“Making Normal Galaxies in a Cosmological Setting”. “Making Galaxies Red and Dead Without Feedback”. T.Naab, P. Johansson, K. Nagamine, G.Efstathiou, RY Cen and J.P.O. Princeton, 27 Feb 2009: jpo. Cambridge, 8 May 2008. Cosmological Simulation: Start with WMAP CBR Sky. Hinshaw et al; 2008.
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“Making Galaxies Red and Dead Without Feedback”
T.Naab, P. Johansson, K. Nagamine, G.Efstathiou, RY Cen and J.P.O.
Princeton, 27 Feb 2009: jpo
Cambridge, 8 May 2008
Hinshaw et al; 2008
linear perturbation theory
DM* = const* x DMgas x dt/Max(Tcool,Tdyn).
(cf R. Kennicutt and M. Kuchner)
C* = 0.05
(better mass resolution)
Naab et al (2007)
(better spatial resolution)
THAT IS ALL THERE IS
But what about “feedback” ?
(but feedback is necessary and does cause some moderate variance: NB digression ->)
Bubbles blown by super-winds from forming galaxies heat the ambient medium and retard subsequent gas infall: Cen et al 2004, Dave …
(feedback important for IGM, but relatively unimportant for galaxy properties)
Feedback Increases Number of Small Mass Galaxies and Reduces Number of High Mass Galaxies.
(effects largely compensate and produce little net change in SF rate)
TVD Hydro vs Data
SPH Hydro & SAM vs Data
Blanton, M.; Cen, R.; Ostriker, J. P.; Strauss, M. A.; Tegmark, M.
ApJ.531, 1 (2000)
TVD Hydro Simulation
In clusters, the fall off in star formation since z=1 is much more rapid than in the field.
Cause is simply
C2x > V2gal,esc
Effect of hot gas in suppressing GF
Naab, Johannson, Ostriker and Eftsatiou
Convergence to low and to a flat rotation curve at high resolution:
Convergence to stellar system formed very early which quickly becomes “red and dead”.
Gas, at all radii, becomes hotter with time despite fact that the “cooling time”< the Hubble time! Why?
Accreted stellar mass, 45% of total is added late ( z < 1.5), and at larger radii.
A Normal Elliptical: fits Sersic Profile
(detailed kinematics ok as well)
Cooling time of gas becomes longer than the dynamical time and star formation ceases. Systems live in hot bubbles and then grow by accretion of smaller stellar systems.
“Simulations of Galaxy Formation in a Λ Cold Dark Matter Universe. I. Dynamical and Photometric Properties of a Simulated Disk Galaxy” & “II. The Fine Structure of Simulated Galactic Disks”
by Abadi, Mario G.; Navarro, Julio F.; Steinmetz, Matthias; Eke, Vincent R. Ap.J;591,499 (2003) & 597, 21
Many other good papers, but typically suffer from same problem, of too bulge dominated and too high a rotation curve, with a recent excellent summary of the issues:
“The formation of disk galaxies in computer simulations”: Mayer, L.; Governato, F.; Kaufmann, T.( astroph0801.3845v )
We review the progress made by numerical simulations carried out on large parallel supercomputers. Recent progress stems from a combination of increased resolution and improved treatment of the astrophysical processes modeled in the simulations, such as the phenomenological description of the interstellar medium and of the process of star formation. High mass and spatial resolution is a necessary condition in order to obtain large disks comparable with observed spiral galaxies avoiding spurious dissipation of angular momentum. A realistic model of the star formation history. gas-to-stars ratio and the morphology of the stellar and gaseous component is instead controlled by the phenomenological description of the non-gravitational energy budget in the galaxy. We show that simulations of gas collapse within cold dark matter halos including a phenomenological description of supernovae blast-waves allow to obtain stellar disks with nearly exponential surface density profiles as those observed in real disk galaxies, counteracting the tendency of gas collapsing in such halos to form cuspy baryonic profiles. However, the ab-initio formation of a realistic rotationally supported disk galaxy with a pure exponential disk in a fully cosmological simulation is still an open problem.
Alternate approach: put in cosmological context, but model the components separately without attempting hydro
“A simple model for the evolution of disc galaxies: the Milky Way”
Naab, Thorsten; Ostriker, Jeremiah P. (MNRAS; 366,899;2006)
A simple model for the evolution of disc galaxies is presented. We adopt three numbers from observations of the Milky Way disc, Σd the local surface mass density, rd the stellar scalelength, Vc, the amplitude of the rotation curve, and physically, the local Kennicutt star formation prescription, standard chemical evolution equations assuming a Salpeter initial mass function and a model for spectral evolution of stellar populations. We can determine the detailed evolution of the model with only the addition of standard cosmological scalings with the time of the dimensional parameters. A surprising wealth of detailed specifications follows from this prescription including the gaseous infall rate as a function of radius and time, the distribution of stellar ages and metallicities with time and radius, surface brightness profiles at different wavelengths, colors, etc.
Models of the chemical evolution of our Galaxy are extended to include radial migration of stars and flow of gas through the disc. The models track the production of both iron and alpha elements. A model is chosen that provides an excellent fit to the metallicity distribution of stars in the Geneva-Copenhagen survey (GCS) of the solar neighbourhood, and an acceptable fit to the local Hess diagram. The model provides a good fit to the distribution of GCS stars in the age-metallicity plane although this plane was not used in the fitting process. Although this model's star-formation rate is monotonic declining, its disc naturally splits into an alpha-enhanced thick disc and a normal thin disc. In particular the model's distribution of stars in the ([O/Fe],[Fe/H]) plane resembles that of Galactic stars in displaying a ridge line for each disc. The thin-disc's ridge line is entirely due to stellar migration and there is the characteristic variation of stellar angular momentum along it that has been noted by Haywood in survey data. Radial mixing of stellar populations with high sigma_z from inner regions of the disc to the solar neighbourhood provides a natural explanation of why measurements yield a steeper increase of sigma_z with age than predicted by theory. The metallicity gradient in the ISM is predicted to be steeper than in earlier models, but appears to be in good agreement with data for both our Galaxy and external galaxies. The absolute magnitude of the disc is given as a function of time in several photometric bands, and radial colour profiles are plotted for representative times.
Cooling time of gas is shorter than the dynamical time and star formation continues via accretion of gas to discs which become the familiar spiral systems.