Comparing the properties of the X-shaped bulges of NGC 4710 and the Milky Way with MUSE

TL;DR

This study uses MUSE data to compare the dynamical and stellar population properties of the X-shaped bulge in NGC 4710 with the Milky Way, revealing remarkable similarities and some differences related to bar orientation and stellar populations.

Contribution

First detailed comparison of NGC 4710's X-shaped bulge with the Milky Way using integral field spectroscopy and stellar population analysis.

Findings

Velocity maps of NGC 4710 resemble those of the Milky Way bulge.

NGC 4710's bulge shows a vertical metallicity gradient of 0.35 dex/kpc.

No evidence of an additional spheroidal, metal-poor component in NGC 4710.

Abstract

We used the new ESO VLT instrument MUSE to obtain spectral and imaging coverage of NGC 4710. The wide area and excellent sampling of the MUSE integral field spectrograph allows us to investigate the dynamical properties of the X-shaped bulge of NGC 4710 and compare it with the properties of the Milky Way's own X-shaped bulge. We measured the radial velocities, velocity dispersion, and stellar populations using a penalized pixel full spectral fitting technique adopting simple stellar populations models, on a 1' x 1' area centred on the bulge of NGC 4710. We have constructed the velocity maps of the bulge of NGC 4710 and we investigated the presence of vertical metallicity gradients. These properties were compared to those of the Milky Way bulge and as well as to a simulated galaxy with boxy/peanut bulge. We find the line-of-sight velocity maps and 1D rotation curves of the bulge of NGC 4710 to be remarkably similar to those of the Milky Way bulge. Some specific differences that were identified are in good agreement with the expectations from variations in the bar orientation angle. The bulge of NGC 4710 has a boxy-peanut morphology with a pronounced X-shape, showing no indication of any additional spheroidally distributed bulge population, in which we measure a vertical metallicity gradient of 0.35 dex/kpc. The general properties of NGC 4710 are very similar to those observed in the MW bulge. However, it has been suggested that the MW bulge has an additional component that is comprised of the oldest, most metal-poor stars and which is not part of the boxy-peanut bulge structure. Such a population is not observed in NGC 4710, but could be hidden in the integrated light we observed.