Abstract Double bars are thought to be important features for secular evolution in the central regions of galaxies. However, observational evidence about their origin and evolution is still scarce. ...We report on the discovery of the first Box/Peanut (B/P) structure in an inner bar detected in the face-on galaxy NGC 1291. We use the integral field data obtained from the MUSE spectrograph within the TIMER project. The B/P structure is detected as bi-symmetric minima of the h4 moment of the line-of-sight velocity distribution along the major axis of the inner bar, as expected from numerical simulations. Our observations demonstrate that inner bars can follow a similar evolutionary path as outer bars, undergoing buckling instabilities. They also suggest that inner bars are long-lived structures, thus imposing tight constraints to their possible formation mechanisms.
Aims. We study the feedback of star formation and nuclear activity on the chemistry of molecular gas in NGC 1068, a nearby (D = 14 Mpc) Seyfert 2 barred galaxy, by analyzing whether the abundances of ...key molecular species such as ethynyl (C2H), which is a classical tracer of photon dominated regions (PDR), change in the different environments of the disk of the galaxy. Methods. We used the Atacama Large Millimeter Array (ALMA) to map the emission of the hyperfine multiplet of C2H(N = 1−0) and its underlying continuum emission in the central r ≃ 35″ (2.5 kpc) region of the disk of NGC 1068 with a spatial resolution 1.̋0 × 0.̋7 (≃ 50−70 pc). We used maps of the dust continuum emission obtained at 349 GHz by ALMA to derive the H2 gas column densities and combined these with the C2H map at matched spatial resolution to estimate the fractional abundance of this species. We developed a set of time-dependent chemical models, which include shocks, gas-phase PDRs, and gas-grain chemical models to determine the origin of the C2H gas. Results. A sizeable fraction of the total C2H line emission is detected from the r ≃ 1.3 kpc starburst (SB) ring, which is a region that concentrates the bulk of the recent massive star formation in the disk traced by the Paα emission complexes imaged by the Hubble Space Telescope (HST). However, the brightest C2H emission originates from a r ≃ 200 pc off-centered circumnuclear disk (CND), where evidence of a molecular outflow has been previously found in other molecular tracers imaged by ALMA. We also detect significant emission that connects the CND with the outer disk in a region that probes the interface between the molecular disk and ionized gas outflow out to r ≃ 400 pc. We derived the fractional abundances of C2H (X(C2H)) assuming local thermodynamic equilibrium (LTE) conditions and a set of excitation temperatures (Tex) constrained by the previous multiline CO studies of the galaxy. Our estimates range from X(C2H) ≃ a few 10-8 in the SB ring up to X(C2H) ≃ a few 10-7 in the outflow region. The PDR models that incorporate gas-grain chemistry are able to account for X(C2H) in the SB ring for moderately dense (n(H2) ≥ 104 cm-3) and moderately UV-irradiated gas (UV-field ≤ 10 × Draine field, where 1 Draine field ≡ 2.74 × 10-3 erg s-1 cm-2) in a steady-state regime, which depending on the initial and physical conditions of the gas may be achieved by 105 yr or as late as 107 yr. However, the high fractional abundances estimated for C2H in the outflow region can only be reached at very early times (T ≤ 102−3 yr) in models of UV or X-ray irradiated dense gas (n(H2) ≥ 104−5 cm-3). Conclusions. We find that the transient conditions required to fit the high values of X(C2H) in the outflow are likely due to UV or X-ray irradiated non-dissociative shocks associated with the highly turbulent interface between the outflow and molecular gas in NGC 1068. Although the inferred local timescales are short, the erosion of molecular clouds by the active galactic nucleus (AGN) wind and/or the jet likely resupplies the interface working surface continuously, making a nearly steady state persist in the disk of the galaxy.
