A New Feature of the Radio Sky

Large, M. I.; Quigley, Muireann; Haslam, C. G. T.

doi:10.1093/mnras/124.5.405

Cited by 59 publications

(33 citation statements)

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“…One is tempted to identify these as shock or sound waves associated with the bubbles (e.g., Figure 4 of Su et al 2010; Figure 1 of Jones et al 2012. ) In particular, the NPS (Bolton & Westfold 1950) emerges north from the Galactic plane at l ∼ 20°-30°and rises to heights above b ∼ 80°, merging with the Loop I radio structure (Large et al 1962;Haslam et al 1982). It parallels the east edge of the north bubble over this extent; indeed, the NPS and Loop I, together, parallel the edge of the northern polarized radio lobe (which subsumes the north bubble) to a remarkable degree.…”

Section: Forward Shock/shell?mentioning

confidence: 98%

A Unified Model of the Fermi Bubbles, Microwave Haze, and Polarized Radio Lobes: Reverse Shocks in the Galactic Center’s Giant Outflows

Crocker

Bicknell

Taylor

et al. 2015

ApJ

121

113

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The Galactic center's giant outflows are manifest in three different, nonthermal phenomena: (1) the hard-spectrum, γ-ray "Fermi bubbles" emanating from the nucleus and extending to b 50  | | ; (2) the hard-spectrum, totalintensity microwave (∼20-40 GHz) "haze" extending to b 35  | | in the lower reaches of the Fermi bubbles; and (3) the steep-spectrum, polarized, "S-PASS" radio (∼2-20 GHz) lobes that envelop the bubbles and extend to b 60  | |. We find that the nuclear outflows inflate a genuine bubble in each Galactic hemisphere that has the classical structure, working outward, of reverse shock, contact discontinuity (CD), and forward shock. Expanding into the finite pressure of the halo and given appreciable cooling and gravitational losses, the CD of each bubble is now expanding only very slowly. We find observational signatures in both hemispheres of giant, reverse shocks at heights of ∼1 kpc above the nucleus; their presence ultimately explains all three of the nonthermal phenomena mentioned above. Synchrotron emission from shock-reaccelerated cosmic-ray electrons explains the spectrum, morphology, and vertical extent of the microwave haze and the polarized radio lobes. Collisions between shockreaccelerated hadrons and denser gas in cooling condensations that form inside the CD account for most of the bubbles' γ-ray emissivity. Inverse Compton emission from primary electrons contributes at the 10%-30% level. Our model suggests that the bubbles are signatures of a comparatively weak but sustained nuclear outflow driven by Galactic center star formation over few × 10 8 yr.

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Section: Forward Shock/shell?mentioning

confidence: 98%

A Unified Model of the Fermi Bubbles, Microwave Haze, and Polarized Radio Lobes: Reverse Shocks in the Galactic Center’s Giant Outflows

Crocker

Bicknell

Taylor

et al. 2015

ApJ

121

113

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“…For example, a comparison with the synchrotron map from Haslam et al (1982) taken at 408 MHz reveals γ-ray counterparts of Radio Loop I (Large et al 1962) and smaller objects like the Large Magellanic Cloud at (l, b) ≈ (−80…”

