8,066 research outputs found
Intermediate-mass black holes in dwarf galaxies out to redshift 2.4 in the Chandra COSMOS Legacy Survey
We present a sample of 40 AGN in dwarf galaxies at redshifts
2.4. The galaxies are drawn from the \textit{Chandra} COSMOS-Legacy survey as
having stellar masses M. Most
of the dwarf galaxies are star-forming. After removing the contribution from
star formation to the X-ray emission, the AGN luminosities of the 40 dwarf
galaxies are in the range erg
s. With 12 sources at , our sample constitutes the
highest-redshift discovery of AGN in dwarf galaxies. The record-holder is
cid\_1192, at and with erg
s. One of the dwarf galaxies has
M and is the least massive galaxy found so far to host an AGN. All
the AGN are of type 2 and consistent with hosting intermediate-mass black holes
(BHs) with masses M and typical Eddington
ratios . We also study the evolution, corrected for completeness, of AGN
fraction with stellar mass, X-ray luminosity, and redshift in dwarf galaxies
out to = 0.7. We find that the AGN fraction for M and erg s is
0.4\% for 0.3 and that it decreases with X-ray luminosity and
decreasing stellar mass. Unlike massive galaxies, the AGN fraction seems to
decrease with redshift, suggesting that AGN in dwarf galaxies evolve
differently than those in high-mass galaxies. Mindful of potential caveats, the
results seem to favor a direct collapse formation mechanism for the seed BHs in
the early Universe.Comment: 16 pages, 10 figures, accepted for publication in MNRA
Mass-Radius Relation for Magnetic White Dwarfs
Recently, several white dwarfs with very strong surface magnetic fields have
been observed. In this paper we explore the possibility that such stars could
have sufficiently strong internal fields to alter their structure. We obtain a
revised white dwarf mass-radius relation in the presence of strong internal
magnetic fields. We first derive the equation of state for a fully degenerate
ideal electron gas in a magnetic field using an Euler-MacLaurin expansion. We
use this to obtain the mass-radius relation for magnetic He, C,
and Fe white dwarfs of uniform composition.Comment: 7 pages, 7 figures and 1 table, To appear in Ap
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Meteorological and chemical factors controlling ozone formation in Seoul during MAPS-Seoul 2015
To understand the chemical mechanisms of controlling factors in ozone (O3) formation in early summer in Seoul, a comprehensive study encompassing measurement and modeling was conducted under the Megacity Air Pollution Study-Seoul (MAPS-Seoul) campaign. From May 18 to June 12, 2015, O3 and peroxyacetyl nitrate (PAN) were measured, along with their precursors, including NOx and volatile organic compounds (VOCs), at the Korea Institute of Science and Technology, located in northeast Seoul. VOCs were sampled in a canister twice a day (at 09:30 and 15:00) and analyzed via gas chromatography. The meteorological conditions and chemical regimes of the air masses were clearly distinguished during the study period. In May, NOx concentrations were higher with more pronounced diurnal cycles of precursors and O3 under constant westerly winds. By contrast, stagnant conditions developed in June, which reduced the inflow of primary emissions from the downtown area but increased the influence from the neighboring forest under high temperatures. As a result, the ratio of O3 to odd oxygen was higher in June, indicating a less efficient removal of O3 by NOx. In the same context, the air mass was chemically more aged with a higher NO2/NOx ratio and enhanced OH reactivity of oxygenated and biogenic VOCs in June. The overall measurement results suggest that O3 formation is slightly more sensitive to VOCs than to NOx in Seoul during this season, when O3 concentrations are the highest of the year
Interplay between carrier and impurity concentrations in annealed GaMnAs intrinsic anomalous Hall Effect
Investigating the scaling behavior of annealed GaMnAs anomalous
Hall coefficients, we note a universal crossover regime where the scaling
behavior changes from quadratic to linear, attributed to the anomalous Hall
Effect intrinsic and extrinsic origins, respectively. Furthermore, measured
anomalous Hall conductivities when properly scaled by carrier concentration
remain constant, equal to theoretically predicated values, spanning nearly a
decade in conductivity as well as over 100 K in T. Both the qualitative
and quantitative agreement confirms the validity of new equations of motion
including the Berry phase contributions as well as tunablility of the intrinsic
anomalous Hall Effect.Comment: 4 pages, 5 figure
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