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Previous studies have shown that the kinematics of the field ellipticalgalaxy NGC 7507 do not necessarily require dark matter. This is troublingbecause, in the context of LCDM cosmologies, all galaxies should have a largedark matter component. We use penalised pixel fitting software to extractvelocities and velocity dispersions from GMOS slit mask spectra. Using Jeansand MONDian modelling we produce best fit models to the velocity dispersion. Wefind that NGC 7507 has a two component stellar halo, with the outer halo andinner haloes counter rotating. The velocity dispersion profile exhibits anincrease at ~70" (~7.9 kpc), reminiscent of several other elliptical galaxies.Our best fit models are those under mild anisotropy which include ~100 timesless dark matter than predicted by LCDM, although mildly anisotropic modelsthat are completely dark matter free fit almost equally well. Our MONDianmodels, both isotropic and anisotropic, systematically fail to reproduce themeasured velocity dispersions at almost all radii. The counter rotating outerhalo implies a merger remnant, as does the increase in velocity dispersion at~70". From simulations it seems plausible that the merger that caused theincrease in velocity dispersion was a spiral-spiral merger. Our Jeans modelsare completely consistent with a no dark matter scenario, however, some darkmatter can be accommodated, although at much lower concentrations thatpredicted by LCDM simulations. This indicates that NGC 7507 may be a darkmatter free elliptical galaxy. Whether NGC 7507 is completely dark matter freeor very dark matter poor, this is at odds with predictions from current LCDMcosmological simulations. It may be possible that the observed velocitydispersions could be reproduced if the galaxy is significantly flattened alongthe line of sight (e.g. due to rotation), however, invoking this flattening isproblematic.

Dark Matter Deprivation in Field Elliptical Galaxy NGC 7507