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Your search keyword '"Yamauchi, Aya"' showing total 22 results
Start Over Author "Yamauchi, Aya" Journal publications of the astronomical society of japan
22 results on '"Yamauchi, Aya"'

1. Trigonometric parallax and proper motion of Sagittarius A* measured by VERA using the new broad-band back-end system OCTAVE-DAS.

Author

Oyama, Tomoaki, Nagayama, Takumi, Yamauchi, Aya, Sakai, Daisuke, Imai, Hiroshi, Honma, Mareki, Asakura, Yu, Hada, Kazuhiro, Hagiwara, Yoshiaki, Hirota, Tomoya, Jike, Takaaki, Kono, Yusuke, Suzuki, Syunsaku, Kobayashi, Hideyuki, and Kawaguchi, Noriyuki

Subjects
PARALLAX, ORBITAL velocity, GALACTIC center, ANGULAR velocity, BLACK holes
Abstract

We successfully measured the trigonometric parallax of Sagittarius A* (Sgr A*) to be 117 ± 17 micro-arcseconds (⁠|$\, \mu \mbox{as}$|⁠) using the VLBI Exploration of Radio Astrometry (VERA) with the newly developed broad-band signal-processing system named "OCTAVE-DAS." The measured parallax corresponds to a Galactocentric distance at the Sun of |$R_0 = 8.5^{+1.5}_{-1.1}\:$| kpc. By combining the astrometric results with VERA and the Very Long Baseline Array (VLBA) over a monitoring period of 25 yr, the proper motion of Sgr A* is obtained to be (μα, μδ) = (−3.133 ± 0.003, −5.575 ± 0.005) mas yr−1 in equatorial coordinates, corresponding to (μ l , μ b ) = (−6.391 ± 0.005, −0.230 ± 0.004) mas yr−1 in Galactic coordinates. This gives an angular orbital velocity of the Sun of Ω⊙ = 30.30 ± 0.02 km s−1 kpc−1. We find upper limits to the core wander, Δθ < 0.20 mas (1.6 au), peculiar motion, Δμ < 0.10 mas yr−1 (3.7 km s−1), and acceleration, a < 2.6 |$\, \mu \mbox{as} \:$| yr−2 (0.10 km s−1 yr−1) for Sgr A*. Thus, we obtained upper mass limits of |$\approx 3 \times 10^{4}\, M_{\odot }$| and |$\approx 3 \times 10^{3}\, M_{\odot }$| for the supposed intermediate-mass black holes at 0.1 and 0.01 pc from the Galactic center, respectively. [ABSTRACT FROM AUTHOR]

Published
2024
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2. High-sensitivity VLBI observations of water masers in the Seyfert galaxy NGC 1068

Author

Morishima, Yuna, Sudou, Hiroshi, Yamauchi, Aya, Taniguchi, Yoshiaki, and Nakai, Naomasa

Subjects
Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies
Abstract

We present observational results of water vapor maser emission with our high-sensitivity 22 GHz VLBI imaging of the Seyfert galaxy NGC 1068. In this galaxy, there are the following four nuclear radio sources; NE, C, S1, and S2. Among them, the S1 component has been identified as the nucleus while the C component has been considered as attributed to the radio jet. In our VLBI observation, we find the following two types of the water maser emission at the S1 component. One is the linearly aligned component that is considered as an edge-on disk with the inner radius of 0.62 pc. The dynamical mass enclosed within the inner radius was estimated to be $1.5\times10^7 M_{\odot}$ by assuming the circular Keplerian motion. Note, however, that the best fit rotation curve shows a sub-Keplerian rotation ($v\propto r^{-0.24\pm0.10}$). The other is the water maser emission distributed around the rotating disk component up to 1.5 pc from the S1 component, suggesting the bipolar outflow from the S1 component. Further, we detected the water maser emission in the C component for the first time with VLBI, and discovered a ring-like distribution of the water maser emission. It is known that a molecular cloud is associated with the C component (both HCN and HCO$^+$ emission lines are detected by ALMA). Therefore, the ring-like maser emission can be explained by the jet collision to the molecular cloud. However, if these ring-like water masing clouds constitute a rotating ring around the C component, it is likely that the C component also has a supermassive black hole with the mass of $\sim 10^6 M_{\odot}$ that could be supplied from a past minor merger of a nucleated satellite galaxy., Comment: 16 pages, 10 figures, accepted for publication in the PASJ

Published
2022

3. High-sensitivity VLBI observations of water masers in the Seyfert galaxy NGC 1068.

Author

Morishima, Yuna, Sudou, Hiroshi, Yamauchi, Aya, Taniguchi, Yoshiaki, and Nakai, Naomasa

