Ryohei Kawabe

AzTEC/ASTE 1.1-mm survey of the AKARI Deep Field South: source catalogue and number counts

We present the first results of a deep 1.1-mm survey of the AKARI Deep Field-South (ADF-S) with the AzTEC camera on the Atacama Submillimetre Telescope Experiment (ASTE ). This survey covers ∼400 arcmin, of which the central 202 arcmin is a uniform low-noise region with an rms noise level of 0.48–0.71 mJy. This is one of the deepest surveys at 1-mm wavelength, to cover such a large contiguous region. We detected 37 sources with a significance of 3.5–10 σ. The expected number of false detections at ≥3.5 σ is at most one, indicating that the detected sources are highly reliable. We construct differential and cumulative number counts and find a difference in number counts among 1-mm blank field surveys: the number counts of the ADF-S are less than those of GOODS-N and COSMOS fields. Most of the sources are not detected in the far-infrared bands of the AKARI, suggesting that they lie mostly at z ∼ > 1 given the detection limits. In this survey, about 10% of cosmic infrared background at 1.1 mm is resolved into discrete sources.

Imaging of an Infalling Disklike Envelope around L1551 IRS 5

Aperture synthesis observations of H13CO+ (J = 1-0) emission from L1551 IRS 5 were made using the Nobeyama Millimeter Array. It is found that the emission has a disklike structure with a size of 5600 × 2800 AU at P.A. = 160°. If we assume a geometrically thin disk, its radius and inclination angle are estimated to be 2800 AU and 60° [= cos–1 (2800/5600)], and the disk major axis is almost perpendicular to the molecular outflow. It is noted that there exists radial motion, i.e., velocity gradient along the disk minor axis in the inner region (r < 1000 AU). The motion can be interpreted as infalling motion because the blueshifted emission is located on the far side of the disk and the redshifted emission on the near side by considering the geometrical relation between the H13CO+ feature and the bipolar outflow. The infalling velocity corrected for the inclination is estimated to be 0.6 km s–1 at r = 800 AU and is smaller than the free-fall velocity (~ 1. 5 km s−1 at r = 800 AU ) with a stellar mass of 1 M☉. The H2 mass of the disk and the mass infall rate are estimated to be 0.27 M☉ and ~1.1 × 10-5 M☉ yr–1, respectively. In addition to the infalling motion, the molecular emission also has a velocity structure along the major axis, suggesting rotating motion. The rotational velocity corrected for the inclination is estimated to be 0.23 km s–1 at r = 900 AU, which is smaller than Keplerian rotational velocity, suggesting that the envelope is not rotationally supported. The H13CO+ disklike structure would be a disklike infalling envelope around L1551 IRS 5.

Discovery of a rotating protoplanetary gas disk around the yound star GG Tauri

We have made aperture synthesis 12 CO(J=1-0) observations of a T Tauri star, GG Tau, in Taurus with 8″ resolution using the Nobeyama Millimeter Array (NMA). We have discovered a rotating gas disk having a radius of about 500 AU around GG Tau. The rotation velocity is 0.8 km s −1 /sin i at the radius, which is roughly consistent with a Kepler rotation around the central star. The inclination angle of the disk, i, is estimated to be about 60°, and the gas kinetic temperature is estimated to be about 8 K at that radius

The Initial Conditions for Formation of Low-Mass Stars: Kinematics and Density Structure of the Protostellar Envelope in B335

We have observed dense molecular gas toward a deeply embedded protostar in B335 using the Nobeyama 45 m telescope and the Nobeyama Millimeter Array. The H13CO+ and C18O maps taken by the 45 m telescope show elongated features perpendicular to the axis of molecular outflow, suggesting that these emission lines arise from a dense disklike envelope surrounding the protostar. The size and mass of the H13CO+ disklike envelope are 0.17 × 0.15 pc and 2.4 M☉, respectively. The C18O envelope gas has a linear velocity gradient along its major axis indicative of a rigid rotation with an angular velocity of 1.1 × 10-14 radians s-1. The density profile derived from the C18O and H13CO+ data shows a power law of ρ(r)~ρ0r-1.95~(a2/2πG)r-2 over the radius range between 0.03 and 0.2 pc. In addition, the coefficient of the density profile is consistent with Shus solution rather than Larsons, though there is uncertainty particularly in the fractional abundance of the H13CO+ molecule. Our results suggest that the protostar in B335 was formed in an isothermal core with a rigid rotation. The interferometric observations of the H13CO+ line reveal a dense compact feature centered on the protostar. This compact feature has a size of 2000 AU, and its elongation is roughly perpendicular to the outflow axis. We thus consider that this compact feature is an inner part of the disklike envelope. There is a velocity gradient along the minor axis of the feature which might be interpreted as a disk infalling motion. The previous observations also suggested the existence of infalling motion toward the protostar B335 IRS. In addition, the inner envelope shows a rotating motion of Vθ=0.14 km s-1 at r=490 AU. This rotational velocity is smaller than the corresponding Keplerian velocity of ~0.42 km s-1, indicating that the inner envelope is not rotationally supported.

