Abstract
We develop a model for the origins and redshift evolution of spheroid scaling relations. We consider spheroid sizes, velocity dispersions, masses, profile shapes (Sersic indices), and black hole (BH) masses, and their related scalings. Our approach combines advantages of observational constraints in halo occupation models and hydrodynamic merger simulations. This allows us to separate the relative roles of dissipation, dry mergers, formation time, and progenitor evolution, and identify their effects on scalings at each redshift. Dissipation is the most important factor determining spheroid sizes and fundamental plane (FP) scalings, and can account for the FP tilt and differences between disk and spheroid scalings. Because disks at high-z have higher gas fractions, mergers are more gas-rich, yielding more compact spheroids. This predicts mass-dependent evolution in spheroid sizes, in agreement with observations. This relates to subtle evolution in the FP, important to studies that assume a fixed intrinsic FP. This also predicts mild evolution in BH-host correlations, towards larger BHs at higher z. Dry mergers are significant, but only for massive systems which form early: they form compact, but undergo dry mergers (consistent with observations) such that their sizes at later times are similar to spheroids of similar mass formed more recently. We model descendants of observed compact high-z spheroids: most will become cores of BCGs, with sizes, velocity dispersions, and BH masses consistent with observations, but we identify a fraction that might survive to z=0 intact.
Highlights
Understanding the scaling relations between the photometric and kinematic properties of galaxy spheroids – their masses, sizes, velocity dispersions, and luminosities – is fundamental to explaining their origin
Compact high-redshift ellipticals will become the cores of present BCGs, and we show how their sizes, velocity dispersions, and black hole masses evolve to become consistent with observations
We have compared a variety of prescriptions for the redshift evolution of various components in the halo occupation model: we have adopted that directly fitted by the authors above at various redshifts, we have considered a complete re-derivation of the halo occupation distribution (HOD) models of Conroy et al (2006) and Vale & Ostriker (2006) at different redshifts from each of the the observed mass functions of Fontana et al (2006); Bundy et al (2005); Borch et al (2006); Blanton (2006), and have found similar results assuming no evolution in P(Mgal | Msubhalo)
Summary
Understanding the scaling relations between the photometric and kinematic properties of galaxy spheroids – their masses, sizes, velocity dispersions, and luminosities – is fundamental to explaining their origin. In order to get around some of these limitations, alternative attempts have been made to instead predict scaling resolutions from semi-analytic models of galaxy formation (Khochfar & Silk 2006; Almeida et al 2007) They could not calibrate the details of their predictions with numerical simulations, Khochfar & Silk (2006) used this to illustrate, with very simple assumptions, that increasing dissipational fractions in ellipticals at higher redshift leads to the expectation that spheroids should be more compact. We adopt this method to combine the advantages of high-resolution simulations, semi-analytic models, and observational constraints on spheroid progenitors in order to develop robust predictions for the evolution of spheroid structure and the correlation between black hole mass and host properties. All magnitudes are in the Vega system, unless otherwise specified
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
