The galaxy-halo size relation of low-mass galaxies in FIRE. Rohr, E., Feldmann, R., Bullock, J., Çatmabacak, O., Boylan-Kolchin, M., Faucher-Giguère, C., Kereš, D., Liang, L., Moreno, J., & Wetzel, A. arXiv:2112.05159 [astro-ph], December, 2021. arXiv: 2112.05159
The galaxy-halo size relation of low-mass galaxies in FIRE [link]Paper  abstract   bibtex   
Galaxy sizes correlate closely with the sizes of their parent dark matter haloes, suggesting a link between halo formation and galaxy growth. However, the precise nature of this relation and its scatter remains to be understood fully, especially for low-mass galaxies. We analyse the galaxy-halo size relation for low-mass (\$M_{\textbackslash}star {\textbackslash}sim 10{\textasciicircum}\{7-9\} \{{\textbackslash}rm M_{\textbackslash}odot\}\$) central galaxies over the past 12.5 billion years with the help of cosmological volume simulations (FIREbox) from the Feedback in Realistic Environments (FIRE) project. We find a nearly linear relationship between the half-stellar mass galaxy size \$R_\{1/2\}\$ and the parent dark matter halo virial radius \$R_\{{\textbackslash}rm vir\}\$. This relation evolves only weakly since redshift \$z = 5\$: \$R_\{1/2\} \{{\textbackslash}rm kpc\} = (0.053{\textbackslash}pm0.002)(R_\{{\textbackslash}rm vir\}/35 \{{\textbackslash}rm kpc\}){\textasciicircum}\{0.934{\textbackslash}pm0.054\}\$, with a nearly constant scatter \${\textbackslash}langle {\textbackslash}sigma {\textbackslash}rangle = 0.084 [\{{\textbackslash}rm dex\}]\$. Whilst this ratio is similar to what is expected from models where galaxy disc sizes are set by halo angular momentum, the low-mass galaxies in our sample are not angular momentum supported, with stellar rotational to circular velocity ratios \$v_\{{\textbackslash}rm rot\} / v_\{{\textbackslash}rm circ\} {\textbackslash}sim 0.15\$. Introducing redshift as another parameter to the GHSR does not decrease the scatter. Furthermore, this scatter does not correlate with any of the halo properties we investigate – including spin and concentration – suggesting that baryonic processes and feedback physics are instead critical in setting the scatter in the galaxy-halo size relation. Given the relatively small scatter and the weak dependence of the galaxy-halo size relation on redshift and halo properties for these low-mass central galaxies, we propose using galaxy sizes as an independent method from stellar masses to infer halo masses.
@article{rohr_galaxy-halo_2021,
	title = {The galaxy-halo size relation of low-mass galaxies in {FIRE}},
	url = {http://arxiv.org/abs/2112.05159},
	abstract = {Galaxy sizes correlate closely with the sizes of their parent dark matter haloes, suggesting a link between halo formation and galaxy growth. However, the precise nature of this relation and its scatter remains to be understood fully, especially for low-mass galaxies. We analyse the galaxy-halo size relation for low-mass (\$M\_{\textbackslash}star {\textbackslash}sim 10{\textasciicircum}\{7-9\} \{{\textbackslash}rm M\_{\textbackslash}odot\}\$) central galaxies over the past 12.5 billion years with the help of cosmological volume simulations (FIREbox) from the Feedback in Realistic Environments (FIRE) project. We find a nearly linear relationship between the half-stellar mass galaxy size \$R\_\{1/2\}\$ and the parent dark matter halo virial radius \$R\_\{{\textbackslash}rm vir\}\$. This relation evolves only weakly since redshift \$z = 5\$: \$R\_\{1/2\} \{{\textbackslash}rm kpc\} = (0.053{\textbackslash}pm0.002)(R\_\{{\textbackslash}rm vir\}/35 \{{\textbackslash}rm kpc\}){\textasciicircum}\{0.934{\textbackslash}pm0.054\}\$, with a nearly constant scatter \${\textbackslash}langle {\textbackslash}sigma {\textbackslash}rangle = 0.084 [\{{\textbackslash}rm dex\}]\$. Whilst this ratio is similar to what is expected from models where galaxy disc sizes are set by halo angular momentum, the low-mass galaxies in our sample are not angular momentum supported, with stellar rotational to circular velocity ratios \$v\_\{{\textbackslash}rm rot\} / v\_\{{\textbackslash}rm circ\} {\textbackslash}sim 0.15\$. Introducing redshift as another parameter to the GHSR does not decrease the scatter. Furthermore, this scatter does not correlate with any of the halo properties we investigate -- including spin and concentration -- suggesting that baryonic processes and feedback physics are instead critical in setting the scatter in the galaxy-halo size relation. Given the relatively small scatter and the weak dependence of the galaxy-halo size relation on redshift and halo properties for these low-mass central galaxies, we propose using galaxy sizes as an independent method from stellar masses to infer halo masses.},
	urldate = {2021-12-17},
	journal = {arXiv:2112.05159 [astro-ph]},
	author = {Rohr, Eric and Feldmann, Robert and Bullock, James and Çatmabacak, Onur and Boylan-Kolchin, Michael and Faucher-Giguère, Claude-André and Kereš, Dušan and Liang, Lichen and Moreno, Jorge and Wetzel, Andrew},
	month = dec,
	year = {2021},
	note = {arXiv: 2112.05159},
	keywords = {Astrophysics - Astrophysics of Galaxies},
}

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