arXiv subjects

R. Bacon

Publications and source records attributed to R. Bacon.

At least 19 recordsLinked to original sources

arXiv2026

Progress of the design of the 12-m optical, Wide-field Spectroscopic Telescope (WST)

The Wide-Field Spectroscopic Telescope (WST) is a 12-m class, Alt-Az optical telescope providing two simultaneous foci, 2 degrees and 3 by 3 arc minutes respectively, for Multi-Object Spectroscopy (MOS) and Integral Field Spectroscopy (IFS) at visible wavelengths. Within the framework of the Horizon Programme, the project has been approved for phase A funding by the EC in 2024 and is currently undergoing intensive development. The optical design relies on a corrected Cassegrain solution feeding multi-object spectrographs through fibres, while the central area of the field is propagated to a gravity-stable Integral Field Station housing an array of spectrographs. We report progress of the design, of the functional and physical definitions of key subsystems, and of the design of high-performance coatings of the telescope optics. The telescope would be located near ESO Paranal - Armazones observatory and protected by a VLT-like enclosure. With a view to minimising risks, from capital investment to operations, designs build extensively on VLT and ELT solutions. Owing to the optical configuration, the telescope can be wavefront-controlled at both foci, with little if any crosstalk between MOS and IFS controls. The optical path is constrained to provide natural guide star, ground-layer adaptive correction at the IFS field, within existing technology. Finally, from its earliest stage of development the system is being scrutinized for its properties in relation to sustainability.

astro-ph.IM↗

arXiv2026

Guiding Design Choices for Wide-Field IFS: Trade-Offs Between Replication and Complexity for WST

The Wide-field Spectroscopic Telescope (WST) is a proposed 12-meter segmented facility optimized for seeing- and Ground Layer Adaptive Optics-limited observations in the visible and designed to operate both a high-multiplex multi-object spectrograph and a panoramic integral field spectrograph (IFS). The WST IFS concept builds on instruments such as MUSE at the VLT (Very Large Telescope), using field splitters and image slicers to reformat a large field into pseudo-slits feeding spectrographs with two optimized spectral channels. This paper presents the integrated design approach adopted for the IFS, focusing on a trade study of spectrograph architectures. We explore design choices such as pixel pitch, detector format, and camera optical design against throughput, image quality, error budgets, volume, cost. The study adds one ecological metric: the carbon footprint of building each spectrograph, to inform design sustainability. The study also explores the potential of curved detectors. Early results suggest that many simpler spectrographs outperform fewer complex units technically and economically.

astro-ph.IM↗

arXiv2026

Sustainability as a design parameter in the early development of the Wide-field Spectroscopic Telescope

The proposed Wide-field Spectroscopic Telescope, a next-generation telescope facility with a 12-meter primary mirror that may be operational in the 2040s, is integrating sustainable considerations from the early design stage. Our preliminary analysis identifies two primary sources of environmental impact that can be mitigated during the design process. First, we are conducting a life-cycle assessment (LCA) to quantify the environmental impact of the ~250 spectrographs and the detector cooling systems across the telescope's three instruments, from construction through operation. The carbon footprint estimated through this LCA has been included as a trade-off parameter in the design choices. Second, the WST is expected to produce 1-3 PB/year, requiring careful evaluation of data processing and storage strategies. We explore approaches to monitoring and reducing the carbon footprint associated with data management. Bringing environmental factors into the design process from the start gives us the chance to weigh sustainability alongside scientific performance and cost. By treating the carbon footprint as a core design consideration, we aim to make progress toward more responsible astronomy.

