Editing Galaxy formation and evolution (section)

====Star formation====

As cold and dense gas accumulates, it undergoes gravitational collapse and eventually forms stars. To simulate this process, a portion of the gas is transformed into collisionless star particles, which represent coeval, single-metallicity stellar populations and are described by an initial underlying mass function. Observations suggest that star formation efficiency in molecular gas is almost universal, with around 1% of the gas being converted into stars per free fall time.<ref name="BigielLeroyWalter2011">{{cite journal | last1 = Bigiel | first1 = F. | last2 = Leroy | first2 = A. K. | last3 = Walter | first3 = F. | last4 = Brinks | first4 = E. | last5 = de Blok | first5 = W. J. G. | last6 = Kramer | first6 = C. | last7 = Rix | first7 = H. W. | last8 = Schruba | first8 = A. | last9 = Schuster | first9 = K.-F. | last10 = Usero | first10 = A. | last11 = Wiesemeyer | first11 = H. W. | title = A Constant Molecular Gas Depletion Time in Nearby Disk Galaxies | journal = The Astrophysical Journal | date = 3 March 2011 | volume = 730 | issue = 2 | page = L13 | issn = 2041-8205 | eissn = 2041-8213 | doi = 10.1088/2041-8205/730/2/L13 | pmid = | url = | arxiv = 1102.1720 | bibcode = 2011ApJ...730L..13B | s2cid = 18832882 }}</ref> In simulations, the gas is typically converted into star particles using a probabilistic sampling scheme based on the calculated star formation rate. Some simulations seek an alternative to the probabilistic sampling scheme and aim to better capture the clustered nature of star formation by treating star clusters as the fundamental unit of star formation. This approach permits the growth of star particles by accreting material from the surrounding medium.<ref name="LiGnedinGnedin2017">{{cite journal | last1 = Li | first1 = Hui | last2 = Gnedin | first2 = Oleg Y. | last3 = Gnedin | first3 = Nickolay Y. | last4 = Meng | first4 = Xi | last5 = Semenov | first5 = Vadim A. | last6 = Kravtsov | first6 = Andrey V. | title = Star Cluster Formation in Cosmological Simulations. I. Properties of Young Clusters | journal = The Astrophysical Journal | date = 3 January 2017 | volume = 834 | issue = 1 | page = 69 | eissn = 1538-4357 | doi = 10.3847/1538-4357/834/1/69 | pmid = | url = | arxiv = 1608.03244 | doi-access = free | bibcode = 2017ApJ...834...69L }}</ref> In addition to this, modern models of galaxy formation track the evolution of these stars and the mass they return to the gas component, leading to an enrichment of the gas with metals.<ref name="VogelsbergerGenelSijacki2013">{{cite journal | last1 = Vogelsberger | first1 = Mark | last2 = Genel | first2 = Shy | last3 = Sijacki | first3 = Debora|author3-link= Debora Šijački | last4 = Torrey | first4 = Paul | last5 = Springel | first5 = Volker | last6 = Hernquist | first6 = Lars | title = A model for cosmological simulations of galaxy formation physics | journal = Monthly Notices of the Royal Astronomical Society | date = 23 October 2013 | volume = 436 | issue = 4 | pages = 3031–3067 | issn = 0035-8711 | eissn = 1365-2966 | doi = 10.1093/mnras/stt1789 | pmid = | url = | doi-access = free | arxiv = 1305.2913 }}</ref>