Astrophys. J., 890, 52-52 (2020/February-2)
The strikingly metal-rich halo of the Sombrero galaxy.
COHEN R.E., GOUDFROOIJ P., CORRENTI M., GNEDIN O.Y., HARRIS W.E., CHANDAR R., PUZIA T.H. and SANCHEZ-JANSSEN R.
Abstract (from CDS):
The nature of the Sombrero galaxy (M104 = NGC 4594) has remained elusive despite many observational studies at a variety of wavelengths. Here we present Hubble Space Telescope imaging of two fields at ∼16 and 33 kpc along the minor axis to examine stellar metallicity gradients in the extended spheroid. We use this imaging, extending more than 2 mag below the tip of the red giant branch, in combination with artificial star tests to forward model observed color-magnitude diagrams, measuring metallicity distribution functions (MDFs) at different radii along the minor axis. An important and unexpected result is that the halo of the Sombrero is strikingly metal-rich: even the outer field, located at ∼17 effective radii of the bulge, has a median metallicity [Z/H] ∼ -0.15, and the fraction of stars with [Z/H] < -1.0 is negligible. This is unprecedented among massive galaxy halos studied to date, even among giant ellipticals. We find significant radial metallicity gradients, characterized by an increase in the fraction of metal-poor stars with radius and a gradient in median metallicity of ∼0.01 dex kpc–1. The density profile is well fit by power laws with slopes that exhibit a dependence on metallicity, with flatter slopes for more metal-poor stars. We discuss our results in the context of recent stellar MDF studies of other nearby galaxies and potential formation scenarios for the Sombrero galaxy.
© 2020. The American Astronomical Society. All rights reserved.
Galaxy stellar halos - Galaxy spheroids - Metallicity - Star formation - Galaxy stellar content
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