Methanol as a Tracer of Fundamental Constants

Levshakov, S. A.; Kozlov, M. G.; Reimers, D.

doi:10.1088/0004-637x/738/1/26

Cited by 84 publications

(111 citation statements)

References 33 publications

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“…We fitted one or more Gaussian profiles to the maser spectra and measured a velocity difference between the two transitions of 8 ± 85ms −1 from a sample of eleven 12.2 GHz spectral peaks (two of the 9 selected sources required two Gaussians to adequately fit the spectrum). This corresponds to ∆µ/µ = −2.4 × 10 −9 ± 2.7 × 10 −8 , or an upper limit |∆µ/µ| < 27 × 10 −9 , essentially identical to the limit obtained towards a single source by Leshakov et al [2]. The observed velocity differences are evenly distributed about the mean (median -2 ms −1 ).…”

supporting

confidence: 84%

Practical Limitations on Astrophysical Observations of Methanol to Investigate Variations in the Proton-to-Electron Mass Ratio

2011

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The possibility of using astrophysical observations of rotational transitions in the methanol molecule to measure, or constrain temporal and spatial variations in the proton-to-electron mass ratio (µ) has recently been investigated by several groups. Here we outline some of the practical considerations of making such observations, including both the instrumental and astrophysical limitations which exist at present. This leads us to conclude that such observations are unlikely to be able to improve evidence either for, or against the presence of variations in the proton-to-electron mass ratio by more than an order of magnitude beyond current limits.PACS numbers: 06.20. Jr, 98.38.Er, 98.58.Ec The possibility of using astrophysical observations of rotational transitions in the methanol molecule to measure, or constrain temporal and spatial variations in the proton-to-electron mass ratio (µ) has recently been suggested by several groups [1,2]. The first attempts to use astronomical observations of methanol masers to constrain µ within the Milky Way show that |∆µ/µ| < 28 × 10 −9 [2].The hindered internal rotation exhibited by methanol produces the degeneracy which makes the different rotational transitions particularly sensitive to the protonto-electron mass ratio [1]. It also leads to the rich rotational and vibrational spectrum, which due to quantum mechanical selection rules produces a large number of centimetre and millimetre maser transitions in interstellar space. The strongest and most common of these is the 5 1 → 6 0 A + transition which has a rest frequency of approximately 6.7 GHz. It has been detected towards more than 900 sites of high-mass star formation in the Milky Way [see for example 3, 4]. The second strongest astrophysical transition of methanol is from the 2 0 → 3 −1 E transition which has a rest frequency of approximately 12.2 GHz, and is observed towards 43% of those sources showing 6.7 GHz emission [5]. In most methanol maser regions multiple spectral features are observed in the spectra of 6.7 or 12.2 GHz methanol masers at different Doppler shifted velocities [3,4]. The spectral features typically have near-Gaussian profiles (although spectral blending between spatially unresolved components affects most observations), and FWHM (full-width half maximum) of a few tenths of kilometers per second.The K µ coefficient measures the sensitivity of a transition to the proton-to-electron mass ratio and for the 6.7 and 12.2 GHz methanol transitions these have been calculated to be -42 and -33 respectively [1]. To improve constraints on |∆µ/µ|, beyond those already achieved [2], requires measurement of the relative Doppler shifted velocities of the different transitions to an accuracy of better than 100 ms −1 . When the 6.7 and 12.2 GHz methanol transitions exhibit peaks at the same velocity they have been demonstrated to arise from the same locations at the milliarcsecond level (corresponding to linear scales of a few AU at distances of a few kpc) [6,7]. The large number of 6.7 and 12.2 GHz methanol...

