J. C. Green

University of Colorado, Denver, Colorado, United States

Are you J. C. Green?

Claim your profile

Publications (64)109.93 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) the COS Science Team has conducted a high signal-to-noise survey of 14 bright QSOs. In a previous paper (Savage et al. 2014) these far-UV spectra were used to discover 14 "warm" ($T > 10^5$ K) absorbers using a combination of broad Ly\alpha\ and O VI absorptions. A reanalysis of a few of this new class of absorbers using slightly relaxed fitting criteria finds as many as 20 warm absorbers can be present in this sample. A shallow, wide spectroscopic galaxy redshift survey has been conducted around these sight lines to investigate the warm absorber environment, which is found to be spiral-rich galaxy groups or cluster outskirts with radial velocity dispersions of \sigma_v = 250-750 km/s. While 2\sigma\ evidence is presented favoring the hypothesis that these absorptions are associated with the galaxy groups and not with the individual nearest galaxies, this evidence has considerable systematic uncertainties and so is not conclusive. However, if the associations are with galaxy groups, the observed frequency of warm absorbers dN/dz = 3.5-5 per unit redshift plus the local density of galaxy groups require these warm absorbers to be very large (~1 Mpc in radius at high covering factor) and, if diffuse (i.e., high filling factor), very massive (> $10^{11} M_{\odot}$). However, with only single probes through each group in this small sample, the conclusion that these "warm absorbers" are detections of a massive intra-group medium in spiral galaxy groups is tentative.
    05/2014;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on the observed properties of the plasma revealed through high signal-to-noise (S/N) observations of 54 intervening O VI absorption systems containing 85 O VI and 133 H I components in a blind survey of 14 QSOs observed at ~18 km s-1 resolution with the Cosmic Origins Spectrograph (COS) over a redshift path of 3.52 at z < 0.5. Simple systems with one or two H I components and one O VI component comprise 50% of the systems. For a sample of 45 well-aligned absorption components where the temperature can be estimated, we find evidence for cool photoionized gas in 31 (69%) and warm gas (6 > log T > 5) in 14 (31%) of the components. The total hydrogen content of the 14 warm components can be estimated from the temperature and the measured value of log N(H I). The very large implied values of log N(H) range from 18.38 to 20.38 with a median of 19.35. The metallicity, [O/H], in the 6 warm components with log T > 5.45 ranges from -1.93 to 0.03 with a median value of -1.0 dex. Ground-based galaxy redshift studies reveal that most of the absorbers we detect sample gas in the IGM extending 200 to 600 kpc beyond the closest associated galaxy. We estimate the warm aligned O VI absorbers contain (4.1+/-1.1)% of the baryons at low z. The warm plasma traced by the aligned O VI and H I absorption contains nearly as many baryons as are found in galaxies.
    03/2014; 212(1).
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have detected and characterized the circumgalactic medium (CGM) of nearby late-type galaxies using both targeted and serendipitous QSO/galaxy pairs at z < 0.2. Photoionization modeling of warm CGM clouds finds volume filling factors of ~5%, cloud sizes of 0.1-30 kpc, cloud masses of 10-108 M⊙, and metallicities of ~0.1-1 Z⊙. The total mass of these warm clouds surrounding L > 0.1 L* galaxies approaches 1010 M⊙, comparable to the total baryons in massive galaxy disks. We also find evidence for an extensive (>500 kpc), hot (105 - 106 K) intracloud medium that is very massive (> 1011 M⊙). We interpret this hot, massive baryon reservoir as the intragroup medium of spiral-rich galaxy groups and find that its inclusion can solve the missing baryon problem in spiral galaxies.
    01/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The unprecedented far-UV throughput of the Cosmic Origins Spectrograph (COS) is revolutionizing studies of the local intergalactic medium (IGM). In particular, COS is allowing us to refine estimates of the baryon content and metallicity of the IGM, as well as the relationship of IGM absorbers to galaxies. For the past several years we have been using WIYN/HYDRA to obtain spectra of all galaxies brighter than g=20 that are within 20 arcminutes of the ~25 AGN targeted by the COS Science Team that are accessible from the northern hemisphere. When combined with the COS spectra of these AGN, this galaxy redshift survey is enhancing our understanding of the composition and topology of the nearby Universe in both gas and galaxies, allowing us to assess the extent of metal transport away from galaxies, the filling factor of gas and metal-enriched gas in galaxy filaments, and the metallicity of gas in galaxy voids. Here we present estimates of the completeness of our survey along these sight lines and examples of close galaxy-absorber associations discovered by our survey.
