Re-growth of stellar disks in mature galaxies: The two component nature of NGC 7217 revisited with VIRUS-W

Abstract

Previous studies have reported the existence of two counter-rotating stellar disks in the early-type spiral galaxy NGC7217. We have obtained high-resolution optical spectroscopic data (R ~ 9000) with the new fiber-based Integral Field Unit instrument VIRUS-W at the 2.7m telescope of the McDonald Observatory in Texas. Our analysis confirms the existence of two components. However, we find them to be co-rotating. The first component is the more luminous (~ 77% of the total light), has the higher velocity dispersion (~ 170 km/s) and rotates relatively slowly (projected $v_{max}$ = 50 km/s). The lower luminosity second component, (~ 23% of the total light), has a low velocity dispersion (~ 20 km/s) and rotates quickly (projected $v_{max}$ = 150 km/s). The difference in the kinematics of the two stellar components allows us to perform a kinematic decomposition and to measure the strengths of their Mg and Fe Lick indices separately. The rotational velocities and dispersions of the less luminous and faster component are very similar to those of the interstellar gas as measured from the [OIII] emission. Morphological evidence of active star formation in this component further suggests that NGC7217 may be in the process of (re)growing a disk inside a more massive and higher dispersion stellar halo. The kinematically cold and regular structure of the gas disk in combination with the central almost dust-free morphology allows us to compare the dynamical mass inside of the central 500pc with predictions from a stellar population analysis. We find agreement between the two if a Kroupa stellar initial mass function is assumed.

accepted for publication by MNRAS

References in corpus (13)

• The GALEX Ultraviolet Atlas of Nearby Galaxies
• The SAURON project -- IX. A kinematic classification for early-type galaxies
• Forming Disk Galaxies in Lambda CDM Simulations
• The Structure of Classical Bulges And Pseudobulges: The Link Between Pseudobulges And Sersic Index
• The SAURON project - VIII. OASIS/CFHT integral-field spectroscopy of elliptical and lenticular galaxy centres
• The supermassive black hole of Fornax A
• Star formation and stellar populations across nuclear rings in galaxies
• Stellar Populations of Bulges in 14 Cluster Disc Galaxies
• The ability of intermediate-band Stromgren photometry to correctly identify dwarf, subgiant, and giant stars and provide stellar metallicities and surface gravities
• NGC5719/13: interacting spirals forming a counter-rotating stellar disc
• Mass Loss From Planetary Nebulae in Elliptical Galaxies
• The search for inner polar disks with integral field spectroscopy: the case of NGC 2855 and NGC 7049
• Stellar Population Gradients in Bulges along the Hubble Sequence: I. The Data

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