scholarly journals Morphological and Kinematical Analysis of the Double-barred Galaxy NGC 3504 Using ALMA CO (2–1) Data

2021 ◽  
Author(s):  
Yu-Ting Wu ◽  
Alfonso Trejo ◽  
Daniel Espada ◽  
Yusuke Miyamoto
Keyword(s):  
Total Mass ◽  
Angular Resolution ◽  
Molecular Gas ◽  
Rotating Frame ◽  
Inflow Rate ◽  
Barred Galaxies ◽  
Nuclear Ring ◽  
Pattern Speed ◽  
Co Emission ◽  
Spiral Arm

Abstract We present results obtained from ALMA CO (2–1) data of the double-barred galaxy NGC 3504. With three times higher angular resolution (∼ 0.″8) than previous studies, our observations reveal an inner molecular gas bar, a nuclear ring, and four inner spiral arm-like structures in the central 1 kpc region. Furthermore, the CO emission is clearly aligned with the two dust lanes in the outer bar region, with differences in shape and intensity between them. The total molecular gas mass in the observed region (50″ × 57″) is estimated to be ∼3.1 × 109 M⊙, which is 17 per cent of the stellar mass. We used the Kinemetry package to fit the velocity field and found that circular motion strongly dominates at R = 0.3 − 0.8 kpc, but radial motion becomes important at R < 0.3 kpc and R = 1.0 − 2.5 kpc, which is expected due to the presence of the inner and outer bars. Finally, assuming that the gas moves along the dust lanes in the bar rotating frame, we derived the pattern speed of the outer bar to be 18 ± 5 km s−1 kpc−1, the average streaming velocities on each of the two dust lanes to be 165 and 221 km s−1, and the total mass inflow rate along the dust lanes to be 12 M⊙ yr−1. Our results give a new example of an inner gas bar within a gas-rich double-barred galaxy and suggest that the formation of double-barred galaxies could be associated with the existence of such gas structures.

scholarly journals 12C18O in OMC-1: Kinematics, Molecular Column Density, and Kinetic Temperature Distribution

1987 ◽  
Vol 115 ◽  
pp. 145-146
Author(s):  
T. L. Wilson ◽  
E. Serabyn ◽  
C. Henkel ◽  
C. M. Walmsley
Keyword(s):  
Column Density ◽  
Angular Resolution ◽  
Dust Emission ◽  
Line Emission ◽  
Molecular Gas ◽  
Kinetic Temperature ◽  
Line Profiles ◽  
Co Emission ◽  
Continuous Strip ◽  
Made In

A fully sampled map of size ∼1′×3′ (R.A. Dec), centered on BN-KL has been made in the J = 1-0 line of 12C18O with 21″ angular resolution. The 12C18O emission is concentrated in a ← 40″ wide continuous strip running S to NE. Several maxima are superposed on the ridge, but none exceeds the average emission level by more than 40%. There is no intense peak of 12C18O J = 1-0 line emission centered on BN-KL, in contrast to maps of the dust emission. The dust and 12C18O results can be reconciled with a constant (CO/H2) ratio if there are variations in the kinetic temperature and column density of ∼50%. Peaks in both temperature and column density are then located near BN-KL, and 90″ to the south. From the estimated CO column density, about 10% of the carbon is in the form of CO. Near the BN-KL region, the 12C18O line profiles tend to become wider. These wider lines appear to be superposed on a weak, 18 km s−1 (FWHP) wide pedestal. In regions 40″ NE and 30″ S of BN-KL, the 12C18O lines have widths of less than 2 km s−1. Presumably, these are the locations of high density, quiescent molecular gas. The radial velocity of the CO emission increases from 6.5 km s−1 (at 90″ S) to 10.5 km s−1 (at 60″ NE) of BN-KL. Close to BN-KL, however, there is evidence that this trend is reversed.

scholarly journals 1.7” Resolution CO(1-0) Observations of ARP220: Nuclear Gas Ring of Merger Remnant

1994 ◽  
Vol 140 ◽  
pp. 376-378 ◽  
Author(s):  
S. K. Okumura ◽  
R. Kawabe ◽  
M. Ishiguro ◽  
S. Ishizuki
Keyword(s):  
Central Region ◽  
Emission Peak ◽  
Molecular Gas ◽  
Velocity Range ◽  
No Emission ◽  
Large Velocity ◽  
Nuclear Ring ◽  
Compact Sources ◽  
Large Velocity Gradient ◽  
Co Emission

