Atacama Submillimeter Telescope Experiment Research Articles

Optical measurements of the silicon vacuum window with anti-reflective sub-wavelength structure for ASTE Band 10.

For millimeter and submillimeter-wave astronomy, it is highly desirable to have vacuum windows within the receiver cryostat that exhibit low reflection, low loss, and a wide bandpass. The use of antireflective (AR) sub-wavelength structures (SWSs) on substrates has expanded the possibilities for creating new vacuum windows. Recently, a novel method of fabricating AR SWS on a silicon-on-insulator wafer has been proposed, and a vacuum window with a two-layer AR SWS has been developed for use with the Atacama Submillimeter Telescope Experiment Band 10 receiver. To thoroughly assess the characteristics of the silicon window sample, we conducted transmittance measurements using terahertz time-domain spectroscopy, and noise and beam measurements using an Atacama Large Millimeter/submillimeter Array (ALMA) Band 10 receiver. We found that the silicon window sample exhibits characteristics comparable to the quartz window of the ALMA Band 10 receiver. The result strongly encourages applications of AR silicon windows in receivers with wider bandwidths.

Molecular clouds at the eastern edge of radio nebula W 50

Abstract Microquasar SS 433 located at the geometric center of radio nebula W 50 is a suitable source for investigating the physical process of how galactic jets affect the surrounding interstellar medium (ISM). Previous studies have searched for evidence of the interaction between the SS 433 jet and ISM, such as neutral hydrogen gas and molecular clouds; however, it is still unclear which ISM interacts with the jet. We looked for new molecular clouds that possibly interact at the terminal of the SS 433 eastern jet using the Nobeyama 45 m telescope and the Atacama Submillimeter Telescope Experiment (ASTE). We identified two molecular clouds, comprising many small clumps, in the velocity range of 30.1–36.5 km s−1 for the first time. These clouds have complex velocity structures, and one of them has a density gradient toward SS 433. Although it is difficult to conclude the relation between the molecular clouds and the SS 433/W 50 system, there is a possibility that the eastern structure of W 50 constructed by the SS 433 jet swept up tiny molecular clumps drifting in the surroundings and formed the molecular clouds that we identified in this study.

ASTE Band 10 (787–950 GHz) heterodyne receiver: System description, commissioning, and science verification

Abstract We report the system description and results of the commissioning and science verification (CSV) of the Band 10 (787–950 GHz) heterodyne receiver for ASTE (Atacama Submillimeter Telescope Experiment), a 10 m submillimeter telescope at the ALMA (Atacama Large Millimeter/submillimeter Array) site in Chile. The new ASTE Band 10 receiver cartridge was refurbished from a prototype ALMA Band 10 receiver with SIS mixers employing high critical current density junctions. We installed the new receiver on ASTE and carried out its CSV. The best double-sideband (DSB) system noise temperature achieved on ASTE toward the zenith was ∼1500 K (PWV ∼ 0.5 mm). As a part of CSV activities, we performed science verification observations to demonstrate ASTE Band 10 capabilities to the community. Wide-field images were successfully obtained toward the well-studied OMC-1 region with both [C i](3P2–3P1) and 12CO(J = 7–6) lines. In addition, we partially carried out observations toward a super star cluster RCW 38, [C i](3P1–3P0), images of which were already obtained by ASTE. We demonstrated the capability of ASTE Band 10 observations toward bright and extended objects like giant molecular clouds.

Associated Molecular and Atomic Clouds with X-Ray Shell of Superbubble 30 Doradus C in the LMC

Abstract 30 Doradus C is a superbubble that emits the brightest non-thermal X- and TeV gamma-rays in the Local Group. To explore the detailed connection between the high-energy radiation and the interstellar medium, we have carried out new CO and Hi observations using the Atacama Large Millimeter/Submillimeter Array (ALMA), Atacama Submillimeter Telescope Experiment, and the Australia Telescope Compact Array with resolutions of up to 3 pc. The ALMA data of 12CO(J = 1–0) emission revealed 23 molecular clouds, with typical diameters of ∼6–12 pc and masses of ∼600–10,000 M ⊙. A comparison with the X-rays of XMM–Newton at ∼3 pc resolution shows that X-rays are enhanced toward these clouds. The CO data were combined with the Hi to estimate the total interstellar protons. A comparison of the interstellar proton column density and the X-rays revealed that the X-rays are enhanced with the total proton column density. These are most likely to be caused by the shock-cloud interaction, which is modeled by magnetohydrodynamical simulations (Inoue et al. 2012). We also note a trend for the X-ray photon index to vary with distance from the center of the high-mass star cluster. This suggests that the cosmic-ray electrons are accelerated by one or multiple supernovae in the cluster. Based on these results, we discuss the role of the interstellar medium in cosmic-ray particle acceleration.

