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Martinez-Badenes V.,Institute Astrofisica Of Andalucia Iaa Csic | Lisenfeld U.,University of Granada | Espada D.,Institute Astrofisica Of Andalucia Iaa Csic | Espada D.,Japan National Astronomical Observatory | And 5 more authors.
Astronomy and Astrophysics | Year: 2012

Aims. We study the effect of the extreme environment in Hickson compact groups (HCGs) on the molecular gas mass, MH2, and the star formation rate (SFR) of galaxies as a function of atomic hydrogen (HI) content and evolutionary phase of the group. Methods. We selected a redshift-limited (D < 100 Mpc) sample of 88 galaxies in 20 HCGs with available atomic hydrogen (HI) VLA maps, covering a wide range of HI deficiencies and evolutionary phases of the groups and containing at least one spiral galaxy. We observed the CO(1-0) and CO(2-1) lines with the IRAM 30 m telescope for 47 galaxies. Together with literature data, our sample contains CO(1-0) spectra for 86 galaxies. We derived the far-infrared (FIR) luminosity (LFIR) from IRAS data and used it as a tracer of the SFR. We calculated the HI mass (MHI), L FIR, and MH2 deficiencies, based on the values expected from LB and LK in isolated galaxies from the AMIGA sample. We limited our statistical analysis to spiral galaxies, since the large number of upper limits did not allow drawing strong conclusions about MH2and LFIR in early-type galaxies. Results. The mean deficiencies of LFIR and MH2 of spiral galaxies in HCGs are close to 0, indicating that their average SFR and molecular gas content are similar to those of isolated galaxies. However, there are indications of an excess of MH2 (∼50%) in spiral galaxies in HCGs, which can be interpreted, assuming that there is no systematic difference in the CO-to-H2 conversion factor, as either an enhanced molecular gas content or as a higher concentration of the molecular component towards the center in comparison to galaxies in lower density environments. In contrast, the mean MHI of spiral galaxies in HCGs is only 12% of the expected value. The specific SFR (sSFR = SFR/stellar mass) tends to be lower for galaxies with higher MH2 or MHI deficiency. This trend is not seen for the star formation efficiency (SFE = SFR/M H2), which is very similar to isolated galaxies. We found tentative indications of an enhancement of MH2 in spiral galaxies in HCGs in an early evolutionary phase and a decrease in later phases. We suggest that this might be due to an enhancement of the conversion from atomic to molecular gas due to ongoing tidal interactions in an early evolutionary phase, followed by HI stripping and a decrease in the molecular gas content because of lack of replenishment. Conclusions. The properties of M H2 and LFIR in galaxies in HCGs are surprisingly similar to those of isolated galaxies, in spite of the much higher Def(MHI) of the former. The trends of the sSFR and Def(M H2) with Def(MHI) and the evolutionary state indicate, however, that the ongoing interaction might have some effect on the molecular gas and SF. © 2012 ESO.

Smajic S.,University of Cologne | Smajic S.,Max Planck Institute for Radio Astronomy | Moser L.,University of Cologne | Eckart A.,University of Cologne | And 8 more authors.
Astronomy and Astrophysics | Year: 2014

