Fourteen candidate RR Lyrae star streams in the inner Galaxy (1711.03967v1)

Abstract: We apply the GC3 stream-finding method to RR Lyrae stars (RRLS) in the Catalina survey. We find two RRLS stream candidates at $>4\sigma$ confidence and another 12 at $>3.5\sigma$ confidence over the Galactocentric distance range $4 < D/{\rm kpc} < 26$. Of these, only two are associated with known globular clusters (NGC 1261 and Arp2). The remainder are candidate `orphan' streams, consistent with the idea that globular cluster streams are most visible close to dissolution. Our detections are likely a lower bound on the total number of dissolving globulars in the inner galaxy, since many globulars have few RRLS while only the brightest streams are visible over the Galactic RRLS background, particularly given the current lack of kinematical information. We make all of our candidate streams publicly available and provide a new GALSTREAMS Python library for the footprints of all known streams and overdensities in the Milky Way.

Analyzing RR Lyrae Star Streams in the Inner Galaxy

The paper "Fourteen candidate RR Lyrae star streams in the inner Galaxy" by Cecilia Mateu and colleagues presents an extensive analysis of RR Lyrae stars (RRLS) to identify stellar streams within the inner region of the Milky Way, using the Catalina Sky Survey data. This research utilizes the GC3 stream-finding method, a significant tool in extragalactic astronomy for detecting tidal streams by exploiting the spatial distribution of RRLS in great-circle bands across the sky.

Methodology

The authors employ the GC3 method, formulated on the concept that tidal streams adhere to nearly planar structures within a symmetrical gravitational potential. This approach does not presuppose specific characteristics of the Galactic potential, offering flexibility and applicability across varying data sets. The research focuses on RRLS due to their reliability as standard candles and their presence in diverse Galactic environments excluding the thin disc, which minimizes foreground contamination.

Results

The paper uncovers two high-confidence and twelve tentative stream candidates ranging from 4 to 26 kpc in Galactocentric distance. These streams provide crucial insights into the satellite populations undergoing tidal disruption by the Milky Way's gravitational forces. Notably, only two high-confidence streams correlate with known globular clusters, hinting at the prevalence of "orphan" streams lacking visible progenitor clusters, in alignment with theoretical simulations predicting mass segregation effects and progressive cluster dissolution.

Implications

The findings bolster our understanding of the missing satellites problem (MSP) within the $\Lambda$CDM framework. They suggest that many satellite populations likely expire through tidal disruption, contributing faint stellar streams as vestiges of once bound systems. This aligns with predictions of a significant depletion in satellite numbers, offering a potential resolution to discrepancies observed in satellite counts versus predictions from cosmological models.

Future Directions

Looking forward, enhancements in survey scopes and capabilities, notably kinematic data acquisition from ongoing and future projects such as Gaia, will refine identification of these streams, allowing robust differentiation of genuine tidal tails from background stellar noise. Moreover, these data will aid in unraveling Galactic halo substructures and refining mass distribution models of the Milky Way's dark matter halo.

Conclusion

This paper contributes substantially to our comprehension of Galactic structure dynamics, exposing the latent complexities in satellite evolution and dissolution processes. The research generates a valuable public resource for ongoing and future investigations of the Milky Way's stellar halo, integrated into the galstreams Python package. This serves both as an analytical framework and a repository advancing collaborative research endeavors in galactic astronomy.