Atomic carbon [C i](3P1–3P0) mapping of the nearby galaxy M 83

Abstract Atomic carbon (C i) has been proposed to be a global tracer of the molecular gas as a substitute for CO, however, its utility remains unproven. To evaluate the suitability of C i as the tracer, we performed [C i](3P1–3P0) [hereinafter [C i](1–0)] mapping observations of the northern part of the nearby spiral galaxy M 83 with the Atacama Submillimeter Telescope Experiment (ASTE) telescope and compared the distributions of [C i](1–0) with CO lines [CO(1–0), CO(3–2), and 13CO(1–0)], H i, and infrared (IR) emission (70, 160, and 250 μm). The [C i](1–0) distribution in the central region is similar to that of the CO lines, whereas [C i](1–0) in the arm region is distributed outside the CO. We examined the dust temperature, Tdust, and dust mass surface density, Σdust, by fitting the IR continuum-spectrum distribution with a single-temperature modified blackbody. The distribution of Σdust shows a much better consistency with the integrated intensity of CO(1–0) than with that of [C i](1–0), indicating that CO(1–0) is a good tracer of the cold molecular gas. The spatial distribution of the [C i] excitation temperature, Tex, was examined using the intensity ratio of the two [C i] transitions. An appropriate Tex at the central, bar, arm, and inter-arm regions yields a constant [C]$/$[H2] abundance ratio of ∼7 × 10−5 within a range of 0.1 dex in all regions. We successfully detected weak [C i](1–0) emission, even in the inter-arm region, in addition to the central, arm, and bar regions, using spectral stacking analysis. The stacked intensity of [C i](1–0) is found to be strongly correlated with Tdust. Our results indicate that the atomic carbon is a photodissociation product of CO, and consequently, compared to CO(1–0), [C i](1–0) is less reliable in tracing the bulk of “cold” molecular gas in the galactic disk.

ALMA CO Observations of Gamma-Ray Supernova Remnant N132D in the Large Magellanic Cloud: Possible Evidence for Shocked Molecular Clouds Illuminated by Cosmic-Ray Protons

Abstract N132D is the brightest gamma-ray supernova remnant (SNR) in the Large Magellanic Cloud (LMC). We carried out 12CO(J = 1–0, 3–2) observations toward the SNR using the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Submillimeter Telescope Experiment. We find diffuse CO emission not only at the southern edge of the SNR as previously known, but also inside the X-ray shell. We spatially resolved nine molecular clouds using ALMA with an angular resolution of 5″, corresponding to a spatial resolution of ∼1 pc at the distance of the LMC. Typical cloud sizes and masses are ∼2.0 pc and ∼100 M ⊙, respectively. High intensity ratios of CO J = 3–2/1–0 > 1.5 are seen toward the molecular clouds, indicating that shock heating has occurred. Spatially resolved X-ray spectroscopy reveals that thermal X-rays in the center of N132D are produced not only behind a molecular cloud but also in front of it. Considering the absence of a thermal component associated with the forward shock toward one molecular cloud located along the line of sight to the center of the remnant, this suggests that this particular cloud is engulfed by shock waves and is positioned on the near side of the remnant. If the hadronic process is the dominant contributor to the gamma-ray emission, the shock-engulfed clouds play a role as targets for cosmic rays. We estimate the total energy of cosmic-ray protons accelerated in N132D to be ∼0.5–3.8 × 1049 erg as a conservative lower limit, which is similar to that observed in Galactic gamma-ray SNRs.

