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3
  • Sang-Sung Lee
  • Sincheol Kang; Sang Hyun Kim
  • Jee Won Lee; Sang-Sung Lee; Juan-Carlos Algaba; Jeffrey Hodgson; Jae-Young Kim; Jongho Park; Motoki Kino; Dae-Won Kim; Sincheol Kang; Sungmin Yoo; Sang Hyun Kim; and Mark Gurwell
  • 2020-10-16
  • ApJ,902,104
We present the results of simultaneous multifrequency imaging observations at 22, 43, 86, and 129 GHz of OJ 287. We used the Korean Very Long Baseline Interferometry Network as part of the Interferometric  Monitoring of Gamma-ray Bright active galactic nuclei (iMOGABA). The  iMOGABA observations were performed during 31 epochs from 2013 January 16 to 2016 December 28. We also used 15 GHz OVRO and 225 GHz SMA flux density data. We analyzed four flux enhancements in the light curves. The estimated timescales of three flux enhancements were similar with  timescales of ~50 days at two frequencies. A fourth flux enhancement had a variability timescale approximately twice as long. We found that 225 GHz enhancements led the 15 GHz enhancements by a range of 7–30 days in  the time delay analysis. We found the fractional variability did not change with frequency between 43 and 86 GHz. We could reliably measure the turnover frequency, nu_c, of the core of the source in three epochs. This was measured to be in a range from 27 to 50 GHz and a flux density at the turnover frequency, S_m, ranging from 3 to 6 Jy. The derived SSA magnetic fields, B_SSA, are in a range from 0.157 ± 0.104 to 0.255 ± 0.146 mG. We estimated the  equipartition magnetic field strengths to be in a range from 0.95 ± 0.15 to 1.93 ± 0.30 mG. The equipartition magnetic field strengths are up to a factor of 10 higher than the values of B_SSA. We conclude that the downstream jet may be more particle energy dominated.
2
  • Lee, Chang Won
  • Kim, Shinyoung
  • Kim, Shinyoung; Lee, Chang Won; Gopinathan, Maheswar; Tafalla, Mario; Sohn, Jungjoo; Kim, Gwanjeong; Kim, Mi-Ryang; Soam, Archana; Myers, Philip C.
  • 2020-03-10
  • ApJ,891,169
The CS molecule is known to be adsorbed onto dust in cold and dense conditions, causing it to be significantly depleted in the central region of cores. This study is aimed to investigate the depletion of the CS molecule using the optically thin C34S molecular line observations. We mapped five prestellar cores, L1544, L1552, L1689B, L694-2, and L1197, using two molecular lines, C34S (J = 2–1) and N2H+ (J = 1–0) with the NRO 45 m telescope, doubling the number of cores where the CS depletion was probed using C34S . In most of our targets, the distribution of C34S emission shows features that suggest that the CS molecule is generally depleted in the center of the prestellar cores. The radial profile of the CS abundance with respect to H2 directly measured from the CS emission and the Herschel dust emission indicates that the CS molecule is depleted by a factor of ?3 toward the central regions of the cores with respect to their outer regions. The degree of the depletion is found to be even more enhanced, by an order of magnitude, when the contaminating effect introduced by the presence of CS molecules in the surrounding envelope that lie along the line of sight is removed. Except for L1197—which is classified as relatively the least evolved core in our targets, based on its observed physical parameters—we found that the remaining four prestellar cores are suffering from significant CS depletion at their central region, regardless of the relative difference in their evolutionary status.
1
  • Jongwan Ko
  • Woowon Byun
  • Woowon Byun; Yun-Kyeong Sheen; Hong Soo Park; Luis C. Ho; Joon Hyeop Lee; Sang Chul Kim; Hyunjin Jeong; Byeong-Gon Park; Kwang-Il Seon; Yongdae Lee; Yongseok Lee; Sang-Mok Cha; Jongwan Ko; Minjin Kim;
  • 2020-03-01
  • ApJ,891,18
We present newly discovered dwarf galaxy candidates in deep and wide-field images of NGC 1291 obtained with the Korea Microlensing Telescope Network. We identify 15 dwarf galaxy candidates by visual inspection. Using imaging simulations, we demonstrate that the completeness rate of our detection is greater than 70% for the central surface-brightness value of μ0,R ? 26 mag arcsec-2 and for magnitudes MR ? -10 mag. The structural and photometric properties of the dwarf galaxy candidates appear to be broadly consistent with those of ordinary dwarf galaxies in nearby groups and clusters, with μ0,R ∼ 22.5 to 26.5 mag arcsec-2 and effective radii of 200 pc to 1 kpc. The dwarf galaxy candidates show a concentration toward NGC 1291 and tend to be redder the closer they are to the center, possibly indicating that they are associated with NGC 1291. The dwarf candidates presented in this paper appear to be bluer than those in denser environments, revealing that the quenching of star formation in dwarf galaxies is susceptible to the environment, while the morphology shaping is not.
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