| 1. |
- Tang, X. D., et al.
(författare)
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ALMA view of the C-12/C-13 isotopic ratio in starburst galaxies
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 629
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Tidskriftsartikel (refereegranskat)abstract
- We derive molecular-gas-phase C-12/C-13 isotope ratios for the central few hundred parsecs of the three nearby starburst galaxies NGC 253, NGC 1068, and NGC 4945 making use of the lambda similar to 3 mm (CN)-C-12 and (CNN)-C-13= 1-0 lines in the ALMA Band 3. The C-12/C-13 isotopic ratios derived from the ratios of these lines range from 30 to 67 with an average of 41.6 +/- 0.2 in NGC 253, from 24 to 62 with an average of 38.3 +/- 0.4 in NGC 1068, and from 6 to 44 with an average of 16.9 +/- 0.3 in NGC 4945. The highest C-12/C-13 isotopic ratios are determined in some of the outskirts of the nuclear regions of the three starburst galaxies. The lowest ratios are associated with the northeastern and southwestern molecular peaks of NGC 253, the northeastern and southwestern edge of the mapped region in NGC 1068, and the very center of NGC 4945. In the case of NGC 1068, the measured ratios suggest inflow from the outer part of NGC 1068 into the circum-nuclear disk through both the halo and the bar. Low C-12/C-13 isotopic ratios in the central regions of these starburst galaxies indicate the presence of highly processed material.
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| 2. |
- Aalto, Susanne, 1964, et al.
(författare)
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ALMA resolves the remarkable molecular jet and rotating wind in the extremely radio-quiet galaxy NGC 1377
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 640
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Tidskriftsartikel (refereegranskat)abstract
- Submillimetre and millimetre line and continuum observations are important in probing the morphology, column density, and dynamics of the molecular gas and dust around obscured active galactic nuclei (AGNs) and their mechanical feedback. With very high-resolution (0.'' 02x0.'' 03 (2x3 pc)) ALMA 345 GHz observations of CO 3-2, HCO+ 4-3, vibrationally excited HCN 4-3 nu (2)=1f, and continuum we have studied the remarkable, extremely radio-quiet, molecular jet and wind of the lenticular galaxy NGC 1377. The outflow structure is resolved, revealing a 150 pc long, clumpy, high-velocity (similar to 600 km s(-1)), collimated molecular jet where the molecular emission is emerging from the spine of the jet with an average diameter of 3-7 pc. The jet widens to 10-15 pc about 25 pc from the centre, which is possibly due to jet-wind interactions. A narrow-angle (50 degrees -70 degrees), misaligned and rotating molecular wind surrounds the jet, and both are enveloped by a larger-scale CO-emitting structure at near-systemic velocity. The jet and narrow wind have steep radial gas excitation gradients and appear turbulent with high gas dispersion (sigma> 40 km s(-1)). The jet shows velocity reversals that we propose are caused by precession, or more episodic directional changes. We discuss the mechanisms powering the outflow, and we find that an important process for the molecular jet and narrow wind is likely magneto-centrifugal driving. In contrast, the large-scale CO-envelope may be a slow wind, or cocoon that stems from jet-wind interactions. An asymmetric, nuclear r similar to 2 pc dust structure with a high inferred molecular column density N(H-2) similar or equal to 1.8x10(24) cm(-2) is detected in continuum and also shows compact emission from vibrationally excited HCN. The nuclear dust emission is hot (T-d> 180 K) and its luminosity is likely powered by a buried AGN. The lopsided structure appears to be a warped disk, which is responsible for a significant part of the nuclear obscuration and possibly formed as a result of uneven gas inflows. The dynamical mass inside r=1.4 pc is estimated to 9(-3)(+2) x 10(6)M(circle dot) 9 - 3 + 2 x 10 6 M circle dot , implying that the supermassive black hole (SMBH) has a high mass with respect to the stellar velocity dispersion of NGC 1377. We suggest that the SMBH of NGC 1377 is currently in a state of moderate growth, at the end of a more intense phase of accretion and also evolving from a state of more extreme nuclear obscuration. The nuclear growth may be fuelled by low-angular momentum gas inflowing from the gas ejected in the molecular jet and wind. Such a feedback-loop of cyclic outflows and central accretion could explain why there is still a significant reservoir of molecular gas in this ageing, lenticular galaxy. A feedback-loop would be an effective process in growing the nuclear SMBH and thus would constitute an important phase in the evolution of NGC 1377. This also invites new questions as to SMBH growth processes in obscured, dusty galaxies.
