Dust growth via accretion of gas species has been proposed as the dominant process to increase the amount of dust in galaxies. We show here that this hypothesis encounters severe difficulties that ...make it unfit to explain the observed UV and IR properties of such systems, particularly at high redshifts. Dust growth in the diffuse ISM phases is hampered by (a) too slow accretion rates, (b) too high dust temperatures, and (c) the Coulomb barrier that effectively blocks accretion. In molecular clouds these problems are largely alleviated. Grains are cold (but not colder than the CMB temperature, T
CMB ≈ 20 K at redshift z = 6). However, in dense environments accreted materials form icy water mantles, perhaps with impurities. Mantles are immediately (≲1 yr) photo-desorbed as grains return to the diffuse ISM at the end of the cloud lifetime, thus erasing any memory of the growth. We conclude that dust attenuating stellar light at high-z must be ready-made stardust largely produced in supernova ejecta.
Abstract
We report on a systematic search for oxygen-bearing complex organic molecules (COMs) in the solar-like protostellar shock region L1157-B1, as part of the IRAM Large Program ‘Astrochemical ...Surveys At IRAM’. Several COMs are unambiguously detected, some for the first time, such as ketene H2CCO, dimethyl ether (CH3OCH3) and glycolaldehyde (HCOCH2OH), and others firmly confirmed, such as formic acid (HCOOH) and ethanol (C2H5OH). Thanks to the high sensitivity of the observations and full coverage of the 1, 2 and 3 mm wavelength bands, we detected numerous (∼10–125) lines from each of the detected species. Based on a simple rotational diagram analysis, we derive the excitation conditions and the column densities of the detected COMs. Combining our new results with those previously obtained towards other protostellar objects, we found a good correlation between ethanol, methanol and glycolaldehyde. We discuss the implications of these results on the possible formation routes of ethanol and glycolaldehyde.
Aims. We investigate the fueling and the feedback of nuclear activity in the nearby (D = 14 Mpc) Seyfert 2 barred galaxy NGC 1068 by studying the distribution and kinematics of molecular gas in the ...torus and its connections to the host galaxy disk. Methods. We used the Atacama Large Millimeter Array (ALMA ) to image the emission of a set of molecular gas tracers in the circumnuclear disk (CND) and the torus of the galaxy using the CO(2–1), CO(3–2), and HCO+(4–3) lines and their underlying continuum emission with high spatial resolutions (0.03″ − 0.09″ ≃ 2 − 6 pc). These transitions, which span a wide range of physical conditions of molecular gas (n(H2)⊂103 − 107 cm−3), are instrumental in revealing the density radial stratification and the complex kinematics of the gas in the torus and its surroundings. Results. The ALMA images resolve the CND as an asymmetric ringed disk of D ≃ 400 pc in size and ≃1.4 × 108 M⊙ in mass. The CND shows a marked deficit of molecular gas in its central ≃130 pc region. The inner edge of the ring is associated with the presence of edge-brightened arcs of NIR polarized emission, which are identified with the current working surface of the ionized wind of the active galactic nucleus (AGN). ALMA proves the existence of an elongated molecular disk/torus in NGC 1068 of Mtorusgas ≃ 3 × 105 M⊙ M torus gas ≃ 3 × 10 5 M ⊙ $ M_{\mathrm{torus}}^{\mathrm{gas}}\simeq3\times10^{5}\,M_{{\odot}} $ , which extends over a large range of spatial scales D ≃ 10 − 30 pc around the central engine. The new observations evidence the density radial stratification of the torus: the HCO+(4–3) torus, with a full size DHCO+(4 − 3) = 11 ± 0.6 pc, is a factor of between two and three smaller than its CO(2–1) and CO(3–2) counterparts, which have full sizes of DCO(3 − 2) = 26 ± 0.6 pc and DCO(2 − 1) = 28 ± 0.6 pc, respectively. This result brings into light the many faces of the molecular torus. The torus is connected to the CND through a network of molecular gas streamers detected inside the CND ring. The kinematics of molecular gas show strong departures from circular motions in the torus, the gas streamers, and the CND ring. These velocity field distortions are interconnected and are part of a 3D outflow that reflects the effects of AGN feedback on the kinematics of molecular gas across a wide range of spatial scales around the central engine. In particular, we estimate through modeling that a significant fraction of the gas inside the torus ( ≃ 0.4 − 0.6 × Mtorusgas ≃ 0.4 − 0.6 × M torus gas $ {\simeq}0.4{-}0.6 \times M_{\mathrm{torus}}^{\mathrm{gas}} $ ) and a comparable amount of mass along the gas streamers are outflowing. However, the bulk of the mass, momentum, and energy of the molecular outflow of NGC 1068 is contained at larger radii in the CND region, where the AGN wind and the radio jet are currently pushing the gas assembled at the Inner Lindblad Resonance (ILR) ring of the nuclear stellar bar. Conclusions. In our favored scenario a wide-angle AGN wind launched from the accretion disk of NGC1068 is currently impacting a sizable fraction of the gas inside the torus. However, a large gas reservoir (≃1.2 − 1.8 × 105 M⊙), which lies close to the equatorial plane of the torus, remains unaffected by the feedback of the AGN wind and can therefore continue fueling the AGN for at least ≃1 − 4 Myr. Nevertheless, AGN fueling currently seems thwarted on intermediate scales (15 pc ≤r ≤ 50 pc).
