136 research outputs found
Determining the core radio luminosity function of radio AGNs via copula
The radio luminosity functions (RLFs) of active galactic nuclei (AGNs) are
traditionally measured based on total emission, which doesn't reflect the
current activity of the central black hole. The increasing interest in compact
radio cores of AGNs requires determination of the RLF based on core emission
(i.e., core RLF). In this work we have established a large sample (totaling
1207) of radio-loud AGNs, mainly consisting of radio galaxies (RGs) and
steep-spectrum radio quasars (SSRQs). Based on the sample, we explore the
relationship between core luminosity () and total luminosity () via a
powerful statistical tool called "Copula". The conditional probability
distribution is obtained. We derive the core
RLF as a convolution of with the total RLF
which was determined by previous work. We relate the separate RG and SSRQ core
RLFs via a relativistic beaming model and find that SSRQs have an average
Lorentz factor of , and that most are seen within
of the jet axis. Compared with
the total RLF which is mainly contributed by extended emission, the core RLF
shows a very weak luminosity-dependent evolution, with the number density
peaking around for all luminosities. Differences between core
and total RLFs can be explained in a framework involving a combination of
density and luminosity evolutions where the cores have significantly weaker
luminosity evolution than the extended emission.Comment: Accepted for publication in the ApJ
Devonian Upper Ocean Redox Trends Across Laurussia: Testing Potential Influences of Marine Carbonate Lithology on Bulk Rock I/Ca Signals
The Devonian is characterized by major changes in ocean-atmosphere O2 concentrations, colonialization of continents by plants and animals, and widespread marine anoxic events associated with rapid d13C excursions and biotic crises. However, the long-term upper ocean redox trend for the Devonian is still not well understood. This study presents new I/Ca data from well-dated Lower Devonian through Upper Devonian limestone sections from the Great Basin (western Laurussia) and the Illinois Basin (central Laurussia). In addition, to better address potential influences of lithology and stratigraphy on I/Ca redox signals, I/Ca data are reported here as carbonate lithology-specific. Results indicate that lithologic changes do not exert a dominant control on bulk carbonate I/Ca trends, but the effects of some diagenetic overprints cannot be ruled out. For the Illinois Basin, low I/Ca values (more reducing) are recorded during the Pragian to Emsian and increased but fluctuating values are recorded during the Eifelian to Givetian. The Great Basin I/Ca trends suggest local upper oceans were more reducing in the Lochkovian, more oxic in the Pragian- Emsian, return to more reducing in the Eifelian, then to increasingly more oxic, but fluctuating in the Givetian-Frasnian. The local I/Ca variations at Great Basin likely share more similarity with global upper ocean condition (compared to the Illinois Basin) based on its position adjacent to the Panthalassic Ocean and its temporal co-variation with global environmental volatility trends. The overall reducing and variable redox conditions of local upper ocean (if not a diagenetic signal) during the Middle and Late Devonian of Great Basin coincide with evidence of increased global environmental volatility suggesting seawater redox may have been an important part of environmental instability at this time
Ikaite Abundance Controlled by Porewater Phosphorus Level: Potential Links to Dust and Productivity
Pore fluid modeling approach to identify recent meltwater signals on the west Antarctic Peninsula
The sensitivity of sea level to melting from polar ice sheets and glaciers during recent natural and
anthropogenic climate fluctuations is poorly constrained beyond the period of direct observation by satellite.
We have investigated glacial meltwater events during the Anthropocene by adapting the pioneering
approach of modeling trends in d18O in the pore waters of deep‐sea cores, previously used to constrain
the size of ice sheets during the Last Glacial Maximum. We show that during recent warm periods, meltwater
from glacier retreat drains into the coastal fjords, leaving a signature of depleted d18O values and low
Cl concentrations in the pore water profiles of rapidly accumulating sediments. Here we model such pore
water profiles in a piston core to constrain the timing and magnitude of an ice sheet retreat event at Caley
Glacier on the west Antarctic Peninsula, and the result is compared with local ice front movement. This
approach of pore water modeling was then applied in another kasten core and tested by a series of sensitivity
analyses. The results suggest that our approach may be applied in fjords of different sedimentary settings
to reconstruct the glacier history and allow insight into the sensitivity of polar glaciers to abrupt
warming events
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