19 research outputs found
Iteration Method to Derive Exact Rotation Curves from Position-Velocity Diagrams of Spiral Galaxies
We present an iteration method to derive exact rotation curves (RC) of spiral
galaxies from observed position-velocity diagrams (PVD), which comprises the
following procedure. An initial rotation curve, RC0, is adopted from an
observed PV diagram (PV0), obtained by any simple method such as the
peak-intensity method. Using this rotation curve and an observed radial
distribution of intensity (emissivity), we construct a simulated PV diagram
(PV1). The difference between a rotation curve obtained from this PV1 and the
original RC (e.g., difference between peak-intensity velocities) is used to
correct the initial RC to obtain a corrected rotation curve, RC1. This RC1 is
used to calculated another PVD (PV2) using the observed intensity distribution,
and to obtain the second iterated RC (RC2). This iteration is repeated until
PV converges to PV0, so that the differences between PV and PV0 becomes
minimum. Finally RC is adopted as the most reliable rotation curve. We apply
this method to some observed PVDs of nearby galaxies, and show that the
iteration successfully converges to give reliable rotation curves. We show that
the method is powerful to detect central massive objects.Comment: To appear in ApJ.Letters, 5 pages Latex with 4 figure
Radial Distribution of the Mass-to-Luminosity Ratio in Spiral Galaxies and Massive Dark Cores
We derive radial profiles of the surface-mass-density for 19 spiral galaxies
directly from their high-resolution rotation curves. Using the corresponding
luminosity profiles, we obtain the radial distribution of the
mass-to-luminosity ratios () from the inner bulge ( a few 100 pc) to
the outer disk ( 2-10 kpc) for 11 galaxies (with inclination <
in order to reduce the influence of the interstellar extinction.
The s in the bulges of two galaxies with sufficient resolution, NGC 4527
and NGC 6946, are found to increase steeply toward the center at radii
100-500 pc at rates of 153 and 72 times per kpc, respectively. Some
other galaxies with fairly high resolution also show signs of an increase
toward the center. Such an increase may indicate the existence of a new
component, a ``massive dark core'', which may be an object linking the bulge
and a central black hole. Based on radial variations of the , we further
discuss the variation of the dark-mass fraction in spiral galaxies.Comment: Latex 19 pages, 30 ps figures. ApJ in pres
Observation of α-decay of ^<229m>Th produced from ^<229>Ac(II. Radiochemistry)
We produced ^Th in the nuclear reaction ^Th(γ, p2n)^ Ac, followed by disintegration to ^Th. The α-decay signals from ^Th were searched for and the alpha-particle events of the energy region between 4.93MeV and 5.05MeV were observed in the separated thorium fraction from an actinium source highly purified from the ^Th+γ reaction products. The energy values of the α-particles coincide with those expected for ^Th
Zinc transporter ZIP13 suppresses beige adipocyte biogenesis and energy expenditure by regulating C/EBP-β expression
<div><p>Given the relevance of beige adipocytes in adult humans, a better understanding of the molecular circuits involved in beige adipocyte biogenesis has provided new insight into human brown adipocyte biology. Genetic mutations in <i>SLC39A13/ZIP13</i>, a member of zinc transporter family, are known to reduce adipose tissue mass in humans; however, the underlying mechanisms remains unknown. Here, we demonstrate that the <i>Zip13</i>-deficient mouse shows enhanced beige adipocyte biogenesis and energy expenditure, and shows ameliorated diet-induced obesity and insulin resistance. Both gain- and loss-of-function studies showed that an accumulation of the CCAAT/enhancer binding protein-β (C/EBP-β) protein, which cooperates with dominant transcriptional co-regulator PR domain containing 16 (PRDM16) to determine brown/beige adipocyte lineage, is essential for the enhanced adipocyte browning caused by the loss of ZIP13. Furthermore, ZIP13-mediated zinc transport is a prerequisite for degrading the C/EBP-β protein to inhibit adipocyte browning. Thus, our data reveal an unexpected association between zinc homeostasis and beige adipocyte biogenesis, which may contribute significantly to the development of new therapies for obesity and metabolic syndrome.</p></div