Void Galaxies in the Nearby Universe. I. Sample Description
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Mon. Not. R. Astron. Soc. 000, 1–19 (2018) Printed 17 December 2018 (MN LATEX style file v2.2) Void galaxies in the nearby Universe. I. Sample description S.A. Pustilnik,1⋆ A.L. Tepliakova,1 D.I. Makarov1 1 Special Astrophysical Observatory of RAS, Nizhnij Arkhyz, Karachai-Circassia 369167, Russia Accepted 2018 August ??. Received 2018 July 30 ABSTRACT The main goal of this work is to form a large, deep and representative sample of dwarf galaxies residing in voids of the nearby Universe. The formed sample is the basement for the comprehensive mass study of the galaxy content, their evolutionary status, clustering and dynamics with respect to their counterparts residing in more typical, denser regions and for study of void small-scale substructures. We present 25 voids over the entire sky within 25 Mpc from the Local Group. They are defined as groups of lumped empty spheres bounded by ‘luminous’ galaxies with the absolute K-band magnitudes brighter than –22.0. The identified void regions include the Local Void and other known nearby voids. The nearest nine voids occupy a substantial part of the Local Volume. Of the total number of 6792 cataloged galaxies in the considered volume, 1354 objects fall into 25 nearby voids. Of this general void galaxy sample, we separate the sub-sample of ‘inner’ void galaxies, residing deeper in voids, with distances to the nearest luminous galaxy DNN > 2.0 Mpc. The ‘inner’ galaxy sample includes 1088 objects, mostly dwarfs with MB distribution peaked near –15.0 and extending down to –7.5 mag. Of them, 195 fall in the Local Volume (space within R=11 Mpc). We present the general statistical properties of this Nearby Void Galaxy sample and discuss the issues related to the sample content and the prospects of its use. Key words: cosmology: large-scale structure of Universe – galaxies: dwarf – galaxies: evolution – galaxies: formation – galaxies: general – catalogues 1 INTRODUCTION quirements of statistical completeness resulted in the strong bias of the studied void galaxies to the upper part of the Voids as elements of the large scale structure fill ∼70 per luminosity function (LF), e.i., MB ∼−16 to −20. The com- cent of the modern Universe volume and represent its the arXiv:1812.02785v2 [astro-ph.GA] 13 Dec 2018 parison of these most luminous void galaxies reveals only lowest density regions. While the void galaxies comprise relatively weak differences of properties with similar galax- only a small fraction (∼15 per cent) of the whole galaxy ies in the adjacent walls (or denser environments). population, their properties can give the important indica- tions on the processes at the earlier epochs in the Universe. In the recent series of papers we suggested a comple- The study of voids and properties of galaxies residing in mentary approach aimed to study galaxy properties in a them remains one of the actual and important field of extra- nearby Lynx-Cancer void, with the emphasis on the least galactic and cosmological research (van de Weygaert 2016; massive void representatives (Pustilnik & Tepliakova 2011; Aragon-Calvo & Szalay 2013). Pustilnik, Tepliakova & Kniazev 2011a; Pustilnik et al. Massive observational studies of voids are mainly based 2011b; Perepelitsyna et al. 2014; Pustilnik & Martin 2016; on the modern surveys such as SDSS and ALFALFA Pustilnik et al. 2016, 2005). These studies resulted in the (Grogin, Geller 1999; Rojas et al. 2004, 2005; Hoyle et al. firm conclusions on a systematically lower metallicity of 2005, 2015; Patiri et al. 2006; Kreckel et al. 2011, 2012; gas and a higher H i-mass fraction of the void galaxy Pan et al 2012) as well on the earlier surveys (Las Cam- population in comparison to the similar galaxies in denser panas, 2dFGRS, 6dF, CfA). As a matter of fact, the great environments. These results imply that void galaxies in majority of the previous works dealt with distant large voids average evolve significantly slower than their counterparts (D ∼ 80–200 Mpc). The common limit of used spectroscopic in typical groups. Besides, it appeared that the substantial redshift surveys (r . 17.8, or B . 