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The shapes of the rotation curves of star-forming galaxies over the last ≈ 10 Gyr.

Tiley, Alfred L. and Swinbank, A. M. and Harrison, C. M. and Smail, Ian and Turner, O. J. and Schaller, M. and Stott, J. P. and Sobral, D. and Theuns, T. and Sharples, R. M. and Gillman, S. and Bower, R. G. and Bunker, A. J. and Best, P. and Richard, J. and Bacon, Roland and Bureau, M. and Cirasuolo, M. and Magdis, G. (2019) 'The shapes of the rotation curves of star-forming galaxies over the last ≈ 10 Gyr.', Monthly notices of the Royal Astronomical Society., 485 (1). pp. 934-960.


We analyse maps of the spatially-resolved nebular emission of ≈1500 star-forming galaxies at z ≈ 0.6–2.2 from deep KMOS and MUSE observations to measure the average shape of their rotation curves. We use these to test claims for declining rotation curves at large radii in galaxies at z ≈ 1–2 that have been interpreted as evidence for an absence of dark matter. We show that the shape of the average rotation curves, and the extent to which they decline beyond their peak velocities, depends upon the normalisation prescription used to construct the average curve. Normalising in size by the galaxy stellar disk-scale length after accounting for seeing effects (⁠R′d⁠), we construct stacked position-velocity diagrams that trace the average galaxy rotation curve out to 6R′d (≈13 kpc, on average). Combining these curves with average HI rotation curves for local systems, we investigate how the shapes of galaxy rotation curves evolve over ≈10 Gyr. The average rotation curve for galaxies binned in stellar mass, stellar surface mass density and/or redshift is approximately flat, or continues to rise, out to at least 6R′d⁠. We find a trend between the outer slopes of galaxies’ rotation curves and their stellar mass surface densities, with the higher surface density systems exhibiting flatter rotation curves. Drawing comparisons with hydrodynamical simulations, we show that the average shapes of the rotation curves for our sample of massive, star-forming galaxies at z ≈ 0–2.2 are consistent with those expected from ΛCDM theory and imply dark matter fractions within 6Rd of at least ≈60 percent.

Item Type:Article
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Publisher statement:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.
Date accepted:05 February 2019
Date deposited:19 February 2019
Date of first online publication:13 February 2019
Date first made open access:27 February 2019

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