%0 Generic %1 beasley2016overmassive %A Beasley, Michael A. %A Romanowsky, Aaron J. %A Pota, Vincenzo %A Navarro, Ignacio Martín %A Delgado, David Martinez %A Neyer, Fabian %A Deich, Aaron L. %D 2016 %K dark diffuse galaxies halos ultra %T An overmassive Dark Halo around an Ultra-diffuse Galaxy in the Virgo Cluster %U http://arxiv.org/abs/1602.04002 %X Ultra diffuse galaxies (UDGs) have the sizes of giant galaxies but the luminosities of dwarfs. A key to understanding their origins comes from their total masses, but their low surface brightnesses ($\mu(V) \geq$ 25.0) generally prohibit dynamical studies. Here we report the first such measurements for a UDG (VCC~1287 in the Virgo cluster), based on its globular cluster system dynamics and size. From 7 GCs we measure a mean systemic velocity $v_sys$ = 1071$^+14_-15$ km/s, thereby confirming a Virgo-cluster association. We measure a velocity dispersion of 33$^+16_-10$ km/s within 8.1 kpc, corresponding to an enclosed mass of $(4.5 2.8)\times10^9$ $M_ødot$ and a $g$-band mass-to-light ratio of $(M/L)_g = 106^+126_-54$. From the cumulative mass curve, along with the GC numbers, we estimate a virial mass of $\sim8\times10^10$ $M_ødot$, yielding a dark-to-stellar mass fraction of $\sim3000$. We show that this UDG is an outlier in $M_star - M_\rm halo$ relations, suggesting extreme stochasticity in relatively massive star-forming halos in clusters. Finally, we discuss how counting GCs offers an efficient route to determining virial masses for UDGs.

@misc{beasley2016overmassive, abstract = {Ultra diffuse galaxies (UDGs) have the sizes of giant galaxies but the luminosities of dwarfs. A key to understanding their origins comes from their total masses, but their low surface brightnesses ($\mu(V) \geq$ 25.0) generally prohibit dynamical studies. Here we report the first such measurements for a UDG (VCC~1287 in the Virgo cluster), based on its globular cluster system dynamics and size. From 7 GCs we measure a mean systemic velocity $v_{\rm sys}$ = 1071$^{+14}_{-15}$ km/s, thereby confirming a Virgo-cluster association. We measure a velocity dispersion of 33$^{+16}_{-10}$ km/s within 8.1 kpc, corresponding to an enclosed mass of $(4.5 \pm 2.8)\times10^{9}$ $M_{\odot}$ and a $g$-band mass-to-light ratio of $(M/L)_g = 106^{+126}_{-54}$. From the cumulative mass curve, along with the GC numbers, we estimate a virial mass of $\sim8\times10^{10}$ $M_{\odot}$, yielding a dark-to-stellar mass fraction of $\sim3000$. We show that this UDG is an outlier in $M_{\rm star} - M_{\rm halo}$ relations, suggesting extreme stochasticity in relatively massive star-forming halos in clusters. Finally, we discuss how counting GCs offers an efficient route to determining virial masses for UDGs.}, added-at = {2016-02-15T09:46:50.000+0100}, author = {Beasley, Michael A. and Romanowsky, Aaron J. and Pota, Vincenzo and Navarro, Ignacio Martín and Delgado, David Martinez and Neyer, Fabian and Deich, Aaron L.}, biburl = {https://www.bibsonomy.org/bibtex/20159ffc460ba9e563991a6980c0ec37c/miki}, description = {[1602.04002] An overmassive Dark Halo around an Ultra-diffuse Galaxy in the Virgo Cluster}, interhash = {f229d12444608e373da6f4f66ef04c82}, intrahash = {0159ffc460ba9e563991a6980c0ec37c}, keywords = {dark diffuse galaxies halos ultra}, note = {cite arxiv:1602.04002Comment: Accepted for publication in ApJ letters}, timestamp = {2016-02-15T09:46:50.000+0100}, title = {An overmassive Dark Halo around an Ultra-diffuse Galaxy in the Virgo Cluster}, url = {http://arxiv.org/abs/1602.04002}, year = 2016 }