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arXiv2024

The MUSE Extremely Deep Field: Classifying the Spectral Shapes of Lya Emitting Galaxies

The Hydrogen Lyman-alpha (Lya) line shows a large variety of shapes which is caused by factors at different scales, from the interstellar medium to the intergalactic medium. This work aims to provide a systematic inventory and classification of the spectral shapes of Lya emission lines to understand the general population of high-redshift Lya emitting galaxies (LAEs). Using the data from the MUSE eXtremely Deep Field, we select 477 galaxies at z=2.8-6.6. We develop a method to classify Lya emission lines in four spectral and three spatial categories, by combining a spectral analysis with a narrow-band image analysis. We measure spectral properties, such as the peak separation and the blue-to-total flux ratio. To ensure a robust sample for statistical analysis, we define a final unbiased sample of 206 galaxies by applying thresholds for signal-to-noise ratio, peak separation, and Lya luminosity. Our analysis reveals that between 32% and 51% of the galaxies exhibit double-peaked profiles. This fraction seems to evolve dependently with the Lya luminosity, while we don't notice a severe decrease of this fraction with redshift. A large amount of these double-peaked profiles shows blue-dominated spectra, suggesting unique gas dynamics and inflow characteristics in some high-redshift galaxies. Among the double-peaked galaxies, 4% are spurious detections. Around 20% out of the 477 sources of the parent sample lie in a complex environment, meaning there are other clumps or galaxies at the same redshift within a distance of 30kpc. Our results suggest that the Lya double-peak fraction may trace the evolution of IGM attenuation, but faintest galaxies are needed to be observed at high redshift. In addition, it is crucial to obtain secure systemic redshifts for LAEs to better constrain the nature of the double-peaks.

astro-ph.GA↗

arXiv2024

MusE GAs FLOw and Wind (MEGAFLOW) XII. Rationale and design of a MgII survey of the cool circum-galactic medium with MUSE and UVES: The MEGAFLOW Survey

We present the design, rationale, properties and catalogs of the MusE Gas FLOw and Wind survey (MEGAFLOW), a survey of the cool gaseous halos of $z\sim1$ galaxies using low-ionization MgII absorption systems. The survey consists of 22 quasar fields selected from the Sloan Digital Sky Survey (SDSS) having multiple ($\geq3$) strong MgII absorption lines over the redshift range $0.3 1$, i.e. more than 60 galaxies per arcmin$^{2}$. They were identified using a dual detection algorithm based on both continuum and emission line objects. The achieved [OII] 50\%\ completeness is 3.7$\times 10^{-18}$ erg/s/cm$^2$ (corresponding to SFR$>0.01$ M$_\odot$ yr$^{-1}$ at $z=1$) using realistic mock [OII] emitters and the 50\%\ completeness is $m_{F775W}\approx26$ AB magnitudes for continuum sources. We find that (i) the fraction of [OII] emitting galaxies which have no continuum is $\sim15$\%; (ii) the success rate in identifying at least one galaxy within 500 km/s and 100 kpc is $\approx90$\%\ for MgII absorptions with $W_r^{2796}\gtrsim0.5$~\AA; (iii) the mean number of galaxies per MgII absorption is $2.9\pm1.6$ within the MUSE field-of-view; (iv) of the 80 MgII systems at $0.3 10^9$ M$_\odot$, and star-formation rates $>1$ M$_\odot$ yr$^{-1}$.

astro-ph.GA↗

arXiv2024

WST -- Widefield Spectroscopic Telescope: design of a new 12m class telescope dedicated to widefield Multi-object and Integral Field Spectroscopy

The Wide-Field Spectroscopic Telescope (WST) is a concept for a 12-m class seeing-limited telescope providing two concentric fields of view for simultaneous Multi-Object Spectroscopy and Integral Field Spectroscopy. The specified wavelength range is 0.35-1.6 microns. The baseline optical design relies on a corrected Cassegrain solution feeding Multi-Object spectrographs through fibres, while the central area of the field is propagated down to a gravity-stable Integral Field Station housing 144 spectrographs. The Cassegrain corrector also provides for atmospheric dispersion compensation. All optical components are within commercially available dimensions. With a view to minimizing risks and costs, to the maximum possible extent the telescope relies on proven subsystem solutions. An exception is the tip-tilt secondary mirror, which would likely have to provide some rejection of wind shake. An iteration of the optical design is ongoing, with a view to mitigating the weaknesses of the first baseline design. The telescope would be wavefront-controlled on-sky at the common-path MOS focus. Controls in the IFS path will need to compensate for the effect of subsequent differentials - wavefront and line of sight. There is no shortage of degrees of freedom and metrology solution to do so. The size of the dome is driven by the Nasmyth footprint and the height of the pier, which houses the IFS station. The baseline assumption is that a VLT-like enclosure would provide suitable shielding and ventilation.