Section: Bubbles Features and Radiomentioning

confidence: 99%

The denoised, deconvolved, and decomposedFermiγ-ray sky

Selig

Vacca

Oppermann

et al. 2015

A&A

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We analyze the 6.5 year all-sky data from the Fermi Large Area Telescope that are restricted to γ-ray photons with energies between 0.6-307.2 GeV. Raw count maps show a superposition of diffuse and point-like emission structures and are subject to shot noise and instrumental artifacts. Using the D 3 PO inference algorithm, we modeled the observed photon counts as the sum of a diffuse and a point-like photon flux, convolved with the instrumental beam and subject to Poissonian shot noise. The D 3 PO algorithm performs a Bayesian inference without the use of spatial or spectral templates; that is, it removes the shot noise, deconvolves the instrumental response, and yields separate estimates for the two flux components. The non-parametric reconstruction uncovers the morphology of the diffuse photon flux up to several hundred GeV. We present an all-sky spectral index map for the diffuse component. We show that the diffuse γ-ray flux can be described phenomenologically by only two distinct components: a soft component, presumably dominated by hadronic processes, tracing the dense, cold interstellar medium, and a hard component, presumably dominated by leptonic interactions, following the hot and dilute medium and outflows such as the Fermi bubbles. A comparison of the soft component with the Galactic dust emission indicates that the dust-to-soft-gamma ratio in the interstellar medium decreases with latitude. The spectrally hard component exists in a thick Galactic disk and tends to flow out of the Galaxy at some locations. Furthermore, we find the angular power spectrum of the diffuse flux to roughly follow a power law with an index of 2.47 on large scales, independent of energy. Our first catalog of source candidates includes 3106 candidates of which we associate 1381 (1897) with known sources from the second (third) Fermi source catalog. We observe γ-ray emission in the direction of a few galaxy clusters hosting known radio halos.

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“…2 is attributed to it. As originally defined by Large et al (1962), the right-hand end of the arc was considered to be the "South Polar Spur" (SPS), which descends from the plane at l = 45 • (visible in Figs. 20 and 21).…”

Section: Other Loops and Spursmentioning

confidence: 99%

Planck2015 results

Ade

Aghanim

Alves

et al. 2016

A&A

162

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We discuss the Galactic foreground emission between 20 and 100 GHz based on observations by Planck and WMAP. The total intensity in this part of the spectrum is dominated by free-free and spinning dust emission, whereas the polarized intensity is dominated by synchrotron emission. The Commander component-separation tool has been used to separate the various astrophysical processes in total intensity. Comparison with radio recombination line templates verifies the recovery of the free-free emission along the Galactic plane. Comparison of the high-latitude Hα emission with our free-free map shows residuals that correlate with dust optical depth, consistent with a fraction (≈30%) of Hα having been scattered by high-latitude dust. We highlight a number of diffuse spinning dust morphological features at high latitude. There is substantial spatial variation in the spinning dust spectrum, with the emission peak (in I ν ) ranging from below 20 GHz to more than 50 GHz. There is a strong tendency for the spinning dust component near many prominent H ii regions to have a higher peak frequency, suggesting that this increase in peak frequency is associated with dust in the photo-dissociation regions around the nebulae. The emissivity of spinning dust in these diffuse regions is of the same order as previous detections in the literature. Over the entire sky, the Commander solution finds more anomalous microwave emission (AME) than the WMAP component maps, at the expense of synchrotron and free-free emission. This can be explained by the difficulty in separating multiple broadband components with a limited number of frequency maps. Future surveys, particularly at 5-20 GHz, will greatly improve the separation by constraining the synchrotron spectrum. We combine Planck and WMAP data to make the highest signal-to-noise ratio maps yet of the intensity of the all-sky polarized synchrotron emission at frequencies above a few GHz. Most of the high-latitude polarized emission is associated with distinct large-scale loops and spurs, and we re-discuss their structure. We argue that nearly all the emission at 40 • > l > −90 • is part of the Loop I structure, and show that the emission extends much further in to the southern Galactic hemisphere than previously recognised, giving Loop I an ovoid rather than circular outline. However, it does not continue as far as the "Fermi bubble/microwave haze", making it less probable that these are part of the same structure. We identify a number of new faint features in the polarized sky, including a dearth of polarized synchrotron emission directly correlated with a narrow, roughly 20 • long filament seen in Hα at high Galactic latitude. Finally, we look for evidence of polarized AME, however many AME regions are significantly contaminated by polarized synchrotron emission, and we find a 2σ upper limit of 1.6% in the Perseus region.

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A New Feature of the Radio Sky

Cited by 59 publications

References 0 publications

A Unified Model of the Fermi Bubbles, Microwave Haze, and Polarized Radio Lobes: Reverse Shocks in the Galactic Center’s Giant Outflows

A Unified Model of the Fermi Bubbles, Microwave Haze, and Polarized Radio Lobes: Reverse Shocks in the Galactic Center’s Giant Outflows

The denoised, deconvolved, and decomposedFermiγ-ray sky

Planck2015 results

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