The Twisting X-Ray Isophotes of the Elliptical Galaxy NGC 720
Abstract
We present spatial analysis of the deep (57 ks) ROSAT HRI X-ray image of the E4 galaxy NGC 720. The orientation of the HRI surface brightness is consistent with the optical position angle (P.A.) interior to semimajor axis a ~ 60" (optical R_e_ ~ 50"). For larger a, the isophotes twist and eventually (a ~> 100") orient along a direction consistent with the P.A. measured with the PSPC data (Buote & Canizares) the ~30^deg^ twist is significant at an estimated 99% confidence level. We argue that this twist is not the result of projected foreground and background sources, ram pressure effects, or tidal distortions. If spheroidal symmetry and a nearly isothermal hot gas are assumed, then the azimuthally averaged radial profile displays features that, when combined with the observed P.A. twist, are inconsistent with the simple assumptions that the X-ray emission arises either entirely from hot gas or from the combined emission of hot gas and discrete sources. We discuss possible origins of the P.A. twist and radial profile features (e.g., triaxiality).
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1996
- DOI:
- 10.1086/177680
- arXiv:
- arXiv:astro-ph/9601043
- Bibcode:
- 1996ApJ...468..184B
- Keywords:
-
- GALAXIES: INDIVIDUAL NGC NUMBER: NGC 720;
- GALAXIES: PHOTOMETRY;
- GALAXIES: STRUCTURE;
- X-RAYS: GALAXIES;
- Astrophysics
- E-Print:
- 17 pages (3 figures), AASTeX manuscript with PostScript figures, to appear in ApJ September 10, 1996. Only a few minor cosmetic changes in this version