Koh-Ichiro Morita

On-The-Fly Observing System of the Nobeyama 45-m and ASTE 10-m Telescopes

We have developed a spectral line On-The-Fly (OTF) observing mode for the Nobeyama Radio Observatory 45- ma nd the Atacama Submillimeter Telescope Experiment 10-m telescopes. Sets of digital autocorrelation spectrometers are available for OTF with heterodyne receivers mounted on the telescopes, including the focal-plane 5 � 5a rray receiver, BEARS, on the 45-m. During OTF observations, the antenna is continuously driven to cover the mapped region rapidly, resulting in a high observing efficiency and accuracy. Pointing of the antenna and readouts from the spectrometer are recorded as fast as 0.1 s. In this paper we report on improvements made to the software and instruments, requirements and optimization of observing parameters, the data-reduction process, and verification of the system. It is confirmed that, using optimal parameters ,t he OTF is about twice as efficient as the conventional position-switch observing method.

Formation of a Massive Black Hole at the Center of the Superbubble in M82

We performed 12CO (1-0), 13CO (1-0), and HCN (1-0) interferometric observations of the central region (about 450 pc in radius) of M82 with the Nobeyama Millimeter Array and have successfully imaged a molecular superbubble and spurs. The center of the superbubble is clearly shifted from the nucleus by 140 pc. This position is close to that of the massive black hole (BH) of 460 M☉ and the 2.2 μm secondary peak (a luminous supergiant-dominated cluster), which strongly suggests that these objects may be related to the formation of the superbubble. Consideration of star formation in the cluster based on the infrared data indicates that (1) the energy release from supernovae can account for the kinetic energy of the superbubble, (2) the total mass of stellar-mass BHs available for building up the massive BH may be much higher than 460 M☉, and (3) it is possible to form the middle-mass BH of 102-103 M☉ within the timescale of the superbubble. We suggest that the massive BH was produced and is growing in the intense starburst region.

New H2O masers in the NGC 7538 region

H2O maser emission in the NGC 7538 molecular cloud has been mapped with the Nobeyama Millimeter Array with absolute and relative positional accuracies of 0.5 arcsec and 0.2 arcsec, respectively. Five new masers have been found within an 8 arcmin x 8 arcmin area. One is associated with IRS 9, and the other four are not associated with any known infrared or optical sources. The brightest H{sub 2}O maser spot is 3 arcmin southwest from IRS 11 with a flux density of 156 Jy. These masers may be related to premain-sequence objects and/or protostars in the NGC 7538 molecular cloud. Two previously known H{sub 2}O masers associated with IRS 1-3 and IRS 11 are resolved into 11 and 12 maser spots, respectively. The H{sub 2}O maser spots associated with IRS 1-3 seem to be separated into two groups: one of which is very close to the ultracompact H II region at IRS 1, and the other far from IRS 1. 36 refs.

Aperture synthesis observations of the molecular environment of the Sgr A complex. I. The M-0. 13-0. 08 molecular cloud

NH{sub 3} and H{sub 2}O maser observations of the 20 km/s molecular cloud M-0.13-0.08 in the Sgr A complex region are reported. NH{sub 3} (1,1) and (2,2) lines were observed simultaneously, and the molecular gas temperature and density are estimated. The NH{sub 3} emission is elongated in the same direction of the entire M-0.13-0.08 cloud and has a large velocity gradient along its major axis. Strong NH{sub 3} emission is located in the northern part of the cloud, where a perturbed velocity field and broad line widths are observed. In addition, a new H{sub 2}O maser spot was detected near one of the nonthermal continuum sources. These observational results suggest the physical association between a part of the M-0.13-0.08 molecular cloud and the nonthermal continuum sources in the Sgr A complex. 39 refs.

A finger-like extension of the 20 kilometer per second cloud toward the Galactic center

High-resolution ammonia-line images of the M − 0.13 − 0.08 («20 km s −1 ») cloud in the Galactic center region have been obtained with the Nobeyama Millimeter Array. The 20 km s −1 cloud has a finger-like structure extending toward the Galactic center. It almost reaches to the circumnuclear ring (disk) surrounding Sgr A West in projection. A large systematic velocity gradient (5-10 km s −1 arcmin −1 ) along the elongation is found over the whole length of the cloud. We suggest that these characteristics are caused by tidal force in the gravitational field of the Galactic center.

