[Paper Review] A disk and no signatures of tidal distortion in the galaxy "lacking" dark matter NGC 1052-DF2

Mireia Montes, Ignacio Trujillo+3 more|arXiv (Cornell University)|Jun 18, 2021

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy77 references29 citations

TL;DR

Using ultra-deep imaging reaching 30.4 mag/arcsec², this study finds no tidal features or signs of stripping around NGC 1052-DF2, a galaxy previously claimed to lack dark matter. Instead, it reveals a disk-like structure extending from 35 to 80 arcsec, with constant ellipticity and position angle, and evidence of rotation. This implies a dynamical mass 2.6 times higher than previously reported, bringing the galaxy’s dark matter content in line with typical galaxies of similar stellar mass.

ABSTRACT

Using ultra-deep imaging ($\mu_g = 30.4$ mag/arcsec$^2$; 3$\sigma$, 10"x10"), we probed the surroundings of the first galaxy "lacking" dark matter KKS2000[04] (NGC 1052-DF2). Signs of tidal stripping in this galaxy would explain its claimed low content of dark matter. However, we find no evidence of tidal tails. In fact, the galaxy remains undisturbed down to a radial distance of 80 arcsec. This radial distance triples previous spatial explorations of the stellar distribution of this galaxy. In addition, the distribution of its globular clusters (GCs) is not extended in relation to the bulk of the galaxy (the radius containing half of the GCs is 21 arcsec). We also found that the surface brightness radial profiles of this galaxy in the g and r bands decline exponentially from 35 to 80 arcsec. That, together with a constant ellipticity and position angle in the outer parts of the galaxy strongly suggests the presence of a low-inclination disk. This is consistent with the evidence of rotation found for this object. This finding implies that the dynamical mass of this galaxy is a factor of 2 higher than previously reported, bringing the dark matter content of this galaxy in line with galaxies of similar stellar mass.

Motivation & Objective

• To test the tidal stripping hypothesis as an explanation for the claimed absence of dark matter in NGC 1052-DF2.
• To probe the outer regions of NGC 1052-DF2 down to unprecedented depth (80 arcsec) to search for tidal tails or distortions.
• To investigate the spatial distribution of globular clusters and surface brightness profiles to assess galactic structure and potential interactions.
• To re-evaluate the dynamical mass and dark matter content of NGC 1052-DF2 using new structural and kinematic evidence.
• To assess the galaxy’s association with nearby massive galaxies (NGC 1052 and NGC 1042) based on tidal features and projected distance.

Proposed method

• Acquired ultra-deep imaging with HST/ACS, GTC/HiPERCAM, and INT/IO:O, reaching a surface brightness limit of 30.4 mag/arcsec² (3σ, 10''×10'').
• Used advanced data reduction techniques including dithering patterns, bias and flat-field correction with a two-step masking process to preserve low-surface-brightness light.
• Applied NoiseChisel and bootstrapping to model and subtract sky background and correct for gradients in the images.
• Generated surface brightness profiles in g and r bands from 35 to 80 arcsec, measuring ellipticity and position angle to assess structural symmetry.
• Analyzed globular cluster distribution to detect extended or anisotropic patterns indicative of tidal stripping.
• Incorporated rotation data from Lewis et al. (2020) to estimate a revised dynamical mass, accounting for rotational support.

Experimental results

Research questions

• RQ1 Are there signs of tidal stripping, such as tidal tails or distortions, in the outer regions of NGC 1052-DF2?
• RQ2 Does the distribution of globular clusters suggest a past interaction or tidal disruption?
• RQ3 Is the surface brightness profile of NGC 1052-DF2 consistent with a disk-like structure in its outer regions?
• RQ4 What is the revised dynamical mass of NGC 1052-DF2 when rotational support is included?
• RQ5 Is NGC 1052-DF2 gravitationally bound to NGC 1052 or NGC 1042, and does the lack of tidal features constrain its distance or orbital history?

Key findings

• No tidal features or signs of distortion are detected in NGC 1052-DF2 down to a radial distance of 80 arcsec, three times deeper than previous studies.
• The surface brightness profiles in g and r bands decline exponentially from 35 to 80 arcsec, indicating a disk-like structure.
• The ellipticity and position angle remain constant in the outer regions, supporting a low-inclination disk morphology.
• The galaxy exhibits rotation, consistent with the presence of a disk and supporting a revised dynamical mass estimate 2.6 times higher than in van Dokkum et al. (2018b).
• The revised dark matter-to-stellar mass ratio is 4.5+8.6−3.4 at 20 Mpc (R < 7.6 kpc) or 12.1+23.0−9.1 at 13.5 Mpc (R < 5.1 kpc), placing it within the range of typical galaxies of similar stellar mass.
• The lack of tidal features implies that if NGC 1052-DF2 is associated with NGC 1052, it is likely in its initial infall, as tidal forces would have already disrupted it if it had undergone strong interaction.