Studying star-forming processes at core and clump scales: the case of the young stellar object G29.862−0.0044

Aims. To advance our knowledge of star formation, in addition to statistical studies and large surveys of young stellar objects (YSOs), it is important to carry out detailed studies towards particular objects. Given that massive molecular clumps fragment into cores where star formation takes place, these kinds of studies should be done on different spatial scales. The aim of this work is to investigate the star-forming processes at core and clump scales. Methods. Using near-infrared (NIR) data obtained with NIRI at the Gemini-North telescope, data of the complex molecular species CH3OCHO and CH3CN obtained from the Atacama Large Millimeter Array (ALMA) database, observations of HCN, HNC, HCO+, and C2H carried out with the Atacama Submillimeter Telescope Experiment (ASTE), and CO data from public surveys observed with the James Clerck Maxwell Telescope (JCMT), we perform a deep study of the YSO G29.862−0.0044 (YSO-G29) at core and clump spatial scales. Results. The NIR emission shows that YSO-G29 is composed of two nebulosities separated by a dark lane, suggesting a scenario consistent with a typical disc plus jets system, albeit in this case highly asymmetric. The northern nebulosity is open, diffuse, and is divided into two branches, while the southern one is smaller and sharper. They are likely produced by the scattered light in cavities carved out by jets or winds on an infalling envelope of material, which also presents line emission of H2 S(1) 1–0 and 2–1, and [FeII]. The presence of the complex molecular species observed with ALMA confirms that we are mapping a hot molecular core. The CH3CN emission concentrates at the position of the dark lane and appears slightly elongated from southwest to northeast in agreement with the inclination of the system as observed in the NIR. The morphology of the CH3OCHO emission is more complex and extends along some filaments and concentrates in knots and clumps, mainly southwards of the dark lane, suggesting that the southern jet is encountering a dense region. The northern jet is able to flow more freely, generating the more extended features as seen in the NIR. This is in agreement with the redshifted molecular outflow traced by the 12CO J = 3–2 line extending towards the northwest and the lack of a blueshifted outflow. This configuration can be explained by considering that G29-YSO is located at the furthest edge of the molecular clump along the line of sight, which is consistent with the position of the source in the cloud mapped in the C18O J = 3–2 line. The detection of HCN, HNC, HCO+, and C2H allowed us to characterise the dense gas at clump scales, yielding results that are in agreement with the presence of a high-mass protostellar object.

The ISM local to the runaway star WR16

ABSTRACT Massive stars leave their imprint on the interstellar medium as they radiate their energy and undergo episodes of mass ejection throughout their lives. In this paper, we analyse the case of the Wolf–Rayet star WR16 combining archival multiwavelength data with new molecular observations obtained with the Atacama Submillimeter Telescope Experiment (ASTE). Our results suggest that during the main-sequence phase, WR16 swept up the surrounding gas creating a molecular structure (which we call Component 1) which also contains very cold dust observed in the infrared band. In a subsequent stage of evolution, as an LBV, the star underwent mass eruptions that were later overrun by the fast winds of the current WR phase. The final result is the round nebula revealed by the optical and IR images, and the molecular clumps detected. We have also computed the peculiar velocity of WR16 using Gaia data and, accordingly, confirm it as a runaway star. We propose that several features observed in different wavelengths can be explained under a bow-shock scenario linked to the high velocity of WR16.

Atacama sub-millimeter telescope experiment polarimeter (APol) I: design and lab-test result.

In this paper, the Atacama Submillimeter Telescope Experiment (ASTE) is presented. A 10-m aperture telescope hosts a camera equipped with a transition edge sensor (TES). We developed a fore-optics module-"APol," to convert the 271 pixels of the TES working at 350 GHz into a sensitive imaging polarimeter without sacrificing the image quality and the ${7.5}^\prime$7.5' field of view. Here, we describe the detailed optical design of APol and present the results of the preliminary test in a laboratory.

