Cold gas in group-dominant elliptical galaxies

We present IRAM 30m telescope observations of the CO(1-0) and (2-1) lines in a sample of 11 group-dominant elliptical galaxies selected from the CLoGS nearby groups sample. Our observations confirm the presence of molecular gas in 4 of the 11 galaxies at >4 sigma significance, and combining these with data from the literature we find a detection rate of 43+-14%, comparable to the detection rate for nearby radio galaxies, suggesting that group-dominant ellipticals may be more likely to contain molecular gas than their non-central counterparts. Those group-dominant galaxies which are detected typically contain ~2x10^8 Msol of molecular gas, and although most have low star formation rates (<1 Msol/yr) they have short depletion times, indicating that the gas must be replenished on timescales ~100 Myr. Almost all of the galaxies contain active nuclei, and we note while the data suggest that CO may be more common in the most radio-loud galaxies, the mass of molecular gas required to power the active nuclei through accretion is small compared to the masses observed. We consider possible origin mechanisms for the gas, through cooling of stellar ejecta within the galaxies, group-scale cooling flows, and gas-rich mergers, and find probable examples of each type within our sample, confirming that a variety of processes act to drive the build up of molecular gas in group-dominant ellipticals.Comment: 9 pages, 5 postscript figures, 4 tables, accepted by A&A. Revised throughout in response to referee's comments, including updates to Table 1 and Figure 4, and addition of Figure

NUGA: the IRAM survey of AGN spiral hosts

The NUclei of GAlaxies (NUGA) project is a combined effort to carry out a high-resolution (<1'') interferometer CO survey of a sample of 12 nearby AGN spiral hosts, using the IRAM array. We map the distribution and dynamics of molecular gas in the inner 1 kpc of the nuclei with resolutions of 10-50 pc, and study the mechanisms for gas fueling of the different low-luminosity AGN. First results show evidence for the occurrence of strong m=1 gas instabilities in Seyferts. NUGA maps allow us to address the origin/nature of m=1 modes and their link with m=2 modes and acoustic instabilities, present in other targets.Comment: 1 gzipped tar file containing 1 Latex file + 3 eps figures. Proceedings of ''Active Galactic Nuclei: from Central Engine to Host Galaxy'', meeting held in Meudon, France, July 23-27, 2002, Eds.: S. Collin, F. Combes and I. Shlosman. To be published in ASP Conference Serie

Detection of CO (2-1) and Radio Continuum Emission from the z = 4.4 QSO BRI 1335-0417

We have detected redshifted CO (2-1) emission at 43 GHz and radio continuum emission at 1.47 and 4.86 GHz from the z = 4.4 QSO BRI 1335-0417 using the Very Large Array. The CO data imply optically thick emission from warm (>30 K) molecular gas with a total mass, M(H_2), of 1.5+/-0.3 x10^{11} M_solar, using the Galactic gas mass-to-CO luminosity conversion factor. We set an upper limit to the CO source size of 1.1", and a lower limit of 0.23"x(T_ex/50K)^{-1/2}, where T_ex is the gas excitation temperature. We derive an upper limit to the dynamical mass of 2x10^{10} x sin^{-2} i M_solar, where i is the disk inclination angle. To reconcile the gas mass with the dynamical mass requires either a nearly face-on disk (i < 25deg), or a gas mass-to-CO luminosity conversion factor significantly lower than the Galactic value. The spectral energy distribution from the radio to the rest-frame infrared of BRI 1335-0417 is consistent with that expected from a nuclear starburst galaxy, with an implied massive star formation rate of 2300+/-600 M_solar yr^{-1}.Comment: standard AAS LATEX forma

The complex molecular absorption line system at z=0.886 towards PKS1830-211

New millimeter wave observations of the molecular absorption line system in the gravitational lens to PKS1830-211 at z=0.88582 is presented. Self-calibrated interferometer data shows unequivocally that the previously detected absorption component is associated with the gravitationally lensed south-west image of the background source. A second absorption line of HCO+(2-1) at z=0.88582 is detected. This component is shifted in velocity by -147 km/s relative to the main absorption line, and is shown to be associated with the north-east image. These two absorption lines are used to constrain the mass of the lensing galaxy. Upper limits to absorption and emission lines from the possible absorption system at z=0.1927, seen in 21cm HI by Lovell et al, are reported.Comment: 16 pages, 7 figures, Accepted for publication in Ap

