Explore the vast range of titles available.

Outflowing winds of multiphase plasma have been proposed to regulate the buildup of galaxies, but key aspects of these outflows have not been probed with observations. By using ultraviolet absorption spectroscopy, we show that \"warm-hot\" plasma at 10 5.5 kelvin contains 10 to 150 times more mass than the cold gas in a post-star burst galaxy wind. This wind extends to distances > 68 kiloparsecs, and at least some portion of it will escape. Moreover, the kinematical correlation of the cold and warm-hot phases indicates that the warm-hot plasma is related to the interaction of the cold matter with a hotter (unseen) phase at »10⁶ kelvin. Such multiphase winds can remove substantial masses and alter the evolution of post-star burst galaxies.

This program is part of QUEST (Quasar/ULIRG Evolutionary Study) and seeks to examine the gaseous environments of z ≲ 0.3 quasars and ULIRGs as a function of host galaxy properties and age across the merger sequence from ULIRGs to quasars. This first paper in the series focuses on 33 quasars from the QUEST sample and on the kinematics of the highly ionized gas phase traced by the N v λ λ 1238,1243 and O vi λ λ 1032,1038 absorption lines in high-quality Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) data. N v and O vi outflows are present in about 60% of the QUEST quasars and span a broad range of properties, both in terms of equivalent widths (from 20 mÅ to 25 Å) and kinematics (outflow velocities from a few×100 km s−1 up to ∼10,000 km s−1). The rate of incidence and equivalent widths of the highly ionized outflows are higher among X-ray weak or absorbed sources. The weighted outflow velocity dispersions are highest among the X-ray weakest sources. No significant trends are found between the weighted outflow velocities and the properties of the quasars and host galaxies, although this may be due to the limited dynamic range of properties of the current sample. These results will be re-examined in an upcoming paper where the sample is expanded to include the QUEST ULIRGs. Finally, a lower limit of ∼0.1% on the ratio of time-averaged kinetic power to bolometric luminosity is estimated in the 2–4 objects with blueshifted P v λ λ 1117,1128 absorption features.

Specifically selected to leverage the unique ultraviolet capabilities of the Hubble Space Telescope, the Hubble Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) is a Director’s Discretionary program of approximately 1000 orbits—the largest ever executed—that produced a UV spectroscopic library of O and B stars in nearby low-metallicity galaxies and accreting low-mass stars in the Milky Way. Observations from ULLYSES combined with archival spectra uniformly sample the fundamental astrophysical parameter space for each mass regime, including spectral type, luminosity class, and metallicity for massive stars, and the mass, age, and disk accretion rate for low-mass stars. The ULLYSES spectral library of massive stars will be critical to characterize how massive stars evolve at different metallicities; to advance our understanding of the production of ionizing photons, and thus of galaxy evolution and the re-ionization of the Universe; and to provide the templates necessary for the synthesis of integrated stellar populations. The massive-star spectra are also transforming our understanding of the interstellar and circumgalactic media of low-metallicity galaxies. On the low-mass end, UV spectra of T Tauri stars contain a plethora of diagnostics of accretion, winds, and the warm disk surface. These diagnostics are crucial for evaluating disk evolution and provide important input to assess atmospheric escape of planets and to interpret powerful probes of disk chemistry, as observed with the Atacama Large Millimeter Array and the James Webb Space Telescope. In this paper, we motivate the design of the program, describe the observing strategy and target selection, and present initial results.

Using data from HST/STIS (Hubble Space Telescope / Space Telescope Imaging Spectrograph) and FUSE (Far Ultraviolet Spectroscopic Explorer) toward two QSOs, H1821+643 and HS0624+6907, we find that the overall metallicity of the Galactic “Outer Arm” is Z=0.3−0.5 Z⊙ with underabundant nitrogen and little depletion by dust. The results are consistent with those based on H II region measurements in the outer galaxy and provide additional constrains on models of the Galactic abundance gradient and Milky Way (MW) chemical evolution. The lower metallicity observed in the outer galaxy is consistent with abundance patterns observed in higher redshift damped Lyα absorbers (DLAs) extrapolated to z=0. The slow metallicity evolution of DLAs could be due to the larger cross sections of the outer regions of galaxies combined with the observed metallicity gradients.

The evolution of dwarf galaxies, particularly any potential morphological evolution among the different types of dwarf galaxies, remains poorly understood. The interstellar medium (ISM) in dwarf galaxies is thought to be more strongly disturbed by star formation episodes in these low mass galaxies, including supernovae-driven winds during starbursts and star formation induced by galaxy-galaxy interactions. Loss of the ISM has been postulated to result in the evolution of dIrrs to dE/dSphs. However, disentangling the relative importance of environmental (galaxy harassment) versus local stocastic processes on star formation, and their effects on subsequent morphological evolution is still a very active area of research. So-called “transition dwarf” galaxies are galaxies that have properties that fall somewhere between gas-rich dIrrs and gas-poor dE/dSphs, and may provide clues to the overall evolutionary history of dwarf galaxies. We report on some recent work on a sample of vigorously star-forming dwarf “transition” galaxies, and suggest that they may be examples of the bridge between dIrrs and dEs/dSphs.

