arXiv subjects

A. Audibert

Publications and source records attributed to A. Audibert.

23 records · Page 2Linked to original sources

arXiv2022

CO in the ALMA Radio-Source Catalogue (ARC): the molecular gas content of radio galaxies as a function of redshift

To evaluate the role of radio activity in galaxy evolution, we designed a large archival CO survey of radio galaxies (RGs) to determine their molecular gas masses at different epochs. We used a sample of 120 RGs representative of the NVSS 1.4 GHz survey, when flux limited at 0.4 Jy. Of those, 66 galaxies belonged to the ALMA Radio-source Catalogue (ARC) of calibrators and had spectral window tunings around CO (1-0), (2-1), (3-2), or (4-3). We reduced their ALMA data, determined their H2 mass contents, and combined the results with similar results for the remaining 54 galaxies from the literature. We found that, while at all epochs the majority of RGs have undetectable reservoirs, there is a rapid increase in the H2 mass content of the CO-detected RGs with z. At 1<z<2.5, one-fourth of the RGs have at least as much molecular gas as simulations would indicate for a typical halo mass of that epoch. These galaxies plausibly have ``normal'' or even starburst hosts. Taking into account the completeness correction of the sample, we created the corresponding H$_2$ mass functions at 0.005<z<0.3 and 1<z<2.5. The local mass function reveals that the number density of low-z RGs with detectable molecular gas reservoirs is only a little lower (a factor of ~4) than that of pure (or little star-forming) type 1 and 2 AGN in simulations. At 1<z<2.5, there is a significant decrease in the number density of high-z RGs due to the rarity of bright radio galaxies. An estimate for the missing faint RGs would, nonetheless, bring populations close again. Finally, we find that the volume density of molecular gas locked up in the brightest 1/5000-1/7000 RGs is similar in the examined $z$ bins. This result likely indicates that the inflow rate on one hand and the star-formation depletion rate plus the jet-driven expulsion rate on the other hand counteract each other in the most luminous RGs of each epoch.

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arXiv2022

The diverse cold molecular gas contents, morphologies, and kinematics of type-2 quasars as seen by ALMA

We present CO(2-1) and adjacent continuum observations of 7 nearby radio-quiet type-2 quasars (QSO2s) obtained with ALMA at ~0.2" resolution (370 pc at z~0.1). The CO morphologies are diverse, including disks and interacting systems. Two of the QSO2s are red early-type galaxies with no CO(2-1) detected. In the interacting galaxies, the central kpc contains 18-25% of the total cold molecular gas, whereas in the spirals it is only 5-12%. J1010+0612 and J1430+1339 show double-peaked CO morphologies which do not have optical counterparts. Based on our analysis of the ionized and molecular kinematics and mm continuum emission, these CO morphologies are most likely produced by AGN feedback in the form of outflows, jets, and/or shocks. The CO kinematics of the QSO2s are dominated by rotation but also reveal noncircular motions. According to our analysis of the kinematics, these noncircular motions correspond to molecular outflows mostly coplanar with the CO discs in four of the QSO2s, and either to a coplanar inflow or vertical outflow in the case of J1010+0612. These outflows represent 0.2-0.7% of the QSO2s' total molecular gas mass and have maximum velocities of 200-350 km/s, radii from 0.4 to 1.3 kpc, and outflow rates of 8-16 Msun/yr. These properties are intermediate between those of the mild molecular outflows measured for Seyferts, and the fast and energetic outflows of ULIRGs. This suggests that it is not only AGN luminosity that drives massive molecular outflows. Other factors such as jet power, coupling between winds, jets, and/or ionized outflows and the CO discs, and amount or geometry of dense gas in the nuclear regions might be also relevant. Thus, although we do not find evidence for a significant impact of quasar feedback on the total molecular gas reservoirs and SFRs, it appears to be modifying the distribution of cold molecular gas in the central kpc of the galaxies.

