Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDoes the galaxy NGC1052-DF2 falsify Milgromian dynamics?
133
0
0.0
(
0
)
Authors
Pavel Kroupa
Ask ChatGPT about the research
No Arabic abstract
A great challenge in present-day physics is to understand whether the observed internal dynamics of galaxies is due to dark matter matter or due to a modification of the law of gravity. Recently, van Dokkum et al. reported that the ultra-diffuse dwarf galaxy NGC1052-DF2 lacks dark matter, and they claimed that this would -- paradoxically -- be problematic for modified gravity theories like Milgromian dynamics (MOND). However, NGC1052-DF2 is not isolated, so that a valid prediction of its internal dynamics in MOND cannot be made without properly accounting for the external gravitational fields from neighbouring galaxies. Including this external field effect following Haghi et al. shows that NGC1052-DF2 is consistent with MOND.
rate research
Read More
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 candidate stream is very narrow and has an unusual and highly curved shape.
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.
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, GC-98, and a revised velocity dispersion measurement for the galaxy. We find that the intrinsic dispersion $sigma=5.6^{+5.2}_{-3.8}$ km/s using Approximate Bayesian Computation, or $sigma=7.8^{+5.2}_{-2.2}$ km/s using the likelihood. The expected dispersion from the stars alone is ~7 km/s. Responding to a request from the Editors of ApJ Letters and RNAAS, we also briefly comment on the recent analysis of our measurements by Martin et al. (2018).
It was recently proposed that the globular cluster system of the very low surface-brightness galaxy NGC1052-DF2 is dynamically very cold, leading to the conclusion that this dwarf galaxy has little or no dark matter. Here, we show that a robust statistical measure of the velocity dispersion of the tracer globular clusters implies a mundane velocity dispersion and a poorly constrained mass-to-light ratio. Models that include the possibility that some of the tracers are field contaminants do not yield a more constraining inference. We derive only a weak constraint on the mass-to-light ratio of the system within the half-light radius (M/L_V<6.7 at the 90% confidence level) or within the radius of the furthest tracer (M/L_V<8.1 at the 90% confidence level). This limit may imply a mass-to-light ratio on the low end for a dwarf galaxy but many Local Group dwarf galaxies fall well within this contraint. With this study, we emphasize the need to reliably account for measurement uncertainties and to stay as close as possible to the data when determining dynamical masses from very small data sets of tracers.
[KKS2000]04 (NGC1052-DF2) has become a controversial and well-studied galaxy after the claims suggesting a lack of dark matter and the presence of an anomalously bright globular cluster (GC) system around it. A precise determination of its overall star formation history (SFH) as well as a better characterisation of its GC or planetary nebulae (PN) systems are crucial aspects to: i) understand its real nature, in particular placing it within the family of ultra diffuse galaxies; ii) shed light on its possible formation, evolution, and survival in the absence of dark matter. With this purpose we expand on the knowledge of [KKS2000]04 from the analysis of OSIRIS@GTC spectroscopic data. On the one hand, we claim the possible detection of two new PNe and confirm membership of 5 GCs. On the other hand, we find that the stars shaping [KKS2000]04 are intermediate-age to old (90% of its stellar mass older than 5 Gyr, average age of 8.7 $pm$ 0.7 Gyr) and metal-poor ([M/H] $sim$ -1.18 $pm$ 0.05), in general agreement with previous results. We do not find any clear hints of significant changes in its stellar content with radius. In addition, the possibility of [KKS2000]04 being a tidal dwarf galaxy with no dark matter is highly disfavoured.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