astro-ph.IM↗

arXiv2023

MAGIC: Muse gAlaxy Groups In Cosmos -- A survey to probe the impact of environment on galaxy evolution over the last 8 Gyr

We introduce the MUSE gAlaxy Groups in COSMOS (MAGIC) survey, which was built to study the impact of environment on galaxy evolution over the last 8 Gyr. It consists of 17 MUSE fields targeting 14 massive structures at intermediate redshift ($0.3 21.5$. The spectroscopic redshift completeness is high: in the redshift range of [OII] emitters ($0.25 \le z < 1.5$), where most of the groups are found, it globally reaches a maximum of 80% down to $z_{app}^{++}=25.9$, and locally decreases from $\sim 100$% to $\sim50$% in magnitude bins from $z_{app}^{++}=23-24$ to $z_{app}^{++}=25.5$. We find that the fraction of quiescent galaxies increases with local density and with the time spent in groups. A morphological dichotomy is also found between bulge-dominated quiescent and disk-dominated star-forming galaxies. As environment gets denser, the peak of the stellar mass distribution shifts towards $M_*>10^{10}~M_\odot$, and the fraction of galaxies with $M_*<10^9~M_\odot$ decreases significantly, even for star-forming galaxies. We also highlight peculiar features such as close groups, extended nebulae, and a gravitational arc. Our results suggest that galaxies are preprocessed in groups of increasing mass before entering rich groups and clusters. We publicly release two catalogs containing the properties of galaxies and groups, respectively.

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arXiv2022

The Lensed Lyman-Alpha MUSE Arcs Sample (LLAMAS) : I. Characterisation of extended Lyman-alpha haloes and spatial offsets

We present the Lensed Lyman-Alpha MUSE Arcs Sample (LLAMAS) selected from MUSE and HST observations of 17 lensing clusters. The sample consists of 603 continuum-faint (-23<M_UV<-14) lensed Lyman-alpha emitters (producing 959 images) with spectroscopic redshifts between 2.9 and 6.7. Combining the power of cluster magnification with 3D spectroscopic observations, we are able to reveal the resolved morphological properties of 268 Lyman-alpha emitters. We use a forward modelling approach to model both Lyman-alpha and rest-frame UV continuum emission profiles in the source plane and measure spatial extent, ellipticity and spatial offsets between UV and Lyman-alpha emission. We find a significant correlation between UV continuum and Lyman-alpha spatial extent. Our characterization of the Lyman-alpha haloes indicates that the halo size is linked to the physical properties of the host galaxy (SFR, Lyman-alpha EW and Lyman-alpha line FWHM). We find that 48% of Lyman-alpha haloes are best-fitted by an elliptical emission distribution with a median axis ratio of q=0.48. We observe that 60% of galaxies detected both in UV and Lyman-alpha emission show a significant spatial offset (Delta). We measure a median offset of Delta= 0.58 \pm 0.14 kpc for the entire sample. By comparing the spatial offset values with the size of the UV component, we show that 40% of the offsets could be due to star-forming sub-structures in the UV component, while the larger offsets are more likely due to larger distance processes such as scattering effects inside the circumgalactic medium or emission from faint satellites or merging galaxies. Comparisons with a zoom-in radiative hydrodynamics simulation of a typical Lyman-alpha emitting galaxy show a good agreement with LLAMAS galaxies and indicate that bright star-formation clumps and satellite galaxies could produce a similar spatial offsets distribution. (abridged)