Abstract
We present a publicly available, open source version of the time-dependent, gas-grain chemical code UCLCHEM. UCLCHEM propagates the abundances of chemical species through a large network of ...chemical reactions in a variety of physical conditions. The model is described in detail, along with its applications. As an example of possible uses, UCLCHEM is used to explore the effect of protostellar collapse on commonly observed molecules, and study the behavior of molecules in C-type shocks. We find the collapse of a simple Bonnor–Ebert sphere successfully reproduces most of the behavior of CO, CS, and NH
3
from cores observed by Tafalla et al. (2004), but cannot predict the behavior of N
2
H
+
. In the C-shock application, we find that molecules can be categorized such that they become useful observational tracers of shocks and their physical properties. Although many molecules are enhanced in shocked gas, we identify two groups of molecules in particular. A small number of molecules are enhanced by the sputtering of the ices as the shock propagates, and then remain high in abundance throughout the shock. A second, larger set is also enhanced by sputtering, but then destroyed as the gas temperature rises. Through these applications, the general applicability of UCLCHEM is demonstrated.
The Cii 158 ...m emission line can arise in all phases of the interstellar medium (ISM), therefore being able to disentangle the different contributions is an important yet unresolved problem when ...undertaking galaxy-wide, integrated Cii observations. We present a new multiphase 3D radiative transfer interface that couples starburst99, a stellar spectrophotometric code, with the photoionization and astrochemistry codes mocassin and 3d-pdr. We model entire star-forming regions, including the ionized, atomic, and molecular phases of the ISM, and apply a Bayesian inference methodology to parametrize how the fraction of the Cii emission originating from molecular regions, f sub( CII,mol), varies as a function of typical integrated properties of galaxies in the local Universe. The main parameters responsible for the variations of f sub( CII,mol) are specific star formation rate (SSFR), gas phase metallicity, H ii region electron number density (n sub( e)), and dust mass fraction. For example, f sub( CII,mol) can increase from 60 to 80 per cent when either n sub( e) increases from 10 super( 1.5) to 10 super( 2.5) cm super( -3), or SSFR decreases from 10 super( -9.6) to 10 super( -10.6) yr super( -1). Our model predicts for the Milky Way that f sub( CII,mol) = 75.8 plus or minus 5.9 per cent, in agreement with the measured value of 75 per cent. When applying the new prescription to a complete sample of galaxies from the Herschel Reference Survey, we find that anywhere from 60 to 80 per cent of the total integrated Cii emission arises from molecular regions. (ProQuest: ... denotes formulae/symbols omitted.)
We report ALMA observations of CO(3–2) emission in the Seyfert/nuclear starburst galaxy NGC 613, at a spatial resolution of 17 pc, as part of our NUclei of GAlaxies (NUGA) sample. Our aim is to ...investigate the morphology and dynamics of the gas inside the central kiloparsec, and to probe nuclear fueling and feedback phenomena. The morphology of CO(3–2) line emission reveals a two-arm trailing nuclear spiral at r ≲ 100 pc and a circumnuclear ring at a radius of ∼350 pc that is coincident with the star-forming ring seen in the optical images. Also, we find evidence for a filamentary structure connecting the ring and the nuclear spiral. The ring reveals two breaks into two winding spiral arms corresponding to the dust lanes in the optical images. The molecular gas in the galaxy disk is in a remarkably regular rotation, however the kinematics in the nuclear region are 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 ±300 km s−1, associated with a molecular outflow emanating from the nucleus (r ∼ 25 pc). We derive a molecular outflow mass Mout = 2 × 106 M⊙ and a mass outflow rate of Ṁout = 27 M⊙ yr−1. The molecular outflow energetics exceed the values predicted by AGN feedback models: the kinetic power of the outflow corresponds to PK, out = 20%LAGN and the momentum rate is Ṁoutv ∼ 400LAGN/c. The outflow is mainly boosted by the AGN through entrainment by the radio jet, but given the weak nuclear activity of NGC 613, we might be witnessing a fossil outflow resulting from a previously strong AGN that has now faded. Furthermore, the nuclear trailing spiral observed in CO emission is inside the inner Lindblad resonance 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 100 pc and the gas loses its angular momentum in a rotation period, providing evidence for a highly efficient inflow towards the center. This phenomenon shows that the massive central black hole has significant dynamical influence on the gas, triggering the inflowing of molecular gas to feed the black hole.
