[en] We present an observational study of the protostellar core B335 harboring a low-mass Class 0 source. The observations of the H¹³CO⁺(J = 1-0) line emission were carried out using the Nobeyama 45 m telescope and Nobeyama Millimeter Array. Our combined image of the interferometer and single-dish data depicts detailed structures of the dense envelope within the core. We found that the core has a radial density profile of n(r)∝r ^–p and a reliable difference in the power-law indices between the outer and inner regions of the core: p ≈ 2 for r ∼> 4000 AU and p ≈ 1.5 for r ∼< 4000 AU. The dense core shows a slight overall velocity gradient of ∼1.0 km s^–1 over the scale of 20, 000 AU across the outflow axis. We believe that this velocity gradient represents a solid-body-like rotation of the core. The dense envelope has a quite symmetrical velocity structure with a remarkable line broadening toward the core center, which is especially prominent in the position-velocity diagram across the outflow axis. The model calculations of position-velocity diagrams do a good job of reproducing observational results using the collapse model of an isothermal sphere in which the core has an inner free-fall region and an outer region conserving the conditions at the formation stage of a central stellar object. We derived a central stellar mass of ∼0.1 M_☉, and suggest a small inward velocity, v_r≥rinf∼0 km s^-1 in the outer core at ∼> 4000 AU. We concluded that our data can be well explained by gravitational collapse with a quasi-static initial condition, such as Shu's model, or by the isothermal collapse of a marginally critical Bonnor-Ebert sphere.

[en] We report the H¹³CO⁺ (J = 1-0) survey observations toward embedded clusters obtained using the Nobeyama 45 m telescope, which were performed to follow up our previous study in the C¹⁸O survey with a dense gas tracer. Our aim is to address the evolution of cluster-forming clumps. We observed the same 14 clusters in C¹⁸O, which are located at distances from 0.3 to 2.1 kpc with a 27'' resolution (corresponding to the Jeans length for most of our targets) in H¹³CO⁺. We detected the 13 clumps in H¹³CO⁺ line emission and obtained the physical parameters of the clumps with radii of 0.24-0.75 pc, masses of 100-1400 M _sun, and velocity widths in FWHM of 1.5-4.0 km s^-1. The mean density is ∼3.9 x 10⁴ cm^-3 and the equivalent Jeans length is ∼0.13 pc at 20 K. We classified the H¹³CO⁺ clumps into three types, type A, type B, and type C according to the relative locations of the H¹³CO⁺ clumps and the clusters (see our previous study). Our classification represents an evolutionary trend of cluster-forming clumps because dense clumps are expected to be converted into stellar constituents, or dispersed by stellar activities. We found a similar, but clearer trend than our previous results, for derived star formation efficiencies to increase from type A to C in the H¹³CO⁺ data, and for the dense gas regions within the clumps traced by H¹³CO⁺ to be sensitive to the physical evolution of the clump-cluster systems. In addition, we found that 4 out of 13 H¹³CO⁺ clumps, which we named 'Distinct Velocity Structure Objects' (DVSOs), have distinct velocity gradients at their central parts, i.e., at the location of the embedded clusters. Assuming that the velocity gradients represent the rigid-like rotation of the clumps, we calculated the virial parameter of the H¹³CO⁺ clumps by taking into account the contribution of the rotation and found that the DVSOs tend to be gravitationally unbound. In order to explain the above physical properties for DVSOs in a consistent way, we propose a clump-clump collision model as a possible mechanism for triggering the formation of clusters.

[en] We present the statistics of faint submillimeter/millimeter galaxies (SMGs) and serendipitous detections of a submillimeter/millimeter line emitter (SLE) with no multi-wavelength continuum counterpart revealed by the deep ALMA observations. We identify faint SMGs with flux densities of 0.1-1.0 mJy in the deep Band-6 and Band-7 maps of 10 independent fields that reduce cosmic variance effects. The differential number counts at 1.2 mm are found to increase with decreasing flux density down to 0.1 mJy. Our number counts indicate that the faint (0.1-1.0 mJy, or SFR_IR ∼ 30-300 M _☉ yr^–1) SMGs contribute nearly a half of the extragalactic background light (EBL), while the remaining half of the EBL is mostly contributed by very faint sources with flux densities of <0.1 mJy (SFR_IR ≲ 30 M _☉ yr^–1). We conduct counts-in-cells analysis with multifield ALMA data for the faint SMGs, and obtain a coarse estimate of galaxy bias, b _g < 4. The galaxy bias suggests that the dark halo masses of the faint SMGs are ≲ 7 × 10¹² M _☉, which is smaller than those of bright (>1 mJy) SMGs, but consistent with abundant high-z star-forming populations, such as sBzKs, LBGs, and LAEs. Finally, we report the serendipitous detection of SLE-1, which has no continuum counterparts in our 1.2 mm-band or multi-wavelength images, including ultra deep HST/WFC3 and Spitzer data. The SLE has a significant line at 249.9 GHz with a signal-to-noise ratio of 7.1. If the SLE is not a spurious source made by the unknown systematic noise of ALMA, the strong upper limits of our multi-wavelength data suggest that the SLE would be a faint galaxy at z ≳ 6.

