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When using galaxy gravity to measure stellar mass, which stars dominate the signal?

 I'm comparing stellar masses from population synthesis models (which are sensitive to the IMF) with dynamical masses from velocity dispersion. There's a systematic offset. To interpret this, I need to know: does the gravity we measure preferentially "see" the luminous, high-mass stars, or is it truly tracing the total stellar mass, including countless faint, low-mass stars?

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By Aryasree Answered 2 years ago

This gets to the heart of the mass discrepancy problem. The gravitational potential you measure via kinematics is fundamentally blind to mass type; it responds to the total enclosed mass. Therefore, the signal is dominated by whatever is most massive at the radii you're probing. In a galaxy's inner regions, this can be the stellar bulge. However, I have seen in many studies that the stellar mass from light is often insufficient, revealing the dominant presence of the dark matter halo even there. The gravity does "see" all stars collectively, but the contribution from low-mass stars is buried within the much larger uncertainty of the dark matter halo's density profile.

 

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