Subjects
MASERS, VERY long baseline interferometry, SEYFERT galaxies, SUPERMASSIVE black holes, GALAXY mergers, JETS (Nuclear physics), ROTATING disks, GAMMA ray bursts, CIRCULAR motion
Abstract

We present observational results of water vapor maser emission with our high-sensitivity 22 GHz very long baseline interferometry (VLBI) imaging of the Seyfert galaxy NGC 1068. In this galaxy, there are the following four nuclear radio sources; NE, C, S1, and S2. Among them, the S1 component has been identified as the nucleus while the C component has been considered as attributed to the radio jet. In our VLBI observation, we find the following two types of water maser emission at the S1 component. One is a linearly aligned component that is considered as an edge-on disk with an inner radius of 0.62 pc. The dynamical mass enclosed within the inner radius was estimated to be 1.5 × 107  M ⊙ by assuming the circular Keplerian motion. Note, however, that the best-fitting rotation curve shows a sub-Keplerian rotation (v ∝ r −0.24±0.10). The other is water maser emission distributed around the rotating disk component up to 1.5 pc from the S1 component, suggesting a bipolar outflow from the S1 component. Further, we detected water maser emission in the C component for the first time with VLBI, and discovered a ring-like distribution of water maser emission. It is known that a molecular cloud is associated with the C component (both HCN and HCO+ emission lines are detected by ALMA). Therefore, the ring-like maser emission can be explained by the jet collision to the molecular cloud. However, if these ring-like water masing clouds constitute a rotating ring around the C component, it is likely that the C component also has a supermassive black hole with a mass of ∼106  M ⊙ that could be supplied from a past minor merger of a nucleated satellite galaxy. [ABSTRACT FROM AUTHOR]

Published
2023
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4. Discovery of H2O megamasers in obscured active galactic nuclei

Author

Yamauchi, Aya, primary, Miyamoto, Yusuke, additional, Nakai, Naomasa, additional, Terashima, Yuichi, additional, Okumura, Taishi, additional, Zhou, Bin, additional, Taniguchi, Kotomi, additional, Kaneko, Hiroyuki, additional, Matsumoto, Naoko, additional, Salak, Dragan, additional, Nishimura, Atsushi, additional, and Ueno, Saeko, additional

Published
2017
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5. A multi-line ammonia survey of the Galactic center region with the Tsukuba 32 m telescope. I. Observations and data

Author

Arai, Hitoshi, primary, Nagai, Makoto, additional, Fujita, Shinji, additional, Nakai, Naomasa, additional, Seta, Masumichi, additional, Yamauchi, Aya, additional, Kaneko, Hiroyuki, additional, Hagiwara, Kenzaburo, additional, Mamyoda, Koh-ichi, additional, Miyamoto, Yusuke, additional, Horie, Masa-aki, additional, Ishii, Shun, additional, Koide, Yusuke, additional, Ogino, Mitsutoshi, additional, Maruyama, Masaki, additional, Hirai, Katsuaki, additional, Oshiro, Wataru, additional, Nagai, Satoshi, additional, Akiyama, Daiki, additional, Konakawa, Keita, additional, Nonogawa, Hiroaki, additional, Salak, Dragan, additional, Terabe, Yuki, additional, Nihonmatsu, Yoshiki, additional, and Funahashi, Fumiyoshi, additional

Published
2016
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9. Fundamental Parameters of the Milky Way Galaxy Based on VLBI Astrometry

Author

Honma, Mareki, primary, Nagayama, Takumi, additional, Ando, Kazuma, additional, Bushimata, Takeshi, additional, Choi, Yoon Kyung, additional, Handa, Toshihiro, additional, Hirota, Tomoya, additional, Imai, Hiroshi, additional, Jike, Takaaki, additional, Kim, Mi Kyoung, additional, Kameya, Osamu, additional, Kawaguchi, Noriyuki, additional, Kobayashi, Hideyuki, additional, Kurayama, Tomoharu, additional, Kuji, Seisuke, additional, Matsumoto, Naoko, additional, Manabe, Seiji, additional, Miyaji, Takeshi, additional, Motogi, Kazuhito, additional, Nakagawa, Akiharu, additional, Nakanishi, Hiroyuki, additional, Niinuma, Kotaro, additional, Oh, Chung Sik, additional, Omodaka, Toshihiro, additional, Oyama, Tomoaki, additional, Sakai, Nobuyuki, additional, Sato, Katsuhisa, additional, Sato, Mayumi, additional, Shibata, Katsunori M., additional, Shiozaki, Satoshi, additional, Sunada, Kazuyoshi, additional, Tamura, Yoshiaki, additional, Ueno, Yuji, additional, and Yamauchi, Aya, additional