    06/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a new ultraviolet spectrum and supporting optical spectra of the young supernova remnant 1E 0102.2-7219 (E0102) in the Small Magellanic Cloud, obtained with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope and the R-C spectrograph mounted on the 4-m Blanco telescope at CTIO. E0102 is a member of the rare oxygen rich SNRs, with strong oxygen emission but lacking hydrogen and helium. The COS observation has yielded the highest signal-to-noise far-UV spectrum of this remnant, and displays strong UV lines in O, C and possibly Si. The optical spectra also show strong O emission over a large ionization range, including the O I recombination lines at 7774A, 8446A, and 9263A, along with Ne and faint S emission in our blue and red spectra, respectively.
    06/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: In three years of science operations onboard HST, the Cosmic OriginsSpectrograph has generated an archive of far-ultraviolet AGN spectra of unprecedented breadth, depth, and quality. COS was designed to be sensitive to many important diagnostic lines in the far-UV (1135-1800A) in the low-redshift, "local" universe: Lya (z<0.47), Lyb (0.1<z<0.7), OVI (0.1<z<0.7), SiIII (z<0.5), CIV (z<0.17), NeVIII (0.45<z<1.3), etc. We report on our ongoing survey of extragalactic absorption systems toward ~200 low- to moderate-redshift (z<1.5), UV-bright AGN. When complete mid-2013), the COS IGM absorber catalog will provide an unbiased, statistical sampling of local intergalactic absorption along ~200 extragalactic sight lines. This significant cornerstone of the scientific legacy of COS is at least an order-of-magnitude improvement over previous low-z IGM surveys in total observed pathlength and number of absorbers as well as substantial improvements in sensitivity and uniformity. Of particular interest is the sensitivity of COS to weak and broad absorption. We discuss the scope of and methodology behind the catalog, several initial discoveries, and the overall statistical findings of the survey. Finally, we discuss the new areas of cosmology enabled by this expanded study.
    01/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: [Abridged.] We present multiwavelength observations of the black hole binary system, A0620-00. Using the Cosmic Origins Spectrograph on the Hubble Space Telescope, we have obtained the first FUV spectrum of A0620-00. The observed spectrum is flat in the FUV and very faint (with continuum fluxes \simeq 1e - 17 ergs/cm^2/s/A). We compiled the dereddened, broadband spectral energy distribution of A0620-00 and compared it to previous SEDs as well as theoretical models. The SEDs show that the source varies at all wavelengths for which we have multiple samples. Contrary to previous observations, the optical-UV spectrum does not continue to drop to shorter wavelengths, but instead shows a recovery and an increasingly blue spectrum in the FUV. We created an optical-UV spectrum of A0620-00 with the donor star contribution removed. The non-stellar spectrum peaks at \simeq3000 {\deg}A. The peak can be fit with a T=10,000 K blackbody with a small emitting area, probably originating in the hot spot where the accretion stream impacts the outer disk. However, one or more components in addition to the blackbody are needed to fit the FUV upturn and the red optical fluxes in the optical-UV spectrum. By comparing the mass accretion rate determined from the hot spot luminosity to the mean accretion rate inferred from the outburst history, we find that the latter is an order of magnitude smaller than the former, indicating that \sim90% of the accreted mass must be lost from the system if the predictions of the disk instability model and the estimated interoutburst interval are correct. The mass accretion rate at the hot spot is 10^5 the accretion rate at the black hole inferred from the X-ray luminosity. To reconcile these requires that outflows carry away virtually all of the accreted mass, a very low rate of mass transfer from the outer cold disk into the inner hot region, and/or radiatively inefficient accretion.
