438 research outputs found
Comparison of Millimeter-wave and X-Ray Emission in Seyfert Galaxies
We compare the emission at multiple wavelengths of an extended Seyfert galaxy
sample, including both types of Seyfert nuclei. We use the Caltech
Submillimeter Observatory to observe the CO J = 2-1 transition line in a sample
of 45 Seyfert galaxies and detect 35 of them. The galaxies are selected by
their joint soft X-ray (0.1-2.4 keV) and far-infrared ({\lambda} = 60-100
{\mu}m) emission from the ROSAT/IRAS sample. Since the CO line widths (W CO)
reflect the orbital motion in the gravitational potential of the host galaxy,
we study how the kinematics are affected by the central massive black hole
(BH), using the X-ray luminosity. A significant correlation is found between
the CO line width and hard (0.3-8 keV from Chandra and XMM-Newton) X-ray
luminosity for both types of Seyfert nuclei. Assuming an Eddington accretion to
estimate the BH mass (M BH) from the X-ray luminosity, the W CO-L X relation
establishes a direct connection between the kinematics of the molecular gas of
the host galaxy and the nuclear activity, and corroborates the previous studies
that show that the CO is a good surrogate for the bulge mass. We also find a
tight correlation between the (soft and hard) X-ray and the CO luminosities for
both Seyfert types. These results indicate a direct relation between the
molecular gas (i.e., star formation activity) of the host galaxy and the
nuclear activity. To establish a clear causal connection between molecular gas
and the fueling of nuclear activity, high-resolution maps (<100 pc) of the CO
emission of our sample will be required and provided in a forthcoming Atacama
Large Millimeter Array observation
Tectonic controls on the long-term carbon isotope mass balance
The long-term, steady-state marine carbon isotope record reflects changes to the proportional burial rate of organic carbon relative to total carbon on a global scale. For this reason, times of high δ¹³C are conventionally interpreted to be oxygenation events caused by excess organic burial. Here we show that the carbon isotope mass balance is also significantly affected by tectonic uplift and erosion via changes to the inorganic carbon cycle that are independent of changes to the isotopic composition of carbon input. This view is supported by inverse co-variance between δ¹³C and a range of uplift proxies, including seawater⁸⁷Sr/⁸⁶Sr, that demonstrates how erosional forcing of carbonate weathering outweighs that of organic burial on geological time scales. A model of the long-term carbon cycle shows that increases in δ¹³C need not be associated with increased organic burial and that alternative tectonic drivers (erosion, outgassing) provide testable and plausible explanations for sustained deviations from the long-term δ¹³C mean. Our approach emphasizes the commonly overlooked difference between how net and gross carbon fluxes affect the long-term carbon isotope mass balance, and may lead to reassessment of the role that the δ¹³C record plays in reconstructing the oxygenation of Earth’s surface environment
Octreotide in the Control of Post-Sclerotherapy Bleeding from Oesophageal Varices, Ulcers and Oesophagitis
Bleeding from oesophageal varices, oesophageal ulcers or oesophagitis is occasionally massive and difficult to control. Octreotide, a synthetic analogue of somatostin lowers portal pressure and collateral blood flow including that through varices, increases lower oesophageal sphincter pressure, and inhibits the gastric secretion of acid as well as pepsin. Our current experience suggests it is effective in controlling acute variceal haemorrhage. Therefore we have examined the efficacy of octreotide in the control of postsclerotherapy bleeding from oesophageal varices, oesophageal ulcers and oesophagitis. During the study period 77 patients experienced a significant gastrointestinal bleed (blood pressure < 100 mm Hg, pulse >
100 beats per min or the need to transfuse 2 or more units of blood to restore the haemoglobin level) following injection sclerotherapy of oesophageal varices. The source of bleeding was varices in 42 patients, oesophageal ulcers in 31 and oesophagitis in 4. All patients received a continuous intravenous infusion of octreotide (50 μg/h) for between 40–140h. If bleeding was not controlled in the first 12h after commencing octreotide hourly bolus doses (50 μg) for 24h were superimposed on the continuous infusion. Haemorrhage was successfully controlled by an infusion of octreotide in 38 of the 42 patients with bleeding from varices, in 30 of 31 patients with oesophageal ulceration, and all patients with oesophagitis. In the 1 patient with persistent bleeding from oesophageal ulceration and in 2 of the 4 with continued haemorrhage from varices, haemostasis was achieved by hourly boluses of 50 μg octreotide for 24h in addition to the continuous infusion. No major complications were associated with octreotide administration. The results of this study clearly indicate that octreotide is a safe and effective treatment for the control of severe haemorrhage after technically successful injection sclerotherapy
