Galactic H II Regions.IV. 1.95-CM Observations with High Angular Resolution and High Positional Accuracy

Schraml, J.; Mezger, P. G.

doi:10.1086/149964

Cited by 186 publications

(89 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For HII regions, we adopt the excitation parameter (Schraml & Mezger 1969) as the weight. The excitation parameter U (in pc cm −2 ) is defined as: Fig.…”

Section: Weights For Tracers Of Galactic Spiral Structurementioning

confidence: 99%

The observed spiral structure of the Milky Way

Hou

Han

2014

A&A

237

233

View full text Add to dashboard Cite

Context. The spiral structure of the Milky Way is not yet well determined. The keys to understanding this structure are to increase the number of reliable spiral tracers and to determine their distances as accurately as possible. HII regions, giant molecular clouds (GMCs), and 6.7 GHz methanol masers are closely related to high mass star formation, and hence they are excellent spiral tracers. The distances for many of them have been determined in the literature with trigonometric, photometric, and/or kinematic methods. Aims. We update the catalogs of Galactic HII regions, GMCs, and 6.7 GHz methanol masers, and then outline the spiral structure of the Milky Way. Methods. We collected data for more than 2500 known HII regions, 1300 GMCs, and 900 6.7 GHz methanol masers. If the photometric or trigonometric distance was not yet available, we determined the kinematic distance using a Galaxy rotation curve with the current IAU standard, R 0 = 8.5 kpc and Θ 0 = 220 km s −1 , and the most recent updated values of R 0 = 8.3 kpc and Θ 0 = 239 km s −1 , after velocities of tracers are modified with the adopted solar motions. With the weight factors based on the excitation parameters of HII regions or the masses of GMCs, we get the distributions of these spiral tracers.Results. The distribution of tracers shows at least four segments of arms in the first Galactic quadrant, and three segments in the fourth quadrant. The Perseus Arm and the Local Arm are also delineated by many bright HII regions. The arm segments traced by massive star forming regions and GMCs are able to match the HI arms in the outer Galaxy. We found that the models of three-arm and four-arm logarithmic spirals are able to connect most spiral tracers. A model of polynomial-logarithmic spirals is also proposed, which not only delineates the tracer distribution, but also matches the observed tangential directions.

show abstract

“…For HII regions, we adopt the excitation parameter (Schraml & Mezger 1969) as the weight. The excitation parameter U (in pc cm −2 ) is defined as: Fig.…”

Section: Weights For Tracers Of Galactic Spiral Structurementioning

confidence: 99%

The observed spiral structure of the Milky Way

Hou

Han

2014

A&A

237

233

View full text Add to dashboard Cite

show abstract

“…Hence, from the flux measured at the optically thin regime of the SED, the number of ionizing photons per second (Ṅ i ) needed in order to keep ionized the region detected in radio continuum can be estimated using the following relation (Schraml & Mezger 1969): Table 1) in Eq. 1 and T e = 9000 K, we obtainṄ i = 8.37 × 10 45 s −1 (D/10.4 kpc) 2 .…”

Section: Radio Continuum Flux: Radio Jet or Hii Region?mentioning

confidence: 99%

Deep into the Water Fountains

Pérez-Sánchez

Tafoya

López

et al. 2017

A&A

View full text Add to dashboard Cite

Context. The formation of large-scale (hundreds to few thousands of AU) bipolar structures in the circumstellar envelopes (CSEs) of post-Asymptotic Giant Branch (post-AGB) stars is poorly understood. The shape of these structures, traced by emission from fast molecular outflows, suggests that the dynamics at the innermost regions of these CSEs does not depend only on the energy of the radiation field of the central star. Aims. Multi-frequency observations towards a group of post-AGB sources known as Water Fountain nebulae can help to constrain the nature of the mechanism responsible for the launching and collimation of the fast molecular outlflows traced by high-velocity features of H 2 O maser emission. Methods. Deep into the Water Fountains is an observational project based on the results of programs carried out with three telescope facilities: The Karl G. Jansky Very Large Array (JVLA), The Australia Telescope Compact Array (ATCA), and the Very Large Telescope (SINFONI-VLT). Results. Here we report the results of the observations towards the WF nebula IRAS 18043−2116: Detection of radio continuum emission in the frequency range 1.5 GHz -8.0 GHz; H 2 O maser spectral features and radio continuum emission detected at 22 GHz, and H 2 ro-vibrational emission lines detected at the near infrared. Conclusions. The high-velocity H 2 O maser spectral features, and the shock-excited H 2 emission detected could be produced in molecular layers which are swept up as a consequence of the propagation of a jet-driven wind. Using the derived H 2 column density, we estimated a molecular mass-loss rate of the order of 10 −9 M yr −1 . On the other hand, if the radio continuum flux detected is generated as a consequence of the propagation of a thermal radio jet, the mass-loss rate associated to the outflowing ionized material is of the order of 10 −5 M yr −1 . The presence of a rotating disk could be a plausible explanation for the mass-loss rates estimated.

