Research Note

Deep imaging of Virgo Z: not a nearby ultrafaint dwarf galaxy, but a distant compact group of galaxies^⋆

¹ Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo , Brazil
e-mail: barbuy@astro.iag.usp.br; andre.lopes.souza@usp.br
² Universidade Federal do Rio Grande do Sul, Departamento de Astronomia, CP 15051, 91501-970 Porto Alegre, Brazil
e-mail: bica@if.ufrgs.br
³ Università di Padova, Dipartimento di Fisica e Astronomia Galileo Galilei, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
e-mail: sergio.ortolani@unipd.it

Received: 22 May 2013
Accepted: 3 October 2013

Abstract

Context. The search for Milky Way faint satellite galaxies and star clusters has been intensified in recent years thanks to the Sloan Digital Sky Survey (SDSS), and other efforts to verify candidate objects.

Aims. We observed the Milky Way satellite candidate Vir Z, reported by Walsh et al. (2009, AJ, 137, 450), from the detection of an overdensity in the SDSS database.

Methods. Deep subarcsec seeing images from the New Technology Telescope (NTT) and Galileo telescopes were obtained in order to infer the nature of the proposed overdensity.

Results. The image and colour-magnitude diagram of the Vir Z field shows no dwarf galaxy. Instead, we identified a compact group of galaxies near the center of the Vir Z field at redshift z ≈ 0.3 ± 0.2, based on the apparent magnitudes of the brightest galaxies assuming L = L∗, and on angular sizes of the spirals assuming physical sizes equal to M 31.