161 research outputs found
Dust and ionized gas in elliptical galaxies: Signatures of merging collisions
Traditionally elliptical galaxies were thought to be essentially devoid of interstellar matter. However, recent advances in instrumental sensitivity have caused a renaissance of interest in dust and gas in - or associated with - elliptical galaxies. In particular, the technique of co-adding IRAS survey scans has led to the detection of more than half of all ellipticals with BT less than 11 mag. in the Revised Shapley-Ames catalog, indicating the presence of 10(exp 7) - 10(exp 8) solar mass of cold interstellar matter (Jura et al. 1987). In addition, CCD multi-color surface photometry shows dust patches in about 30 percent of the cases studied to date (e.g., Veron-Cetty & Veron 1988). Thorough study of the gas and dust in ellipticals is important to (1) determine its origin (mass-loss from late-type stars, merging collisions with other galaxies or accretion inflows from cooling X-ray gas), and (2) investigate the 3-D shape of ellipticals, as can be derived from the orientation of the dust lanes and the 2-D velocity field of the gas. An important result of our comprehensive CCD imaging program is that a relevant fraction (approximately 40 percent) of the sample objects exhibits dust patches within extended H-alpha+(NII) line-emitting filaments. This common occurrence can be easily accounted for if the dust and gas have an external origin, i.e., mergers or interactions with gas-rich galaxies. Evidence supporting this suggestion: (1) the ionized gas is usually dynamically decoupled from the stellar velocity field (see, e.g., Sharples et al. 1983, Bertola & Bettoni 1988); (2) it is shown in a companion paper (Goudfrooij et al. 1992) that internal stellar mass loss alone can not account for the dust content of elliptical galaxies
The Optical Colors of Giant Elliptical Galaxies and their Metal-Rich Globular Clusters Indicate a Bottom-Heavy Initial Mass Function
We report a systematic and statistically significant offset between the
optical (g-z or B-I) colors of seven massive elliptical galaxies and the mean
colors of their associated massive metal-rich globular clusters (GCs) in the
sense that the parent galaxies are redder by 0.12-0.20 mag at a given
galactocentric distance. However, spectroscopic indices in the blue indicate
that the luminosity-weighted ages and metallicities of such galaxies are equal
to that of their averaged massive metal-rich GCs at a given galactocentric
distance, to within small uncertainties. The observed color differences between
the red GC systems and their parent galaxies cannot be explained by the
presence of multiple stellar generations in massive metal-rich GCs, as the
impact of the latter to the populations' integrated g-z or B-I colors is found
to be negligible. However, we show that this paradox can be explained if the
stellar initial mass function (IMF) in these massive elliptical galaxies was
significantly steeper at subsolar masses than canonical IMFs derived from star
counts in the solar neighborhood, with the GC colors having become bluer due to
dynamical evolution, causing a significant flattening of the stellar MF of the
average surviving GC.Comment: 12 pages (in emulateapj format), incl. 12 figures and 3 tables;
published in The Astrophysical Journa
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