Aperture synthesis observations of NH3 in OMC-1 : filamentary structures around Orion-KL

Aperture synthesis observations of the Orion molecular cloud 1 (OMC-1) have been made in NH{sub 3} (1, 1) and (2, 2) emission at 23.7 GHz, using the Nobeyama Millimeter Array (NMA), and obtained 16 arcsec resolution maps for OMC-1 and 8 arcsec resolution maps for the Orion-KL region. Filamentary structures extending over 0.5 pc from the Orion-KL region to the north and northwest directions were found. These structures are associated with the H2 finger structures and Herbig-Haro objects which are located at the blue-shifted side of the bipolar molecular outflow. The results suggest that these filaments are ambient molecular cloudlets with shocked surfaces caused by the strong stellar wind from the Orion-KL region. The 8 arcsec resolution NH{sub 3} (2, 2) maps show the extended features around the hot core of Orion-KL. These extended features correspond to the rotating disk and shocked shell associated with the bipolar molecular outflow. 37 refs.

Molecular gas bar and expanding molecular ring in the nucleus of the spiral galaxy Maffei 2

Aperture synthesis observations of the central 1.5 kpc region of the spiral galaxy Maffei 2 have been made in CO(J = 1-0) line. A central narrow ridge of molecular gas with a size 1000 pc x 200 pc and a ringlike feature with a large noncircular motion (60 km/s) with a size 500 pc x 240 pc have been found. The narrow ridge is interpreted as a bar of molecular gas in shocks generated at the leading edges in the bar potential. The observational results suggest that the ring is an expanding and rotating ring of molecular gas in the plane of the galaxy. The ring may have been formed by a starburst induced by the efficient gas supply in the bar potential. 38 refs.

High-resolution observations of CO from the bipolar nebula CRL 2688

The results of high spatial resolution mapping observations of CO emission from the bipolar nebula CRL 2688 are reported. The CO spectrum toward the center shows line wings with a full width of 85 km/s. On the blueshifted wing, a narrow and deep absorption feature is seen at a velocity shifted by 20 km/s from the systemic velocity. A central compact core elongated perpendicularly to the bipolar axis and blueshifted high-velocity emission distributed along the optical lobes suggest the presence of an expanding disk of molecular gas and fast stellar wind as the acceleration agent. The absorption feature suggests that an expanding cold absorbing envelope surrounds the relatively warm molecular envelope. The absorbing envelope has an excitation temperature lower than about 5 K and an optical depth larger than 1.2 in the CO(J = 1-0) line, and it is expanding at 20 km/s. The size of this envelope is larger than about 0.6 pc and its mass is larger than 0.016-0.044 solar mass. 16 references.

Interferometric 13CO Observations of the Cometary Bright-rimmed Cloud 37 in IC 1396: Evidence for Collapse Phase of Radiation-driven Implosion?

Interferometric observations of the cometary bright-rimmed cloud BRC 37 (GN 21.38.9) located at the periphery of the H II region IC 1396 were made with the Nobeyama Millimeter Array in the 13CO (J = 1-0) transition. Although the global distribution of the molecular gas is consistent with the previous single-dish results, our high-resolution data clearly show small-scale structures with blueshifted velocity components corresponding to two clear tails stretching from the globule head in the opposite direction toward the exciting star of IC 1396. The elongation direction of these tails and other circumstances suggest an interaction with the UV radiation from the exciting star of IC 1396. The position-velocity diagram along the cloud axis shows a velocity pattern which may be explained by the collapsing gas motion. The morphology as well as the position-velocity diagram seems to be in agreement with the collapse phase of the recent two-dimensional simulations of the radiation-driven implosion of the neutral globule due to UV radiation from OB stars.

The array configuration design of the Atacama Compact Array

The Atacama Compact Array (ACA) is an array composed of twelve 7-m dishes and four 12-m dishes. The ACA is designed for use as a part of the ALMA (Atacama Large Millimeter / Submillimeter Array) to provide high fidelity imaging capability for large extended objects. Basic parameters of the array configuration of the ACA were selected based on the analysis of the sensitivity in uv plane for mosaicing observations with the ACA and the ALMA. For detailed design of the sub-array with 7-m dishes (7-m Array), we adopted the compact spiral concept, which realizes higher uv response at the short uv spacings and better sidelobe performance. To satisfy the sky coverage requirement, the north-south elongation is needed. The 7-m Array was designed to have two configurations, one (Inner Array) is a compact spiral array with small north-south elongation (× 1.1) and the other (NS Array) is a dedicated configuration with large north-south elongation (× 1.7). In actual design, inner 6 antenna pads are shared by both configurations because of construction constraints.