| 1. |
- Adamo, Angela, et al.
(author)
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Star cluster formation in the most extreme environments: Insights from the HiPEEC survey
- 2020
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In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:3, s. 3267-3294
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Journal article (peer-reviewed)abstract
- We present the Hubble imaging Probe of Extreme Environments and Clusters (HiPEEC) survey. We fit HST NUV to NIR broad-band and H α fluxes to derive star cluster ages, masses, and extinctions and determine the star formation rate (SFR) of six merging galaxies. These systems are excellent laboratories to trace cluster formation under extreme gas physical conditions, rare in the local Universe, but typical for star-forming galaxies at cosmic noon. We detect clusters with ages of 1-500 Myr and masses that exceed 107 M☉. The recent cluster formation history and their distribution within the host galaxies suggest that systems such as NGC 34, NGC 1614, and NGC 4194 are close to their final coalescing phase, while NGC 3256, NGC 3690, and NGC 6052 are at an earlier/intermediate stage. A Bayesian analysis of the cluster mass function in the age interval 1-100 Myr provides strong evidence in four of the six galaxies that an exponentially truncated power law better describes the observed mass distributions. For two galaxies, the fits are inconclusive due to low number statistics. We determine power-law slopes β ∼ −1.5 to −2.0 and truncation masses, Mc, between 106 and a few times 107 M☉, among the highest values reported in the literature. Advanced mergers have higher Mc than early/intermediate merger stage galaxies, suggesting rapid changes in the dense gas conditions during the merger. We compare the total stellar mass in clusters to the SFR of the galaxy, finding that these systems are among the most efficient environments to form star clusters in the local Universe.
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| 2. |
- Hayes, Matthew J., et al.
(author)
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Spectral Shapes of the Lyα Emission from Galaxies. : II. The influence of stellar properties and nebular conditions on the emergent line profiles
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Other publication (other academic/artistic)abstract
- We demonstrate how the stellar properties and nebular conditions in star-forming galaxies modulate the emission and spectral profile of HI Lyman-alpha (Lyα) emission line. In this second paper in a series, we examine the net Lyα output, kinematics, and in particular emission of blue-shifted Lyαradiation. We use intermediate resolution spectroscopy obtained with the Cosmic Origins Spectrograph on HST, giving a sample of 87 galaxies at redshift (z) between 0.05 and 0.44. We contrast the Lyα spectral measurements with properties of the ionized gas (from optical spectroscopy) and stars(from stellar spectral modeling). We demonstrate correlations of unprecedented strength between the Lyα escape fraction (or equivalent width) and properties correlating with ionization parameter(p ≈ 10−15). The same data reveal evolution in the relative contribution of blue-shifted emission to the total Lyα, which varies from ≈ 0 to ≈ 40 % on average (p ≈ 10−6). We also find particularly strong correlations with estimators of stellar evolutionary stage, nebular abundance, and weaker correlations regarding thermodynamic variables. Analysis of the low ionization stage absorption lines suggests the net emission and line profile is predominantly governed by the column of absorbing gas close to zero velocity. Multi-parametric analysis of the many variables presented here reveals that we can reliably predict up to 80 % of the Lyα luminosity variance, and ∼ 50 % of the variance on the EW. We also analyze the most crucial predictive variables, finding that for tracers of the high and low ionization gas and Hβ luminosity dominate the luminosity prediction whereas the Lyα EW is most well predicted by Hβ EW and the Hα/Hβ ratio. We discuss our results with reference to high redshift observations, with particular focus upon the use of Lyα to probe the nebular conditions in star forming galaxies and the reionization of the universe.
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| 3. |
- Hayes, Matthew J., et al.
(author)
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Spectral Shapes of the Lyα Emission from Galaxies. I. Blueshifted Emission and Intrinsic Invariance with Redshift*
- 2021
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 908:1, s. 1-17
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Journal article (peer-reviewed)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 (LB/R) increases rapidly with increasing equivalent width (WLyα). This correlation does not, however, emerge at z = 3–4, and we use bootstrap simulations to demonstrate that trends in LB/R should be suppressed by variations in IGM absorption. Our main result is that the observed blueshifted contribution evolves rapidly downward with increasing redshift: LB/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.
