A gas-rich AGN near the centre of a galaxy cluster at z ~ 1.4

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, implying 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.Comment: 5 pages, 3 figures, accepted for publication in Astronomy & Astrophysic

ALMA observations of cool dust in a low-metallicity starburst, SBS0335-052

We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 Band 7 observations of an extremely metal-poor dwarf starburst galaxy in the Local Universe, SBS0335-052 (12+log(O/H)~7.2). With these observations, dust is detected at 870micron (ALMA Band 7), but 87% of the flux in this band is due to free-free emission from the starburst. We have compiled a spectral energy distribution (SED) of SBS0335-052 that spans almost 6 orders of magnitude in wavelength and fit it with a spherical dust shell heated by a single-age stellar population; the best-fit model gives a dust mass of (3.8+/-0.6)x10^4 Msun. We have also constructed a SED including Herschel archival data for IZw18, another low-metallicity dwarf starburst (12+log(O/H)=7.17), and fit it with a similar model to obtain a dust mass of (3.4+/-1.0)x10^2 Msun. Compared with their atomic gas mass, the dust mass of SBS0335-052 far exceeds the prediction of a linear trend of dust-to-gas mass ratio with metallicity, while IZw18 falls far below. We use gas scaling relations to assess a putative missing gas component in both galaxies and find that the missing, possibly molecular, gas in SBS0335-052 is a factor of 6 times higher than the value inferred from the observed HI column density; in IZw18 the missing component is 4 times smaller. Ultimately, despite their similarly low metallicity, the differences in gas and dust column densities in SBS0335-052 and IZw18 suggest that metal abundance does not uniquely define star-formation processes. At some level, self-shielding and the survival of molecules may depend just as much on gas and dust column density as on metallicity. The effects of low metallicity may at least be partially compensated for by large column densities in the interstellar medium.Comment: 15 pages, 11 figures, accepted for publication in A&

Molecular depletion times and the CO-to-H2 conversion factor in metal-poor galaxies

Tracing molecular hydrogen content with carbon monoxide in low-metallicity galaxies has been exceedingly difficult. Here we present a new effort, with IRAM 30-m observations of 12CO(1-0) of a sample of 8 dwarf galaxies having oxygen abundances ranging from 12+logO/H=7.7 to 8.4. CO emission is detected in all galaxies, including the most metal-poor galaxy of our sample (0.1 Zsun); to our knowledge this is the largest number of 12CO(1-0) detections ever reported for galaxies with 12+logO/H<=8 (0.2 Zsun) outside the Local Group. We calculate stellar masses (Mstar) and star-formation rates (SFRs), and analyze our results by combining our observations with galaxy samples from the literature. Extending previous results for a correlation of the molecular gas depletion time, tau(dep), with Mstar and specific SFR (sSFR), we find a variation in tau(dep) of a factor of 200 or more (from <50 Myr to 10 Gyr) over a spread of 1000 in sSFR and Mstar. We exploit the variation of tau(dep) to constrain the CO-to-H2 mass conversion factor alpha(CO) at low metallicity, and assuming a power-law variation find alpha(CO) \propto (Z/Zsun)^1.9, similar to results based on dust continuum measurements compared with gas mass. By including HI measurements, we show that the fraction of total gas mass relative to the baryonic mass is higher in galaxies that are metal poor, of low mass, and of high sSFR. Finally, comparisons of the data with star-formation models of the molecular gas phases suggest that, at metallicities Z/Zsun<=0.2, there are some discrepancies with model predictions.Comment: 18 pages, 15 figures, accepted for publication in A&

Molecular Gas in NUclei of GAlaxies (NUGA) XIV. The barred LINER/Seyfert 2 galaxy NGC 3627

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.Comment: 24 pages, 28 figures, 2 tables. Accepted for publication in Astronomy and Astrophysic

ALMA reveals the feeding of the Seyfert 1 nucleus in NGC 1566

We report ALMA observations of CO(3-2) emission in the Seyfert 1 galaxy NGC 1566, at a spatial resolution of 25 pc. Our aim is to investigate the morphology and dynamics of the gas inside the central kpc, and to probe nuclear fueling and feedback phenomena. NGC 1566 has a nuclear bar of 1.7 kpc radius and a conspicuous grand design spiral starting from this radius. The ALMA field of view, of diameter 0.9 kpc, lies well inside the nuclear bar and reveals a molecular trailing spiral structure from 50 to 300~pc in size, which is contributing to fuel the nucleus, according to its negative gravity torques. The spiral starts with a large pitch angle from the center and then winds up in a pseudo-ring at the inner Lindblad resonance (ILR) of the nuclear bar. This is the first time that a trailing spiral structure is clearly seen driving the gas inwards inside the ILR ring of the nuclear bar. This phenomenon shows that the massive central black hole has a significant dynamical influence on the gas, triggering its fueling. The gaseous spiral is well correlated with the dusty spiral seen through extinction in HST images, and also with a spiral feature emitting 0.87mm continuum. This continuum emission must come essentially from cold dust heated by the interstellar radiation field. The HCN(4-3) and HCO+(4-3) lines were simultaneously mapped and detected in the nuclear spiral. The HCO+(4-3) line is 3 times stronger than the HCN(4-3), as expected when star formation excitation dominates over active galactic nucleus (AGN) heating. The CO(3-2)/HCO+(4-3) integrated intensity ratio is \sim 100. The molecular gas is in remarkably regular rotation, with only slight non-circular motions at the periphery of the nuclear spiral arms. These perturbations are quite small, and no outflow nor AGN feedback is detected.Comment: 11 pages, 16 figures, accepted in Astronomy and Astrophysic

