分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Star formation in disk galaxies is observed to follow the empirical Kennicutt-Schmidt law, a power-law relationship between the surface density of gas ($\Sigma_{gas}$) [$\textrm{M}_{\odot}\; \textrm{kpc}^{-2}$] and the star formation rate ($\Sigma_{SFR}$) [$\textrm{M}_{\odot}\; \textrm{kpc}^{-2} \; \textrm{Gyr}^{-1}$]. In contrast to disk galaxies, early-type galaxies (ETGs) are typically associated with little to no star formation and therefore no Kennicutt-Schmidt law; recent observations, however, have noted the presence of massive gaseous cold disks in ETGs, raising the question as to why the conversion of gas into stars is so inefficient. With our latest simulations, performed with our high-resolution hydrodynamic numerical code MACER, we reevaluate the traditional classification of ETGs as quiescent, dead galaxies. We predict the inevitable formation of stellar disks following cooling episodes of the ISM of the host galaxy in the presence of galactic rotation via a simple but robust star formation model combining local Toomre instabilities and local gas cooling timescales. We find that resolved Kennicutt-Schmidt star formation laws for our simulated ETGs, in both surface density and volumetric forms, reproduce the observed threshold, slope, and normalization observed in disk galaxies. At the same time, through analysis of global Kennicutt-Schmidt laws, we suggest that increased star formation and high gaseous outflows offers a partial remedy to the observed star formation inefficiency problem. Observational checks of our star formation predictions are thus essential for confirming the form of local star formation laws and reassessing star formation inefficiency in ETGs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The cosmological inflow of a galaxy is speculated to be able to enter the galaxy and enhance the star formation rate (SFR) and black hole accretion rate (BHAR). In this paper, by performing high-resolution hydrodynamic simulations in the framework of {\it MACER}, we investigate the fate of the inflow and its impacts on the evolution of a massive elliptical galaxy. The inflow properties are adopted from the cosmological simulation IllustrisTNG. We find that, the inflow gas hardly enters but is blocked beyond $\sim 20$ kpc from the central galaxy and becomes part of the circumgalactic medium (CGM). The gas pressure gradient, mainly contributed by the thermalized stellar wind and subdominantly by the energy input from the AGN, balances gravity and prevents the inflow from entering the galaxy. The SFR and BHAR are almost not affected by the normal inflow. However, if the rate of cosmological inflow were increased by a factor of 3, a small fraction of the inflow would enter the galaxy and contribute about 10\% of the gas in the galaxy. In this case, the gas density in the galaxy would increase by a factor of $\ga$ 20. This increase is not because of the additional gas supply by the inflow but the increase of gas density in the CGM caused by the inflow. Consequently, the SFR and BHAR would increase by a factor of $\sim$ 5 and $\sim 1000$ respectively. Finally, AGN feedback can perturb the motion of the inflow and heat the CGM through its intermittent outbursts.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The cosmological inflow of a galaxy is speculated to be able to enter the galaxy and enhance the star formation rate (SFR) and black hole accretion rate (BHAR). In this paper, by performing high-resolution hydrodynamic simulations in the framework of {\it MACER}, we investigate the fate of the inflow and its impacts on the evolution of a massive elliptical galaxy. The inflow properties are adopted from the cosmological simulation IllustrisTNG. We find that, the inflow gas hardly enters but is blocked beyond $\sim 20$ kpc from the central galaxy and becomes part of the circumgalactic medium (CGM). The gas pressure gradient, mainly contributed by the thermalized stellar wind and subdominantly by the energy input from the AGN, balances gravity and prevents the inflow from entering the galaxy. The SFR and BHAR are almost not affected by the normal inflow. However, if the rate of cosmological inflow were increased by a factor of 3, a small fraction of the inflow would enter the galaxy and contribute about 10\% of the gas in the galaxy. In this case, the gas density in the galaxy would increase by a factor of $\ga$ 20. This increase is not because of the additional gas supply by the inflow but the increase of gas density in the CGM caused by the inflow. Consequently, the SFR and BHAR would increase by a factor of $\sim$ 5 and $\sim 1000$ respectively. Finally, AGN feedback can perturb the motion of the inflow and heat the CGM through its intermittent outbursts.
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