Tomoka Tosaki

Arclike Distribution of High CO (J = 3-2)/CO (J = 1-0) Ratio Gas Surrounding the Central Star Cluster of the Supergiant H II Region NGC 604

We report the discovery of a high CO (J = 3-2)/CO (J = 1-0) ratio gas with an arclike distribution (high-ratio gas arc) surrounding the central star cluster of the supergiant H II region NGC 604 in the nearby spiral galaxy M33, based on multi-J CO observations of a 5 × 5 region of NGC 604 conducted using the ASTE 10 m and NRO 45 m telescopes. The discovered high-ratio gas arc extends to the southeast-northwest direction with a size of ~200 pc. The western part of the high-ratio gas arc closely coincides with the shells of the H II regions traced by Hα and radio continuum peaks. The CO (J = 3-2)/CO (J = 1-0) ratio, R3-2/1-0, ranges between 0.3 and 1.2 in the observed region, and the R3-2/1-0 values of the high-ratio gas arc are around or higher than unity, indicating very warm (Tkin ≥ 60 K) and dense (n ≥ 103-104 cm-3) conditions of the high-ratio gas arc. We suggest that the dense gas formation and second-generation star formation occur in the surrounding gas compressed by the stellar wind and/or supernova of the first-generation stars of NGC 604, i.e., the central star cluster of NGC 604.

High-density and high-temperature molecular gas around the AGN in M51

Abstract We investigated the physical properties of molecular gas in the nuclear region of M51 (Seyfert 2). We obtained an aperture synthesis 13 CO(J = 1 − 0) image using the Nobeyama Millimeter Array (NMA), and compared it with NMA 12 CO(J = 1 − 0) and HCN(J = 1 − 0) maps at similar spatial resolutions. Within a radius of 180 pc from the center, the 13 CO(1 − 0) integrated intensity was found to be 3 times weaker than that of HCN(1 − 0). Large-Velocity-Gradient (LVG) calculations suggest that the observed high HCN(1 − 0)/ 13 CO(1 − 0) intensity ratio would arise from dense ( n H 2 ∼ 10 5 cm −3 ) and hot ( T kin ≳ 300 K) molecular clouds in the nuclear molecular disk. We also observed in the 12 CO(1 − 0), (3 − 2), 13 CO(1 − 0), and (3 − 2) lines using the Nobeyama 45m and JCMT 15m telescopes. We detected weak 13 CO lines as well as strong 12 CO lines. The LVG calculations assuming a two-component model suggest that there is a large amount of low-density ( n H 2 ∼ 3 − 6 × 10 2 cm −3 ), low-temperature ( T kin ∼ 20 – 50 K) gas, and a small amount of high-density ( n H 2 ≳ 10 4 cm −3 ), high-temperature ( T kin ≳ 500 K) gas. The existence of the high-density and high-temperature component, although having a quite small beam filling factor, supports the aperture synthesis observation results mentioned above. Since this dense, hot gas is located in the nuclear molecular disk around the Active Galactic Nucleus (AGN), it may be heated by the strong X-ray radiation and/or by the shock induced by the radio jet.

Temperature Variations of Cold Dust in the Triangulum Galaxy M 33

We present wide-field 1.1 mm continuum imaging of the nearby spiral galaxy M 33, conducted with the AzTEC bolometer camera on ASTE. We show that the 1.1 mm flux traces the distribution of dust with T∼ 20 K. Combined with far-infrared imaging at 160 µm, we derive the dust temperature distribution out to a galactic radius of ∼ 7 kpc with a spatial resolution of ∼ 100 parsecs. Although the 1.1 mm flux is observed predominantly near star forming regions, we find a smooth radial

AzTEC/ASTE 1.1 mm Deep Surveys: Number Counts and Clustering of Millimeter‐bright Galaxies

We present number counts and clustering properties of millimeter‐bright galaxies uncovered by the AzTEC camera mounted on the Atacama Submillimeter Telescope Experiment (ASTE). We surveyed the AKARI Deep Field South (ADF‐S), the Subaru/XMM Newton Deep Field (SXDF), and the SSA22 fields with an area of ∼0.25u2009deg2 each with an rms noise level of ∼0.4–1.0u2009mJy. We constructed differential and cumulative number counts, which provide currently the tightest constraints on the faint end. The integration of the best‐fit number counts in the ADF‐S find that the contribution of 1.1 mm sources with fluxes ≥1 mJy to the cosmic infrared background (CIB) at 1.1 mm is 12–16%, suggesting that the large fraction of the CIB originates from faint sources of which the number counts are not yet constrained. We estimate the cosmic star‐formation rate density contributed by 1.1 mm sources with ≥1 mJy using the best‐fit number counts in the ADF‐S and find that it is lower by about a factor of 5–10 compared to those derived from U...

Dense gas formation triggered by spiral density wave in M31

We present the high-resolution 12 CO( J = 1 − 0), 13 CO( J = 1 − 0) and 12 CO( J = 3 − 2) maps toward a GMA located on the southern arm region of M31 using Nobeyama 45 m and ASTE 10 m telescopes. The GMA consists of two velocity-components, i.e., red and blue. The blue component shows a strong and narrow peak, whereas the red one shows a weak and broad profile. The red component has a lower 12 CO( J = 1 − 0)/ 13 CO( J = 1 − 0) ratio (~ 5) than that of the blue one (~ 16), indicating that the red component is denser than the blue one. The red component could be the decelerated gas if we consider the galactic rotational velocity in this region. We suggest that the red component is “post shock” dense gas decelerated due to a spiral density wave. This could be observational evidence of dense molecular gas formation due to galactic shock by spiral density waves. We also present results from on-going observations toward NGC 604, which is the supergiant HII region of M33, using Nobeyama 45 m and ASTE 10 m telescopes. The ratio of 12 CO( J = 3 − 2) to 12 CO( J = 1 − 0) ranges from 0.3 to 1.2 in NGC 604. The 12 CO( J = 1 − 0) map shows the clumpy structure while 12 CO( J = 3 − 2) shows a strong peak near to the central star cluster of NGC 604. The high ratio gas is distributed on the arc-like or shell-like structure along with Hα emission and HII region detected by radio continuum. These suggest that the dense gas formation and second generation star formation occur in the surrounding gas compressed by the stellar wind and/or supernova in central star cluster.

ASTE observations of dense molecular gas in galaxies

Atacama Submillimeter Telescope Experiment (ASTE) is a joint project between Japan and Chile for installing and operating a 10 m high precision telescope in the Atacama Desert in order to explore the southern sky through the submillimeter wavelength. We have achieved an accuracy of 19 μm (rms) for the main reflector surface and a stable radio pointing accuracy of about 2 arcsec (rms). A 350 GHz cartridge type SIS mixer receiver achieves good performance with a typical system noise temperature of 150 ~ 250 K in DSB and a main beam efficiency of 0.6 ~ 0.7 during winter nights. A large scale CO(3-2) imaging survey of nearby galaxies using ASTE is now in progress. One of our goals is to compare our wide area CO(3-2) images with existing CO(1-0) data as well as distributions of massive star formation tracers (i.e., Hα and radio continuum emission) in order to understand the physical mechanism which controls the global star formation properties such as star formation efficiency. Initial CO(3-2) maps of some sample galaxies (M 83, NGC 604 in M 33, NGC 1672, & NGC 7130) are reported.