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arXiv2021

Recovery and analysis of rest-frame UV emission lines in 2052 galaxies observed with MUSE at $1.5 < z < 6.4$

[Abbreviated] Rest-frame UV emission lines probe physical parameters of the emitting star-forming galaxies and their environments. The strongest main UV line, Ly$\alpha$, has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Ly$\alpha$ emission becomes increasingly challenging at $z \gtrsim 6$ when the neutral hydrogen fraction of the CGM and IGM increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large sample of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxies' physical properties and their Ly$\alpha$ emission. The sample of 2052 emission line sources with $1.5 < z < 6.4$ was selected through untargeted source detection in three-dimensional MUSE data cubes. We searched optimally extracted 1D spectra of the full sample for UV emission features via emission line template matching, resulting in a sample of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Ly$\alpha$) UV emission lines increases with survey depth, and that the UV emission line strength often correlate with the strength of Ciii]. We measured the velocity offsets of resonant emission lines with respect to systemic tracers as well as the electron density and the gas-phase abundance. Lastly, using "PhotoIonization Model Probability Density Functions" we find that the UV line emitters generally have ionization parameter log10(U) $\approx$ -2.5 and metal mass fractions that scatter around Z $\approx$ 10$^{-2}$, that is Z $\approx$ 0.66Z$\odot$. Value-added catalogs of the full sample of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper.

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arXiv2020

Reconstruction of the ground-layer adaptive-optics point spread function for MUSE Wide Field Mode observations

Here we describe a simple, efficient, and most importantly fully operational point-spread-function(PSF)-reconstruction approach for laser-assisted ground layer adaptive optics (GLAO) in the frame of the Multi Unit Spectroscopic Explorer (MUSE) Wide Field Mode. Based on clear astrophysical requirements derived by the MUSE team and using the functionality of the current ESO Adaptive Optics Facility we aim to develop an operational PSF-reconstruction (PSFR) algorithm and test it both in simulations and using on-sky data. The PSFR approach is based on a Fourier description of the GLAO correction to which the specific instrumental effects of MUSE Wide Field Mode (pixel size, internal aberrations, etc.) have been added. It was first thoroughly validated with full end-to-end simulations. Sensitivity to the main atmospheric and AO system parameters was analysed and the code was re-optimised to account for the sensitivity found. Finally, the optimised algorithm was tested and commissioned using more than one year of on-sky MUSE data. We demonstrate with an on-sky data analysis that our algorithm meets all the requirements imposed by the MUSE scientists, namely an accuracy better than a few percent on the critical PSF parameters including full width at half maximum and global PSF shape through the kurtosis parameter of a Moffat function. The PSFR algorithm is publicly available and is used routinely to assess the MUSE image quality for each observation. It can be included in any post-processing activity which requires knowledge of the PSF.

astro-ph.IM↗

arXiv2019

NGC6240: A triple nucleus system in the advanced or final state of merging

NGC6240 is a well-studied nearby galaxy system in the process of merging. Based on optical, X-ray, and radio observations, it is thought to harbor two active nuclei We carried out a detailed optical 3D spectroscopic study to investigate the inner region of this system in connection with existing MERLIN and VLBA data. We observed NGC6240 with very high spatial resolution using the MUSE instrument in the Narrow-Field Mode with the four-laser GALACSI adaptive optics system on the ESO VLT under seeing conditions of 0.49 arcsec. Our 3D spectra cover the wavelength range from 4725 to 9350 AA at a spatial resolution of ~75 mas. We report the discovery of three nuclei in the final state of merging within a region of only 1 kpc in the NGC6240 system.Thanks to MUSE we are able to show that the formerly unresolved southern component actually consists of two distinct nuclei separated by only 198 pc. In combination with Gaia data we reach an absolute positional accuracy of only 30 mas that is essential to compare optical spectra with MERLIN and VLBA radio positions. The verification and detailed study of a system with three nuclei, two of which are active and each with a mass in excess of $9\times10^{7} M_{\odot}$, is of great importance for the understanding of hierarchical galaxy formation via merging processes since multiple mergers lead to a faster evolution of massive galaxies in comparison to binary mergers. So far it has been suggested that the formation of galactic nuclei with multiple supermassive black holes (SMBHs) is expected to be rare in the local universe.Triple massive black hole systems might be of fundamental importance for the coalescence of massive black hole binaries in less than a Hubble time leading to the loudest sources of gravitational waves in the millihertz regime.

