We have used the Submillimeter Array to image a flux-limited sample of seven submillimeter galaxies, selected by the AzTEC camera on the JCMT at 1.1 mm, in the COSMOS field at 890 mu m with similar ...to 2" resolution. All of the sources-two radio-bright and five radio-dim-are detected as single point sources at high significance (>6 sigma ), with positions accurate to similar to 0.2" that enable counterpart identification at other wavelengths observed with similarly high angular resolution. All seven have IRAC counterparts, but only two have secure counterparts in deep HST ACS imaging. As compared to the two radio-bright sources in the sample, and those in previous studies, the five radio-dim sources in the sample (1) have systematically higher submillimeter-to-radio flux ratios, (2) have lower IRAC 3.6-8.0 mu m fluxes, and (3) are not detected at 24 mu m. These properties, combined with size constraints at 890 mu m ( theta unk 1.2"), suggest that the radio-dim submillimeter galaxies represent a population of very dusty starbursts, with physical scales similar to local ultraluminous infrared galaxies, with an average redshift higher than radio-bright sources.
The blazar 1156+295 was active at ...-ray energies, exhibiting three prominent flares during the year 2010. Here, we present results using the combination of broad-band (X-ray through mm single-dish) ...monitoring data and radio-band imaging data at 43 GHz on the connection of ...-ray events to the ejections of superluminal components and other changes in the jet of 1156+295. The kinematics of the jet over the interval 2007.0-2012.5 using 43 GHz Very Long Baseline Array observations reveal the presence of four moving and one stationary component in the inner region of the blazar jet. The propagation of the third and fourth components in the jet corresponds closely in time to the active phase of the source in ...-rays. We briefly discuss the implications of the structural changes in the jet for the mechanism of ...-ray production during bright flares. To localize the ...-ray emission site in the blazar, we performed the correlation analysis between the 43. GHz radio core and the ...-ray light curve. The time lag obtained from the correlation constrains the ...-ray emitting region in the parsec-scale jet. (ProQuest: ... denotes formulae/symbols omitted.)
We present thermal observations of Ganymede from the Atacama Large Millimeter Array (ALMA) in 2016-2019 at a spatial resolution of 300-900 km (0 1-0 2 angular resolution) and frequencies of 97.5, ...233, and 343.5 GHz (wavelengths of 3, 1.3, and 0.87 mm); the observations collectively covered all Ganymede longitudes. We determine the global thermophysical properties using a thermal model that considers subsurface emission and depth- and temperature-dependent thermophysical and dielectric properties, in combination with a retrieval algorithm. The data are sensitive to emission from the upper ∼0.5 m of the surface, and we find a millimeter emissivity of 0.75-0.78 and (sub)surface porosities of 10%-40%, corresponding to effective thermal inertias of 400-800 J m−2 K−1 s−1/2. Combined with past infrared results, as well as modeling presented here of a previously unpublished night-time infrared observation from Galileo's photopolarimeter-radiometer instrument, the multiwavelength constraints are consistent with a compaction profile whereby the porosity drops from ∼85% at the surface to at depth over a compaction length scale of tens of centimeters. We present maps of temperature residuals from the best-fit global models, which indicate localized variations in thermal surface properties at some (but not all) dark terrains and at impact craters, which appear 5-8 K colder than the model. Equatorial regions are warmer than predicted by the model, in particular near the centers of the leading and trailing hemispheres, while the midlatitudes (∼30°-60°) are generally colder than predicted; these trends are suggestive of an exogenic origin.
► This paper explores the capabilities of the Atacama Large Millimeter Array applied to the observation of Centaurs and Trans-Neptunian Objects. ► More than 500 objects can be thermally detected in ...bands 6 or 7, allowing determination of sizes and albedo through the radiometric method. ► Using extended configurations to spatially resolve the targets, model-independent size and ellipticity measurements could be obtained on 30 large bodies. ► The first thermal maps of the 6 largest Centaurs and TNOs could be obtained with a spatial resolution down to ∼14 mas.