Detection of an ultrabright submillimetre galaxy in the Subaru/XMM-Newton Deep Field using AzTEC/ASTE

We report on the detection of an extremely bright (∼37 mJy at 1100 μm and ∼91 mJy at 880 μm) submillimetre galaxy (SMG), AzTEC-ASTE-SXDF1100.001 (hereafter referred to as SXDF1100.001 or Orochi), discovered in the 1100 μm observations of the Subaru/XMM–Newton Deep Field using AzTEC on ASTE. Subsequent CARMA 1300-μm and SMA 880-μm observations successfully pinpoint the location of Orochi and suggest that it has two components, one extended [full width at half-maximum (FWHM) of ∼4 arcsec] and one compact (unresolved). Z-Spec on CSO has also been used to obtain a wide-band spectrum from 190 to 308 GHz, although no significant emission/absorption lines were found. The derived upper limit to the line-to-continuum flux ratio is 0.1–0.3 (2σ) across the Z-Spec band. Based on the analysis of the derived spectral energy distribution from optical to radio wavelengths of possible counterparts near the SMA/CARMA peak position, we suggest that Orochi is a lensed, optically dark SMG lying at z ∼ 3.4 behind a foreground, optically visible (but red) galaxy at z ∼ 1.4. The deduced apparent (i.e., no correction for magnification) infrared luminosity (L_(IR)) and star formation rate (SFR) are 6 × 10^(13) L_⊙ and 11 000 M_⊙ yr^(−1), respectively, assuming that the L_(IR) is dominated by star formation. These values suggest that Orochi will consume its gas reservoir within a short time-scale (3 × 10^7 yr), which is indeed comparable to those in extreme starbursts like the centres of local ultraluminous infrared galaxies (ULIRGs).

An H13CO+ Survey for Dense Envelopes around Low-Mass Embedded Sources in Taurus

A dense gas survey was carried out toward 10 low-mass embedded young sources in Taurus with the Nobeyama Millimeter Array (NMA) to investigate protostellar evolution. All the sources were observed in the H13CO+(J = 1-0) line, a high-density tracer. Significant H13CO+ emission (≥4.5 σ) was detected toward six of them. The H13CO+ emission is distributed roughly perpendicular to the molecular outflow axes, indicating that the H13CO+ line traces the dense envelopes associated with the central stars. The sizes and masses of the dense envelopes are estimated to be (1-7) × 103 AU and 0.01-0.2 M☉, respectively. The 10 sources are divided into the following three classes based on their H13CO+ intensities of the NMA maps, and their properties are studied using our own and other available data. Class A sources have H13CO+ emission centered on the star with its elongation perpendicular to the molecular outflow axes. These sources also have dense outflowing gas and centrally condensed parent cores. Class B sources have H13CO+ emission near the source positions and dense outflowing gas. The parent cores around class B sources, however, have a shallower density profile. Class C sources have neither H13CO+ emission nor wing emission in dense gas tracers. From these properties, we conclude that low-mass protostars evolve from class A, B to C sources by dissipating their parent cloud cores, which is consistent with the widely accepted ideas of star formation. In addition, these observational data suggest that significant dispersion of a parent core by a molecular outflow and main accretion phase ends at the early protostellar phase. Six of the 10 sources are detected in continuum emission at 87 GHz. The intensities of the H13CO+ emission do not correlate with the flux densities at 87 GHz. This is because our continuum maps trace compact disks on a 102 AU scale and not dense gas on a 103-4 AU scale.

AzTEC/ASTE 1.1-mm survey of SSA22: Counterpart identification and photometric redshift survey of submillimetre galaxies

This article has been accepted for publication in Monthly Notices Of The Royal Astronomical Society ©: 2014 H. Umehata et al. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

Molecular Outflow Search in the ρ Ophiuchi A and B2 Regions

We have searched for CO molecular outflows associated with the cloud A and B2 of the ρ Ophiuchi star-forming region. On the basis of single -dish 12CO (J = 3-2) and interferometric 12CO (J = 1-0) observations, we have identified three molecular outflows in the ρ Oph A cloud and one in the ρ Oph B2 cloud. Out of the four outflows observed in these regions, one is the known outflow driven by the Class 0 source, VLA 1623, and the other three are newly discovered ones. The inclination and opacity corrected momentum flux FCO of newly detected outflows are roughly comparable to those of Class I objects observed by Bontemps et al. (1996). All the newly discovered outflows are likely to be driven by Class II sources or near-infrared sources, and none of them is associated with the cold submillimeter-millimeter sources without infrared counter parts. These results indicate that protostars associated with outflows whose mass and momentum flux exceed our detection limit are not formed yet in the high-density ridge of the ρ Oph A region and the northeastern condensation in the ρ Oph B2 region, suggesting that they are considered to be pre-protostellar cores.

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.

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.