A correlation between the number of satellites and the bulge-to-total baryonic mass ratio extending beyond the Local Group

Abstract

Recent observations of the fields surrounding a few Milky-Way-like galaxies in the local Universe have become deep enough to enable investigations of the predictions of the standard ΛCDM cosmological model down to small scales outside the Local Group. Motivated by an observed correlation between the number of dwarf satellites (N sat ) and the bulge-to-total baryonic mass ratios (B/T) of the three main galaxies in the Local Group, i.e. the Milky Way, Andromeda, and Triangulum (M33), we use published data of three well-studied galaxies outside the Local Group, namely M81, Centaurus A, and M101, and their confirmed satellites, and we find a strong and significant correlation between N sat and B/T. This presents itself in contradiction with the hitherto published results from cosmological simulations reporting an absence of a correlation between N sat and B/T in the ΛCDM model. We conclude that, based on the current data, the N sat vs. B/T correlation is no longer a property confined to only the Local Group.

Can cosmological simulations capture the diverse satellite populations of observed Milky Way analogues?

“…6 we investigate the relation between the number of satellites and the bulge-to-total ratios of the host galaxies. Such a relation was suggested by Javanmardi & Kroupa (2020), who found a very strong correlation between these two parameters (with a Spearman coefficient of 0.9), although on a very small sample of galaxies. For our comparison, we include four Milky Way-mass analogues from the Local Volume sample of Carlsten et al (2020a) with complete samples of bright ( < −9) satellites within 150 kpc of their hosts, and with measured / values (Kormendy et al 2010;Fisher & Drory 2011), to which we add similar data for the Milky Way and M31.…”

“…• As already noted, a number of possible scaling relations between the abundance of surviving satellites and the properties of their hosts galaxies have been examined, including correlations with the host total mass (Trentham & Tully 2009;Starkenburg et al 2013;Fattahi et al 2016;Garrison-Kimmel et al 2019), stellar mass or magnitude (Geha et al 2017), or even with the bulge-to-total ratio of the host (Javanmardi & Kroupa 2020). The local environment in which the host galaxy lives is also believed to play a role and a relation between the number of satellites and tidal index has (Θ 5 ) been investigated (Karachentsev et al 2013;Bennet et al 2019).…”

Abundance of dwarf galaxies around low-mass spiral galaxies in the Local Volume

“…This scatter seems to be larger than what is expected from the concordance model (but see also Carlsten et al 2020 for a different view). On the other hand, there seems to be a correlation between the number of satellites and the bulge-to-disk ratio of the host galaxies, which is again unexpected in ΛCDM (Javanmardi et al 2019;Javanmardi & Kroupa 2020). All these findings require more observations of different environments.…”

The Formation of Exponential Disk Galaxies in MOND

“…Note that this means that there would be fewer mergers than in ΛCDM at intermediate redshifts, and in those rare mergers and much more numerous encounters between spirals, tidal dwarf galaxies would be formed and survive more easily than in ΛCDM (Sanders 1998). This may indeed plausibly be the source of satellite galaxies and their observed phasespace correlation (Banik et al 2018b;Bílek et al 2018;Okazaki & Taniguchi 2000;Javanmardi & Kroupa 2020) At this point we want to focus on one important difference between simulations done in ΛCDM and MOND. Simulations done in the ΛCDM framework depend strongly on the feedback processes that are implemented in the code that is used, which are assumed by the community to be very uncertain.…”