Once completed, the Atacama Large Millimeter Array (ALMA) will be the most powerful (sub)millimeter interferometer in terms of sensitivity, spatial resolution and imaging. This paper presents the capabilities of ALMA applied to the observation of Centaurs and Trans-Neptunian Objects, and their possible output in terms of physical properties. Realistic simulations were performed to explore the performances of the different frequency bands and array configurations, and several projects are detailed along with their feasibility, their limitations and their possible targets. Determination of diameters and albedos via the radiometric method appears to be possible on ∼500 objects, while sampling of the thermal lightcurve to derive the bodies’ ellipticity could be performed at least 30 bodies that display a significant optical lightcurve. On a limited number of objects, the spatial resolution allows for direct measurement of the size or even surface mapping with a resolution down to 13
milliarcsec. Finally, ALMA could separate members of multiple systems with a separation power comparable to that of the HST. The overall performance of ALMA will make it an invaluable instrument to explore the outer Solar System, complementary to space-based telescopes and spacecrafts.
We present high-resolution 345-GHz interferometric observations of two extremely luminous (Lir≳ 1013 L⊙), submillimetre-selected galaxies (SMGs) in the Cosmic Evolution Survey (COSMOS) field with the ...Submillimeter Array (SMA). Both targets were previously detected as unresolved point sources by the SMA in its compact configuration, also at 345 GHz. These new data, which provide a factor of ≳3 improvement in resolution, allow us to measure the physical scale of the far-infrared in the submillimetre directly. The visibility functions of both targets show significant evidence for structure on ∼0.5–1-arcsec scales, which at z≳ 1.5 translates into a physical scale of ∼5–8 kpc. Our results are consistent with the angular and physical scales of two comparably luminous objects with high-resolution SMA follow-up, as well as radio continuum and CO sizes of other SMGs. These relatively compact sizes (≲5–10 kpc) argue strongly for merger-driven starbursts, rather than extended gas-rich discs, as the preferred channel for forming SMGs.
Abstract
We present a thermal observation of Callisto's leading hemisphere obtained using the Atacama Large Millimeter/submillimeter Array at 0.87 mm (343 GHz). The angular resolution achieved for ...this observation was ∼0.″16, which for Callisto at the time of this observation (
D
∼ 1.″05) was equivalent to ∼six elements across the surface. Our disk-integrated brightness temperature of 116 ± 5 K (8.03 ± 0.40 Jy) is consistent with prior disk-integrated observations. Global surface properties were derived from the observation using a thermophysical model constrained by spacecraft data. We find that models parameterized by two thermal inertia components more accurately fit the data than single thermal inertia models. Our best-fit global parameters adopt a lower thermal inertia of 15–50 J m
−2
K
−1
s
−1/2
and a higher thermal inertia component of 1200–2000 J m
−2
K
−1
s
−1/2
, with retrieved millimeter emissivities of 0.89–0.91. We identify several thermally anomalous regions, including spots ∼3 K colder than model predictions colocated with the Valhalla impact basin and a complex of craters in the southern hemisphere; this indicates the presence of materials possessing either a higher thermal inertia or a lower emissivity. A warm region confined to the midlatitudes in these leading hemisphere data may be indicative of regolith property changes due to exogenic sculpting.
