Kinematic study of planetary nebulae in NGC 6822

Abstract

Context. The kinematics of planetary nebulae in external galaxies and in our own is a clue for understanding the behavior of the lowand intermediate-mass stars and their relation with other components of the galaxies.Aims. By measuring precise radial velocities of planetary nebulae (which belong to the intermediate-age population), H ii regions and A-type supergiant stars (which are members of the young population) in NGC 6822, we aim to determine whether both types of population share the kinematics of the disk of H i found in this galaxy.Methods. Spectroscopic data for six planetary nebulae were obtained with the high spectral-resolution spectrograph Magellan Inamori Kyocera Echelle (MIKE) on the Magellan telescope at Las Campanas Observatory. Data for another three PNe and one H ii region were obtained from the SPM Catalog of Extragalactic Planetary Nebulae, which employed the Manchester Echelle Spectrometer attached to the 2.1m telescope at the Observatorio Astronómico Nacional, México. An additional PN and one H ii region were observed with this same telescope-spectrograph in 2013. Thus, in total we have high-quality data for 10 of the 26 PNe detected in this galaxy. In the wavelength calibrated spectra, the heliocentric radial velocities were measured with a precision better than 5-6 km s −1 . Data for two additional H ii regions and two A-type supergiant stars were collected from the literature. The heliocentric radial velocities of the different objects were compared to the velocities of the H i disk at the same position.Results. From the analysis of radial velocities we found that H ii regions and A-type supergiants do share the kinematics of the H i disk at the same position, as expected for these young objects. In contrast, most planetary nebula velocities differ significantly (more than 12 km s −1 ) from that of the H i at the same position. The kinematics of planetary nebulae is different from the young population kinematics and is more similar to the behavior shown by carbon stars, which are intermediate-age members of the stellar spheroid existing in this galaxy. Our results confirm that there are at least two very different kinematical systems in NGC 6822.

The planetary nebulae and H II regions in NGC 6822 revisited. Clues to AGB nucleosynthesis

“…The ADF is usually between 1.5 and 3, but in PNe it has a significant tail that extends to much higher values, up to 120 (Corradi et al 2015a). By analysing high-resolution spectra, Flores-Durán et al (2014) demonstrate that the kinematics of PNe is closer to the one shown by the stellar spheroid than to the H  disk, thus PNe would belong to the intermediate age population.…”

The rotation of the halo of NGC 6822 from the radial velocities of carbon stars

“…In Flores-Durán et al (2014), the motion of 10 planetary nebulae (PNe) in the galaxy are studied. PNe are the evolutionary stage reached by AGBs after the end of their lives, and may thus provide complementary kinematic information of the galaxy.…”

Kinematic and chemical study of planetary nebulae and H II regions in NGC 3109

“…5) but not chemical gradients. In the irregular galaxy NGC 6822 different populations have also been found and in this case these populations do show different dynamics and different chemical composition, although no chemical gradients (Hernández-Martínez et al 2009;Flores-Durán et al 2014;García-Rojas et al 2016).…”

“…The objects analyzed in this work are listed in Table 2. A similar analysis was performed by our group in NGC 6822 (García-Rojas et al 2016;Flores-Durán et al 2014), where we studied the chemical behavior of photoionized nebulae and their kinematics relative to the H i disk and the huge spheroid of C stars in this galaxy. There we probed that the young population (H i and H ii gas) and intermediate-age population (C stars and PNe) display different kinematics and chemistry.…”

“…For this case they reported a kinematical connection between both populations. In NGC 6822, PN kinematics was analyzed by Flores-Durán et al (2014), who found significant differences between the PNe velocities and the velocities of the H i disk at the same position. These authors reported that, in NGC 6822, PNe share the rotation of the middleage C stars.…”