Multi Unit Spectroscopic Explorer Research Articles

AlFoCS + F3D – II. Unexpectedly low gas-to-dust ratios in the Fornax galaxy cluster

ABSTRACT We combine observations from Atacama Large Millimeter/submillimeter Array (ALMA), Australia Telescope Compact Array, Multi Unit Spectroscopic Explorer (MUSE), and Herschel to study gas-to-dust ratios in 15 Fornax cluster galaxies detected in the FIR/sub-mm by Herschel and observed by ALMA as part of the ALMA Fornax Cluster Survey. The sample spans a stellar mass range of 8.3 ≤ log(M⋆/M⊙) ≤ 11.16, and a variety of morphological types. We use gas-phase metallicities derived from MUSE observations (from the Fornax3D survey) to study these ratios as a function of metallicity, and to study dust-to-metal ratios, in a sub-sample of nine galaxies. We find that gas-to-dust ratios in Fornax galaxies are systematically lower than those in field galaxies at fixed stellar mass/metallicity. This implies that a relatively large fraction of the metals in these Fornax systems is locked up in dust, which is possibly due to altered chemical evolution as a result of the dense environment. The low ratios are not only driven by H i deficiencies, but H2-to-dust ratios are also significantly decreased. This is different in the Virgo cluster, where low gas-to-dust ratios inside the virial radius are driven by low H i-to-dust ratios, while H2-to-dust ratios are increased. Resolved observations of NGC 1436 show a radial increase in H2-to-dust ratio, and show that low ratios are present throughout the disc. We propose various explanations for the low H2-to-dust ratios in the Fornax cluster, including the more efficient stripping of H2 compared to dust, more efficient enrichment of dust in the star formation process, and altered interstellar medium physics in the cluster environment.

An atlas of MUSE observations towards twelve massive lensing clusters

Context. Spectroscopic surveys of massive galaxy clusters reveal the properties of faint background galaxies thanks to the magnification provided by strong gravitational lensing. Aims. We present a systematic analysis of integral-field-spectroscopy observations of 12 massive clusters, conducted with the Multi Unit Spectroscopic Explorer (MUSE). All data were taken under very good seeing conditions (∼0″​​.6) in effective exposure times between two and 15 h per pointing, for a total of 125 h. Our observations cover a total solid angle of ∼23 arcmin2 in the direction of clusters, many of which were previously studied by the MAssive Clusters Survey, Frontier Fields (FFs), Grism Lens-Amplified Survey from Space and Cluster Lensing And Supernova survey with Hubble programmes. The achieved emission line detection limit at 5σ for a point source varies between (0.77–1.5) × 10−18 erg s−1 cm−2 at 7000 Å. Methods. We present our developed strategy to reduce these observational data, detect continuum sources and line emitters in the datacubes, and determine their redshifts. We constructed robust mass models for each cluster to further confirm our redshift measurements using strong-lensing constraints, and identified a total of 312 strongly lensed sources producing 939 multiple images. Results. The final redshift catalogues contain more than 3300 robust redshifts, of which 40% are for cluster members and ∼30% are for lensed Lyman-α emitters. Fourteen percent of all sources are line emitters that are not seen in the available HST images, even at the depth of the FFs (∼29 AB). We find that the magnification distribution of the lensed sources in the high-magnification regime (μ = 2–25) follows the theoretical expectation of N(z) ∝ μ−2. The quality of this dataset, number of lensed sources, and number of strong-lensing constraints enables detailed studies of the physical properties of both the lensing cluster and the background galaxies. The full data products from this work, including the datacubes, catalogues, extracted spectra, ancillary images, and mass models, are made available to the community.