ALMA observations of feeding and feedback in nearby Seyfert galaxies: an AGN-driven outflow in NGC 1433

We report ALMA observations of CO(3-2) emission in the Seyfert 2 double-barred galaxy NGC1433, at the unprecedented spatial resolution of 0.5"=24 pc. Our aim is to probe AGN feeding and feedback phenomena through the morphology and dynamics of the gas inside the central kpc. The CO map, which covers the whole nuclear region (nuclear bar and ring), reveals a nuclear gaseous spiral structure, inside the nuclear ring encircling the nuclear stellar bar. This gaseous spiral is well correlated with the dusty spiral seen in Hubble Space Telescope images. The nuclear spiral winds up in a pseudo-ring at 200 pc radius, which might correspond to the inner ILR. Continuum emission is detected at 0.87 mm only at the very centre, and its origin is more likely thermal dust emission than non-thermal emission from the AGN. It might correspond to the molecular torus expected to exist in this Seyfert 2 galaxy. The HCN(4-3) and HCO+(4-3) lines were observed simultaneously, but only upper limits are derived, with a ratio to the CO(3-2) line lower than 1/60 at 3sigma, indicating a relatively low abundance of very dense gas. The kinematics of the gas over the nuclear disk reveal rather regular rotation only slightly perturbed by streaming motions due to the spiral; the primary and secondary bars are too closely aligned with the galaxy major or minor axis to leave a signature in the projected velocities. Near the nucleus, there is an intense high-velocity CO emission feature redshifted to 200 km/s (if located in the plane), with a blue-shifted counterpart, at 2" (100 pc) from the centre. While the CO spectra are quite narrow in the centre, this wide component is interpreted as an outflow involving a molecular mass of 3.6 10^6 Mo and a flow rate 7 Mo/yr. The flow could be in part driven by the central star formation, but is mainly boosted by the AGN through its wind or radio jets.Comment: 11 pages, 9 figures, Accepted in Astronomy and Astrophysic

Italian Science Case for ALMA Band 2+3

The Premiale Project "Science and Technology in Italy for the upgraded ALMA Observatory - iALMA" has the goal of strengthening the scientific, technological and industrial Italian contribution to the Atacama Large Millimeter/submillimeter Array (ALMA), the largest ground based international infrastructure for the study of the Universe in the microwave. One of the main objectives of the Science Working Group (SWG) inside iALMA, the Work Package 1, is to develop the Italian contribution to the Science Case for the ALMA Band 2 or Band 2+3 receiver. ALMA Band 2 receiver spans from ~67 GHz (bounded by an opaque line complex of ozone lines) up to 90 GHz which overlaps with the lower frequency end of ALMA Band 3. Receiver technology has advanced since the original definition of the ALMA frequency bands. It is now feasible to produce a single receiver which could cover the whole frequency range from 67 GHz to 116 GHz, encompassing Band 2 and Band 3 in a single receiver cartridge, a so called Band 2+3 system. In addition, upgrades of the ALMA system are now foreseen that should double the bandwidth to 16 GHz. The science drivers discussed below therefore also discuss the advantages of these two enhancements over the originally foreseen Band 2 system.Comment: 43 pages, 21 figure

Fractal Subsystem Symmetries, 't Hooft Anomalies, and UV/IR Mixing

In this work, we study unconventional anisotropic topologically ordered phases in 3d that manifest type-II fractonic physics along sub-manifolds. While they behave as usual topological order along a preferred spatial direction, their physics along perpendicular planes is dictated by the presence of fractal subsystem symmetries, completely restricting the mobility of anyonic excitations and their bound states. We consider an explicit lattice model realization of such phases and proceed to study their properties under periodic boundary conditions and, later, in the presence of boundaries. We find that for specific lattice sizes, the system possesses line and fractal membrane symmetries that are mutually anomalous, resulting in a non-trivially gapped ground state space. This amounts to the spontaneous breaking of the fractal symmetries, implying a sub-extensive ground state degeneracy. For the remaining system sizes the fractal symmetries are explicitly broken by the periodic boundary conditions, which is intrinsically related to the uniqueness of the ground state. Despite of that, the system is still topologically ordered since locally created quasi-particles have nontrivial mutual statistics and, in the presence of boundaries, it still presents anomalous edge modes. The intricate symmetry interplay dictated by the lattice size is a wild manifestation of ultraviolet/infrared (UV/IR) mixing.Comment: 7+7 pages, 5+5 figure