Kinematic study of the molecular gas associated with two cometary globules in Sh2−236

Aims. Cometary globules, dense molecular gas structures exposed to UV radiation, are found inside H II regions. Understanding the nature and origin of these structures through a kinematic study of the molecular gas could be useful to advance in our knowledge of the interplay between radiation and molecular gas. Methods. Using the Atacama Submillimeter Telescope Experiment (Chile), we carried out molecular observations toward two cometary globules (Sim129 and Sim130) in the H II region Sh2−236. We mapped two regions of about 1′ × 1′ with the 12CO J = 3−2 and HCO+ J = 4−3 lines. Additionally, we carried out two single pointings with the C2H N = 4–3, HNC, and HCN J = 4−3 transitions. The angular resolution was about 22′′. We combined our molecular observations with public infrared and optical data to analyze the distribution and kinematics of the molecular gas. Results. We find kinematic signatures of infalling gas in the 12CO J = 3−2 and C2H N = 4−3 spectra toward Sim 129. We detect HCO+, HCN, and HNC J = 4−3 only toward Sim 130. The HCN/HNC integrated ratio of about three found in Sim 130 suggests that the possible star-formation activity inside this globule has not yet ionized the gas. The location of the NVSS source 052255+33315, which peaks toward the brightest border of the globule, supports this scenario. The non-detection of these molecules toward Sim 129 could be due to the radiation field arising from the star-formation activity inside this globule. The ubiquitous presence of the C2H molecule toward Sim 129 and Sim 130 evidences the action of the nearby O-B stars irradiating the external layer of both globules. Based on the mid-infrared 5.8 μm emission, we identify two new structures: (1) a region of diffuse emission (R1) located, in projection, in front of the head of Sim 129 and (2) a pillar-like feature (P1) placed besides Sim 130. Based on the 12CO J = 3−2 transition, we find molecular gas associated with Sim 129, Sim 130, R1, and P1 at radial velocities of −1.5, −11, +10, and +4 km s−1, respectively. Therefore, while Sim 129 and P1 are located at the far side of the shell, Sim 130 is placed at the near side, consistent with earlier results. Finally, the molecular gas related to R1 exhibits a radial velocity that differs in more than 11 km s−1 with the radial velocity of S129, which suggests that while S129 is located at the far side of the expanding shell, R1 would be placed well beyond.

Discovery of Shocked Molecular Clouds Associated with the Shell-type Supernova Remnant RX J0046.5−7308 in the Small Magellanic Cloud

RX J0046.5$-$7308 is a shell-type supernova remnant (SNR) in the Small Magellanic Cloud (SMC). We carried out new $^{12}$CO($J$ = 1-0, 3-2) observations toward the SNR using Mopra and the Atacama Submillimeter Telescope Experiment. We found eight molecular clouds (A-H) along the X-ray shell of the SNR. The typical cloud size and mass are $\sim$10-15 pc and $\sim$1000-3000 $M_{\odot}$, respectively. The X-ray shell is slightly deformed and has the brightest peak in the southwestern shell where two molecular clouds A and B are located. The four molecular clouds A, B, F, and G have high intensity ratios of $^{12}$CO($J$ = 3-2) / $^{12}$CO($J$ = 1-0) $> 1.2$, which are not attributable to any identified internal infrared sources or high-mass stars. The HI cavity and its expanding motion are found toward the SNR, which are likely created by strong stellar winds from a massive progenitor. We suggest that the molecular clouds A-D, F, and G and HI clouds within the wind-blown cavity at $V_\mathrm{LSR} = 117.1$-122.5 km s$^{-1}$ are to be associated with the SNR. The X-ray spectroscopy reveals the dynamical age of $26000^{+1000}_{-2000}$ yr and the progenitor mass of $\gtrsim 30$ $M_{\odot}$, which is also consistent with the proposed scenario. We determine physical conditions of the giant molecular cloud LIRS 36A using the large velocity gradient analysis with archival datasets of the Atacama Large Millimeter/submillimeter Array; the kinematic temperature is $72^{+50}_{-37}$ K and the number density of molecular hydrogen is $1500^{+600}_{-300}$ cm$^{-3}$. The next generation of $\gamma$-ray observations will allow us to study the pion-decay $\gamma$-rays from the molecular clouds in the SMC SNR.