ALMA Lensing Cluster Survey: An ALMA Galaxy Signposting a MUSE Galaxy Group at z = 4.3 Behind “El Gordo”

Abstract We report the discovery of a Multi Unit Spectroscopic Explorer (MUSE) galaxy group at z = 4.32 lensed by the massive galaxy cluster ACT-CL J0102-4915 (aka El Gordo) at z = 0.87, associated with a 1.2 mm source that is at a 2.07 ± 0.88 kpc projected distance from one of the group galaxies. Three images of the whole system appear in the image plane. The 1.2 mm source has been detected within the Atacama Large Millimetre/submillimetre Array (ALMA) Lensing Cluster Survey (ALCS). As this ALMA source is undetected at wavelengths λ < 2 μm, its redshift cannot be independently determined, however, the three lensing components indicate that it belongs to the same galaxy group at z = 4.32. The four members of the MUSE galaxy group have low to intermediate stellar masses (∼107–1010 M ⊙) and star formation rates (SFRs) of 0.4–24 M ⊙ yr−1, resulting in high specific SFRs (sSFRs) for two of them, which suggest that these galaxies are growing fast (with stellar mass doubling times of only ∼2 × 107 yr). This high incidence of starburst galaxies is likely a consequence of interactions within the galaxy group, which is compact and has high velocity dispersion. Based on the magnification-corrected sub-/millimeter continuum flux density and estimated stellar mass, we infer that the ALMA source is classified as an ordinary ultra-luminous infrared galaxy (with associated dust-obscured SFR ∼ 200–300 M ⊙ yr−1) and lies on the star formation main sequence. This reported case of an ALMA/MUSE group association suggests that some presumably isolated ALMA sources are in fact signposts of richer star-forming environments at high redshifts.

Spectral Shapes of the Lyα Emission from Galaxies. I. Blueshifted Emission and Intrinsic Invariance with Redshift*

Abstract We demonstrate the redshift evolution of the spectral profile of H i Lyα emission from star-forming galaxies. In this first study we pay special attention to the contribution of blueshifted emission. At redshift z = 2.9–6.6, we compile spectra of a sample of 229 Lyα-selected galaxies identified with the Multi-Unit Spectroscopic Explorer at the Very Large Telescope, while at low z ( < 0.44) we use a sample of 74 ultraviolet-selected galaxies observed with the Cosmic Origin Spectrograph on board the Hubble Space Telescope. At low z, where absorption from the intergalactic medium (IGM) is negligible, we show that the ratio of Lyα luminosity blueward and redward of line center (L B/R) increases rapidly with increasing equivalent width (W Lyα ). This correlation does not, however, emerge at z = 3–4, and we use bootstrap simulations to demonstrate that trends in L B/R should be suppressed by variations in IGM absorption. Our main result is that the observed blueshifted contribution evolves rapidly downward with increasing redshift: L B/R ≈ 30% at z ≈ 0, but dropping to 15% at z ≈ 3, and to below 3% by z ≈ 6. Applying further simulations of the IGM absorption to the unabsorbed COS spectrum, we demonstrate that this decrease in the blue-wing contribution can be entirely attributed to the thickening of intervening Lyα absorbing systems, with no need for additional H i opacity from local structure, companion galaxies, or cosmic infall. We discuss our results in light of the numerical radiative transfer simulations, the evolving total Lyα and ionizing output of galaxies, and the utility of resolved Lyα spectra in the reionization epoch.

Heavy Elements Unveil the Non-primordial Origin of the Giant H I Ring in Leo

Abstract The origin and fate of the most extended extragalactic neutral cloud known in the local universe, the Leo ring, is still debated 38 yr after its discovery. Its existence is alternatively attributed to leftover primordial gas with some low level of metal pollution versus enriched gas stripped during a galaxy−galaxy encounter. Taking advantage of Multi Unit Spectroscopic Explorer operating at the Very Large Telescope, we performed optical integral field spectroscopy of three H I clumps in the Leo ring where ultraviolet continuum emission has been found. We detected, for the first time, ionized hydrogen in the ring and identify four nebular regions powered by massive stars. These nebulae show several metal lines ([O III], [N II], [S II]) that allowed reliable measures of metallicities, found to be close to or above the solar value (0.8 ≤ Z/Z ⊙ ≤ 1.4). Given the faintness of the diffuse stellar counterparts, less than 3% of the observed heavy elements could have been produced locally in the main body of the ring and not much more than 15% in the H I clump toward M96. This inference, and the chemical homogeneity among the regions, convincingly demonstrates that the gas in the ring is not primordial, but has been pre-enriched in a galaxy disk, then later removed and shaped by tidal forces and it is forming a sparse population of stars.