[en] We present maps of seven young massive molecular clumps within five target regions in C¹⁸O (J = 1-0) line emission, using the Nobeyama 45 m telescope. These clumps, which are not associated with clusters, lie at distances between 0.7 and 2.1 kpc. We find C¹⁸O clumps with radii of 0.5-1.7 pc, masses of 470-4200 M_☉, and velocity widths of 1.4-3.3 km s^–1. All of the clumps are massive and approximately in virial equilibrium, suggesting they will potentially form clusters. Three of our target regions are associated with H II regions (CWHRs), while the other two are unassociated with H II regions (CWOHRs). The C¹⁸O clumps can be classified into two morphological types: CWHRs with a filamentary or shell-like structure and spherical CWOHRs. The two CWOHRs have systematic velocity gradients. Using the publicly released WISE database, Class I and Class II protostellar candidates are identified within the C¹⁸O clumps. The fraction of Class I candidates among all YSO candidates (Class I+Class II) is ≥50% in CWHRs and ≤50% in CWOHRs. We conclude that effects from the H II regions can be seen in (1) the spatial distributions of the clumps: filamentary or shell-like structure running along the H II regions; (2) the velocity structures of the clumps: large velocity dispersion along shells; and (3) the small age spreads of YSOs. The small spreads in age of the YSOs show that the presence of H II regions tends to trigger coeval cluster formation.

[en] We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidates. We detected two ortho-H₂O lines at 321 GHz (10_{2, 9}-9_{3, 6}) and 336 GHz (ν₂ = 1, 5_{2, 3}-6_{1, 6}) for the first time in Source I. The latter one is in a vibrationally excited state at the lower state energy of 2939 K, suggesting evidence of hot molecular gas close to Source I. The integrated intensity map of the 321 GHz line is elongated along the bipolar outflow while the 336 GHz line map is unresolved with a beam size of 0.''4. Both of these maps show velocity gradients perpendicular to the bipolar outflow. The velocity centroid map of the 321 GHz line implies a spatial and velocity structure similar to that of vibrationally excited SiO masers tracing the root of the outflow emanating from the disk surface. In contrast, the 336 GHz line is most likely emitting from the disk midplane with a diameter of 0.''2 (84 AU) as traced by radio continuum emission and a dark lane devoid of the vibrationally excited SiO maser emission. The observed velocity gradient and the spectral profile of the 336 GHz H₂O line can be reconciled with a model of an edge-on ring-like structure with an enclosed mass of >7 M_☉ and an excitation temperature of >3000 K. The present results provide further evidence of a hot and neutral circumstellar disk rotating around Source I with a diameter of ∼100 AU scale

[en] We have carried out a survey of the dense clumps associated with 14 embedded clusters in the C¹⁸O (J = 1-0) line emission with the Nobeyama 45 m telescope in order to understand the formation and evolution of stellar clusters in dense clumps of molecular clouds. We have selected these clusters at distances from 0.3 to 2.1 kpc and have mapped about 6' x 6'-10' x 10' regions (corresponding to 3.8 pc x 3.8 pc at 2.1 kpc) for all the clumps with 22'' resolution (corresponding to Jeans length at 2.1 kpc). We have obtained dense clumps with radii of 0.40-1.6 pc, masses of 150-4600 M _sun, and velocity widths in FWHM of 1.4-3.3 km s^-1. Most of the clumps are found to be approximately in virial equilibrium, which implies that C¹⁸O gas represents parental dense clumps for cluster formation. From the spatial relation between the distributions of clumps and clusters, we classified C¹⁸O clumps into three types (Type A, B, and C). Type A clumps have emission distributions with a single peak at the stellar clusters and higher brightness contrast than that of other target sources. Type B clumps have double or triple peaks, which are associated with the cluster, and moderately high brightness contrast structure. Type C clumps also have multiple peaks, although they are not associated with the cluster, and low brightness contrast structure. We suggest that our classification represents an evolutionary trend of cluster-forming dense clumps because dense gas in molecular clouds is expected to be converted into stellar constituents, or dispersed by stellar activities. Moreover, although there is a scatter, we found a tendency that the star formation efficiencies of the dense clumps increase from Type A to Type C, which also supports our scenario.

