TY - JOUR
T1 - High-redshift star-formation galaxies
T2 - angular momentum and baryon fraction, turbulent pressure effects, and the origin turbulence
AU - Burkert..[et al.], A.
AU - Genzel, R.
AU - Bouche, N.
AU - Sommer-Larsen, Jesper
PY - 2010/12/20
Y1 - 2010/12/20
N2 - The structure of a sample of high-redshift (z ∼ 2), rotating galaxies with high star formation rates and turbulent gas velocities of σ ≈ 40-80 km s-1 is investigated. Fitting the observed disk rotational velocities and radii with a Mo et al. (MMW) model requires unusually large disk spin parameters λd > 0.1 and disk-to-dark halo mass fractions of md ≈ 0.2, close to the cosmic baryon fraction. The galaxies segregate into dispersion-dominated systems with 1 ≤ νmax/σ ≤ 3, maximum rotational velocities νmax ≤ 200 km s-1, and disk half-light radii r 1/2 ≈ 1-3 kpc, and rotation-dominated systems with νmax > 200 km s-1, vmax/σ > 3, and r 1/2 ≈ 4-8 kpc. For the dispersion-dominated sample, radial pressure gradients partly compensate the gravitational force, reducing the rotational velocities. Including this pressure effect in the MMW model, dispersion-dominated galaxies can be fitted well with spin parameters of λd = 0.03-0.05 for high disk mass fractions of md ≈ 0.2 and with λd = 0.01-0.03 for md ≈ 0.05. These values are in good agreement with cosmological expectations. For the rotation-dominated sample, however, pressure effects are small and better agreement with theoretically expected disk spin parameters can only be achieved if the dark halo mass contribution in the visible disk regime (2-3×r 1/2) is smaller than predicted by the MMW model. We argue that these galaxies can still be embedded in standard cold dark matter halos if the halos do not contract adiabatically in response to disk formation. In this case, the data favor models with small disk mass fractions of md = 0.05 and disk spin parameters of λd ≈ 0.035. It is shown that the observed high turbulent gas motions of the galaxies are consistent with a Toomre instability parameter Q = 1 which is equal to the critical value, expected for gravitational disk instability to be the major driver of turbulence. The dominant energy source of turbulence is then the potential energy of the gas in the disk.
AB - The structure of a sample of high-redshift (z ∼ 2), rotating galaxies with high star formation rates and turbulent gas velocities of σ ≈ 40-80 km s-1 is investigated. Fitting the observed disk rotational velocities and radii with a Mo et al. (MMW) model requires unusually large disk spin parameters λd > 0.1 and disk-to-dark halo mass fractions of md ≈ 0.2, close to the cosmic baryon fraction. The galaxies segregate into dispersion-dominated systems with 1 ≤ νmax/σ ≤ 3, maximum rotational velocities νmax ≤ 200 km s-1, and disk half-light radii r 1/2 ≈ 1-3 kpc, and rotation-dominated systems with νmax > 200 km s-1, vmax/σ > 3, and r 1/2 ≈ 4-8 kpc. For the dispersion-dominated sample, radial pressure gradients partly compensate the gravitational force, reducing the rotational velocities. Including this pressure effect in the MMW model, dispersion-dominated galaxies can be fitted well with spin parameters of λd = 0.03-0.05 for high disk mass fractions of md ≈ 0.2 and with λd = 0.01-0.03 for md ≈ 0.05. These values are in good agreement with cosmological expectations. For the rotation-dominated sample, however, pressure effects are small and better agreement with theoretically expected disk spin parameters can only be achieved if the dark halo mass contribution in the visible disk regime (2-3×r 1/2) is smaller than predicted by the MMW model. We argue that these galaxies can still be embedded in standard cold dark matter halos if the halos do not contract adiabatically in response to disk formation. In this case, the data favor models with small disk mass fractions of md = 0.05 and disk spin parameters of λd ≈ 0.035. It is shown that the observed high turbulent gas motions of the galaxies are consistent with a Toomre instability parameter Q = 1 which is equal to the critical value, expected for gravitational disk instability to be the major driver of turbulence. The dominant energy source of turbulence is then the potential energy of the gas in the disk.
U2 - 10.1088/0004-637X/725/2/2324
DO - 10.1088/0004-637X/725/2/2324
M3 - Journal article
SN - 0004-637X
VL - 725
SP - 2324
EP - 2332
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
ER -