Carbon monoxide as an extragalactic mass tracer

Dickman, R. L.; Snell, R.; Schloerb, F. Peter

doi:10.1086/164604

Cited by 227 publications

(221 citation statements)

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“…The molecular gas mass is computed with the following hypotheses. Given that metallicity is half solar and the gradient in M 33 is weak (12 + log(O/H) = 8.4 − 0.03R kpc , Rosolowsky & Simon 2008;Magrini et al 2009), we use a constant "standard" Milky Way factor (Dickman et al 1986) multiplied by a factor of two N(H 2 )/I CO(1−0) = 4 × 10 20 cm −2 /(K km s −1 ), implicitly assuming an inverse linear dependence between the conversion factor and metallicity (Wilson 1995) but see Israel (2000). Using the CO(1-0) observations from Rosolowsky et al (2007) and our CO(2-1) observations we compute a CO(2-1)/C0(1-0) ratio of 0.8 in the central kiloparsec of M 33.…”

Section: Molecular Gasmentioning

confidence: 99%

Molecular and atomic gas in the Local Group galaxy M 33

Gratier

Braine

Rodríguez-Fernández

et al. 2010

A&A

143

154

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We present high-resolution large-scale observations of the molecular and atomic gas in the Local Group galaxy M 33. The observations were carried out using the HEterodyne Receiver Array (HERA) at the 30 m IRAM telescope in the CO(2-1) line, achieving a resolution of 12 × 2.6 km s −1 , enabling individual giant molecular clouds (GMCs) to be resolved. The observed region is 650 square arcminutes mainly along the major axis and out to a radius of 8.5 kpc, and covers entirely the 2 × 40 radial strip observed with the HIFI and PACS Spectrometers as part of the HERM33ES Herschel key program. The achieved sensitivity in main-beam temperature is 20-50 mK at 2.6 km s −1 velocity resolution. The CO(2-1) luminosity of the observed region is 1.7 ± 0.1 × 10 7 K km s −1 pc 2 and is estimated to be 2.8 ± 0.3 × 10 7 K km s −1 pc 2 for the entire galaxy, corresponding to H 2 masses of 1.9 × 10 8 M and 3.3 × 10 8 M respectively (including He), calculated with N(H 2 )/I CO(1−0) twice the Galactic value due to the half-solar metallicity of M 33. The H i 21 cm VLA archive observations were reduced, and the mosaic was imaged and cleaned using the multi-scale task in the CASA software package, yielding a series of datacubes with resolutions ranging from 5 to 25 . The H i mass within a radius of 8.5 kpc is estimated to be 1.4 × 10 9 M . The azimuthally averaged CO surface brightness decreases exponentially with a scale length of 1.9 ± 0.1 kpc whereas the atomic gas surface density is constant at Σ H i = 6± 2 M pc −2 deprojected to face-on. For an N(H 2 )/I CO(1−0) conversion factor twice that of the Milky Way, the central kiloparsec H 2 surface density is Σ H 2 = 8.5 ± 0.2 M pc −2 . The star formation rate per unit molecular gas (SF efficiency, the rate of transformation of molecular gas into stars), as traced by the ratio of CO to H α and FIR brightness, is constant with radius. The SFE, with a N(H 2 )/I CO(1−0) factor twice galactic, appears 2-4 times greater than for large spiral galaxies. A morphological comparison of molecular and atomic gas with tracers of star formation is presented showing good agreement between these maps both in terms of peaks and holes. A few exceptions are noted. Several spectra, including those of a molecular cloud situated more than 8 kpc from the galaxy center, are presented.

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Section: Molecular Gasmentioning

confidence: 99%

Molecular and atomic gas in the Local Group galaxy M 33

Gratier

Braine

Rodríguez-Fernández

et al. 2010

A&A

143

154

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“…Dickman et al 1986). The relation between CO luminosity and molecular mass is then M gas = αL CO , where the constant of proportionality, α, is ∼4.6 M (K km s −1 pc 2 ) −1 for the J = 1-0 line in Galactic giant molecular clouds or nearby disk galaxies.…”

Section: Molecular and Dynamical Massmentioning

confidence: 99%

Molecular gas and dust in the highly magnifiedz ~ 2.8 galaxy behind the Bullet Cluster