Aims. We present the results of near-infrared (NIR) H- and K-band European Southern Observatory SINFONI integral field spectroscopy (IFS) of the Seyfert 2 galaxy NGC 1433. We investigate the central 500 pc of this nearby galaxy, concentrating on excitation conditions, morphology, and stellar content. NGC 1433 was selected from our extended NUGA(-south) sample, which was additionally observed with the Atacama Large Millimeter/submillimeter Array (ALMA). NGC 1433 is a ringed, spiral galaxy with a main stellar bar in roughly east-west direction (PA 94°) and a secondary bar in the nuclear region (PA 31°). Several dusty filaments are detected in the nuclear region with the Hubble Space Telescope. ALMA detects molecular CO emission coinciding with these filaments. The active galactic nucleus is not strong and the galaxy is also classified as a low-ionization emission-line region (LINER). Methods. The NIR is less affected by dust extinction than optical light and is sensitive to the mass-dominating stellar populations. SINFONI integral field spectroscopy combines NIR imaging and spectroscopy, allowing us to analyse several emission and absorption lines to investigate the stellar populations and ionization mechanisms over the 10″ × 10″ field of view (FOV). Results. We present emission and absorption line measurements in the central kpc of NGC 1433. We detect a narrow Balmer line and several H2 lines. We find that the stellar continuum peaks in the optical and NIR in the same position, indicating that there is no covering of the center by a nuclear dust lane. A strong velocity gradient is detected in all emission lines at that position. The position angle of this gradient is at 155° whereas the galactic rotation is at a position angle of 201°. Our measures of the molecular hydrogen lines, hydrogen recombination lines, and [Fe II] indicate that the excitation at the nucleus is caused by thermal excitation, i.e., shocks that can be associated with active galactic nuclei emission, supernovae, or outflows. The line ratios [Fe ii]/Paβ and H2/Brγ show a Seyfert to LINER identification of the nucleus. We do not detect high star formation rates in our FOV. The stellar continuum is dominated by spectral signatures of red-giant M stars. The stellar line-of-sight velocity follows the galactic field whereas the light continuum follows the nuclear bar. Conclusions. The dynamical center of NGC 1433 coincides with the optical and NIR center of the galaxy and the black hole position. Within the central arcsecond, the molecular hydrogen and the 12CO(3-2) emissions - observed in the NIR and in the submillimeter with SINFONI and ALMA, respectively - are indicative for a nuclear outflow originating from the galaxy's SMBH. A small circum-nuclear disk cannot be fully excluded. Derived gravitational torques show that the nuclear bar is able to drive gas inward to scales where viscosity torques and dynamical friction become important. The black hole mass, derived using stellar velocity dispersion, is ~107M⊙. © ESO, 2014.

Kramer C.,Instituto Radioastronomia Milimetrica IRAM | Abreu-Vicente J.,Instituto Radioastronomia Milimetrica IRAM | Garcia-Burillo S.,Observatorio Astronomico Nacional OAN Observatorio de Madrid | Relano M.,University of Granada | And 11 more authors.
Astronomy and Astrophysics | Year: 2013

Aims. We aim to better understand the heating of gas by observing the prominent gas cooling line [C ii] at 158 μm in the low-metallicity environment of the Local Group spiral galaxy M 33 on scales of 280 pc. In particular, we describe the variation of the photoelectric heating efficiency with the galactic environment. Methods. In this study, we present [C ii] observations along the major axis of M 33 using the Infrared Space Observatory in combination with Herschel continuum maps, IRAM 30 m CO 2-1, and VLA H i data to study the variation in velocity integrated intensities. The ratio of [C ii] emission over the far-infrared continuum is used as a proxy for the heating efficiency, and models of photon-dominated regions are used to study the local physical densities, far-ultraviolet radiation fields, and average column densities of the molecular clouds. Results. The heating efficiency stays constant at 0.8% in the inner 4.5 kpc radius of the galaxy, where it increases to reach values of ~3% in the outskirts at about a 6 kpc radial distance. The rise of efficiency is explained in the framework of PDR models by lowered volume densities and FUV fields for optical extinctions of only a few magnitudes at constant metallicity. For the significant fraction of H i emission stemming from PDRs and for typical pressures found in the Galactic cold neutral medium (CNM) traced by H i emission, the CNM contributes ~15% to the observed [C ii] emission in the inner 2 kpc radius of M 33. The CNM contribution remains largely undetermined in the south, while positions between radial distances of 2 and 7.3 kpc in the north of M 33 show a contribution of ~40% ± 20%. © ESO, 2013.

