Book contents
- Frontmatter
- Contents
- Preface
- Dedication: In Memory of Olin Eggen
- Part 1 Introduction
- Part 2 The Epoch of Bulge Formation
- Part 3 The Timescales of Bulge Formation
- Part 4 Physical Processes in Bulge Formation
- Part 5 Bulge Phenomenology
- Bulge-Disk Decomposition of Spiral Galaxies in the Near-Infrared
- The Triaxial Bulge of NGC 1371
- The Bulge-Disk Orthogonal Decoupling in Galaxies: NGC 4698 and NGC 4672
- The Kinematics and the Origin of the Ionized Gas in NGC 4036
- Optically Thin Thermal Plasma in the Galactic Bulge
- X-Ray Properties of Bulges
- The Host Galaxies of Radio-Loud AGN
- The Centers of Radio-Loud Early-Type Galaxies with HST
- Central UV Spikes in Two Galactic Spheroids
- Part 6 Conference Summary
- Index
Optically Thin Thermal Plasma in the Galactic Bulge
from Part 5 - Bulge Phenomenology
Published online by Cambridge University Press: 10 November 2010
- Frontmatter
- Contents
- Preface
- Dedication: In Memory of Olin Eggen
- Part 1 Introduction
- Part 2 The Epoch of Bulge Formation
- Part 3 The Timescales of Bulge Formation
- Part 4 Physical Processes in Bulge Formation
- Part 5 Bulge Phenomenology
- Bulge-Disk Decomposition of Spiral Galaxies in the Near-Infrared
- The Triaxial Bulge of NGC 1371
- The Bulge-Disk Orthogonal Decoupling in Galaxies: NGC 4698 and NGC 4672
- The Kinematics and the Origin of the Ionized Gas in NGC 4036
- Optically Thin Thermal Plasma in the Galactic Bulge
- X-Ray Properties of Bulges
- The Host Galaxies of Radio-Loud AGN
- The Centers of Radio-Loud Early-Type Galaxies with HST
- Central UV Spikes in Two Galactic Spheroids
- Part 6 Conference Summary
- Index
Summary
We present preliminary results of our ASCA observation of the Galactic bulge. We confirm the diffuse (spatially-unresolved) soft X-ray emission in the direction of the bulge. We also detect iron-L and neon-K complex lines in the spectrum. Therefore, the bulge emission undoubtedly originates from an optically thin thermal plasma. The plasma temperature is 0.4 keV. With the results, we present possible implications of the Galactic bulge emission.
Introduction
A Galactic Soft X-ray Diffuse Background (SXDB) below ∼2 keV was discovered by Bowyer, Field & Mack (1968). Four soft X-ray all-sky surveys produced maps of this SXDB (McCammon et al. 1983; Marshall & Clark 1984; Garmire et al. 1992; Snowden et al. 1995, 1997) which show complex features, indicating that the SXDB must be made up of several components. However, Snowden et al. (1997) established that the SXDB maps above 0.5 keV are smooth on the south side of the plane, which can be reproduced with only one component: a hot gas in the bulge with a scale height of ∼1.9 kpc. Thus they named this component as the ‘bulge’ emission. The typical temperature was estimated to be ∼0.3 keV.
The ASCA satellite has the capability to observe the SXDB with a reasonable energy resolution (Tanaka et al. 1994), which allows an improved study of line emission. We present here results of our initial analysis of the ASCA spectrum and discuss the bulge emission.
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- The Formation of Galactic Bulges , pp. 175 - 179Publisher: Cambridge University PressPrint publication year: 2000