The Green Bank Telescope H Ii Region Discovery Survey. Ii. The Source Catalog

Anderson, L. D.; Bania, T. M.; Balser, Dana S.; Rood, Robert T.

doi:10.1088/0067-0049/194/2/32

Cited by 210 publications

(333 citation statements)

References 88 publications

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“…All the known optical and radio H ii regions are labelled. With the exception of G351.61+0.17, all H ii regions have velocities (Anderson et al 2011) in agreement with the mean velocity of the NGC 6334 complex, −4 km s −1 ) and are thus associated with the complex. On the upper left-hand side of the image, a 10 pc scale bar, as well as the equatorial and the Galactic cardinal directions, is indicated.…”

Section: Observationssupporting

confidence: 70%

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TheHerschelview of the massive star-forming region NGC 6334

Russeil

Schneider

Anderson

et al. 2013

A&A

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Aims. Fundamental to any theory of high-mass star formation are gravity and turbulence. Their relative importance, which probably changes during cloud evolution, is not known. By investigating the spatial and density structure of the high-mass star-forming complex NGC 6334 we aim to disentangle the contributions of turbulence and gravity. Methods. We used Herschel PACS and SPIRE imaging observations from the HOBYS key programme at wavelengths of 160, 250, 350, and 500 μm to construct dust temperature and column density maps. Using probability distribution functions (PDFs) of the column density determined for the whole complex and for four distinct sub-regions (distinguished on the basis of differences in the column density, temperature, and radiation field), we characterize the density structure of the complex. We investigate the spatial structure using the Δ-variance, which probes the relative amount of structure on different size scales and traces possible energy injection mechanisms into the molecular cloud. Results. The Δ-variance analysis suggests that the significant scales of a few parsec that were found are caused by energy injection due to expanding H ii regions, which are numerous, and by the lengths of filaments seen everywhere in the complex. The column density PDFs have a lognormal shape at low densities and a clearly defined power law at high densities for all sub-regions whose slope is linked to the exponent α of an equivalent spherical density distribution. In particular with α = 2.37, the central sub-region is largly dominated by gravity, caused by individual collapsing dense cores and global collapse of a larger region. The collapse is faster than free-fall (which would lead only to α = 2) and thus requires a more dynamic scenario (external compression, flows). The column density PDFs suggest that the different sub-regions are at different evolutionary stages, especially the central sub-region, which seems to be in a more evolved stage.

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Section: Observationssupporting

confidence: 70%

“…In Fig. 1, we label H ii regions in the field from Anderson et al (2011), Caswell & Haynes (1987), and Gum (1955. These images illustrate the complexity of NGC 6334, in particular the relative distribution of the warm and cold dust.…”

Section: Observationsmentioning

confidence: 99%

TheHerschelview of the massive star-forming region NGC 6334

Russeil

Schneider

Anderson

et al. 2013

A&A

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“…Although we cannot firmly establish whether the 100 and 50 km s −1 gas components are spatially associated or just chance alignments, the close projected association of them as well as the extremely busy and active nature of that part of the Galaxy at the interface of the Galactic bar with the inner spiral arm, where streaming motions between both components are likely to occur, makes spatial association and interaction of different cloud components here a fair possibility. See also Anderson et al (2011) for a similar discussion of the origin of the ionized gas.…”

Section: Colliding Clouds or Chance Alignment?mentioning

confidence: 99%

“…5, and a scale-bar for a distance of 5.5 kpc is shown as well. The crosses in the bottom-left panel mark the positions of a double-component radio recombination line Hii region from Anderson et al (2011), the W43-MM1 position from Motte et al (2003) as well as the approximate center of the Wolf-Rayet/OB cluster (Blum et al 1999;Motte et al 2003). to search for and to study these initial conditions. Early work from the first data revealed already exciting results, e.g., we identified candidate high-mass starless cores (HMSCs) as well as weak 70 μm sources within IRDCs that may be the very first manifestation of high-mass star formation Henning et al 2010;Linz et al 2010).…”

Section: Introductionmentioning

confidence: 99%

The onset of high-mass star formation in the direct vicinity of the Galactic mini-starburst W43

