Published Papers - TOMITA Akihiko

THE COMPLEX H-ALPHA VELOCITY-FIELD OF NGC-1569

A TOMITA, K OHTA, M SAITO （Part： Lead author )

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN ( ASTRONOMICAL SOC JAPAN )  46 ( 4 ) 335 - 341   1994  [Refereed]

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We obtained an Her velocity field for the entire optical region of NGC 1569, a very actively star-forming dwarf irregular galaxy. The Ha velocities have two components with separations of several tens to one hundred km s(-1) at about one-fourth of the observed positions, and show bumpy features over the entire region. We suggest that these features are due to expanding bubbles. Kinematically, the peculiar 'Ha arm' feature is also part of a large-scale expanding bubble. We discuss some possible triggering mechanisms for the current star formation in NGC 1569.

SEARCH FOR CO EMISSION FROM THE DAMPED LYMAN-ALPHA SYSTEM TOWARD QSO 1215+333

K OHTA, T USUI, T YAMADA, T TAKATA, A TOMITA, N NAKAI

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN ( ASTRONOMICAL SOC JAPAN )  46 ( 4 ) L163 - L166   1994  [Refereed]

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A search for redshifted (CO)-C-12 (J = 1-0) emission from the damped Lya system at z = 2.00 toward QSO 1215+333 was made. No emission was found, and the upper limit of the molecular-hydrogen mass is 1.6 x 10(11)h(-2)M. (q(0) = 0.5) if we assume a velocity width of 400 km s(-1) and the Galactic CO-to-H-2 conversion factor. We estimated the far-infrared luminosity from the HP luminosity, and found that the upper limit of the molecular-hydrogen mass and far-infrared luminosity are comparable to those of ultraluminous far-infrared galaxies. However, the upper limit of the molecular-hydrogen mass obtained in this system is much smaller than the molecular-hydrogen mass found in other damped Lya systems at z = 2-3. It seems that the star-formation properties in these damped Lya systems are quite different from those of the system toward QSO 1215+333 and nearby galaxies. Further observations of more damped Lya systems in CO lines as well as in other wavelengths are indispensable to trace the star-formation history of damped Lya systems.

4 ACTIVE GALAXIES NEWLY DETECTED BEHIND THE MILKY-WAY

T TAKATA, A TOMITA, T YAMADA, T TAKEUCHI, K NAKANISHI, M SAITO

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN ( ASTRONOMICAL SOC JAPAN )  46 ( 4 ) 343 - 347   1994  [Refereed]

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In the course of our redshift; survey of IRAS galaxies behind the Milky Way, we newly detected four galaxies with active galactic nuclei, including one quasar and two Seyfert-type galaxies. The quasar, IRAS 07483+0328, is at z approximate to 0.1 and Mv = -24.0 mag. The quasar may be appropriate for investigating the nature of quasars because of its low redshift as well as the bright apparent magnitude.

Connection of Large-Scale Structure of the Galaxy Distribution behind the Southern Milky Way

Toru Yamada, Tadafumi Takata, Thomas Djamaluddin, Akihiko Tomita, Kentaro Aoki, Aki Takeda, Mamoru Saito

Monthly Notices of the Royal Astronomical Society   262 ( 1 ) 79 - 84   1993  [Refereed]

A search for IRAS galaxies behind the southern milky way

Toru Yamada, Tadafumi Takata, Thomas Djamaluddin, Akihiko Tomita, Kentaro Aoki, Aki Takeda, Mamoru Saito

Astrophysical Journal, Supplement Series ( University of Chicago Press )  89 ( 1 ) 57 - 84   1993  [Refereed]

