The Green Bank Telescope Galactic H Ii Region Discovery Survey

Bania, T. M.; Balser, Dana S.; Rood, Robert T.

doi:10.1088/2041-8205/718/2/l106

Cited by 99 publications

(117 citation statements)

References 37 publications

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“…(1) 8 μmemission is often indicative of UV excitation (Bania et al 2010 show that nearly all GLIMPSE bubbles, 8 μm emission, are associated with UCHII regions), (2) "starry" pixels show warmer dust temperatures, and (3) UCHII regions were found toward two-thirds of the regions surveyed by Wood & Churchwell (1989b) in our field, as shown above. The assumption that 50%-100% of "starry" pixels are associated with UCHII regions ( f UCHII ) corresponds to total DMR lifetimes (t total ) of 2.4 or 1.2 Myr (for 50% or 100%, respectively) when we assume a starry fraction of 30% ( f starry ) as shown in the equation below:…”

Section: Uchii Region Association and Lifetimessupporting

confidence: 62%

The Lifetimes of Phases in High-mass Star-forming Regions

Battersby

Bally

Svoboda

2017

ApJ

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High-mass stars form within star clusters from dense, molecular regions (DMRs), but is the process of cluster formation slow and hydrostatic or quick and dynamic? We link the physical properties of high-mass star-forming regions with their evolutionary stage in a systematic way, using Herschel and Spitzer data. In order to produce a robust estimate of the relative lifetimes of these regions, we compare the fraction of DMRs above a column density associated with high-mass star formation, N(H 2 ) > 0.4-2.5×10 22 cm −2 , in the "starless" (no signature of stars 10  M forming) and star-forming phases in a 2°×2°region of the Galactic Plane centered at ℓ=30°. Of regions capable of forming high-mass stars on ∼1 pc scales, the starless (or embedded beyond detection) phase occupies about 60%-70% of the DMR lifetime, and the star-forming phase occupies about 30%-40%. These relative lifetimes are robust over a wide range of thresholds. We outline a method by which relative lifetimes can be anchored to absolute lifetimes from large-scale surveys of methanol masers and UCHII regions. A simplistic application of this method estimates the absolute lifetime of the starless phase to be 0.2-1.7 Myr (about 0.6-4.1 fiducial cloud free-fall times) and the star-forming phase to be 0.1-0.7 Myr (about 0.4-2.4 free-fall times), but these are highly uncertain. This work uniquely investigates the star-forming nature of high column density gas pixel by pixel, and our results demonstrate that the majority of high column density gas is in a starless or embedded phase.

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Section: Uchii Region Association and Lifetimessupporting

confidence: 62%

The Lifetimes of Phases in High-mass Star-forming Regions

Battersby

Bally

Svoboda

2017

ApJ

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“…D07 determine an average systemic velocity v LSR = 110 km s −1 for Ste 2. The distribution of H ii regions (Bania et al 2010) confirms the low number of tracers associated with the Sagittarius arm, but reflects a more homogeneous distribution in velocities between 40 and 90 km s −1 , with again a high concentration in the v LSR ≈ 90−115 km s −1 range.…”

