Molecular gas conditions in NGC 4945 and the Circinus galaxy

Curran, Stephen J.; Johansson, Lars; Bergman, P.; Heikkilä, Arto; Aalto, S.

doi:10.1051/0004-6361:20000462

Cited by 56 publications

(108 citation statements)

References 65 publications

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“…This value of 12 C/ 13 C is less than half the ratio measured in the Solar System (89, Lodders 2003), but closer to that derived in the local interstellar medium (59 ± 2, Lucas & Liszt 1998) and especially close to that in the starburst galaxies NGC 253 and NGC 4945 (40-50, Henkel et al 1993;Curran et al 2001;Wang et al 2004). It is, however, much lower than the value that would be expected in a poorly processed environment (e.g.…”

Section: Carbonsupporting

confidence: 78%

Molecules atz= 0.89

Müller

Beelen

Guèlin

et al. 2011

A&A

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We present the results of a 7 mm spectral survey of molecular absorption lines originating in the disk of a z = 0.89 spiral galaxy located in front of the quasar PKS 1830−211. Our survey was performed with the Australia Telescope Compact Array and covers the frequency interval 30-50 GHz, corresponding to the rest-frame frequency interval 57-94 GHz. A total of 28 different species, plus 8 isotopic variants, were detected toward the south-west absorption region, located about 2 kpc from the center of the z = 0.89 galaxy, which therefore has the largest number of detected molecular species of any extragalactic object so far. The results of our rotation diagram analysis show that the rotation temperatures are close to the cosmic microwave background temperature of 5.14 K that we expect to measure at z = 0.89, whereas the kinetic temperature is one order of magnitude higher, indicating that the gas is subthermally excited. The molecular fractional abundances are found to be in-between those in typical Galactic diffuse and translucent clouds, and clearly deviate from those observed in the dark cloud TMC 1 or in the Galactic center giant molecular cloud Sgr B2. The isotopic ratios of carbon, nitrogen, oxygen, and silicon deviate significantly from the solar values, which can be linked to the young age of the z = 0.89 galaxy and a release of nucleosynthesis products dominated by massive stars. Toward the north-east absorption region, where the extinction and column density of gas is roughly one order of magnitude lower than toward the SW absorption region, only a handful of molecules are detected. Their relative abundances are comparable to those in Galactic diffuse clouds. We also report the discovery of several new absorption components, with velocities spanning between −300 and +170 km s −1 . Finally, the line centroids of several species (e.g., CH 3 OH, NH 3 ) are found to be significantly offset from the average velocity. If caused by a variation in the proton-to-electron mass ratio μ with redshift, these offsets yield an upper limit | Δμ μ | < 4×10 −6 , which takes into account the kinematical noise produced by the velocity dispersion measured from a large number of molecular species.

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Section: Carbonsupporting

confidence: 78%

Molecules atz= 0.89

Müller

Beelen

Guèlin

et al. 2011

A&A

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“…6 Again this may affect the CO 1→0 HCN 1→0 intensity ratio (Curran et al 2001a), raising it from ≈17 to ≈23, and, for the same reason as before (Sect. 2.1.4), this does not alter the kinetic temperature and molecular hydrogen density constrained from the CO isotopomer intensity ratios.…”

Section: Ngc 6814mentioning

confidence: 64%

“…30 cf. 20 .This would have the effect of increasing the central CO 1→0 HCN 1→0 intensity ratio from ≈8 to ≈16 in Curran et al (2001a), although it does not significantly change their results as the kinetic temperature and molecular hydrogen density are constrained from the CO isotopomer intensity ratios. If true, it would, however, lower the density of the dense gas component slightly, which supports the authors' hypothesis that Circinus possesses denser cloud cores in comparison to NGC 4945.…”

Section: Ngc 4945mentioning

confidence: 98%

“…4 Usually, in the absence of maps, the HCN 1 → 0 line is assumed to have the same source size as the CO 2 → 1 line, i.e. as Curran et al (2001a). But here we may find the former to be considerably larger, i.e.…”

Section: Ngc 4945mentioning

confidence: 99%

“…However, in the case of Seyferts this excess of (denser) gas traced by the HCN (as well as the excess FIR) may also be due to the accumulation of gas around the active nucleus, terminating in the obscuration (Kohno et al 1999;Curran et al 2000), and a large fraction of the gas traced by the CO may act as a resevoir for star formation in Seyferts (Curran 2000a;Curran et al 2001a). In this paper we shall also discuss the CO 2 → 1/CO 1 → 0 ratios for the Southern sources in which we could observe this higher CO transition with SEST.…”

Section: Introductionmentioning

confidence: 99%

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Global molecular gas properties of Seyfert galaxies

Curran

Polatidis

Aalto

et al. 2001

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Abstract.We use the data published in Paper I and Curran et al. (2000) to determine the global molecular gas luminosities and distributions in a sample of 22 Seyfert galaxies. From this we find definite differences in the CO to HCN luminosity ratios between the near-by and distant galaxies of the sample. This is perhaps due to a selection effect where we only observe the brightest of the distant sources. With regard to distributions, we find in the near-by (mapped) sample that the CO is usually much wider distributed than the central telescope beam and that the HCN is considerably more extended beyond the ∼1 kpc often cited in the literature. In fact this molecule has been detected as far as ≈5 kpc from the centre of NGC 1365. We may also have detected a bar in HCN in NGC 5033. Also, using the data to complement the results of.e. no difference in the molecular gas luminosities between the two main Seyfert classes. In fact we consider it more meaningful to discuss the differences between the near-by and distant sample (irrespective of Seyfert type), although both of these samples may show evidence that much of the far infrared luminosity could arise from an active galactic nucleus as opposed to being predominantly due to vigorous star formation. We do believe, however, that improved statistics would be of little value in distinguishing between these two scenarios and that future high resolution observations are the key to resolving this issue.

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