AbstractWe made aperture synthesis CO(l-O) observations of the central region of Arp220 with the Nobeyama Millimeter Array. Central CO emission was resolved with a size of 975 kpc. It shows a ring-like structure (ɪ ~ 500 pc) with a large velocity gradient, 393 km · s−1 · kpc−1, from southwest to northeast direction. The ring-like emission is located around double radio compact sources. No emission peak was found in the center of the double sources within the velocity range 5100 km s−1to 5800 km s−1. These results suggest that an inclined massive gas ring has been or is being formed in the central 1 kpc of Arp220. Most of the molecular gas in Arp220 is concentrated on this nuclear ring. The radio compact sources are probably located at the inner egde of the ring.

scholarly journals Molecular gas in the Small Magellanic Cloud

1991 ◽  
Vol 148 ◽  
pp. 429-430
Author(s):  
Monica Rubio
Keyword(s):  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
Column Density ◽  
Angular Resolution ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Molecular Gas ◽  
Small Magellanic Cloud ◽  
Hydrogen Column Density ◽  
Co Emission

We summarize the results of observations of molecular gas from the Small Magellanic Cloud (SMC) made with low angular resolution (8'.8). These observations show that the CO emission is weak (TA˜ 0.04K) and that the CO luminosities of the Clouds are low compared to those of Galactic molecular clouds. The factor to convert the CO luminosity to molecular hydrogen column density for the SMC is ˜20 and three times larger than those derived for clouds in our Galaxy and in the Large Magellanic Cloud (LMC) respectively. In addition, we present preliminary results of high resolution (40″) observations of SMC molecular clouds made with the SEST telescope.

scholarly journals High-J CO emission spatial distribution and excitation in the Orion Bar

2018 ◽  
Vol 617 ◽  
pp. A77 ◽  
Author(s):  
A. Parikka ◽  
E. Habart ◽  
J. Bernard-Salas ◽  
M. Köhler ◽  
A. Abergel
Keyword(s):  
Angular Resolution ◽  
Volume Density ◽  
High Angular Resolution ◽  
Molecular Gas ◽  
Vibrationally Excited ◽  
Physical Conditions ◽  
Ionization Fronts ◽  
Polycyclic Aromatic ◽  
Imaging Receiver ◽  
Co Emission

Context. With Herschel, we can for the first time observe a wealth of high-J CO lines in the interstellar medium with a high angular resolution. These lines are specifically useful for tracing the warm and dense gas and are therefore very appropriate for a study of strongly irradiated dense photodissocation regions (PDRs). Aims. We characterize the morphology of CO J = 19–18 emission and study the high-J CO excitation in a highly UV-irradiated prototypical PDR, the Orion Bar. Methods. We used fully sampled maps of CO J = 19–18 emission with the Photoconductor Array Camera and Spectrometer (PACS) on board the Herschel Space Observatory over an area of ~110′′ × 110′′ with an angular resolution of 9′′. We studied the morphology of this high-J CO line in the Orion Bar and in the region in front and behind the Bar, and compared it with lower-J lines of CO from J = 5–4 to J = 13–12 and 13CO from J = 5–4 to J = 11–10 emission observed with the Herschel Spectral and Photometric Imaging Receiver (SPIRE). In addition, we compared the high-J CO to polycyclic aromatic hydrocarbon (PAH) emission and vibrationally excited H2. We used the CO and 13CO observations and the RADEX model to derive the physical conditions in the warm molecular gas layers. Results. The CO J = 19–18 line is detected unambiguously everywhere in the observed region, in the Bar, and in front and behind of it. In the Bar, the most striking features are several knots of enhanced emission that probably result from column and/or volume density enhancements. The corresponding structures are most likely even smaller than what PACS is able to resolve. The high-J CO line mostly arises from the warm edge of the Orion Bar PDR, while the lower-J lines arise from a colder region farther inside the molecular cloud. Even if it is slightly shifted farther into the PDR, the high-J CO emission peaks are very close to the H/H2 dissociation front, as traced by the peaks of H2 vibrational emission. Our results also suggest that the high-J CO emitting gas is mainly excited by photoelectric heating. The CO J = 19–18/J = 12–11 line intensity ratio peaks in front of the CO J = 19–18 emission between the dissociation and ionization fronts, where the PAH emission also peak. A warm or hot molecular gas could thus be present in the atomic region where the intense UV radiation is mostly unshielded. In agreement with recent ALMA detections, low column densities of hot molecular gas seem to exist between the ionization and dissociation fronts. As found in other studies, the best fit with RADEX modeling for beam-averaged physical conditions is for a density of 106 cm−3 and a high thermal pressure (P∕k = nH × T) of ~1–2 × 108 K cm−3. Conclusions. The high-J CO emission is concentrated close to the dissociation front in the Orion Bar. Hot CO may also lie in the atomic PDR between the ionization and dissociation fronts, which is consistent with the dynamical and photoevaporation effects.