Combes F.,Paris Observatory | Garcia-Burillo S.,Observatorio Astronomico Nacional OAN Observatorio de Madrid | Casasola V.,National institute for astrophysics | Hunt L.K.,National institute for astrophysics | And 8 more authors.
Astronomy and Astrophysics | Year: 2014

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 0.87 mm 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 ~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. © 2014 ESO.

Combes F.,Paris Observatory | Garcia-Burillo S.,Observatorio Astronomico Nacional OAN Observatorio de Madrid | Casasola V.,National institute for astrophysics | Hunt L.,National institute for astrophysics | And 8 more authors.
Astronomy and Astrophysics | Year: 2013

We report ALMA observations of CO(3-2) emission in the Seyfert 2 galaxy NGC 1433 at the unprecedented spatial resolution of 0.′′. ′′ 5 = 24 pc. Our aim is to probe active galactic nucleus (AGN) feeding and feedback phenomena through the morphology and dynamics of the gas inside the central kpc. The galaxy NGC 1433 is a strongly barred spiral with three resonant rings: one at the ultra-harmonic resonance near corotation, and the others at the outer and inner Lindblad resonances (OLR and ILR). A nuclear bar of 400 pc radius is embedded in the large-scale primary bar. 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 (HST) 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 3σ, 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-1 (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 × 106 M⊙ and a flow rate ~7 M⊙/yr. The flow could be in part driven by the central star formation, but is mainly boosted by the AGN through its radio jets. © 2013 ESO.

Casasola V.,National institute for astrophysics | Hunt L.,National institute for astrophysics | Combes F.,Paris Observatory | Garcia-Burillo S.,Observatorio Astronomico Nacional OAN Observatorio de Madrid
Astronomy and Astrophysics | Year: 2015

Aims. We present an analysis of the relation between the star formation rate (SFR) surface density (ΣSFR) and mass surface density of molecular gas (ΣH2), commonly referred to as the Kennicutt-Schmidt (K-S) relation, on 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). These are AGN extracted from the NUclei of GAlaxies (NUGA) survey. This study investigates the correlations and slopes of the K-S relation, as a function of spatial resolution and of the different 12CO emission lines used to trace ΣH2, and tests its validity in the high-density central regions of spiral galaxies. Methods. We used interferometric IRAM 12CO(1-0) and 12CO(2-1) and SMA 12CO(3-2) emission line maps to derive ΣH2 and HST-Hα images to estimate ΣSFR. Results. Each galaxy is characterized by a distinct molecular SF relation on spatial scales between 20 to 200 pc. The K-S relations can be sublinear, but also superlinear, with slopes ranging from ∼0.5 to ∼1.3; slopes are generally superlinear on spatial scales >100 pc and sublinear on smaller scales. Depletion times range from ∼1 and 2 Gyr, which is compatible with results for nearby normal galaxies. These findings are valid independently of which transition - 12CO(1-0), 12CO(2-1), or 12CO(3-2) - is used to derive ΣH2. Because of either star-formation feedback, the lifetime 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 of this, even on scales as small as ∼20 pc, and this might be because of the higher density of GMCs in galaxy centers that have to resist higher shear forces. The proportionality between ΣH2 and ΣSFR found between 10 and 100 M pc-2 is valid even at high densities, ∼103 M pc-2. However, by adopting a common CO-to-H2 conversion factor (αCO), the central regions of the NUGA galaxies have higher ΣSFR for a given gas column than those expected from the models, with a behavior that lies between the mergers or high-redshift starburst systems and the more quiescent star-forming galaxies, assuming that the first ones require a lower value of αCO. © 2015 ESO.

