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- Goovaerts, I., et al.
(author)
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Galaxy main sequence and properties of low-mass Lyman-α emitters towards reionisation as viewed by VLT/MUSE and JWST/NIRCam
- 2024
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 683
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Journal article (peer-reviewed)abstract
- Context. Faint, star-forming galaxies are likely to play a dominant role in cosmic reionisation. Great strides have been made in recent years to characterise these populations at high redshifts (z > 3). Now, for the first time, with JWST photometry beyond 1 μm in the rest frame, we can derive accurate stellar masses and position these galaxies on the galaxy main sequence.Aims. We seek to assess the place of 96 individual Lyman-α emitters (LAEs) selected behind the A2744 lensing cluster with MUSE IFU spectroscopy on the galaxy main sequence. We also compare the derived stellar masses to Lyman-α luminosities and equivalent widths to better quantify the relationship between the Lyman-α emission and the host galaxy.Methods. These 96 LAEs lie in the redshift range of 2.9 < z < 6.7, with their range of masses extending down to 106 M⊙ (over half with M⋆ < 108 M⊙). We used the JWST/NIRCam and HST photometric catalogues from the UNCOVER project, giving us excellent wavelength coverage from 450 nm to 4.5 μm. We also performed an SED fitting using CIGALE, fixing the redshift of the LAEs to the secure, spectroscopic value. This combination of photometric coverage with spectroscopic redshifts allows us to robustly derive stellar masses for these galaxies.Results. We found a main sequence relation for these low-mass LAEs of log SFR = (0.88 ± 0.07 − 0.030 ± 0.027 × t) log M⋆ − (6.31 ± 0.41 − 0.08 ± 0.37 × t). This is in relative agreement with the best-fit results of prior collated studies; however, here we see a steeper slope and a higher normalisation. This indicates that low-mass LAEs towards the epoch of reionisation lie above the typical literature main sequence relations derived at lower redshift and higher masses. In addition, by comparing our results to UV-selected samples, we can see that while low-mass LAEs lie above these typical main sequence relations, they are likely not singular in this respect at these particular masses and redshifts. While low-mass galaxies have been shown to play a significant role in cosmic reionisation, our results point to the likelihood that LAEs hold no special position in this regard.
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| 3. |
- Goovaerts, I., et al.
(author)
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Evolution of the Lyman-α-emitting fraction and UV properties of lensed star-forming galaxies in the range 2.9 < z < 6.7
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
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Journal article (peer-reviewed)abstract
- Context. Faint galaxies are theorised to have played a major role, perhaps the dominant role, in reionising the Universe. Their properties, as well as the Lyman-α emitter (LAE) fraction, XLAE, could provide useful insights into this epoch.Aims. We used four clusters of galaxies from the Lensed Lyman-alpha MUSE Arcs Sample (LLAMAS) that also have deep HST photometry to select a population of intrinsically faint Lyman break galaxies (LBGs) and LAEs. We study the interrelation between these two populations, their properties, and the fraction of LBGs that display Lyman-α emission.Methods. The use of lensing clusters allows us to access an intrinsically faint population of galaxies, the largest such sample collected for this purpose: 263 LAEs and 972 LBGs with redshifts between 2.9 and 6.7, Lyman-α luminosities in the range 39.5 ≲ log(LLyα)(erg s−1)≲42, and absolute UV magnitudes in the range −22 ≲ M1500 ≲ −12. In addition to matching LAEs and LBGs, we define an LAE+continuum sample for the LAEs that match with a continuum object that is not selected as an LBG. Additionally, with the use of MUSE integral field spectroscopy, we detect a population of LAEs completely undetected in the continuum.Results. We find a redshift evolution of XLAE in line with literature results, with diminished values above z = 6. In line with past studies, we take this as signifying an increasingly neutral intervening intergalactic medium. When inspecting this redshift evolution with different limits on EWLyα and M1500, we find that the XLAE for the UV-brighter half of our sample is higher than the XLAE for the UV-fainter half, a difference that increases at higher redshifts. This is a surprising result and can be interpreted as the presence of a population of low Lyman-α equivalent width (EWLyα), UV-bright galaxies situated in reionised bubbles and overdensities. This result is especially interesting in the context of similar, UV-bright, low EWLyα objects recently detected during and around the epoch of reionisation. For intrinsically fainter objects, we confirm the previously observed trend of LAEs among LBGs as galaxies with high star formation rates and low dust content, as well as the trend of the strongest LAEs having, in general, fainter M1500 and steeper UV slopes.
