A Search for Faint Resolved Galaxies Beyond the Milky Way in DES Year 6: A New Faint, Diffuse Dwarf Satellite of NGC 55
M. McNanna, K. Bechtol, S. Mau, Ethan O. Nadler, Jonah Medoff, A. Drlica-Wagner, W. Cerny, Denija Crnojević, Burçı̇n Mutlu-Pakdı̇l, A. K. Vivas, Andrew B. Pace, Jeffrey L. Carlin, Michelle Collins, P. S. Ferguson, David Martínez‐Delgado, C. E. Martínez-Vázquez, N. E. D. Noel, A. H. Riley, D. J. Sand, Adam Smercina, Erik Tollerud, Risa H. Wechsler, T. M. C. Abbott, M. Aguena, O. Alves, David Bacon, Clécio R. Bom, D. Brooks, D. L. Burke, J. A. Carballo-Bello, A. Carnero Rosell, J. Carretero, L. N. da Costa, T. M. Davis, J. De Vicente, H. T. Diehl, P. Doel, I. Ferrero, J. Frieman, G. Giannini, D. Gruen, G. Gutiérrez, R. A. Gruendl, S. R. Hinton, D. L. Hollowood, K. Honscheid, D. J. James, K. Kuehn, J. L. Marshall, J. Mena-Fernández, R. Miquel, M. E. S. Pereira, A. Pieres, A. A. Plazas, J. D. Sakowska, E. Sánchez, D. Sanchez Cid, B. Santiago, I. Sevilla-Noarbe, M. Smith, Guy S. Stringfellow, E. Suchyta, M. E. C. Swanson, G. Tarle, N. Weaverdyck, P. Wiseman
Abstract
Abstract We report results from a systematic wide-area search for faint dwarf galaxies at heliocentric distances from 0.3 to 2 Mpc using the full 6 yr of data from the Dark Energy Survey (DES). Unlike previous searches over the DES data, this search specifically targeted a field population of faint galaxies located beyond the Milky Way virial radius. We derive our detection efficiency for faint, resolved dwarf galaxies in the Local Volume with a set of synthetic galaxies and expect our search to be complete to M V ∼ (−7, −10) mag for galaxies at D = (0.3, 2.0) Mpc. We find no new field dwarfs in the DES footprint, but we report the discovery of one high-significance candidate dwarf galaxy at a distance of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>2.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.12</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>Mpc</mml:mi> </mml:math> , a potential satellite of the Local Volume galaxy NGC 55, separated by 47′ (physical separation as small as 30 kpc). We estimate this dwarf galaxy to have an absolute V -band magnitude of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>8.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>mag</mml:mi> </mml:math> and an azimuthally averaged physical half-light radius of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>2.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>kpc</mml:mi> </mml:math> , making this one of the lowest surface brightness galaxies ever found with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>μ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>32.3</mml:mn> <mml:mspace width="0.25em"/> <mml:mi>mag</mml:mi> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>arcsec</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> . This is the largest, most diffuse galaxy known at this luminosity, suggesting possible tidal interactions with its host.