Isolated galaxies vs. void galaxies


In general, isolated galaxies and void galaxies are different objects due to different selection criteria: isolated galaxies can be found in different type of global environment even in the loose clusters (or its borders) while the void’s population by definition is located in the underdense global environments in the regions that almost free of galaxies. Therefore the isolated galaxies are “normal” galaxies but the void’s population is fainter and bluer than isolated galaxies and mostly consists of dwarf galaxies. However in our work (Elyiv et al. 2013) we showed that the void’s population could be a subsample of isolated galaxies.

Distribution of 48 dwarf galaxies in the nearby (D < 40 Mpc) voids by absolute magnitude MB and the bedding depth under the surface of hypervoid. Squares trace the objects common with the galaxies from the Catalog of Nearby Isolated Galaxies (Karachentsev et al. 2011), triangles denote the late-type dwarf galaxies from the list of (Karachentseva, Karachentsev & Sharina, 2010).
Fig.7. (void_m_r) Distribution of 48 dwarf galaxies in the nearby (D < 40 Mpc) voids by absolute magnitude MB and the bedding depth under the surface of hypervoid. Squares trace the objects common with the galaxies from the Catalog of Nearby Isolated Galaxies (Karachentsev et al. 2011), triangles denote the late-type dwarf galaxies from the list of (Karachentseva, Karachentsev & Sharina, 2010). (Fig. 6 from Elyiv et al., 2013).

Elyiv et al. (2013) mapped the Local Voids within distance of 40 Mpc. The total volume of these voids incorporates about 30% of the Local Universe. We showed that only 68 from  2906  (2%) of dwarf galaxies are located in cosmic voids.  These galaxies are characterized by late morphological types (85% are Ir, Im, BCD, Sm), absolute magnitudes MB ranging from −13.0 to −16.7, moderate star formation rates (log SSFR ∼ −10 M⊙ yr−1L−1 ⊙ ) and gas reserves per luminosity unit twice to three times larger than in the other dwarf galaxies located in normal environments. The dwarf population of the voids shows a certain tendency to sit shallow near the surfaces of cosmic voids (fig. 7). The paper presents the list of voids and the list of void’s galaxies.