Galaxy pair interaction and star formation rate, color, morphology from a semi-analytical model

1. Galaxy pair interaction and star formation rate, color, morphology from a semi-analytical model Jianling Gan Korea Astronomy and Space Science Institute Shanghai Astronomical Observatory

2. Background • The cosmic structure is formed during the collapse of dark matter due to gravitational instability, and the virial structure is seen as dark matter halo. • The baryonic gas condense in the radiative cooling and fall into the halo, and finally form a galaxy, before which there exist a complicated set of physical processes. • The halo formation is processed in a hierarchical manner that small haloes form first, and they subsequently merge to form bigger haloes.

3. Motivation • Galaxy merger is an important process in the formation and evolution of galaxies. • How does it affect the star formation, color and morphology of galaxies? • The circumstances of a galaxy are of diversity and complex. • Finding some statistical law from a large sample of galaxies.

4. Model • Phoenix (Gao et al. 2011), N-body simulation, code: Gadget-3 (springel et al. 2008) • 9 clusters, Mh=6.59*1014M⊙ ~2.43*1015M⊙ • millions of haloes, thousands of halo merger trees • The semi-analytical model implements the physical processes of baryon into the merger trees of dark matter halo. • Galacticus (Benson et al. 2010), an open source galaxy formation code.

5. Physical implementation I • Accretion of gas into haloes and gas cooling inside halo (e.g., White & Frenk 1991; Benson et al. 2002) • Initial mass function for star formation (Chabrier et al. 2001) • Stellar population spectra, FSPS v2.3 (Conroy et al. 2009) • Star formation model (Krumholz et al. 2009) • Black hole formation model (Rezzolla et al. 2008)

6. Physical implementation II • Feedback by stellar winds, supernovae and black hole (e.g., Leitherer et al. 1992; Nagashima et al. 2005; Ostriker et al. 2010) • Exponential disk (e.g., Mo et al. 1998; Binney & Tremaine 2008) • Hernquist spheroid, including bulges of disk galaxies and ellipticals (Hernquist 1990; Kormendy & Kennicutt 2004) • ……

7. Galaxy pairs selection • Mass: Mh > 1010M⊙, massive • Distance: dR=d/(Rvir,1+Rvir,2)<?, close • Energy: K < |W|, gravitationally bound

8. Results

9. Global history The cluster which has more number of galaxy pairs will has higher star formation rate.

10. Effect on the satellite galaxy Cumulative probability: the number of galaxies, which have a physical component less than a specific value, over the total number of galaxies. The effects of pair interaction on the satellite galaxy are weak.

11. Cold gas in the host galaxy • Stronger interaction leads to more gas accretion in the host galaxies. • Pair interactions induce gas compression and a noticeable increasing of gas cooling; • Beside the direct gas cooling, accretions of cold gas from satellite galaxy also increase the gas of the host galaxy.

12. SFR and Stellar mass • Stronger interaction leads to higher SFR and more star formation. • The mass ratio play a much more important role than the distance.

13. Disk scale length and spheroid scale length • Stronger interaction leads to the formation of larger disk and spheroid.

14. Black hole mass • For massive black hole, the interaction boost the growth of black hole; • For small black hole, the inaction inhibit the growth of black hole.

15. Summary We study the effects of galaxy interaction on the star formation and galactic morphology. We find that stronger interaction lead to more gas accretion, star formation, larger disk and spheroid formation. The mass ratio between galaxies play a much more important role in the interaction than their distance. The interactions between galaxies exhibit an opposite effect on the small and massive black hole.

16. Thank you!