We present an analysis of the relation between star formation rate (SFR) surface density (sigmasfr) and mass surface density of molecular gas (sigmahtwo), commonly referred to as the Kennicutt-Schmidt (K-S) relation, at its intrinsic spatial scale, i
.e. the size of giant molecular clouds (10-150 pc), in the central, high-density regions of four nearby low-luminosity active galactic nuclei (AGN). We used interferometric IRAM CO(1-0) and CO(2-1), and SMA CO(3-2) emission line maps to derive sigmahtwo and HST-Halpha images to estimate sigmasfr. Each galaxy is characterized by a distinct molecular SF relation at spatial scales between 20 to 200 pc. The K-S relations can be sub-linear, but also super-linear, with slopes ranging from 0.5 to 1.3. Depletion times range from 1 and 2Gyr, compatible with results for nearby normal galaxies. These findings are valid independently of which transition, CO(1-0), CO(2-1), or CO(3-2), is used to derive sigmahtwo. Because of star-formation feedback, life-time of clouds, turbulent cascade, or magnetic fields, the K-S relation might be expected to degrade on small spatial scales (<100 pc). However, we find no clear evidence for this, even on scales as small as 20 pc, and this might be because of the higher density of GMCs in galaxy centers which have to resist higher shear forces. The proportionality between sigmahtwo and sigmasfr found between 10 and 100 Msun/pc2 is valid even at high densities, 10^3 Msun/pc2. However, by adopting a common CO-to-H2 conversion factor (alpha_CO), the central regions of the galaxies have higher sigmasfr for a given gas column than those expected from the models, with a behavior that lies between the mergers/high-redshift starburst systems and the more quiescent star-forming galaxies, assuming that the first ones require a lower value of alpha_CO.
The formation of the first virialized structures in overdensities dates back to ~9 Gyr ago, i.e. in the redshift range z ~ 1.4 - 1.6. Some models of structure formation predict that the star formation activity in clusters was high at that epoch, impl
ying large reservoirs of cold molecular gas. Aiming at finding a trace of this expected high molecular gas content in primeval clusters, we searched for the 12CO(2-1) line emission in the most luminous active galactic nucleus (AGN) of the cluster around the radio galaxy 7C 1756+6520 at z ~ 1.4, one of the farthest spectroscopic confirmed clusters. This AGN, called AGN.1317, is located in the neighbourhood of the central radio galaxy at a projected distance of ~780 kpc. The IRAM Plateau de Bure Interferometer was used to investigate the molecular gas quantity in AGN.1317, observing the 12CO(2-1) emission line. We detect CO emission in an AGN belonging to a galaxy cluster at z ~ 1.4. We measured a molecular gas mass of 1.1 x 10^10 Msun, comparable to that found in submillimeter galaxies. In optical images, AGN.1317 does not seem to be part of a galaxy interaction or merger.We also derived the nearly instantaneous star formation rate (SFR) from Halpha flux obtaining a SFR ~65 Msun/yr. This suggests that AGN.1317 is actively forming stars and will exhaust its reservoir of cold gas in ~0.2-1.0 Gyr.
We present CO(1-0) and CO(2-1) maps of the interacting barred LINER/Seyfert 2 galaxy NGC 3627 obtained with the IRAM interferometer at resolutions of 2.1 x 1.3 and 0.9 x 0.6, respectively. The molecular gas emission shows a nuclear peak, an elongated
bar-like structure of ~18 (~900 pc) diameter in both CO maps and, in CO(1-0), a two-arm spiral feature from r~9 (~450 pc) to r~16 (~800 pc). The inner ~18 bar-like structure, with a north/south orientation (PA = 14{deg}), forms two peaks at the extremes of this elongated emission region. The kinematics of the inner molecular gas shows signatures of non-circular motions associated both with the 18 bar-like structure and the spiral feature detected beyond it. The 1.6 micron H-band 2MASS image of NGC 3627 shows a stellar bar with a PA = -21{deg}, different from the PA (= 14{deg}) of the CO bar-like structure, indicating that the gas is leading the stellar bar. The torques computed with the HST-NICMOS F160W image and our PdBI maps are negative down to the resolution limit of our images, ~60 pc in CO(2-1). If the bar ends at ~3 kpc, coincident with corotation (CR), the torques are negative between the CR of the bar and the nucleus, down to the resolution limit of our observations. This scenario is compatible with a recently-formed rapidly rotating bar which has had insufficient time to slow down because of secular evolution, and thus has not yet formed an inner Lindblad resonance (ILR). The presence of molecular gas inside the CR of the primary bar, where we expect that the ILR will form, makes NGC 3627 a potential smoking gun of inner gas inflow. The gas is fueling the central region, and in a second step could fuel directly the active nucleus.
We present $^{12}$CO(1--0) and $^{12}$CO(2--1) maps of the interacting Seyfert 2/LINER galaxy NGC 5953 obtained with the IRAM interferometer at resolutions of 2farcs1 $times$ 1farcs4 and 1farcs1 $times$ 0farcs7, respectively. The CO emission is distr
ibuted over a disk of diameter $sim$16arcsec ($sim$2.2 kpc), within which are several, randomly distributed peaks. The strongest peak does not coincide with the nucleus, but is instead offset from the center, $sim2-3^{primeprime}$ ($sim$340 pc) toward the west/southwest. The kinematics of the molecular component are quite regular, as is typical of a rotating disk. We also compared the $^{12}$CO distribution of NGC 5953 with observations at other wavelengths in order to study correlations between different tracers of the interstellar medium. Using NIR images, we computed the gravity torques exerted by the stellar potential on the gas. The torques are predominantly positive in both $^{12}$CO(1--0) and $^{12}$CO(2--1), suggesting that gas is not flowing into the center, and less than 5% of the gas angular momentum is exchanged in each rotation. This comes from the regular and almost axisymmetric total mass and gas distributions in the center of the galaxy. In NGC 5953, the AGN is apparently not being actively fueled in the current epoch.
We present a review on bar pattern speeds from preliminary results in the context of the Nuclei of Galaxies (NUGA) project. The large variety of molecular circumnuclear morphologies found in NUGA is a challenging result that implies the refinement of current dynamical models of galaxies.
We present CO(1-0) and CO(2-1) observations of the SA(rs)bc Seyfert 2 galaxy NGC 3147, obtained with the IRAM interferometer at 1farcs9 $times$1farcs6 and 1farcs6 $times$1farcs4 resolutions, respectively. A central peak seen mainly in CO(2-1) and a r
ing-like structure at $r simeq 10$arcsec $sim$2 kpc dominate the CO maps. In CO(1-0) an outer spiral at $r simeq 20$arcsec $sim$4 kpc is also detected, not visible in CO(2-1) emission because it falls outside the field-of-view of the primary beam. The kinematics of the molecular structures are quite regular, although there is evidence for local non-circular or streaming motions. We show that the molecular gas distribution is similar but not exactly identical to those of star formation tracers. Using a NIR image obtained with adaptive optics at the CFHT Telescope, we identify a weak bar in NGC 3147, which is classified as non-barred galaxy in the optical. We then compute the gravity torques exerted by this stellar bar on the gas. We find that the gas inside the inner CO ring is subject to a net negative torque and loses angular momentum. This is expected for gas at the UHR, just inside the corotation resonance of the stellar bar. In contrast, the gas outside corotation, in the spiral arms comprising the outer spiral structure, suffers positive torques and is driven outwards. We conclude that some molecular gas is presently flowing into the central region, since we find negative torques down to the resolution limit of our images.
