Observations of the nucleus of 67P/Churyumov-Gerasimenko in the millimeter-wave continuum have been obtained by the Microwave Instrument for the Rosetta Orbiter (MIRO). We present data obtained at ...wavelengths of 0.5 mm and 1.6 mm during September 2014 when the nucleus was at heliocentric distances between 3.45 and 3.27 AU. The data are fit to simple models of the nucleus thermal emission in order to characterize the observed behavior and make quantitative estimates of important physical parameters, including thermal inertia and absorption properties at the MIRO wavelengths. MIRO brightness temperatures on the irregular surface of 67P are strongly affected by the local solar illumination conditions, and there is a strong latitudinal dependence of the mean brightness temperature as a result of the seasonal orientation of the comet’s rotation axis with respect to the Sun. The MIRO emission exhibits strong diurnal variations, which indicate that it arises from within the thermally varying layer in the upper centimeters of the surface. The data are quantitatively consistent with very low thermal inertia values, between 10–30 J K-1 m-2 s-1/2, with the 0.5 mm emission arising from 1 cm beneath the surface and the 1.6 mm emission from a depth of 4 cm. Although the data are generally consistent with simple, homogeneous models, it is difficult to match all of its features, suggesting that there may be some vertical structure within the upper few centimeters of the surface. The MIRO brightness temperatures at high northern latitudes are consistent with sublimation of ice playing an important role in setting the temperatures of these regions where, based on observations of gas and dust production, ice is known to be sublimating.
Heat transport and ice sublimation in comets are interrelated processes reflecting properties acquired at the time of formation and during subsequent evolution. The Microwave Instrument on the ...Rosetta Orbiter (MIRO) acquired maps of the subsurface temperature of comet 67P/Churyumov-Gerasimenko, at 1.6 mm and 0.5 mm wavelengths, and spectra of water vapor. The total H2O production rate varied from 0.3 kg s-1 in early June 2014 to 1.2 kg s-1 in late August and showed periodic variations related to nucleus rotation and shape. Water outgassing was localized to the "neck" region of the comet. Subsurface temperatures showed seasonal and diurnal variations, which indicated that the submillimeter radiation originated at depths comparable to the diurnal thermal skin depth. A low thermal inertia (~10 to 50 J K-1 m-2 s-0.5), consistent with a thermally insulating powdered surface, is inferred.
Abstract We present emission maps ( 1 .′ 5 × 1 .′ 5 scale, corresponding to 0.18 pc) of the DCN ( J = 2 − 1) and DCO + ( J = 2 − 1) lines in the 2 mm band toward the Orion KL region obtained with the ...2 mm receiver system named B4R installed on the Large Millimeter Telescope. The DCN emission shows a peak at the Orion KL hot core position, whereas no DCO + emission has been detected there. The DCO + emission shows enhancement at the west side of the hot core, which is well shielded from the UV radiation from OB massive stars in the Trapezium cluster. We have derived the abundance ratio of DCN/DCO + at three representative positions where both species have been detected. The gas components with V LSR ≈ 7.5–8.7 km s −1 are associated with low abundance ratios of ∼4–6, whereas much higher abundance ratios (∼22–30) are derived for the gas components with V LSR ≈ 9.2–11.6 km s −1 . We have compared the observed abundance ratio to our chemical models and found that the observed differences in the DCN/DCO + abundance ratios are explained by different densities.
The landmark black hole images recently taken by the Event Horizon Telescope (EHT) have allowed the detailed study of the immediate surroundings of supermassive black holes (SMBHs) via direct ...imaging. These tantalizing early results motivate an expansion of the array, its instrumental capabilities, and dedicated long-term observations to resolve and track faint dynamical features in the black hole jet and accretion flow. The next-generation Event Horizon Telescope (ngEHT) is a project that plans to double the number of telescopes in the VLBI array and extend observations to dual-frequency 230 + 345 GHz, improving total and snapshot coverage, as well as observational agility. The Large Millimeter Telescope (LMT) is the largest sub-mm single dish telescope in the world at 50 m in diameter, and both its sensitivity and central location within the EHT array make it a key anchor station for the other telescopes. In this work, we detail current and planned future upgrades to the LMT that will directly impact its Very Large Baseline Interferometry (VLBI) performance for the EHT and ngEHT. These include the commissioning of a simultaneous 230 + 345 GHz dual-frequency, dual-polarization heterodyne receiver, improved real-time surface measurement and setting, and improvements to thermal stability, which should enable expanded daytime operation. We test and characterize the performance of an improved LMT joining future ngEHT observations through simulated observations of Sgr A* and M 87.