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| 4. |
- Hayes, Matthew J., et al.
(author)
-
Spectral shapes of the Ly α emission from galaxies – II. The influence of stellar properties and nebular conditions on the emergent Ly α profiles
- 2023
-
In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 520:4, s. 5903-5927
-
Journal article (peer-reviewed)abstract
- We demonstrate how the stellar and nebular conditions in star-forming galaxies modulate the emission and spectral profile of H I Ly α emission line. We examine the net Ly α output, kinematics, and in particular emission of blueshifted Ly α radiation, using spectroscopy from with the Cosmic Origins Spectrograph on Hubble Space Telescope (HST), giving a sample of 87 galaxies at redshift z = 0.05−0.44. We contrast the Ly α spectral measurements with properties of the ionized gas (from optical spectra) and stars (from stellar modelling). We demonstrate correlations of unprecedented strength between the Ly α escape fraction (and equivalent width) and the ionization parameter (p ≈ 10−15). The relative contribution of blueshifted emission to the total Ly α also increases from ≈0 to ≈40 per cent over the range of O32 ratios (p ≈ 10−6). We also find particularly strong correlations with estimators of stellar age and nebular abundance, and weaker correlations regarding thermodynamic variables. Low ionization stage absorption lines suggest the Ly α emission and line profile are predominantly governed by the column of absorbing gas near zero velocity. Simultaneous multiparametric analysis over many variables shows we can predict 80 per cent of the variance on Ly α luminosity, and ∼50 per cent on the EW. We determine the most crucial predictive variables, finding that for tracers of the ionization state and H β luminosity dominate the luminosity prediction whereas the Ly α EW is best predicted by H β EW and the H α/H β ratio. We discuss our results with reference to high-redshift observations, focussing upon the use of Ly α to probe the nebular conditions in high-z galaxies and cosmic reionization.
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| 5. |
- Melinder, Jens, et al.
(author)
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Lyman alpha escape from 45 star forming galaxies– the Lyα Reference Sample XIV
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Other publication (other academic/artistic)abstract
- We present Lyα imaging of 45 low redshift star-forming galaxies observed with the Hubble space telescope. The galaxies have been selected to have moderate to high star formation rates using FUVluminosity and Hα equivalent width criteria, but no constraints on Lyα luminosity have been applied. We employ a pixel SED fitting code to obtain accurate continuum subtracted Lyα, Hα and Hβ maps. We find that Lyα is less concentrated than FUV and optical line emission in almost all galaxies with significant Lyα emission. We present global measurements of Lyα and other quantities measured in apertures designed to capture all of the Lyα emission. We then show how the escape fraction ofLyα relates to a number of other measured quantities (mass, metallicity, star formation, ionization parameter, and extinction). We find that the escape fraction is strongly anti-correlated with both nebular and stellar extinction, weakly anti-correlated with stellar mass, but no conclusive evidence for correlations to other quantities. We show that Lyα escape fractions are inconsistent with common dust extinction laws and discuss how a combination of radiative transfer effects and clumpy dust models can help resolve the discrepancies. We present a star formation rate calibration based on Lyαluminosity, where the equivalent width of Lyα is used to correct for non-unity escape fraction, and show that this relation provides a reasonably accurate calibration but with a large scatter. We also show stacked growth curves of Lyα for the galaxies that can be used to find aperture loss fractions at a given physical radius
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| 6. |
- Melinder, Jens, 1977-, et al.
