NGC 6340: an old S0 galaxy with a young polar disc. Clues from morphology, internal kinematics, and stellar populations - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2009

NGC 6340: an old S0 galaxy with a young polar disc. Clues from morphology, internal kinematics, and stellar populations

Résumé

Context: Lenticular galaxies are believed to form by a combination of environmental effects and secular evolution.
Aims: We study the nearby disc-dominated S0 galaxy NGC 6340 photometrically and spectroscopically to understand the mechanisms of S0 formation and evolution in groups.
Methods: We use SDSS images to build colour maps and the light profile of NGC 6340, which we decompose using a three-component model including Sérsic and two exponential profiles. We also use Spitzer Space Telescope archival near-infrared images to study the morphology of regions containing warm interstellar medium and dust. Then, we re-process and re-analyse deep long-slit spectroscopic data for NGC 6340, applying a novel sky subtraction technique and recover its stellar and gas kinematics, distribution of age and metallicity with the NBursts full spectral fitting.
Results: We obtain the profiles of internal kinematics, age, and metallicity out to >2 half-light radii. The three structural components of NGC 6340 are found to have distinct kinematic and stellar population properties. We see a kinematic misalignment between inner and outer regions of the galaxy. We confirm the old metal-rich centre and a wrapped inner gaseous polar disc (r˜ 1 kpc) having weak ongoing star formation, counter-rotating in projection with respect to the stars. The central compact pseudo-bulge of NGC 6340 looks very similar to compact elliptical galaxies.
Conclusions: In accordance with the results of numerical simulations, we conclude that the properties of NGC 6340 can be explained as the result of a major merger of an early-type galaxy and a spiral galaxy that occurred about 12 Gyr ago. The intermediate exponential structure might be a triaxial pseudo-bulge formed by a past bar structure. The inner compact bulge could be the result of a nuclear starburst triggered by the merger. The inner polar disc appeared recently, 1/3-1/2 Gyr ago, as a result of another minor merger or cold gas accretion.

Dates et versions

hal-03743021 , version 1 (02-08-2022)

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Igor V. Chilingarian, A. P. Novikova, Véronique Cayatte, Françoise Combes, Paola Di Matteo, et al.. NGC 6340: an old S0 galaxy with a young polar disc. Clues from morphology, internal kinematics, and stellar populations. Astronomy and Astrophysics - A&A, 2009, 504, pp.389-400. ⟨10.1051/0004-6361/200911684⟩. ⟨hal-03743021⟩
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