48 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
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
Oxygen depletion recorded in upper waters of the glacial Southern Ocean
Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ~2.5 μmol mol−1 indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg−1 during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth’s climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline
(Table S) Planktonic foraminifera I/Ca during the PETM
As yet no evidence has been presented for pervasive deoxygenation in the upper water column through expansion of Oxygen Minimum Zones (OMZs) during the PETM. We apply a novel proxy for paleo-redox conditions, the iodine to calcium ratio (I/Ca) in bulk coarse fraction sediment and planktonic foraminiferal tests from pelagic sites in different oceans, and compared our reconstruction with modeled oxygen levels. The reconstructed iodate gradients indicate that deoxygenation occurred in the upper water column in the Atlantic, Indian Oceans, and possibly the Pacific Ocean as well during the PETM, due to vertical and potentially lateral expansion of OMZs
Benthic foraminiferal I/Ca, fish teeth Ce anomaly, and Mn enrichment factor of bulk sediment during the late Paleocene-early Eocene
Important insight into the relationship between de-oxygenation and warming can be obtained from the geological record, but evidence is limited because few ocean oxygenation records are available for past greenhouse climate conditions. We use I/Ca in benthic foraminifera to reconstruct late Paleocene through early Eocene bottom and pore-water redox conditions in the South Atlantic and Southern Indian Oceans, and compare our results with those derived from Mn speciation and the Ce anomaly in fish teeth