S ⁵: The Orbital and Chemical Properties of One Dozen Stellar Streams

Abstract

We report the kinematic, orbital, and chemical properties of 12 stellar streams with no evident progenitors using line-of-sight velocities and metallicities from the Southern Stellar Stream Spectroscopic Survey (S 5), proper motions from Gaia EDR3, and distances derived from distance tracers or the literature. This data set provides the largest homogeneously analyzed set of streams with full 6D kinematics and metallicities. All streams have heliocentric distances between ∼10 and 50 kpc. The velocity and metallicity dispersions show that half of the stream progenitors were disrupted dwarf galaxies (DGs), while the other half originated from disrupted globular clusters (GCs), hereafter referred to as DG and GC streams. Based on the mean metallicities of the streams and the mass–metallicity relation, the luminosities of the progenitors of the DG streams range between those of Carina and Ursa Major I (−9.5 ≲ M V ≲ −5.5). Four of the six GC streams have mean metallicities of [Fe/H] < −2, more metal poor than typical Milky Way (MW) GCs at similar distances. Interestingly, the 300S and Jet GC streams are the only streams on retrograde orbits in our dozen-stream sample. Finally, we compare the orbital properties of the streams with known DGs and GCs in the MW, finding several possible associations. Some streams appear to have been accreted with the recently discovered Gaia–Enceladus–Sausage system, and others suggest that GCs were formed in and accreted together with the progenitors of DG streams whose stellar masses are similar to those of Draco to Carina (∼105–106 M ⊙).

The Complexity of the Cetus Stream Unveiled from the Fusion of STREAMFINDER and StarGO

“…The Southern Stellar Stream Spectroscopy Survey (S5; Li et al 2019) reported observations of 25 Palca members in the field of the ATLAS-Aliqa-Uma (AAU) stream (Li et al 2021), which overlaps Palca on the sky but with a perpendicular stream track. Most of the Palca members near AAU have kinematics consistent with the Cetus model (Li et al 2022), as will be shown in detail in this study. This confirmation encourages us to search for more Cetus-Palca members in the southern sky.…”

“…The Palca stream has a fairly large width, and extends over 60°, almost reaching the edge of the DES survey at δ = −60°. The potential connection between the Palca and Cetus streams was already discussed by Chang et al (2020) and Li et al (2022). Using the 24 Palca members with radial velocity measurements from S5 (cyan diamonds in Figure 3) in the field of AAU (Li et al 2021), we apply the technique described in Section 4.1 to quantify the confidence of their association.…”

“…As shown by Li et al (2022), the AAU and Palca streams overlap each other in the (L z , E) space, with a slight difference in the longitudinal angle of orbital poles (i.e., f). This is consistent with this study, where most of the AAU realizations (maroon right-pointing triangles) are not mapped in the zoomin Cetus region in Figure 2(c).…”

“…Note that this is one possible scenario for the origin of EriPhe, although other scenarios are also discussed in Li et al (2016) and Donlon et al (2020), which is before the discovery of the southern Cetus stream. For the Willka Yaku stream, we take the distance estimate (d = 36.3 kpc), and radial velocity measurements of its nine members from Li et al (2022). The resulting confidence  = 13% is similar to that of the Palca stream.…”

“…In parallel, the library of stellar debris is continuously increasing, including streams of globular cluster origins, detected based on their coherence in phase space (see, e.g., Price-Whelan & Bonaca 2018;Bonaca et al 2019;Ibata et al 2019bIbata et al , 2021Li et al 2022), and substructures of dwarf galaxy origins, identified from their clustering signatures in dynamical space (see, e.g., Helmi et al 1999Helmi et al , 2018Belokurov et al 2018;Myeong et al 2018aMyeong et al , 2019Koppelman et al 2019;Matsuno et al 2019). A list of studies have shown that these disrupted stellar systems, together with globular clusters and chemically peculiar stars with halo orbits, can be grouped based on similar orbital properties, suggestive of their common origins (Myeong et al 2018b(Myeong et al , 2019Roederer et al 2018;Massari et al 2019;Naidu et al 2020;Yuan et al 2020b;Bonaca et al 2021;Gudin et al 2021;Li et al 2022;Limberg et al 2021;Shank et al 2022). Detailed abundance studies for these stellar debris have been made possible by HRspectroscopic follow-up studies (Ji et al 2020;Aguado et al 2021aAguado et al , 2021bGull et al 2021;Matsuno et al 2021), as well as by HR-spectroscopic surveys, such as the GALAH survey (Buder et al 2022;Simpson et al 2021).…”