The baryonic Tully–Fisher relation cares about the galaxy sample

Abstract

The Baryonic Tully-Fisher relation (BTFR) is a clear manifestation of the underlying physics of galaxy formation. As such, it is used to constrain and test galaxy formation and evolution models. Of particular interest, apart from the slope of the relation, is its intrinsic scatter. In this paper, we use the eagle simulation to study the dependence of the BTFR on the size of the simulated galaxy sample. The huge number of datapoint available in the simulation is indeed not available with current observations. Observational studies that computed the BTFR used various (small) size samples with the only obligation to have galaxies spanning over a large range of masses and rotation rates. Accordingly, to compare observational and theoretical results, we build a large number of various size datasets using the same criterion and derive the BTFR for all of them. Unmistakably, their is an effect of the number of galaxies used to derive the relation. The smaller the number, the larger the standard deviation around the average slope and intrinsic scatter of a given size sample of galaxies. This observation allows us to alleviate the tensions between observational measurements and ΛCDM predictions. Namely, the size of the observational samples adds up to the complexity in comparing observed and simulated relations to discredit or confirm ΛCDM. Similarly, samples, even large, that do not reflect the galaxy distribution give on average biased results. Large size samples reproducing the underlying distribution of galaxies constitute a supplementary necessity to compare efficiently observations and simulations.

The multiwavelength Tully–Fisher relation with spatially resolved H i kinematics

“…As was shown by Sorce & Guo (2016), the size of the sample may have a significant impact on the scatter of the TFr. Therefore, it is necessary to point out that the limited size of our sample might contribute to the uncertainties in the slope, scatter and zero point of the TFrs.…”

A Break in Spiral Galaxy Scaling Relations at the Upper Limit of Galaxy Mass

“…This baryonic Tully-Fisher relation (BTFR) demonstrates a strong connection between the cold baryonic (stars + cold atomic and molecular gas) and dark matter content of spiral galaxies. The slope and scatter of the BTFR depend in detail on the prescription used to estimate the mass-to-light ratio of stars and which galaxy samples are selected (McGaugh & Schombert 2015;Sorce & Guo 2016;Ponomareva et al 2018). Evidence for a flatter ITFR slope is found for high-redshift galaxies (Christensen & Hjorth 2017).…”

An accurate measurement of the baryonic Tully-Fisher relation with heavily gas-dominated ALFALFA galaxies

“…Once again, it is difficult to explain the relation's tightness theoretically, given that several sources of scatter for the relation are expected in ΛCDM (scatter in halo concentrations and spins, scatter in galactic baryon fractions, etc.). In response, a large number of theoretical works are devoted to modeling the BTFR as realistically as possible, and assessing how well the relation expected in ΛCDM can reproduce the observed one Desmond 2012;Desmond & Wechsler 2015;Sorce & Guo 2016;Di Cintio & Lelli 2016;Sales et al 2016, to name a few). Other works argue instead that the observed properties of the BTFR disfavor altogether a cosmological theory in which DM is the dominant mass component, and rather point to a modification of the law of gravity (e.g., MOND ;Milgrom 1983a).…”