Tracing the simulated high-redshift circum-galactic medium with Lyman α emission

Abstract With the Multi Unit Spectroscopic Explorer (MUSE), it is now possible to detect spatially extended Lyman α (Lyα) emission from individual faint (MUV ∼ −18) galaxies at redshifts, 3 < z < 6, tracing gas out to circum-galactic scales. To explore the implications of such observations, we present a cosmological radiation hydrodynamics simulation of a single galaxy, chosen to be typical of the Lyα-emitting galaxies detected by MUSE in deep fields. We use this simulation to study the origin and dynamics of the high-redshift circum-galactic medium (CGM). We find that the majority of the mass in the diffuse CGM is comprised of material infalling for the first time towards the halo center, but with the inner CGM also containing a comparable amount of mass that has moved past first-pericentric passage, and is in the process of settling into a rotationally supported configuration. Making the connection to Lyα emission, we find that the observed extended surface brightness profile is due to a combination of three components: scattering of galactic Lyα emission in the CGM, in-situ emission of CGM gas (mostly infalling), and Lyα emission from small satellite galaxies. The weight of these contributions vary with distance from the galaxy such that (1) scattering dominates the inner regions (r < 7 kpc), at surface brightness larger than a few 10−19 cgs, (2) all components contribute equally around r ∼ 10 kpc (or SB∼10−19), and (3) the contribution of small satellite galaxies takes over at large distances (or SB∼10−20).

The MAGPI survey: Science goals, design, observing strategy, early results and theoretical framework

AbstractWe present an overview of theMiddleAgesGalaxyProperties withIntegral Field Spectroscopy (MAGPI) survey, a Large Program on the European Southern Observatory Very Large Telescope. MAGPI is designed to study the physical drivers of galaxy transformation at a lookback time of 3–4 Gyr, during which the dynamical, morphological, and chemical properties of galaxies are predicted to evolve significantly. The survey uses new medium-deep adaptive optics aided Multi-Unit Spectroscopic Explorer (MUSE) observations of fields selected from the Galaxy and Mass Assembly (GAMA) survey, providing a wealth of publicly available ancillary multi-wavelength data. With these data, MAGPI will map the kinematic and chemical properties of stars and ionised gas for a sample of 60 massive (${>}7 \times 10^{10} {\mathrm{M}}_\odot$) central galaxies at$0.25 < z <0.35$in a representative range of environments (isolated, groups and clusters). The spatial resolution delivered by MUSE with Ground Layer Adaptive Optics ($0.6-0.8$arcsec FWHM) will facilitate a direct comparison with Integral Field Spectroscopy surveys of the nearby Universe, such as SAMI and MaNGA, and at higher redshifts using adaptive optics, for example, SINS. In addition to the primary (central) galaxy sample, MAGPI will deliver resolved and unresolved spectra for as many as 150 satellite galaxies at$0.25 < z <0.35$, as well as hundreds of emission-line sources at$z < 6$. This paper outlines the science goals, survey design, and observing strategy of MAGPI. We also present a first look at the MAGPI data, and the theoretical framework to which MAGPI data will be compared using the current generation of cosmological hydrodynamical simulations includingEAGLE,Magneticum,HORIZON-AGN, andIllustris-TNG. Our results show that cosmological hydrodynamical simulations make discrepant predictions in the spatially resolved properties of galaxies at$z\approx 0.3$. MAGPI observations will place new constraints and allow for tangible improvements in galaxy formation theory.