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| 3. |
- Scourfield, M., et al.
(författare)
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ALMA observations of CS in NGC 1068: chemistry and excitation
- 2020
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 496:4, s. 5308-5329
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Tidskriftsartikel (refereegranskat)abstract
- We present results from Atacama Large Millimeter/submillimeter Array (ALMA) observations of CS from the nearby galaxy NGC 1068 (similar to 14 Mpc). This Seyfert 2 barred galaxy possesses a circumnuclear disc (CND, r similar to 200 pc) and a starburst ring (SB ring, r similar to 1.3 kpc). These high-resolution maps (similar to 0.5 arcsec, similar to 35 pc) allow us to analyse specific sub-regions in the galaxy and investigate differences in line intensity ratios and physical conditions, particularly those between the CND and SB ring. Local thermodynamic equilibrium (LTE) analysis of the gas is used to calculate CS densities in each sub-region, followed by the non-LTE analysis conducted using the radiative transfer code RADEX to fit observations and constrain gas temperature, CS column density and hydrogen density. Finally, the chemical code UCLCHEM is used to reconstruct the gas, allowing an insight into its origin and chemical history. The density of hydrogen in the CND is found to be >= 10(5) cm(-2), although exact values vary, reaching 10(6) cm(-2) at the active galactic nucleus. The conditions in the two arms of the SB ring appear similar to one another, though the density found (similar to 10(4) cm(-2)) is lower than in the CND. The temperature in the CND increases from east to west, and is also overall greater than found in the SB ring. These modelling methods indicate the requirement for multiphase gas components in order to fit the observed emission over the galaxy. A larger number of high-resolution transitions across the SLED may allow for further constraining of the conditions, particularly in the SB ring.
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| 4. |
- Treviño Morales, Sandra, 1985, et al.
(författare)
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Dynamics of cluster-forming hub-filament systems The case of the high-mass star-forming complex Monoceros R2
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 629
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Tidskriftsartikel (refereegranskat)abstract
- Context. High-mass stars and star clusters commonly form within hub-filament systems. Monoceros R2 (hereafter Mon R2), at a distance of 830 pc, harbors one of the closest of these systems, making it an excellent target for case studies. Aims. We investigate the morphology, stability and dynamical properties of the Mon R2 hub-filament system. Methods. We employed observations of the (CO)-C-13 and (CO)-O-18 1 -> 0 and 2 -> 1 lines obtained with the IRAM-30m telescope. We also used H-2 column density maps derived from Herschel dust emission observations. Results. We identified the filamentary network in Mon R-2 with the DisPerSE algorithm and characterized the individual filaments as either main (converging into the hub) or secondary (converging to a main filament). The main filaments have line masses of 30-100 M-circle dot pc(-1) and show signs of fragmentation, while the secondary filaments have line masses of 12-60 M-circle dot pc(-1) and show fragmentation only sporadically. In the context of Ostriker's hydrostatic filament model, the main filaments are thermally supercritical. If non-thermal motions are included, most of them are transcritical. Most of the secondary filaments are roughly transcritical regardless of whether non-thermal motions are included or not. From the morphology and kinematics of the main filaments, we estimate a mass accretion rate of 10(-4)-10(-3) M-circle dot yr(-1) into the central hub. The secondary filaments accrete into the main filaments at a rate of 0.1-0.4 x 10(-4) M-circle dot yr(-1). The main filaments extend into the central hub. Their velocity gradients increase toward the hub, suggesting acceleration of the gas. We estimate that with the observed infall velocity, the mass-doubling time of the hub is similar to 2.5 Myr, ten times longer than the free-fall time, suggesting a dynamically old region. These timescales are comparable with the chemical age of the HII region. Inside the hub, the main filaments show a ring-or a spiral-like morphology that exhibits rotation and infall motions. One possible explanation for the morphology is that gas is falling into the central cluster following a spiral-like pattern.
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| 5. |
- Aladro, Rebeca, 1979, et al.
