12 research outputs found
Stringent bounds to spatial variations of the electron-to-proton mass ratio in the Milky Way
The ammonia method to probe variations of the electron-to-proton mass ratio,
Delta_mu/mu, is applied for the first time to dense prestellar molecular clouds
in the Milky Way. Carefully selected sample of 21 NH_3/CCS pairs observed in
the Perseus molecular cloud provide the offset Delta V (CCS-NH_3)=
36+/-7_{stat}+/-13.5_{sys} m/s . A similar offset of Delta V = 40.8 +/-
12.9_{stat} m/s between NH_3 (J,K) = (1,1) and N_2H+ J = 1-0 has been found in
an isolated dense core L183 by Pagani et al. (2009). Overall these observations
provide a safe bound of a maximum offset between ammonia and the other
molecules at the level of Delta V < 100 m/s. This bound corresponds to
Delta_mu/mu < 1E-7, which is an order of magnitude more sensitive than
available extragalactic constraints. Taken at face value the measured Delta V
shows positive shifts between the line centers of NH_3 and these two other
molecules and suggest a real offset, which would imply a Delta_mu/mu about
4E-8. If Delta_mu/mu follows the gradient of the local gravitational potential,
then the obtained results are in conflict with laboratory atomic clock
experiments in the solar system by 5 orders of magnitude, thus requiring a
chameleon-type scalar field model. New measurements involving other molecules
and a wider range of objects along with verification of molecular rest
frequencies are currently planned to confirm these first indications.Comment: 7 pages +2 figures. Galileo Galilei Institute Conferences on Dark
Matter and Dark Energ
Constraining fundamental constants of physics with quasar absorption line systems
We summarize the attempts by our group and others to derive constraints on
variations of fundamental constants over cosmic time using quasar absorption
lines. Most upper limits reside in the range 0.5-1.5x10-5 at the 3sigma level
over a redshift range of approximately 0.5-2.5 for the fine-structure constant,
alpha, the proton-to-electron mass ratio, mu, and a combination of the proton
gyromagnetic factor and the two previous constants, gp(alpha^2/mu)^nu, for only
one claimed variation of alpha. It is therefore very important to perform new
measurements to improve the sensitivity of the numerous methods to at least
<0.1x10-5 which should be possible in the next few years. Future
instrumentations on ELTs in the optical and/or ALMA, EVLA and SKA pathfinders
in the radio will undoutedly boost this field by allowing to reach much better
signal-to-noise ratios at higher spectral resolution and to perform
measurements on molecules in the ISM of high redshift galaxies.Comment: 11 pages, 3 figure
Search for varying constants of nature from astronomical observation of molecules
The status of searches for possible variation in the constants of nature from
astronomical observation of molecules is reviewed, focusing on the
dimensionless constant representing the proton-electron mass ratio
. The optical detection of H and CO molecules with large
ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as
the detection of H with the Cosmic Origins Spectrograph aboard the Hubble
Space Telescope is discussed in the context of varying constants, and in
connection to different theoretical scenarios. Radio astronomy provides an
alternative search strategy bearing the advantage that molecules as NH
(ammonia) and CHOH (methanol) can be used, which are much more sensitive to
a varying than diatomic molecules. Current constraints are
for redshift , corresponding to
look-back times of 10-12.5 Gyrs, and for
, corresponding to half the age of the Universe (both at 3
statistical significance). Existing bottlenecks and prospects for future
improvement with novel instrumentation are discussed.Comment: Contribution to Workshop "High Performance Clocks in Space" at the
International Space Science Institute, Bern 201
Primordial nucleosynthesis with a varying fine structure constant: An improved estimate
We compute primordial light-element abundances for cases with fine structure
constant alpha different from the present value, including many sources of
alpha dependence neglected in previous calculations. Specifically, we consider
contributions arising from Coulomb barrier penetration, photon coupling to
nuclear currents, and the electromagnetic components of nuclear masses. We find
the primordial abundances to depend more weakly on alpha than previously