The complex physical, kinematic, and chemical properties of galaxy centres make them interesting environments to examine with molecular line emission. We present new 2 − 4″ (∼75 − 150 pc at 7.7 Mpc) ...observations at 2 and 3 mm covering the central 50″ (∼1.9 kpc) of the nearby double-barred spiral galaxy NGC 6946 obtained with the IRAM Plateau de Bure Interferometer. We detect spectral lines from ten molecules: CO, HCN, HCO
+
, HNC, CS, HC
3
N, N
2
H
+
, C
2
H, CH
3
OH, and H
2
CO. We complemented these with published 1 mm CO observations and 33 GHz continuum observations to explore the star formation rate surface density Σ
SFR
on 150 pc scales. In this paper, we analyse regions associated with the inner bar of NGC 6946 – the nuclear region (NUC), the northern (NBE), and southern inner bar end (SBE) and we focus on short-spacing corrected bulk (CO) and dense gas tracers (HCN, HCO
+
, and HNC). We find that HCO
+
correlates best with Σ
SFR
, but the dense gas fraction (
f
dense
) and star formation efficiency of the dense gas (SFE
dense
) fits show different behaviours than expected from large-scale disc observations. The SBE has a higher Σ
SFR
,
f
dense
, and shocked gas fraction than the NBE. We examine line ratio diagnostics and find a higher CO(2−1)/CO(1−0) ratio towards NBE than for the NUC. Moreover, comparison with existing extragalactic datasets suggests that using the HCN/HNC ratio to probe kinetic temperatures is not suitable on kiloparsec and sub-kiloparsec scales in extragalactic regions. Lastly, our study shows that the HCO
+
/HCN ratio might not be a unique indicator to diagnose AGN activity in galaxies.
ABSTRACT
The low-J rotational transitions of 12CO are commonly used to trace the distribution of molecular gas in galaxies. Their ratios are sensitive to excitation and physical conditions in the ...molecular gas. Spatially resolved studies of CO ratios are still sparse and affected by flux calibration uncertainties, especially since most do not have high angular resolution or do not have short-spacing information and hence miss any diffuse emission. We compare the low-J CO ratios across the disc of two massive, star-forming spiral galaxies NGC 2903 and NGC 3627 to investigate whether and how local environments drive excitation variations at GMC scales. We use Atacama Large Millimeter Array (ALMA) observations of the three lowest-J CO transitions at a common angular resolution of 4 arcsec (190 pc). We measure median line ratios of $R_{21}=0.67^{+0.13}_{-0.11}$, $R_{32}=0.33^{+0.09}_{-0.08}$, and $R_{31}=0.24^{+0.10}_{-0.09}$ across the full disc of NGC 3627. We see clear CO line ratio variation across the galaxy consistent with changes in temperature and density of the molecular gas. In particular, towards the centre, R21, R32, and R31 increase by 35 per cent, 50 per cent, and 66 per cent, respectively, compared to their average disc values. The overall line ratio trends suggest that CO(3–2) is more sensitive to changes in the excitation conditions than the two lower J transitions. Furthermore, we find a similar radial R32 trend in NGC 2903, albeit a larger disc-wide average of $\langle R_{32}\rangle =0.47^{+0.14}_{-0.08}$. We conclude that the CO low-J line ratios vary across environments in such a way that they can trace changes in the molecular gas conditions, with the main driver being changes in temperature.
AGN feedback in the nucleus of M51 Querejeta, M; Schinnerer, E; Garcia-Burillo, S ...
Astronomy and astrophysics (Berlin),
09/2016, Letnik:
593
Journal Article
Recenzirano
Odprti dostop
AGN feedback is invoked as one of the most relevant mechanisms that shape the evolution of galaxies. Our goal is to understand the interplay between AGN feedback and the interstellar medium in M51, a ...nearby spiral galaxy with a modest AGN and a kpc-scale radio jet expanding through the disc of the galaxy. For this purpose, we combine molecular gas observations in the CO(1-0) and HCN(1-0) lines from the Plateau de Bure interferometer with archival radio, X-ray, and optical data. We show that there is a significant scarcity of CO emission in the ionisation cone, while molecular gas emission tends to accumulate towards the edges of the cone. The distribution and kinematics of CO and HCN line emission reveal AGN feedback effects out to r~ 500 pc, covering the whole extent of the radio jet, with complex kinematics in the molecular gas which displays strong local variations. We propose that this is the result of the almost coplanar jet pushing on molecular gas in different directions as it expands; the effects are more pronounced in HCN than in CO emission, probably as the result of radiative shocks. Following previous interpretation of the redshifted molecular line in the central 5" as caused by a molecular outflow, we estimate the outflow rates to be M sub(H2)~ 0.9 M sub(middot in circle)/ yr and M sub(dense)~ 0.6 M sub(middot in circle)/ yr, which are comparable to the molecular inflow rates (~1 M sub(middot in circle)/ yr); gas inflow and AGN feedback could be mutually regulated processes. The agreement with findings in other nearby radio galaxies suggests that this is not an isolated case, and is probably the paradigm of AGN feedback through radio jets, at least for galaxies hosting low-luminosity active nuclei.
