Probing the dark matter haloes of external galaxies with stellar streams

Abstract: Stellar streams have proven to be powerful tools for measuring the Milky Way's gravitational potential and hence its dark matter halo. In the coming years, Vera Rubin, Euclid, ARRAKIHS, and NGRST will uncover a plethora of streams around external galaxies. Although great in number, observations of these distant streams will often be limited to only the on-sky position of the stream. In this work, we explore how well we will be able to measure the dark matter haloes of these galaxies by fitting simplified mock streams with a variety of intrinsic and orbital properties in a range of data availability scenarios. We find that streams with multiple wraps around their host galaxy can constrain the overall radial profile and scale radius of the potential without radial velocities. In many other cases, a single radial velocity measurement often provides a significant boost to constraining power for the radial profile, scale radius, and enclosed mass of the dark matter halo. Given the wealth of data expected soon, this suggests that we will be able to measure the dark matter haloes of a statistically significant sample of galaxies with stellar streams in the coming years.

• The paper demonstrates that stellar streams serve as effective probes to constrain dark matter halo properties like mass, scale radius, and radial profile.
• The study uses mock stream simulations under different potential models, showing that even one radial velocity measurement substantially reduces parameter degeneracies.
• Long, multi-wrapped, and edge-on streams yield more robust constraints, highlighting the role of stream morphology in mapping external dark matter halos.

Probing Dark Matter Haloes of External Galaxies Using Stellar Streams

Stellar streams, formed as satellite galaxies or globular clusters are disrupted by a host galaxy's gravitational potential, offer a promising means to probe the intricate architecture of dark matter (DM) haloes in galaxies beyond the Milky Way (MW). These streams, composed of stars that trace the orbit of the disrupted satellite, provide an opportunity to infer detailed properties of a host galaxy's DM halo. Motivated by the abundance of upcoming data from surveys such as Vera Rubin, Euclid, ARRAKIHS, and NGRST, which are set to uncover numerous streams surrounding external galaxies, the paper investigates the extent to which these stellar streams can inform us about the DM halo parameters of their host galaxies, even in the absence of full dynamical information.

Several models of DM, including Lambda Cold Dark Matter ($\Lambda$CDM), self-interacting dark matter (SIDM), and warm dark matter (WDM), predict different DM halo properties ranging from density distributions to the number and nature of subhaloes. The nature of DM—whether it is prone to self-interactions or consists of fuzzy or warm particles—can significantly alter the halo structure and subhalo distribution. Thus, studying the baryonic constructs such as stellar streams within different galaxies can potentially discriminate between these models.

The study utilizes mock streams, assumed to approximate orbits, within varying galactic potentials to evaluate how effectively different aspects of DM haloes can be constrained. These include NFW-only DM potentials, composite galaxy-laden potentials with baryonic components, and simplified power-law potentials governed by circular velocity. Derived constraints on parameters such as the DM mass, the scale radius, and the radial profile of the potential are assessed under scenarios of differing data availability—most crucially, whether stream tracks alone or combined with radial velocity information, are employed.

The research affirms the hypothesis that longer streams with multiple wraps around their hosts yield superior constraints on the overall radial profile of the host galaxy's potential, with the effect amplified with additional data dimensionality. Notably, orbits that are more edge-on, have apocenters beyond the NFW scale radius, or possess moderate to low eccentricities, tend to be more informative about the halo's mass profile and scale. These intrinsic characteristics—stream length, inclination, distance, and eccentricity—play critical roles as modulating factors for maximizing the potential information extracted from streams.

Importantly, while degeneracies among parameters such as halo mass, scale radius, and progenitor velocities limit some constraints, introducing even a single radial velocity measurement along the stream markedly refines constraints and alleviates these ambiguities. This acknowledgment aligns with and extends prior findings, suggesting that even partial dynamical data can significantly recover halo properties.

Future measurements of stellar streams in distant galaxies—coupled with radial velocity data gleaned possibly from capabilities beyond forthcoming surveys—promise significant enhancements in our understanding of DM halo characteristics. These enhancements hold dual implications: refining the parameters of dark matter models themselves and mapping the shape and extent of external galactic haloes with increasing precision.

In conclusion, this work lays pivotal groundwork for the application of stellar streams as probes of dark matter potential, emphasizing their utility in dark matter research and galactic evolution studies. As the astronomical community stands on the threshold of a new epoch with substantial survey data incoming, such analyses will become instrumental in elucidating the dark scaffolding that underpins galaxy formation and structure across the observable universe.