show abstract

“…Radio studies have concentrated on "" compact ÏÏ H II regions, which are relatively young and have high surface brightness. Schraml & Mezger (1969) observed 18 free-free emission complexes at j \ 2 cm with 2@ resolution (typically corresponding to 0.5È5 pc), and we make use of their sample for our discussion. Their results are summarized in Table 3 for M43, M42 (Orion Nebula), IC 1795 (W3), W51, and W49 (ordered with increasing luminosity).…”

Section: Comparison With Galactic H II Regionsmentioning

confidence: 99%

“…These di †erences have several likely explanations : the Galactic regions were selected for high surface brightness free-free emission (i.e., compact a Excitation parameters from Schraml & Mezger 1969 have been summed (U \ R s n e 2@3) for all H II region components, except in the case of W51, for which we took only the strongest component, since this direction is along a spiral arm tangent, and there is likely to be confusion.…”

Section: Comparison With Galactic H II Regionsmentioning

confidence: 99%

High-Mass, OB Star Formation in M51: [ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Hα and P[CLC]a[/CLC]α Imaging

Scoville

Polletta

Ewald

et al. 2001

The Astronomical Journal

209

233

View full text Add to dashboard Cite

We have obtained Ha and Paa emission-line images covering the central 3@È4@ of M51 using the WFPC2 and NICMOS instruments on the Hubble Space T elescope to study the high-mass stellar population. The pixels provide 4.6È9 pc resolution in M51, and the Ha/Paa line ratios are used to 0A .1È0A .2 obtain extinction estimates. A sample of 1373 Ha emission regions is cataloged using an automated and uniform measurement algorithm. Their sizes are typically 10È100 pc. The luminosity function for the Ha emission regions is obtained over the range to 2 ] 1039 ergs s~1. The luminosity function is L Ha \ 1036 Ðtted well by a power law with dN/d ln L P L~1.01. The power law is signiÐcantly truncated, and no regions were found with observed above 2 ] 1039 ergs s~1 (uncorrected for extinction). (The L Ha maximum seen in ground-based studies is approximately a factor of 5 higher, very likely because of the blending of multiple regions.) The extinctions derived here increase the maximum intrinsic luminosity to above 1040 ergs s~1. The logarithmically binned luminosity function is also somewhat steeper (a \ [1.01) than that found from ground-based imaging (a \ [0.5 to [0.8)Èprobably also a result of our resolving regions that were blended in the ground-based images. The two-point correlation function for the H II regions exhibits strong clustering on scales ¹2A, or 96 pc.To analyze the variations of H II region properties the galactic structure, the spiral arm areas vis-a`-vis were deÐned independently from millimeter-CO and optical continuum imaging. Although the arms constitute only 25% of the disk surface area, the arms contain 45% of the cataloged H II regions. The luminosity function is somewhat Ñatter in spiral arm regions than in the interarm areas ([0.72 to [0.95) ; however, this is very likely the result of increased blending of individual H II regions in the arms that have higher surface density. No signiÐcant di †erence is seen in the sizes and electron densities of the H II regions in spiral arm and interarm regions. For 209 regions that had º5 p detections in both Paa and Ha, the observed line ratios indicate visual extinctions in the range mag. The mean extinction A V \ 0È6 was mag (weighting each region equally), 2.4 mag (weighting each by the observed Ha A V \ 3.1 luminosity), and 3.0 mag (weighting by the extinction-corrected luminosity). On average, the observed Ha luminosities should be increased by a factor of D10, implying comparable increases in global OB star cluster luminosities and star formation rates. The full range of extinction-corrected Ha luminosities is between 1037 and 2 ] 1040 ergs s~1.The most luminous regions have sizes º100 pc, so it is very likely that they are blends of multiple regions. This is clear based on their sizes, which are much larger than the maximum diameter (¹50 pc) to which an H II region might conceivably expand within the D3 ] 106 yr lifetime of the OB stars. It is also consistent with the observed correlation (L P D2) between the measured luminosities and sizes of th...

show abstract

Galactic H II Regions.IV. 1.95-CM Observations with High Angular Resolution and High Positional Accuracy

Cited by 186 publications

References 0 publications

The observed spiral structure of the Milky Way

The observed spiral structure of the Milky Way

Deep into the Water Fountains

High-Mass, OB Star Formation in M51: [ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Hα and P[CLC]a[/CLC]α Imaging

Contact Info

Product

Resources

About