Summary of Ph.D. thesis

The title of my thesis is “Galaxy evolution by chemical and spectro-photometric models”. In my thesis, I studied the chemical and spectro-photometric evolution of galaxies. By comparing some high and low redshift data with model predictions, this thesis will try to answer several questions: 1) What is the galaxy formation and evolution scenario suggested by chemical and spectro-photometric models which can reproduce observational data? 2) Which properties of galaxies can be constrained by models and how well do these constraints work? 3) How could ingredients of models affect the model predictions? To do that I have adopted detailed chemical evolution models including dust evolution, as well as spectro-photometric models including radiative transfer be- tween stars and dust. In particular, I have studied “The chemical evolution of elliptical galaxies with stellar and QSO dust production” (A&A, 2011, 525, 61), and the main results are that 1) The elliptical galaxies should formed at high redshift very quickly with very intense star formation, and both the infall and the star formation timescales are needed to decrease with galactic mass, in order to reproduce the “chemical down- sizing”. 2) The dust is clearly due to the production from supernovae and the most massive AGB stars as well as from the grain growth in the interstellar medium, and 3) The QSO dust is likely to dominate only in the very central regions of the galaxies and during the early development of the galactic wind. Then, an evolutionary sequence of long Gamma-ray burst (LGRB) hosts at low and high redshift is suggested by irregu- lar chemical evolution models in the paper “The nature of LGRB host galaxies from chemical abundances” (A&A, 2010, 521, 73), while models for spirals and particularly ellipticals fit neither the high-redshift hosts of LGRBs (damped Lyman-α systems) nor the low redshift hosts. We also found that the predicted Type Ib/c supernova rate for irregulars is in good agreement with observations in that paper. The monolithic formation and evolution scenario of elliptical galaxies suggested by chemical evolution models is confirmed by spectro-photometric models, which can fit the pan-spectral en- ergy distribution (pan-SED) of the average MIPS 24μm detected Lyman break galaxies (MIPS-LBGs) at z 3 in the paper “From dust to galaxy: the nature of LBGs at z 3 from pan-spectral energy distribution modeling” (in progress). In that paper, the galaxy-wide properties of MIPS-LBGs derived by spectro-photometric models are discussed. We found that: 1) MIPS-LBGs are likely young (0.3-0.6 Gyr) elliptical galaxies with average mass Mtot 1011M, 2) The molecular clouds in average MIPS- LBGs are likely more dense dusty environments than in the Milky Way, 3) The dust size distribution in average MIPS-LBGs may be flatter than in the Milky Way and 4) Non-negligible polycyclic aromatic hydrocarbons are needed to reproduce the SED of the stacked MIPS-LBG. In the paper “IGIMF on [α/Fe] of starburst galaxies” (in progress), the IMF effects on the [α/Fe] ratios of LBGs are investigated by adopting a particular time-dependent initial mass function (IMF), the integrated galactic initial mass function (IGIMF). The dust effects on the [α/Fe] ratios are also discussed in that paper. We found that: 1) The IGIMF of starburst galaxies improves the [α/Fe] ratios, but it still cannot solve the discrepancy between predictions and data, 2) The most plausible approach to solve the discrepancy is differential dust depletion in ISM, such as more Fe locked in dust or fewer α element locked in ISM or both.

The thesis will be organized as follows. Chapter 1 will give an introduction on galaxy formation and evolution, chemical and SED models, dust and the particular objects studied in this thesis (LBGs, LGRB hosts and QSOs). The details of the chemical and SED models will be described in Chapter 2 and 3, respectively. Chapter 4 will show the general results of chemical evolution models. The results of elliptical models with stellar and QSO dust will be shown in more details comparing to spiral and irregular models. Chapter 5 will show the results on the LGRB host and QSO by the chemical evolution models. Chapter 6 will discuss the nature of LBGs at redshift z 3 by chemical and sed models. The IGIMF effects on the [α/Fe] ratios on starburst galaxies will be briefly discussed in Chapter 7. Finally, the summary will be shown in Chapter 8.