Section: Radial Velocitiesmentioning

confidence: 54%

Red supergiants around the obscured open cluster Stephenson 2

Negueruela

Marco

González-Fernández

et al. 2012

A&A

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Context. Several clusters of red supergiants have been discovered in a small region of the Milky Way close to the base of the ScutumCrux Arm and the tip of the Long Bar. Population synthesis models indicate that they must be very massive to harbour so many supergiants. Amongst these clusters, Stephenson 2, with a core grouping of 26 red supergiants, is a strong candidate to be the most massive young cluster in the Galaxy. Aims. Stephenson 2 is located close to a region where a strong over-density of red supergiants had been found. We explore the actual cluster size and its possible connection to this over-density. Methods. Taking advantage of Virtual Observatory tools, we have performed a cross-match between the DENIS, USNO-B1 and 2MASS catalogues to identify candidate obscured luminous red stars around Stephenson 2, and in a control nearby region. More than 600 infrared bright stars fulfill our colour criteria, with the vast majority having a counterpart in the I band and >400 being sufficiently bright in I to allow observation with a 4-m class telescope. We observed a subsample of ∼250 stars, using the multi-object, wide-field, fibre spectrograph AF2 on the WHT telescope in La Palma, obtaining intermediate-resolution spectroscopy in the 7500-9000 Å range. We derived spectral types and luminosity classes for all these objects and measured their radial velocities. Results. Our targets turned out to be G and K supergiants, late (≥M4) M giants, and M-type bright giants (luminosity class II) and supergiants. We found ∼35 red supergiants with radial velocities similar to Stephenson 2 members, spread over the two areas surveyed. In addition, we found ∼40 red supergiants with radial velocities incompatible in principle with a physical association. Conclusions. Our results show that Stephenson 2 is not an isolated cluster, but part of a huge structure likely containing hundreds of red supergiants, with radial velocities compatible with the terminal velocity at this Galactic longitude (and a distance ∼6 kpc). In addition, we found evidence of several populations of massive stars at different distances along this line of sight.

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“…The latter are good tracers of massive stars because O-B stars are required to ionise the hydrogen bubbles. For the number density of pulsars at birth as a function of Galactocentric distance, we used the HII region profile recently obtained by Bania et al (2010) from radio observations that can probe HII regions to large distance with little absorption. Figure 2 shows the comparison between the Paczyński (1990) birth distribution used in earlier publications (Gonthier et al 2004;Takata et al 2011) and the HII region profile used here.…”

Section: Birth Location and Velocity In The Galactic Planementioning

confidence: 99%

Constrainingγ-ray pulsar gap models with a simulated pulsar population

Pierbattista

Grenier

Harding

et al. 2012

A&A

111

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With the large sample of young γ-ray pulsars discovered by the Fermi Large Area Telescope (LAT), population synthesis has become a powerful tool for comparing their collective properties with model predictions. We synthesised a pulsar population based on a radio emission model and four γ-ray gap models (Polar Cap, Slot Gap, Outer Gap, and One Pole Caustic). Applying γ-ray and radio visibility criteria, we normalise the simulation to the number of detected radio pulsars by a select group of ten radio surveys. The luminosity and the wide beams from the outer gaps can easily account for the number of Fermi detections in 2 years of observations. The wide slot-gap beam requires an increase by a factor of ∼10 of the predicted luminosity to produce a reasonable number of γ-ray pulsars. Such large increases in the luminosity may be accommodated by implementing offset polar caps. The narrow polar-cap beams contribute at most only a handful of LAT pulsars. Using standard distributions in birth location and pulsar spin-down power (Ė), we skew the initial magnetic field and period distributions in a an attempt to account for the highĖ Fermi pulsars. While we compromise the agreement between simulated and detected distributions of radio pulsars, the simulations fail to reproduce the LAT findings: all models under-predict the number of LAT pulsars with highĖ, and they cannot explain the high probability of detecting both the radio and γ-ray beams at highĖ. The beaming factor remains close to 1.0 over 4 decades inĖ evolution for the slot gap whereas it significantly decreases with increasing age for the outer gaps. The evolution of the enhanced slot-gap luminosity withĖ is compatible with the large dispersion of γ-ray luminosity seen in the LAT data. The stronger evolution predicted for the outer gap, which is linked to the polar cap heating by the return current, is apparently not supported by the LAT data. The LAT sample of γ-ray pulsars therefore provides a fresh perspective on the early evolution of the luminosity and beam width of the γ-ray emission from young pulsars, calling for thin and more luminous gaps.

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The Green Bank Telescope Galactic H Ii Region Discovery Survey

Cited by 99 publications

References 37 publications

The Lifetimes of Phases in High-mass Star-forming Regions

The Lifetimes of Phases in High-mass Star-forming Regions

Red supergiants around the obscured open cluster Stephenson 2

Constrainingγ-ray pulsar gap models with a simulated pulsar population

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