Krips M.,Institut Universitaire de France | Martin S.,European Southern Observatory | Eckart A.,University of Cologne | Neri R.,Institut Universitaire de France | And 11 more authors.
Astrophysical Journal | Year: 2011

We present high angular resolution (05-20) observations of the millimeter continuum and the 12CO(J = 3-2), 13CO(J = 3-2), 13CO(J = 2-1), C18O(J = 2-1), HCN(J = 3-2), HCO +(J = 4-3), and HCO+(J = 3-2) line emission in the circumnuclear disk (r ≲ 100pc) of the prototypical Seyfert 2 galaxy NGC1068, carried out with the Submillimeter Array. We also include in our analysis new 13CO(J = 1-0) and improved 12CO(J = 2-1) observations of NGC1068 at high angular resolution (10-20) and sensitivity, conducted with the Institute de Radioastronomie Millimetrique Plateau de Bure Interferometer. Based on the complex dynamics of the molecular gas emission indicating non-circular motions in the central 100pc, we propose a scenario in which part of the molecular gas in the circumnuclear disk of NGC1068 is blown radially outward as a result of shocks. This shock scenario is further supported by quite warm (Tkin ≥ 200K) and dense (n(H2)≃ 104cm-3) gas constrained from observed molecular line ratios. The HCN abundance in the circumnuclear disk is found to be [HCN]/[ 12CO] ≈ 10-3.5. This is slightly higher than the abundances derived for Galactic and extragalactic star-forming/starbursting regions. This result lends further support to X-ray-enhanced HCN formation in the circumnuclear disk of NGC1068 as suggested by earlier studies. The HCO + abundance ([HCO+]/[12CO] ≈ 10 -5) appears to be somewhat lower than that of Galactic and extragalactic star-forming/starbursting regions. When trying to fit the centimeter-to-millimeter continuum emission by different thermal and non-thermal processes, it appears that electron-scattered synchrotron emission yields the best results while thermal free-free emission seems to overpredict the millimeter continuum emission. © 2011. The American Astronomical Society. All rights reserved.

Van Der Laan T.P.R.,Max Planck Institute for Astronomy | Schinnerer E.,Max Planck Institute for Astronomy | Boone F.,Toulouse 1 University Capitole | Boone F.,Roche Holding AG | And 6 more authors.
Astronomy and Astrophysics | Year: 2011

Within the NUclei of GAlaxies (NUGA) project we have obtained IRAM PdBI and 30 m 12CO(1â̂'0) and 12CO(2â̂'1) observations of the spiral galaxy NGC6951. Previous work shows that there is indirect evidence of gas inflow from 3 kpc down to small radii: a largescale 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 1.8 Ã- 106 M⊙, 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 NGC6951. © 2011 ESO.

Garcia-Burillo S.,Observatorio Astronomico Nacional OAN Observatorio de Madrid | Usero A.,Observatorio Astronomico Nacional OAN Observatorio de Madrid | Fuente A.,Observatorio Astronomico Nacional OAN Observatorio de Madrid | Martin-Pintado J.,CSIC - National Institute of Aerospace Technology | And 6 more authors.
Astronomy and Astrophysics | Year: 2010

