News and Views

Author: Peter Berczik

1. National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China (berczik@nao.cas.cn)

Described in the RAA letter "Chemo-dynamical modelling with Schwarzschild's method" (R.J. Long, Shude Mao) are the means by which an existing stellar dynamical modelling method, first described nearly 40 years ago, can be extended into a chemo-dynamical modelling system for use in modelling galaxies. Schwarzschild's method (Schwarzschild, 1979) provides a mechanism by which a stellar orbit library can be weighted to reproduce observations of an external galaxy.

The method has been well-utilized and has currently over 100 citations. The extensions mean that not only can the stellar luminosity and kinematics of a galaxy be modelled but also the galaxy's underlying stellar chemistry and its relationship to stellar orbits. This is the first time that such a capability has been included in Schwarzschild's method. It is important that the astronomical community has this capability. As stated in an earlier related RAA paper (Long, 2016), the creation and evolution of galaxies are signficant research topics involving, for example, an understanding of galaxy mergers and in situ star formation.

A galaxy's construction and evolution are imprinted in its kinematics and chemistry but they require significant analysis to identify the contributing componentry. IFU-based galaxy surveys such as MaNGA (Bundy et al., 2015), providing spatially dense spectral data cubes from which complementary measurements of kinematics and spectral line strength can be obtained, offer major opportunities to investigate the underlying componentry and its assembly, provided appropriate techniques can be developed. This letter represents the second such technique developed by the authors. The first was in Long (2016) where the made-to-measure method (M2M) of Syer & Tremaine (1996) was extended to model galaxies using absorption line strength data. As with this letter, the 2016 paper was also the first time that M2M had been used in this way.

Overall, the modelling developments in this letter and the earlier paper are seen to be very promising first steps in creating stellar chemo-dynamical modelling schemes and in understanding some of the issues to be addressed.

References

• Bundy, K., Bershady, M. A., Law, D. R., et al. 2015, ApJ, 798, 7ADS

• Long, R. J. 2016, RAA(Research in Astronomy and Astrophysics), 16, 189ADS

• Schwarzschild, M. 1979, ApJ, 232, 236ADS

• Syer, D., & Tremaine, S. 1996, MNRAS, 282, 223ADS