(author)
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The Lyα Reference Sample. XIV. Lyα Imaging of 45 Low-redshift Star-forming Galaxies and Inferences on Global Emission
- 2023
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In: Astrophysical Journal Supplement Series. - 0067-0049 .- 1538-4365. ; 266:1
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Journal article (peer-reviewed)abstract
- We present Lyα imaging of 45 low-redshift star-forming galaxies observed with the Hubble Space Telescope. The galaxies have been selected to have moderate to high star formation rates (SFRs) using far-ultraviolet (FUV) luminosity and Hα equivalent width criteria, but no constraints on Lyα luminosity. We employ a pixel stellar continuum fitting code to obtain accurate continuum-subtracted Lyα, Hα, and Hβ maps. We find that Lyα is less concentrated than FUV and optical line emission in almost all galaxies with significant Lyα emission. We present global measurements of Lyα and other quantities measured in apertures designed to capture all of the Lyα emission. We then show how the escape fraction of Lyα relates to a number of other measured quantities (mass, metallicity, star formation, ionization parameter, and extinction). We find that the escape fraction is strongly anticorrelated with nebular and stellar extinction, weakly anticorrelated with stellar mass, but no conclusive evidence for correlations with other quantities. We show that Lyα escape fractions are inconsistent with common dust extinction laws, and discuss how a combination of radiative transfer effects and clumpy dust models can help resolve the discrepancies. We present an SFR calibration based on Lyα luminosity, where the equivalent width of Lyα is used to correct for nonunity escape fraction, and show that this relation provides a reasonably accurate SFR estimate. We also show stacked growth curves of Lyα for the galaxies that can be used to find aperture loss fractions at a given physical radius.
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| 7. |
- Rasekh, Armin, et al.
(author)
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A Lyman alpha imaging study of green pea galaxies
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Other publication (other academic/artistic)abstract
- Aims. We present Hubble space telescope (HST) imaging data of six green pea (GP) galaxies (two of which are confirmed Lymancontinuum leakers, and a third is a probable leaker). We investigate their Lyα photometric properties by measuring their Lyα global observables, study their Lyα halos, and how their compactness is related to some of the primary diagnostics used to predict whether a galaxy is a Lyman continuum (LyC) leaker.Methods. We constructed Lyα images from multi-filter HST imaging from the far UV to the red and Hα, using a continuum subtraction method from the literature. In the resulting Lyα images, we measured global observables: Lyα luminosity, Lyα equivalent width and Lyα escape fraction by estimating a global aperture for each galaxy and measured these quantities within this aperture. To study the Lyα morphology of these galaxies, we studied their Lyα surface brightness (SB) using two different methods i) a method devised to study the Lyα SB of high−z Lyα emitters and ii) a method used to study more nearby star-forming galaxies. Moreover, we measured the concentration parameter for each galaxy. We studied the fraction of Lyα emission recovered within the COS/HST field-of-view compared to the global aperture we derived in our analysis. We also looked at how O32 and the red/blue peak separation of the Lyα line profile relate to Lyα compactness and the Lyα escape fraction.Results. We detect Lyα emission (> 10σ) for all galaxies. Despite their compactness (far UV Petrosian radii rp20 ∼ 1 kpc), all galaxies show extended Lyα emission detected out to radii 13 to 34 kpc. Our analysis suggests that the known correlation between fLyαesc and EWLyα in nearby SFGs holds for GPs, too. We also see that the method used to study the Lyα SB profiles of high−z LAEs is not applicable to low-redshift galaxies. Our analysis shows that (except for one galaxy) the majority of the total measured Lyα flux is emitted within the HST/COS aperture. Furthermore, we found that O32 does not correlate with the quantities related to the Lyα compactness or the Lyα escape fraction. However, the peak separation strongly anti-correlates with the Lyα escape fraction and strongly correlates with the Lyα halo fraction. Finally, our findings suggest that one additional galaxy is a good candidate for being a significant LyC emitter.
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| 8. |
- Rasekh, Armin, et al.
