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16 pages, 3439 KiB

Open AccessArticle

Dark Supernova Remnants Revealed by CO-Line Bubbles in the W43 Molecular Complex along the 4-kpc Galactic Arm

by Yoshiaki Sofue

Galaxies 2021, 9(1), 13; https://doi.org/10.3390/galaxies9010013 - 4 Feb 2021

Cited by 6 | Viewed by 3044

Fine structure of the density distribution in giant molecular clouds (GMCs) around W43 (G31+00+90 km s

^{- 1}

at ∼5.5 kpc) was analyzed using the FUGIN

^{*}

CO-line survey at high-angular (20”∼0.5 pc) and velocity (1.3 km s

^{- 1}

) resolutions ( [...] Read more.

Fine structure of the density distribution in giant molecular clouds (GMCs) around W43 (G31+00+90 km s

^{- 1}

at ∼5.5 kpc) was analyzed using the FUGIN

^{*}

CO-line survey at high-angular (20”∼0.5 pc) and velocity (1.3 km s

^{- 1}

) resolutions (

^{*}

Four-receiver-system Unbiased Galactic Imaging survey with the Nobeyama 45-m telescope). The GMCs show highly turbulent structures, and the eddies are found to exhibit spherical bubble morphology appearing in narrow ranges of velocity channels. The bubbles are dark in radio continuum emission, unlike usual supernova remnants (SNR) or HII regions, and in infrared dust emission, unlike molecular bubbles around young stellar objects. The CO bubbles are interpreted as due to fully evolved buried SNRs in molecular clouds after rapid exhaustion of the released energy in dense molecular clouds. Then, the CO bubbles may be a direct evidence for exciting and maintaining the turbulence in GMCs by SN origin. Search for CO bubbles as “dark SNRs” (dSNR) will have implication to estimate the supernova rate more accurately, and hence the star formation activity in the Milky Way. Full article

(This article belongs to the Collection A Trip across the Universe: Our Present Knowledge and Future Perspectives)

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8 pages, 704 KiB

Open AccessArticle

Gravitational Focusing of Low-Velocity Dark Matter on the Earth’s Surface

by Yoshiaki Sofue

Galaxies 2020, 8(2), 42; https://doi.org/10.3390/galaxies8020042 - 16 May 2020

Cited by 20 | Viewed by 3933

Abstract

We show that the Earth acts as a high-efficiency gravitational collector of low-velocity flow of dark matter (DM). The focal point appears on the Earth’s surface, when the DM flow speed is about 17 km/s with respect to the geo-center. We discuss diurnal modulation of the local DM density influenced by the Earth’s gravity. We also touch upon similar effects on galactic and solar system objects. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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20 pages, 742 KiB

Open AccessReview

Rotation Curve of the Milky Way and the Dark Matter Density

by Yoshiaki Sofue

Galaxies 2020, 8(2), 37; https://doi.org/10.3390/galaxies8020037 - 29 Apr 2020

Cited by 89 | Viewed by 13837

Abstract

We review the current status of the study of rotation curve (RC) of the Milky Way, and present a unified RC from the Galactic Center to the galacto-centric distance of about 100 kpc. The RC is used to directly calculate the distribution of the surface mass density (SMD). We then propose a method to derive the distribution of dark matter (DM) density in the in the Milky Way using the SMD distribution. The best-fit dark halo profile yielded a local DM density of

ρ_{⊙} = 0.36 \pm 0.02

GeV cm

^{- 3}

. We also review the estimations of the local DM density in the last decade, and show that the value is converging to a value at

ρ_{⊙} = 0.39 \pm 0.09

GeV cm

^{- 3}

. Full article

(This article belongs to the Special Issue Debate on the Physics of Galactic Rotation and the Existence of Dark Matter)

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20 pages, 5956 KiB

Open AccessFeature PaperEditor’s ChoiceReview

X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures

by Jun Kataoka, Yoshiaki Sofue, Yoshiyuki Inoue, Masahiro Akita, Shinya Nakashima and Tomonori Totani

Galaxies 2018, 6(1), 27; https://doi.org/10.3390/galaxies6010027 - 26 Feb 2018

Cited by 50 | Viewed by 8728

Abstract

The Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray emission associated with Loop I, a radio continuum loop spanning across 100° on the sky, is still being debated. The northern-most part of Loop I, known as the North Polar Spur (NPS), is the brightest arm and is even clearly visible in the ROSAT X-ray sky map. In this paper, we present a comprehensive review on the X-ray observations of the Fermi bubbles and their possible association with the NPS and Loop I structures. Using uniform analysis of archival Suzaku and Swift data, we show that X-ray plasma with kT~0.3 keV and low metal abundance (Z~0.2 Z_◉) is ubiquitous in both the bubbles and Loop I and is naturally interpreted as weakly shock-heated Galactic halo gas. However, the observed asymmetry of the X-ray-emitting gas above and below the GC has still not been resolved; it cannot be fully explained by the inclination of the axis of the Fermi bubbles to the Galactic disk normal. We argue that the NPS and Loop I may be asymmetric remnants of a large explosion that occurred before the event that created the Fermi bubbles, and that the soft gamma-ray emission from Loop I may be due to either π⁰ decay of accelerated protons or electron bremsstrahlung. Full article

(This article belongs to the Special Issue Searching for Connections among the Fermi Bubbles, the Galactic Center GeV Excess, and Loop I)

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