next up previous contents
Next: Millimetre detection of GRB Up: Scientific results Previous: Disks in the UYAur

Molecular gas in the barred spiral M 100: II. tex2html_wrap_inline1766 CO(1-0) interferometer observations and numerical simulations

S. García-Burillo tex2html_wrap_inline1968 , M.J.Sempere tex2html_wrap_inline1968 , F. Combes tex2html_wrap_inline1978 , R. Neri tex2html_wrap_inline1974
tex2html_wrap_inline1968 Observatorio Astronómico Nacional, Apartado 1143, E-28800 Alcalá de Henares, Spain
tex2html_wrap_inline1978 Observatoire de Paris, DEMIRM, 61 Av. de l'Observatoire, F-75014, France
tex2html_wrap_inline1974 Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint Martin d'Hères, France
Abstract: Using the IRAM interferometer we have mapped at high resolution ( tex2html_wrap_inline2246 ) the tex2html_wrap_inline1766 CO(1-0) emission in the nucleus of the doubled barred SABbc spiral M 100. Our synthesized map includes the zero spacing flux of the single-dish 30m map (Sempere & García-Burillo, 1997, paper I). Molecular gas is distributed in a two spiral arm structure starting from the end points of the nuclear bar (r=600 pc) up to r=1.2 kpc, and a central source ( tex2html_wrap_inline2254 100 pc). The kinematics of the gas indicates the existence of a steep rotation curve (v tex2html_wrap_inline2256 =180 km s tex2html_wrap_inline1740 at tex2html_wrap_inline2260 pc) and strong streaming motions characteristic of a trailing spiral wave inside corotation.

Interpretation of the CO observations and their relation with stellar and gaseous tracers (K, optical, H tex2html_wrap_inline1796 , HI and radiocontinuum maps) are made in the light of a numerical model of the clouds hydrodynamics. Gas flow simulations analyse the gas response to a gravitational potential derived from the K-band plate, including the two nested bars. We develop two families of models: first, a single pattern speed solution shared by the outer bar+spiral and by the nuclear bar, and secondly, a two independent bars solution, where the nuclear bar is dynamically decoupled and rotates faster than the primary bar.

We found the best fit solution consisting of a fast pattern ( tex2html_wrap_inline1816 =160 kms tex2html_wrap_inline1740 kpc tex2html_wrap_inline1740 ) for the nuclear bar (with corotation at R tex2html_wrap_inline2270 =1.2 kpc) decoupled from the slow pattern of the outer bar+spiral ( tex2html_wrap_inline1816 =23 kms tex2html_wrap_inline1740 kpc tex2html_wrap_inline1740 ) (with corotation at R tex2html_wrap_inline2278 =8-9 kpc). As required by non-linear coupling of spirals (Tagger et al 1987), the corotation of the fast pattern falls in the ILR region of the slow pattern, allowing an efficient transfer of molecular gas towards the nuclear region. Solutions based on a single pattern hypothesis for the whole disk cannot fit the observed molecular gas response and fail to account for the relation between other stellar and gaseous tracers. In the two-bar solution, the gas morphology and kinematics are strongly varying in the rotating frame of the slow large-scale bar, and fit the data periodically during a short fraction (about 20%) of the relative nuclear bar period of 46 Myr (Fig. 10).

   figure1064
Figure 10: We display the particle orbits for molecular clouds in the region where the bar instability develops, as they are seen, firstly, a(top): from the frame rotating at tex2html_wrap_inline1804 =23kms tex2html_wrap_inline1740 kpc tex2html_wrap_inline1740 , for the solution of a single slow pattern and b(bottom): from the frame rotating at tex2html_wrap_inline1804 =23kms tex2html_wrap_inline1740 kpc tex2html_wrap_inline1740 for the best-fit solution of a double pattern ( tex2html_wrap_inline1816 =160kms tex2html_wrap_inline1740 kpc tex2html_wrap_inline1740 (from r=0 tex2html_wrap_inline2151 to 10 tex2html_wrap_inline2151 ), tex2html_wrap_inline1826 =23kms tex2html_wrap_inline1740 kpc tex2html_wrap_inline1740 (for r>10 tex2html_wrap_inline2151 ). The length of the arrows is proportional to the particle speed in the rotating frame. These simulations illustrate the efficiency of fast nuclear bars, dynamically decoupled form the outer bar+spiral structure, in driving the gas towards the nucleus, hence accounting for the observations.


next up previous contents
Next: Millimetre detection of GRB Up: Scientific results Previous: Disks in the UYAur

lucas@iram.fr