The predicted luminous satellite populations around SMC- and LMC-mass galaxies – a missing satellite problem around the LMC?

Abstract

Recent discovery of many dwarf satellite galaxies in the direction of the Small and Large Magellanic Clouds (SMC and LMC) provokes questions of their origins, and what they can reveal about galaxy evolution theory. Here, we predict the satellite stellar mass function of Magellanic Cloud-mass host galaxies using abundance matching and reionization models applied to the Caterpillar simulations. Specifically focusing on the volume within 50 kpc of the LMC, we predict a mean of 4-8 satellites with stellar mass M * > 10 4 M , and 3-4 satellites with 80 < M * ≤ 3000 M . Surprisingly, all 12 currently known satellite candidates have stellar masses of 80 < M * ≤ 3000 M . Reconciling the dearth of large satellites and profusion of small satellites is challenging and may require a combination of a major modification of the M * − M halo relationship (steep, but with an abrupt flattening at 10 3 M ), late reionization for the Local Group (z reion 9 preferred), and/or strong tidal stripping. We can more robustly predict that ∼ 53% of satellites within this volume were accreted together with the LMC and SMC, and ∼ 47% were only ever Milky Way satellites. Observing satellites of isolated LMC-sized field galaxies is essential to placing the LMC in context, and to better constrain the M * − M halo relationship. Modeling known LMC-sized galaxies within 8 Mpc, we predict 1-6 (2-12) satellites with M * > 10 5 M (M * > 10 4 M ) within the virial volume of each, and 1-3 (1-7) within a single 1.5• diameter field of view, making their discovery likely.

The Orbital Histories of Magellanic Satellites Using Gaia DR2 Proper Motions

“…Our findings that a total of 3-6 of the 18 galaxies analyzed in this work are identified as Magellanic satellites are consistent with the low end of cosmological expectations (e.g. Sales et al 2013Sales et al , 2017Deason et al 2015;Dooley et al 2017;Jahn et al 2019). The recent findings of Nadler et al (2019) are most applicable to our analysis as they account for the survey footprints in which our sample of UFDs were discovered.…”

“…Recent studies have quantified predictions for the populations of satellites expected around the LMC and M33, finding that each should host approximately 5-10 ultra-arXiv:2001.01746v2 [astro-ph.GA] 2 Mar 2020 faint dwarf galaxies (UFDs) with M * ≈ 10 2 − 10 5 M (e.g. Sales et al 2011Sales et al , 2013Dooley et al 2017;Patel et al 2018;Jahn et al 2019) at minimum.…”

“…Similarly, existing predictions for the total number of satellites hosted by the LMC and SMC today, in a ΛCDM paradigm, also omit the dynamical significance of the Clouds' binary dynamics. Dooley et al (2017) quantified the number of satellites expected around both the LMC and SMC under the assumption that each of the Clouds can be treated as an isolated halo. However, this assumption implies that the SMC continued to accrete substructures up until z = 0, whereas if it were captured > 5 Gyr ago by the LMC, its mass growth may have been truncated at the time of capture and some of those SMC satellites might have been destroyed by the LMC.…”

“…However, this assumption implies that the SMC continued to accrete substructures up until z = 0, whereas if it were captured > 5 Gyr ago by the LMC, its mass growth may have been truncated at the time of capture and some of those SMC satellites might have been destroyed by the LMC. Thus, while the predictions in Dooley et al (2017) are helpful benchmarks, they may overestimate the number and longevity of Magellanic satellites. Jethwa et al (2016) do consider the combined gravitational influence of the MW, LMC, and SMC to calculate the probabilities that the Dark Energy Survey UFDs belong to the LMC and SMC.…”

The Imprint of Cosmic Reionization on the Luminosity Function of Galaxies

“…Recently, Dooley et al (2017) made use of abundance matching to infer the total satellite population around LMC-mass Figure 9. Cumulative luminosity function of satellites in LMC-mass hosts predicted by various GALFORM models.…”