How Dense Is Your Gas? On the Recoverability of LVG Model Parameters

Tunnard, R.; Greve, T. R.

doi:10.3847/0004-637x/819/2/161

Cited by 28 publications

(21 citation statements)

References 57 publications

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“…The excitation conditions of a multi-phase, multiple gas component ISM are also expected to change for each galaxy. One would expect that the density and kinetic temperature of the CO (1 − 0) emitting gas (and the gradients across the galaxy) to factor into the total attenuation of the CO (1−0) line emission (Tunnard & Greve 2016 and any selfshielding. As the intense star-forming conditions during the redshifts indicated in these three samples (SPT, H-ATLAS, Planck-Herschel) will give rise to a dynamic set of ISM conditions, these varying gas excitation conditions will therefore have non-negligible effects in the observed LIR-to-L CO(1−0) values.…”

Section: Ratio Of Ir Luminosity To Co Line Luminositymentioning

confidence: 99%

Total molecular gas masses of Planck – Herschel selected strongly lensed hyper luminous infrared galaxies

Harrington

Yun

Magnelli³

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We report the detection of CO(1 − 0) line emission from seven Planck and Herschel selected hyper luminous (L IR(8−1000µm) > 10 13 L ) infrared galaxies with the Green Bank Telescope (GBT ). CO(1 − 0) measurements are a vital tool to trace the bulk molecular gas mass across all redshifts. Our results place tight constraints on the total gas content of these most apparently luminous high-z star-forming galaxies (apparent IR luminosities of L IR > 10 13−14 L ), while we confirm their predetermined redshifts measured using the Large Millimeter Telescope, LMT (z CO = 1.33 − 3.26). The CO(1 − 0) lines show similar profiles as compared to J up = 2 − 4 transitions previously observed with the LMT. We report enhanced infrared to CO line luminosity ratios of < L IR /L CO(1−0) >= 110 ± 22 L (K km s −1 pc −2 ) −1 compared to normal star-forming galaxies, yet similar to those of well-studied IR-luminous galaxies at high-z. We find average brightness temperature ratios of < r 21 >= 0.93 (2 sources), < r 31 >= 0.34 (5 sources), and < r 41 >= 0.18 (1 source). The r 31 and r 41 values are roughly half the average values for SMGs. We estimate the total gas mass content as µM H2 = (0.9 − 27.2) × 10 11 (α CO /0.8)M , where µ is the magnification factor and α CO is the CO line luminosity to molecular hydrogen gas mass conversion factor. The rapid gas depletion times, < τ depl >= 80 Myr, reveal vigorous starburst activity, and contrast the Gyr depletion timescales observed in local, normal star-forming galaxies.

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Section: Ratio Of Ir Luminosity To Co Line Luminositymentioning

confidence: 99%

Total molecular gas masses of Planck – Herschel selected strongly lensed hyper luminous infrared galaxies

Harrington

Yun

Magnelli³

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…In particular one could use tables, such as those presented in this study, to determine a priori whether similar line intensities arise from very different physical conditions and viceversa. This may be of particular importance in light of the results from Tunnard & Greve (2016) who find that LVG models struggle to recover any parameter better than to within half a dex and they find no evidence of systemic offsets. While these Tables are not exhaustive we hope that they can be used to track the origin of multiple solutions.…”

Section: Radiative Transfer Calculations: Intensities and Intensitiesmentioning

confidence: 97%

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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“…At the same time, the CMB background against which the line is measured increases too. This twofold effect shifts the peak of the CO SLED at higher transitions up to J up ∼ 6 − 7 (Tunnard & Greve 2016;Vallini et al 2018). Mid-J CO observations can be therefore used in the early Universe for investigating the molecular gas reservoir and ISM properties in both star-forming (e.g.…”

Section: Introductionmentioning

confidence: 99%

Constraints on high-J CO emission lines in z ∼ 6 quasars

Carniani

Gallerani

Vallini

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present Atacama Large Millimiter/submillimiter Array (ALMA) observations of eight highly excited CO (J up > 8) lines and continuum emission in two z ∼ 6 quasars: SDSS J231038.88+185519.7 (hereafter J2310), for which CO(8-7), CO(9-8), and CO(17-16) lines have been observed, and ULAS J131911.29+095951.4 (J1319), observed in the CO(14-13), CO(17-16) and CO(19-18) lines. The continuum emission of both quasars arises from a compact region (< 0.9 kpc). By assuming a modified black-body law, we estimate dust masses of Log(M dust /M ) = 8.75 ± 0.07 and Log(M dust /M ) = 8.8 ± 0.2 and dust temperatures of T dust = 76 ± 3 K and T dust = 66 +15 −10 K, respectively for J2310 and J1319. Only CO(8-7) and CO(9-8) in J2310 are detected, while 3σ upper limits on luminosities are reported for the other lines of both quasars. The CO line luminosities and upper limits measured in J2310 and J1319 are consistent with those observed in local AGN and starburst galaxies, and other z ∼ 6 quasars, except for SDSS J1148+5251 (J1148), the only quasar at z = 6.4 with a previous CO(17-16) line detection. By computing the CO SLEDs normalised to the CO(6-5) line and FIR luminosities for J2310, J1319, and J1149, we conclude that different gas heating mechanisms (X-ray radiation and/or shocks) may explain the different CO luminosities observed in these z ∼ 6 quasar. Future J up > 8 CO observations will be crucial to understand the processes responsible for molecular gas excitation in luminous high-z quasars.

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How Dense Is Your Gas? On the Recoverability of LVG Model Parameters

Cited by 28 publications

References 57 publications

Total molecular gas masses of Planck – Herschel selected strongly lensed hyper luminous infrared galaxies

Total molecular gas masses of Planck – Herschel selected strongly lensed hyper luminous infrared galaxies

Molecular transitions as probes of the physical conditions of extragalactic environments

Constraints on high-J CO emission lines in z ∼ 6 quasars

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