Molecular Gas in the Centers of Barred and Starburst Galaxies

1994 ◽  
Vol 140 ◽  
pp. 282-292
Author(s):  
Jeffrey D. P. Kenney
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Starburst Galaxy ◽  
Molecular Gas ◽  
Barred Galaxies ◽  
Twin Peaks ◽  
Ngc 1068 ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance ◽  
Co Emission

AbstractHigh resolution interferometric CO maps of the circumnuclear regions of several barred galaxies show intense CO emission arising from twin peaks, which are oriented perpendicular to the large-scale stellar bars and located where dust lanes intersect nuclear rings of HII regions. These twin gas concentrations can be explained by the crowding of gas streamlines near stellar inner Lindblad resonances. In the barred nuclear starburst galaxy NGC 3504, a large concentration of molecular gas is centered on the nucleus, apparently inside an inner Lindblad resonance. Star formation is consuming the gas most rapidly where the rotation curve is nearly solid body, suggesting that tidal shear helps control the rate of star formation. A comparison with M82 and NGC 1068 suggests that the starburst in NGC 3504 is in an early phase of its evolution, and that starburst evolution is strongly influenced by shear.

scholarly journals Large Scale Dissociation of Molecular Gas and Star Formation in M83

1987 ◽  
Vol 115 ◽  
pp. 628-628
Author(s):  
R. J. Allen ◽  
P. D. Atherton ◽  
R.P.J. Tilanus
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Angular Resolution ◽  
Molecular Gas ◽  
Late Type ◽  
Ngc 6946 ◽  
Central Regions ◽  
Spiral Arm ◽  
Co Observations

Observations of the distribution of the CO-molecule in several prominent late-type galaxies indicate that the central HI depressions may very well be filled in with molecular gas. One such galaxy is M83 (NGC 5236) and, although the angular resolution of the CO-observations is insufficient to discern details on the scale of a spiral arm, it is known that CO is concentrated in the central regions within a radius of 1′. Furthermore, at a resolution of 50″, the CO profile at the position of the nucleus is as bright in M83 as it is for example in NGC 6946, IC 346 and M51.

scholarly journals Small Scale Structure in Nearby Molecular Gas

1997 ◽  
Vol 166 ◽  
pp. 251-260 ◽  
Author(s):  
Edith Falgarone
Keyword(s):  
Molecular Clouds ◽  
Column Density ◽  
Angular Resolution ◽  
Ambient Pressure ◽  
Solar Neighborhood ◽  
Small Scale ◽  
High Angular Resolution ◽  
Molecular Gas ◽  
Hierarchy Of Structures ◽  
Co Emission

AbstractRecent observations at high angular resolution of molecular clouds of low column density have revealed the presence of a conspicuous net of small scale filamentary structures, visible in the 12CO rotational lines only. In addition, the existence of unresolved structure at scales as small as ~ 200 AU in space and/or velocity space is inferred from the spectral properties of the 12CO and 13CO emission. The resolved structures are part of the hierarchy of structures observed in molecular gas in the Solar Neighborhood and appear as non self-gravitating elements confined by an ambient pressure P0/kB ~ 3 × 104cm−3 K. We show why these structures might have their origin in the intermittent structures of turbulence in which viscous dissipation is concentrated in space and time.

scholarly journals MOLECULAR GAS EVOLUTION ACROSS A SPIRAL ARM IN M51

2010 ◽  
Vol 726 (2) ◽  
pp. 85 ◽  
Author(s):  
Fumi Egusa ◽  
Jin Koda ◽  
Nick Scoville
Keyword(s):  
Molecular Gas ◽  
Gas Evolution ◽  
Spiral Arm

scholarly journals Double X/Peanut Structures in Barred Galaxies – Insights from an N–body Simulation

2020 ◽  
Author(s):  
Bogdan C Ciambur ◽  
Francesca Fragkoudi ◽  
Sergey Khoperskov ◽  
Paola Di Matteo ◽  
Françoise Combes
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Large Fraction ◽  
Formation Time ◽  
Dark Matter Halo ◽  
Barred Galaxies ◽  
Pattern Speed ◽  
Nearby Galaxies ◽  
Dynamical Instabilities ◽  
Bow Tie

