The formation of galaxies through gravitational collapse of dark matter is not an easy problem to understand. A good model for galaxy formation has to take into account all the observed features of real galaxies. For example, it seems that many disc galaxies contain a black hole in their center, but others do not \cite{Galx-bh}. Typical galaxies are spiral, elliptical or dwarf galaxies (irregular galaxies may be galaxies still evolving). In most spiral and elliptical galaxies the luminous matter extends to \sim 10-30kpc, and the total content of matter (including dark matter) is of the order of 10^{10}-10^{12}M_{\odot }, with about 10 times more dark matter than luminous one. The central density profile of the dark matter in galaxies should not be cusp \cite{Smooth}. Even though the luminous matter represents only a small fraction of the total amount of matter in galaxies, it plays an important role in galaxy formation and stability \cite{DMCQG}. On the other hand, it is still not well established if the mass of the central black hole and the mass of the halo are correlated \cite{correlated}, etc.

There are some ideas in this respect when dealing with a scalar field. It is known that the final stage of a collapsed scalar field could be a massive object made of scalar field particles in quantum coherent states, like boson stars (for a complex scalar field) or oscillatons (for a real scalar field) \cite{seidel91,seidel94,franky,luis}. It is thus important to investigate whether the scalar field would collapse to form structures of the size of galaxies and provide the correct properties of any galactic dark matter candidate, like growing rotation curves and appropriate dark matter distribution functions. Also, we need to know which are the conditions that must be imposed on the scalar field particles.

Our main aim has been to give a plausible scenario for galaxy formation under the scalar field dark matter (SFDM) hypothesis. Through a gravitational cooling process \cite{seidel91,seidel94}, a cosmological fluctuation of the scalar field collapses to form a compact oscillaton by ejecting part of the field. The key idea consists precisely in assuming that such final object could distribute as galactic dark matter does \cite{franky}. The final configuration then should consist of a central object (a core), i.e. an oscillaton, surrounded by a diffuse cloud of scalar field, both formed at the same time due to the same collapse process. For details see gr-qc/0110102.

The results of the numerical simulations are as follows. Essentially, we have found three different types of behavior for the scalar field collapse. In the first case, a generic feature is that scalar field distributions with an initial mass slightly larger than the critical mass collapse very violently and form a black hole. In the second type of behavior, fluctuations with an initial mass significantly smaller than the critical mass can not form stable oscillatons: the scalar field is completely ejected out as the system evolves \cite{futuro}. The third behavior corresponds to a case where a fraction of the initial density is spread out, leaving an oscillating object that appears to be stable. This situation happens in a narrow window of initial conditions, between 0.05-1\times M_{crit} \cite{futuro}.


Galaxies Formations with Scalar Field Dark Matter





































Simulation of the collapse of a galaxy in the SFDM model. Make click in the picture. On the right, the corresponding rotation curves.









In this simulation we show the evolution in time of the collapse of an oscillaton (halo of a galaxy).
After the halo has formed, the luminous matter comes to the regions where the dark matter concentrates. But, for different initial fluctuations of the luminous matter, it will form different kind of galaxies. Here we show two exemples of simulations from two different initial conditions for the formation of the luminoues matter in the scalar field dark matter halo formed in the previus one. Observe the formation of bars and spiral arms, something that is a challenge for all DM models and seems to be so natural in the Scalar Field Dark Matter model. (The simulatins are big, so, make click in the pictures and please wait a moment).











































{seidel91}E. Seidel and W. Suen, Phys. Rev. Lett. 66, 1659 (1991).

{seidel94}E. Seidel and W. Suen, Phys. Rev. Lett. 72, 2516 (1994).

{firmani}B. Moore, F. Governato, T. Quinn, J. Stadel and G. Lake, ApJ 499, L15 (1998). Y. P. Jing and Y. Suto, ApJ 529, L69 (2000).

{DMCQG}F. S. Guzman and T. Matos, Class. Quantum Grav. 17, L9 (2000). T. Matos and F. S. Guzman, Ann. Phys. (Leipzig) 9, SI-133 (2000).

{SPHPRD}T. Matos, F. S. Guzman and D. Nunez, Phys. Rev. D 62, 061301 (2000).

{QSDMCQG}T. Matos and L. A. Urena-Lopez, Class. Quantum Grav. 17, L75 (2000).

{COSPRD}T. Matos and L. A. Urena-Lopez, Phys. Rev. D63, 63506 (2001).

{franky}T. Matos and F. S. Guzman, Class. Quantum Grav. 18, (2001), 5055. E-print gr-qc/0108027.

{jeremy}J. Goodman, E-print astro-ph/0003018.

{peebles}P. J. E. Peebles, E-print astro-ph/0002495.

{cross}T. Matos and L. A. Urena-Lopez, Phys. Lett.B538, (2002), 246. E-print astro-ph/0010226.

{Galx-bh}D. Merritt, L. Ferrarese, and C. L. Joseph, Science 293, 1116 (2001).

{Smooth}B. Moore, Nature 370, 629 (1994). A. Burkert, ApJ 477, L25 (1995). J. A. Tyson, G. P. Kochanski and I. P. Dell'Antonio, ApJ 498, L107 (1998).

{correlated}L. Ferrarese and D. Merritt, ApJL, 539, L9 (2000). K. Gebhardt et al., ApJL, 539, L13 (2000).

{luis}L. A. Urena-Lopez, Class. Quantum Grav. 19, (2002), 2617. E-print gr-qc/0104093. L. A. Urena-Lopez, T. Matos, Ricardo Becerril. In preparation.

{Hu}W. Hu, R. Barkana and A. Gruzinov, Phys. Rev. Lett. 85, 1158 (2000).

{Hawley}S. H. Hawley and M. W. Choptuik, Phys. Rev. D 62, 104024 (2000). E. P. Honda and M. W. Choptuik, E-print hep-ph/0110065.

{futuro}M. Alcubierre, T. Matos and D. Nunez, in preparation.