    The Astrophysical Journal 09/2011; 743. · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present moderate-resolution Cosmic Origins Spectrograph (COS) far-UV spectra of three QSOs that probe the extended gaseous halo of the nearby spiral galaxy ESO 157-G049 (cz = 1673 km/s; L = 0.1 L*) at impact parameters of 53, 66, and 124 kpc. H I Lyman-alpha absorption is detected at the galaxy redshift in the spectra of all three QSOs and metal lines of Si III, Si IV, and C IV are detected in two of the three spectra. No metals are detected in the sight line that probes ESO 157-G049 along its minor axis at an impact parameter of 124 kpc, implying that there is no galactic wind that reaches these radii. Further, no low ions (i.e., C II, Si II) associated with ESO 157-G049 are detected in any of the QSO spectra so its gaseous halo is highly ionized even at radii of 50 kpc. These spectra allow us to probe the three-dimensional structure of low- and intermediate-ionization gas in nearby galaxy halos for the first time and begin to map the distribution of metals and energy as a function of impact parameter and position angle with respect to the galaxy.
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present an analysis of the far-ultraviolet spectrum of the post-AGB star Barnard 29 in the globular cluster M13 (NGC 6205) obtained with COS and FUSE. The data extend from the Lyman limit to about 1780 A with a spectral resolution R 20,000. Previous observers have derived the star's effective temperature (Teff = 20,000 K), surface gravity (log g = 3.0), and abundances of He, C, N, O, Mg, Si, Al, S, and Fe. In addition to these species, we detect absorption from the light elements P and Cl, the iron-peak elements Ti, Cr, and Ni, and the heavy elements Ge and Zr. Using LTE and NLTE stellar atmosphere models, we derive the abundances of these elements and set upper limits for several more. Our Ge and Zr abundances will provide useful constraints on models of nucleosynthesis in AGB stars. This work is supported by NASA grant NNX08AC14G.
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present far-UV spectra obtained with the Cosmic Origins Spectrograph (COS) of the QSOs VII Zw 244 and SBS 1122+594, which both have foreground galaxies within a projected distance of 35 kpc. The COS spectrum of VII Zw 244 (z = 0.131) shows strong (but not damped) Lyman alpha absorption as well as absorption from C II, C IV, Si III, and Si IV at the redshift of UGC 4527 (z = 0.002), a low surface brightness galaxy located 7 kpc from the QSO sight line. The relatively low H I column density and high ionization state of this metal-line system is somewhat surprising since one typically expects QSO/galaxy pairs with such small physical separations to host damped Ly-alpha absorbers. The COS spectrum of SBS 1122+594 (z = 0.852) shows Ly-alpha and C IV absorption at the redshift of IC 691 (z = 0.004), a dwarf starburst galaxy located 33 kpc away. We argue that the gas seen in absorption in the SBS 1122+594 sight line originated in a starburst wind from IC 691.
    01/2010;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present initial results from an HST Cycle 17 program to search for atomic and molecular emissions from the well-studied transiting planet HD209458b. HD209248b is a hot-Jupiter (M 0.7 MJ) known to have a hydrogen-rich atmosphere. We describe recent observations with the HST/Cosmic Origins Spectrograph aimed at detecting molecular hydrogen and/or atomic emission from aurorae present in the planet's atmosphere. We use a total of 12 orbits to acquire moderate resolution (R 20,000) far-UV (1140 - 1750 A) spectra at both the Phase 0.25 and Phase 0.75 quadrature positions. We have used high-quality spectra of a template G0V star (alpha Cen) to identify stellar features that may overlap with planetary signal. We also describe a model for H2 emission from the Jovian aurora/dayglow that has been adapted for the interpretation of the COS spectra.
    01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The G140L segment B channel (R 2,000) of the Cosmic Origins Spectrograph (COS) recently installed on the Hubble Space Telescope (HST) has an effective area consistent with 10 cm2 in the bandpass between the Lyman edge at 912 Å and Lybeta. It has a slight plateau of 20 cm2 near 1050 Å and rises to a peak in excess of 1100 cm2 longward of 1140 Å. Up until now the general astronomical community has had only limited access to a low resolving power R 2,000 far-UV spectrograph, extending down to the Lyman limit, in the form of the shuttle carried instruments; the Hopkins Ultraviolet Telescope and the Berkeley Extreme and Far-UV Spectrograph. The low resolving power provides a unique capability to reach extremely faint flux limits and will enable new science investigations, such as those seeking to quantify the escape fraction of Lyman continuum photons from galaxies at low redshift, study the He II Gunn-Peterson effect in the redshift range 2 < z < 2.8, measure CO/H2 in dense interstellar environments, or make observations of the O VI lambdalambda 1032, 1038 doublet. Observations of point sources will have the highest spectral resolution, since the small 2."5 diameter entrance aperture of COS is not optimized for extended source observations.