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- Pelkmans, L., et al.
(author)
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Monitoring the Impact of Sustainability Certification in Relation to Biomass Use for Energy
- 2012
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In: EUBCE 2012 proceedings. - 9788889407547 ; , s. 2013-2018
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Conference paper (other academic/artistic)abstract
- Since the public has expressed concern about unintended consequences associated with potentially unsustainable biomass production and use for energy (or biofuels), producers of biomass feedstocks in the private sector as well as governmental and non-governmental organisations have initiated many generally unlinked efforts to define 'sustainable' bioenergy production and supply chains. These 'sustainability' standards may be implemented through certification systems involving 3rd party audit, and influence production systems and trade of bioenergy products from producers to consumers of ‘green' energy. At present numerous biomass and biofuel sustainability certification systems are being developed or implemented by a variety of private and public organisations. Systems are applicable to different feedstock production sectors (forests, agricultural crops), different bioenergy products (relatively unprocessed forest residues, ethanol, biodiesel, electricity), and whole or segments of supply chains (production system, chain of custody from growers to energy consumers). It is expected that such a wide range of systems, developed largely without coordination among the organisations involved, could be problematic for all stakeholders along the supply chain in individual sectors and for those involved in deployment of bioenergy systems globally. These are individual feedstock producers, companies and commodity sectors that must comply with these systems either to maintain market access and share or to comply with legislative mandates, and also consumers who prefer to purchase certified green energy, and regulatory agencies and local to national governments that may be involved in enforcing sustainability standards. The potential for confusion among the actors, depression of markets, and unnecessary restrictions on sustainable trade seems high. Within IEA Bioenergy a strategic study was initiated between Task 40, Task 43 and Task 38 to monitor the actual implementation process of sustainability certification of bioenergy, evaluate how stakeholders are affected by certification initiatives, quantify the anticipated impact on worldwide bioenergy trade, assess the level of coordination among schemes, and make recommendations to remove barriers which may depress markets and reduce sustainable trade. Interaction with different stakeholder groups is one of the main objectives of this study, so we anticipate the recommendations being representative of the whole bioenergy certification sector and therefore having high potential to improve an otherwise uncoordinated interest in ensuring bioenergy trade is sustainable.
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| 8. |
- Pelkmans, Luc, et al.
(author)
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The role of sustainability requirements in international bioenergy markets
- 2013
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In: International Bioenergy Trade. - : Springer. - 9789400769816 ; , s. 125-149
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Book chapter (peer-reviewed)abstract
- As the main driver for bioenergy is to enable society to transform to more sustainable fuel and energy production systems, it is important to safeguard that bioenergy deployment happens within certain sustainability constraints. There is currently a high number of initiatives, including binding regulations and several voluntary sustainability standards for biomass, bioenergy and/or biofuels. Within IEA Bioenergy studies were performed to monitor the actual implementation process of sustainability regulations and certification, evaluate how stakeholders are affected and envisage the anticipated impact on worldwide markets and trade. On the basis of these studies, recommendations were made on how sustainability requirements could actually support further bioenergy deployment. Markets would gain from more harmonization and cross-compliance. A common language is needed as ‘sustainability’ of biomass involves different policy arenas and legal settings. Policy pathways should be clear and predictable, and future revisions of sustainability requirements should be open and transparent. Sustainability assurance systems (both through binding regulations and voluntary certification) should take into account how markets work, in relation to different biomass applications (avoiding discrimination among end-uses and users). It should also take into account the way investment decisions are taken, administrative requirements for smallholders, and the position of developing countries.