We present the first detections of the ground-state H
2
16O (
1
10
–
1
01
) rotational transition (at 556.9 GHz) and the
13CO (5–4) rotational transition from the atmosphere of Venus, measured with ...the Submillimeter Wave Astronomy Satellite (SWAS). The observed spectral features of these submillimeter transitions originate primarily from the 70–100 km altitude range, within the Venus mesosphere. Observations were obtained in December 2002, and January, March, and July 2004, coarsely sampling one Venus diurnal period as seen from Earth. The measured water vapor absorption line depth shows large variability among the four observing periods, with strong detections of the line in December 2002 and July 2004, and no detections in January and March 2004. Retrieval of atmospheric parameters was performed using a multi-transition inversion algorithm, combining simultaneous retrievals of temperature, carbon monoxide, and water profiles under imposed constraints. Analysis of the SWAS spectra resulted in measurements or upper limits for the globally averaged mesospheric water vapor abundance for each of the four observation periods, finding variability over at least two orders of magnitude. The results are consistent with both temporal and diurnal variability, but with short-term fluctuations clearly dominating. These results are fully consistent with the long-term study of mesospheric water vapor from millimeter and submillimeter observations of HDO Sandor, B.J., Clancy, R.T., 2005. Icarus 177, 129–143. The December 2002 observations detected very rapid change in the mesospheric water abundance. Over five days, a deep water absorption feature consistent with a water vapor abundance of
4.5
±
1.5
parts per million suddenly gave way to a significantly shallower absorption, implying a decrease in the water vapor abundance by a factor of nearly 50 in less that 48 h. In 2004, similar changes in the water vapor abundance were measured between the March and July SWAS observing periods, but variability on time scales of less than a week was not detected. The mesospheric water vapor is expected to be in equilibrium with aerosol particles, primarily composed of concentrated sulfuric acid, in the upper haze layers of the Venus atmosphere. If true, moderate amplitude (10–15 K) variability in mesospheric temperature, previously noted in millimeter spectroscopy observations of Venus, can explain the rapid water vapor variability detected by SWAS.
Titan’s atmospheric composition and dynamical state have previously been studied over numerous epochs by both ground- and space-based facilities. However, stratospheric measurements remain sparse ...during Titan’s northern summer and fall. The lack of seasonal symmetry in observations of Titan’s temperature field and chemical abundances raises questions about the nature of the middle atmosphere’s meridional circulation and evolution over Titan’s 29 yr seasonal cycle that can only be answered through long-term monitoring campaigns. Here, we present maps of Titan’s stratospheric temperature, acetonitrile (or methyl cyanide; CH _3 CN) abundance, and monodeuterated methane (CH _3 D) abundance following Titan’s northern summer solstice obtained with Band 9 (∼0.43 mm) Atacama Large Millimeter/submillimeter Array observations. We find that increasing temperatures toward high southern latitudes, currently in winter, resemble those observed during Titan’s northern winter by the Cassini mission. Acetonitrile abundances have changed significantly since previous (sub)millimeter observations, and we find that the species is now highly concentrated at high southern latitudes. The stratospheric CH _3 D content is found to range between 4 and 8 ppm in these observations, and we infer the CH _4 abundance to vary between ∼0.9% and 1.6% through conversion with previously measured D/H values. A global value of CH _4 = 1.15% was retrieved, lending further evidence to the temporal and spatial variability of Titan’s stratospheric methane when compared with previous measurements. Additional observations are required to determine the cause and magnitude of stratospheric enhancements in methane during these poorly understood seasons on Titan.
Abstract
The nearby Seyfert type galaxy NGC 1275 contains a bright radio nucleus at its center, revealed through high-spatial resolution imaging to be the source of the jets emanating from the ...galaxy. Coincident with the emergence of a new component C3 in the nucleus since 2005, flux densities from NGC 1275, at least at radio, millimeter, and
γ
-ray frequencies, had been increasing up through 2017 and leveled off afterwards. We analyze the long-term light curves of the nucleus that span the rising trend to 2015 July, and find a pair of approximately year-long quasi-periodic oscillations, with periods of
P
l
≃ 345 days and
P
h
≃ 386 days, respectively, in emission at 1.3 mm wavelength. We discuss the case that there would be a long precession period,
P
prec
≃ 9 yr, causing the appearance of
P
h
that is slightly higher than
P
l
. The accretion disk around the central supermassive black hole (SMBH) would be precessing at
P
prec
, induced by either the Lense–Thirring effect or the existence of a companion SMBH. In the two scenarios,
P
l
would be the jet wobbling timescale or the SMBH binary period, respectively. The finding, which could be verified through high-spatial resolution millimeter imaging, would not only identify the nature of the jet variation but also help reveal the full features of the galaxy.
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