12CO and 13CO J = 3–2 observations toward N11 in the Large Magellanic Cloud

Aims. After 30 Doradus, N11 is the second largest and brightest nebula in the Large Magellanic Cloud (LMC). This large nebula has several OB associations with bright nebulae at its surroundings. N11 was previously mapped at the lowest rotational transitions of 12CO (J = 1–0 and 2–1), and in some particular regions, pointings of the 13CO J = 1–0 and 2–1 lines were also performed. Observations of higher CO rotational transitions are needed to map gas with higher critical densities, which are useful to study the physical conditions of the gas component and its relation with the UV radiation more accurately. Methods. Using the Atacama Submillimeter Telescope Experiment, we mapped the whole extension of the N11 nebula in the 12CO J = 3–2 line and three subregions in the 13CO J = 3–2 line. The regions mapped in the 13CO J = 3–2 were selected with the criterion that they were to be exposed to the radiation in different ways: a region lying across the nebula, which is related to the OB association LH10 (N11B), another region that it is associated with the southern part of the nebula, which is related to the OB association LH13 (N11D), and finally an area farther away in the southwest without any embedded OB association (N11I). Results. We found that the morphology of the molecular clouds lying in each region shows some signatures that could be explained by the expansion of the nebulae and the action of the radiation. Fragmentation generated in a molecular shell due to the expansion of the N11 nebula is suggested. The integrated line ratios 12CO/13CO show evidence of selective photodissociation of the 13CO, and probably other mechanisms such as chemical fractionation. The values found for the integrated line ratios 12CO J = 3–2/1–0 are in agreement with values that were assumed in previous works, and the CO contribution to the continuum at 870 μm was derived directly. The distribution of the integrated line ratios 12CO J = 3–2/2–1 show indications of stellar feedback in N11B and N11D. The ratio between the virial and local thermal equilibrium (LTE) mass (Mvir/MLTE) is higher than unity in all analyzed molecular clumps, which suggests that the clumps are not gravitationally bounded and may be supported by external pressure. A non-LTE analysis suggests that we map gas with densities of about a few 103 cm−3. The molecular clump at N11B, the unique molecular feature with direct evidence of ongoing star formation, is the densest of the clumps we analyzed.

ALMA CO Observations of Supernova Remnant N63A in the Large Magellanic Cloud: Discovery of Dense Molecular Clouds Embedded within Shock-ionized and Photoionized Nebulae

Abstract We carried out new 12CO(J = 1–0, 3–2) observations of a N63A supernova remnant (SNR) from the LMC using the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Submillimeter Telescope Experiment. We find three giant molecular clouds toward the northeast, east, and near the center of the SNR. Using the ALMA data, we spatially resolved clumpy molecular clouds embedded within the optical nebulae in both the shock-ionized and photoionized lobes discovered by previous Hα and [S ii] observations. The total mass of the molecular clouds is ∼800 M ☉ for the shock-ionized region and ∼1700 M ☉ for the photoionized region. Spatially resolved X-ray spectroscopy reveals that the absorbing column densities toward the molecular clouds are ∼(1.5–6.0) × 1021 cm−2, which are ∼1.5–15 times less than the averaged interstellar proton column densities for each region. This means that the X-rays are produced not only behind the molecular clouds, but also in front of them. We conclude that the dense molecular clouds have been completely engulfed by the shock waves, but have still survived erosion owing to their high density and short interacting time. The X-ray spectrum toward the gas clumps is well explained by an absorbed power-law model or a high-temperature plasma model, in addition to thermal plasma components, implying that the shock-cloud interaction is efficiently working for both cases through the shock ionization and magnetic field amplification. If the hadronic gamma-ray is dominant in the GeV band, the total energy of the cosmic-ray protons is calculated to be ∼(0.3–1.4) × 1049 erg, with an estimated interstellar proton density of ∼190 ± 90 cm−3, containing both the shock-ionized gas and neutral atomic hydrogen.

HCN J = 4–3, HNC J = 1–0, H13CN J = 1–0, and HC3N J = 10–9 Maps of the Galactic Center Region. I. Spatially Resolved Measurements of Physical Conditions and Chemical Composition