    01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The launch of the Far Ultraviolet Spectroscopic Explorer (FUSE) has been followed by an extensive period of calibration and characterization as part of the preparation for normal satellite operations. Major tasks carried out during this period include the initial coalignment, focusing, and characterization of the four instrument channels and a preliminary measurement of the resolution and throughput performance of the instrument. We describe the results from this test program and present preliminary estimates of the on-orbit performance of the FUSE satellite based on a combination of these data and prelaunch laboratory measurements.
    The Astrophysical Journal 12/2008; 538(1):L7. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Because of a lack of spectral resolution in existing spectroscopic data, current white dwarf atmospheric models cannot explain the atmospheric structure, and resultant extreme-ultraviolet (EUV) emission, of G191-B2B unambiguously. Therefore, a new rocket-borne EUV spectrograph was designed, built, calibrated, and launched. This instrument observed G191-B2B over a bandpass of 254-317 Å and with a resolving power of λ/Δλ ≈ 2800. Highly statistically significant absorption features within the flight spectrum, coupled with metal-rich modeled stellar spectra, provide evidence for blended features of Fe IV/Fe V and Fe IV/O III in G191-B2B's atmosphere. A 3 σ upper limit of 2 × 10-5 has been placed on the photospheric helium abundance, arguing against models that rely on He II as a major EUV opacity source.
    The Astrophysical Journal 12/2008; 562(2):992. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Observations obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) have been used to determine the column densities of D I, N I, and O I along seven sight lines that probe the local interstellar medium (LISM) at distances from 37 to 179 pc. Five of the sight lines are within the Local Bubble, and two penetrate the surrounding H I wall. Reliable values of N(H I) were determined for five of the sight lines from Hubble Space Telescope (HST) data, International Ultraviolet Explorer (IUE) data, and published Extreme Ultraviolet Explorer (EUVE) measurements. The weighted mean of D I/H I for these five sight lines is (1.52 ± 0.08) × 10-5 (1 σ uncertainty in the mean). It is likely that the D I/H I ratio in the Local Bubble has a single value. The D I/O I ratio for the five sight lines within the Local Bubble is (3.76 ± 0.20) × 10-2. It is likely that O I column densities can serve as a proxy for H I in the Local Bubble. The weighted mean for O I/H I for the seven FUSE sight lines is (3.03 ± 0.21) × 10-4, comparable to the weighted mean (3.43 ± 0.15) × 10-4 reported for 13 sight lines probing larger distances and higher column densities. The FUSE weighted mean of N I/H I for five sight lines is half that reported by Meyer and colleagues for seven sight lines with larger distances and higher column densities. This result combined with the variability of O I/N I (six sight lines) indicates that at the low column densities found in the LISM, nitrogen ionization balance is important. Thus, unlike O I, N I cannot be used as a proxy for H I or as a metallicity indicator in the LISM.
    The Astrophysical Journal Supplement Series 12/2008; 140(1):3. · 16.24 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present Far Ultraviolet Spectroscopic Explorer (FUSE) observations of the sight line toward the Seyfert 1 galaxy Markarian 876, which passes through high-velocity cloud (HVC) complex C. This sight line demonstrates the ability of FUSE to measure ionic absorption lines in Galactic HVCs. High-velocity absorption is clearly seen in both members of the O VI doublet. This is the first detection of O VI in a neutral hydrogen HVC. One component of HVC complex C is resolved in multiple Fe II lines from which we derive N(Fe II)/N(H I) = 0.48 (Fe/H)☉. This value of N(Fe II)/N(H I) implies that the metallicity of complex C along this sight line may be higher than that along the Mrk 290 sight line (0.1 solar) found by Wakker et al. On the other hand, if the metallicity of complex C is also 0.1 solar along this line of sight, the observed value of N(Fe II)/N(H I) suggests there may be a significant amount of H+ along the line of sight. In any case, little, if any, iron can be depleted into dust grains if the intrinsic metallicity of complex C is subsolar. Absorption from complex C is also seen in C II, N I, and N II, and upper limits based on nondetections can be determined for Ar I, P II, and Fe III. Although molecular hydrogen in the Milky Way is obvious in the FUSE data, no H2 absorption is seen in the HVC to a limit N(H2) < 2.0 × 1014 cm-2. Future FUSE observations of extragalactic objects behind Galactic HVCs will allow us to better constrain models of HVC origins.