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We systematically searched for IRAS galaxies with 60 μm flux density larger than 0.6 Jy by using the UK Schmidt Infrared and IIIa-J Atlases in the Milky Way region (|b| &lt
15°) between l = 210° and 360°. We first selected about 4000 IRAS point sources by using our far-infrared criteria, which are optimized for the search of IRAS galaxies behind the Milky Way region, and then inspected visually the optical counterparts of them on the Schmidt Atlas film copies. We found 966 IRAS sources associated with galaxy-like objects. The list of the objects is presented here with the IRAS source name, Galactic coordinates, IRAS flux densities, field number and emulsion of the Atlas, type and size of galaxy (-like) image, redshift, multiplicity, and cross-identification. Of these, 423 galaxies are already cataloged in the Catalog of Galaxies and Quasars Observed in the IRAS Survey, and most of the remaining 543 galaxy candidates are newly identified in this search. Although the radial velocities are known for only 387 galaxies, of which 60 were newly measured by us so far, we inferred the contamination by Galactic objects to be small from the good correlation between the sky distributions of the newly identified galaxy candidates and the previously cataloged galaxies. In the regions where the Galactic molecular clouds dominate, almost all the sources were not identified as galaxies. The detected galaxies are clustered in the three regions around l = 240°, 280°, and 315°, where the projected number densities are higher than the whole-sky average of IRAS galaxies of the same flux limit.

DOI

H-ALPHA VELOCITY-FIELDS OF GIANT H-II REGIONS IN 4 NEARBY DWARF IRREGULAR GALAXIES

A TOMITA, K OHTA, M SAITO （Part： Lead author )

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN ( ASTRONOMICAL SOC JAPAN )  45 ( 5 ) 693 - &   1993  [Refereed]

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We carried out Halpha spectroscopies of six giant H II regions in four isolated, nearby, face-on dwarf irregular galaxies: I Zw 36, NGC 6822, Sex A, and IC 1613. The Halpha velocity field maps were obtained for three galaxies, but not for IC 1613. These Halpha velocity fields have the following common features: (1) At the central parts of the H II regions the velocity fields are rather flat, i.e., the velocity ranges are 5 km s-1 or less over a scale of 50 to 200 pc. In particular, in the H II region in NGC 6822, observed with a spatial resolution of about 10 pc, the velocity field at the central part is more calm than that expected in gravitationally relaxed systems. (2) The Halpha velocities at the central parts axe nearly the same as the CO velocities, but several km s-1 larger than the velocities of H I gas surrounding the H II regions. (3) At the outer regions the Halpha velocities are shifted by 10 to 15 km s-1 from those at the central parts. By also considering the ages and locations of the H II regions as well as the extent of the H I envelopes, these features seem to be consistent with a model in which the star formation bursts are triggered by the collisions of infalling clouds with the H I disk.

CO-TO-H2 CONVERSION FACTOR IN DWARF IRREGULAR GALAXIES

K OHTA, A TOMITA, M SAITO, M SASAKI, N NAKAI

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN ( ASTRONOMICAL SOC JAPAN )  45 ( 2 ) L21 - L26   1993  [Refereed]

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(CO)-C-12 (J = 1-0) observations of five nearby dwarf irregular galaxies were made with a beam size of 15'', which is comparable to the size of a giant molecular cloud in the galaxies. We observed star-forming regions and/or H I clumps with a column density exceeding 10(21) cm-2, where molecular clouds tend to be detected. CO emission was detected toward two H I clumps in NGC 4214 and one clump in NGC 6822. For another three galaxies (IC 1613, Sex A, and GR 8) very low upper limits of the CO luminosity were obtained. We examined the relation between the CO luminosities and the line widths of molecular clouds in twelve galaxies, including other previous observations with a beam size comparable to the size of a giant molecular cloud and/or complex. The general tendency of this relation is that the CO luminosity for the same line width decreases with decreasing metallicity (O/H) of a galaxy; that is, if the line width is an indicator of the mass of a molecular cloud, the CO-to-H-2 conversion factor increases as the metallicity of a galaxy decreases. However, there is a large scatter in the CO luminosity among galaxies with the same metallicity; the conversion factors for dwarf irregular galaxies with the same metallicity are not always the same. For example, although NGC 6822 has a metallicity that is similar to those of IC 10 and the Small Magellanic Cloud, the CO luminosities of the molecular clouds axe much smaller than those in the other two galaxies and, thus, the conversion factor is considerably larger. The UV intensity in the star-forming region does not seem to be the main cause for this large scatter; some other factors may also affect the CO luminosity.