Kinematic and stellar population properties of the counter-rotating components in the S0 galaxy NGC 1366⋆
1 Dipartimento di Fisica e Astronomia “G. Galilei”Università di Padova, vicolo dell’Osservatorio 3, 35122 Padova, Italy
2 INAF–Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 2, 35122 Padova, Italy
3 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
4 European Southern Observatory, Avenida Alonso de Córdova 3107, Vitacura, 19001 Casilla, Santiago de Chile, Chile
Received: 11 November 2016
Accepted: 16 January 2017
Context. Many disk galaxies host two extended stellar components that rotate in opposite directions. The analysis of the stellar populations of the counter-rotating components provides constraints on the environmental and internal processes that drive their formation.
Aims. The S0 NGC 1366 in the Fornax cluster is known to host a stellar component that is kinematically decoupled from the main body of the galaxy. Here we successfully separated the two counter-rotating stellar components to independently measure the kinematics and properties of their stellar populations.
Methods. We performed a spectroscopic decomposition of the spectrum obtained along the galaxy major axis and separated the relative contribution of the two counter-rotating stellar components and of the ionized-gas component. We measured the line-strength indices of the two counter-rotating stellar components and modeled each of them with single stellar population models that account for the α/Fe overabundance.
Results. We found that the counter-rotating stellar component is younger, has nearly the same metallicity, and is less α/Fe enhanced than the corotating component. Unlike most of the counter-rotating galaxies, the ionized gas detected in NGC 1366 is neither associated with the counter-rotating stellar component nor with the main galaxy body. On the contrary, it has a disordered distribution and a disturbed kinematics with multiple velocity components observed along the minor axis of the galaxy.
Conclusions. The different properties of the counter-rotating stellar components and the kinematic peculiarities of the ionized gas suggest that NGC 1366 is at an intermediate stage of the acquisition process, building the counter-rotating components with some gas clouds still falling onto the galaxy.
Key words: galaxies: abundances / galaxies: kinematics and dynamics / galaxies: formation / galaxies: stellar content / galaxies: individual: 1366
© ESO, 2017