10 research outputs found
Hubble Space Telescope Planetary Camera Images of NGC 1316
We present HST Planetary Camera V and I~band images of the central region of
the peculiar giant elliptical galaxy NGC 1316. The inner profile is well fit by
a nonisothermal core model with a core radius of 0.41" +/- 0.02" (34 pc). At an
assumed distance of 16.9 Mpc, the deprojected luminosity density reaches \sim
2.0 \times 10^3 L_{\sun} pc.
Outside the inner two or three arcseconds, a constant mass-to-light ratio of
is found to fit the observed line width measurements. The
line width measurements of the center indicate the existence of either a
central dark object of mass 2 \times 10^9 M_{\sun}, an increase in the
stellar mass-to-light ratio by at least a factor of two for the inner few
arcseconds, or perhaps increasing radial orbit anisotropy towards the center.
The mass-to-light ratio run in the center of NGC 1316 resembles that of many
other giant ellipticals, some of which are known from other evidence to harbor
central massive dark objects (MDO's).
We also examine twenty globular clusters associated with NGC 1316 and report
their brightnesses, colors, and limits on tidal radii. The brightest cluster
has a luminosity of 9.9 \times 10^6 L_{\sun} (), and the
faintest detectable cluster has a luminosity of 2.4 \times 10^5 L_{\sun}
(). The globular clusters are just barely resolved, but their core
radii are too small to be measured. The tidal radii in this region appear to be
35 pc. Although this galaxy seems to have undergone a substantial merger
in the recent past, young globular clusters are not detected.Comment: 21 pages, latex, postscript figures available at
ftp://delphi.umd.edu/pub/outgoing/eshaya/fornax
Hubble Space Telescope Observations of M32: The Color-Magnitude Diagram
We present a V-I color-magnitude diagram for a region 1'-2' from the center
of M32 based on Hubble Space Telescope WFPC2 images. The broad color-luminosity
distribution of red giants shows that the stellar population comprises stars
with a wide range in metallicity. This distribution cannot be explained by a
spread in age. The blue side of the giant branch rises to M_I ~ -4.0 and can be
fitted with isochrones having [Fe/H] ~ -1.5. The red side consists of a heavily
populated and dominant sequence that tops out at M_I ~ -3.2, and extends beyond
V-I=4. This sequence can be fitted with isochrones with -0.2 < [Fe/H] < +0.1,
for ages running from 15 Gyr to 5 Gyr respectively. We do not find the
optically bright asymptotic giant branch stars seen in previous ground-based
work and argue that the majority of them were artifacts of crowding. Our
results are consistent with the presence of the infrared-luminous giants found
in ground-based studies, though their existence cannot be directly confirmed by
our data. There is little evidence for an extended or even a red horizontal
branch, but we find a strong clump on the giant branch itself. If the age
spread is not extreme, the distribution of metallicities in M32 is considerably
narrower than that of the closed-box model of chemical evolution, and also
appears somewhat narrower than that of the solar neighborhood. Overall, the M32
HST color-magnitude diagram is consistent with the average luminosity-weighted
age of 8.5 Gyr and [Fe/H] = -0.25 inferred from integrated spectral indices.Comment: 22 pages, AASTeX, aaspp4 and flushrt style files included, 11
postscript figures, figures 1,2,5,7, and 8 available at
ftp://bb3.jpl.nasa.gov/pub/m32 . Submitted to the Astronomical Journa