(författare)
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Molecular gas in the northern nucleus of Mrk 273: Physical and chemical properties of the disc and its outflow
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 617
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Tidskriftsartikel (refereegranskat)abstract
- Aiming to characterise the properties of the molecular gas in the ultra-luminous infrared galaxy Mrk 273 and its outflow, we used the NOEMA interferometer to image the dense-gas molecular tracers HCN, HCO+, HNC, HOC+ and HC3N at similar to 86 GHz and similar to 256 GHz with angular resolutions of 4.'' 9 x 4.'' 5 (similar to 3.7 x 3.4 kpc) and 0.'' 61 x 0.'' 55 (similar to 460 x 420 pc). We also modelled the flux of several H2O lines observed with Herschel using a radiative transfer code that includes excitation by collisions and far-infrared photons. The disc of the Mrk 273 north nucleus has two components with decoupled kinematics. The gas in the outer parts (R similar to 1.5 kpc) rotates with a south-east to north-west direction, while in the inner disc (R similar to 300 pc) follows a north-east to south-west rotation. The central 300 pc, which hosts a compact starburst region, is filled with dense and warm gas, and contains a dynamical mass of (4-5) x 10(9) M-circle dot, a luminosity of L'HCN = (3-4) x 10(8) K km s(-1) pc(2), and a dust temperature of 55 K. At the very centre, a compact core with R similar to 50 pc has a luminosity of LIR = 4 x 10(11) L-circle dot (30% of the total infrared luminosity), and a dust temperature of 95 K. The core is expanding at low velocities similar to 50-100 km s(-1), probably affected by the outflowing gas. We detect the blue-shifted component of the outflow, while the red-shifted counterpart remains undetected in our data. Its cold and dense phase reaches fast velocities up to similar to 1000 km s(-1), while the warm outflowing gas has more moderate maximum velocities of similar to 600 km s(-1). The outflow is compact, being detected as far as 460 pc from the centre in the northern direction, and has a mass of dense gas <= 8 x 10(8) M-circle dot. The difference between the position angles of the inner disc (similar to 70 degrees) and the outflow (similar to 10 degrees) indicates that the outflow is likely powered by the AGN, and not by the starburst. Regarding the chemistry in Mrk 273, we measure an extremely low HCO+/HOC+ ratio of 10 +/- 5 in the inner disc of Mrk 273.
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| 6. |
- Buchbender, C., et al.
(författare)
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Dense gas in M 33 (HerM33es)
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 549, s. 17-36
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We aim to better understand the emission of molecular tracers of the diffuse and dense gas in giant molecular clouds and the influence that metallicity, optical extinction, density, far-UV field, and star formation rate have on these tracers.Methods. Using the IRAM 30 m telescope, we detected HCN, HCO+, 12CO, and 13CO in six GMCs along the major axis of M 33 at a resolution of ~114 pc and out to a radial distance of 3.4 kpc. Optical, far-infrared, and submillimeter data from Herschel and other observatories complement these observations. To interpret the observed molecular line emission, we created two grids of models of photon-dominated regions, one for solar and one for M 33-type subsolar metallicity.Results. The observed HCO+/HCN line ratios range between 1.1 and 2.5. Similarly high ratios have been observed in the Large Magellanic Cloud. The HCN/CO ratio varies between 0.4% and 2.9% in the disk of M 33. The 12CO/13CO line ratio varies between 9 and 15 similar to variations found in the diffuse gas and the centers of GMCs of the Milky Way. Stacking of all spectra allowed HNC and C2H to be detected. The resulting HCO+/HNC and HCN/HNC ratios of ~8 and 6, respectively, lie at the high end of ratios observed in a large set of (ultra-)luminous infrared galaxies. HCN abundances are lower in the subsolar metallicity PDR models, while HCO+ abundances are enhanced. For HCN this effect is more pronounced at low optical extinctions. The observed HCO+/HCN and HCN/CO line ratios are naturally explained by subsolar PDR models of low optical extinctions between 4 and 10 mag and of moderate densities of n 3 × 103–3 × 104 cm-3, while the FUV field strength only has a small effect on the modeled line ratios. The line ratios are almost equally well reproduced by the solar-metallicity models, indicating that variations in metallicity only play a minor role in influencing these line ratios.
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| 7. |
- Fuente, A., et al.