    The Astrophysical Journal 12/2008; 538(1):L35. · 6.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Far-ultraviolet spectra of 11 active galactic nuclei observed by Far Ultraviolet Spectroscopic Explorer (FUSE) are analyzed to obtain measures of O VI λ1031.93 absorption occurring over very long paths through Milky Way halo gas. Strong O VI absorption is detected along 10 of 11 sight lines. Values of log[N(O VI) sin |b|] range from 13.80 to 14.64, with a median value of 14.21. The observations reveal the existence of a widespread but irregular distribution of O VI in the Milky Way halo. Combined with estimates of the O VI midplane density, n0 = 2 × 10-8 cm-3, from the Copernicus satellite, the FUSE observations imply an O VI exponential scale height of 2.7 ± 0.4 kpc. We find that N(C IV)/N(O VI) ranges from ~0.15 in the disk to ~0.6 along four extragalactic sight lines. The changing ionization state of the gas from the disk to the halo is consistent with a systematic decrease in the scale heights of Si IV, C IV, N V, to O VI from ~5.1 to ~2.7 kpc. While conductive heating models can account for the highly ionized atoms at low |z|, a combination of models (and processes) appears to be required to explain the highly ionized atoms found in the halo. The greater scale heights of Si IV and C IV compared to O VI suggests that some of the Si IV and C IV in the halo is produced in turbulent mixing layers or by photoionization by hot halo stars or the extragalactic background.
    The Astrophysical Journal 12/2008; 538(1):L27. · 6.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This concept study defines the scientific requirements and instrumental performance needed for a space mission to detect and characterize the cosmic web of matter, the processes that produce and govern its structure, and its influence on the formation and evolution of galaxies. Our new numerical simulations explicitly track the observational signatures of the web gas as a function of time (redshift) up to the present day. The simulations include prescriptions for feedback interactions between galaxies and the intergalactic medium, and demonstrate that the ultraviolet O VI lines and the H I Lyman alpha line are premier diagnostics of low-density cosmic web regions. We define the field of view, angular resolution, and sensitivity needed to detect the web filaments in emission and absorption, and the spectral resolution needed to separate the gas signatures from foreground signals. These results define the driving science requirements for the Baryonic Structure Probe and any other future missions seeking to characterize the cosmic web. The science requirements can be met with a dedicated observatory in an L2 orbit capable of simultaneously observing both the faint emissions and weak absorption lines from the cosmic web. Our mission concept baselines a low risk 5-year core science mission with a 10-year design lifetime. Technological investments that would improve performance include the development of high quantum efficiency ultraviolet detectors, large format diffraction gratings, and improved optical coatings.
    11/2005; 37:1197.
  • [Show abstract] [Hide abstract]
    ABSTRACT: A recent (June 2004) sounding rocket mission has obtained an image of a non-radiative shock in the OVI doublet 1032, 1038 Å. The shock observed was the P7 shock, a very bright, edge-on shock in the NE section of the Cygnus Loop. For the majority of the cooling time of the post-shock ISM, the gas is well described by a Maxwellian and its behavior follows normal hydrodynamics. However, the discontinuity of the shockwave causes the gas to become briefly non-Maxwellian, and the physical process which allows the gas to attain thermal equilibrium is unknown. The main science goal of the mission was to compare the location of the OVI emission with respect to the shock front location, as defined by the Halpha emission in previous observations. The distance between these two locations will depend on the method of ion-electron temperature equilibration behind the shock.
    12/2004;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present new observations of the oxygen-rich supernova remnant N132D in the Large Magellanic Cloud using the Hubble Space Telescope's Advanced Camera for Surveys. By using wide filters around several key emission lines (such as [\ion{O}{3}] 5007 Å) we image structure that is doppler shifted out of standard narrow band filters. The high spatial resolution provided by ACS allows us to study the morphology of high velocity filaments within the remnant. We compare our observations with previous Wide Field Planetary Camera 2 images.
    11/2004; 36:1510.

Publication Stats

151 Citations
109.93 Total Impact Points

Institutions

  • 2014
    • University of Colorado
      Denver, Colorado, United States
  • 1991–2011
    • University of Colorado at Boulder
      • Center for Astrophysics and Space Astronomy
      Boulder, Colorado, United States
  • 2000–2003
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, Maryland, United States