Context This paper is part of a multi-species survey of line emission from the molecular gas in the circum-nuclear disk (CND) of the Seyfert 2 galaxy NGC 1068. Unlike in other active galaxies, the intensely star-forming regions in NGC 1068 and the CND can be resolved with current instrumentation. This makes this galaxy an optimal test-bed to probe the effects of AGN on the molecular medium at ∼100 pc scales. Aims. Single-dish observations have provided evidence that the abundance of silicon monoxide (SiO) in the CND of NGC 1068 is enhanced by 3-4 orders of magnitude with respect to the values typically measured in quiescent molecular gas in the Galaxy. We aim at unveiling the mechanism(s) underlying the SiO enhancement. Methods. We have imaged the emission of the SiO(2-1) (86.8 GHz) and CN(2-1) (226.8 GHz) lines in NGC 1068 at ∼150 pc and 60 pc spatial resolution with the IRAM Plateau de Bure interferometer (PdBI). We have also obtained complementary IRAM 30 m observations of HNCO and methanol (CH3OH) lines. These species are known as tracers of shocks in the Galaxy. Results. SiO is detected in a disk of ∼400 pc size around the AGN. SiO abundances in the CND of ∼(1-5)× 10-9 are about 1-2 orders of magnitude above those measured in the starburst ring. The overall abundance of CN in the CND is high: ∼(0.2-1) × 10-7. The abundances of SiO and CN are enhanced at the extreme velocities of gas associated with non-circular motions close to the AGN (r < 70 pc). On average, HNCO/SiO and CH3OH/SiO line ratios in the CND are similar to those measured in prototypical shocked regions in our Galaxy. Yet the strength and abundance of CN in NGC 1068 can be explained neither by shocks nor by photon-dominated region (PDR) chemistry. Abundances measured for CN and SiO and the correlation of CN/CO and SiO/CO ratios with hard X-ray irradiation suggest that the CND of NGC 1068 has become a giant X-ray-dominated region (XDR). Conclusions. The extreme properties of molecular gas in the circum-nuclear molecular disk of NGC 1068 result from the interplay between different processes directly linked to nuclear activity. The results presented here highlight in particular the footprint of shocks and X-ray irradiation on the properties of molecular gas in this Seyfert. Whereas XDR chemistry offers a simple explanation for CN and SiO in NGC 1068, the relevance of shocks deserves further scrutiny. The inclusion of dust grain chemistry would help solve the controversy regarding the abundances of other molecular species, like HCN, which are under-predicted by XDR models. © ESO 2010.

Villar-Martin M.,CSIC - National Institute of Aerospace Technology | Rodriguez M.,Institute Astrofisica Of Andalucia Csic | Drouart G.,European Southern Observatory | Drouart G.,CNRS Paris Institute of Astrophysics | And 9 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present results of CO(1-0) spectroscopic observations of 10 Sloan Digital Sky Survey type 2 quasars (QSO2) at z ~ 0.2-0.3 observed with the 30-m IRAM radio telescope and the Australia Telescope Compact Array. We report five new confirmed CO(1-0) detections and one tentative detection. They have L'CO ~ several × 109 K km s-1 pc2, while upper limits for the non-detections are L'CO < 3s = several × 109 K km s-1 pc2. This study increases the total number of QSO2 with CO measurements at z 1 to 20, with a 50 per cent detection rate. The vast majority are at z ~ 0.1-0.4. Assuming a conversion factor α = 0.8 M⊙(K km s-1pc2)-1, the implied molecular gas masses are in the range MH2 4 × 108 to ~5 × 109 M⊙. We compare with samples of type 1 quasars (QSO1), luminous and ultraluminous infrared galaxies. We find no difference in the molecular gas content of QSO1 and QSO2 of a given infrared luminosity, although the QSO2 sample is affected by small number statistics. This result, if confirmed, is consistent with the unification model for quasars. QSO2 fall on the L'COversus z, L'COversus LFIR and λ = LFIR LCO versus LFIR correlations defined by quasars at different z. The location of the QSO2 in these diagrams is discussed in comparison with samples of QSO1, luminous and ultraluminous infrared galaxies, and high-z submm sources. CO(1-0) has full width at half-maximum (FWHM) ~ 180-370 km s-1 when detected, with a variety of kinematic profiles (single or double horned). In general, the CO line is narrower than [O III]5007, as observed in low-z QSO1, with FWHM[O III]/FWHMCO ~ 1-2). This probably reveals different spatial sizes and/or geometry of the ionized and molecular phases and a higher sensitivity of the [O III] emission to non-gravitational motions, such as outflows. Considering the z ~ 0.1-0.4 range, where CO measurements for both QSO1 and QSO2 exist, we find no difference in FWHMCO between them, although this result is tentative. In the unification scenario between QSO1 and QSO2, this suggests that the distribution of CO gas is not related to the obscuring torus. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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