wanglan@bao.ac.cn

I am a staff at National Astronomical Observatories, Chinese Academy of Sciences (NAOC). My research interests are galaxy formation and evolution, including related models, simulations and observations. In recent years, my works mainly focus on topics of galaxy morphology and galactic bulges, both from simulation point of view and from observational statistics.

Galaxy morphology

Based on a wrok of comparing galaxy morphology in Illustris simulation and semi-analytic models, we further explore the formation of massive disc galaxies, and the formation of low-mass galaxies with different morphologies in TNG simulation. In addition, an observaional work is done which studies the HI content of massive red spirals using the FAST radio telescope.

• Wang et al. 2019c: comparing galaxy morphology in hydrodynamical simulation Illustris and in semi-analytic model.

• Zeng, Wang & Gao 2021: the formation of massive disc galaxies in the IllustrisTNG simulation. We find that major mergers with a spiral-in falling orbit mostly lead to disc-dominant remnants, and major mergers of head-on galaxy–galaxy collision mostly form ellipticals. This dependence of remnant morphology on orbit type is much stronger than the dependence on cold gas fraction or orbital configuration of merger system.

• Zeng, Wang et al. 2024: kinematic morphology of low-mass galaxies in IllustrisTNG. If the cold gas disc remains aligning with the galaxy during its evolution, stars formed at different times share the same rotational direction, leading to a rotation-dominated system. The simulated morphology of galaxies is reliable when their number of stellar particles exceeds about 10,000, and bulge morphology of galaxies can not be resolved robustly at the resolution level of TNG50-1.

• Wang et al. 2022: We observe H I content of the rest 113 massive red spiral galaxies using the FAST telescope. Galaxies with higher HI masses have bluer outer discs. Optically selected massive red spirals are not fully quenched, and the HI gas observed in many of the galaxies may exist in their outer blue discs.

Galactic bulges

Observations indicate that there are two main categories of bulges: classical bulges and pseudo-bulges. We perform studies of clustering and neighbor counts of galaxies with different types of bulges, to invesitgate the environment that may affect the formation of bulges. We also compare properties of classical and pseudo-bulges and properties of their hosting galaxies to dig more their possible formation paths.

• Wang et al. 2019b: the clustering properties and close neighbour counts for galaxies with different types of bulges and stellar masses. Neither the presence of a central bulge, nor the bulge type is related to intermediate-to-large scale environments. On smaller scales, pseudo bulge and pure-disc galaxies similarly show strong excess in close neighbour count.

• Hu, Wang et al. 2024: resolved properties of classical and pseudo-bulges and properties of their hosting galaxies selected from the MaNGA survey. At given stellar mass, disc components of pseudo-bulge galaxies are younger, have more active star formation, rotate more, and may contain more H I content compared with those of classical bulge galaxies, and the differences are larger than those between bulges themselves. Different types of bulges are shaped by different processes that may regulate both growth of central components and evolution of outer discs in galaxies.

Comparison and degenereacy of galaxy formation models

The current models of galaxy formation and evolution have achieved many successes. However, the detail descriptions on different physical processes still have a lot of uncertainties, and degeneracies exist among these processes in reproducing observational statistics of galaxies. For example, for semi-analytic galaxy formation models, modification to the star formation law has similar effect as increasing supernovae feedback, in suppressing star formation in low mass galaxies in low redshift to match observation. Even when the relations between galaxy stellar mass and its host dark matter halo mass in different models show the same median relation, how galaxies populate the scatters of the relation can result to different galaxy clustering properties, due to the detail dependence of galaxy stellar mass on halo formation time. Apart from the degeneracies of physical processes, cosmology also adds degeneracy in the picture of galaxy formation. Warm dark matter and cold dark matter cosmologies result to similar galaxy properties of many aspects that are difficult to be distinguished within current observational accuracy.

• Wang, Weinmann & Neistein 2012: A modified star formation law as a solution to open problems in galaxy evolution.

• Wang, De Lucia & Weinmann 2013: On the scatter in the relation between stellar mass and halo mass: random or halo formation time dependent?

• Wang et al. 2013: Detection of galaxy assembly bias. At fixed stellar mass, SAMs predict that the clustering of central galaxies depends on the specific star formation rate, with more passive galaxies having a higher clustering amplitude. We find similar trends using the SDSS group catalogues. The clustering dependence on sSFR represent a direct detection of assembly bias.

• Wang et al. 2017: The galaxy population in cold and warm dark matter cosmologies. Combining a pair of N-body simulations implementing the standard CDM cosmogony and a WDM, with the GALFORM semi-analytical galaxy formation model, the only significant difference of galaxy populations in the local universe we find is in the galaxy populations of ‘Local Volumes’.

• Wang et al. 2019a: Starburst galaxies in semi-analytic models of galaxy formation and evolution. We study the shape and evolution of the star formation main sequence, and in particular, starburst galaxies in three independently developed semi-analytic models of galaxy formation. Starburst galaxies are not necessarily associated with merger episodes, especially at the low-mass end.

• Wang et al. 2019c: comparing galaxy morphology in hydrodynamical simulation and in semi-analytic model.

Models on statistical relations between galaxy and (sub)halo

A methodology was developed that falls midway between the traditional semi-analytic approach and the halo occupation distribution (HOD) approach. In our models, the positions and velocities of the galaxies are predicted by following the orbits and merging histories of the substructures in simulation. Parametrized functions are modelled to relate galaxy properties to the halo mass at infall time. A series of works have been done based on this method.

• Wang et al. 2006: relations between the luminosities and the stellar masses of galaxies in the local Universe and their host halo masses are constrained, by fitting the luminosity function, the stellar mass function and the shape and amplitude of the two-point correlation function evaluated in different stellar mass and luminosity ranges in SDSS.

• Wang et al. 2007: Modelling and interpreting the dependence of clustering on the spectral energy distributions of galaxies. Star formtion histories of central and satellite galaxies are further modelled and constrained, by fitting the observed abundances and projected correlations of galaxies as a function of 4000-Å break strength/g-r color in the SDSS.

• Wang & Jing 2010: applied to redshift of around 0.8, the stellar mass - halo mass relation is constrained by fitting both the stellar mass function and the correlation functions at different stellar mass intervals of VVDS observations. A unified model of the stellar mass - halo mass relation as a function of time is also proposed, by fitting both SDSS and VVDS observations simultaneously.

• Wang 2017 (in Chinese): a review on models that link galaxies with (sub)haloes, which study the relation between galaxy properties and (sub)halo properties in a statistical way.

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E-mail: wanglan@bao.ac.cn