Galaxies in a simulated ΛCDM universe - II. Observable properties and constraints on feedback
Abstract
We compare the properties of galaxies that form in a cosmological simulation without strong feedback to observations of the z = 0 galaxy population. We confirm previous findings that models without strong feedback overproduce the observed galaxy baryonic mass function, especially at the low- and high-mass extremes. Through post-processing we investigate what kinds of feedback would be required to reproduce the statistics of observed galaxy masses and star formation rates. To mimic an extreme form of `preventive' feedback, such as a highly efficient active galactic nucleus `radio mode', we remove all baryonic mass that was originally accreted from shock-heated gas (`hot-mode' accretion). This removal does not bring the high-mass end of the galaxy mass function into agreement with observations because much of the stellar mass in these systems formed at high redshift from baryons that originally accreted via `cold mode' on to lower mass progenitors. An efficient `ejective' feedback mechanism, such as supernova-driven galactic winds, must reduce the masses of these progenitors before they merge to form today's massive galaxies. Feedback must also reduce the masses of lower mass z = 0 galaxies, which assemble at lower redshifts and have much lower star formation rates. If we monotonically remap galaxy masses to reproduce the observed mass function, but retain the simulation-predicted star formation rates, we obtain fairly good agreement with the observed sequence of star-forming galaxies. However, we fail to recover the observed population of passive, low star formation rate galaxies, especially at the high-mass end. Suppressing all hot-mode accretion improves the agreement for high-mass galaxies, but it worsens the agreement at intermediate masses. Reproducing these z = 0 observations requires a feedback mechanism that dramatically suppresses star formation in a fraction of galaxies, increasing with mass, while leaving star formation rates of other galaxies essentially unchanged.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2009
- DOI:
- 10.1111/j.1365-2966.2009.14924.x
- arXiv:
- arXiv:0901.1880
- Bibcode:
- 2009MNRAS.396.2332K
- Keywords:
-
- methods: numerical;
- cooling flows;
- galaxies: evolution;
- galaxies: formation;
- galaxies: luminosity function;
- mass function;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- MNRAS in press. 15 pages, 5 figures, minimal changes from the first version