Elisabeth A. C. Mills

DETECTION OF WIDESPREAD HOT AMMONIA IN THE GALACTIC CENTER

We present the detection of metastable inversion lines of ammonia (NH3) from energy levels high above the ground state. We detect these lines in both emission and absorption toward 15 of 17 positions in the central 300 pc of the Galaxy. In total, we observe seven metastable transitions of NH3: (8, 8), (9, 9), (10, 10), (11, 11), (12, 12), (13, 13) and (15, 15), with energies (in Kelvins) ranging from 680 to 2200 K. We also mapped emission from NH3 (8, 8) and (9, 9) in two clouds in the Sgr A complex (M-0.02–0.07 and M-0.13–0.08), and we find that the line emission is concentrated toward the dense centers of these molecular clouds. The rotational temperatures derived from the metastable lines toward M-0.02–0.07 and M-0.13–0.08 and an additional cloud (M0.25+0.01) range from 350 to 450 K. Similarly highly-excited lines of NH3 have previously been observed toward Sgr B2, where gas with kinetic temperatures of ~600 K had been inferred. Our observations show that the existence of a hot molecular gas component is not unique to Sgr B2, but rather appears common to many Galactic center molecular clouds. In M-0.02–0.07, we find that the hot NH3 contributes ~10% of the clouds total NH3 column density, and further, that the hot NH3 in this cloud arises in gas which is extended or uniformly distributed on 10 arcsec scales. We discuss the implications of these constraints upon the nature of this hot gas component. In addition to the detection of hot metastable NH3 line emission, we also detect for the first time emission from nonmetastable inversion transitions of NH3 in both M-0.02–0.07 and M-0.13–0.08.

HST Paschen-alpha Survey of the Galactic Center: Data Reduction and Products

Our Hubble Space Telescope/Near-Infrared Camera and Multi-Object Spectrometer (HST/NICMOS) Paschen α survey of the Galactic Centre, first introduced by Wang et al., provides a uniform, panoramic, high-resolution map of stars and an ionized diffuse gas in the central 416 arcmin^2 of the Galaxy. This survey was carried out with 144 HST orbits using two narrow-band filters at 1.87 and 1.90 μm in NICMOS Camera 3. In this paper, we describe in detail the data reduction and mosaicking procedures followed, including background level matching and astrometric corrections. We have detected ~570 000 near-infrared (near-IR) sources using the ‘starfinder’ software and are able to quantify photometric uncertainties of the detections. The source detection limit varies across the survey field, but the typical 50 per cent completion limit is ~17th magnitude (Vega system) in the 1.90 μm band. A comparison with the expected stellar magnitude distribution shows that these sources are primarily main-sequence massive stars (≳7 M_⊙) and evolved lower mass stars at the distance of the Galactic Centre. In particular, the observed source magnitude distribution exhibits a prominent peak, which could represent the red clump (RC) stars within the Galactic Centre. The observed magnitude and colour of these RC stars support a steep extinction curve in the near-IR towards the Galactic Centre. The flux ratios of our detected sources in the two bands also allow for an adaptive and statistical estimate of extinction across the field. With the subtraction of the extinction-corrected continuum, we construct a net Paschen α emission map and identify a set of Paschen α emitting sources, which should mostly be evolved massive stars with strong stellar winds. The majority of the identified Paschen α point sources are located within the three known massive Galactic Centre stellar clusters. However, a significant fraction of our Paschen α emitting sources are located outside the clusters and may represent a new class of ‘field’ massive stars, many of which may have formed in isolation and/or in small groups. The maps and source catalogues presented here are available electronically.

ABUNDANT CH3OH MASERS BUT NO NEW EVIDENCE FOR STAR FORMATION IN GCM0.253+0.016

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 the K (24–26 GHz) and Ka (27 and 36 GHz) bands, with velocity resolutions of 1–3 km s−1 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 4−1–30, the latter of which is known to be a collisionally excited maser. We identify 148 CH3OH 4−1–30 (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.

PROPERTIES OF THE COMPACT H II REGION COMPLEX G-0.02-0.07

We present new extinction maps and high-resolution Paschen-alpha images of G-0.02-0.07, a complex of compact H II regions located adjacent to the M-0.02-0.07 giant molecular cloud, 6 pc in projection from the center of the Galaxy. These H II regions, which lie in projection just outside the boundary of the Sgr A East supernova remnant, represent one of the most recent episodes of star formation in the central parsecs of the Galaxy. The 1.87 μm extinctions of regions A, B, and C are almost identical, approximately 3.7 mag. Region D, in contrast, has a peak extinction of A_(1.87) = 5.9 mag. Adopting an extinction law specific to the Galactic center, we find that these extinctions correspond to visual extinctions of A V = 45 and A V = 71. The similar and uniform extinctions of regions A, B, and C are consistent with that expected for foreground extinction in the direction of the Galactic center, suggesting that they lie at the front side of the M-0.02-0.07 molecular cloud. Region D is more compact, has a higher extinction, and is thus suspected to be younger and embedded in a dense core in a compressed ridge on the western edge of this cloud.

High-mass star-forming cloud G0.38+0.04 in the Galactic center dust ridge contains H2CO and SiO masers

We have discovered a new H

The Molecular Gas Environment in the 20 km s−1 Cloud in the Central Molecular Zone

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Thermal Feedback in the High-mass Star- and Cluster-forming Region W51

CO (formaldehyde)

The Survey of Water and Ammonia in the Galactic Center (SWAG) : Molecular Cloud Evolution in the Central Molecular Zone

1_{1,0}-1_{1,1}

The 492 GHz emission of Sgr A* constrained by ALMA

4.82966 GHz maser in Galactic Center Cloud C, G0.38+0.04. At the time of submission, this is the eighth region containing an H

ORIGINS OF SCATTER IN THE RELATIONSHIP BETWEEN HCN 1-0 AND DENSE GAS MASS IN THE GALACTIC CENTER

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