(author)
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The Lyman Alpha Reference Sample XII. Morphology of extended Lyman alpha emission in star-forming galaxies
- 2022
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 662
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Journal article (peer-reviewed)abstract
- Aims. We use Hubble Space Telescope data of 45 nearby star-forming galaxies to investigate properties of Lyman-alpha (Lyα) halos, Lyα morphology, and the star-forming characteristics of galaxies. We study how the morphology of Lyα emission is related to other Lyα observables. Furthermore, we study the interdependencies of Lyα morphological quantities.Methods. We studied the spatial extent of Lyα using surface brightness profiles in the following two ways (i) using circular apertures and (ii) within faint Lyα isophotes. We also measured the average intensity and the size of the regions with a high star formation rate density. The morphology of the galaxies was quantified by computing centroid position, axis ratio, and position angle in the Lyα, ultraviolet continuum, and I band maps.Results. We found that galaxies with more extended star-forming regions possess larger Lyα halos. Furthermore, galaxies with more elongated Lyα morphology are also more extended in Lyα. Our data suggest that Lyα bright galaxies appear rounder in their Lyα morphology, and there is less of a contribution from their Lyα halo to their overall luminosity. We compared our results with studies at high redshift and found that whilst the Lyα extent in the inner regions of the galaxies in our sample are similar to the high-z Lyα emitters (LAEs), Lyα halos are more extended in high-z LAEs.Conclusions. Our analysis suggests that the Lyα morphology affects the measurement of other observable quantities concerning Lyα emission, and some of the conclusions drawn from high redshift LAEs might be biased towards galaxies with specific Lyα shapes. In particular, faint Lyα emitters have larger Lyα scale lengths and halo fractions. This implies that faint Lyα emitters are harder to detect at high redshift than previously believed.
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| 9. |
- Runnholm, Axel, 1992-, et al.
(author)
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On the evolution of the size of Lyman alpha haloes across cosmic time : no change in the circumgalactic gas distribution when probed by line emission
- 2023
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In: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 522:3, s. 4275-4293
-
Journal article (peer-reviewed)abstract
- Lyman alpha (Ly alpha) is now routinely used as a tool for studying high-redshift galaxies, and its resonant nature means it can trace neutral hydrogen around star-forming galaxies. Integral field spectrograph measurements of high-redshift Ly alpha emitters indicate that significant extended Ly alpha halo emission is ubiquitous around such objects. We present a sample of redshift 0.23 to 0.31 galaxies observed with the Hubble Space Telescope selected to match the star formation properties of high-z samples while optimizing the observations for detection of low surface brightness Ly alpha emission. The Ly alpha escape fractions range between 0.7 and 37 per cent, and we detect extended Ly alpha emission around six out of seven targets. We find Ly alpha halo to UV scale length ratios around 6:1, which is marginally lower than high-redshift observations, and halo flux fractions between 60 and 85 per cent - consistent with high-redshift observations - when using comparable methods. However, our targets show additional extended stellar UV emission: we parametrize this with a new double exponential model. We find that this parametrization does not strongly affect the observed Ly alpha halo fractions. We find that deeper H alpha data would be required to firmly determine the origin of Ly alpha halo emission; however, there are indications that H alpha is more extended than the central FUV profile, potentially indicating conditions favourable for the escape of ionizing radiation. We discuss our results in the context of high-redshift galaxies, cosmological simulations, evolutionary studies of the circumgalactic medium in emission, and the emission of ionizing radiation.
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| 10. |
- Runnholm, Axel, et al.
(author)
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On the evolution of the size of Lyman alpha halos across cosmic time: no change in the circumgalactic gas distribution when probed by line emission
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Other publication (other academic/artistic)abstract
- Lyman ? (Ly?) is now routinely used as a tool for detecting high redshift galaxies and its resonant nature means it can trace neutral hydrogen around star-forming galaxies. Integral field spectrograph measurements of high-? Ly? emitters indicate that significant extended Ly? halo emission is ubiquitous around such objects. We present a sample of redshift 0.23 to 0.32 galaxies observed with the Hubble Space Telescope selected to match the star formation properties of high-? samples while optimizing the observations for detection of low surface brightness Ly? emission. All seven targets show Ly? emission, with total escape fractions between 0.7% and 37%, and extended Ly? emission. We find Ly? halo to UV scale length ratios around 10:1, and halo flux fractions between 60% and 85% —consistent with high redshift observations—when using comparable methods. However, our targets show additional extended stellar UV emission which we parametrize with a new three exponential component model for Ly? emission. Halo fractions become much smaller with this methodology and some become consistent with zero. Comparing UV and H? emission reveals that H? is also extended and can partially explain the origin of diffuse Ly?. We interpret this as evidence that the creation of Ly? halos cannot be attributed to one single process but rather a combination of in-situ recombination and spatial scattering or possibly collisional excitation. We discuss our results in the context of high-redshift galaxies, evolutionary studies of the circumgalactic medium in emission, and inferences concerning the emission of ionizing radiation.
