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Context. The intergalactic medium (IGM) is believed to contain the majority of baryons in the universe and to trace the same dark matter structure as galaxies, forming filaments and sheets. Ly alpha absorbers, which sample the neutral component of the IGM, have been extensively studied at low and high redshift, but the exact relation between Ly alpha absorption, galaxies, and the large-scale structure is observationally not well constrained.Aims. In this study, we aim at characterising the relation between Ly alpha absorbers and nearby over-dense cosmological structures (galaxy filaments) at recession velocities Delta v <= 6700 km s(-1) by using archival observational data from various instruments.Methods. We analyse 587 intervening Ly alpha absorbers in the spectra of 302 extragalactic background sources obtained with the Cosmic Origins Spectrograph (COS) installed on the Hubble Space Telescope (HST). We combine the absorption line information with galaxy data of five local galaxy filaments from the V8k catalogue.Results. Along the 91 sightlines that pass close to a filament, we identify 215 (227) Ly alpha absorption systems (components). Among these, 74 Ly alpha systems are aligned in position and velocity with the galaxy filaments, indicating that these absorbers and the galaxies trace the same large-scale structure. The filament-aligned Ly alpha absorbers have a similar to 90% higher rate of incidence (d?/dz=189 for log N(HI) >= 13.2) and a slightly shallower column density distribution function slope (-beta=-1.47) relative to the general Ly alpha population at z=0, reflecting the filaments' matter over-density. The strongest Ly alpha absorbers are preferentially found near galaxies or close to the axis of a filament, although there is substantial scatter in this relation. Our sample of absorbers clusters more strongly around filament axes than a randomly distributed sample would do (as confirmed by a Kolmogorov-Smirnov test), but the clustering signal is less pronounced than for the galaxies in the filaments.
We investigate whether the dust content of the circum-galactic medium (CGM) depends on the location of the quasar sightline with respect to the galaxy major-axis using 13 galaxy-Mg II absorber pairs (9-81 kpc distance) from the MusE GAs FLOw and Wind (MEGAFLOW) survey at 0.4 < z < 1.4. The dust content of the CGM is obtained from [Zn/Fe] using ultraviolet and visual echelle spectrograph data. When a direct measurement of [Zn/Fe] is unavailable, we estimate the dust depletion from a method that consists in solving for the depletion from multiple singly ionized ions (e.g. Mn II, Cr II, and Zn II) since each ion depletes on dust grains at different rates. We find a positive correlation between the azimuthal angle and [Zn/Fe] with a Pearson's gamma = 0.70 +/- 0.14. The sightlines along the major axis show [Zn/Fe] < 0.5, whereas the [Zn/Fe] is > 0.8 along the minor axis. These results suggest that the CGM along the minor axis is on average more metal enriched (by approximate to 1 dex) than the gas located along the major axis of galaxies provided that dust depletion is a proxy for metallicity. This anisotropic distribution is consistent with recent results on outflow and accretion in hydro-dynamical simulations.
Medientechnisches Wissen
(2020)
Das mehrbändige Lehrbuch vermittelt Studierenden und Medienwissenschaftlern eine Einführung aus den Naturwissenschaften, Ingenieurwissenschaften und Technik-Disziplinen. Dabei steht im Zentrum, die Lesekompetenz für die jeweilige Disziplin zu etablieren und zu verbessern, damit innerhalb medien- und kulturwissenschaftlicher Studienprogramme Fachtexte der einzelnen Disziplinen diskutiert werden können
We present results from our on-going MusE GAs FLOw and Wind (MEGAFLOW) survey, which consists of 22 quasar lines of sight, each observed with the integral field unit MUSE and the UVES spectrograph at the ESO Very Large Telescopes (VLT). The goals of this survey are to study the properties of the circumgalactic medium around z similar to 1 star-forming galaxies. The absorption-line selected survey consists of 79 strong MgII absorbers (with rest-frame equivalent width greater than or similar to 0.3 angstrom) and, currently, 86 associated galaxies within 100 projected kpc of the quasar with stellar masses (M-star) from 109 to 1011 M-circle dot. We find that the cool halo gas traced by MgII is not isotropically distributed around these galaxies from the strong bi-modal distribution in the azimuthal angle of the apparent location of the quasar with respect to the galaxy major axis. This supports a scenario in which outflows are bi-conical in nature and co-exist with a co-planar gaseous structure extending at least up to 60-80 kpc. Assuming that absorbers near the minor axis probe outflows, the current MEGAFLOW sample allowed us to select 26 galaxy-quasar pairs suitable for studying winds. From this sample, using a simple geometrical model, we find that the outflow velocity only exceeds the escape velocity when M-star less than or similar to 4 x 10(9) M-circle dot, implying the cool material is likely to fall back except in the smallest haloes. Finally, we find that the mass loading factor., the ratio between the ejected mass rate and the star formation rate, appears to be roughly constant with respect to the galaxy mass.
