Measuring the X-shaped structures in edge-on galaxies

Abstract

We present a detailed photometric study of a sample of 22 edge-on galaxies with clearly visible X-shaped structures. We propose a novel method to derive geometrical parameters of these features, along with the parameters of their host galaxies based on the multi-component photometric decomposition of galactic images. To include the X-shaped structure into our photometric model, we use the IMFIT package, in which we implement a new component describing the X-shaped structure. This method is applied for a sample of galaxies with available SDSS and Spitzer IRAC 3.6 µm observations. In order to explain our results, we perform realistic N -body simulations of a Milky Way-type galaxy and compare the observed and the model X-shaped structures. Our main conclusions are as follows: (1) galaxies with strong Xshaped structures reside in approximately the same local environments as field galaxies; (2) the characteristic size of the X-shaped structures is about 2/3 of the bar size; (3) there is a correlation between the X-shaped structure size and its observed flatness: the larger structures are more flattened; (4) our N -body simulations qualitatively confirm the observational results and support the bar-driven scenario for the X-shaped structure formation.

What determines the flatness of X-shaped structures in edge-on galaxies?

“…They are inherent in high surface brightness galaxies falling within the range 1 µ 3 (see de Blok & McGaugh 1997). As to the X-structures, we find them, as a rule, in bright galaxies Savchenko et al 2017). The rotation curves of the models with the contributions of individual subsystems are shown in Fig.…”

“…Whatever is the formation mechanism of B/PS bulges, there are no strong differences in the resulting end-stage structures. This conclusion can be particularly applied to X-structures, which look very symmetrical in edge-on galaxies (Ciambur & Graham 2016;Savchenko et al 2017). From an observational point of view, X-structures are characterised by two parameters: an opening angle (an angle between the ray and the major axis of the galaxy) and the length of rays.…”

“…For real galaxies the length of X-structure rays is defined as the distance measured along the ray from the centre to the specific isophote. Magnitude of this isophote is determined from the background intensity and its variation (Savchenko et al 2017). Such a threshold does not exist in modelled galaxies.…”

Structural and photometric properties of barred galaxies from the Auriga cosmological simulations

“…Several methods to measure the B/P strength (or B/P scaleheight) and size have been proposed, not necessarily from edge-on unsharp-masked images (e.g. Erwin & Debattista 2013, Fragkoudi et al 2015, Ciambur & Graham 2016, Savchenko et al 2017). The method followed in this paper is based on Laurikainen & Salo (2017).…”

The haloes and environments of nearby galaxies (HERON) – II. The outer structure of edge-on galaxies

“…Edge-on galaxies are unique targets in the sense that they allow us to directly study their vertical structure without contamination from unknown inclinations (van der Kruit & Searle 1981a; Barteldrees & Dettmar 1994;de Grijs & van der Kruit 1996;Bizyaev & Mitronova 2002;Mosenkov et al 2010;Bizyaev et al 2014) and to uniquely decompose them into different structural components such as thin E-mail: aleksandr.mosenkov@tdtu.edu.vn truncations Kregel et al 2002;Comerón et al 2012;Martínez-Lombilla et al 2019), disc flaring (Comerón et al 2011c;López-Corredoira & Molgó 2014), X-shaped or boxy structure of a bar (Bureau et al 2006;Savchenko et al 2017). The disc flattening, which can be measured in the case of the edge-on view , is related to the ratio of dark-matter halo to the total galaxy mass (Zasov et al 2002;Mosenkov et al 2010) and the minor-merger history (Read et al 2008).…”