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supporting

confidence: 84%

Practical Limitations on Astrophysical Observations of Methanol to Investigate Variations in the Proton-to-Electron Mass Ratio

2011

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“…96,97 Similar calculations were performed by Levshakov et al 91 The large number of both positive and negative sensitivity coefficients makes methanol a preferred target system for probing a possible variation of μ, since this makes it possible to test variation of μ using transitions in a single molecular species, thereby avoiding the many systematic effects that plague tests that are based on comparing transitions in different molecules. Following the recent detection of methanol in the gravitationally lensed object PKS1830-211 (PKS referring to the Parkes catalog of celestial objects, with 1830 and −211 referring to RA and dec coordinates as for quasars; the PKS1830-211 system is a radio-loud quasar at z emis = 2.51) in an absorbing galaxy at a redshift of z abs = 0.89, 99 Bagdonaite et al 98 used four transitions that were observed in this system using the 100 m radio telescope in Effelsberg to constrain μ/μ at (0.0 ± 1.0) × 10 −7 at a look-back time of 7× 10 9 years.…”

Section: Internal Rotation: From Methanol To Methylaminementioning

confidence: 87%

Perspective: Tipping the scales: Search for drifting constants from molecular spectra

Jansen

Bethlem

Ubachs

2014

The Journal of Chemical Physics

114

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Precision measurement of the rotational energy-level structure of the three-electron molecule He 2 + Transitions in atoms and molecules provide an ideal test ground for constraining or detecting a possible variation of the fundamental constants of nature. In this perspective, we review molecular species that are of specific interest in the search for a drifting proton-to-electron mass ratio μ.In particular, we outline the procedures that are used to calculate the sensitivity coefficients for transitions in these molecules and discuss current searches. These methods have led to a rate of change in μ bounded to 6 × 10 −14 /yr from a laboratory experiment performed in the present epoch. On a cosmological time scale, the variation is limited to | μ/μ| < 10 −5 for look-back times of 10-12 × 10 9 years and to | μ/μ| < 10 −7 for look-back times of 7× 10 9 years. The last result, obtained from high-redshift observation of methanol, translates intoμ/μ = (1.4 ± 1.4) × 10 −17 /yr if a linear rate of change is assumed.

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“…For comparison, in the Milky Way the [C i]/CO pairs restrict ΔF/F at the level of |ΔF/F| < 0.4 ppm (Levshakov et al 2010a) leading to a limit on |Δα/α| < 0.2 ppm since the spatial variations in μ are restricted to |Δμ/μ| < 0.03 ppm in the disk of the Milky Way (Levshakov et al 2010b;Levshakov et al 2010c;Levshakov et al 2011;Ellingsen et al 2011).…”

Section: Discussionmentioning

confidence: 99%

An upper limit to the variation in the fundamental constants at redshiftz= 5.2

Levshakov

Combes

Boone

et al. 2012

A&A

Self Cite

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Aims. We constrain a hypothetical variation in the fundamental physical constants over the course of cosmic time. Methods. We use unique observations of the CO(7-6) rotational line and the [C i] 3 P 2 − 3 P 1 fine-structure line towards a lensed galaxy at redshift z = 5.2 to constrain temporal variations in the constant F = α 2 /μ, where μ is the electron-to-proton mass ratio and α is the fine-structure constant. The relative change in F between z = 0 and z = 5.2, ΔF/F = (F obs − F lab )/F lab , is estimated from the radial velocity offset, ΔV = V rot − V fs , between the rotational transitions in carbon monoxide and the fine-structure transition in atomic carbon. Results. We find a conservative value ΔV = (1±5) km s −1 (1σ C.L.), which when interpreted in terms of ΔF/F gives ΔF/F < 2×10 −5 . Independent methods restrict the μ-variations at the level of Δμ/μ < 1 × 10 −7 at z = 0.7 (look-back time t z0.7 = 6.4 Gyr). Assuming that temporal variations in μ, if any, are linear, this leads to an upper limit on Δμ/μ < 2 × 10 −7 at z = 5.2 (t z5.2 = 12.9 Gyr). From both constraints on ΔF/F and Δμ/μ , one obtains for the relative change in α the estimate Δα/α < 8 × 10 −6 , which is at present the tightest limit on Δα/α at early cosmological epochs.

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Methanol as a Tracer of Fundamental Constants

Cited by 84 publications

References 33 publications

Practical Limitations on Astrophysical Observations of Methanol to Investigate Variations in the Proton-to-Electron Mass Ratio

Practical Limitations on Astrophysical Observations of Methanol to Investigate Variations in the Proton-to-Electron Mass Ratio

Perspective: Tipping the scales: Search for drifting constants from molecular spectra

An upper limit to the variation in the fundamental constants at redshiftz= 5.2

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