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تسجيل مستخدم جديدCos observations of metal line and broad lyman alpha absorption in the multi-phase o vi and ne viii system toward he 02226-4110
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Observations of the QSO HE 0226-4110 (zem = 0.495) with the Cosmic Origins Spectrograph (COS) from 1134 to 1796 {AA} with a resolution of ~17 km s-1 and signal-to- noise (S/N) per resolution element of 20 to 40 are used to study the multi-phase absorption system at z = 0.20701 containing O VI and Ne VIII. The system was previously studied with lower S/N observations with FUSE and STIS. The COS observations provide more reliable measures of the H I and metal lines present in the system and reveal the clear presence of broad Lyman {alpha} (BLA) absorption with b = 72(+13, -6) km s-1 and logN(H I) = 13.87pm0.08. Detecting BLAs associated with warm gas absorbers is crucial for determining the temperature, metallicity and total baryonic content of the absorbers. The BLA is probably recording the trace amount of thermally broadened H I in the collisionally ionized plasma with log T ~5.7 that also produces the O VI and Ne VIII absorption. The total hydrogen column in the collisionally ionized gas, logN(H) ~ 20.1, exceeds that in the cooler photoionized gas in the system by a factor of ~22. The oxygen abundance in the collisionally ionized gas is [O/H] = -0.89pm0.08pm0.07. The absorber probably occurs in the circumgalactic environment (halo) of a foreground L = 0.25L* disk galaxy with an impact parameter of 109h70-1 kpc identified by Mulchaey & Chen (2009).
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We report on the detection of Ne VIII in an intervening multiphase absorption line system at z=0.32566 in the FUSE spectrum of the quasar 3C 263. The Ne VIII 770 A line detection has a 3.9 sigma significance. At the same velocity we also find absorpt
ion lines from C IV, O III, O IV and N IV. The line parameter measurements yield log [N(Ne VIII), cm^-2] =13.98 (+0.10,-0.13) and b = 49.8 +/- 5.5 km/s. We find that the ionization mechanism in the gas phase giving rise to the Ne VIII absorption is inconsistent with photoionization. The absorber has a multi-phase structure, with the intermediate ions produced in cool photoionized gas and the Ne VIII most likely in a warm collisionally ionized medium in the temperature range (0.5 - 1.0) x 10^6 K. This is the second ever detection of an intervening Ne VIII absorption system. Its properties resemble the previous Ne VIII absorber reported by Savage et al. (2005). Direct observations of H I and O VI are needed to better constrain the physical conditions in the collisionally ionized gas phase of this absorber.
We present VLT/UVES spectroscopy of the quasar Q0841+129, whose spectrum shows a proximate damped Lyman-alpha (PDLA) absorber at z=2.47621 and a proximate sub-DLA at z=2.50620, both lying close in redshift to the QSO itself at z_em=2.49510+/-0.00003.
This fortuitous arrangement, with the sub-DLA acting as a filter that hardens the QSOs ionizing radiation field, allows us to model the ionization level in the foreground PDLA, and provides an interesting case-study on the origin of the high-ion absorption lines Si IV, C IV, and O VI in DLAs. The high ions in the PDLA show at least five components spanning a total velocity extent of ~160 km/s, whereas the low ions exist predominantly in a single component spanning just 30 km/s. We examine various models for the origin of the high ions. Both photoionization and turbulent mixing layer models are fairly successful at reproducing the observed ionic ratios after correcting for the non-solar relative abundance pattern, though neither model can explain all five components. We show that the turbulent mixing layer model, in which the high ions trace the interfaces between the cool PDLA gas and a hotter phase of shock-heated plasma, can explain the average high-ion ratios measured in a larger sample of 12 DLAs.
We study the physical conditions, elemental abundances, and kinematics of the high-velocity clouds (HVCs) along the sight lines toward active galaxies HE0226-4110 and PG0953+414 using Hubble Space Telescope Imaging Spectrograph and Far Ultraviolet Sp
ectroscopic Explorer data. Our observations reveal multiple components of HVC absorption in lines of HI, CII, CIII, CIV, OVI, SiII, SiIII, and SiIV in both directions. We investigate whether photoionization by the extragalactic background radiation or by escaping Milky Way radiation can explain the observed ionization pattern. We find that photoionization is a good explanation for the CII, CIII, SiII, and SiIII features, but not for the OVI or CIV associated with the HVCs, suggesting that two principal phases exist: a warm (T~10^4K), photoionized phase and a hotter (T=1-3x10^5K), collisionally-ionized phase. The warm HVCs toward HE0226-4110 have high levels of ionization (97-99%), and metallicities ([Z/H] between -0.9 and -0.4) close to those in the Magellanic Stream, which lies eleven degrees away on the sky at similar velocities. These HVCs have thermal pressures that would place them close to equilibrium in a fully ionized 10^6 K Galactic corona with n_H=4-9x10^{-5}cm^{-3} at 50 kpc. A mini-survey of the hot, collisionally ionized HVC components seen here and in five other sight lines finds that in 11/12 cases, the high ions have kinematics and ionic ratios that are consistent with an origin in conductive interfaces. However, the broad absorption wing on the OVI profile toward PG0953+414 is not completely explained by the interface scenario, and may be tracing the outflow of hot gas into the Milky Way halo as part of a Galactic fountain or wind.
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Observations of the QSO HE 0153-4520 (z-em = 0.450) with the Cosmic Origins Spectrograph (COS) from 1134 to 1796 A with a resolution of ~17 km/s and signal-to- noise per resolution element of 20 to 40 are used to study a multi-phase partial Lyman lim
it system (LLS) at z = 0.22601 tracing both cool and hot gas. FUSE observations of the Lyman limit break yield log N(H I) = 16.61(0.12, -0.17) The observed UV absorption lines of H I 1216 to 926, C III, C II, N III, N II, Si III, and Si II imply the existence of cool photoionized gas in the LLS with log U = -2.8pm0.1 and log N(H) = 19.35pm0.18, log n(H) = -2.9pm0.2, log T = 4.27pm0.02, log (P/k) = 1.75pm0.17, and log L(kpc) = 0.70pm0.25. The abundances are [X/H] = -0.8 (+0.3, -0.2) for N, Si and C but the result is sensitive to the assumed shape of the ionizing background radiation field. The multi-phase system has strong O VI and associated broad Ly {alpha} absorption (BLA) with log N(O VI) = 14.21pm0.02, b(O VI) = 37pm1 km/s, log N(H I) = 13.70(+0.05,-0.08), b(H I)=140 (+14, -16) km/s and b(H I)/b(O VI) = 3.9pm0.4. The O VI does not arise in the cool photoionized gas of the LLS. The O VI and BLA imply the direct detection of thermally broadened absorption by hot gas with log T = 6.07 (+0.09, -0.12), [O/H] = -0.28 (+0.09, -0.08), and log N(H) = 20.41 (+0.13, -0.17). The absorber probably occurs in the circumgalactic environment (halo) of a foreground galaxy.
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