Unravelling the Mystery within Dwarf Elliptical Galaxies
Bonita De Swardt¹, Renée Kraan-Korteweg¹, Helmut Jerjen^2
1 University of Cape Town
² Research School of Astronomy and Astrophysics, Australian National University
It is well known that dwarf galaxies constitute the most common galaxy type in the Local Group and in neighboring clusters. Even though dwarf elliptical (dE) galaxies are the most numerous galaxy type in the local universe, they still remain amongst the most poorly studied stellar systems. This is mainly due to their low luminosities (M_V < -17 mag) and characteristic low effective surface brightness (V > 22 mag arcsec^-2), making observations of these galaxies, even with 10m-class telescopes, extremely challenging. The birth of Extremely Large Telescopes (ELTs) with apertures well above the 10m mark will have a profound impact on our understanding of the nature of dwarf galaxies in general. They will provide vital clues to their formation and evolution history, illustrating their importance not only on astronomical scales but on the global cosmological scale too.

In particular, our interest in dE galaxies lies in the detection of the postulated intermediate-mass black hole (IMBH), believed to have a mass in the range of 10³ < M_\odot < 10⁶. The well-known "BH mass - host galaxy bulge" relationship established for early-type galaxies implies that IMBHs should be present in dE galaxies given their low central velocity dispersion. The known stellar-mass black holes (BHs, 10¹ < M_\odot < 10²) and supermassive black holes (SMBHs, 10^7.5 < M_\odot < 10⁹) currently define the slope of the BH mass - host galaxy bulge relationship. Only with the secure detection of an IMBH will we able to find how far this relation extends, providing a lower mass limit for SMBHs.

With the development of ELTs, we will be able to detect these faint dEs with a significant reduction in exposure time. In addition, there will be a dramatic increase in spectral and angular resolution, allowing for studies of both stellar kinematics and dynamics in unprecedented detail. This will provide tighter constraints for BH models for which a mass estimate could be obtained with greater precision. The long awaited question of how much dark matter lies within dE galaxies will also be answered, given the superb quality of the dynamical data. These are some of the pressing questions for which an ELT can provide answers. Clearly, we need a growing interest in the construction of ELTs to make the next giant leap in astrophysics.

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On 20 Oct 2005, 17:41.