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-H sub(2)O lines at 321 GHz (10 sub(2,9)-9 sub(3,6)) and 336 GHz (v sub(2) = 1, 5 sub(2,3)-6 sub(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 H sub(2)O line can be reconciled with a model of an edge-on ring-like structure with an enclosed mass of >7 M sub(middot in circle) 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.
We have developed a spectral line On-The-Fly (OTF) observing mode for the Nobeyama Radio Observatory 45-m and the Atacama Submillimeter Telescope Experiment 10-m telescopes. Sets of digital ...autocorrelation spectrometers are available for OTF with heterodyne receivers mounted on the telescopes, including the focal-plane 5
$\times$
5 array receiver, BEARS, on the 45-m. During OTF observations, the antenna is continuously driven to cover the mapped region rapidly, resulting in a high observing efficiency and accuracy. Pointing of the antenna and readouts from the spectrometer are recorded as fast as 0.1s. In this paper we report on improvements made to the software and instruments, requirements and optimization of observing parameters, the data-reduction process, and verification of the system. It is confirmed that, using optimal parameters, the OTF is about twice as efficient as the conventional position-switch observing method.
We have developed an FX-architecture digital spectro-correlator for the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array. The correlator is able to simultaneously process ...four pairs of dual polarization signals with a bandwidth of 2 GHz, which are received by up to sixteen antennas. It can calculate auto- and cross-correlation spectra, including cross-polarization in all combinations of all the antennas, and output correlation spectra with flexible spectral configuration, such as multiple frequency ranges and multiple frequency resolutions. Its spectral dynamic range is estimated to be higher than 10
$^{4}$
relative to
$T_{\rm sys}$
from processing results of thermal noise for eight hours with a typical correlator configuration. The sensitivity loss is also confirmed to be 0.9% with the same configuration. In this paper, we report on the detailed design of the correlator and the verification results of the developed hardware.
Abstract
The 22 GHz H2O maser in Orion KL has shown extraordinary burst events in 1979–1985 and 1998–1999, sometimes called supermaser. We have conducted monitoring observations of the supermaser in ...Orion KL using VERA (VLBI Exploration of Radio Astrometry) in the current third burst since 2011 March. Three flux maxima are detected in 2011 and 2012 with rising and falling timescales of 2–7 months. Time variations of the supermaser seem symmetric for all of the active phases. The maximum total flux density of 135000 Jy is observed in 2012 June while it is still one order of magnitude lower than those in previous bursts. The supermaser consists of two spatially different components at different velocities. They are elongated along a northwest–southeast direction perpendicular to the low-velocity outflow driven by Source I. Proper motions of the supermaser features with respect to Source I are measured toward west and southwest directions, almost parallel to the low-velocity outflow. The flux density and linewidth show an anti-correlation as expected for an unsaturated maser emission. The supermaser is located close to the methylformate (HCOOCH3) line and continuum emission peaks in the Orion Compact Ridge detected by ALMA (Atacama Large Millimeter/Submillimeter Array). The broader velocity range of the weak HCOOCH3 emission at the supermaser position would be evidence of a shock front. On the other hand, the 321 GHz H2O line is not detected at the position of the supermaser. It can be explained qualitatively by one of the theoretical H2O excitation models without extraordinary conditions. Our results support a scenario that the supermaser is excited in the dense gas interacting with the low-velocity outflow in the Compact Ridge. The extremely high flux density and its symmetric time variation for rising and falling phases could be explained by a beaming effect during the amplification process rather than changes in physical conditions.
We present maps of seven young massive molecular clumps within five target regions in C super(18)O (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 C super(18)O clumps with radii of 0.5-1.7 pc, masses of 470-4200 M sub(middot in circle), and velocity widths of 1.4-3.3 km s super(-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 n regions (CWHRs), while the other two are unassociated with H II regions (CWOHRs). The C super(18)O 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 C super(18)O clumps. The fraction of Class I candidates among all YSO candidates (Class I+Class II) is > or =, slanted50% in CWHRs and < or =, slant50% 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 Hu regions tends to trigger coeval cluster formation.
We have investigated a technique of combining single-dish data and interferometer data in the spatial frequency domain, using imaging simulations and analytical considerations. Our study shows that ...there is an optimum of the relative weights between the visibility data of a single-dish and an interferometer. The quality of the reconstructed combined image achieves the highest values at relative weights where the mean of the difference between the synthesized beam and the CLEAN beam is close to zero. We also examined the (
$u$
,
$v$
)-range that can be effectively used for the data combining by considering a blurring effect due to a pointing error. The error in single-dish deconvolution caused by the beam approximation is small with a large diameter of the single-dish aperture. The diameter should be at least 1.7-times larger than the minimum baseline of the interferometer for an amplitude accuracy better than 10%. Furthermore, we derived an estimate of the noise variance in the combined image, which agrees with our simulation results. The noise-added simulations demonstrate that there is a threshold of the noise level of the single-dish image, beyond which a large-scale error is emphasized in the combined image. We should take observation times to make at least the same noise level at the border of the spatial frequency between the single-dish and the interferometer. Although our examinations were assumed to use the 45 m telescope and NMA, our results concerning the required conditions for observations and data processes can be used in a general case of heterogeneous array imaging.
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 sub(IR) ~ 30-300 M sub(middot in circle) yr super(-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 sub(IR) lap 30 M sub(middot in circle) yr super(-1)). We conduct counts-in-cells analysis with multifield ALMA data for the faint SMGs, and obtain a coarse estimate of galaxy bias, b sub(g) < 4. The galaxy bias suggests that the dark halo masses of the faint SMGs are lap7 x 10 super(12) M sub(middot in circle) 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 gap 6.
ABSTRACT 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.
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