Oceanic redox conditions during the terminal Cambrian extinction event
Marine animal diversity during the late Cambrian was reduced by a series of extinctions that have generally been attributed to oceanic anoxic events associated with positive carbon isotope excursions. Here we present carbon and uranium isotope ratios (δ13C and δ238U values) as proxies for global carbon cycle and oceanic redox conditions, respectively, from carbonate rocks of the Wa'ergang section, South China. The dataset spans an interval that includes the last major negative δ13C excursion (TOCE) of the Cambrian Period. The TOCE is a globally documented event, recovery from which corresponds to the terminal Cambrian extinction event. The δ13C and δ238U values covary through the section, shifting initially to lower values, with δ238U falling below the modern open-ocean seawater value from the start to the middle of the profile, followed by a shift to higher values towards the end of the Cambrian. Neither the co-occurrence of δ13C and δ238U negative excursions, nor the association of rising δ238U with extinction have been commonly reported. Here we argue that robust positive coupling of δ13C and δ238U relates to the existence of extensive intermediate reducing settings (from low-O2 suboxia to intermittent anoxia) during the late Cambrian alongside low atmospheric pO2 and a greenhouse climate. Similarly, a stepwise increase in the δ238U baseline in carbonates across the Ediacaran−Cambrian boundary is consistent with the growing importance of an intermediate reducing sink through that interval. We propose further that divergent trends in lower and upper ocean redox conditions could have driven the parallel isotope excursions. An expansion of intermediate reducing conditions, rather than persistent anoxic euxinia, is consistent with the recovery of δ13C and δ238U to higher values, as well as the presence of benthic fauna and shoreward extension of deeper-water fauna that may have had a greater tolerance against hypoxia
The 1126 Ma volcanic event in the Dechang Area, SW Yangtze Block, and its significance
Traditionally, the strata of the Luonie Valley, Dechang County, SW Sichuan, China, are considered to contain a suite of felsic volcanic rocks (the Huili Group) that erupted after c. 1050 Ma. However, we report here new age constraints, elemental and Lu–Hf isotope geochemistry for a different suite of older basaltic agglomerate lava, basaltic tuff lava and basalt from the same area, which we name the Luonie Formation. New dating results show that the basaltic volcanic suite of the upper part of the Luonie Formation formed at 1126.1 ± 9.9 Ma, significantly earlier than deposition of the Huili Group, but comparable in age to the 1142 ± 16 Ma Laowushan Formation in central Yunnan Province. Granite intrusion into the Luonie Formation dated 1050.7 ± 12.7 Ma provides crucial supporting evidence for this earlier depositional age. We also report a maximum sedimentary age of c. 1158 Ma for the underlying arkose, implying stratigraphic conformity with the basaltic volcanic rock suite.
The ϵHf(t) values of the basaltic volcanic rocks are mainly positive, indicating that the rocks are mainly derived from the depleted mantle and slightly stained by crustal materials. The characteristics of P*, Nb* and Zr* anomalies also support this view. The distribution patterns of trace and rare earth elements indicate that the basaltic volcanic rocks formed in an extensional setting. The Zr/4–Y–2Nb and Th–Nb/16–Zr/117 discrimination diagrams also provide evidence for this understanding. Lithofacies analysis shows that basaltic volcanic wrocks with the characteristics of both continental and marine facies should be formed in a littoral–neritic environment. We propose here that the evidence is consistent with a phase of continental extension that preceded the convergence of the SW Yangtze Block to form part of Rodinia
Calibrating the temporal and spatial dynamics of the Ediacaran - Cambrian radiation of animals
On the Correlations between Galaxy Properties and Supermassive Black Hole Mass
We use a large sample of upper limits and accurate estimates of supermassive
black holes masses coupled with libraries of host galaxy velocity dispersions,
rotational velocities and photometric parameters extracted from Sloan Digital
Sky Survey i-band images to establish correlations between the SMBH and host
galaxy parameters. We test whether the mass of the black hole, MBH, is
fundamentally driven by either local or global galaxy properties. We explore
correlations between MBH and stellar velocity dispersion sigma, bulge
luminosity, bulge mass Sersic index, bulge mean effective surface brightness,
luminosity of the galaxy, galaxy stellar mass, maximum circular velocity Vc,
galaxy dynamical and effective masses. We verify the tightness of the MBH-sigma
relation and find that correlations with other galaxy parameters do not yield
tighter trends. We do not find differences in the MBH-sigma relation of barred
and unbarred galaxies. The MBH-sigma relation of pseudo-bulges is also coarser
and has a different slope than that involving classical bulges. The MBH-bulge
mass is not as tight as the MBH-sigma relation, despite the bulge mass proving
