Long-slit spectral observations and stellar mass-to-light ratio of spiral galaxy UGC11919

TL;DR

This study uses long-slit spectral observations of galaxy UGC11919 to analyze its kinematics and stellar population, revealing that its low mass-to-light ratio may be explained by a normal stellar initial mass function when considering a lower inclination angle.

Contribution

It provides a detailed analysis of UGC11919's kinematics and stellar populations, challenging previous assumptions about its low mass-to-light ratio and proposing a revised inclination angle.

Findings

The galaxy's mass-to-light ratio depends on the assumed inclination angle.

A lower inclination angle (~13°) aligns the data with a normal stellar initial mass function.

Detection of a kinematically decoupled nuclear disc in UGC11919.

Abstract

We performed the long-slit observations of spiral galaxy UGC11919 with the Russian 6-m telescope to study its kinematics and stellar population. The previous studies gave basis to suspect that this galaxy possesses a peculiarly low mass-to-light ratio $M/L_B$ of stellar population which could indicate the presence of bottom-light stellar initial mass function (IMF). The ratio $M/L_B$ estimated for different evolutionary models of stellar population using both the broad-band magnitudes and the detailed spectral data confirms this peculiarity if the disc inclination angle $i>30^o$, as it was obtained earlier from the optical photometry, in a good agreement with the HI data cube modelling. However the re-processing of HI data cube we carried out showed that it is compatible with much lower value $i=13^o$ corresponding to the "normal" ratio $M/L_B$, which does not need any peculiar stellar IMF. Stellar velocity dispersion measured at one disc radial scalelength from the center also better agrees with the low disc inclination. However in this case we should admit that the disc possesses a non-axisymmetric shape even after taking into account a two-armed spiral structure. The derived stellar kinematic profiles reveal a signature of kinematically decoupled nuclear disc in the galaxy. Using different evolution models of stellar population we estimated the stellar metallicity [Z/H] (-0.4, -0.5 and -0.3 dex) and the mean luminosity-weighted (for the luminosity in the spectral range $4800-5570$ \AA) stellar age (4.2, 2.6 and 2.3 Gyr) for the bulge, disc and nuclear disc of this galaxy respectively.