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Cited by 27Astrophysics and Cosmic PhenomenaAstrophysical Phenomena and ObservationsAstrophysics and Star Formation Studies

Possible connection between the asymmetry of the North Polar Spur and Loop I and Fermi bubbles

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Sarkar, Kartick C·2019·Monthly Notices of the Royal Astronomical Society
DOI 10.1093/mnras/sty2944
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Abstract

The origins of the North Polar Spur (NPS) and Loop I have been debated for almost half a century, and are still unresolved. Most of the confusion is caused by the absence of any prominent counterparts of these structures in the Southern Galactic hemisphere (SGH). This has also led to doubts over the claimed connection between the NPS and Fermi bubbles (FBs). In this paper, I show that such asymmetries of the NPS and Loop I in both X-rays and γ-rays can be easily produced if the density of the circumgalactic medium in the SGH is only ≈20 per cent smaller than its northern counterpart for a star-formation-driven wind scenario. The required mechanical luminosity, |$\mathcal {L} \approx 4\!-\!5\times 10^{40}$| erg s−1 (which reduces to ≈0.3 M⊙ yr−1 when including non-thermal pressure), and the age of the FBs, tage ≈ 28 Myr, are consistent with previous estimations for a star-formation-driven wind scenario. One of the main reasons for the asymmetry is the projection effects at the solar location. Such a proposition is also consistent with the fact that the southern FB is ≈5° bigger than the northern FB. Therefore, the results indicate a possible common origin of the NPS, Loop I and FBs from the Galactic Centre. I also estimate the average sky brightness in X-rays towards the South Galactic Pole and North Galactic Pole in the ROSAT-R67 band, and I find that the error in average brightness is far too large to provide any estimation of the deficiency in the SGH.

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  • The model shows that only a 20% lower density in the southern hemisphere compared to the northern one could make the southern X-ray bubble significantly faint, owing to the projection effects at the Solar vantage point and a density^2 effect on the emissivity.

    “The model shows that only a 20% lower density in the southern hemisphere compared to the northern one could make the southern X-ray bubble significantly faint, owing to the projection effects at the Solar vantage point and a density 2 effect on the emissivity.”

    From The Fermi/eROSITA bubbles: a look into the nuclear outflow from the Milky Way (2024) · cites this paper as Sarkar 2019

  • A possible sign of such an asymmetry could also explain the relatively larger (3°-5°) southern Fermi Bubble.

    “A possible sign of such an asymmetry could also explain the relatively larger (3 ◦ -5 ◦ ) southern Fermi Bubble.”

    From The Fermi/eROSITA bubbles: a look into the nuclear outflow from the Milky Way (2024) · cites this paper as Sarkar 2019

  • Sarkar (2019) proposed that the absence of the south polar spur in the ROSAT X-ray maps could be due to a density asymmetry between the northern and southern hemispheres.

    “Sarkar (2019) proposed that the absence of the south polar spur in the ROSAT X-ray maps could be due to a density asymmetry between the northern and southern hemispheres.”

    From The Fermi/eROSITA bubbles: a look into the nuclear outflow from the Milky Way (2024) · cites this paper as Sarkar 2019

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Authors
Sarkar, K. C.
Affiliations
Hebrew University of Jerusalem (IL)
Corresponding author
Sarkar, Kartick C
ORCID
Sarkar, Kartick C
Venue
Monthly Notices of the Royal Astronomical Society
Publisher
Oxford University Press (OUP)
Published
2018-11-28
Volume
482
Issue
4
Pages
4813-4823
ISSN
  • 0035-8711 (ISSN-L)
  • 1365-2966
DOI
10.1093/mnras/sty2944
OpenAlex
W2898161175
Cited by
27
References
61
Citations by year
2025: 3 · 2024: 4 · 2023: 6 · 2022: 5 · 2021: 3 · 2020: 3 · 2019: 1 · 2018: 2
FWCI
1.19
Type
journal article
Language
en
Open access
Licence
academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model (vor)
Locations
  • Monthly Notices of the Royal Astronomical Society (publishedVersion)
  • arXiv (Cornell University) (submittedVersion)
  • arXiv (Cornell University)
Funders
  • Israeli Science Foundation (857/14)
  • Deutsche Forschungsgemeinschaft (STE 1869/2-1 GE 625/17-1)
Topics
  • Physical Sciences › Physics and Astronomy › Nuclear and High Energy Physics › Astrophysics and Cosmic Phenomena
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysical Phenomena and Observations
  • Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Astrophysics and Star Formation Studies
Keywords
North Polar Spur, Loop I, Fermi bubbles, circumgalactic medium, Galactic Center, X-ray emission, gamma-ray emission, projection effects, ROSAT, mechanical luminosity, Galactic halo

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