The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey – IX. 12CO J = 3→2 observations of NGC 2976 and NGC 3351

Tan, Boon-Kok; Leech, J.; Rigopoulou, D.; Warren, B. E.; Wilson, C. D.; Attewell, D.; Azimlu, Mohaddesseh; Bendo, G. J.; Butner, H. M.; Brinks, E.; Chanial, P.; Clements, D. L.; Heesen, V.; Israel, F. P.; Knapen, Johan H.; Matthews, H. E.; Mortier, A. M. J.; Mühle, S.; Sánchez-Gallego, José R.; Tilanus, R. P. J.; Usero, A.; Werf, P. van der; Zhu, Meiping

doi:10.1093/mnras/stt1625

Cited by 10 publications

(3 citation statements)

References 66 publications

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“…In our previous simulations of synthetic spectra the velocity resolution equals δv = 0.5 km s −1 , which is quite high for extragalactic observations. Although this value is comparable to that used in several studies (e.g., Tan et al 2013), most of the recent extragalactic surveys in molecular lines have been done with much lower spectral resolution (Engargiola et al 2003;Donovan Meyer et al 2013;Schinnerer et al 2013;Combes et al 2014).…”

Section: Variation Of the Spectra Resolutionsupporting

confidence: 71%

Giant molecular cloud scaling relations: the role of the cloud definition

Khoperskov

Vasiliev

Ladeyschikov

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We investigate physical properties of molecular clouds in disc galaxies with different morphology: a galaxy without prominent structure, a spiral barred galaxy and a galaxy with flocculent structure. Our N -body/hydrodynamical simulations take into account non-equilibrium H 2 and CO chemical kinetics, self-gravity, star formation and feedback processes. For the simulated galaxies the scaling relations of giant molecular clouds or so called Larson's relations are studied for two types of a cloud definition (or extraction methods): the first one is based on total column density position-position (PP) datasets and the second one is indicated by the CO (1-0) line emission used position-position-velocity (PPV) data. We find that the cloud populations obtained by using both cloud extraction methods generally have similar physical parameters. Except that for the CO data the mass spectrum of clouds has a tail with low-massive objects M ∼ 10 3 − 10 4 M . Varying column density threshold the power-law indices in the scaling relations are significantly changed. In contrast, the relations are invariant to CO brightness temperature threshold. Finally, we find that the mass spectra of clouds for the PPV data are almost insensitive to the galactic morphology, whereas the spectra for the PP data demonstrate significant variations.

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Section: Variation Of the Spectra Resolutionsupporting

confidence: 71%

Giant molecular cloud scaling relations: the role of the cloud definition

Khoperskov

Vasiliev

Ladeyschikov

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…We detect but do not resolve the circumnuclear ring in our observations, but do not recover the extended structure of the galaxy. HARP 12 CO 𝐽 = 3 → 2 observations of NGC 3351 were presented by (Wilson et al 2012) and Tan et al (2013).…”

Section: Ngc 3351mentioning

confidence: 98%

The JCMT Nearby Galaxies Legacy Survey: SCUBA-2 observations of nearby galaxies

Pattle¹,

Gear²,

Wilson³

2023

Preprint

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We present 850𝜇m observations of a sample of 8 nearby spiral galaxies, made using the SCUBA-2 camera on the James Clerk Maxwell Telescope (JCMT) as part of the JCMT Nearby Galaxies Legacy Survey (NGLS). We corrected our data for the presence of the 12 CO 𝐽 = 3 → 2 line in the SCUBA-2 850𝜇m bandwidth using NGLS HARP data, finding a typical 12 CO contribution of ∼ 20%. We measured dust column densities, temperatures and opacity indices by fitting spectral energy distributions constructed from SCUBA-2 and archival Herschel observations, and used archival GALEX and Spitzer data to make maps of surface density of star formation (Σ ). Typically, comparing SCUBA-2-derived H 2 surface densities (Σ H 2 ) to Σ gives shallow star formation law indices within galaxies, with SCUBA-2-derived values typically being sublinear and Herschel-derived values typically being broadly linear. This difference is likely due to the effects of atmospheric filtering on the SCUBA-2 data. Comparing the mean values of Σ H 2 and Σ of the galaxies in our sample returns a steeper star formation law index, broadly consistent with both the Kennicutt-Schmidt value of 1.4 and linearity. Our results show that a SCUBA-2 detection is a good predictor of star formation. We suggest that Herschel emission traces gas in regions which will form stars on timescales ∼ 5 − 100 Myr, comparable to the star formation timescale traced by GALEX and Spitzer data, while SCUBA-2 preferentially traces the densest gas within these regions, which likely forms stars on shorter timescales.

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“…While the focus of this paper is purely on the characterization of the dense gas, CO (whose critical density is low and hence ubiquitously traces all gas above ∼ 100 cm −3 ) is included because it is still routinely used to interpret molecular ratios or determine the star formation rate density (e.g. Kohno et al 2001Kohno et al , 2005Tan et al 2013), especially if high-J CO observations are available (Zhao et al 2016). Secondly, for completeness, we also extend our abundance and line intensities analyses to further species, not as commonly observed in external galaxies as those above, but often used as tracers of particular energetic events (e.g.…”

Section: Introductionmentioning

confidence: 99%

Molecular transitions as probes of the physical conditions of extragalactic environments

Viti

2017

A&A

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Aims. We present a method to interpret molecular observations and molecular line ratios in nearby extragalactic regions. Methods. Ab initio grids of time dependent chemical models, varying in gas density, temperature, cosmic ray ionization rate, and radiation field, are used as inputs into RADEX calculations. Tables of abundances, column densities, theoretical line intensities, and line ratios for some of the most used dense gas tracers are provided. The degree of correlation as well as degeneracy inherent in molecular ratios is discussed. Comparisons of the theoretical intensities with example observations are also provided. Results. We find that, within the parameters space explored, chemical abundances can be constrained by a well-defined set of gas density, gas temperature, and cosmic ray ionization rates for the species we investigate here. However, line intensities, and more importantly line ratios, from different chemical models can be very similar, thereby leading to a clear degeneracy. We also find that the gas subjected to a galactic cosmic ray ionization rate will not necessarily have reached steady state in 1 million years. The species most affected by time dependency effects are HCN and CS, which are both high density tracers. We use our ab initio method to fit an example set of data from two galaxies, i.e. M82 and NGC 253. We find that (i) molecular line ratios can be easily matched even with erroneous individual line intensities, (ii) no set of species can be matched by a one-component interstellar medium (ISM), and (iii) a species may be a good tracer of an energetic process but only under specific density and temperature conditions. Conclusions. We provide tables of chemical abundances and line intensities ratios for some of the most commonly observed extragalactic tracers of dense gas for a grid of models. We show that by taking the chemistry behind each species and the individual line intensities into consideration, many degeneracies that arise by just using molecular line ratios can be avoided. Finally we show that using a species or a ratio as a tracer of an individual energetic process, such as cosmic rays and UV, ought to be done with caution.

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The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey – IX. 12CO J = 3→2 observations of NGC 2976 and NGC 3351

Cited by 10 publications

References 66 publications

Giant molecular cloud scaling relations: the role of the cloud definition

Giant molecular cloud scaling relations: the role of the cloud definition

The JCMT Nearby Galaxies Legacy Survey: SCUBA-2 observations of nearby galaxies

Molecular transitions as probes of the physical conditions of extragalactic environments

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