Achievements & Publications

Infrared 3-4\ensuremathμm Spectroscopy of Nearby PG QSOs and AGN-Nuclear Starburst Connections in High-luminosity AGN Populations

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Imanishi, Masatoshi,   Ichikawa, Kohei,   Takeuchi, Tomoe,   Kawakatu, Nozomu,   Oi, Nagisa,   Imase, Keisuke

We present the results of infrared L-band (3-4\ensuremathμm) slit spectroscopy of 30 PG QSOs at z < 0.17, a representative sample of local high-luminosity, optically selected AGNs. The 3.3\ensuremathμm polycyclic aromatic hydrocarbon (PAH) emission feature is used to probe nuclear (< a few kpc) starburst activity and to investigate the...

Successive Merger of Multiple Massive Black Holes in a Primordial Galaxy

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Tanikawa, A.,   Umemura, M.

Using highly accurate N-body simulations, we explore the evolution of multiple massive black holes (hereafter MBHs) in a primordial galaxy that is composed of stars and MBHs. The evolution is pursed with a fourth-order Hermite scheme, where not only three- body interaction of MBHs but also dynamical friction by stars...

The Subaru Ly\ensuremathα blob survey: a sample of 100-kpc Ly\ensuremathα blobs at z = 3

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Matsuda, Y.,   Yamada, T.,   Hayashino, T.,   Yamauchi, R.,   Nakamura, Y.,   Morimoto, N.

We present results of a survey for giant Ly\ensuremathα blobs (LABs) at z = 3 with Subaru/Suprime-Cam. We obtained Ly\ensuremathα imaging at z = 3.09 \ensuremath± 0.03 around the SSA22 protocluster and in several blank fields. The total survey area is 2.1 deg$^2$, corresponding to a comoving volume of 1.6...

Orientation Effects on the Inner Region of Dusty Torus of Active Galactic Nuclei

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Kawaguchi, Toshihiro,   Mori, Masao

A sublimation process governs the innermost region of the dusty torus of active galactic nuclei. However, the observed inner radius of the torus is systematically smaller than the expected radius by a factor of åisebox-0.5ex~1/3. We show that the anisotropy of the emission from accretion disks resolves this conflict naturally...

Long-term Spectral Variations of Ultraluminous X-ray Sources in the Interacting Galaxy Systems M 51 and NGC 4490/85

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Yoshida, Tessei,   Ebisawa, Ken,   Matsushita, Kyoko,   Tsujimoto, Masahiro,   Kawaguchi, Toshihiro

Variable ultraluminous X-ray sources (ULXs), which are considered to be black hole binaries (BHBs), are known to show state transitions similar to Galactic BHBs. However, the relation between the ULX states and the Galactic BHB states is still unclear, primarily due to the less well-understood behaviors of ULXs in contrast...

START: smoothed particle hydrodynamics with tree-based accelerated radiative transfer

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Hasegawa, K.,   Umemura, M.

We present a novel radiation hydrodynamics code, START, which is a smoothed particle hydrodynamics (SPH) scheme coupled with accelerated radiative transfer. The basic idea for the acceleration of radiative transfer is parallel to the tree algorithm that is hitherto used to speed up the gravitational force calculation in an N-body...

Two types of Lyman \ensuremathα emitters envisaged from hierarchical galaxy formation

Image

Shimizu, Ikkoh,   Umemura, Masayuki

In the last decade, numerous Lyman \ensuremathα (Ly\ensuremathα) emitters (LAEs) have been discovered with narrow-band filters at various redshifts. Recently, multiwavelength observations of LAEs have been performed and revealed that while many LAEs appear to be young and less massive, a noticeable fraction of LAEs possess much older populations of...

Hydrodynamic Simulations of Merging Galaxy Clusters: Non-Equilibrium Ionization State and Two-Temperature Structure

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Akahori, Takuya,   Yoshikawa, Kohji

We investigate a non-equilibrium ionization state and an electron-ion two-temperature structure of the intracluster medium (ICM) in merging galaxy clusters using a series of N-body and hydrodynamic simulations. Mergers with various sets of mass ratios and impact parameters are systematically investigated, and it is found that, in most cases, ICM...

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Infrared 3-4\ensuremathμm Spectroscopy of Nearby PG QSOs and AGN-Nuclear Starburst Connections in High-luminosity AGN Populations

Imanishi, Masatoshi,   Ichikawa, Kohei,   Takeuchi, Tomoe,   Kawakatu, Nozomu,   Oi, Nagisa,   Imase, Keisuke

We present the results of infrared L-band (3-4\ensuremathμm) slit spectroscopy of 30 PG QSOs at z < 0.17, a representative sample of local high-luminosity, optically selected AGNs. The 3.3\ensuremathμm polycyclic aromatic hydrocarbon (PAH) emission feature is used to probe nuclear (< a few kpc) starburst activity and to investigate the...

March 2011   Publications of the Astronomical Society of Japan
Image

Successive Merger of Multiple Massive Black Holes in a Primordial Galaxy

Tanikawa, A.,   Umemura, M.

Using highly accurate N-body simulations, we explore the evolution of multiple massive black holes (hereafter MBHs) in a primordial galaxy that is composed of stars and MBHs. The evolution is pursed with a fourth-order Hermite scheme, where not only three- body interaction of MBHs but also dynamical friction by stars...

