Outer Galactic Disks and a Quantitative Test of Gravity at Low Accelerations

Details Outer Galactic Disks and a Quantitative Test of Gravity at Low Accelerations Outer Galactic Disks and a Quantitative Test of Gravity at Low Accelerations

2010-07-19

arxiv.org/abs/1007.3269v1

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

accepted for publication in ApJ Letters

Scientific paper

We use the recent measurement of the velocity dispersion of star-forming, outer-disk knots by Herbert-Fort et al. in the nearly face-on galaxy NGC 628, in combination with other data from the literature, to execute a straightforward test of gravity at low accelerations. Specifically, the rotation curve at large radius sets the degree of non-standard acceleration and then the predicted scaleheight of the knots at that radius provides the test of the scenario. For our demonstration, we presume that the H alpha knots, which are young (age < 10 Myr), are distributed like the gas from which they have recently formed and find a marginal (> 97% confidence) discrepancy with a modified gravity scenario given the current data. More interestingly, we demonstrate that there is no inherent limitation that prevents such a test from reaching possible discrimination at the > 4 sigma level with a reasonable investment of observational resources.

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