Beuther

Tackenberg

Linz

et al. 2012

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Context. The earliest stages of high-mass star formation are still poorly characterized. Densities, temperatures and kinematics are crucial parameters for simulations of high-mass star formation. It is also unknown whether the initial conditions vary with environment. Aims. We want to investigate the youngest massive gas clumps in the environment of extremely active star formation. Methods. We selected the IRDC 18454 complex, directly associated with the W43 Galactic mini-starburst, and observed it in the continuum emission between 70 μm and 1.2 mm with Herschel, APEX and the 30 m telescope, and in spectral line emission of N 2 H + and 13 CO with the Nobeyama 45 m, the IRAM 30 m and the Plateau de Bute Interferometer. Results. The multi-wavelength continuum study allows us to identify clumps that are infrared dark even at 70 μm and hence the best candidates to be genuine high-mass starless gas clumps. The spectral energy distributions reveal elevated temperatures and luminosities compared to more quiescent environments. Furthermore, we identify a temperature gradient from the W43 mini-starburst toward the starless clumps. We discuss whether the radiation impact of the nearby mini-starburst changes the fragmentation properties of the gas clumps and by that maybe favors more high-mass star formation in such an environment. The spectral line data reveal two different velocity components of the gas at 100 and 50 km s −1 . While chance projection is a possibility to explain these components, the projected associations of the emission sources as well as the prominent location at the Galactic bar -spiral arm interface also allow the possibility that these two components may be spatially associated and even interacting. Conclusions. High-mass starless gas clumps can exist in the close environment of very active star formation without being destroyed. The impact of the active star formation sites may even allow for more high-mass stars to form in these 2nd generation gas clumps. This particular region near the Galactic bar -spiral arm interface has a broad distribution of gas velocities, and cloud interactions may be possible.

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“…Sgr E is a region of active star formation associated with a CO molecular cloud with V lsr ∼ −210 km s −1 (Oka et al 1998). The radio recombination line survey, H ii Region Discovery Survey (HRDS: Anderson et al 2011Anderson et al , 2012 detected eight of these H ii sources towards Sgr E at V lsr ∼ −208 km s −1 , the same velocity as the CO cloud. Along the line of sight outside the CMZ there are giant magnetic loops, large scale molecular gas loop-like features, with large line widths and large scale flows detected in CO (Fukui et al 2006;Fujishita et al 2009).…”

Section: Observations Of [C Ii] and [N Ii]mentioning

confidence: 99%

Ionized gas at the edge of the central molecular zone

Langer

Goldsmith

Pineda

et al. 2015

A&A

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Context. The edge of the central molecular zone (CMZ) is the location where massive dense molecular clouds with large internal velocity dispersions transition to the surrounding more quiescent and lower CO emissivity region of the Galaxy. Little is known about the ionized gas surrounding the molecular clouds and in the transition region. Aims. We determine the properties of the ionized gas at the edge of the CMZ near Sgr E using observations of N + and C + .Methods. We observed a small portion of the edge of the CMZ near Sgr E with spectrally resolved [C ii] 158 μm and [N ii] 205 μm fine structure lines at six positions with the GREAT instrument on SOFIA and in [C ii] using Herschel HIFI on-the-fly strip maps. We use the [N ii] spectra along with a radiative transfer model to calculate the electron density of the gas and the [C ii] maps to illuminate the morphology of the ionized gas and model the column density of CO-dark H 2 .Results. We detect two [C ii] and [N ii] velocity components, one along the line of sight to a CO molecular cloud at −207 km s −1 associated with Sgr E and the other at −174 km s −1 outside the edge of another CO cloud. From the [N ii] emission we find that the average electron density is in the range of ∼5 to 21 cm −3 for these features. This electron density is much higher than that of the disk's warm ionized medium, but is consistent with densities determined for bright diffuse H ii nebula. The column density of the CO-dark H 2 layer in the −207 km s −1 cloud is ∼1−2× 10 21 cm −2 in agreement with theoretical models. The CMZ extends further out in Galactic radius by ∼7 to 14 pc in ionized gas than it does in molecular gas traced by CO. Conclusions. The edge of the CMZ likely contains dense hot ionized gas surrounding the neutral molecular material. The high fractional abundance of N + and high electron density require an intense EUV field with a photon flux of order 10 6 to 10 7 photons cm −2 s −1 , and/or efficient proton charge exchange with nitrogen, at temperatures of order 10 4 K, and/or a large flux of X-rays. Sgr E is a region of massive star formation as indicated by the presence of numerous compact H ii regions. The massive stars are potential sources of the EUV radiation that ionizes and heat the gas. In addition, X-ray sources and the diffuse X-ray emission in the CMZ are candidates for ionizing nitrogen.

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The Green Bank Telescope H Ii Region Discovery Survey. Ii. The Source Catalog

Cited by 210 publications

References 88 publications

TheHerschelview of the massive star-forming region NGC 6334

TheHerschelview of the massive star-forming region NGC 6334

The onset of high-mass star formation in the direct vicinity of the Galactic mini-starburst W43

Ionized gas at the edge of the central molecular zone

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