18.5) and the applied re- fraction of the faintest LSB dwarfs in the Lynx-Cancer void (mostly those with MB & −13.5 mag) show the very low O/H, extremely high gas mass fraction and blue ⋆ E-mail: [email protected] (SAP),[email protected] (DIM) colour of stars at the galaxy periphery. These properties c 2018 RAS 2 S.A. Pustilnik, A.L. Tepliakova, D.I. Makarov indicate the atypical young evolutionary status of such LSB voids allows us with the use of the deep wide-field redshift dwarfs (Pustilnik et al. 2010; Chengalur, Pustilnik 2013; surveys (like SDSS, 2dFGRS, ALFALFA) to find and study Pustilnik et al. 2013, 2016; Chengalur, Pustilnik, Egorova many intrinsically faint dwarfs with MB down to –12 mag 2017). and even to –10 mag. Despite the lack of the statistical com- To study the fainter part of void galaxies, one needs pleteness, the understanding of properties of the least mas- first of all, to use the samples of sufficiently close objects. sive void dwarfs can provide us with the important clues on Since the available wide-field spectral surveys of galaxies the origin and evolution of the majority of galaxy popula- have the limiting apparent magnitudes no fainter than (or tion within the major part of the Universe volume occupied close to) Btot = 18.5 – 19 mag, in order to deal with dwarfs by voids. as faint as MB = −13 mag, we need in a galaxy sample with Apart the void galaxy evolution issues (e.g. Hoeft et al. the distance moduli less than ∼ 32 mag, which implies the 2006; Hahn et al. 2006, 2007, 2009), the nearby void sample distances of D < 25 Mpc. should be useful for the study of voids themselves. Accord- Unlike the most of the last decade studies of voids ing to Aragon-Calvo & Szalay (2013), the internal filaments and their galaxies, we limit our task by the separation of of voids with scales of . 2 Mpc are still in the linear regime large ‘simply connected’ ‘empty’ volumes devoid of galax- of mass assembly and therefore reflect the initial mass dis- ∗ ∗ ies brighter than MK = MK + 2. Here MK = -24.0 is the tribution. This, in less extent can relate to the low mass DM characteristic absolute magnitude of the K-band luminosity halos and their dwarfs. We can probe the small-scale struc- function. ture of voids and study its properties only with a denser It is worth to mention that several nearest voids were filling of a void volume with the test particles. Due to the identified by Fairall (1998) and shown in his Atlas. How- known rise of the galaxy LF for lower luminosities (masses), ever, over the past 20 years, the number of known nearby to reach a larger galaxy number density, one needs to go galaxies increased substantially. Therefore it is necessary to deeper for void galaxy selection in their luminosity or mass. fulfill a new analysis of distribution and galaxy population of Another interesting implication of the study of the least nearby voids. Recently, Elyiv et al. (2013) studied the prop- massive objects and their structures in voids is the expected erties of voids in the local Universe (R < 50 Mpc). They sensitivity of filaments, DM halos and their galaxies to the found many empty spheres interconnected into elongated admixture of Warm Dark Matter (WDM), since the presence structures (tunnels). While this work allowed the authors to of the WDM component can wash out the small-scale distur- probe the most rarefied space regions, their original selec- bances and thus limit the existence of the smallest galaxies tion causes significant limitations for void parameters and and their structures (e.g., Angulo, Hahn, Abel 2013). void galaxy sample. Namely, their voids were constructed The rest of the paper is designed as follows. In Sec- with the sample of galaxies delineating voids to be of low tion 2 we describe in detail all main procedures to construct luminosity: MK < −18.4 mag. This limit is 5.6 magnitudes ‘empty’ regions as defined by the ‘luminous’ galaxy sam- fainter than the characteristic absolute magnitude of galaxy ple. In Section 3 we describe the selection of void galaxies. ∗ Luminosity Function MK = −24.0 mag (Hill et al. 2010). Section 4 presents the list with the main geometrical param- Galaxies with L somewhat lower than the luminosity L∗ eters of the separated Nearby Voids and parameters of void are commonly used to define void boundaries. In numerical galaxies taken from HyperLEDA and/or NED. In Section 5 cosmological simulations, the masses of Dark Matter (DM) we briefly discuss statistical properties of the Nearby Voids’ halos, delineating voids, usually correspond to objects with galaxies, compare them with the previous results and draw the luminosity ∼2–3 times smaller than the characteristic the prospects of the galaxy sample study. We finally sum- one. For example, in simulations by Aragon-Calvo & Szalay marize the results of this work and conclude in Section 6. (2013), voids are determined by Cold DM halos correspond- For all distance dependent parameters, we adopt the Hub- −1 −1 ing to Mr . −20.7 mag, what is ∼ 0.8 mag (or a factor ble constant of H0 = 73 km s Mpc . Due to their large ∗ of 2) fainter than Mr = −21.5 mag (Montero-Dorta, Prada volume for the printed version, the major part of tables and 2009; Hill et al. 2010). The galaxies with the intermediate illustrative materials like the finding charts of the Nearby luminosities, of Mr .