Mon. Not. R. Astron. Soc. 000,1{ ?? (2018) Printed 18 December 2019 (MN LATEX style file v2.2) Newly discovered dwarf galaxies in the MATLAS low density fields Rebecca Habas1;2?, Francine R. Marleau1, Pierre-Alain Duc2, Patrick R. Durrell3, Sanjaya Paudel4, M´elinaPoulain1, Rub´enS´anchez-Janssen5, Sreevarsha Sreejith6, Joanna Ramasawmy7, Bryson Stemock3, Christopher Leach3, Jean-Charles Cuillandre8, Stephen Gwyn9, Adriano Agnello10, Michal B´ılek2, J´er´emy Fensch11;12, Oliver M¨uller2, Eric W. Peng13, Remco F.J. van der Burg11 1Institut f¨urAstro- und Teilchenphysik, Universit¨atInnsbruck, Technikerstraße 25/8, Innsbruck, A-6020, Austria 2Observatoire Astronomique, Universit´ede Strasbourg, CNRS, 11, rue de l'Universit´e.F-67000 Strasbourg, France 3Department of Physics and Astronomy, Youngstown State University, Youngstown, OH, 44555, USA 4Department of Astronomy and Center for Galaxy Evolution Research, Yonsei University, Seoul 03722 5UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK 6Universite Clermont Auvergne, CNRS/IN2P3, LPC, F-63000 Clermont-Ferrand, France 7Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK 8IRFU, CEA, Universit´eParis-Saclay, Universit´eParis Diderot, AIM, Sorbonne Paris Cit´e,CEA, CNRS, Observatoire de Paris, PSL Research University, F-91191 Gif-sur-Yvette Cedex, France 9NRC Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada 10DARK, Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, 2100 Copenhagen, Denmark 11European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching, Germany 12Univ. Lyon, ENS de Lyon, Univ. Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon, UMR5574, F-69007 Lyon, France 13Department of Astronomy and Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, 100871, China ABSTRACT We present the photometric properties of 2210 newly identified dwarf galaxy candi- dates in the MATLAS fields. The Mass Assembly of early Type gaLAxies with their fine Structures (MATLAS) deep imaging survey mapped ∼142 deg2 of the sky around nearby isolated early type galaxies using MegaCam on the Canada-France-Hawaii Telescope, reaching surface brightnesses of ∼ 28.5 { 29 in the g-band. The dwarf can- didates were identified through a direct visual inspection of the images and by visually cleaning a sample selected using a partially automated approach, and were morpho- logically classified at the time of identification. Approximately 75% of our candidates are dEs, indicating that a large number of early type dwarfs also populate low density environments, and 23.2% are nucleated. Distances were determined for 13.5% of our sample using pre-existing zspec measurements and HI detections. We confirm the dwarf nature for 99% of this sub-sample based on a magnitude cut Mg = −18. Additionally, most of these (∼ 90%) have relative velocities suggesting that they form a satellite arXiv:1910.13462v2 [astro-ph.GA] 17 Dec 2019 population around nearby massive galaxies rather than an isolated field sample. As- suming that the candidates over the whole survey are satellites of the nearby galaxies, we demonstrate that the MATLAS dwarfs follow the same scaling relations as dwarfs in the Local Group as well as the Virgo and Fornax clusters. We also find that the nu- cleated fraction increases with Mg, and find evidence of a morphology-density relation for dwarfs around isolated massive galaxies. Key words: galaxies: dwarf | galaxies: photometry | galaxies: structure | galax- ies, fundamental parameters. 1 Introduction ? E-mail: [email protected] The properties of low surface brightness dwarf galaxies in low-density environments are poorly constrained observa- c 2018 RAS 2 R Habas et al. tionally. Deep observations over large portions of the sky nificantly smaller than the 20:1 ratio in the Virgo cluster. are required to detect a large sample of such galaxies, which Geha et al.(2012) used data from the SDSS to study star for- is expensive in terms of telescope time. As a result, most mation rates of almost 3000 dwarf galaxies, concluding that studies focus on dwarfs in the Local Group, where they can essentially all isolated dwarfs (those without a neighbouring be studied in detail, selected nearby groups, and those in galaxy within 1 Mpc) have ongoing star formation. More re- nearby clusters (in particular Virgo, Coma, and Fornax) cently, Ann(2017) supplemented SDSS DR7 spectroscopic where dwarfs can be found in greater numbers and their distances with redshifts from other sources to confirm ∼2600 association with the cluster can be used to constrain their dwarf galaxies in the Catalogue of Visually Classified Galax- distances. By comparison, relatively few observing programs ies (CVCG; Ann et al. 2015) in the nearby Universe; the have focused on dwarf populations around otherwise isolated catalogue also includes morphological classifications, and the massive galaxies. morphologies of the dwarf satellites appear to correlate with However, dwarfs in low density environments provide a the morphology of the host galaxy, such that more dEs are crucial sample to test whether or not the dwarfs in the Local found around massive early type galaxies. Group are representative of dwarfs in general. In terms of Several deep optical imaging observing programs have their star formation histories, Weisz et al.