Martin Wendt

The UVES Large Program for testing fundamental physics I. Bounds on a change in alpha towards quasar HE 2217-2818

Context. Absorption-line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, , measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations in on cosmological scales. These variations may reach a fractional level of 10 ppm (parts per million). Aims. To test these claims we are conducting a Large Program of observations with the Very Large Telescope’s Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high-resolution (R 60 000) and high signal-to-noise ratio (S=N 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this programme, that of HE 2217 2818. Methods. We applied the many multiplet method to measure in five absorption systems towards this quasar: zabs = 0:7866, 0.9424, 1.5558, 1.6279 , and 1.6919. Results. The most precise result is obtained for the absorber at zabs = 1:6919 where 3 Feii transitions and Alii 1670 have high S/N and provide a wide range of sensitivities to . The absorption profile is complex with several very narrow features, and it requires 32 velocity components to be fitted to the data. We also conducted a range of tests to estimate the systematic error budget. Our final result for the relative variation in in this system is = = +1:3 2:4stat 1:0sys ppm. This is one of the tightest current bounds on -variation from an individual absorber. A second, separate approach to the data reduction, calibration, and analysis of this system yielded a slightly di erent result of 3.8 2:1stat ppm, possibly suggesting a larger systematic error component than our tests indicated. This approach used an additional 3 Feii transitions, parts of which were masked due to contamination by telluric features. Restricting this analysis to the Feii transitions alone and using a modified absorption profile model gave a result that is consistent with the first approach, = = +1:1 2:6stat ppm. The four other absorbers have simpler absorption profiles, with fewer and broader features, and o er transitions with a narrower range of sensitivities to . They therefore provide looser bounds on = at the > 10 ppm precision level.

QSO 0347-383 and the invariance of mp/me in the course of cosmic time

Context. The variation of the dimensionless fundamental physical constant μ = mp/me – the proton to electron mass ratio – can be constrained via observation of Lyman and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha systems (DLAs) in the line of sight to distant QSOs. Aims. Our intention is to maximize the possible precision of quasar absorption spectroscopy with regard to the investigation of the variation of the proton-to-electron mass-ratio μ. The demand for precision requires an understanding of the errors involved and effective techniques to handle present systematic errors. Methods. An analysis based on UVES high resolution data sets of QSO 0347-383 and its DLA is put forward and new approaches to some of the steps involved in the data analysis are introduced. We apply corrections for the observed offsets between discrete spectra and for the first time we find indications for inter-order distortions. Results. Drawing on VLT-UVES observations of QSO 0347-383 in 2009 our analysis yields Δμ/μ = (4.3±7.2)×10 −6 at zabs = 3.025. Conclusions. Current analyzes tend to underestimate the impact of systematic errors. Based on the scatter of the measured redshifts and the corresponding low significance of the redshift-sensitivity correlation we estimate the limit of accuracy of line position measurements to ∼220 m s −1 , consisting of roughly 150 m s −1 due to the uncertainty of the absorption line fit and about 150 m s −1 allocated

The UVES Large Program for testing fundamental physics – III. Constraints on the fine-structure constant from three telescopes

Large statistical samples of quasar spectra have previously indicated possible cosmological variations in the fine-structure constant, . A smaller sample of higher signal-to-noise ratio spectra, with dedicated calibration, would allow a detailed test of this evidence. Towards that end, we observed equatorial quasar HS 1549+1919 with three telescopes: the Very Large Telescope, Keck and, for the first time in such analyses, Subaru. By directly comparing these spectra to each other, and by ‘supercalibrating’ them using asteroid and iodine-cell tests, we detected and removed long-range distortions of the quasar spectra’s wavelength scales which would have caused significant systematic errors in our measurements. For each telescope we measure the relative deviation in from the current laboratory value, = , in 3 absorption systems at redshifts zabs = 1:143, 1.342, and 1.802. The nine measurements of = are all consistent with zero at the 2- level, with 1- statistical (systematic) uncertainties 5.6‐ 24 (1.8‐7.0) parts per million (ppm). They are also consistent with each other at the 1level, allowing us to form a combined value for each telescope and, finally, a single value for this line of sight: = = 5:4 3:3stat 1:5sys ppm, consistent with both zero and previous, large samples. We also average all Large Programme results measuring = = 0:6 1:9stat 0:9sys ppm. Our results demonstrate the robustness and reliability at the 3 ppm level afforded by supercalibration techniques and direct comparison of spectra from different telescopes.