Abstract This supplement paper presents the maps of HCN J = 4–3, HNC J = 1–0, J = 1–0, and HC3N J = 10–9 for the Galactic central molecular zone (CMZ), which have been obtained using the Atacama Submillimeter Telescope Experiment and Nobeyama Radio Observatory 45 m telescope. Three-dimensional maps (2D in space and 1D in velocity) of the gas kinetic temperature (T kin), hydrogen volume density ( ), and fractional abundances of eight molecules (HCN, HNC, , HCO+, , SiO, CS, and ) have been constructed from our and archival data. We have developed a method with hierarchical Bayesian inference for this analysis, which has successfully suppressed the artificial correlations among the parameters created by systematic errors due to the deficiency in the simple one-zone excitation analysis and the calibration uncertainty. The typical values of T kin and are and , respectively, and the presence of an additional cold, low-density component is also indicated. The distribution of high-temperature regions is poorly correlated with known active star-forming regions, while a few of them coincide with shocked clouds. Principal component analysis has identified two distinct groups in the eight analyzed molecules: one group with large PC1 and PC2 scores, and the other with a large T kin dependence, which could be explained using two regimes of shock chemistry with fast ( ) and slow ( ) velocity shocks, respectively. This supports the idea that the mechanical sputtering of dust grains and the mechanical heating play primary roles in the chemical and thermal processes in CMZ clouds.

The molecular environment of the pillar-like features in the H ii region G46.5–0.2

At the interface of HII regions and molecular gas peculiar structures appear, some of them with pillar-like shapes. Understanding their origin is important for characterizing triggered star formation and the impact of massive stars on the interstellar medium. In order to study the molecular environment and the influence of the radiation on two pillar-like features related to the HII region G46.5-0.2, we performed molecular line observations with the Atacama Submillimeter Telescope Experiment, and spectroscopic optical observations with the Isaac Newton Telescope. From the optical observations we identified the star that is exciting the HII region as a spectral type O4-6. The molecular data allowed us to study the structure of the pillars and a HCO+ cloud lying between them. In this HCO+ cloud, which have not any well defined 12CO counterpart, we found direct evidence of star formation: two molecular outflows and two associated near-IR nebulosities. The outflows axis orientation is perpendicular to the direction of the radiation flow from the HII region. Several Class I sources are also embedded in this HCO+ cloud, showing that it is usual that the YSOs form large associations occupying a cavity bounded by pillars. On the other hand, it was confirmed that the RDI process is not occurring in one of the pillar tips.

A Massive Molecular Outflow in the Dense Dust Core AGAL G337.916-00.477

Abstract Massive molecular outflows erupting from high-mass young stellar objects (YSOs) provide important clues to understanding the mechanism of high-mass star formation. Based on new CO J = 3–2 and J = 1–0 observations using the Atacama Submillimeter Telescope Experiment (ASTE) and Mopra telescope facilities, we discovered a massive bipolar outflow associated with the dense dust core AGAL G337.916-00.477 (AGAL337.9-S), located 3.48 kpc from the Sun. The outflow lobes have extensions of less than 1 pc—and thus were not fully resolved in the angular resolutions of ASTE and Mopra—and masses of ∼50 M ⊙. The maximum velocities of the outflow lobes are as high as 36–40 . Our analysis of the infrared and submillimeter data indicates that AGAL337.9-S is in an early evolutionary stage of high-mass star formation, having the total far-infrared luminosity of . We also found that another dust core, AGAL G337.922-00.456 (AGAL337.9-N), located 2′ north of AGAL337.9-S, is a high-mass YSO in an earlier evolutionary stage than AGAL337.9-S, as it is less bright in the mid-infrared than AGAL337.9-S.

Detection of Submillimeter-wave [C i] Emission in Gaseous Debris Disks of 49 Ceti and β Pictoris

Abstract We have detected [C i] 3 P 1–3 P 0 emissions in the gaseous debris disks of 49 Ceti and β Pictoris with the 10 m telescope of the Atacama Submillimeter Telescope Experiment, which is the first detection of such emissions. The line profiles of [C i] are found to resemble those of CO(J = 3–2) observed with the same telescope and the Atacama Large Millimeter/submillimeter Array. This result suggests that atomic carbon (C) coexists with CO in the debris disks and is likely formed by the photodissociation of CO. Assuming an optically thin [C i] emission with the excitation temperature ranging from 30 to 100 K, the column density of C is evaluated to be (2.2 ± 0.2) × 1017 and (2.5 ± 0.7) × 1016 cm−2 for 49 Ceti and β Pictoris, respectively. The C/CO column density ratio is thus derived to be 54 ± 19 and 69 ± 42 for 49 Ceti and β Pictoris, respectively. These ratios are higher than those of molecular clouds and diffuse clouds by an order of magnitude. The unusually high ratios of C to CO are likely attributed to a lack of H2 molecules needed to reproduce CO molecules efficiently from C. This result implies a small number of H2 molecules in the gas disk, i.e., there is an appreciable contribution of secondary gas from dust grains.