(författare)
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Gas phase Elemental abundances in Molecular cloudS (GEMS) I. The prototypical dark cloud TMC 1
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 624
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Tidskriftsartikel (refereegranskat)abstract
- GEMS is an IRAM 30 m Large Program whose aim is determining the elemental depletions and the ionization fraction in a set of prototypical star-forming regions. This paper presents the first results from the prototypical dark cloud Taurus molecular cloud (TMC) 1. Extensive millimeter observations have been carried out with the IRAM 30 m telescope (3 and 2mm) and the 40 m Yebes telescope (1.3 cm and 7 mm) to determine the fractional abundances of CO, HCO+, HCN, CS, SO, HCS+, and N2H+ in three cuts which intersect the dense filament at the well-known positions TMC 1-CP, TMC 1-NH3, and TMC 1-C, covering a visual extinction range from A(v) similar to 3 to similar to 20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1-5 x 10(3) cm(-3); and (ii) the dense phase, located at A(v) > 10 mag, with molecular hydrogen densities >10(4) cm(-3). Observations and modeling show that the gas phase abundances of C and O progressively decrease along the C+/C/CO transition zone (A(v) similar to 3 mag) where C/H similar to 8 x 10(-5) and C/O similar to 0.8-1, until the beginning of the dense phase at A(v) similar to 10 mag. This is consistent with the grain temperatures being below the CO evaporation temperature in this region. In the case of sulfur, a strong depletion should occur before the translucent phase where we estimate an S/H similar to (0.4-2.2) x 10(-6), an abundance similar to 7-40 times lower than the solar value. A second strong depletion must be present during the formation of the thick icy mantles to achieve the values of S/H measured in the dense cold cores (S/H similar to 8 x 10(-8)). Based on our chemical modeling, we constrain the value of zeta(H2) to similar to(0.5-1.8) x 10(-16) s(-1) in the translucent cloud.
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| 8. |
- Lutz, D., et al.
(författare)
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Molecular outflows in local galaxies: Method comparison and a role of intermittent AGN driving
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 633
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Tidskriftsartikel (refereegranskat)abstract
- We report new detections and limits from a NOEMA and ALMA CO(1-0) search for molecular outflows in 13 local galaxies with high far-infrared surface brightness, and combine these with local universe CO outflow results from the literature. The CO line ratios and spatial outflow structure of our targets provide some constraints on the conversion steps from observables to physical quantities such as molecular mass outflow rates. Where available, ratios between outflow emission in higher J CO transitions and in CO(1-0) are typically consistent with excitation R-i1 less than or similar to 1. However, for IRAS 13120 5453, R-31 = 2.10 +/- 0.29 indicates optically thin CO in the outflow. Like much of the outflow literature, we use ff CO(1 0) = 0.8, and we present arguments for using C = 1 in deriving molecular mass outflow rates. (M)over dot(out) = CM(out)v(out)/R-out. We compare the two main methods for molecular outflow detection: CO millimeter interferometry and Herschel OH-based spectroscopic outflow searches. For 26 sources studied with both methods, we find an 80% agreement in detecting vout & 150 km s 1 outflows, and non-matches can be plausibly ascribed to outflow geometry and signal-to-noise ratio. For a published sample of 12 bright ultraluminous infrared galaxies with detailed OH-based outflow modeling, CO outflows are detected in all but one. Outflow masses, velocities, and sizes for these 11 sources agree well between the two methods, and modest remaining di fferences may relate to the di fferent but overlapping regions sampled by CO emission and OH absorption. Outflow properties correlate better with active galactic nucleus (AGN) luminosity and with bolometric luminosity than with far-infrared surface brightness. The most massive outflows are found for systems with current AGN activity, but significant outflows in nonAGN systems must relate to star formation or to AGN activity in the recent past. We report scaling relations for the increase of outflow mass, rate, momentum rate, and kinetic power with bolometric luminosity. Short flow times of similar to 10(6) yr and some sources with resolved multiple outflow episodes support a role of intermittent driving, likely by AGNs.
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| 9. |
- Navarro-Almaida, D., et al.