astro-ph.GA↗

arXiv2019

Two accreting protoplanets around the young star PDS 70

Newly forming proto-planets are expected to create cavities and substructures in young, gas-rich proto-planetary disks, but they are difficult to detect as they could be confused with disk features affected by advanced image-analysis techniques. Recently, a planet was discovered inside the gap of the transitional disk of the T-Tauri star PDS 70. Here we report on the detection of strong H-alpha emission from two distinct locations in the PDS 70 system, one corresponding to the previously discovered planet PDS 70 b, which confirms the earlier H$\alpha$ detection, and another located close to the outer-edge of the gap, coinciding with a previously identified bright dust spot in the disk and with a small opening in a ring of molecular emission. We identify this second H$\alpha$ peak as a second proto-planet in the PDS 70 system. The H$\alpha$ emission spectra of both proto-planets indicate ongoing accretion onto the proto-planets, which appear to be near a 2:1 mean motion resonance. Our observations show that adaptive-optics-assisted, medium-resolution, integral-field spectroscopy with MUSE targeting accretion signatures will be a powerful way to trace ongoing planet formation in transitional disks at different stages of their evolution. Finding more young planetary systems in mean motion resonance would give credibility to the Grand Tack hypothesis in which Jupiter and Saturn migrated in a resonance orbit during the early formation period of our Solar System.

astro-ph.EP↗

arXiv2018

The MUSE-Wide Survey: Survey Description and First Data Release

We present the MUSE-Wide survey, a blind, 3D spectroscopic survey in the CANDELS/GOODS-S and CANDELS/COSMOS regions. Each MUSE-Wide pointing has a depth of 1 hour and hence targets more extreme and more luminous objects over 10 times the area of the MUSE-Deep fields (Bacon et al. 2017). The legacy value of MUSE-Wide lies in providing "spectroscopy of everything" without photometric pre-selection. We describe the data reduction, post-processing and PSF characterization of the first 44 CANDELS/GOODS-S MUSE-Wide pointings released with this publication. Using a 3D matched filtering approach we detected 1,602 emission line sources, including 479 Lyman-$\alpha$ (Lya) emitting galaxies with redshifts $2.9 \lesssim z \lesssim 6.3$. We cross-match the emission line sources to existing photometric catalogs, finding almost complete agreement in redshifts and stellar masses for our low redshift (z < 1.5) emitters. At high redshift, we only find ~55% matches to photometric catalogs. We encounter a higher outlier rate and a systematic offset of $\Delta$z$\simeq$0.2 when comparing our MUSE redshifts with photometric redshifts. Cross-matching the emission line sources with X-ray catalogs from the Chandra Deep Field South, we find 127 matches, including 10 objects with no prior spectroscopic identification. Stacking X-ray images centered on our Lya emitters yielded no signal; the Lya population is not dominated by even low luminosity AGN. A total of 9,205 photometrically selected objects from the CANDELS survey lie in the MUSE-Wide footprint, which we provide optimally extracted 1D spectra of. We are able to determine the spectroscopic redshift of 98% of 772 photometrically selected galaxies brighter than 24th F775W magnitude. All the data in the first data release - datacubes, catalogs, extracted spectra, maps - are available on the website https://musewide.aip.de. [abridged]

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arXiv2018

Nearly all the sky is covered by Lyman-alpha emission around high redshift galaxies