Combined high-dispersion IUE spectra of interstellar Si IV, IV, and N v absorption along distant sight lines toward early-type stars in the Galactic disk and low halo are discussed. The highly ionized species have complex profiles and exhibit stronger absorption toward distant low-latitude stars than toward high-latitude stars. Absorption along low-latitude directions is often broadened substantially (up to 100 km s⁻ⁱ in some cases) by Galactic rotation. Along these sight lines the Si iv, IV, and N v profiles are more similar in shape to each other than to those of Al III, which is a tracer of photoionized interstellar gas. The observed column density ratios of the high ions, (N(Clv)/N(Si iv)) = 3.6 ± 1.3 and < N(C IV)/N(N v)> = 4.6 ± 2.7, are similar in widely different regions within the Galaxy. The similarities in the high ion profile shapes along individual sight lines and integrated column density ratios along different sight lines suggest a common origin for these species in collisionally ionized gas associated with a global process such as a Galactic fountain.

This program is part of QUEST (Quasar/ULIRG Evolutionary Study) and seeks to examine the gaseous environments of z < 0.3 quasars and ULIRGs as a function of host galaxy properties and age across the merger sequence from ULIRGs to quasars. This first paper in the series focuses on 33 quasars from the QUEST sample and on the kinematics of the highly ionized gas phase traced by the N V 1238, 1243 A and O VI 1032, 1038 A absorption lines in high-quality Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) data. N V and O VI outflows are present in about 60% of the QUEST quasars and span a broad range of properties, both in terms of equivalent widths (from 20 mA to 25 A) and kinematics (outflow velocities from a few x 100 km/s up to ~10,000 km/s). The rate of incidence and equivalent widths of the highly ionized outflows are higher among X-ray weak or absorbed sources. The weighted outflow velocity dispersions are highest among the X-ray weakest sources. No significant trends are found between the weighted outflow velocities and the properties of the quasars and host galaxies although this may be due to the limited dynamic range of properties of the current sample. These results will be re-examined in an upcoming paper where the sample is expanded to include the QUEST ULIRGs. Finally, a lower limit of ~0.1% on the ratio of time-averaged kinetic power to bolometric luminosity is estimated in the 2-4 objects with blueshifted P V 1117, 1128 absorption features.

Specifically selected to leverage the unique ultraviolet capabilities of the Hubble Space Telescope, the Hubble Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) is a Director's Discretionary program of approximately 1000 orbits - the largest ever executed - that produced a UV spectroscopic library of O and B stars in nearby low metallicity galaxies and accreting low mass stars in the Milky Way. Observations from ULLYSES combined with archival spectra uniformly sample the fundamental astrophysical parameter space for each mass regime, including spectral type, luminosity class, and metallicity for massive stars, and the mass, age, and disk accretion rate for low-mass stars. The ULLYSES spectral library of massive stars will be critical to characterize how massive stars evolve at different metallicities; to advance our understanding of the production of ionizing photons, and thus of galaxy evolution and the re-ionization of the Universe; and to provide the templates necessary for the synthesis of integrated stellar populations. The massive star spectra are also transforming our understanding of the interstellar and circumgalactic media of low metallicity galaxies. On the low-mass end, UV spectra of T Tauri stars contain a plethora of diagnostics of accretion, winds, and the warm disk surface. These diagnostics are crucial for evaluating disk evolution and provide important input to assess atmospheric escape of planets and to interpret powerful probes of disk chemistry, as observed with ALMA and JWST. In this paper we motivate the design of the program, describe the observing strategy and target selection, and present initial results.

We report on the detection of deuterated molecular hydrogen, HD, at \\(z = 0.18\\). HD and H\\(_ 2\\) are detected in HST/COS data of a low metallicity (\\(Z 0.07Z_\\)) damped Ly\\(\\) system at \\(z = 0.18562\\) toward QSO B0120\\(-\\)28, with log \\(N\\)(H I) = 20.50 \\(\\) 0.10. Four absorption components are clearly resolved in H\\(_ 2\\) while two components are resolved in HD; the bulk of the molecular hydrogen is associated with the components traced by HD. We find total column densities log \\(N\\)(HD) = 14.82 \\(\\) 0.15 and log \\(N\\)(H\\(_ 2\\)) = 20.00 \\(\\) 0.10. This system has a high molecular fraction, \\(f\\)(H\\(_ 2\\)) = 0.39 \\(\\) 0.10 and a low HD to H\\(_ 2\\) ratio, log (HD/2H\\(_ 2\\)) \\(= -5.5 0.2\\) dex. The excitation temperature, \\(T_01 = 65 2\\) K, in the component containing the bulk of the molecular gas is lower than in other DLAs. These properties are unlike those in other higher redshift DLA systems known to contain HD, but are consistent with what is observed in dense clouds in the Milky Way.

The Smith Cloud is a gaseous high-velocity cloud (HVC) in an advanced state of accretion, only 2.9 kpc below the Galactic plane and due to impact the disk in 27 Myr. It is unique among HVCs in having a known distance (12.4+/-1.3 kpc) and a well-constrained 3D velocity (296 km/s), but its origin has long remained a mystery. Here we present the first absorption-line measurements of its metallicity, using HST/COS UV spectra of three AGN lying behind the Cloud together with Green Bank Telescope 21 cm spectra of the same directions. Using Voigt-profile fitting of the S II 1250, 1253, 1259 triplet together with ionization corrections derived from photoionization modeling, we derive the sulfur abundance in each direction; a weighted average of the three measurements gives [S/H]=-0.28+/-0.14, or 0.53+0.21-0.15 solar metallicity. The finding that the Smith Cloud is metal-enriched lends support to scenarios where it represents recycled Galactic material rather than the remnant of a dwarf galaxy or accreting intergalactic gas. The metallicity and trajectory of the Cloud are both indicative of an origin in the outer disk. However, its large mass and prograde kinematics remain to be fully explained. If the cloud has accreted cooling gas from the corona during its fountain trajectory, as predicted in recent theoretical work, its current mass would be higher than its launch mass, alleviating the mass concern.