February 2011   The Astrophysical Journal Letters
Image

The Subaru Ly\ensuremathα blob survey: a sample of 100-kpc Ly\ensuremathα blobs at z = 3

Matsuda, Y.,   Yamada, T.,   Hayashino, T.,   Yamauchi, R.,   Nakamura, Y.,   Morimoto, N.

We present results of a survey for giant Ly\ensuremathα blobs (LABs) at z = 3 with Subaru/Suprime-Cam. We obtained Ly\ensuremathα imaging at z = 3.09 \ensuremath± 0.03 around the SSA22 protocluster and in several blank fields. The total survey area is 2.1 deg$^2$, corresponding to a comoving volume of 1.6...

January 2011   Monthly Notices of the Royal Astronomical Society
Image

Orientation Effects on the Inner Region of Dusty Torus of Active Galactic Nuclei

Kawaguchi, Toshihiro,   Mori, Masao

A sublimation process governs the innermost region of the dusty torus of active galactic nuclei. However, the observed inner radius of the torus is systematically smaller than the expected radius by a factor of åisebox-0.5ex~1/3. We show that the anisotropy of the emission from accretion disks resolves this conflict naturally...

December 2010   The Astrophysical Journal Letters
Image

Long-term Spectral Variations of Ultraluminous X-ray Sources in the Interacting Galaxy Systems M 51 and NGC 4490/85

Yoshida, Tessei,   Ebisawa, Ken,   Matsushita, Kyoko,   Tsujimoto, Masahiro,   Kawaguchi, Toshihiro

Variable ultraluminous X-ray sources (ULXs), which are considered to be black hole binaries (BHBs), are known to show state transitions similar to Galactic BHBs. However, the relation between the ULX states and the Galactic BHB states is still unclear, primarily due to the less well-understood behaviors of ULXs in contrast...

October 2010   The Astrophysical Journal
Image

START: smoothed particle hydrodynamics with tree-based accelerated radiative transfer

Hasegawa, K.,   Umemura, M.

We present a novel radiation hydrodynamics code, START, which is a smoothed particle hydrodynamics (SPH) scheme coupled with accelerated radiative transfer. The basic idea for the acceleration of radiative transfer is parallel to the tree algorithm that is hitherto used to speed up the gravitational force calculation in an N-body...

October 2010   Monthly Notices of the Royal Astronomical Society
Image

Two types of Lyman \ensuremathα emitters envisaged from hierarchical galaxy formation

Shimizu, Ikkoh,   Umemura, Masayuki

In the last decade, numerous Lyman \ensuremathα (Ly\ensuremathα) emitters (LAEs) have been discovered with narrow-band filters at various redshifts. Recently, multiwavelength observations of LAEs have been performed and revealed that while many LAEs appear to be young and less massive, a noticeable fraction of LAEs possess much older populations of...

August 2010   Monthly Notices of the Royal Astronomical Society
Image

Hydrodynamic Simulations of Merging Galaxy Clusters: Non-Equilibrium Ionization State and Two-Temperature Structure

Akahori, Takuya,   Yoshikawa, Kohji

We investigate a non-equilibrium ionization state and an electron-ion two-temperature structure of the intracluster medium (ICM) in merging galaxy clusters using a series of N-body and hydrodynamic simulations. Mergers with various sets of mass ratios and impact parameters are systematically investigated, and it is found that, in most cases, ICM...

April 2010   Publications of the Astronomical Society of Japan

Infrared 3-4\ensuremathμm Spectroscopy of Nearby PG QSOs and AGN-Nuclear Starburst Connections in High-luminosity AGN Populations

Imanishi, Masatoshi,   Ichikawa, Kohei,   Takeuchi, Tomoe,   Kawakatu, Nozomu,   Oi, Nagisa,   Imase, Keisuke
March 2011   Publications of the Astronomical Society of Japan

Successive Merger of Multiple Massive Black Holes in a Primordial Galaxy

Tanikawa, A.,   Umemura, M.
February 2011   The Astrophysical Journal Letters

The Subaru Ly\ensuremathα blob survey: a sample of 100-kpc Ly\ensuremathα blobs at z = 3

Matsuda, Y.,   Yamada, T.,   Hayashino, T.,   Yamauchi, R.,   Nakamura, Y.,   Morimoto, N.
January 2011   Monthly Notices of the Royal Astronomical Society

Orientation Effects on the Inner Region of Dusty Torus of Active Galactic Nuclei

Kawaguchi, Toshihiro,   Mori, Masao
December 2010   The Astrophysical Journal Letters

Long-term Spectral Variations of Ultraluminous X-ray Sources in the Interacting Galaxy Systems M 51 and NGC 4490/85

Yoshida, Tessei,   Ebisawa, Ken,   Matsushita, Kyoko,   Tsujimoto, Masahiro,   Kawaguchi, Toshihiro
October 2010   The Astrophysical Journal

START: smoothed particle hydrodynamics with tree-based accelerated radiative transfer

Hasegawa, K.,   Umemura, M.
October 2010   Monthly Notices of the Royal Astronomical Society

Two types of Lyman \ensuremathα emitters envisaged from hierarchical galaxy formation

Shimizu, Ikkoh,   Umemura, Masayuki
August 2010   Monthly Notices of the Royal Astronomical Society

Hydrodynamic Simulations of Merging Galaxy Clusters: Non-Equilibrium Ionization State and Two-Temperature Structure

Akahori, Takuya,   Yoshikawa, Kohji
April 2010   Publications of the Astronomical Society of Japan