MUSE crowded field 3D spectroscopy of over 12 000 stars in the globular cluster NGC 6397 - II. Probing the internal dynamics and the presence of a central black hole

We present a detailed analysis of the kinematics of the Galactic globular cluster NGC 6397 based on more than ~18,000 spectra obtained with the novel integral field spectrograph MUSE. While NGC 6397 is often considered a core collapse cluster, our analysis suggests a flattening of the surface brightness profile at the smallest radii. Although it is among the nearest globular clusters, the low velocity dispersion of NGC 6397 of <5km/s imposes heavy demands on the quality of the kinematical data. We show that despite its limited spectral resolution, MUSE reaches an accuracy of 1km/s in the analysis of stellar spectra. We find slight evidence for a rotational component in the cluster and the velocity dispersion profile that we obtain shows a mild central cusp. To investigate the nature of this feature, we calculate spherical Jeans models and compare these models to our kinematical data. This comparison shows that if a constant mass-to-light ratio is assumed, the addition of an intermediate-mass black hole with a mass of 600M_sun brings the model predictions into agreement with our data, and therefore could be at the origin of the velocity dispersion profile. We further investigate cases with varying mass-to-light ratios and find that a compact dark stellar component can also explain our observations. However, such a component would closely resemble the black hole from the constant mass-to-light ratio models as this component must be confined to the central ~5arcsec of the cluster and must have a similar mass. Independent constraints on the distribution of stellar remnants in the cluster or kinematic measurements at the highest possible spatial resolution should be able to distinguish the two alternatives.

MUSE crowded field 3D spectroscopy of over 12 000 stars in the globular cluster NGC 6397 - I. The first comprehensive HRD of a globular cluster

Aims. We demonstrate the high multiplex advantage of crowded field 3D spectroscopy using the new integral field spectrograph MUSE by means of a spectroscopic analysis of more than 12 000 individual stars in the globular cluster NGC 6397. Methods. The stars are deblended with a PSF fitting technique, using a photometric reference catalogue from HST as prior, including relative positions and brightnesses. This catalogue is also used for a first analysis of the extracted spectra, followed by an automatic in-depth analysis using a full-spectrum fitting method based on a large grid of PHOENIX spectra. Results. With 18 932 spectra from 12 307 stars in NGC 6397 we have analysed the largest sample so far available for a single globular cluster. We derived a mean radial velocity of vrad=17.84±0.07 km s−1 and a mean metallicity of [Fe/H]=-2.120±0.002, with the latter seemingly varying with temperature for stars on the RGB. We determine Teff and [Fe/H] from the spectra, and log g from HST photometry. This is the first very comprehensive HRD for a globular cluster based on the analysis of several thousands of stellar spectra, ranging from the main sequence to the tip of the RGB. Furthermore, two interesting objects were identified with one being a post-AGB star and the other a possible millisecond-pulsar companion.

Observations of metals in the z ≈ 3.5 intergalactic medium and comparison to the EAGLE simulations

We study the z ≈ 3.5 intergalactic medium (IGM) by comparing new, high-quality absorption spectra of eight QSOs with _zQSO_ = 3.75, to virtual observations of the Evolution and Assembly of Galaxies and their Environments (EAGLE) cosmological hydrodynamical simulations. We employ the pixel optical depth method and uncover strong correlations between various combinations of HI, CIII, CIV, Si III, Si IV, and OVI.We find good agreement between many of the simulated and observed correlations, including τOVI(τHI). However, the observed median optical depths for the τCIV(τHI) and τSi IV(τHI) relations are higher than those measured from the mock spectra. The discrepancy increases from up to ≈0.1 dex at τHI = 1 to ≈1 dex at τHI = 102, where we are likely probing dense regions at small galactocentric distances. As possible solutions, we invoke (a) models of ionizing radiation softened above 4 Ryd to account for delayed completion of He II reionization; (b) simulations run at higher resolution; (c) the inclusion of additional line broadening due to unresolved turbulence; and (d) increased elemental abundances; however, none of these factors can fully explain the observed differences. Enhanced photoionization of HI by local sources, which was not modelled, could offer a solution. However, the much better agreement with the observed OVI(H I) relation, which we find probes a hot and likely collisionally ionized gas phase, indicates that the simulations are not in tension with the hot phase of the IGM, and suggests that the simulated outflows may entrain insufficient cool gas.

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, α, and the proton-to-electron mass ratio, μ = mp/me, 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 α on cosmological scales which may reach a fractional level of ≈ 10 ppm (parts per million). We are conducting a Large Programme of observations with the Very Large Telescopes Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high-resolution (R ≈ 60000) and high signal-to-noise ratio (S/N ≈ 100) spectra calibrated specifically to study the variations of the fundamental constants. 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. (2013) and Rahmani et al. (2013). A stringent bound for Δα /α is obtained for the absorber at zabs = 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 α in this system is +1.3 ± 2.4stat ± 1.0sys ppm if Al II λ 1670 A and three FeII transitions are used, and +1.1 ± 2.6stat ppm in a slightly different analysis with only FeII transitions used. This is one of the tightest bounds on α -variation from an individual absorber and reveals no evidence for variation in α at the 3-ppm precision level (1σ confidence). The expectation at this sky position of the recently-reported dipolar variation of α is (3.2–5.4) ± 1.7 ppm depending on dipole model used and this constraint of Δα /α at face value is not supporting this expectation but not inconsistent with it at the 3σ level. For the proton-to-electron mass ratio the analysis of the H2 absorption lines of the zabs ≈ 2.4018 damped Lyα system towards HE 0027–1836 provides Δμ /μ = (–7.6 ± 8.1stat ± 6.3sys) ppm which is also consistent with a null variation. The cross-correlation analysis between individual exposures taken over three years and comparison with almost simultaneous asteroid observations revealed the presence of a possible wavelength dependent velocity drift as well as of inter-order distortions which probably dominate the systematic error and are a significant obstacle to achieve more accurate measurements. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A stellar census in globular clusters with MUSE: The contribution of rotation to cluster dynamics studied with 200 000 stars