Published
2012
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19. Japanese VLBI Network Mapping of SiO v= 3 J= 1–0 Maser Emission in W Hydrae

Author

Imai, Hiroshi, Nakashima, Jun-ichi, Deguchi, Shuji, Yamauchi, Aya, Nakagawa, Akiharu, and Nagayama, Takumi

Abstract

We report first on two-epoch mapping observations of SiO $v =$3 $J =$1–0 maser emission in the semiregular variable W Hydrae using the Japanese VLBI Network. The flux density of the $v =$3 $J =$1–0 emission detected on 2009 February 28 was two orders of magnitude smaller than those of the $v =$1 and $v =$2 emissions, while a month and half later the $v =$3 flux density suddenly increased by a factor of $\sim $25. In contrast, the $v =$1 and $v =$2 flux densities decreased during this period, as expected from the optical light curve. At the first epoch, the $v =$3 maser features were located inside of a ring composed of the $v =$1 and $v =$2 features by 6 mas ($\gtrsim $0.5 AU) toward the central star. These offsets are meaningfully larger than the error of the fitted ring radius and the difference in the ring sizes of $v =$1 and $v =$2 masers ($\lesssim $0.2 AU). The present result at the first epoch suggests that $v =$3 $J =$1–0 SiO masers are predominantly excited in a pumping mechanism (e.g., collisional pumping) different from that recently proposed on the basis of the line overlap with infrared H$_{2}$O lines. Interestingly, the second-epoch observation revealed that the $v =$3 features were located on almost the same ring as the $v =$2 ring, which is consistent with what line-overlap theory suggests.

Published
2010
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20. VLBI Detections of Parsec-Scale Nonthermal Jets in Radio-Loud Broad Absorption Line Quasars

Author

Doi, Akihiro, Kawaguchi, Noriyuki, Kono, Yusuke, Oyama, Tomoaki, Fujisawa, Kenta, Takaba, Hiroshi, Sudou, Hiroshi, Wakamatsu, Ken-ichi, Yamauchi, Aya, Murata, Yasuhiro, Mochizuki, Nanako, Wajima, Kiyoaki, Omodaka, Toshihiro, Nagayama, Takumi, Nakai, Naomasa, Sorai, Kazuo, Kawai, Eiji, Sekido, Mamoru, Koyama, Yasuhiro, Asano, Shoichiro, and Uose, Hisao

Abstract

We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey Third Data Release, by a very-long-baseline interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network. We aimed to select BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversial issues of whether BAL quasars are viewed nearly edge-on, and of whether BAL quasars are in a short-lived evolutionary phase of the quasar population. We detected 20 out of 22 sources using the OCTAVE baselines, implying brightness temperatures greater than 10$^{5}$K, which presumably come from nonthermal jets. Hence, BAL outflows and nonthermal jets can be generated simultaneously in these central engines. We also found four inverted-spectrum sources, which are interpreted as Doppler-beamed, pole-on-viewed relativistic jet sources, or young radio sources: single edge-on geometry cannot describe all BAL quasars. We discuss the implications of the OCTAVE observations for investigations for the orientation and evolutionary stage of BAL quasars.

Published
2009
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21. The First VERA Astrometry Catalog

Author

Hirota, Tomoya, Nagayama, Takumi, Honma, Mareki, Adachi, Yuuki, Burns, Ross A, Chibueze, James O, Choi, Yoon Kyung, Hachisuka, Kazuya, Hada, Kazuhiro, Hagiwara, Yoshiaki, Hamada, Shota, Handa, Toshihiro, Hashimoto, Mao, Hirano, Ken, Hirata, Yushi, Ichikawa, Takanori, Imai, Hiroshi, Inenaga, Daichi, Ishikawa, Toshio, Jike, Takaaki, Kameya, Osamu, Kaseda, Daichi, Kim, Jeong Sook, Kim, Jungha, Kim, Mi Kyoung, Kobayashi, Hideyuki, Kono, Yusuke, Kurayama, Tomoharu, Matsuno, Masako, Morita, Atsushi, Motogi, Kazuhito, Murase, Takeru, Nakagawa, Akiharu, Nakanishi, Hiroyuki, Niinuma, Kotaro, Nishi, Junya, Oh, Chung Sik, Omodaka, Toshihiro, Oyadomari, Miyako, Oyama, Tomoaki, Sakai, Daisuke, Sakai, Nobuyuki, Sawada-Satoh, Satoko, Shibata, Katsunori M, Shizugami, Makoto, Sudo, Jumpei, Sugiyama, Koichiro, Sunada, Kazuyoshi, Suzuki, Syunsaku, Takahashi, Ken, Tamura, Yoshiaki, Tazaki, Fumie, Ueno, Yuji, Uno, Yuri, Urago, Riku, Wada, Koji, Wu, Yuan Wei, Yamashita, Kazuyoshi, Yamashita, Yuto, Yamauchi, Aya, and Yuda, Akito

