Abstract We present NH 3 and H64α+H63α VLA observations of the Radio Arc region, including the M0.20 – 0.033 and G0.10 – 0.08 molecular clouds. These observations suggest the two velocity components of M0.20 – 0.033 are physically connected in the south. Additional ATCA observations suggest this connection is due to an expanding shell in the molecular gas, with the centroid located near the Quintuplet cluster. The G0.10 – 0.08 molecular cloud has little radio continuum, strong molecular emission, and abundant CH 3 OH masers, similar to a nearby molecular cloud with no star formation: M0.25+0.01. These features detected in G0.10 – 0.08 suggest dense molecular gas with no signs of current star formation.
Over the course of the cryogenic mission of the Spitzer Space Telescope, the responsivity of the Red Peak-Up sub-array on the Infrared Spectograph (IRS) varied by ~2%, based on an analysis of five standard stars. The sensitivity dropped 1.7% after the first 14 IRS campaigns, then climbed back up 1.0% later in the mission. The uncertainty in these measurements is better than ~0.3%. The random variations in the Peak-Up photometry of the standard stars has a gaussian distribution of width ~2%, similar to the magnitude of the systematic temporal variations.
This report describes in detail the generation of a "truth" spectrum of HR 6348, using observations with the Short-Low (SL) module of the Infrared Spectrograph of HR 6348, and the A dwarfs alpha Lac and delta UMi. Using spectral ratios, we can propagate Kurucz models of the A dwarfs to the K giant HR 6348, which can then serve to calibrate the remaining database of SL spectra. Mitigation in the vicinity of the Pfund-a line is necessary to reduce residual artifacts at 7.45 um. In general, the new SL spectrum of HR 6348 has a spectroscopic fidelity of ~0.5% or better. Artifacts from the hydrogen recombination lines in the A dwarfs will generally be smaller than this limit, although the residual artifact from the blend of lines near Pfund-alpha exceeds the limit at ~0.7%.
We investigate how the shape of a spectrum in the Short-Low module on the IRS varies with its overall throughput, which depends on how well centered a source is in the spectroscopic slit. Using flux ratios to quantify the overall slope or color of the spectrum and plotting them vs. the overall throughput reveals a double-valued function, which arises from asymmetries in the point spread function. We use this plot as a means of determining which individual spectra are valid for calibrating the IRS.
We present new observations of the quiescent giant molecular cloud GCM0.253+0.016 in the Galactic center, using the upgraded Karl G. Jansky Very Large Array. Observations were made at wavelengths near 1 cm, at K (24 to 26 GHz) and Ka (27 and 36 GHz) bands, with velocity resolutions of 1-3 km/s and spatial resolutions of ~0.1 pc, at the assumed 8.4 kpc distance of this cloud. The continuum observations of this cloud are the most sensitive yet made, and reveal previously undetected emission which we attribute primarily to free-free emission from external ionization of the cloud. In addition to the sensitive continuum map, we produce maps of 12 molecular lines: 8 transitions of NH3 -- (1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7) and (9,9), as well as the HC3N (3-2) and (4-3) lines, and CH3OH 4(-1) - 3(0) the latter of which is known to be a collisionally-excited maser. We identify 148 CH3OH 4(-1) - 3(0) (36.2 GHz) sources, of which 68 have brightness temperatures in excess of the highest temperature measured for this cloud (400 K) and can be confirmed to be masers. The majority of these masers are concentrated in the southernmost part of the cloud. We find that neither these masers nor the continuum emission in this cloud provide strong evidence for ongoing star formation in excess of that previously inferred by the presence of an H2O maser.
We present evidence of 6.7 GHz methanol (CH3OH) and 4.8 GHz formaldehyde (H2CO) absorption toward the Galactic Center (GC) point source "N3." Both absorption features are unresolved and spatially aligned with N3. The 6.7 GHz CH3OH contains a single-velocity component (centered at ∼10 km s−1), while the 4.8 GHz H2CO shows two-velocity components (centered at ∼−3 and +8 km s−1). We find that the velocities of these absorption components are similar to that of emission lines from other molecules (e.g., SiO and HC3N) detected toward this compact source (−13 to +25 km s−1; "N3 cloud"). The detection of these absorption features is a firm indication that some of the molecular gas in the N3 molecular cloud is on the near side of the continuum source. Analysis of the CH3OH absorption kinematics shows a relatively large velocity dispersion (3.8 km s−1) for the size scale of this feature (<01, <0.01 pc at the GC), when compared with other similarly sized GC clouds in the Larson line width–size relationship. Furthermore, this line width is closer to velocity dispersion measurements for size scales of 1.3 pc, which is roughly the width of the N3 cloud (25''; 1.0 pc). We argue that this relatively broad line width, over a small cross-sectional area, is due to turbulence through the depth of the cloud, where the cloud has a presumed line-of-sight thickness of ∼1 pc.
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