ABSTRACT
Between 2014 December 31 and 2015 March 17, the OSIRIS cameras on Rosetta documented the growth of a $140\, \mathrm{\hbox{-}m}$ wide and $0.5\, \mathrm{\hbox{-}m}$ deep depression in the ...Hapi region on Comet 67P/Churyumov–Gerasimenko. This shallow pit is one of several that later formed elsewhere on the comet, all in smooth terrain that primarily is the result of airfall of coma particles. We have compiled observations of this region in Hapi by the microwave instrument MIRO on Rosetta, acquired during October and November 2014. We use thermophysical and radiative transfer models in order to reproduce the MIRO observations. This allows us to place constraints on the thermal inertia, diffusivity, chemical composition, stratification, extinction coefficients, and scattering properties of the surface material, and how they evolved during the months prior to pit formation. The results are placed in context through long-term comet nucleus evolution modelling. We propose that (1) MIRO observes signatures that are consistent with a solid-state greenhouse effect in airfall material; (2) CO2 ice is sufficiently close to the surface to have a measurable effect on MIRO antenna temperatures, and likely is responsible for the pit formation in Hapi observed by OSIRIS; (3) the pressure at the CO2 sublimation front is sufficiently strong to expel dust and water ice outwards, and to compress comet material inwards, thereby causing the near-surface compaction observed by CONSERT, SESAME, and groundbased radar, manifested as the ‘consolidated terrain’ texture observed by OSIRIS.
An understanding of the mass build-up in galaxies over time necessitates tracing the evolution of cold gas (molecular and atomic) in galaxies. To that end, we have conducted a pilot study called CO ...Observations with the LMT of the Blind Ultra-Deep H i Environment Survey (COOL BUDHIES). We have observed 23 galaxies in and around the two clusters Abell 2192 (z = 0.188) and Abell 963 (z = 0.206), where 12 are cluster members and 11 are slightly in the foreground or background, using about 28 total hours on the Redshift Search Receiver on the Large Millimeter Telescope (LMT) to measure the 12CO J = 1 → 0 emission line and obtain molecular gas masses. These new observations provide a unique opportunity to probe both the molecular and atomic components of galaxies as a function of environment beyond the local Universe. For our sample of 23 galaxies, nine have reliable detections (S/N ≥ 3.6) of the 12CO line, and another six have marginal detections (2.0 < S/N < 3.6). For the remaining eight targets we can place upper limits on molecular gas masses roughly between 109 and 1010 M⊙. Comparing our results to other studies of molecular gas, we find that our sample is significantly more abundant in molecular gas overall, when compared to the stellar and the atomic gas component, and our median molecular gas fraction lies about 1σ above the upper limits of proposed redshift evolution in earlier studies. We discuss possible reasons for this discrepancy, with the most likely conclusion being target selection and Eddington bias.
ABSTRACT The radio emission from Sgr A is thought to be powered by accretion onto a supermassive black hole of at the Galactic Center. At millimeter wavelengths, Very Long Baseline Interferometry ...(VLBI) observations can directly resolve the bright innermost accretion region of Sgr A . Motivated by the addition of many sensitive long baselines in the north-south direction, we developed a full VLBI capability at the Large Millimeter Telescope Alfonso Serrano (LMT). We successfully detected Sgr A at 3.5 mm with an array consisting of six Very Long Baseline Array telescopes and the LMT. We model the source as an elliptical Gaussian brightness distribution and estimate the scattered size and orientation of the source from closure amplitude and self-calibration analysis, obtaining consistent results between methods and epochs. We then use the known scattering kernel to determine the intrinsic two-dimensional source size at 3.5 mm: , at position angle east of north. Finally, we detect non-zero closure phases on some baseline triangles, but we show that these are consistent with being introduced by refractive scattering in the interstellar medium and do not require intrinsic source asymmetry to explain.
The molecular gas, H sub(2), that fuels star formation in galaxies is difficult to observe directly. As such, the ratio of L sub(IR) to L super(l) sub(CO) is an observational estimate of the star ...formation rate compared with the amount of molecular gas available to form stars, which is related to the star formation efficiency and the inverse of the gas consumption timescale. We test what effect an IR luminous active galactic nucleus (AGN) has on the ratio L sub(IR)/L super(l ) sub(CO) in a sample of 24 intermediate redshift galaxies from the 5 mJy Unbiased Spitzer Extragalactic Survey (5MUSES). We obtain new CO(1-0) observations with the Redshift Search Receiver on the Large Millimeter Telescope. We diagnose the presence and strength of an AGN using Spitzer IRS spectroscopy. We find that removing the AGN contribution to L super(tot) sub(IR) results in a mean L super(SF) sub(IR)/L super(l) sub(CO) for our entire sample consistent with the mean L sub(IR)/L super(l ) sub(CO) derived for a large sample of star forming galaxies from z ~ 0-3. We also include in our comparison the relative amount of polycyclic aromatic hydrocarbon emission for our sample and a literature sample of local and high-redshift ultra luminous infrared galaxies and find a consistent trend between L sub(6.2)/L super(SF) sub(IR) and L super(SF) sub(IR)/L super(l) sub(CO), such that small dust grain emission decreases with increasing L super(SF) sub(IR)/L super(l) sub(CO) for both local and high-redshift dusty galaxies.
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