The M 101 group complex: new dwarf galaxy candidates and spatial structure

Abstract

Context. The fine details of the large-scale structure in the local universe provide important empirical benchmarks for testing cosmological models of structure formation. Dwarf galaxies are key object for such studies. Aims. Enlarge the sample of known dwarf galaxies in the local universe. We performed a search for faint, unresolved low-surface brightness dwarf galaxies in the M 101 group complex, including the region around the major spiral galaxies M 101, M 51, and M 63 lying at a distance 7.0, 8.6, and 9.0 Mpc, respectively. The new dwarf galaxy sample can be used in a first step to test for significant substructure in the 2D-distribution and in a second step to study the spatial distribution of the galaxy complex. Methods. Using filtering algorithms we surveyed 330 square degrees of imaging data obtained from the Sloan Digital Sky Survey. The images were visually inspected. The spatial distribution of known galaxies and candidates was analyzed transforming the system into a M 101 eigenframe, using the geometrical alignment of the group. Results. We discovered 15 new dwarf galaxies and carried out surface photometry in the g and r bands. The similarity of the photometric properties of these dwarfs to those of Local Group dwarfs suggest membership to the M 101 group complex. The sky distribution of the candidates follows the thin planar structure outlined by the known members of the three subgroups. The ∼ 3 Mpc long filamentary structure has a rms thickness of 67 kpc. The planar structure of the embedded M 101 subgroup is even thinner, with rms = 46 kpc. The formation of this structure might be due to the expansion of the Local Void to which it borders. Other implications are discussed as well. Conclusions. We show the viability of SDSS data to extend the sample of dwarfs in the local universe and test cosmological models on small scales.

Origin of the Local Group satellite planes

“…The satellites of M81 also appear to lie in a flattened distribution, though their kinematics are not currently known (Chiboucas et al 2013). These discoveries may be related to a vast plane of dwarf galaxies recently found near M101 (Müller et al 2017). This is not a satellite galaxy plane as it extends over 3 Mpc.…”

The origin of lopsided satellite galaxy distribution in galaxy pairs

“…Most of these studies have explicitly focused on the anisotropy of satellite distributions of field galaxies (as opposed to galaxies in clusters or pair of galaxies). Yet recently, the anisotropic distribution of the satellites of galaxies pairs has been brought to attention, which has been seen in the Local Group as well as in the Centaurus group (Müller et al (2015), Müller et al (2017)).…”

DGSAT: Dwarf Galaxy Survey with Amateur Telescopes

“…If these are tidal dwarfs, then they further constrain the statistics of galaxy encounters and thus cosmological models. Less sensitive and less complete studies of nearby galaxies outside the Local Group (LG) also suggest highly flattened distributions, such as those around M 81, NGC3109, Cen A, and M 83 (Bellazzini et al 2013;Chiboucas et al 2013;Ibata et al 2014;Müller et al 2015Müller et al , 2016Müller et al , 2017bTully et al 2015), but -given the deep implications for fundamental physics and recent less conclusive results (e.g. Blauensteiner et al 2017;Müller et al 2017a) -more observations are mandatory to obtain a clearer picture.…”