Galaxies are surrounded by large reservoirs of gas, mostly hydrogen, fed by inflows from the intergalactic medium and by outflows due to galactic winds. Absorption-line measurements along the sightlines to bright and rare background quasars indicate that this circumgalactic medium pervades far beyond the extent of starlight in galaxies, but very little is known about the spatial distribution of this gas. A new window into circumgalactic environments was recently opened with the discovery of ubiquitous extended Lyman-alpha emission from hydrogen around high-redshift galaxies, facilitated by the extraordinary sensitivity of the MUSE instrument at the ESO Very Large Telescope. Due to the faintness of this emission, such measurements were previously limited to especially favourable systems or to massive statistical averaging. Here we demonstrate that low surface brightness Lyman-alpha emission surrounding faint galaxies at redshifts between 3 and 6 adds up to a projected sky coverage of nearly 100%. The corresponding rate of incidence (the mean number of Lyman-alpha emitters penetrated by any arbitrary line of sight) is well above unity and similar to the incidence rate of high column density absorbers frequently detected in the spectra of distant quasars. This similarity suggests that most circumgalactic atomic hydrogen at these redshifts has now been detected also in emission.

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arXiv2018

MUSE crowded field 3D spectroscopy in NGC300 I. First results from central fields

Aims. As a new approach to the study of resolved stellar populations in nearby galaxies, our goal is to demonstrate in NGC300 that integral field spectroscopy with high spatial resolution and excellent seeing conditions reaches an unprecedented depth in severely crowded fields. Methods. MUSE observations with seven pointings in NGC300 have resulted in datacubes that are analyzed in four ways: (1) PSF-fitting 3D spectroscopy with PampelMUSE yields deblended spectra of individually distinguishable stars. The technique also provides samples of planetary nebulae that are complete down to m5007=28. (2) pseudo-monochromatic images, created at the wavelengths of the most important emission lines and corrected for continuum light by using the P3D visualization tool, provide maps of HII regions, SNR, and the diffuse ISM at a high level of sensitivity, allowing for the discovery of planetary nebulae, WR stars etc. (3) The use of the P3D line-fitting tool yields emission line fluxes, surface brightness, and kinematic information for gaseous objects, corrected for absorption line profiles of the underlying stellar population. (4) Visual inspection of the datacubes is demonstrated to be effcient for data mining and the discovery of background galaxies and unusual objects. Results. We present a catalogue of luminous stars, rare stars such as WR and other emission line stars, carbon stars, symbiotic star candidates, planetary nebulae, HII regions, supernova remnants, giant shells, peculiar diffuse and filamentary emission line objects, and background galaxies, along with their spectra. Conclusions. The technique of crowded-field 3D spectroscopy is capable of deblending individual bright stars, the unresolved background of faint stars, gaseous nebulae, and the diffuse component of the interstellar medium, resulting in unprecedented legacy value for observations of nearby galaxies with MUSE.

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arXiv2018

Recovering the systemic redshift of galaxies from their Lyman-alpha line profile

The Lyman alpha (lya) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km/s compared to the systemic redshift. This large offset hampers follow-up surveys, galaxy pair statistics and correlations with quasar absorption lines when only lya is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the lya line profile. We use spectroscopic observations of Lyman-Alpha Emitters (LAEs) for which a precise measurement of the systemic redshift is available. Our sample contains 13 sources detected between z~3 and z~6 as part of various Multi Unit Spectroscopic Explorer (MUSE) Guaranteed Time Observations (GTO). We also include a compilation of spectroscopic lya data from the literature spanning a wide redshift range (z~0-8). First, restricting our analysis to double-peaked lya spectra, we find a tight correlation between the velocity offset of the red peak with respect to the systemic redshift, Vpeak, and the separation of the peaks. Secondly, we find a correlation between Vpeak and the full width at half maximum of the lya line. Fitting formulas, to estimate systemic redshifts of galaxies with an accuracy of +-100 km/s when only the lya emission line is available, are given for the two methods.