[en] We have carried out high-resolution observations with the Atacama Large Millimeter/Submillimeter Array (ALMA) of continuum emission from the Orion Kleinmann–Low (KL) region. We identify 11 compact sources at ALMA band 6 (245 GHz) and band 7 (339 GHz), including the Hot Core, Compact Ridge, SMA1, IRc4, IRc7, and a radio source I (Source I). A spectral energy distribution (SED) of each source is determined by using previous 3 mm continuum emission data. Physical properties such as size, mass, hydrogen number density, and column density are discussed based on the dust graybody SED. Among 11 identified sources, Source I, a massive protostar candidate, is a dominant energy source in Orion KL. We extensively investigate its SED from centimeter to submillimeter wavelengths. The SED of Source I can be fitted with a single power-law index of 1.97, suggesting an optically thick emission. We employ the H"− free–free emission as an opacity source of this optically thick emission. The temperature, density, and mass of the circumstellar disk associated with Source I are constrained by the SED of H"− free–free emission. Still, the fitting result shows a significant deviation from the observed flux densities. Combined with the thermal dust graybody SED to explain excess emission at higher frequency, a smaller power-law index of 1.60 for the H"− free–free emission is obtained in the SED fitting. The power-law index smaller than two would suggest a compact source size or a clumpy structure unresolved with the present study. Future higher resolution observations with ALMA are essential to reveal more detailed spatial structure and physical properties of Source I

[en] This paper presents the results of millimeter to sub-millimeter observations of CO, HCN, N₂H⁺, and HCO⁺ lines in the dense molecular cloud L328, which harbors L328-IRS, a Very Low Luminosity Object (VeLLO). Our analysis of the line width finds that ¹³CO and N₂H⁺ lines are broadened right over the smallest sub-core S2 where L328-IRS is located, while they are significantly narrower in other regions of L328. Thus, L328-IRS has a direct association with the sub-core. CO observations show a bipolar outflow from this VeLLO with an extent of ∼0.08 pc. The outflow momentum flux and efficiency are much less than those of low-mass protostars. The most likely mass accretion rate (∼3.6 × 10^–7 M_☉ yr^–1) inferred from the analysis of the CO outflow is an order of magnitude smaller than the canonical value for a protostar. If the main accretion lasts during the typical Class 0 period of a protostar, L328-IRS will accrete the mass of a brown dwarf, but not that of a star. Given that its envelope mass is small (∼0.09 M_☉) and 100% star formation rate is unlikely, we suggest that L328-IRS is likely a proto-brown dwarf. Inward motions are found in global scale in the L328 cloud and its sub-cores with a typical infall speed found in starless cores. L328 is found to be fairly well isolated from other nearby clouds and seems to be forming three sub-cores simultaneously through a gravitational fragmentation process. Altogether, these all leave L328-IRS as the best example supporting the idea that a brown dwarf forms like a normal star

[en] We present the results from new Nobeyama Millimeter Array observations of CO(1-0), HCN(1-0), and 89 GHz continuum emission toward NGC 604, known as the supergiant H II region in the nearby galaxy M33. Our high spatial resolution images (4.''2 x 2.''6, corresponding to 17 pc x 11 pc physical size) of CO emission allowed us to uncover 10 individual molecular clouds that have masses of (0.8-7.4) x10⁵ M_sun and sizes of 5-29 pc, comparable to those of typical Galactic giant molecular clouds. Moreover, we detected for the first time HCN emission in the two most massive clouds and 89 GHz continuum emission at the rims of the 'Hα shells'. The HCN and 89 GHz continuum emission are offset from the CO peak and are distributed in the direction of the central cluster. Three out of ten CO clouds are well correlated with the Hα shells both in spatial and velocity domains, implying an interaction between molecular gas and the expanding H II region. The CO clouds show varieties in star formation efficiencies (SFEs), which are estimated from the 89 GHz emission and combination of Hα and Spitzer 24 μm data. Furthermore, we found that the SFEs decrease with increasing projected distance measured from the heart of the central OB star cluster in NGC 604, suggesting radial changes in the evolutionary stages of the molecular clouds in the course of stellar cluster formation. Our results provide further support to the picture of sequential star formation in NGC 604 initially proposed by Tosaki et al. with the higher spatially resolved molecular clouds, in which an isotropic expansion of the H II region pushes gases outward, which accumulates to form dense molecular clouds, and then induces massive star formations.

[en] We present the results of CO (J = 3 - 2) and CO (J = 1 - 0) mapping observations toward the active cluster-forming clump, L1688, in the ρ Ophiuchi molecular cloud. From the CO (J = 3 - 2) and CO (J = 1 - 0) data cubes, we identify five outflows, whose driving sources are VLA 1623, EL 32, LFAM 26, EL 29, and IRS 44. Among the identified outflows, the most luminous outflow is the one from the prototypical Class 0 source, VLA 1623. We also discover that the EL 32 outflow located in the Oph B2 region has very extended blueshifted and redshifted lobes with wide opening angles. This outflow is most massive and has the largest momentum among the identified outflows in the CO (J = 1 - 0) map. We estimate the total energy injection rate due to the molecular outflows identified by the present and previous studies to be about 0.2 L_sun, larger than or at least comparable to the turbulence dissipation rate [∼(0.03 - 0.1)L_sun]. Therefore, we conclude that the protostellar outflows are likely to play a significant role in replenishing the supersonic turbulence in this clump.