Formation of S0 galaxies through mergers Eliche-Moral, M. C.; Rodríguez-Pérez, C.; Borlaff, A. ...
Astronomy and astrophysics (Berlin),
09/2018, Letnik:
617
Journal Article
Recenzirano
Odprti dostop
Context. Major mergers are popularly considered too destructive to produce the relaxed regular structures and the morphological inner components (ICs) usually observed in lenticular (S0) galaxies. ...Aims. We aim to test if major mergers can produce remnants with realistic S0 morphologies. Methods. We have selected a sample of relaxed discy remnants resulting from the dissipative merger simulations of the GalMer database and derived their properties mimicking the typical conditions of current observational data. We have compared their global morphologies, visual components, and merger relics in mock photometric images with their real counterparts. Results. Only Ȉ1–2 Gyr after the full merger, we find that: 1) many remnants (67 major and 29 minor events) present relaxed structures and typical S0 or E/S0 morphologies, for a wide variety of orbits and even in gas-poor cases. 2) Contrary to popular expectations, most of them do not exhibit any morphological traces of their past merger origin under typical observing conditions and at distances as nearby as 30 Mpc. 3) The merger relics are more persistent in minor mergers than in major ones for similar relaxing time periods. 4) No major-merger S0-like remnant develops a significant bar. 5) Nearly 58% of the major-merger S0 remnants host visually detectable ICs, such as embedded inner discs, rings, pseudo-rings, inner spirals, nuclear bars, and compact sources, very frequent in real S0s too. 6) All remnants contain a lens or oval, identically ubiquitous in local S0s. 7) These lenses and ovals do not come from bar dilution in major-merger cases, but are associated with stellar halos or embedded inner discs instead (thick or thin). Conclusions. The relaxed morphologies, lenses, ovals, and other ICs of real S0s do not necessarily come from internal secular evolution, gas infall, or environmental mechanisms, as traditionally assumed, but they can result from major mergers as well.
We present new H
I
observations of the nearby massive spiral galaxy M 83 taken with the JVLA at 21″ angular resolution (≈500 pc) of an extended (∼1.5 deg
2
) ten-point mosaic combined with GBT ...single-dish data. We study the super-extended H
I
disk of M 83 (∼50 kpc in radius), in particular disk kinematics, rotation, and the turbulent nature of the atomic interstellar medium. We define distinct regions in the outer disk (
r
gal
> central optical disk), including a ring, a southern area, a southern arm and a northern arm. We examine H
I
gas surface density, velocity dispersion, and noncircular motions in the outskirts, which we compare to the inner optical disk. We find an increase of velocity dispersion (
σ
v
) toward the pronounced H
I
ring, indicative of more turbulent H
I
gas. Additionally, we report over a large galactocentric radius range (until
r
gal
∼ 50 kpc) where
σ
v
is slightly larger than thermal component (i.e., > 8 km s
−1
). We find that a higher star-formation rate (as traced by far UV emission) is not necessarily always associated with a higher H
I
velocity dispersion, suggesting that radial transport could be a dominant driver for the enhanced velocity dispersion. Furthermore, we find a possible branch that connects the extended H
I
disk to the dwarf irregular galaxy UGCA 365 and that deviates from the general direction of the northern arm. Lastly, we compare mass flow rate profiles (based on 2D and 3D tilted ring models) and find evidence for outflowing gas at
r
gal
∼ 2 kpc, inflowing gas at
r
gal
∼ 5.5 kpc, and outflowing gas at
r
gal
∼ 14 kpc. We caution that mass flow rates are highly sensitive to the assumed kinematic disk parameters, in particular to inclination.
