666 research outputs found
Highly Ionized Collimated Outflow from HE 0238 - 1904
We present a detailed analysis of a highly ionized, multiphased and
collimated outflowing gas detected through O V, O VI, Ne VIII and Mg X
absorption associated with the QSO HE 0238 - 1904 (z_em ~ 0.629). Based on the
similarities in the absorption line profiles and estimated covering fractions,
we find that the O VI and Ne VIII absorption trace the same phase of the
absorbing gas. Simple photoionization models can reproduce the observed N(Ne
VIII), N(O VI) and N(Mg X) from a single phase whereas the low ionization
species (e.g. N III, N IV, O IV) originate from a different phase. The measured
N(Ne VIII)/N(O VI) ratio is found to be remarkably similar (within a factor of
~ 2) in several individual absorption components kinematically spread over ~
1800 km/s. Under photoionization this requires a fine tuning between hydrogen
density (nH) and the distance of the absorbing gas from the QSO. Alternatively
this can also be explained by collisional ionization in hot gas with T >
10^{5.7} K. Long-term stability favors the absorbing gas being located outside
the broad line region (BLR). We speculate that the collimated flow of such a
hot gas could possibly be triggered by the radio jet interaction.Comment: Minor revision (accepted for publication in MNRAS letter
Parentage reconstruction in eucalyptus nitens using SNPs and microsatellite markers: a comparative analysis of marker data power and robustness.
Reionization Bias in High Redshift Quasar Near-Zones
Absorption spectra of high redshift quasars exhibit an increasingly thick
Ly-alpha forest towards z~6. However, the interpretation of these spectra is
complicated by the fact that the Ly-alpha optical depth is already large for
neutral hydrogen fractions in excess of 10^-4, and also because quasars are
expected to reside in dense regions of the IGM. We present a model for the
evolution of the ionization state of the IGM which is applicable to the dense,
biased regions around high-redshift quasars as well as more typical regions in
the IGM, and combine this with numerical radiative transfer simulations. Our
model is able to simultaneously reproduce the observed Ly-alpha forest opacity
at 4<z<6, the ionizing photon mean-free-path at z~4 and the rapid evolution of
highly ionized near-zone sizes around high-redshift quasars at 5.8<z<6.4. We
find that within 5 physical Mpc of a high redshift quasar, the evolution of the
ionization state of the IGM precedes that in more typical regions by around 0.3
redshift units. More importantly, when combined with the rapid increase in the
ionizing photon mean-free-path expected shortly after overlap, this offset
results in an ionizing background near the quasar which exceeds the value in
the rest of the IGM by a factor of ~2-3. We further find that in the
post-overlap phase of reionization the size of the observed quasar near-zones
is not directly sensitive to the neutral hydrogen fraction of the IGM. Instead,
these sizes probe the level of the background ionization rate and the
temperature of the surrounding IGM. The observed rapid evolution of the quasar
near-zone sizes at 5.8<z<6.4 can thus be explained by the rapid evolution of
the ionizing background, which in our model is caused by the completion of
overlap at the end of reionization by 6<z<7.Comment: 16 Pages, 9 figures. Submitted for publication to MNRA
Extreme Ultraviolet Absorption Lines in LyA Forest Absorbers and the Oxygen Abundance in the Intergalactic Medium
We create stacked composite absorption spectra from Hubble Space Telescope
Faint Object Spectrograph data from four quasi-stellar objects to search for
absorption lines in the extreme ultraviolet wavelength region associated with
LyA forest absorbers in the redshift range 1.6 < z < 2.9. We successfully
detect O V 630 in LyA absorbers throughout the 10^13 to 10^16.2 cm^-2 column
density range. For a sample of absorbers with 10^13.2 < N(H I) < 10^14.2 cm^-2,
corresponding to gas densities ranging from around the universal mean to
overdensities of a few, we measure an O V 630 equivalent width of 10.9 +/- 3.7
mA. We estimate the detection is real with at least 99% confidence. We only
detect O IV 788, O IV 554, O III 833, and HeI 584 in absorbers with LyA
equivalent widths > 0.6 A, which are likely associated with traditional
metal-line systems. We find no evidence in any subsamples for absorption from N
IV 765, NeV 568, NeVI 559, NeVIII 770, 780, or MgX 610, 625. The measured
equivalent widths of O V suggest values of in the range -1.7 to
-0.6 for 10^13.2 < N(H I) < 10^15 cm^-2. The lack of detectable O IV absorption
except in the strongest absorption systems suggests a hard ionizing background
similar to the standard Haardt & Madau spectrum. Using photoionization models,
we estimate that the oxygen abundance in the intergalactic medium with respect
to the solar value is [O / H] around -2.2 to -1.3. Comparing to studies of C
IV, we estimate [O / C] around 0.3 to 1.2. The overabundance of oxygen relative
to carbon agrees with other low-metallicity abundance measurements and suggests
enrichment of the intergalactic medium by Type II supernovae.Comment: Accepted for publication in Nov 10, 2002 Ap
Calibration of myocardial T2 and T1 against iron concentration.
BACKGROUND: The assessment of myocardial iron using T2* cardiovascular magnetic resonance (CMR) has been validated and calibrated, and is in clinical use. However, there is very limited data assessing the relaxation parameters T1 and T2 for measurement of human myocardial iron.
METHODS: Twelve hearts were examined from transfusion-dependent patients: 11 with end-stage heart failure, either following death (n=7) or cardiac transplantation (n=4), and 1 heart from a patient who died from a stroke with no cardiac iron loading. Ex-vivo R1 and R2 measurements (R1=1/T1 and R2=1/T2) at 1.5 Tesla were compared with myocardial iron concentration measured using inductively coupled plasma atomic emission spectroscopy.
RESULTS: From a single myocardial slice in formalin which was repeatedly examined, a modest decrease in T2 was observed with time, from mean (± SD) 23.7 ± 0.93 ms at baseline (13 days after death and formalin fixation) to 18.5 ± 1.41 ms at day 566 (p<0.001). Raw T2 values were therefore adjusted to correct for this fall over time. Myocardial R2 was correlated with iron concentration [Fe] (R2 0.566, p<0.001), but the correlation was stronger between LnR2 and Ln[Fe] (R2 0.790, p<0.001). The relation was [Fe] = 5081•(T2)-2.22 between T2 (ms) and myocardial iron (mg/g dry weight). Analysis of T1 proved challenging with a dichotomous distribution of T1, with very short T1 (mean 72.3 ± 25.8 ms) that was independent of iron concentration in all hearts stored in formalin for greater than 12 months. In the remaining hearts stored for <10 weeks prior to scanning, LnR1 and iron concentration were correlated but with marked scatter (R2 0.517, p<0.001). A linear relationship was present between T1 and T2 in the hearts stored for a short period (R2 0.657, p<0.001).
CONCLUSION: Myocardial T2 correlates well with myocardial iron concentration, which raises the possibility that T2 may provide additive information to T2* for patients with myocardial siderosis. However, ex-vivo T1 measurements are less reliable due to the severe chemical effects of formalin on T1 shortening, and therefore T1 calibration may only be practical from in-vivo human studies
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