NGC 2782: a merger remnant with young stars in its gaseous tidal tail

Authors

  • S. Torres-Flores,

    Corresponding author
    1. Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP, Rua do Matão 1226, Cidade Universitária, 05508-090, São Paulo, Brazil
    2. Laboratoire d’Astrophysique de Marseille, OAMP, Université de Provence & CNRS, 38 rue F. Joliot–Curie, 13388 Marseille, Cedex 13, France
    3. Departamento de Física, Universidad de La Serena, Av. Cisternas 1200 Norte, La Serena, Chile
    Search for more papers by this author
  • C. Mendes de Oliveira,

    1. Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP, Rua do Matão 1226, Cidade Universitária, 05508-090, São Paulo, Brazil
    Search for more papers by this author
  • D. F. de Mello,

    1. Observational Cosmology Laboratory, Code 665, Goddard Space Flight Center, Greenbelt, MD 20771, USA
    2. Catholic University of America, Washington, DC 20064, USA
    Search for more papers by this author
  • S. Scarano Jr,

    1. Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP, Rua do Matão 1226, Cidade Universitária, 05508-090, São Paulo, Brazil
    Search for more papers by this author
  • F. Urrutia-Viscarra

    1. Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP, Rua do Matão 1226, Cidade Universitária, 05508-090, São Paulo, Brazil
    Search for more papers by this author

Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina) – Observing run: GN-2009B-Q-113.

E-mail: storres@dfuls.cl

ABSTRACT

We have searched for young star-forming regions around the merger remnant NGC 2782. By using Galaxy Evolution Explorer far-ultraviolet and near-ultraviolet imaging and H i data we found seven ultraviolet sources, located at distances greater than 26 kpc from the centre of NGC 2782, and coinciding with its western H i tidal tail. These regions were resolved in several smaller systems when Gemini/Gemini multi-object spectrograph (GMOS) r-band images were used. We compared the observed colours to stellar population synthesis models and found that these objects have ages of ∼1 to 11 Myr and masses ranging from 103.9 to 104.6 M. By using Gemini/GMOS spectroscopic data we confirm memberships and derive high metallicities for three of the young regions in the tail (12+log(O/H) = 8.74 ± 0.20, 8.81 ± 0.20 and 8.78 ± 0.20). These metallicities are similar to the value presented by the nuclear region of NGC 2782 and also similar to the value presented for an object located close to the main body of NGC 2782. The high metallicities measured for the star-forming regions in the gaseous tidal tail of NGC 2782 could be explained if they were formed out of highly enriched gas which was once expelled from the centre of the merging galaxies when the system collided. An additional possibility is that the tail has been a nursery of a few generations of young stellar systems which ultimately polluted this medium with metals, further enriching the already pre-enriched gas ejected to the tail when the galaxies collided.

Ancillary