astro-ph.GA↗

arXiv2017

The MUSE Hubble Ultra Deep Field Survey VI: The Faint-End of the Lya Luminosity Function at 2.91 < z < 6.64 and Implications for Reionisation

We present the deepest study to date of the Lya luminosity function (LF) in a blank field using blind integral field spectroscopy from MUSE. We constructed a sample of 604 Lya emitters (LAEs) across the redshift range 2.91 < z < 6.64 using automatic detection software in the Hubble Ultra Deep Field. We calculate accurate total Lya fluxes capturing low surface brightness extended Lya emission now known to be a generic property of high-redshift star-forming galaxies. We simulated realistic extended LAEs to characterise the selection function of our samples, and performed flux-recovery experiments to test and correct for bias in our determination of total Lya fluxes. We find an accurate completeness correction accounting for extended emission reveals a very steep faint-end slope of the LF, alpha, down to luminosities of log10 L erg s^-1< 41.5, applying both the 1/Vmax and maximum likelihood estimators. Splitting the sample into three broad redshift bins, we see the faint-end slope increasing from -2.03+1.42-inf at z ~ 3.44 to -2.86+0.76-inf at z ~ 5.48, however no strong evolution is seen between the 68% confidence regions in L*-alpha parameter space. Using the Lya line flux as a proxy for star formation activity, and integrating the observed LFs, we find that LAEs' contribution to the cosmic SFRD rises with redshift until it is comparable to that from continuum-selected samples by z ~ 6. This implies that LAEs may contribute more to the star-formation activity of the early Universe than previously thought - any additional interglactic medium correction would act to further boost the Lya luminosities. Finally, assuming fiducial values for the escape of Lya and LyC radiation, and the clumpiness of the IGM, we integrated the maximum likelihood LF at 5.00 < z < 6.64 and find we require only a small extrapolation beyond the data (< 1 dex in L) for LAEs alone to maintain an ionised IGM at z ~ 6.

astro-ph.CO↗

arXiv2017

The MUSE Hubble Ultra Deep Field Survey. IX. Evolution of galaxy merger fraction since z~6

We provide, for the first time, robust observational constraints on the galaxy major merger fraction up to $z\approx 6$ using spectroscopic close pair counts. Deep Multi Unit Spectroscopic Explorer (MUSE) observations in the Hubble Ultra Deep Field (HUDF) and Hubble Deep Field South (HDF-S) are used to identify 113 secure close pairs of galaxies among a parent sample of 1801 galaxies spread over a large redshift range ($0.2<z<6$) and stellar masses ($10^7-10^{11} M_\odot$), thus probing about 12 Gyr of galaxy evolution. Stellar masses are estimated from spectral energy distribution (SED) fitting over the extensive UV-to-NIR HST photometry available in these deep Hubble fields, adding Spitzer IRAC bands to better constrain masses for high-redshift ($z\geqslant 3$) galaxies. These stellar masses are used to isolate a sample of 54 major close pairs with a galaxy mass ratio limit of 1:6. Among this sample, 23 pairs are identified at high redshift ($z\geqslant 3$) through their Ly$\alpha$ emission. The sample of major close pairs is divided into five redshift intervals in order to probe the evolution of the merger fraction with cosmic time. Our estimates are in very good agreement with previous close pair counts with a constant increase of the merger fraction up to $z\approx 3$ where it reaches a maximum of 20%. At higher redshift, we show that the fraction slowly decreases down to about 10% at $z\approx6$. The sample is further divided into two ranges of stellar masses using either a constant separation limit of $10^{9.5} M_\odot$ or the median value of stellar mass computed in each redshift bin. Overall, the major close pair fraction for low-mass and massive galaxies follows the same trend. These new, homogeneous, and robust estimates of the major merger fraction since $z\approx6$ are in good agreement with recent predictions of cosmological numerical simulations.

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