Abstract

We present the first astrometry catalog from the Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). We have compiled all the astrometry results from VERA, providing accurate trigonometric-annual-parallax and proper-motion measurements. In total, 99 maser sources are listed in the VERA catalog. Among them, 21 maser sources are newly reported, while the rest of the 78 sources are referred to in previously published results or those in preparation for forthcoming papers. The accuracy in the VERA astrometry is revisited and compared with that from the other VLBI astrometry projects such as BeSSeL (The Bar and Spiral Structure Legacy) Survey and GOBELINS (the Gould’s Belt Distances Survey) with the VLBA (Very Long Baseline Array). We have confirmed that most of the astrometry results are consistent with each other, and the largest error sources are due to source structure of the maser features and their rapid variation, along with the systematic calibration errors and different analysis methods. Combined with the BeSSeL results, we estimate the up-to-date fundamental Galactic parameters of $R_{0}=7.92\pm 0.16_{\rm {stat.}}\pm 0.3_{\rm {sys.}}\:$kpc and $\Omega _{\odot }=30.17\pm 0.27_{\rm {stat.}}\pm 0.3_{\rm {sys.}}\:$km$\:$s$^{-1}\:$kpc$^{-1}$, where $R_{0}$and $\Omega _{\odot }$are the distance from the Sun to the Galactic center and the Sun’s angular velocity of the Galactic circular rotation, respectively.

Published
2020
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22. Hot ammonia in the center of the Seyfert 2 galaxy NGC 3079.

Author

Miyamoto, Yusuke, Nakai, Naomasa, Seta, Masumichi, Salak, Dragan, Hagiwara, Kenzaburo, Nagai, Makoto, Ishii, Shun, and Yamauchi, Aya

Subjects
GALACTIC center, INTERSTELLAR gases, AMMONIA gas, SEYFERT galaxies, CATACLYSMIC variable stars, OPTICAL spectroscopy, VERY large array telescopes, FLUX (Energy)
Abstract

We present the results of ammonia observations toward the center of NGC 3079. The NH3(J, K) = (1, 1) and (2, 2) inversion lines were detected in absorption with the Tsukuba 32 m telescope, and the NH3(1, 1) through (6, 6) lines with the VLA, although the profile of NH3(3, 3) was in emission in contrast to the other transitions. The background continuum source, whose flux density was ∼ 50 mJy, could not be resolved with the VLA beam of ≲ 0${^{\prime\prime}_{.}}$09 × 0${^{\prime\prime}_{.}}$08. All ammonia absorption lines have two distinct velocity components: one is at the systemic velocity and the other is blueshifted, and both components are aligned along the nuclear jets. For the systemic components, the relatively low temperature gas is extended more than the high temperature gas. The blueshifted NH3(3, 3) emission can be regarded as ammonia masers associated with shocks by strong winds probably from newly formed massive stars or supernova explosions in dense clouds in the nuclear megamaser disk. Using para-NH3(1, 1), (2, 2), (4, 4), and (5, 5) lines with VLA, we derived the rotational temperature Trot = 120 ± 12 K and 157 ± 19 K for the systemic and blueshifted components, respectively. The total column densities of NH3(0, 0)–(6, 6), assuming Tex ≈ Trot, were (8.85 ± 0.70) × 1016 cm−2 and (4.47 ± 0.78) × 1016 cm−2 for the systemic and blueshifted components, respectively. The fractional abundance of NH3 relative to molecular hydrogen H2 for the systemic and blueshifted was [NH3]/[H2] = 1.3 × 10−7 and 6.5 × 10−8, respectively. We also found the F = 4–4 and F = 5–5 doublet lines of OH 2Π3/2 J = 9/2 in absorption, which could be fitted by two velocity components, systemic and redshifted components. The rotational temperature of OH was estimated to be Trot, OH ≥ 175 K, tracing hot gas associated with the interaction of the fast nuclear outflow with dense molecular material around the nucleus. [ABSTRACT FROM PUBLISHER]

Published
2015
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