(författare)
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Gas phase Elemental abundances in Molecular cloudS (GEMS): II. On the quest for the sulphur reservoir in molecular clouds: the H2S case
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 637
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Tidskriftsartikel (refereegranskat)abstract
- Context. Sulphur is one of the most abundant elements in the Universe. Surprisingly, sulphuretted molecules are not as abundant as expected in the interstellar medium and the identity of the main sulphur reservoir is still an open question. Aims. Our goal is to investigate the H2S chemistry in dark clouds, as this stable molecule is a potential sulphur reservoir. Methods. Using millimeter observations of CS, SO, H2S, and their isotopologues, we determine the physical conditions and H2S abundances along the cores TMC 1-C, TMC 1-CP, and Barnard 1b. The gas-grain model NAUTILUS is used to model the sulphur chemistry and explore the impact of photo-desorption and chemical desorption on the H2S abundance. Results. Our modeling shows that chemical desorption is the main source of gas-phase H2S in dark cores. The measured H2S abundance can only be fitted if we assume that the chemical desorption rate decreases by more than a factor of 10 when n(H) > 2 x 10(4). This change in the desorption rate is consistent with the formation of thick H2O and CO ice mantles on grain surfaces. The observed SO and H2S abundances are in good agreement with our predictions adopting an undepleted value of the sulphur abundance. However, the CS abundance is overestimated by a factor of 5-10. Along the three cores, atomic S is predicted to be the main sulphur reservoir. Conclusions. The gaseous H2S abundance is well reproduced, assuming undepleted sulphur abundance and chemical desorption as the main source of H2S. The behavior of the observed H2S abundance suggests a changing desorption efficiency, which would probe the snowline in these cold cores. Our model, however, highly overestimates the observed gas-phase CS abundance. Given the uncertainty in the sulphur chemistry, we can only conclude that our data are consistent with a cosmic elemental S abundance with an uncertainty of a factor of 10.
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| 10. |
- Pereira-Santaella, M., et al.
(författare)
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Spatially resolved cold molecular outflows in ULIRGs
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
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Tidskriftsartikel (refereegranskat)abstract
- We present new CO(2-1) observations of three low-z (d similar to 350 Mpc) ultra-luminous infrared galaxy (ULIRG) systems (six nuclei) observed with the Atacama large millimeter/submillimeter array (ALMA) at high spatial resolution (similar to 500 pc). We detect massive cold molecular gas outflows in five out of six nuclei (M-out - (0.3-5) x 10(8) M-circle dot). These outflows are spatially resolved with deprojected effective radii between 250 pc and 1 kpc although high-velocity molecular gas is detected up to R-max similar to 0.5-1.8 kpc (1-6 kpc deprojected). The mass outflow rates are 12-400 M circle dot yr(-1) and the inclination corrected average velocity of the outflowing gas is 350-550 km s(-1) (v(max) = 500-900 km s(-1)). The origin of these outflows can be explained by the strong nuclear starbursts although the contribution of an obscured active galactic nucleus cannot be completely ruled out. The position angle (PA) of the outflowing gas along the kinematic minor axis of the nuclear molecular disk suggests that the outflow axis is perpendicular to the disk for three of these outflows. Only in one case is the outflow PA clearly not along the kinematic minor axis, which might indicate a different outflow geometry. The outflow depletion times are 15-80 Myr. These are comparable to, although slightly shorter than, the star-formation (SF) depletion times (30-80 Myr). However, we estimate that only 15-30% of the outflowing molecular gas will escape the gravitational potential of the nucleus. The majority of the outflowing gas will return to the disk after 5-10 Myr and become available to form new stars. Therefore, these outflows will not likely completely quench the nuclear starbursts. These star-forming powered molecular outflows would be consistent with being driven by radiation pressure from young stars (i.e., momentum-driven) only if the coupling between radiation and dust increases with increasing SF rates. This can be achieved if the dust optical depth is higher in objects with higher SF. This is the case in at least one of the studied objects. Alternatively, if the outflows are mainly driven by supernovae (SNe), the coupling efficiency between the interstellar medium and SNe must increase with increasing SF levels. The relatively small sizes (<1 kpc) and dynamical times (<3 Myr) of the cold molecular outflows suggests that molecular gas cannot survive longer in the outflow environment or that it cannot form efficiently beyond these distances or times. In addition, the ionized and hot molecular phases have been detected for several of these outflows, so this suggests that outflowing gas can experience phase changes and indicates that the outflowing gas is intrinsically multiphase, likely sharing similar kinematics, but different mass and, therefore, different energy and momentum contributions.
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