Why Buckling Stellar Bars Weaken in Disk Galaxies

Young stellar bars in disk galaxies experience a vertical buckling instability which terminates their growth and thickens them, resulting in a characteristic peanut/boxy shape when viewed edge on. Using N-body simulations of galactic disks embedded in live halos, we have analyzed the bar structure throughout this instability and found that the outer third of the bar dissolves completely while the inner part (within the vertical inner Lindblad resonance) becomes less oval. The bar acquires the frequently observed peanut/boxy-shaped isophotes. We also find that the bar buckling is responsible for a mass injection above the plane, which is subsequently trapped by specific 3-D families of periodic orbits of particular shapes explaining the observed isophotes, in line with previous work. Using a 3-D orbit analysis and surfaces of sections, we infer that the outer part of the bar is dissolved by a rapidly widening stochastic region around its corotation radius -- a process related to the bar growth. This leads to a dramatic decrease in the bar size, decrease in the overall bar strength and a mild increase in its pattern speed, but is not expected to lead to a complete bar dissolution. The buckling instability appears primarily responsible for shortening the secular diffusion timescale to a dynamical one when building the boxy isophotes. The sufficiently long timescale of described evolution, ~1 Gyr, can affect the observed bar fraction in local universe and at higher redshifts, both through reduced bar strength and the absence of dust offset lanes in the bar.Comment: 7 pages, 4 figures, ApJ Letters, in pres

Anisotropic Null String Cosmologies

We study string propagation in an anisotropic, cosmological background. We solve the equations of motion and the constraints by performing a perturbative expansion of the string coordinates in powers of c^2, the world-sheet speed of light. To zeroth order the string is approximated by a tensionless string (since c is proportional to the string tension T). We obtain exact, analytical expressions for the zeroth and the first order solutions and we discuss some cosmological implications.Comment: 9 pages, plain Te

Molecular Gas Dynamics in NGC 6946: a Bar-driven Nuclear Starburst "Caught in the Act"

We present high angular resolution ~1" and 0.6" mm-interferometric observations of the 12CO(1-0) and 12CO(2-1) line emission in the central 300pc of the late-type spiral galaxy NGC6946. The data, obtained with the IRAM Plateau de Bure Interferometer (PdBI), allow the first detection of a molecular gas spiral in the inner ~10" (270pc) with a large concentration of molecular gas (M(H_2) ~1.6x10^7M_sun) within the inner 60pc. This nuclear clump shows evidence for a ring-like geometry with a radius of ~10pc as inferred from the p-v diagrams. Both the distribution of the molecular gas as well as its kinematics can be well explained by the influence of an inner stellar bar of about 400pc length. A qualitative model of the expected gas flow shows that streaming motions along the leading sides of this bar are a plausible explanation for the high nuclear gas density. Thus, NGC6946 is a prime example of molecular gas kinematics being driven by a small-scale, secondary stellar bar.Comment: accepted for publication in the Astrophysical Journal; 47 pages, 17 figures, 1 tabl

Molecular gas in NUclei of GAlaxies (NUGA) XV. Molecular gas kinematics in the inner 3kpc of NGC6951

Within the NUclei of GAlaxies project we have obtained IRAM PdBI and 30m 12CO(1-0) and 12CO(2-1) observations of the spiral galaxy NGC 6951. Previous work shows that there is indirect evidence of gas inflow from 3 kpc down to small radii: a large-scale stellar bar, a prominent starburst ring (r~580 pc) and a LINER/Seyfert 2 nucleus. In this paper we study the gas kinematics as traced by the CO line emission in detail. We quantify the influence of the large-scale stellar bar by constructing an analytical model of the evolution of gas particles in a barred potential. From this model gravitational torques and mass accumulation rates are computed. We compare our model-based gravitational torque results with previous observationally-based ones. The model also shows that the large-scale stellar bar is indeed the dominant force for driving the gas inward, to the starburst ring. Inside the ring itself a nuclear stellar oval might play an important role. Detailed analysis of the CO gas kinematics there shows that emission arises from two co-spatial, but kinematically distinct components at several locations. The main emission component can always be related to the overall bar-driven gas kinematics. The second component exhibits velocities that are larger than expected for gas on stable orbits, has a molecular gas mass of 1.8x10^6Msun, is very likely connected to the nuclear stellar oval, and is consistent with inflowing motion towards the very center. This may form the last link in the chain of gas inflow towards the active galactic nucleus in NGC 6951.Comment: 17 pages, accepted by A&A (17 feb 2011