Resolving the Extended Stellar Halos of Nearby Galaxies: The Wide-Field PISCeS Survey

Abstract

Abstract:The wide-field Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) investigates the resolved stellar halos of two nearby galaxies (the spiral NGC 253 and the elliptical Centaurus A, D ∼ 4 Mpc) out to a galactocentric radius of 150 kpc. The survey to date has led to the discovery of 11 confirmed faint satellites and stunning streams/substructures in two environments substantially different from the Local Group; i.e., the loose Sculptor group of galaxies and the Centaurus A group dominated by an elliptical. The newly discovered satellites and substructures, with surface brightness limits as low as ∼32 mag/arcsec 2 , are then followed-up with HST imaging and Keck/VLT spectroscopy to investigate their stellar populations. The PISCeS discoveries clearly testify the past and ongoing accretion processes shaping the halos of these nearby galaxies, and provide the first census of their satellite systems down to an unprecedented M V < −8. Keywords: galaxies: evolution; galaxies: groups; galaxies: halos; galaxies: photometry The Past, Present, and Future of Near-Field CosmologyThe past decade has seen a tremendous effort to study the properties of our Milky Way (MW) and its neighbouring Local Group (LG) galaxies in great detail. In particular, the wide-field surveys of the MW-analogue M31 (PAndAS, SPLASH; [1,2]) have highlighted significant differences in the halo properties, accretion history, and satellite populations of the two LG giant spirals. This is unsurprising, as theoretical simulations predict a large halo-to-halo scatter in the properties of MW-sized halos (e.g., [3]), but it certainly underlines the need for in-depth surveys of galaxies beyond the LG.A variety of approaches can be adopted to refine our knowledge of galaxy halos and their inhabitants: for example, deep pencil-beam surveys of a select sample of nearby (<10-15 Mpc) galaxies can be performed from the space (the Galaxy Halos, Outer disks, Substructure, Thick disks, and Star clusters, or GHOSTS, survey; e.g., [4]); or a larger number of more distant (>15-20 Mpc), unresolved galaxies can be investigated in integrated light (e.g., [5][6][7]). However, it remains an observational challenge to produce wide and deep resolved stellar maps such as those available for LG galaxies. With the advent of ground-based wide-field imagers, the first PAndAS-like maps for nearby MW-analogues are finally starting to be obtained (e.g., [8,9]). The PISCeS SurveyThe Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) was designed to help bridge the gap between our detailed knowledge of LG galaxies' properties and the integrated light information from unresolved galaxies at larger distances by targeting two resolved galaxies at ∼4 Mpc. To facilitate a comparison to the MW and M31, the PISCeS targets are ∼ MW-mass galaxies, a spiral (NGC 253, also known as Sculptor) and an elliptical (NGC 5128, or Centaurus A, Cen A). The former is part of a

Hidden depths in the local Universe: The Stellar Stream Legacy Survey

“…Further deep imaging surveys of the outskirts of local galaxies have been completed over the past decade (Tal et al 2009;Ludwig et al 2012;Duc et al 2015;Laine et al 2014;Rich et al 2019) or are currently ongoing (Kado-Fong et al 2018). Resolved stellar population studies of stellar halo substructure (similar to PAndAS, McConnachie et al 2009 are only feasible for a select number of nearby galaxies within a distance of a few Megaparsecs using very large telescopes (Mouhcine & Ibata 2009;Crnojević 2017) or from space (Mouhcine et al 2010;Crnojević et al 2016;Carlin et al 2019).…”

Hidden Depths in the Local Universe: the Stellar Stream Legacy Survey

“…Further deep imaging surveys of the outskirts of local galaxies have been completed over the past decade (Tal et al 2009;Ludwig et al 2012;Duc et al 2015;Laine et al 2014;Rich et al 2019) or are currently ongoing (Kado-Fong et al 2018). Resolved stellar population studies of stellar halo substructure (similar to PAndAS, McConnachie et al 2009) are only feasible for a handful of nearby galaxies within a distance of a few Mpc using very large telescopes (Mouhcine & Ibata 2009;Crnojević 2017) or from space (Mouhcine et al 2010;Crnojević et al 2016;Carlin et al 2019).…”