Latitudinal variation of methane mole fraction above clouds in Neptune's atmosphere from VLT/MUSE-NFM: Limb-darkening reanalysis

We present a reanalysis of visible/near-infrared (480–930 nm) observations of Neptune, made in 2018 with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope (VLT) in Narrow Field Adaptive Optics mode, reported by Irwin et al., Icarus, 311, 2019. We find that the inferred variation of methane abundance with latitude in our previous analysis, which was based on central meridian observations only, underestimated the retrieval errors when compared with a more complete assessment of Neptune's limb darkening. In addition, our previous analysis introduced spurious latitudinal variability of both the abundance and its uncertainty, which we reassess here. Our reanalysis of these data incorporates the effects of limb-darkening based upon the Minnaert approximation model, which provides a much stronger constraint on the cloud structure and methane mole fraction, makes better use of the available data and is also more computationally efficient. We find that away from discrete cloud features, the observed reflectivity spectrum from 800 to 900 nm is very well approximated by a background cloud model that is latitudinally varying, but zonally symmetric, consisting of a H2S cloud layer, based at 3.6–4.7 bar with variable opacity and scale height, and a stratospheric haze. The background cloud model matches the observed limb darkening seen at all wavelengths and latitudes and we find that the mole fraction of methane at 2–4 bar, above the H2S cloud, but below the methane condensation level, varies from 4–---6% at the equator to 2–4% at south polar latitudes, consistent with previous analyses, with a equator/pole ratio of 1.9 ± 0.2 for our assumed cloud/methane vertical distribution model. The spectra of discrete cloudy regions are fitted, to a very good approximation, by the addition of a single vertically thin methane ice cloud with opacity ranging from 0 to 0.75 and pressure less than ~0.4 bar.

MUSE observations towards the lensing cluster A2744: Intersection between the LBG and LAE populations at z ∼ 3–7

We present a study of the intersection between the populations of star forming galaxies selected as either Lyman break galaxies (LBGs) or Lyman-alpha emitters (LAEs) in the redshift range 2.9 − 6.7 and within the same volume of universe sampled by the Multi-Unit Spectroscopic Explorer (MUSE) behind the Hubble Frontier Fields lensing cluster A2744. We define three samples of star-forming galaxies: LBG galaxies with an LAE counterpart (92 galaxies), LBG galaxies without an LAE counterpart (408 galaxies), and LAE galaxies without an LBG counterpart (46 galaxies). All these galaxies are intrinsically faint because of the lensing nature of the sample (M1500 ≥ −20.5). The fraction of LAEs among all selected star-forming galaxies increases with redshift up to z ∼ 6 and decreases for higher redshifts, in agreement with previous findings. The evolution of LAE/LBG populations with UV magnitude and Lyα luminosity shows that the LAE selection is able to identify intrinsically UV faint galaxies with M1500 ≥ −15 that are typically missed in the deepest lensing photometric surveys. The LBG population seems to fairly represent the total population of star-forming galaxies down to M1500 ∼ −15. Galaxies with M1500 < −17 tend to have SFRLyα < SFRuv, whereas the opposite trend is observed within our sample for faint galaxies with M1500 > −17, including galaxies only detected by their Lyα emission, with a large scatter. These trends, previously observed in other samples of star-forming galaxies at high-z, are seen here for very faint M1500 ∼ −15 galaxies; that is, much fainter than in previous studies. The present results show no clear evidence for an intrinsic difference between the properties of the two populations selected as LBG and/or LAE. The observed trends could be explained by a combination of several phenomena, like the existence of different star-formation regimes, the dust content, the relative distribution and morphology of dust and stars, or the stellar populations.

Dust and gas in the central region of NGC 1316 (Fornax A)

