TY - JOUR
T1 - The formation and hierarchical assembly of globular cluster populations
AU - El-Badry, Kareem
AU - Quataert, Eliot
AU - Weisz, Daniel R.
AU - Choksi, Nick
AU - Boylan-Kolchin, Michael
N1 - Funding Information:
We also thank Mike Grudic, Charlie Conroy, Chris McKee, Joss Bland-Hawthorn, Aldo Rodriguez-Puebla, and Rohan Naidu for helpful discussions. Ideas for this project were developed in part at the Near/Far Globular Cluster Workshop in Napa in 2017 December. KE and DRW are grateful for the hospitality provided by the MPIA in Heidelberg during the writing of this paper. KE acknowledges support from an NSF Graduate Research Fellowship. EQ and KE are supported by a Simons Investigator Award from the Simons Foundation and by NSF grant AST-1715070. DRW is supported by fellowships provided by the Alfred P. Sloan Foundation and the Alexander von Humboldt Foundation. MBK acknowledges support from NSF grant AST-1517226 and CAREER grant AST-1752913 and from NASA grants NNX17AG29G and HST-AR-13888, HST-AR-13896, HST-AR-14282, HST-AR-14554, HST-AR-15006, HST-GO-12914, and HST-GO-14191 from STScI. The analysis in this paper relied on the PYTHON packages NumPy (Van Der Walt, Colbert & Varoquaux 2011), Matplotlib (Hunter 2007), and AstroPy (Astropy Collaboration 2013).
Funding Information:
We are grateful to Yu Lu for making public his implementation of the Parkinson & Cole merger tree algorithm. We thank the anonymous referee for constructive comments that improved the paper. We also thank Mike Grudic, Charlie Conroy, Chris McKee, Joss Bland-Hawthorn, Aldo Rodriguez-Puebla, and Rohan Naidu for helpful discussions. Ideas for this project were developed in part at the Near/Far Globular Cluster Workshop in Napa in 2017 December. KE and DRW are grateful for the hospitality provided by the MPIA in Heidelberg during the writing of this paper. KE acknowledges support from an NSF Graduate Research Fellowship. EQ and KE are supported by a Simons Investigator Award from the Simons Foundation and by NSF grant AST-1715070. DRW is supported by fellowships provided by the Alfred P. Sloan Foundation and the Alexander von Humboldt Foundation. MBK acknowledges support from NSF grant AST-1517226 and CAREER grant AST-1752913 and from NASA grants NNX17AG29G and HST-AR-13888, HST-AR-13896, HST-AR-14282, HST-AR-14554, HST-AR-15006, HST-GO-12914, and HST-GO-14191 from STScI. The analysis in this paper relied on the PYTHON packages NumPy (Van Der Walt, Colbert & Varoquaux 2011), Matplotlib (Hunter 2007), and AstroPy (Astropy Collaboration 2013).
Publisher Copyright:
© 2018 The Author(s).
PY - 2019/2/1
Y1 - 2019/2/1
N2 - We use a semi-analytic model for globular cluster (GC) formation built on dark matter merger trees to explore the relative role of formation physics and hierarchical assembly in determining the properties of GC populations. Many previous works have argued that the observed linear relation between total GC mass and halo mass points to a fundamental GC–dark matter connection or indicates that GCs formed at very high redshift before feedback processes introduced non-linearity in the baryon-to-dark matter mass relation. We demonstrate that at Mvir(z = 0) 1011.5 M, a constant ratio between halo mass and total GC mass is in fact an almost inevitable consequence of hierarchical assembly: by the central limit theorem, it is expected at z = 0 independent of the GC-to-halo mass relation at the time of GC formation. The GC-to-halo mass relation at Mvir(z = 0) < 1011.5 M is more sensitive to the details of the GC formation process. In our fiducial model, GC formation occurs in galaxies when the gas surface density exceeds a critical value. This model naturally predicts bimodal GC colour distributions similar to those observed in nearby galaxies and reproduces the observed relation between GC system metallicity and halo mass. It predicts that the cosmic GC formation rate peaked at z ∼ 4, too late for GCs to contribute significantly to the UV luminosity density during reionization.
AB - We use a semi-analytic model for globular cluster (GC) formation built on dark matter merger trees to explore the relative role of formation physics and hierarchical assembly in determining the properties of GC populations. Many previous works have argued that the observed linear relation between total GC mass and halo mass points to a fundamental GC–dark matter connection or indicates that GCs formed at very high redshift before feedback processes introduced non-linearity in the baryon-to-dark matter mass relation. We demonstrate that at Mvir(z = 0) 1011.5 M, a constant ratio between halo mass and total GC mass is in fact an almost inevitable consequence of hierarchical assembly: by the central limit theorem, it is expected at z = 0 independent of the GC-to-halo mass relation at the time of GC formation. The GC-to-halo mass relation at Mvir(z = 0) < 1011.5 M is more sensitive to the details of the GC formation process. In our fiducial model, GC formation occurs in galaxies when the gas surface density exceeds a critical value. This model naturally predicts bimodal GC colour distributions similar to those observed in nearby galaxies and reproduces the observed relation between GC system metallicity and halo mass. It predicts that the cosmic GC formation rate peaked at z ∼ 4, too late for GCs to contribute significantly to the UV luminosity density during reionization.
KW - Galaxies: formation
KW - Galaxies: star clusters: general
KW - Globular clusters: general
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U2 - 10.1093/mnras/sty3007
DO - 10.1093/mnras/sty3007
M3 - Article
AN - SCOPUS:85059432964
SN - 0035-8711
VL - 482
SP - 4528
EP - 4552
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -