APOGEE physical properties of globular cluster tidal tails

TL;DR

This work tests whether globular cluster tidal-tail properties reflect their formation environment (in situ vs accreted in dark-matter halos with varying density profiles) by exploiting APOGEE DR17 data and an APOGEE-based cluster catalog. It compiles a large sample of tidal-tail member stars across 17 Milky Way GCs, computing the tail width $w$ and dispersions in $V_{LOS}$, $V_{Tan}$, and $L_z$ along the tail, with uncertainties from Monte Carlo realizations. The key result is a near identity relation between $\sigma_{V_{LOS}}$ and $\sigma_{V_{Tan}}$, in broad agreement with predictions for different formation scenarios, while $\sigma_{L_z}$ and $w$ show milder or no clear discriminants; when mapped to MW accretion groups, tails can be kinematically cold or hot across all groups, suggesting GC formation in a variety of DM halos. Overall, the $\sigma_{V_{LOS}}$–$\sigma_{V_{Tan}}$ plane provides a robust observational discriminator for GC origins, supporting the notion that globular clusters can form in galaxies with diverse dark matter halo properties.

Abstract

A recent model prediction claimed that exists a correlation between the formation scenarios of globular clusters, i.e., whether they formed in situ, or in dark matter halos that were accreted into the Milky way, with some properties of their tidal tails, particularly, their widths ($w$), their dispersion in the z-component of the angular momentum ($σ$$_{\rm L_z}$ ), and in the line-of-sight ($σ$$_{\rm V_{LOS}}$) and tangential ($σ$$_{\rm V_{Tan}}$) velocities. I exploited the APOGEE DR17 data base and selected highly confident tidal tails members of 17 Milky Way globular clusters, for which the above four properties were computed for the first time. From all possible paired property combinations, I found that $σ$$_{\rm V_{LOS}}$ and $σ$$_{\rm V_{Tan}}$ resulted to be highly correlated, nearly to the identity relationship. This observation-based correlation resulted to be in an overall very good agreement with that arising from the aforementioned predictions. Additionally, when the four analyzed properties are linked to the accretion groups of the Milky way to which the globular clusters are meant to be associated, I found kinematically cold and hot tidal tails pertaining to globular clusters distributed in all the considered accretion groups. This outcome could be an evidence that globular clusters form in galaxies within a wide variety of dark matter halos, with different masses and profiles.

Figures (7)

• Figure 1: log $g$ vs. $T_{\rm eff}$ plane with all the stars retrieved from the APOGEE DR17 data base (see text for details).
• Figure 2: Spatial diatribution in the ($\phi_1$,$\phi_2$) plane piatti2025b of selected tidal tails stars of NGC 5139.
• Figure 3: V$_{\rm LOS}$ (km/s), V$_{\rm Tan}$ (km/s), and L$_{\rm z}$ (km/s kpc) as a function of $\phi_1$ for selected tidal tails stars of NGC 5139 drawn with black dots. The orange line is the best-fitted polynomial.
• Figure 4: Correlation between different globular cluster's tidal tails properties using information of Table \ref{['tab2a']}.
• Figure 5: Same as Figure \ref{['fig4']} with the predictions from malhanetal2021 and malhanetal2021, superimposed. Different colors refers to globular clusters formed in situ (magenta), in 10$^8$$\hbox{M$_\odot$}$ and 10$^9$$\hbox{M$_\odot$}$ cored profiles (blue and yellow, respectively), and in 10$^8$$\hbox{M$_\odot$}$ and 10$^9$$\hbox{M$_\odot$}$ cuspy profiles (orange and red, respectively).