Context. The early-type galaxy NGC 1316, associated with the radio source Fornax A, hosts about 107 M⊙ of dust within a central radius of 5 kpc. These prominent dust structures are believed to have an external origin, which is also a popular interpretation for other dusty early-type galaxies. Moreover, it has been long known that ionised gas is present in NGC 1316, but to date there has been a lack of detailed investigation. Aims. Our aim is to understand the nature of ionised gas and dust in NGC 1316 and to offer an interpretation for the origin of the dust. Methods. We use archival Hubble Space Telescope/Advanced Camera for Surveys data to construct colour maps that delineate the dust pattern in detail, and we compare these data with maps constructed with data from the Multi Unit Spectroscopic Explorer (MUSE) instrument of the Very Large Telescope at the European Southern Observatory. Twelve MUSE pointings in wide field mode form a mosaic of the central 3.3 × 2.4 arcmin2. We use the tool PyParadise to fit the stellar population. We use the residual emission lines and the residual interstellar absorption NaI D-lines, and we measure line strengths, the velocity field, and the velocity dispersion field. Results. The emission lines resemble low-ionisation nuclear emission-line region lines, with [NII] being the strongest line everywhere. Ionising sources are plausibly the post-asymptotic giant branch stars of the old or intermediate-age stellar population. There is a striking match between the dust structures, ionised gas, and atomic gas distributions, the last of which is manifested by interstellar absorption residuals of the stellar NaI D-lines. In the dust-free regions, the interstellar NaI D-lines appear in emission, which is indicative of a galactic wind. The velocity field of the ionised gas (and thus of the dust) is characterised by small-scale turbulent movements that indicate short lifetimes. At the very centre, a bipolar velocity field of the ionised gas is observed, which we interpret as an outflow. The low-velocity part is associated with dust. We identify a strongly inclined gaseous dusty disc along the major axis of NGC 1316. A straight beam of ionised gas with a length of about 4 kpc emanates from the centre. Conclusions. The dust in NGC 1316 has different origins. Our findings are strongly suggestive of a dusty outflow that is curved along the line-of-sight. Nuclear outflows may be important dust-producing machines in galaxies. Another dusty gaseous component forms a disc that we identify as the predecessor of a central dust lane.

Joint estimation of atmospheric and instrumental defects using a parsimonious point spread function model

Context. Modeling the optical point spread function (PSF) is particularly challenging for adaptive optics (AO)-assisted observations owing to the its complex shape and spatial variations. Aims. We aim to (i) exhaustively demonstrate the accuracy of a recent analytical model from comparison with a large sample of imaged PSFs, (ii) assess the conditions for which the model is optimal, and (iii) unleash the strength of this framework to enable the joint estimation of atmospheric parameters, AO performance and static aberrations. Methods. We gathered 4812 on-sky PSFs obtained from seven AO systems and used the same fitting algorithm to test the model on various AO PSFs and diagnose AO performance from the model outputs. Finally, we highlight how this framework enables the characterization of the so-called low wind effect on the Spectro-Polarimetic High contrast imager for Exoplanets REsearch (LWE; SPHERE) instrument and piston cophasing errors on the Keck II telescope. Results. Over 4812 PSFs, the model reaches down to 4% of error on both the Strehl-ratio (SR) and full width at half maximum (FWHM). We particularly illustrate that the estimation of the Fried’s parameter, which is one of the model parameters, is consistent with known seeing statistics and follows expected trends in wavelength using the Multi Unit Spectroscopic Explorer instrument (λ6/5) and field (no variations) from Gemini South Adaptive Optics Imager images with a standard deviation of 0.4 cm. Finally, we show that we can retrieve a combination of differential piston, tip, and tilt modes introduced by the LWE that compares to ZELDA measurements, as well as segment piston errors from the Keck II telescope and particularly the stair mode that has already been revealed from previous studies. Conclusions. This model matches all types of AO PSFs at the level of 4% error and can be used for AO diagnosis, post-processing, and wavefront sensing purposes.

