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The ultra-diffuse galaxy NGC1052-DF2 has a very low velocity dispersion,indicating that it has little or no dark matter. Here we report the discoveryof a second galaxy in this class, residing in the same group. NGC1052-DF4closely resembles NGC1052-DF2 in terms of its size, surface brightness, andmorphology; has a similar distance of $D=19.9\pm 2.8$ Mpc; and also has apopulation of luminous globular clusters extending out to 7 kpc from the centerof the galaxy. Accurate radial velocities of the diffuse galaxy light and sevenof the globular clusters were obtained with the Low Resolution ImagingSpectrograph on the Keck I telescope. The velocity of the diffuse light isidentical to the median velocity of the clusters, $v_{\rm sys}=\langle v_{\rmgc} \rangle=1445$ km/s, and close to the central velocity of the NGC1052 group.The rms spread of the observed velocities is very small at $\sigma_{\rmobs}=5.8$ km/s. Taking observational uncertainties into account we determine anintrinsic velocity dispersion of $\sigma_{\rm intr}=4.2^{+4.4}_{-2.2}$ km/s,consistent with the expected value from the stars alone ($\sigma_{\rmstars}\approx 7$ km/s) and lower than expected from a standard NFW halo($\sigma_{\rm halo}\sim 30$ km/s). We conclude that NGC1052-DF2 is not anisolated case but that a class of such objects exists. The origin of theselarge, faint galaxies with an excess of luminous globular clusters and anapparent lack of dark matter is, at present, not understood.

A second galaxy missing dark matter in the NGC1052 group