The Milky Way and other spiral galaxies

Abstract

Abstract.Cosmologists have often considered the Milky Way as a typical spiral galaxy, and its properties have considerably influenced the current scheme of galaxy formation. Here we compare the general properties of the Milky Way disk and halo with those of galaxies selected from the SDSS. Assuming the recent measurements of its circular velocity results in the Milky Way being offset by ∼2 from the fundamental scaling relations. On the basis of their location in the (M K , R d , V f lat ) volume, the fraction of SDSS spirals like the MilkyWay is only 1.2% in sharp contrast with M31, which appears to be quite typical.Comparison of the Milky Way with M31 and with other spirals is also discussed to investigate whether or not there is a fundamental discrepancy between their mass assembly histories. Possibly the Milky Way is one of the very few local galaxies that could be a direct descendant of very distant, z = 2-3 galaxies, thanks to its quiescent history since thick disk formation.

The Galaxy in Context: Structural, Kinematic, and Integrated Properties

“…3 that the Milky Way is a very luminous, reddish galaxy, somewhat at odds with its traditional classification as an Sb−Sbc galaxy. This has raised questions in the past about where it falls on the Tully-Fisher relation (e.g., Malhotra et al 1996;Hammer et al 2012). But this high luminosity is consistent with its high circular velocity (∼ 240 km s −1 ) discussed in §6.4.…”

Weighing the local dark matter with RAVE red clump stars

“…In fact, combining the circular velocity from the BeSSeL project V c ∼ 240 km s −1 (McMillan 2011; Bobylev & Bajkova 2013;Reid et al 2014), with a nearly flat rotation curve at the Sun position, and a flattening of 0.8, leads to our estimated value of the local dark matter density, in accordance with Piffl et al (2014b). This value of the circular velocity makes the Milky Way a clear outlier from the Tully-Fisher relation Hammer et al 2012).…”