Faint LAEs near z > 4.7 C iv absorbers revealed by MUSE

ABSTRACT We present the results from the search for Lyman alpha emitters (LAEs) in the proximity of 11 C iv absorption systems at z > 4.7 in the spectrum of the QSO J1030+0524, using data from Multi-Unit Spectroscopic Explorer. We have found multiple LAE candidates close to four C iv systems at $z_{{\rm{C {\small IV}}}}=4.94$–5.74 with $\log _{10}(N_{{\rm{C {\small IV}}}}[$cm−2]) > 13.5. At z = 5–6, C iv systems with W$_0({\rm{C {\small IV}}})\gt 0.2$ Å seem more likely to have galaxies with Ly α emission within ρ < 200 proper kpc (4/5 cases) than the C iv systems with W$_0({\rm{C {\small IV}}})\lt 0.2$ Å (0/6 cases). The impact parameter of LAE–C iv systems with equivalent widths W0(C iv) > 0.5 Å is in the range $11\, \lesssim \, \rho \, \lesssim \, 200$ proper kpc (pkpc). Furthermore, all candidates are in the luminosity range 0.18–1.15 L$^{\star }_{\rm{{Ly\alpha}}}(z=5.7)$, indicating that the environment of C iv systems within 200 pkpc is populated by the faint end of the Ly α luminosity function. We report a 0.28 L$^{\star }_{\rm{{Ly\alpha}}}$ galaxy at a separation of ρ = 11 pkpc from a strong C iv absorption ($\log _{10}(N_{{\rm{C {\small IV}}}}[$cm−2]) = 14.52) at $z_{{\rm{C {\small IV}}}}=5.72419$. The prevalence of sub-L$^{\star }_{\rm{{Ly\alpha}}}$ galaxies in the proximity of z > 4.9 C iv systems suggest that the absorbing material is rather young, likely ejected in the recent past of the identified galaxies. The connection between faint LAEs and high-ionization absorption systems reported in this work is potentially a consequence of the role of low-mass galaxies in the early evolution of the circum-galactic and intergalactic media.

Wolf–Rayet stars in the Antennae unveiled by MUSE

ABSTRACT We present the analysis of archival Very Large Telescope (VLT) Multi-Unit Spectroscopic Explorer (MUSE) observations of the interacting galaxies NGC 4038/39 (a.k.a. the Antennae) at a distance of 18.1 Mpc. Up to 38 young star-forming complexes with evident contribution from Wolf–Rayet (WR) stars are unveiled. We use publicly available templates of Galactic WR stars in conjunction with available photometric extinction measurements to quantify and classify the WR population in each star-forming region, on the basis of its nearly Solar oxygen abundance. The total estimated number of WR stars in the Antennae is 4053 ± 84, of which there are 2021 ± 60 WNL and 2032 ± 59 WC-types. Our analysis suggests a global WC to WN-type ratio of 1.01 ± 0.04, which is consistent with the predictions of the single star evolutionary scenario in the most recent bpass stellar population synthesis models.

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Constraining the Molecular Content at log(M*/M⊙) ∼ 9.5 with CO Stacking of MUSE-detected z ∼ 1.5 Galaxies

Abstract We report molecular gas mass estimates obtained from a stacking analysis of CO line emission in the ALMA Spectroscopic Survey (ASPECS) using the spectroscopic redshifts from the optical integral field spectroscopic survey by the Multi Unit Spectroscopic Explorer (MUSE) of the Hubble Ultra Deep Field (HUDF). Stacking was performed on subsets of the sample of galaxies classified by their stellar mass and position relative to the main-sequence relation (on, above, below). Among all the CO emission lines, from CO(2–1) to CO(6–5), with redshifts accessible via the ASPECS Band 3 and the MUSE data, CO(2–1) provides the strongest constraints on the molecular gas content. We detect CO(2–1) emission in galaxies down to stellar masses of . Below this stellar mass, we present a new constraint on the molecular gas content of main-sequence galaxies by stacking based on the MUSE detections. We find that the molecular gas mass of main-sequence galaxies continuously decreases with stellar mass down to . Assuming a metallicity-based CO–to–H 2 conversion factor, the molecular gas-to-stellar mass ratio from to ∼10.0 does not seem to decrease as fast as for , which is in line with simulations and studies at lower redshift. The inferred molecular gas density of MUSE-selected galaxies at is comparable with the one derived in the HUDF with a different CO selection. Using the MUSE data we recover most of the CO emission in our deep ALMA observations through stacking, demonstrating the synergy between volumetric surveys obtained at different wave bands.