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| 9. |
- Pelkmans, Luc, et al.
(author)
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The role of sustainability requirements in international bioenergy markets
- 2014
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In: Lecture Notes in Energy. - Dordrecht : Springer Netherlands. - 2195-1292 .- 2195-1284. ; 17:1, s. 125-149
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Journal article (peer-reviewed)abstract
- As the main driver for bioenergy is to enable society to transform to more sustainable fuel and energy production systems, it is important to safeguard that bioenergy deployment happens within certain sustainability constraints. There is currently a high number of initiatives, including binding regulations and several voluntary sustainability standards for biomass, bioenergy and/or biofuels. Within IEA Bioenergy studies were performed to monitor the actual implementation process of sustainability regulations and certification, evaluate how stakeholders are affected and envisage the anticipated impact on worldwide markets and trade. On the basis of these studies, recommendations were made on how sustainability requirements could actually support further bioenergy deployment. Markets would gain from more harmonization and cross-compliance. A common language is needed as 'sustainability' of biomass involves different policy arenas and legal settings. Policy pathways should be clear and predictable, and future revisions of sustainability requirements should be open and transparent. Sustainability assurance systems (both through binding regulations and voluntary certification) should take into account how markets work, in relation to different biomass applications (avoiding discrimination among end-uses and users). It should also take into account the way investment decisions are taken, administrative requirements for smallholders, and the position of developing countries.
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| 11. |
- Thai, T. T., et al.
(author)
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Probing the faint-end luminosity function of Lyman-alpha emitters at 3 < z < 7 behind 17 MUSE lensing clusters
- 2023
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
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Journal article (peer-reviewed)abstract
- Context. This paper presents a study of the galaxy Lyman-alpha luminosity function (LF) using a large sample of 17 lensing clusters observed by the Multi Unit Spectroscopic Explorer (MUSE) at the ESO Very Large Telescope (VLT). The magnification resulting from strong gravitational lensing by clusters of galaxies and MUSE spectroscopic capabilities allows for blind detections of LAEs without any photometric pre-selection, reaching the faint luminosity regime.Aims. The present work aims to constrain the abundance of Lyman-alpha emitters (LAEs) and quantify their contribution to the total cosmic reionization budget.Methods. We selected 600 lensed LAEs behind these clusters in the redshift range of 2.9 < z < 6.7, covering four orders of magnitude in magnification-corrected Ly-α luminosity (39.0 < log(L)[erg s−1] < 43.0). These data were collected behind lensing clusters, indicating an increased complexity in the computation of the LF to properly account for magnification and dilution effects. We applied a non-parametric Vmax method to compute the LF to carefully determine the survey volume where an individual source could have been detected. The method used in this work follows the recipes originally developed in previous works, with some improvements to better account for the effects of lensing when computing the effective volume.Results. The total co-moving volume at 2.9 < z < 6.7 in the present survey is ∼50 103 Mpc3. Our LF points in the bright end (log(L) [erg s−1] > 42) are consistent with those obtained from blank field observations. In the faint luminosity regime, the density of sources is well described by a steep slope, α ∼ −2 for the global redshift range. Up to log(L) [erg s−1] ∼ 41, the steepening of the faint end slope with redshift, suggested in earlier works, is observed, but the uncertainties are still large. A significant flattening is observed towards the faintest end, for the highest redshift bins, namely, log(L)[erg s−1] < 41.Conclusions. When taken at face value, the steep slope at the faint-end causes the star formation rate density (SFRD) to dramatically increase with redshift, implying that LAEs could play a major role in the process of cosmic reionization. The flattening observed towards the faint end for the highest redshift bins still requires further investigation. This turnover is similar to the one observed for the UV LF at z ≥ 6 in lensing clusters, with the same conclusions regarding the reliability of current results. Improving the statistical significance of the sample in this low-luminosity high-redshift regime is a difficult endeavour that may lead to potentially valuable leads in understanding the process of reionization.
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