ASCA observation of NGC 4636: Dark matter and metallicity gradient

Details ASCA observation of NGC 4636: Dark matter and metallicity gradient ASCA observation of NGC 4636: Dark matter and metallicity gradient

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...436l..79m&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 436, no. 1, p. L79-L82

Astronomy and Astrophysics

Astrophysics

58

Dark Matter, Elliptical Galaxies, Galactic Evolution, Metallicity, Spectrum Analysis, Temperature Measurement, X Ray Spectra, Cooling Flows (Astrophysics), Interstellar Matter, Temperature Profiles, Virgo Galactic Cluster

Scientific paper

We present our analysis of ASCA PV phase observation of the elliptical galaxy NGC 4636. Solid state imaging spectrometer (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 min the temperature is roughly constant at approximately 0.85 keV, while the metallicity decreases from greater than 0.36 solar at the center to less than 0.12 solar at R approximately 9 min. 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 position sensitive proportional counter (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 approximately 100 kpc, the ratio of dark to luminous matter density is approximately 80 and solar mass/solar luminosity approximately equal to 150. Evidence for the presence of a cooling flow is also discussed.

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