The Ionized- and Cool-gas Content of the BR1202−0725 System as Seen by MUSE and ALMA

Abstract We present Multi Unit Spectroscopic Explorer (MUSE) observations of the gas-rich major merger BR1202−0725 at z ∼ 4.7, which constitutes one of the most overdense fields known in the early universe. We utilize these data in conjunction with existing Atacama Large Millimeter/submillimeter Array (ALMA) observations to compare and contrast the spatially resolved ionized- and cool-gas content of this system, which hosts a quasar (QSO), a submillimeter galaxy (SMG), the two known optical companion Lyα emitters (“LAE 1” and “LAE 2”), and an additional companion discovered in this work “LAE 3” just 5″ to the north of the QSO. We find that QSO BR1202−0725 exhibits a large Lyα halo, covering ≈55 pkpc on-sky at surface-brightness levels of SB ≥ 1 × 10−17 erg s−1 cm−2 arcsec−2. In contrast, the SMG, of similar far-infrared luminosity and star formation rate (SFR), does not exhibit such a Lyα halo. The QSO’s halo exhibits high velocity widths (∼1000 km s−1) but the gas motion is to some extent kinematically coupled with the previously observed [C ii] bridge between the QSO and the SMG. We note that the object known in the literature as LAE 2 shows no local peak of Lyα emission, rather, its profile is more consistent with being part of the QSO’s extended Lyα halo. The properties of LAE 3 are typical of high-redshift LAEs; we measure F Lyα (LAE 3) = 0.24 ± 0.03 × 10−16 erg s−1 cm−2, corresponding to SFRLyα ≈ 5.0 ± 0.5 M ⊙ yr−1. The velocity width is Δv(LAE 3) ≈ 400 km s−1, and the equivalent width is EW0( Å, consistent with star formation being the primary driver of Lyα emission. We also note a coherent absorption feature at ∼−400 km s−1 in spectra from at least three objects; the QSO, LAE 1, and LAE 2, which could imply the presence of an expanding neutral gas shell with an extent of at least 24 pkpc.

Leveraging HST with MUSE – I. Sodium abundance variations within the 2-Gyr-old cluster NGC 1978

ABSTRACT Nearly all of the well-studied ancient globular clusters (GCs), in the Milky Way and in nearby galaxies, show star-to-star variations in specific elements (e.g. He, C, N, O, Na, and Al), known as ‘multiple populations’ (MPs). However, MPs are not restricted to ancient clusters, with massive clusters down to ∼2 Gyr showing signs of chemical variations. This suggests that young and old clusters share the same formation mechanism but most of the work to date on younger clusters has focused on N variations. Initial studies even suggested that younger clusters may not host spreads in other elements beyond N (e.g. Na), calling into question whether these abundance variations share the same origin as in the older GCs. In this work, we combine Hubble Space Telescope (HST) photometry with Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy of a large sample of red giant branch (RGB) stars (338) in the Large Magellanic Cloud cluster NGC 1978, the youngest globular to date with reported MPs in the form of N spreads. By combining the spectra of individual RGB stars into N-normal and N-enhanced samples, based on the ‘chromosome map’ derived from HST, we search for mean abundance variations. Based on the NaD line, we find a Na difference of Δ[Na/Fe] = 0.07 ± 0.01 between the populations. While this difference is smaller than typically found in ancient GCs (which may suggest a correlation with age), this result further confirms that the MP phenomenon is the same, regardless of cluster age and host galaxy. As such, these young clusters offer some of the strictest tests for theories on the origin of MPs.

The data processing pipeline for the MUSE instrument

The processing of raw data from modern astronomical instruments is often carried out nowadays using dedicated software, known as pipelines, largely run in automated operation. In this paper we describe the data reduction pipeline of the Multi Unit Spectroscopic Explorer (MUSE) integral field spectrograph operated at the ESO Paranal Observatory. This spectrograph is a complex machine: it records data of 1152 separate spatial elements on detectors in its 24 integral field units. Efficiently handling such data requires sophisticated software with a high degree of automation and parallelization. We describe the algorithms of all processing steps that operate on calibrations and science data in detail, and explain how the raw science data is transformed into calibrated datacubes. We finally check the quality of selected procedures and output data products, and demonstrate that the pipeline provides datacubes ready for scientific analysis.

