[Paper Review] Fundamental properties of the dark and the luminous matter from Low Surface Brightness discs

Chiara Di Paolo, P. Salucci|arXiv (Cornell University)|May 7, 2020

Galaxies: Formation, Evolution, Phenomena254 references4 citations

TL;DR

This review investigates the fundamental properties of dark matter (DM) and luminous matter (LM) in low surface brightness (LSB) galaxies through detailed mass modeling of individual and stacked rotation curves. It reveals a tight, physically meaningful relationship between gravitational acceleration (g) and baryonic acceleration (gb), dependent on galactic radius and disk scale length, challenging the ΛCDM paradigm and suggesting a non-gravitational interaction between LM and DM.

ABSTRACT

Dark matter (DM) is one of the biggest mystery in the Universe. In this review, after a brief discussion of the DM evidences and the main proposed candidates and scenarios for the DM phenomenon, we focus on recent results on rotating disc galaxies giving a special attention to the Low Surface Brightness (LSB) galaxies. The main observational properties related to the baryonic matter in LSBs, investigated over the last decades, are briefly recalled. Next, the LSBs are analysed by means of the mass modelling of their rotation curves both individually and stacked. The latter analysis, via the Universal Rotation Curve (URC) method, results really powerful in giving a global/universal description of the disc galaxies properties. We show the presence in LSBs of scaling relations between the galactic structural properties and we compare them with those of galaxies of different morphologies. The findings confirm, for all disc systems, a strong entanglement between the luminous matter (LM) and the DM. Moreover, we report how in LSBs the tight relationship between their radial gravitational acceleration $g$ and their baryonic component $g_b$ results to also depend on the galactic radius at which the former have been measured. Finally, LSB galaxies strongly challenge the $Λ$CDM scenario with the relative collisionless dark particle and, alongside with the non-detection of the latter, contribute to guide us towards a new scenario for the DM phenomenon.

Motivation & Objective

• To analyze the structural and dynamical properties of low surface brightness (LSB) galaxies as probes of dark matter (DM) and luminous matter (LM) interplay.
• To test the universality of rotation curve (RC) relationships in LSBs using individual and stacked RC modeling.
• To investigate whether the observed g-gb relation in LSBs implies a direct interaction between luminous and dark matter beyond gravity.
• To challenge the ΛCDM scenario by highlighting discrepancies in LSB galaxies, especially given the non-detection of WIMPs.
• To guide future observational strategies for probing the nature of dark matter through kinematic and structural studies of LSBs.

Proposed method

• Utilizes individual and stacked rotation curve (RC) modeling of LSB galaxies to derive mass distributions and test universal relationships.
• Applies the Universal Rotation Curve (URC) method to extract global, statistically robust properties of LSB systems.
• Employs a normalized radius x ≡ r/Ropt to quantify the dependence of gravitational acceleration g on baryonic acceleration gb and galactic structure.
• Analyzes the intrinsic scatter in the g-gb relation to assess the physical significance of the correlation and its dependence on disk scale length.
• Compares observed scaling relations in LSBs with those in normal spirals to identify systematic differences.
• Considers the role of galactic compactness (C⋆) and halo mass range (5 dex) in shaping DM and LM distributions.

Experimental results

Research questions

• RQ1 Does the g-gb relation in LSB galaxies depend on galactic structural parameters such as disk scale length and radius of measurement?
• RQ2 To what extent do the observed scaling relations in LSB galaxies differ from those in normal spiral galaxies, and what does this imply for universal DM and LM correlations?
• RQ3 Can the tightness of the g-gb relation in LSBs be explained solely by ΛCDM, or does it require a non-gravitational interaction between luminous and dark matter?
• RQ4 How do the kinematic and structural properties of giant LSBs (with HSB discs) differ from dwarf LSBs, and what does this reveal about halo mass evolution?
• RQ5 What observational strategies can most effectively probe the existence of a direct LM-DM interaction in LSB galaxies?

Key findings

• A tight relationship between gravitational acceleration g and baryonic acceleration gb is observed in LSB galaxies, with a significantly reduced intrinsic scatter when normalized by galactic radius x ≡ r/Ropt.
• The g-gb relation in LSBs depends on the stellar disk length scale and the radius at which accelerations are measured, indicating a deeper physical connection between LM and DM.
• Systematic differences of approximately 0.2 dex exist between structural relations in LSBs and normal spirals, suggesting distinct formation or evolution histories.
• The observed scaling relations in LSBs are comparable in form to those in galaxies of other morphologies, indicating a universal entanglement between luminous and dark matter in disc systems.
• The non-detection of WIMPs, combined with the robust g-gb correlation in LSBs, strongly suggests the need to consider a direct interaction between luminous and dark matter beyond gravity.
• Future high-redshift kinematic observations and improved resolution from ALMA, SKA, WFIRST, and ELT are expected to provide critical evidence on the evolution and nature of DM and LM in LSBs.