Context.
Studying the stellar kinematics of galaxies is a key tool in the reconstruction of their evolution. However, the current measurements of the stellar kinematics are complicated by several ...factors, including dust extinction and the presence of multiple stellar populations.
Aims.
We use integral field spectroscopic data of four galaxies from the Time Inference with MUSE in Extragalactic Rings (TIMER) survey to explore and compare the kinematics measured in different spectral regions that are sensitive to distinct stellar populations.
Methods.
We derive the line-of-sight velocity and velocity dispersion of both a young (≲2 Gyr) and an old stellar population from the spectral regions around the H
β
line and the Ca II Triplet. In addition, we determine colour excess, mean age, and metallicity.
Results.
We report a correlation of the colour excess with the difference in the kinematic parameters of the H
β
line and the Ca II Triplet range, which are dominated by young and old stellar populations, respectively. Young stellar populations, located primarily in nuclear rings, have higher velocity dispersions than old ones. These differences in the rings are typically ∼10 km s
−1
in velocity dispersion but can have a mean value as high as ∼24 km s
−1
in the most extreme case. Trends with age exist in the nuclear rings but are less significant than those with dust extinction. We report different degrees of correlation for these trends among the galaxies in the sample, which are related to the size of the Voronoi bins in their rings. No clear trends for the line-of-sight velocity differences are observed. The absence of these trends can be explained as a consequence of the H
β
line masking process during the kinematic extraction, as confirmed by dedicated simulations.
Conclusions.
Our study demonstrates that kinematic differences caused by different stellar populations can be identified in the central regions of nearby galaxies, even from intermediate resolution spectroscopy. This opens the door to future detailed chemo-kinematic studies of galaxies, but also serves as a warning against deriving kinematics from full-spectrum fitting across very wide wavelength ranges when intense star formation is taking place.
The transport of gas towards the centre of galaxies is critical for black hole feeding and, indirectly, it can control active galactic nucleus (AGN) feedback. We have quantified the molecular gas ...inflow in the central R< 1kpc of M51 to be 1 M sub(middot in circle)/yr, using a new gravitational torque map and the molecular gas traced by the Plateau de Bure Interferometer Arcsecond Whirlpool Survey (PAWS). The nuclear stellar bar is responsible for this gas inflow. We also used torque profiles to estimate the location of dynamical resonances, and the results suggest a corotation for the bar CR sub(bar)~ 20'', and a corotation for the spiral CR sub(sp)~ 100''. We demonstrate how important it is to correct 3.6 mu m images for dust emission when gravitational torques are to be computed, and we examine further sources of uncertainty. Our observational measurement of gas inflow can be compared with nuclear molecular outflow rates and provide useful constraints for numerical simulations.
We have developed a method for finding dynamical resonances in disk galaxies using the change in sense of the radial component of the in-plane velocity at a resonance radius. Using simulations we ...show that we would expect to find these changes at corotation radii with a weaker effect at the Lindblad resonances. The method works well with observations at high spectral and angular resolutions, and is suited to the analysis of two-dimensional velocity fields in He alpha from Fabry-Perot spectroscopy. We find clear indications of resonance effects in the disk velocity fields of virtually all of the 104 galaxies. The number of resonance radii detected ranges from one to seven, with a median of four. The frequency curves Omega, Omega + or - Kappa /2, Omega + or - Kappa /4 against radius for all the galaxies led us to discover a pattern in over 70% of the sample: given two pattern speeds, say Omega sub(1) and Omega sub(2), the OLR of Omega sub(1) coincides with the corotation of Omega sub(2), and the inner 4:1 resonance of Omega sub(2) coincides with the corotation of Omega sub(1). Although the second coincidence has been predicted, a prediction of this double coincidence is not found in the literature. This pattern is found once in 42 of the galaxies, twice in a further 26, three times in 5, and even four times in 1 galaxy. We also compute the ratio of corotation radius to bar length where we have sufficient image quality, finding a mean value of 1.3, and a shallow increase toward later type galaxies.
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