Detection of submillimeter-wave [C I]emission in gaseous debris disks of 49 Ceti and β Pictoris

AbstractWe have detected [C I] 3P1–3P0 emissions in the gaseous debris disks of 49 Ceti and β Pictoris with the 10 m telescope of the Atacama Submillimeter Telescope Experiment, which is the first detection of such emissions. The line profiles of [C I] are found to resemble those of CO(J=3–2) observed with the same telescope and the Atacama Large Millimeter/submillimeter Array. This result suggests that atomic carbon (C) coexists with CO in the debris disks, and is likely formed by the photodissociation of CO. Assuming an optically thin [C I] emission with the excitation temperature ranging from 30 to 100 K, the column density of C is evaluated to be (2.2 ± 0.2) × 1017 and (2.5 ± 0.7) × 1016 cm−2 for 49 Ceti and β Pictoris, respectively. The C/CO column density ratio is thus derived to be 54 ± 19 and 69 ± 42 for 49 Ceti and β Pictoris, respectively. These ratios are higher than those of molecular clouds and diffuse clouds by an order of magnitude. The unusually high ratios of C to CO are likely attributed to a lack of H2 molecules needed to reproduce CO molecules efficiently from C. This result implies a small number of H2 molecules in the gas disk; i.e., there is an appreciable contribution of secondary gas from dust grains.

ALMA Deep Field in SSA22: Source Catalog and Number Counts

Abstract We present results from a deep 2′ × 3′ (comoving scale of 3.7 Mpc × 5.5 Mpc at z = 3) survey at 1.1 mm, taken with the Atacama Large Millimeter/submillimeter Array (ALMA) in the SSA22 field. We observe the core region of a z = 3.09 protocluster, achieving a typical rms sensitivity of 60 μJy beam−1 at a spatial resolution of 0.″7. We detect 18 robust ALMA sources at a signal-to-noise ratio (S/N) > 5. Comparison between the ALMA map and a 1.1 mm map, taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment (ASTE), indicates that three submillimeter sources discovered by the AzTEC/ASTE survey are resolved into eight individual submillimeter galaxies (SMGs) by ALMA. At least 10 of our 18 ALMA SMGs have spectroscopic redshifts of z ≃ 3.09, placing them in the protocluster. This shows that a number of dusty starburst galaxies are forming simultaneously in the core of the protocluster. The nine brightest ALMA SMGs with S/N > 10 have a median intrinsic angular size of ( physical kpc at z = 3.09), which is consistent with previous size measurements of SMGs in other fields. As expected, the source counts show a possible excess compared to the counts in the general fields at S 1.1mm ≥ 1.0 mJy, due to the protocluster. Our contiguous mm mapping highlights the importance of large-scale structures on the formation of dusty starburst galaxies.

KINEMATICS OF ULTRA-HIGH-VELOCITY GAS IN THE EXPANDING MOLECULAR SHELL ADJACENT TO THE W44 SUPERNOVA REMNANT

ABSTRACT We mapped the ultra-high-velocity feature (the “Bullet”) detected in the expanding molecular shell associated with the W44 supernova remnant using the Nobeyama Radio Observatory 45 m telescope and the Atacama Submillimeter Telescope Experiment 10 m telescope. The Bullet clearly appears in the CO J = 1–0, CO J = 3–2, CO J = 4–3, and HCO+ J = 1–0 maps with a compact appearance (0.5 × 0.8 pc2) and an extremely broad-velocity width (ΔV ≃ 100 km s−1). The line intensities indicate that the Bullet has a higher density and temperature than those in the expanding molecular shell. The kinetic energy of the Bullet amounts to 1048.0 erg, which is approximately 1.5 orders of magnitude greater than the kinetic energy shared to the small solid angle of it. Two possible formation scenarios with an inactive isolated black hole are presented.