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 $\mu=m_p/m_e$. The optical detection of H$_2$ and CO molecules with large ground-based telescopes (as the ESO-VLT and the Keck telescopes), as well as the detection of H$_2$ 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$_3$ (ammonia) and CH$_3$OH (methanol) can be used, which are much more sensitive to a varying $\mu$ than diatomic molecules. Current constraints are $|\Delta\mu/\mu| < 5 \times 10^{-6}$ for redshift $z=2.0-4.2$, corresponding to look-back times of 10-12.5 Gyrs, and $|\Delta\mu/\mu| < 1.5 \times 10^{-7}$ for $z=0.88$, corresponding to half the age of the Universe (both at 3$\sigma$ 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

CUBES: a UV spectrograph for the future

In spite of the advent of extremely large telescopes in the UV/optical/NIR range, the current generation of 8-10m facilities is likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R>20,000, although a lower-resolution, sky-limited mode of R ~ 7,000 is also planned. CUBES will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the Phase B dedicated to detailed design and construction. First science operations are planned for 2028. In this paper, we briefly describe the CUBES project development and goals, the main science cases, the instrument design and the project organization and management

A New Precise Determination of the Primordial Abundance of Deuterium: Measurement in the metal-poor sub-DLA system at z=3.42 towards quasar J1332+0052

International audienceThe theory of Big Bang nucleosynthesis, coupled with an estimate of the primordial deuterium abundance (D/H)_pr, offers insights into the baryon density of the Universe. Independently, the baryon density can be constrained during a different cosmological era through the analysis of cosmic microwave background (CMB) anisotropy. The comparison of these estimates serves as a rigorous test for the self-consistency of the Standard Cosmological Model and stands as a potent tool in the quest for new physics beyond the Standard Model of Particle Physics. For a meaningful comparison, a clear understanding of the various systematic errors affecting deuterium measurements is crucial. Given the limited number of D/H measurements, each new estimate carries significant weight. This study presents the detection of DI absorption lines in a metal-poor sub-Damped Lyman-alpha system ([O/H]=-1.71+-0.02, logN(HI)=19.304+-0.004) at z_abs=3.42 towards the quasar J1332+0052. Through simultaneous fitting of HI and DI Lyman-series lines, as well as low-ionization metal lines, observed at high spectral resolution and high signal-to-noise using VLT/UVES and Keck/HIRES, we derive log(DI/HI)=-4.622+-0.014, accounting for statistical and systematic uncertainties of 0.008dex and 0.012dex, respectively. Thanks to negligible ionization corrections and minimal deuterium astration at low metallicity, this D/H ratio provides a robust measurement of the primordial deuterium abundance, consistent and competitive with previous works. Incorporating all prior measurements, the best estimate of the primordial deuterium abundance is constrained as: (D/H)_pr=(2.533+-0.024)*10^-5. This represents a 5% improvement in precision over previous studies and reveals a moderate tension with the expectation from the Standard Model (~2.2sig). This discrepancy underscores the importance of further measurements in the pursuit of new physics

HD molecules at high redshift: cosmic ray ionization rate in the diffuse interstellar medium

International audienceWe present a systematic study of deuterated molecular hydrogen (HD) at high redshift, detected in absorption in the spectra of quasars. We present four new identifications of HD lines associated with known |$\rm H_2$|-bearing Damped Lyman-α systems. In addition, we measure upper limits on the |$\rm HD$| column density in 12 recently identified |$\rm H_2$|-bearing DLAs. We find that the new |$\rm HD$| detections have similar |$N({\rm HD})/N(\rm H_2)$| ratios as previously found, further strengthening a marked difference with measurements through the Galaxy. This is likely due to differences in physical conditions and metallicity between the local and the high-redshift interstellar media. Using the measured N(HD)/N(H_2) ratios together with priors on the UV flux (χ) and number densities (n), obtained from analysis of |$\rm H_2$| and associated C i lines, we are able to constrain the cosmic ray ionization rate (CRIR, ζ) for the new |$\rm HD$| detections and for eight known HD-bearing systems where priors on n and χ are available. We find significant dispersion in ζ, from a few × 10^−18 s^−1 to a few × 10^−15 s^−1. We also find that ζ strongly correlates with χ – showing almost quadratic dependence, slightly correlates with Z, and does not correlate with n, which probably reflects a physical connection between cosmic rays and star-forming regions

The MeerKAT Absorption Line Survey: Homogeneous continuum catalogues towards a measurement of the cosmic radio dipole

International audienceThe number counts of homogeneous samples of radio sources are a tried and true method of probing the large scale structure of the Universe, as most radio sources outside the galactic plane are at cosmological distances. As such they are expected to trace the cosmic radio dipole, an anisotropy analogous to the dipole seen in the cosmic microwave background (CMB). Results have shown that although the cosmic radio dipole matches the direction of the CMB dipole, it has a significantly larger amplitude. This result challenges our assumption of the Universe being isotropic, which can have large repercussions for the current cosmological paradigm. Though significant measurements have been made, sensitivity to the radio dipole is generally hampered by systematic effects that can cause large biases in the measurement. Here we assess these systematics with data from the MeerKAT Absorption Line Survey (MALS). We present the analysis of ten MALS pointings, focusing on systematic effects that could lead to an inhomogeneous catalogue. We describe the calibration and creation of full band continuum images and catalogues, producing a combined catalogue containing 16,313 sources and covering 37.5 square degrees of sky down to a sensitivity of 10 $\mu$Jy/beam. We measure the completeness, purity, and flux recovery statistics for these catalogues using simulated data. We investigate different source populations in the catalogues by looking at flux densities and spectral indices, and how they might influence source counts. Using the noise characteristics of the pointings, we find global measures that can be used to correct for the incompleteness of the catalogue, producing corrected number counts down to 100 - 200 $\mu$Jy. We show that we can homogenise the catalogues and properly account for systematic effects. We determine that we can measure the dipole to $3\sigma$ significance with 100 MALS pointings