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تسجيل مستخدم جديدSelf-Interacting Dark Matter and the Origin of Ultra-Diffuse Galaxies NGC1052-DF2 and -DF4
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Observations of ultra-diffuse galaxies NGC 1052-DF2 and -DF4 show they may contain little dark matter, challenging our understanding of galaxy formation. Using controlled N-body simulations, we explore the possibility that their properties can be reproduced through tidal stripping from the elliptical galaxy NGC 1052, in both cold dark matter (CDM) and self-interacting dark matter (SIDM) scenarios. To explain the dark matter deficiency, we find that a CDM halo must have a very low concentration so that it can lose sufficient inner mass in the tidal field. In contrast, SIDM favors a higher and more reasonable concentration as core formation enhances tidal mass loss. Final stellar distributions in our SIDM benchmarks are more diffuse than the CDM one, and hence the former are in better agreement with the data. We further show that a cored CDM halo model modified by strong baryonic feedback is unlikely to reproduce the observations. Our results indicate that SIDM is more favorable for the formation of dark-matter-deficient galaxies.
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NGC1052-DF2 and NGC1052-DF4 are ultra-diffuse galaxies (UDGs) that were found to have extremely low velocity dispersions, indicating that they have little or no dark matter. Both galaxies host anomalously luminous globular cluster (GC) systems, with
a peak magnitude of their GC luminosity function (GCLF) that is $sim1.5$ magnitudes brighter than the near-universal value of $M_V approx -7.5$. Here we present an analysis of the joint GCLF of the two galaxies, making use of new HST photometry and Keck spectroscopy, and a recently improved distance measurement. We apply a homogeneous photometric selection method to the combined GC sample of DF2 and DF4. The new analysis shows that the peak of the combined GC luminosity function remains at $M_V approx -9$ mag. In addition, we find a subpopulation of less luminous GCs at $M_V approx -7.5$ mag, where the near-universal GCLF peak is located. The number of GCs in the magnitude range of $-5$ to $-8$ is $7.1_{-4.34}^{+7.33}$ in DF2 and $8.6_{-4.83}^{+7.74}$ in DF4, similar to that expected from other galaxies of the same luminosity. The total GC number between $M_V$ of $-5$ to $-11$ is $18.5_{-4.42}^{+8.99}$ for DF2 and $18.6_{-4.92}^{+9.37}$ for DF4, calculated from the background-subtracted GCLF. The updated total number of GCs in both galaxies is $37^{+11.08}_{-6.54}$. The number of GCs do not scale with the halo mass in either DF2 or DF4, suggesting that $N_{GC}$ is not directly determined by the merging of halos.
Recently van Dokkum et al. (2018b) reported that the galaxy NGC 1052-DF2 (DF2) lacks dark matter if located at $20$ Mpc from Earth. In contrast, DF2 is a dark-matter-dominated dwarf galaxy with a normal globular cluster population if it has a much sh
orter distance near $10$ Mpc. However, DF2 then has a high peculiar velocity wrt. the cosmic microwave background of $886$ $rm{km,s^{-1}}$, which differs from that of the Local Group (LG) velocity vector by $1298$ $rm{km,s^{-1}}$ with an angle of $117 , ^{circ}$. Taking into account the dynamical $M/L$ ratio, the stellar mass, half-light radius, peculiar velocity, motion relative to the LG, and the luminosities of the globular clusters, we show that the probability of finding DF2-like galaxies in the lambda cold dark matter ($Lambda$CDM) TNG100-1 simulation is at most $1.0times10^{-4}$ at $11.5$ Mpc and is $4.8times10^{-7}$ at $20.0$ Mpc. At $11.5$ Mpc, the peculiar velocity is in significant tension with the TNG100-1, TNG300-1, and Millennium simulations, but occurs naturally in a Milgromian cosmology. At $20.0$ Mpc, the unusual globular cluster population would challenge any cosmological model. Estimating that precise measurements of the internal velocity dispersion, stellar mass, and distance exist for $100$ galaxies, DF2 is in $2.6sigma$ ($11.5$ Mpc) and $4.1sigma$ ($20.0$ Mpc) tension with standard cosmology. Adopting the former distance for DF2 and assuming that NGC 1052-DF4 is at $20.0$ Mpc, the existence of both is in tension at $geq4.8sigma$ with the $Lambda$CDM model. If both galaxies are at $20.0$ Mpc the $Lambda$CDM cosmology has to be rejected by $geq5.8sigma$.
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We report tentative evidence for a cold stellar stream in the ultra-diffuse galaxy NGC1052-DF2. If confirmed, this stream (which we refer to as The Maybe Stream) would be the first cold stellar stream detected outside of the Local Group. The candidat
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We recently published velocity measurements of luminous globular clusters in the galaxy NGC1052-DF2, concluding that it lies far off the canonical stellar mass - halo mass relation. Here we present a revised velocity for one of the globular clusters,
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