Johansson¹,

Horellou²,

López-Cruz³

et al. 2012

A&A

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Context. The gravitational magnification provided by massive galaxy clusters makes it possible to probe the physical conditions in distant galaxies that are of lower luminosity than those in blank fields and likely more representative of the bulk of the high-redshift galaxy population. Aims. We aim to constrain the basic properties of molecular gas in a strongly magnified submm galaxy located behind the massive Bullet Cluster (1E 0657-56). This galaxy (SMM J0658) is split into three images, with a total magnification factor of almost 100. Methods. We used the Australia Telescope Compact Array (ATCA) to search for 12 CO(1-0) and 12 CO(3-2) line emission from SMM J0658. We also used the SABOCA bolometer camera on the Atacama Pathfinder EXperiment (APEX) telescope to measure the continuum emission at 350 μm. Results. CO(1-0) and CO(3-2) are detected at 6.8σ and 7.5σ significance when the spectra toward the two brightest images of the galaxy are combined. From the CO(1-0) luminosity we derive a mass of cold molecular gas of (1.8 ± 0.3) × 10 9 M , using the CO to H 2 conversion factor commonly used for luminous infrared galaxies. This is 45 ± 25% of the stellar mass. From the width of the CO lines we derive a dynamical mass within the CO-emitting region L of (1.3 ± 0.4) × 10 10 (L/1 kpc) M . We refine the redshift determination of SMM J0658 to z = 2.7793 ± 0.0003. The CO(3-2) to CO(1-0) brightness temperature ratio is 0.56 +0.21 −0.15 , which is similar to the values found in other star-forming galaxies. Continuum emission at 350 μm from SMM J0658 was detected with SABOCA at a signal-to-noise ratio of 3.6. The flux density is consistent with previous measurements at the same wavelength by the Herschel satellite and BLAST balloon-borne telescope. We study the spectral energy distribution of SMM J0658 and derive a dust temperature of 33 ± 5 K and a dust mass of 1.1 +0.8 −0.3 × 10 7 M . Conclusions. SMM J0658 is one of the least massive submm galaxies discovered so far. As a likely representative of the bulk of the submm galaxy population, it is a prime target for future observations.

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“…The reliability of the CO(1-0) line luminosity as an extragalactic mass tracer (e.g., Dickman et al 1986;Solomon & Barrett 1991) allows us to convert the line fluxes of various structures in the CO(1-0) map into molecular gas masses. Including a factor of 1.36 to account for helium, the gas mass bound into molecular clouds can be calculated as…”

Section: Co Line Morphologiesmentioning

confidence: 99%

Molecular gas in NUclei of GAlaxies (NUGA)

Combes

Baker²,

Schinnerer³

et al. 2009

A&A

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We present high-resolution maps of the CO(1-0) and CO(2-1) emission from the LINER 2 galaxy NGC 1961. This galaxy is unusual among late-type (Sc) disk galaxies in having a very large radial extent and inferred dynamical mass. We propose a head-on collision scenario to explain the perturbed morphology of this galaxy -both the off-centered rings and the inflated radius. This scenario is supported by the detection of a steep velocity gradient in the CO(1-0) map at the position of a southwest peak in radio continuum and near-infrared emission. This peak would represent the remnant of the disrupting companion. We use numerical models to demonstrate the plausibility of the scenario. While ram pressure stripping could in principle be important for shocking the atomic gas and produce the striking head-tail morphology, the non detection of this small galaxy group in X-ray emission suggests that any hot intragroup medium has too low a density. A prediction of the collision model is the propagation of ring waves from the center to the outer parts, superposed on a probable pre-existing m = 2 barred spiral feature, accounting for the observed complex structure of rings and spokes. This lopsided wave accounts for the sharp boundary observed in the atomic gas on the southern side. Through dynamical friction, the collision finishes quickly in a minor merger, the best fit being for a companion with a mass ratio 1:4. We argue that NGC 1961 has a strongly warped disk, which gives the false impression of a nearly face-on system; the main disk is actually more edge-on, and this error in the true inclination has led to the surprisingly high dynamical mass for a morphologically late-type galaxy. In addition, the outwardly propagating ring artificially enlarges the disk. The collision de-stabilizes the inner disk and can provide gas inflow to the active nucleus.

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Carbon monoxide as an extragalactic mass tracer

Cited by 227 publications

References 0 publications

Molecular and atomic gas in the Local Group galaxy M 33

Molecular and atomic gas in the Local Group galaxy M 33

Molecular gas and dust in the highly magnifiedz ~ 2.8 galaxy behind the Bullet Cluster

Molecular gas in NUclei of GAlaxies (NUGA)

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