to be a better proxy of MBH than bulge luminosity. We find a rather poor
correlation between MBH and Sersic index suggesting that MBH is not related to
the bulge light concentration. The correlations between MBH and galaxy
luminosity or mass are not a marked improvement over the MBH sigma relation. If
Vc is a proxy for the dark matter halo mass, the large scatter of the MBH-Vc
relation then suggests that MBH is more coupled to the baryonic rather than the
dark matter. We have tested the need for a third parameter in the MBH scaling
relations, through various linear correlations with bulge and galaxy
parameters, only to confirm that the fundamental plane of the SMBH is mainly
driven by sigma, with a small tilt due to the effective radius. (Abridged)Comment: 32 pages, 18 figures, 6 tables, accepted for publication in MNRA
Searching for an Intermediate Mass Black Hole in the Blue Compact Dwarf galaxy MRK 996
The possibility is explored that accretion on an intermediate mass black hole
contributes to the ionisation of the interstellar medium of the Compact Blue
Dwarf galaxy MRK996. Chandra observations set tight upper limits (99.7 per cent
confidence level) in both the X-ray luminosity of the posited AGN,
Lx(2-10keV)<3e40erg/s, and the black hole mass, <1e4/\lambda Msolar, where
\lambda, is the Eddington ratio. The X-ray luminosity upper limit is
insufficient to explain the high ionisation line [OIV]25.89\mu m, which is
observed in the mid-infrared spectrum of the MRK996 and is proposed as evidence
for AGN activity. This indicates that shocks associated with supernovae
explosions and winds of young stars must be responsible for this line. It is
also found that the properties of the diffuse X-ray emission of MRK996 are
consistent with this scenario, thereby providing direct evidence for shocks
that heat the galaxy's interstellar medium and contribute to its ionisation.Comment: Submitted to MNRA
Detection of optical coronal emission from 10^6 K gas in the core of the Centaurus cluster
We report a detection (3.5x10^37 \pm 5.6x10^36 ergps) of the optical coronal
emission line [Fe X]6374 and upper limits of four other coronal lines using
high resolution VIMOS spectra centred on NGC 4696, the brightest cluster galaxy
in the Centaurus cluster. Emission from these lines is indicative of gas at
temperatures between 1 and 5 million K so traces the interstellar gas in NGC
4696. The rate of cooling derived from the upper limits is consistent with the
cooling rate from X-ray observations (~10 solar masses per year) however we
detect twice the luminosity expected for [Fe X]6374 emission, at 1 million K,
our lowest temperature probe. We suggest this emission is due to the gas being
heated rather than cooling out of the intracluster medium. We detect no coronal
lines from [Ca XV], which are expected from the 5 million K gas seen near the
centre in X-rays with Chandra. Calcium is however likely to be depleted from
the gas phase onto dust grains in the central regions of NGC 4696.Comment: 11 pages, 13 figures, 2 tables, accepted for publication in MNRA
Selection effects in the black hole-bulge relation and its evolution
We present an investigation of sample selection effects that influence the
observed black hole - bulge relations and its evolution with redshift. We
provide a common framework in which all kinds of selection effects on the
BH-bulge relations can be investigated, but our main emphasis is on the
consequences of using broad-line AGN and their host galaxies to search for
evolution in the BH-bulge relation. We identified relevant sources of bias that
were not discussed in the literature so far. A particularly important effect is
caused by the fact that the active fraction among SMBHs varies considerably
with BH mass, in the sense that high-mass BHs are less likely to be active than
lower mass ones. In the connection with intrinsic scatter of the BH-bulge
relation this effect implies a bias towards a low BH mass at given bulge
property. This effect adds to the bias caused by working with luminosity or
flux limited samples that were already discussed by others. A quantitative
prediction of these biases requires (i) a realistic model of the sample
selection function, and (ii) knowledge of relevant underlying distribution
functions. For low-redshift AGN samples we can naturally reproduce the
flattening of the relation observed in some studies. When extending our
analysis to higher redshift samples we are clearly hampered by limited
empirical constraints on the various relevant distribution functions. Using a
best-guess approach for these distributions we estimate the expected magnitude
of sample selection biases for a number of recent observational attempts to
study the BH-bulge evolution. In no case do we find statistically significant
evidence for an evolving BH-bulge relation. We suggest a possible practical
approach to circumvent several of the most problematic issues connected with
AGN selection; this could become a powerful diagnostic in future investigations
(abridged).Comment: 20 pages, 20 figures, accepted for publication in A&
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