%0 Generic %1 stevens2014where %A Stevens, Adam R. H. %A Martig, Marie %A Croton, Darren J. %A Feng, Yu %D 2014 %K end galaxy simulation %T Where do galaxies end? A study of hydrodynamic-simulation galaxies and their integrated properties %U http://arxiv.org/abs/1404.4053 %X Many techniques have been used in the literature for determining which particles or cells in a hydrodynamic simulation are attached to a galaxy. Often these invoke a spherical aperture that defines the boundary between the galaxy and the rest of its parent (sub)halo, sometimes coupled with, or alternatively involving, the use of a subhalo finder and gas property restrictions. Using the suite of high-resolution zoom re-simulations of individual haloes by Martig et al., and the large-scale simulation MassiveBlack-II, we examine the differences in measured galaxy properties from techniques with various aperture definitions. We perform techniques popular in the literature and present a new technique of our own, based on the baryonic mass profiles of simulated (sub)haloes. For the average Milky-Way-mass system, we find the two most popular techniques in the literature return differences of order 30 per cent for stellar mass, a factor of 3 for gas mass, 40 per cent for star formation rate, and factors of several for gas accretion and ejection rates. Individual cases can show variations greater than this, with the severity dependent on the concentration of a given system. The average difference in integrated properties for a more general galaxy population are not as striking, but are still significant for stellar and gas mass. The large differences that can occur are problematic for comparing results from various publications. We stress the importance of both defining and justifying a technique choice and discourage using popular apertures that use an exact fraction of the virial radius, due to the unignorable variation in galaxy-to-(sub)halo size. Finally, we note that technique choice does not greatly affect simulated galaxies from lying within the scatter of observed scaling relations, but it can alter the derived best-fit slope for the Kennicutt-Schmidt relation.

@misc{stevens2014where, abstract = {Many techniques have been used in the literature for determining which particles or cells in a hydrodynamic simulation are attached to a galaxy. Often these invoke a spherical aperture that defines the boundary between the galaxy and the rest of its parent (sub)halo, sometimes coupled with, or alternatively involving, the use of a subhalo finder and gas property restrictions. Using the suite of high-resolution zoom re-simulations of individual haloes by Martig et al., and the large-scale simulation MassiveBlack-II, we examine the differences in measured galaxy properties from techniques with various aperture definitions. We perform techniques popular in the literature and present a new technique of our own, based on the baryonic mass profiles of simulated (sub)haloes. For the average Milky-Way-mass system, we find the two most popular techniques in the literature return differences of order 30 per cent for stellar mass, a factor of 3 for gas mass, 40 per cent for star formation rate, and factors of several for gas accretion and ejection rates. Individual cases can show variations greater than this, with the severity dependent on the concentration of a given system. The average difference in integrated properties for a more general galaxy population are not as striking, but are still significant for stellar and gas mass. The large differences that can occur are problematic for comparing results from various publications. We stress the importance of both defining and justifying a technique choice and discourage using popular apertures that use an exact fraction of the virial radius, due to the unignorable variation in galaxy-to-(sub)halo size. Finally, we note that technique choice does not greatly affect simulated galaxies from lying within the scatter of observed scaling relations, but it can alter the derived best-fit slope for the Kennicutt-Schmidt relation.}, added-at = {2014-04-17T09:37:30.000+0200}, author = {Stevens, Adam R. H. and Martig, Marie and Croton, Darren J. and Feng, Yu}, biburl = {https://www.bibsonomy.org/bibtex/2945177214097917441908e374e759dff/miki}, description = {[1404.4053] Where do galaxies end? A study of hydrodynamic-simulation galaxies and their integrated properties}, interhash = {1433da5a5096d4aef3790b5a36892740}, intrahash = {945177214097917441908e374e759dff}, keywords = {end galaxy simulation}, note = {cite arxiv:1404.4053Comment: Submitted to MNRAS, 18 pages, 16 figures}, timestamp = {2014-04-17T09:37:30.000+0200}, title = {Where do galaxies end? A study of hydrodynamic-simulation galaxies and their integrated properties}, url = {http://arxiv.org/abs/1404.4053}, year = 2014 }