Abstract Boxy, peanut– or X–shaped “bulges” are observed in a large fraction of barred galaxies viewed in, or close to, edge-on projection, as well as in the Milky Way. They are the product of dynamical instabilities occurring in stellar bars, which cause the latter to buckle and thicken vertically. Recent studies have found nearby galaxies that harbour two such features arising at different radial scales, in a nested configuration. In this paper we explore the formation of such double peanuts, using a collisionless N–body simulation of a pure disc evolving in isolation within a live dark matter halo, which we analyse in a completely analogous way to observations of real galaxies. In the simulation we find a stable double configuration consisting of two X/peanut structures associated to the same galactic bar – rotating with the same pattern speed – but with different morphology, formation time, and evolution. The inner, conventional peanut-shaped structure forms early via the buckling of the bar, and experiences little evolution once it stabilises. This feature is consistent in terms of size, strength and morphology, with peanut structures observed in nearby galaxies. The outer structure, however, displays a strong X, or “bow-tie”, morphology. It forms just after the inner peanut, and gradually extends in time (within 1 to 1.5 Gyr) to almost the end of the bar, a radial scale where ansae occur. We conclude that, although both structures form, and are dynamically coupled to, the same bar, they are supported by inherently different mechanisms.

scholarly journals Major impact from a minor merger

2018 ◽  
Vol 615 ◽  
pp. A122 ◽  
Author(s):  
S. König ◽  
S. Aalto ◽  
S. Muller ◽  
J. S. Gallagher III ◽  
R. J. Beswick ◽  
...  
Keyword(s):  
Star Formation ◽  
Brightness Temperature ◽  
Central Region ◽  
Molecular Clouds ◽  
Molecular Gas ◽  
Transfer Model ◽  
Dense Gas ◽  
Giant Molecular Clouds ◽  
Minor Mergers ◽  
Co Emission

Context. Minor mergers are important processes contributing significantly to how galaxies evolve across the age of the Universe. Their impact on the growth of supermassive black holes and star formation is profound – about half of the star formation activity in the local Universe is the result of minor mergers. Aims. The detailed study of dense molecular gas in galaxies provides an important test of the validity of the relation between star formation rate and HCN luminosity on different galactic scales – from whole galaxies to giant molecular clouds in their molecular gas-rich centers. Methods. We use observations of HCN and HCO+ 1−0 with NOEMA and of CO3−2 with the SMA to study the properties of the dense molecular gas in the Medusa merger (NGC 4194) at 1′′ resolution. In particular, we compare the distribution of these dense gas tracers with CO2−1 high-resolution maps in the Medusa merger. To characterize gas properties, we calculate the brightness temperature ratios between the three tracers and use them in conjunction with a non-local thermodynamic equilibrium (non-LTE) radiative line transfer model. Results. The gas represented by HCN and HCO+ 1−0, and CO3−2 does not occupy the same structures as the less dense gas associated with the lower-J CO emission. Interestingly, the only emission from dense gas is detected in a 200 pc region within the “Eye of the Medusa”, an asymmetric 500 pc off-nuclear concentration of molecular gas. Surprisingly, no HCN or HCO+ is detected for the extended starburst of the Medusa merger. Additionally, there are only small amounts of HCN or HCO+ associated with the active galactic nucleus. The CO3−2/2−1 brightness temperature ratio inside “the Eye” is ~2.5 – the highest ratio found so far – implying optically thin CO emission. The CO2−1/HCN 1−0 (~9.8) and CO2−1/HCO+ 1−0 (~7.9) ratios show that the dense gas filling factor must be relatively high in the central region, consistent with the elevated CO3−1/2−1 ratio. Conclusions. The line ratios reveal an extreme, fragmented molecular cloud population inside the Eye with large bulk temperatures (T > 300 K) and high gas densities (n(H2) > 104 cm-3). This is very different from the cool, self-gravitating structures of giant molecular clouds normally found in the disks of galaxies. The Eye of the Medusa is found at an interface between a large-scale minor axis inflow and the central region of the Medusa. Hence, the extreme conditions inside the Eye may be the result of the radiative and mechanical feedback from a deeply embedded, young and massive super star cluster formed due to the gas pile-up at the intersection. Alternatively, shocks from the inflowing gas entering the central region of the Medusa may be strong enough to shock and fragment the gas. For both scenarios, however, it appears that the HCN and HCO+ dense gas tracers are not probing star formation, but instead a post-starburst and/or shocked ISM that is too hot and fragmented to form newstars. Thus, caution is advised in taking the detection of emission from dense gas tracers as evidence of ongoing or imminent star formation.

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