Context.
Chemical modelling serves two purposes in dynamical models: accounting for the effect of microphysics on the dynamics and providing observable signatures. Ideally, the former must be done as ...part of the hydrodynamic simulation but this comes with a prohibitive computational cost that leads to many simplifications being used in practice.
Aims.
We aim to produce a statistical emulator that replicates a full chemical model capable of solving the temperature and abundances of a gas through time. This emulator should suffer only a minor loss of accuracy when compared to a full chemical solver and would have a fraction of the computational cost allowing it to be included in a dynamical model.
Methods.
The gas-grain chemical code UCLCHEM was updated to include heating and cooling processes, and a large dataset of model outputs from possible starting conditions was produced. A neural network was then trained to map directly from inputs to outputs.
Results.
Chemulator replicates the outputs of UCLCHEM with an overall mean squared error (MSE) of 1.7 × 10
−4
for a single time step of 1000 yr, and it is shown to be stable over 1000 iterations with an MSE of 3 × 10
−3
on the log-scaled temperature after one timzze step and 6 × 10
−3
after 1000 time steps. Chemulator was found to be approximately 50 000 times faster than the time-dependent model it emulates but can introduce a significant error to some models.
Enhanced emission from the dense gas tracer HCN (relative to HCO+) has been proposed as a signature of active galactic nuclei (AGN). In a previous single-dish millimeter line survey we identified ...galaxies with HCN/HCO+ (1-0) intensity ratios consistent with those of many AGN but whose mid-infrared spectral diagnostics are consistent with little to no ( 15%) contribution of an AGN to the bolometric luminosity. To search for putative heavily obscured AGN, we present and analyze NuSTAR hard X-ray (3-79 keV) observations of four such galaxies from the Great Observatories All-sky LIRG Survey. We find no X-ray evidence for AGN in three of the systems and place strong upper limits on the energetic contribution of any heavily obscured ( ) AGN to their bolometric luminosity. The upper limits on the X-ray flux are presently an order of magnitude below what XDR-driven chemistry models predict are necessary to drive HCN enhancements. In a fourth system we find a hard X-ray excess consistent with the presence of an AGN, but contributing only ∼3% of the bolometric luminosity. It is also unclear if the AGN is spatially associated with the HCN enhancement. We further explore the relationship between HCN/HCO+ (for several Jupper levels) and / for a larger sample of systems in the literature. We find no evidence for correlations between the line ratios and the AGN fraction derived from X-rays, indicating that HCN/HCO+ intensity ratios are not driven by the energetic dominance of AGN, nor are they reliable indicators of ongoing supermassive black hole accretion.
We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO(3-2) emission in a sample of seven Seyfert/LINER galaxies at the unprecedented spatial resolution of 0.″1 = 4−8 0 . ″ ...1 = 4 − 9 $ 0 {{\overset{\prime\prime}{.}}}1=4{-}9 $ pc. Our aim is to explore the close environment of active galactic nuclei (AGN), and the dynamical structures leading to their fueling, through the morphology and kinematics of the gas inside the sphere of influence of the black hole. The selected galaxies host low-luminosity AGN and have a wide range of activity types (Seyferts 1 to 2, LINERs), and barred or ringed morphologies. The observed maps reveal the existence of circumnuclear disk structures, defined by their morphology and decoupled kinematics, in most of the sample. We call these structures molecular tori, even though they often appear as disks without holes in the center. They have varying orientations along the line of sight, unaligned with the host galaxy orientation. The radius of the tori ranges from 6 to 27 pc, and their mass from 0.7 × 107 to 3.9 × 107 M⊙. The most edge-on orientations of the torus correspond to obscured Seyferts. In only one case (NGC 1365), the AGN is centered on the central gas hole of the torus. On a larger scale, the gas is always piled up in a few resonant rings 100 pc in scale 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. More 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. In some cases, AGN feedback is revealed through a molecular outflow, which will be studied in detail in a subsequent article.
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