ASCA Observation of NGC 4636: Dark Matter and Metallicity Gradient
Abstract
We present our analysis of ASCA PV phase observation of the elliptical galaxy NGC 4636. SIS spectra in six concentric annuli centered on NGC 4636 are used to derive temperature, metallicity, and column density profiles for the hot interstellar medium. Outside of the central 3' the temperature is roughly constant at ~0.85 keV, while the metallicity decreases from > 0.36 solar at the center to < 0.12 solar at R ~ 9'. The implications of this gradient for elliptical galaxy formation and the enrichment of intracluster gas are discussed. We derive a detailed mass profile consistent with the stellar velocity dispersion and with ROSAT PSPC and ASCA SIS X-ray temperature profiles. We find that NGC 4636 becomes dark matter dominated at roughly the de Vaucouleurs radius, and, at r ~ 100 kpc, the ratio of dark to luminous matter density is ~80 and M_sun_/L_sun_ ~ 150. Evidence for the presence of a cooling flow is also discussed.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 1994
- DOI:
- 10.1086/187637
- Bibcode:
- 1994ApJ...436L..79M
- Keywords:
-
- Dark Matter;
- Elliptical Galaxies;
- Galactic Evolution;
- Metallicity;
- Spectrum Analysis;
- Temperature Measurement;
- X Ray Spectra;
- Cooling Flows (Astrophysics);
- Interstellar Matter;
- Temperature Profiles;
- Virgo Galactic Cluster;
- Astrophysics;
- COSMOLOGY: DARK MATTER;
- GALAXIES: ABUNDANCES;
- GALAXIES: FORMATION;
- GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4636