Search for Hot Gas in the Local Group with ASCA
Abstract
An X-ray study was made to examine whether some part of the soft X-ray background is coming from hot gas in the Local Group. For this purpose, four consecutive pointings were made with ASCA toward a sky region between M31 and M33, which is close to the direction of the center of the Local Group. By comparing the X-ray surface brightness in this sky direction with that in another blank sky region near the north equatorial pole, an upper limit on any soft excess X-ray background was determined to be 2.8 × 10 -9 erg cm-2 s-1 sr-1 with a 90% confidence level statistical error. Assuming an optically-thin thermal bremsstrahlung energy spectrum (Raymond-Smith model) for a temperature of 1keV and a β-model electron density distribution for a core radius of 100kpc for the X-ray halo, the upper limit of the central plasma density was obtained to be 1.3 × 10-4 cm-3. The plasma column density is too low to contribute significantly to the observed quadrupole anisotropy in the cosmic microwave background.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- June 2002
- DOI:
- 10.1093/pasj/54.3.387
- arXiv:
- arXiv:astro-ph/0205197
- Bibcode:
- 2002PASJ...54..387O
- Keywords:
-
- cosmology: cosmic microwave background;
- galaxies: Local Group;
- X-rays: diffuse background;
- Astrophysics
- E-Print:
- 21pages, 6 figures, paper will be published to PASJ Vol.54, No.3