This is the first of a series of papers presenting the results from our survey of 25 Galactic globular clusters with the MUSE integral-field spectrograph. In combination with our dedicated algorithm for source deblending, MUSE provides unique multiplex capabilities in crowded stellar fields and allows us to acquire samples of up to 20 000 stars within the half-light radius of each cluster. The present paper focuses on the analysis of the internal dynamics of 22 out of the 25 clusters, using about 500 000 spectra of 200 000 individual stars. Thanks to the large stellar samples per cluster, we are able to perform a detailed analysis of the central rotation and dispersion fields using both radial profiles and two-dimensional maps. The velocity dispersion profiles we derive show a good general agreement with existing radial velocity studies but typically reach closer to the cluster centres. By comparison with proper motion data we derive or update the dynamical distance estimates to 14 clusters. Compared to previous dynamical distance estimates for 47 Tuc, our value is in much better agreement with other methods. We further find significant (>3sigma) rotation in the majority (13/22) of our clusters. Our analysis seems to confirm earlier findings of a link between rotation and the ellipticities of globular clusters. In addition, we find a correlation between the strengths of internal rotation and the relaxation times of the clusters, suggesting that the central rotation fields are relics of the cluster formation that are gradually dissipated via two-body relaxation.

Galactic winds with MUSE : A direct detection of Fe II* emission from a z 1.29 galaxy

Emission signatures from galactic winds provide an opportunity to directly map the outflowing gas, but this is traditionally challenging because of the low surface brightness. Using deep observations (27 hours) of the Hubble Deep Field South from the Multi Unit Spectroscopic Explorer (MUSE) instrument, we identify signatures of an outflow in both emission and absorption from a spatially resolved galaxy at z = 1.29 with a stellar mass M* = 8 x 10^9 Msun, star formation rate SFR = 77 Msun/yr, and star formation rate surface brightness 1.6 Msun/kpc^2 within the [OII] half-light radius R_1/2,[OII] = 2.76 +- 0.17 kpc. From a component of the strong resonant MgII and FeII absorptions at -350 km/s, we infer a mass outflow rate that is comparable to the star formation rate. We detect non-resonant FeII* emission, at lambda 2626, 2612, 2396, and 2365, at 1.2-2.4-1.5-2.7 x 10^-18 egs s-1 cm-2 respectively. These flux ratios are consistent with the expectations for optically thick gas. By combining the four non-resonant FeII* emission lines, we spatially map the FeII* emission from an individual galaxy for the first time. The FeII* emission has an elliptical morphology that is roughly aligned with the galaxy minor kinematic axis, and its integrated half-light radius R_1/2,FeII* = 4.1 +- 0.4 kpc is 50% larger than the stellar continuum (R_1/2,* = 2.34 +- 0.17 kpc) or the [OII] nebular line. Moreover, the FeII* emission shows a blue wing extending up to -400 km/s, which is more pronounced along the galaxy minor kinematic axis and reveals a C-shaped pattern in a p-v diagram along that axis. These features are consistent with a bi-conical outflow.

An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way’s circumgalactic medium and the Local Group

To characterize the absorption properties of this circumgalactic medium (CGM) and its relation to the LG we present the so-far largest survey of metal absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet (UV) spectra of extragalactic background sources. The UV data are obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST) and are supplemented by 21 cm radio observations of neutral hydrogen. Along 270 sightlines we measure metal absorption in the lines of SiII, SiIII, CII, and CIV and associated HI 21 cm emission in HVCs in the velocity range |v_LSR|=100-500 km s^-1. With this unprecedented large HVC sample we were able to improve the statistics on HVC covering fractions, ionization conditions, small-scale structure, CGM mass, and inflow rate. For the first time, we determine robustly the angular two point correlation function of the high-velocity absorbers, systematically analyze antipodal sightlines on the celestial sphere, and compare the absorption characteristics with that of Damped Lyman alpha absorbers (DLAs) and constrained cosmological simulations of the LG. Our study demonstrates that the Milky Way CGM contains sufficient gaseous material to maintain the Galactic star-formation rate at its current level. We show that the CGM is composed of discrete gaseous structures that exhibit a large-scale kinematics together with small-scale variations in physical conditions. The Magellanic Stream clearly dominates both the cross section and mass flow of high-velocity gas in the Milky Ways CGM. The possible presence of high-velocity LG gas underlines the important role of the local cosmological environment in the large-scale gas-circulation processes in and around the Milky Way (abridged).