We utilise multi-epoch MUSE spectroscopy to study binary stars in the core of the Galactic globular cluster NGC 3201. Our sample consists of 3553 stars with 54 883 spectra in total comprising 3200 main-sequence stars up to 4 magnitudes below the turn-off. Each star in our sample has between 3 and 63 (with a median of 14) reliable radial velocity measurements within five years of observations. We introduce a statistical method to determine the probability of a star showing radial velocity variations based on the whole inhomogeneous radial velocity sample. Using HST photometry and an advanced dynamical MOCCA simulation of this specific cluster we overcome observational biases that previous spectroscopic studies had to deal with. This allows us to infer a binary frequency in the MUSE field of view and enables us to deduce the underlying true binary frequency of (6.75 +/- 0.72)% in NGC 3201. The comparison of the MUSE observations with the MOCCA simulation suggests a large portion of primordial binaries. We can also confirm a radial increase in the binary fraction towards the cluster centre due to mass segregation. We discovered that in the core of NGC 3201 at least (57.5 +/- 7.9)% of blue straggler stars are in a binary system. For the first time in a study of globular clusters, we were able to fit Keplerian orbits to a significant sample of 95 binaries. We present the binary system properties of eleven blue straggler stars and the connection to SX Phoenicis-type stars. We show evidence that two blue straggler formation scenarios, the mass transfer in binary (or triple) star systems and the coalescence due to binary-binary interactions, are present in our data. We also describe the binary and spectroscopic properties of four sub-subgiant (or red straggler) stars. Furthermore, we discovered two new black hole candidates with minimum masses (M sin i) of (7.68 +/- 0.50)M-circle dot, (4.4 +/- 2.8)M-circle dot, and refine the minimum mass estimate on the already published black hole to (4.53 +/- 0.21)M-circle dot, These black holes are consistent with an extensive black hole subsystem hosted by NGC 3201.
Context. Galactic globular clusters (GCs) are now known to host multiple populations displaying particular abundance variations. The different populations within a GC can be well distinguished following their position in the pseudo two-colors diagrams, also referred to as "chromosome maps". These maps are constructed using optical and near-UV photometry available from the Hubble Space Telescope (HST) UV survey of GCs. However, the chemical tagging of the various populations in the chromosome maps is hampered by the fact that HST photometry and elemental abundances are both only available for a limited number of stars. Aims. The spectra collected as part of the MUSE survey of globular clusters provide a spectroscopic counterpart to the HST photometric catalogs covering the central regions of GCs. In this paper, we use the MUSE spectra of 1115 red giant branch (RGB) stars in NGC 2808 to characterize the abundance variations seen in the multiple populations of this cluster. Methods. We used the chromosome map of NGC 2808 to divide the RGB stars into their respective populations. We then combined the spectra of all stars belonging to a given population, resulting in one high signal-to-noise ratio spectrum representative of each population. Results. Variations in the spectral lines of O, Na, Mg, and Al are clearly detected among four of the populations. In order to quantify these variations, we measured equivalent width differences and created synthetic populations spectra that were used to determine abundance variations with respect to the primordial population of the cluster. Our results are in good agreement with the values expected from previous studies based on high-resolution spectroscopy. We do not see any significant variations in the spectral lines of Ca, K, and Ba. We also do not detect abundance variations among the stars belonging to the primordial population of NGC 2808. Conclusions. We demonstrate that in spite of their low resolution, the MUSE spectra can be used to investigate abundance variations in the context of multiple populations.
A nova is a cataclysmic event on the surface of a white dwarf in a binary system that increases the overall brightness by several orders of magnitude. Although binary systems with a white dwarf are expected to be overabundant in globular clusters compared with in the Galaxy, only two novae from Galactic globular clusters have been observed. We present the discovery of an emission nebula in the Galactic globular cluster M 22 (NGC 6656) in observations made with the integral-field spectrograph MUSE. We extracted the spectrum of the nebula and used the radial velocity determined from the emission lines to confirm that the nebula is part of NGC 6656. Emission-line ratios were used to determine the electron temperature and density. It is estimated to have a mass of 1-17 x 10(-5) M-circle dot. This mass and the emission-line ratios indicate that the nebula is a nova remnant. Its position coincides with the reported location of a "guest star", an ancient Chinese term for transients, observed in May 48 BCE. With this discovery, this nova may be one of the oldest confirmed extra-solar events recorded in human history.