Lyα Radiative Transfer: Modeling Spectrum and Surface Brightness Profiles of Lyα-emitting Galaxies at Z = 3–6

Abstract We perform Lyα radiative transfer calculations to reproduce the Lyα properties of star-forming galaxies at high redshifts. We model a galaxy as a halo in which the density distributions of Lyα sources and H i plus dust medium are described with exponential functions. We also consider an outflow of the medium that represents a momentum-driven wind in a gravitational potential well. We successfully reproduce both the spectra and the surface brightness profiles of eight star-forming galaxies at z = 3–6 observed with the Multi-Unit Spectroscopic Explorer using this outflowing-halo model with Lyα scattering. The best-fit model parameters (i.e., the outflowing velocity and optical depth) for these galaxies are consistent with those in other studies. We examine the impacts of individual model parameters and input spectrum on the emerging spectrum and surface brightness profile. Further investigations of the correlations among observables (i.e., the spatial extent of Lyα halos and Lyα spectral features) and model parameters, and of spatially resolved spectra are presented as well. We demonstrate that the combination of spectrum and surface brightness profile provides strong constraints on model parameters and thus on the spatial/kinematic distributions of the medium.

Less than the sum of its parts: the dust-corrected H α luminosity of star-forming galaxies explored at different spatial resolutions with MaNGA and MUSE

ABSTRACT The H α and H β emission-line luminosities measured in a single integrated spectrum are affected in non-trivial ways by point-to-point variations in dust attenuation in a galaxy. This work investigates the impact of this variation when estimating global H α luminosities corrected for the presence of dust by a global Balmer decrement. Analytical arguments show that the dust-corrected H α luminosity is always underestimated when using the global H α/H β flux ratio to correct for dust attenuation. We measure this effect on 156 face-on star-forming galaxies from the Mapping Nearby Galaxies at APO (MaNGA) survey. At 1–2 kpc spatial resolution, the effect is small but systematic, with the integrated dust-corrected H α luminosity underestimated by 2–4 per cent (and typically not more than by 10 per cent), and depends on the specific star formation rate of the galaxy. Given the spatial resolution of MaNGA, these are lower limits for the effect. From Multi Unit Spectroscopic Explorer (MUSE) observations of NGC 628 with a resolution of 36 pc, we find the discrepancy between the globally and the point-by-point dust-corrected H α luminosity to be 14 ± 1 per cent, which may still underestimate the true effect. We use toy models and simulations to show that the true difference depends strongly on the spatial variance of the H α/H β flux ratio, and on the slope of the relation between H αluminosity and dust attenuation within a galaxy. Larger samples of higher spatial resolution observations are required to quantify the dependence of this effect as a function of galaxy properties.

Stellar populations and physical properties of starbursts in the antennae galaxy from self-consistent modelling of MUSE spectra

ABSTRACT We have modelled the stellar and nebular continua and emission-line intensity ratios of massive stellar populations in the Antennae galaxy using high resolution and self-consistent libraries of model H ii regions around central clusters of ageing stars. The model libraries are constructed using the stellar population synthesis code, starburst99, and photoionization model, and cloudy. The Geneva and PARSEC stellar evolutionary models are plugged into starburst99 to allow comparison between the two models. Using a spectrum-fitting methodology that allows the spectral features in the stellar and nebular continua [e.g. Wolf–Rayet (WR) features, Paschen jump], and emission-line diagnostics to constrain the models, we apply the libraries to the high-resolution Multi-Unit Spectroscopic Explorer spectra of the starbursting regions in the Antennae galaxy. Through this approach, we were able to model the continuum emission from WR stars and extract stellar and gas metallicities, ages, electron temperatures, and densities of starbursts by exploiting the full spectrum. From the application to the Antennae galaxy, we find that (1) the starbursts in the Antennae galaxy are characterized by stellar and gas metallicities of around solar, (2) the star-forming gas in starbursts in the Western loop of NGC 4038 appears to be more enriched, albeit slightly, than the rest of galaxy, (3) the youngest starbursts are found across the overlap region and over parts of the western-loop, though in comparison, the regions in the western-loop appear to be at a slightly later stage in star formation than the overlap region, and (4) the results obtained from fitting the Geneva and Parsec models are largely consistent.