We report the discovery of a powerful molecular wind from the nucleus of the non-interacting nearby S0 field galaxy NGC 1266. The single-dish CO profile exhibits emission to ?400 km s--1 and requires ...a nested Gaussian fit to be properly described. Interferometric observations reveal a massive, centrally concentrated molecular component with a mass of 1.1 X 109 M and a molecular outflow with a molecular mass of 2.4 X 107 M . The molecular gas close to the systemic velocity consists of a rotating, compact nucleus with a mass of about 4.1 X 108 M within a radius of 60 pc. This compact molecular nucleus has a surface density of 2.7 X 104 M pc--2, more than two orders of magnitude larger than that of giant molecular clouds in the disk of the Milky Way, and it appears to sit on the Kennicutt-Schmidt relation despite its extreme kinematics and energetic activity. We interpret this nucleus as a disk that confines the outflowing wind. A mass outflow rate of 13 M yr--1 leads to a depletion timescale of 85 Myr. The star formation in NGC 1266 is insufficient to drive the outflow, and thus it is likely driven by the active galactic nucleus. The concentration of the majority of the molecular gas in the central 100 pc requires an extraordinary loss of angular momentum, but no obvious companion or interacting galaxy is present to enable the transfer. NGC 1266 is the first known outflowing molecular system that does not show any evidence of a recent interaction.
The structure of a sample of high-redshift (z ~ 2), rotating galaxies with high star formation rates and turbulent gas velocities of Delta *s 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 Delta *l d >0.1 and disk-to-dark halo mass fractions of m d 0.2, close to the cosmic baryon fraction. The galaxies segregate into dispersion-dominated systems with 1 <= v max/ Delta *s <= 3, maximum rotational velocities v max<= 200 km s--1, and disk half-light radii r 1/2 1-3 kpc, and rotation-dominated systems with v max> 200 km s--1, v max/ Delta *s>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 Delta *l d = 0.03-0.05 for high disk mass fractions of m d 0.2 and with Delta *l d = 0.01-0.03 for m d 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 X 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 m d = 0.05 and disk spin parameters of Delta *l d 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.
How galaxies lose their angular momentum D'Onghia, Elena; Burkert, Andreas; Murante, Giuseppe ...
Monthly notices of the Royal Astronomical Society,
11/2006, Letnik:
372, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The processes are investigated by which gas loses its angular momentum during the protogalactic collapse phase, leading to disc galaxies that are too compact with respect to the observations. ...High-resolution N-body/SPH simulations in a cosmological context are presented including cold gas and dark matter (DM). A halo with quiet merging activity since redshift z∼ 3.8 and with a high-spin parameter is analysed that should be an ideal candidate for the formation of an extended galactic disc. We show that the gas and the DM have similar specific angular momenta until a merger event occurs at z∼ 2 with a mass ratio of 5:1. All the gas involved in the merger loses a substantial fraction of its specific angular momentum due to tidal torques and dynamical friction processes falls quickly into the centre. In contrast, gas infall through small subclumps or accretion does not lead to catastrophic angular momentum loss. In fact, a new extended disc begins to form from gas that was not involved in the 5:1 merger event and that falls in subsequently. We argue that the angular momentum problem of disc galaxy formation is a merger problem: in cold dark matter cosmology substantial mergers with mass ratios of 1:1 to 6:1 are expected to occur in almost all galaxies. We suggest that energetic feedback processes could in principle solve this problem, however only if the heating occurs at the time or shortly before the last substantial merger event. Good candidates for such a coordinated feedback would be a merger-triggered starburst or central black hole heating. If a large fraction of the low angular momentum gas would be ejected, late-type galaxies could form with a dominant extended disc component, resulting from late infall, a small bulge-to-disc ratio and a low baryon fraction, in agreement with observations.
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