estimated, by up to a factor of 2 in the case of ^7Li. We discuss the
constraints on variations in alpha from the individual abundance measurements
and the uncertainties affecting these constraints. While the present best
measurements of primordial D/H, ^4He/H, and ^7Li/H may be reconciled pairwise
by adjusting alpha and the universal baryon density, no value of alpha allows
all three to be accommodated simultaneously without consideration of systematic
error. The combination of measured abundances with observations of acoustic
peaks in the cosmic microwave background favors no change in alpha within the
uncertainties.Comment: Phys. Rev. D accepted version; minor changes in response to refere
Molecules at early epochs. VI - A search for the molecular hydrogen in the Z = 3.391 damped Lyman alpha system toward Q0000-263
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Fundamental constants and high-resolution spectroscopy
Absorption-line systems detected in high resolution quasar spectra can be
used to compare the value of dimensionless fundamental constants such as the
fine-structure constant, alpha, and the proton-to-electron mass ratio, mu =
m_p/m_e, as measured in remote regions of the Universe to their value today on
Earth. In recent years, some evidence has emerged of small temporal and also
spatial variations in alpha on cosmological scales which may reach a fractional
level of 10 ppm . We are conducting a Large Programme of observations with VLT
UVES to explore these variations. We here provide a general overview of the
Large Programme and report on the first results for these two constants,
discussed in detail in Molaro et al. and Rahmani et al. A stringent bound for
Delta(alpha)/Alpha is obtained for the absorber at_abs = 1.6919 towards HE
2217-2818. The absorption profile is complex with several very narrow features,
and is modeled with 32 velocity components. The relative variation in alpha in
this system is +1.3+-2.4_{stat}+-1.0_{sys} ppm if Al II lambda 1670AA and three
Fe II transitions are used, and +1.1+-2.6_{stat} ppm in a lightly different
analysis with only Fe II transitions used. The expectation at this sky position
of the recently-reported dipolar variation of alpha is (3.2--5.4)+-1.7 ppm
depending on dipole model. This constraint of Delta(alpha)/alpha at face value
is not supporting this expectation but is not inconsistent with it at the 3
sigma level. For the proton-to-electron mass ratio the analysis of the H_2
absorption lines of the z_{abs}~2.4018 damped Ly alpha system towards HE 0027-
1836 provides Delta(mu)/mu = (-7.6 +- 8.1_{stat} +- 6.3_{sys}) ppm which is
also consistent with a null variation. (abridged)Comment: Invited talk at the 10th AIP Thinkshop, AN, in pres
LMC N113 and N159W ALMA para-H_2_CO datacubes
We mapped the kinetic temperature structure of two massive star-forming regions, N113 and N159W, in the Large Magellanic Cloud (LMC). We have used ∼1.6" (∼0.4pc) resolution measurements of the para-H2CO JKaKc=303-202, 322-221, and 321-220 transitions near 218.5GHz to constrain RADEX non local thermodynamic equilibrium models of the physical conditions. The gas kinetic temperatures derived from the para-H2CO line ratios 322-221/303-202 and 321-220/303-202 range from 28 to 105K in N113 and 29 to 68K in N159W. Distributions of the dense gas traced by para-H2CO agree with those of the 1.3mm dust and Spitzer 8.0um emission, but they do not significantly correlate with the H emission. The high kinetic temperatures (Tkin≳50K) of the dense gas traced by para-H2CO appear to be correlated with the embedded infrared sources inside the clouds and/or young stellar objects in the N113 and N159W regions. The lower temperatures (Tkin<50K) were measured at the outskirts of the H2CO-bearing distributions of both N113 and N159W. It seems that the kinetic temperatures of the dense gas traced by para-H2CO are weakly affected by the external sources of the Hα emission. The non thermal velocity dispersions of para-H2CO are well correlated with the gas kinetic temperatures in the N113 region, implying that the higher kinetic temperature traced by para-H2CO is related to turbulence on a ∼0.4pc scale. The dense gas heating appears to be dominated by internal star formation activity, radiation, and/or turbulence. It seems that the mechanism heating the dense gas of the star-forming regions in the LMC is consistent with that in Galactic massive star-forming regions located in the Galactic plane