A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources
(2019)
Aims. Globular clusters produce many exotic stars due to a much higher frequency of dynamical interactions in their dense stellar environments. Some of these objects were observed together with several hundred thousand other stars in our MUSE survey of 26 Galactic globular clusters. Assuming that at least a few exotic stars have exotic spectra (i.e. spectra that contain emission lines), we can use this large spectroscopic data set of over a million stellar spectra as a blind survey to detect stellar exotica in globular clusters. Methods. To detect emission lines in each spectrum, we modelled the expected shape of an emission line as a Gaussian curve. This template was used for matched filtering on the di fferences between each observed 1D spectrum and its fitted spectral model. The spectra with the most significant detections of H alpha emission are checked visually and cross-matched with published catalogues. Results. We find 156 stars with H alpha emission, including several known cataclysmic variables (CV) and two new CVs, pulsating variable stars, eclipsing binary stars, the optical counterpart of a known black hole, several probable sub-subgiants and red stragglers, and 21 background emission-line galaxies. We find possible optical counterparts to 39 X-ray sources, as we detected H alpha emission in several spectra of stars that are close to known positions of Chandra X-ray sources. This spectral catalogue can be used to supplement existing or future X-ray or radio observations with spectra of potential optical counterparts to classify the sources.
This paper presents a study of the galactic environment of a chemically pristine (<0.6 per cent solar metallicity) Lyman Limit system (LLS) discovered along the sightline towards QSO SDSSJ 135726.27+043541.4 (Z(QSO) = 1.233) at projected distance d = 126 physical kpc (pkpc) from a luminous red galaxy (LRG) at z = 0.33. Combining deep Hubble Space Telescope images, MUSE integral field spectroscopic data, and wide-field redshift survey data has enabled an unprecedented, ultradeep view of the environment around this LRG-LLS pair. A total of 12 galaxies, including the LRG, are found at d less than or similar to 400 pkpc and line-of-sight velocity Delta v < 600 km S-1 of the LLS, with intrinsic luminosity ranging from 0.001 L-* to 2 L-* and a corresponding stellar mass range of M-star approximate to 10(7-11) M-circle dot. All 12 galaxies contribute to a total mass of M-star = 1.6 x 10(11) M-circle dot with approximate to 80 per cent contained in the LRG. The line-of-sight velocity dispersion of these galaxies is found to be sigma (group) = 230 km s(-1) with the centre of mass at d(group) = 118 pkpc and line-of-sight velocity offset of Delta v(group) = 181 km s(-1) from the LLS. Three of these are located at d less than or similar to 100 pkpc from the LLS, and they are all faint with intrinsic luminosity less than or similar to 0.02 L-* and gas-phase metallicity of approximate to 10 per cent solar in their interstellar medium. The disparity in the chemical enrichment level between the LLS and the group members suggests that the LLS originates in infalling intergalactic medium and that parts of the intergalactic gas near old and massive galaxies can still remain chemically pristine through the not too distant past.
We use the MusE GAs FLOw and Wind (MEGAFLOW) survey to study the kinematics of extended disc-like structures of cold gas around z approximate to 1 star-forming galaxies. The combination of VLT/MUSE and VLT/UVES observations allows us to connect the kinematics of the gas measured through MgII quasar absorption spectroscopy to the kinematics and orientation of the associated galaxies constrained through integral field spectroscopy. Confirming previous results, we find that the galaxy-absorber pairs of the MEGAFLOW survey follow a strong bimodal distribution, consistent with a picture of MgII absorption being predominantly present in outflow cones and extended disc-like structures. This allows us to select a bona-fide sample of galaxy-absorber pairs probing these discs for impact paramometers of 10-70 kpc. We test the hypothesis that the disc-like gas is co-rotating with the galaxy discs, and find that for seven out of nine pairs the absorption velocity shares the sign of the disc velocity, disfavouring random orbits. We further show that the data are roughly consistent with inflow velocities and angular momenta predicted by simulations, and that the corresponding mass accretion rates are sufficient to balance the star formation rates.