting results on the interstellar medium (ISM) of our own Milky Way and other galaxies. Some of its most important contributions in this area are in the physics of the highly ionized gas traced by O VI and of the molecular medium traced by the Lyman and Werner bands of I briefly note a few of these successes and discuss future directions and wishes for studying the ISM with next generation instruments.
1135(2009); http://dx.doi.org/10.1063/1.3154090View Description Hide Description
Determining the abundance of deuterium in the Galaxy was one of the primary goals of the FUSE mission. FUSE ‐based D/H and D/O measurements have been published for about thirty new lines of sight, probing column densities and distances that had not been previously accessible. The measurements confirmed that the deuterium abundance is variable on relatively small spatial scales. This had been observed before by Copernicus and IMAPS, albeit for a small number of sightlines. Together with previous D/H measurements, the FUSE observations led to a model that explains the D/H variations in terms of variable depletion of deuterium onto dust grains. Although not perfect and probably not the complete final answer this model is a big step forward in trying to understand the abundance of deuterium in the Milky Way. Such a model would not have been possible without the backdrop of the many FUSE measurements.
In this paper we review all the Galactic measurements of D/H and discuss the causes of uncertainty in these measurements and how they can be affected by systematic errors. We consider the possible causes of the D/H variability and explore future scientific directions that will allow us to better understand the behavior of D/H in the Galaxy.
O VI Absorption in the Milky Way Disk, and Future Prospects for Studying Absorption at the Galaxy‐IGM Interface1135(2009); http://dx.doi.org/10.1063/1.3154091View Description Hide Description
We present a brief summary of results from our FUSE program designed to study O VI absorption in the disk of the Milky Way. As a full analysis of our data has now been published, we focus on the improvements that FUSE afforded us compared to Copernicus data published thirty years ago. We discuss FUSE’S limitations in studying O VI absorption from nearby galaxies using background QSOs, but present FUSE spectra of two probes which indicate the absence of O VI (but the presence of ) absorption 8 and 63 kpc from a foreground galaxy. Finally, we discuss the need for a more sensitive UV spectrograph to map out the physical conditions of baryons around galaxies.
1135(2009); http://dx.doi.org/10.1063/1.3154093View Description Hide Description
The primordial abundance of deuterium produced during Big Bang Nucleosynthesis (BBN) depends sensitively on the universal ratio of baryons to photons, an important cosmological parameter probed independently by the Cosmic Microwave Background (CMB) radiation. Observations of deuterium in high‐redshift, low‐metallicity QSO Absorption Line Systems (QSOALS) provide a key baryometer, determining the baryon abundance at the time of BBN to a precision of Alternatively, if the CMB‐determined baryon to photon ratio is used in the BBN calculation of the primordial abundances, the BBN‐predicted deuterium abundance may be compared with the primordial value inferred from the QSOALS, testing the standard cosmological model. In the post‐BBN universe, as gas is cycled through stars, deuterium is only destroyed so that its abundance measured anytime, anywhere in the Universe, bounds the primordial abundance from below. Constraints on models of post‐BBN Galactic chemical evolution follow from a comparison of the relic deuterium abundance with the FUSE‐inferred deuterium abundances in the chemically enriched, stellar processed material of the local ISM.