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arXiv2021

Black hole feeding and star formation in NGC 1808

We report on Atacama Large Millimeter Array (ALMA) observations of CO(3-2) emission in the Seyfert2/starburst galaxy NGC1808, at a spatial resolution of 4pc. Our aim is to investigate the morphology and dynamics of the gas inside the central 0.5kpc and to probe the nuclear feeding and feedback phenomena. We discovered a nuclear spiral of radius 1"=45pc. Within it, we found a decoupled circumnuclear disk or molecular torus of a radius of 0.13"=6pc. The HCN(4-3) and HCO$\rm^+$(4-3) and CS(7-6) dense gas line tracers were simultaneously mapped and detected in the nuclear spiral and they present the same misalignment in the molecular torus. At the nucleus, the HCN/HCO$^+$ and HCN/CS ratios indicate the presence of an active galactic nucleus (AGN). The molecular gas shows regular rotation, within a radius of 400pc, except for the misaligned disk inside the nuclear spiral arms. The computations of the torques exerted on the gas by the barred stellar potential reveal that the gas within a radius of 100pc is feeding the nucleus on a timescale of five rotations or on an average timescale of ~60Myr. Some non-circular motions are observed towards the center, corresponding to the nuclear spiral arms. We cannot rule out that small extra kinematic perturbations could be interpreted as a weak outflow attributed to AGN feedback. The molecular outflow detected at $\geqslant$250pc in the NE direction is likely due to supernovae feedback and it is connected to the kpc-scale superwind.

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arXiv2019

ALMA captures feeding and feedback from the active galactic nucleus in NGC613

We report ALMA observations of CO(3-2) emission in the Seyfert galaxy NGC613, at a spatial resolution of 17pc, as part of our NUclei of GAlaxies sample. Our aim is to investigate the morphology and dynamics of the gas inside the central kpc, and to probe nuclear fueling and feedback phenomena. The morphology of CO(3-2) line emission reveals a 2-arm trailing nuclear spiral at $r\lesssim$100pc and a circumnuclear ring at ~350pc radius, that is coincident with the star-forming ring seen in the optical images. The molecular gas in the galaxy disk is in a remarkably regular rotation, however, the kinematics in the nuclear region is very skewed. The nuclear spectrum of CO and dense gas tracers HCN(4-3), HCO+(4-3), and CS(7-6) show broad wings up to $\pm$300km/s, associated with a molecular outflow emanating from the nucleus (r~25pc). We derive a molecular outflow mass $M_{out}$=2x10$^6$M$_\odot$ and a mass outflow rate of $\dot{M}_{out}=$27$\rm M_\odot yr^{-1}$. The molecular outflow energetics exceed the values predicted by AGN feedback models: the kinetic power of the outflow corresponds to 20%L_AGN and the momentum rate is $\dot{M}_{out}v\sim400L_{AGN}/c$. The outflow is mainly boosted by the AGN through entrainment by the radio jet, but given the weak nuclear activity of NGC613, we might be witnessing a fossil outflow, resulted from a strong past AGN that now has already faded. The nuclear trailing spiral observed in CO emission is inside the ILR ring of the bar. We compute the gravitational torques exerted in the gas to estimate the efficiency of the angular momentum exchange. The gravity torques are negative from 25 to 100pc and the gas loses its angular momentum in a rotation period, providing evidence of a highly efficient inflow towards the center. This phenomenon shows that the massive central black hole has a significant dynamical influence on the gas, triggering its fueling.

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arXiv2019

ALMA observations of molecular tori around massive black holes

We report ALMA observations of CO(3-2) emission in a sample of 7 Seyfert/LINER galaxies at the unprecedented spatial resolution of 0.1'' = 4-9 pc. Our aim is to explore the close environment of AGN, and the dynamical structures leading to its fueling. The selected galaxies host low-luminosity AGN, and have a wide range of activity types, and barred or ringed morphologies. The observed maps reveal the existence of circum-nuclear disk structures, defined by their morphology and decoupled kinematics. We call these structures "molecular tori", even though they appear often as disks, without holes in the center. They have varied orientations, unaligned with their host galaxy. The radius of the tori ranges from 6 to 27 pc, and their mass from 0.7 10$^7$ to 3.9 10$^7$ Msun. At larger scale, the gas is always piled up in a few 100~pc scale resonant rings, that play the role of a reservoir to fuel the nucleus. In some cases, a trailing spiral is observed inside the ring, providing evidence for feeding processes. Most frequently, the torus and the AGN are slightly off-centered, with respect to the bar-resonant ring position, implying that the black hole is wandering by a few 10~pc amplitude around the center of mass of the galaxy. Our spatial resolution allows us to measure gas velocities inside the sphere of influence of the central black holes. By fitting the observations with different simulated cubes, varying the torus inclination and the black hole mass, it is possible to estimate the mass of the central black hole, which is in general difficult for such late-type galaxies, with only a pseudo-bulge.

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