A HIGH STELLAR VELOCITY DISPERSION AND ∼100 GLOBULAR CLUSTERS FOR THE ULTRA-DIFFUSE GALAXY DRAGONFLY 44

By P. V. van Dokkum, R. Abraham, J. Brodie, C. Conroy, S. Danieli, A. Merritt, L. Mowla, A. Romanowsky, Jielai Zhang. 2016

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Recently a population of large, very low surface brightness, spheroidal galaxies was identified in the Coma cluster. The apparent survival of these ultra-diffuse galaxies (UDGs) in a rich cluster suggests that they have very high masses. Here, we present the stellar kinematics of Dragonfly 44, one of the largest Coma UDGs, using a 33.5 hr integration with DEIMOS on the Keck II telescope. We find a velocity dispersion of σ = 47 − 6 + 8 km s − 1 , which implies a dynamical mass of M dyn ( < r 1 / 2 ) = 0.7 − 0.2 + 0.3 × 10 10 M ⊙ within its deprojected half-light radius of r 1 / 2 = 4.6 ± 0.2 kpc . The mass-to-light ratio is M / L I ( < r 1 / 2 ) = 48 − 14 + 21 M ⊙ / L ⊙ , and the dark matter fraction is 98% within r 1 / 2 . The high mass of Dragonfly 44 is accompanied by a large globular cluster population. From deep Gemini imaging taken in 0 .″ 4 seeing we infer that Dragonfly 44 has 94 − 20 + 25 globular clusters, similar to the counts for other galaxies in this mass range. Our results add to other recent evidence that many UDGs are “failed” galaxies, with the sizes, dark matter content, and globular cluster systems of much more luminous objects. We estimate the total dark halo mass of Dragonfly 44 by comparing the amount of dark matter within r = 4.6 kpc to enclosed mass profiles of NFW halos. The enclosed mass suggests a total mass of ∼ 10 12 M ⊙ , similar to the mass of the Milky Way. The existence of nearly dark objects with this mass is unexpected, as galaxy formation is thought to be maximally efficient in this regime.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c39e0d40dc3dad70dcaaa84b069da8be39532dd5

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Citations in the corpus

Ultralight scalars as cosmological dark matter (2016, background): “The sharp peak in the rotation curve due to a massive central soliton may be observable in ultra-diffuse galaxies such as Dragonfly 44 [189].”
(Almost) Dark Galaxies in the ALFALFA Survey: Isolated H i-bearing Ultra-diffuse Galaxies (2017, background): “All three sources have measured dynamical masses consistent with or slightly larger than the measurements from Beasley et al. (2016) of VCC 1287, and slightly smaller than the measurement from van Dokkum et al. (2016).”
Ultra-diffuse galaxies outside clusters: clues to their formation and evolution (2016, background): “For instance, van Dokkum et al. (2015, 2016) suggest the intriguing hypothesis that these galaxies could be failed Milky Way-like objects (L?).”
Illuminating Low Surface Brightness Galaxies with the Hyper Suprime-Cam Survey (2017, background): “This scenario also appears to be viable for at least some fraction of UDGs (e.g., van Dokkum et al. 2016).”
NIHAO - XI. Formation of ultra-diffuse galaxies by outflows (2016, methodology): “Favouring a massive halo for UDGs is the inferred virial mass of ∼8×1011M for DF 441, one of the brightest Coma UDGs (van Dokkum et al. 2016).”