(2011) have con- begun collecting data in recent years, either for the express firmed that dwarfs in the Local Group are indeed similar to purpose of detecting new dwarf galaxies or with this as a sec- those found at d . 4 Mpc in the ACS Nearby Galaxy Survey ondary science goal. These include large sky surveys such as Treasury Program (ANGST; Dalcanton et al. 2009). How- the Panoramic Survey Telescope and RApid Response Sys- ever, it remains an open question if other properties of Local tem (PAN-STARRS1; Chambers et al. 2016), the Dark En- Group dwarfs, such as the number and distribution of dwarf ergy Survey (DES; The Dark Energy Survey Collaboration satellites, are also representative. For example, it is known 2005), Survey of the MAgellanic Stellar History (SMASH; that bright satellites like the Large Magellanic Cloud (LMC) Nidever et al. 2017), and the VLT Survey Telescope AT- are relatively rare; Tollerud et al.(2011) found that only LAS (Shanks et al. 2015), as well as deep imaging projects ∼12% of isolated Milky Way analogues in the Sloan Digital of the regions around nearby massive galaxies such as the Sky Survey (SDSS; York et al. 2000) have an LMC-like satel- Dwarf Galaxy Survey with Amateur Telescopes (DGSAT; lite within a projected distance of 75 kpc. More generally, Mart´ınez-Delgadoet al. 2010), the Giant Galaxies, Dwarfs, any variation in the number of dwarf satellites around mas- and Debris Survey (GGADDS; Ludwig et al. 2012), the Tief sive galaxies is not well constrained observationally, and this Belichtete Galaxien project (Karachentsev et al. 2015), and may have important implications for the missing satellite observations taken with the Dragonfly Telephoto Array (van problem (Kauffmann et al. 1993; Klypin et al. 1999; Moore Dokkum et al. 2014; Abraham & van Dokkum 2014). Deep et al. 1999) and/or constraining cosmological simulations. imaging programs of nearby clusters, such as the Next Gen- Observations have revealed, however, that dwarfs around eration Virgo cluster Survey (NGVS; Ferrarese et al. 2012) the Milky Way and Andromeda lie in a thin planes around and the Next Generation Fornax Survey (NGFS; Mu~noz their respective hosts (e.g., Pawlowski et al. 2012; Ibata et al. 2015) are also revealing fainter dwarf populations that et al. 2013; Santos-Santos et al. 2019); several other satellite were previously missed. A large number of dwarf galaxies are planes have since been identified around M81, NGC 3109, expected to be found in these programs, which will greatly Centaurus A, M101, and potentially M83 (Chiboucas et al. contribute to our understanding of dwarf formation and evo- 2013; Bellazzini et al. 2013; Tully et al. 2015; M¨ulleret al. lution across all environments. 2017, 2018a,b), suggesting that the Local Group satellites Another deep imaging survey is the Mass Assembly of are typical, but this remains a challenge to explain in the early Type gaLAxies with their fine Structures (MATLAS) standard cosmological model (see Pawlowski 2018 and Bul- large observing program. MATLAS was designed to study lock & Boylan-Kolchin 2017 for reviews, and Kroupa 2015 low surface brightness features in the outskirts of nearby or B´ıleket al. 2018 for an alternative explanation). massive early type galaxies (ETGs), many of which are iso- Dwarfs in low density environments are also impor- lated, and mapped ∼142 deg2 of the sky using MegaCam on tant to understand evolutionary trends in low mass galax- the Canada-France-Hawaii Telescope (CFHT), reaching sur- ies within clusters. There is growing evidence that dwarfs face brightnesses of ∼ 28:5−29:0 mag/arcsec2 in the g-band are pre-processed in group environments | impacting both (Duc et al. 2015). These three conditions | the coverage, their star formation rates and morphologies | before they depth, and environment of the primary targets | create fall into a cluster potential (e.g., Cortese et al. 2006; Cybul- an ideal dataset on which to search for low surface bright- ski et al. 2014; Roberts & Parker 2017; Mendelin & Binggeli ness dwarf galaxies. Indeed, several tidal dwarf candidates 2017). have already been identified in a subset of the images (Duc Over the years there has been a growing interest in et al. 2014). The MATLAS observations complement previ- observing dwarfs within low density environments. Some ous and ongoing dwarf searches; the MATLAS images are 2 groups have focused on building catalogues of nearby galax- deeper than SDSS (µg ∼ 26:4 mag/arcsec ; York et al. 2000; ies | including dwarfs | with a range of consistent ob- Kniazev et al. 2004), the imaged galaxies are more distant servables (Impey et al.