Diffuse light in Hickson compact groups: the dynamically young system HCG 44

¹ Instituto de Astrofísica de Canarias, Calle Via Lactea s/n, 38200 La Laguna, Spain e-mail: jalfonso@iac.es
² Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
³ INAF, Osservatorio Astronomico di Pino Torinese, 10025 Pino Torinese, Italy
⁴ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁵ Max-Planck-Institut Institut für Extraterrestrische Physik, Giessenbachstrasse, 85741 Garching, Germany

Received: 8 June 2006
Accepted: 10 July 2006

Abstract

Context.Compact groups are associations of a few galaxies in which the environment plays an important role in galaxy evolution. The low group velocity dispersion favors tidal interactions and mergers, which may bring stars from galaxies to the diffuse intragroup light. Numerical simulations of galaxy clusters in hierarchical cosmologies show that the amount of the diffuse light increases with the dynamical evolution of the cluster.

Aims.We search for diffuse light in the galaxy group HCG 44 in order to determine its luminosity and luminosity fraction. Combining with literature data, we aim to constrain the dynamical status of Hickson compact groups.

Methods.We use Intra Group planetary nebulae (IGPNe) as tracers of diffuse light. These are detected by the so-called on band-off band technique.

Results.We found 12 emission line objects in HCG 44, none of them associated with the galaxies of the group. The absence of PNe in the elliptical galaxy, NGC 3193, implies that this galaxy is located behind the group, leaving only three spiral galaxy members in HCG 44. 6/12 emission line objects are consistent with being IGPNe in HCG 44, but are also consistent with being Lyα background galaxies. Thus we derive an upper limit to the diffuse light fraction in HCG 44 of , corresponding to and mean surface brightness of  mag arcsec^-2. We find a correlation between the fraction of elliptical galaxies and the amount of diffuse light in Hickson compact groups. Those with large fraction of diffuse light are those with large fractions in number and luminosity of E/S0 galaxies. This indicates that the diffuse light is mainly created in dynamical processes during the formation of bright elliptical galaxies in major mergers.

Conclusions.We propose an evolutionary sequence for Hickson compact groups in which the amount of diffuse light increases with the dynamical evolution of the group.