ON THE IONIZATION OF LUMINOUS<i>WMAP</i>SOURCES IN THE GALAXY: CONSTRAINTS FROM He RECOMBINATION LINE OBSERVATIONS WITH THE GBT

Roshi, D. Anish; Plunkett, Adele; Rosero, Viviana; Vaddi, Sravani

doi:10.1088/0004-637x/749/1/49

Cited by 11 publications

(15 citation statements)

References 44 publications

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“…They find that He I/Hα is significantly reduced only for low escape fractions (∼ 15%). This result is in disagreement with Roshi et al (2012), who observed a N ( 4 He + )/N (H + ) upper limit of only 0.024 in the diffuse gas near the H II region G49, despite an apparent escape fraction of ∼ 63% and N ( 4 He + )/N (H + ) ratios of > 0.066 within the H II region (Churchwell et al 1974;Lichten et al 1979;Thum et al 1980;McGee & Newton 1981;Mehringer 1994;Bell et al 2011). Clearly, a larger sample size is required for further study.…”

Section: Introductioncontrasting

confidence: 75%

Ionization Profiles of Galactic H ii Regions

Luisi

Liu

Roshi

et al. 2019

ApJS

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Using Green Bank Telescope radio recombination line (RRL) data, we analyze the role of leaking radiation from H II regions in maintaining the ionization of the interstellar medium. We observed a sample of eight Galactic H II regions of various sizes, morphologies, and luminosities. For each region the hydrogen RRL intensity decreases roughly as a power-law with distance from the center of the region. This suggests that radiation leaking from the H II region is responsible for the majority of surrounding ionized gas producing RRL emission. Our results further indicate that the hydrogen RRL intensity appears to be fundamentally related to the H II region sizes traced by their photodissociation regions, such that physically smaller H II regions show a steeper decrease in intensity with increasing distance from the region centers. As a result, giant H II regions may have a much larger effect in maintaining the ionization of the interstellar medium. For six of the eight observed H II regions we find a decrease in the 4 He + /H + abundance ratio with increasing distance, indicating that He-ionizing photons are being absorbed within the ionization front of the H II region. There is enhanced carbon RRL emission toward directions with strong continuum background, suggesting that the carbon emission is amplified by stimulated emission.

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Section: Introductioncontrasting

confidence: 75%

Ionization Profiles of Galactic H ii Regions

Luisi

Liu

Roshi

et al. 2019

ApJS

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“…This hypothesis is supported by wide area RRL mapping at ∼15 resolution (Alves et al 2012) which finds that the distribution of the diffuse medium is correlated with HII regions. However, constraints on the ionising spectrum from He RRLs are not fully consistent with this hypothesis (Roshi et al 2012). Thus higher resolution observations of H RRLs and more sensitive observations to detect He RRLs are required.…”

Section: Early Science: the Structure And Kinematics Of The Most Lumimentioning

confidence: 99%

“…Helium lines are typically ∼8 percent of the brightness of Hydrogen RRLs, but are valuable tracers of both the metallicity of the ionised gas (e.g. Balser et al (2001)) and the hardness of the illuminating UV spectrum (Roshi et al 2012). More than 90% of the observed 4 He in the ISM of the Milky Way was produced via primordial nucleosynthesis (Wilson & Rood 1994).…”

Section: Pos(aaska14)126mentioning

confidence: 99%

The ionised,radical and molecular Milky Way: spectroscopic surveys with the SKA

Beuther¹,

Dickinson²,

Mottram³

et al. 2015

Proceedings of Advancing Astrophysics With the Square Kilometre Array — PoS(AASKA14)

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The bandwith, sensitivity and sheer survey speed of the SKA offers unique potential for deep spectroscopic surveys of the Milky Way. Within the frequency bands available to the SKA lie many transitions that trace the ionised, radical and molecular components of the interstellar medium and which will revolutionise our understanding of many physical processes. In this chapter we describe the impact on our understanding of the Milky Way that can be achieved by spectroscopic SKA surveys, including "out of the box" early science with radio recombination lines, Phase 1 surveys of the molecular ISM using anomalous formaldehyde absorption, and full SKA surveys of ammonia inversion lines.Advancing Astrophysics with the Square Kilometre Array

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“…It is therefore suggested that using a completely different observing technique may be the best way to address the problem, at least empirically (see for example Roshi et al, 2012). This is especially true when the problem is now reduced simply to one of determining whether the linewidths in question are stronger and narrower than predicted.…”

Section: Future Workmentioning

confidence: 99%

More on the narrowing of impact broadened radio recombination lines at high principal quantum number

Bell

2012

Astrophys Space Sci

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Recently Alexander and Gulyaev have suggested that the apparent decrease in impact broadening of radio recombination lines seen at high principal quantum number n may be a product of the data reduction process, possibly resulting from the presence of noise on the telescope spectra that is not present on the calculated comparison spectra. This is an interesting proposal. However, there are serious problems with their analysis that need to be pointed out. Perhaps the most important of these is the fact that for principal quantum numbers below n = 200, where the widths are not in question, their processed generated profile widths do not fit the widths of the processed lines obtained at the telescope. After processing, the halfwidths of the generated and telescope profiles must agree below n = 200 if we are to believe that the processed generated linewidths above n = 200 are meaningful. Theirs do not. Furthermore, we find that after applying the linewidth reduction factors found by Alexander and Gulyaev for their noise added profiles to our generated profiles to simulate their noise adding effect, the processed widths we obtain still do not come close to explaining the narrowing seen in the telescope lines for n values in the range 200 < n < 250. It is concluded that what is needed to solve this mystery is a completely new approach using a different observing technique instead of simply a further manipulation of the frequency-switched data.

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ON THE IONIZATION OF LUMINOUSWMAPSOURCES IN THE GALAXY: CONSTRAINTS FROM He RECOMBINATION LINE OBSERVATIONS WITH THE GBT

Cited by 11 publications

References 44 publications

Ionization Profiles of Galactic H ii Regions

Ionization Profiles of Galactic H ii Regions

The ionised,radical and molecular Milky Way: spectroscopic surveys with the SKA

More on the narrowing of impact broadened radio recombination lines at high principal quantum number

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