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| 11. |
- Runnholm, Axel, et al.
(author)
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The Lyman Alpha Reference Sample. X. Predicting Lyα Output from Star-forming Galaxies Using Multivariate Regression
- 2020
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 892:1
-
Journal article (peer-reviewed)abstract
- Understanding the production and escape of Ly alpha radiation from star-forming galaxies is a long-standing problem in astrophysics. The ability to predict the Ly alpha luminosity of galaxies would open up new ways of exploring the epoch of reionization (EOR) and estimating Ly alpha emission from galaxies in cosmological simulations where radiative transfer calculations cannot be done. We apply multivariate regression methods to the Lyman Alpha Reference Sample data set to obtain a relation between the galaxy properties and the emitted Ly alpha. The derived relation predicts the Ly alpha luminosity of our galaxy sample to good accuracy, regardless of whether we consider only direct observables (rms dispersion around the relation of similar to 0.19 dex) or derived physical quantities (rms similar to 0.27 dex). We confirm the predictive ability on a separate sample of compact star-forming galaxies and find that the prediction works well, but that aperture effects on measured Ly alpha luminosity may be important, depending on the redshift of the galaxy. We apply statistical feature selection techniques to determine an order of importance of the variables in our data set, enabling future observations to be optimized for predictive ability. When using physical variables, we are able to determine that the most important predictive parameters are, in order, star formation rate, dust extinction, compactness, and the gas covering fraction. We discuss the application of our results in terms of studying the EOR and intensity mapping experiments.
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| 12. |
- Runnholm, Axel, et al.
(author)
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The Lyman Alpha Spectral Database (LASD)
- 2021
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In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 133:1021
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Journal article (peer-reviewed)abstract
- Lyman alpha (Ly alpha) emission from star-forming galaxies is an important tool to study a large range of astrophysical questions: it has the potential to carry information about the source galaxy, its nearby circumgalactic medium, and also the surrounding intergalactic medium. Substantial observational and theoretical work has therefore focused on understanding the details of this emission line. These efforts have been hampered, however, by an absence of spectroscopic reference samples that can be used both as comparisons for observational studies and as critical tests for theoretical work. For this reason, we have compiled a large sample of Ly alpha spectra, at both low and high redshift, and created a publicly available online database, at lasdlyman-alpha.com. The Lyman Alpha Spectral Database (LASD) hosts these spectra, as well as a large set of spectral and kinematic quantities that have been homogeneously measured for the entire sample. As part of this we have developed an automated redshift determination algorithm which we show is accurate to within less than +/- 180 kms(-1) on average, across many different Ly alpha profiles. The measurements can conveniently be viewed online and downloaded in tabular form. The LASD has the capacity for users to easily upload their own Ly alpha spectra, and all the same spectral measurements will be made, reported, and ingested into the database. We actively invite the community to do so, and the LASD is intended to be a long-term community resource. In this paper we present the design of the database as well as descriptions of the underlying algorithms and the initial Ly alpha emitter samples that are in the database.
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| 13. |
- Runnholm, Axel, 1992-
(author)
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Using Lyα to illuminate the circumgalactic medium and the Epoch of Reionization : Lessons from low redshift
- 2022
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Doctoral thesis (other academic/artistic)abstract
- The field of extragalactic astronomy is progressing rapidly but there is still much to understand and many questions that remain open. During recent years the Lyα emission line has come to the fore as a potentially very powerful astrophysical tool and is now routinely used to find galaxies at the very highest redshifts. However, using Lyα is complicated by the fact that it is a resonant line, which means that it undergoes radiative transfer as it travels through neutral hydrogen when escaping from galaxies. This makes Lyα observations very difficult to interpret, but it also means that Lyα can provide information about the neutral hydrogen in the universe, giving it the potential to, for instance, map the progression of the Epoch of Reionization—the large scale phase transition during which the universe went from being completely neutral to being dominated by ionized gas. In order to make the most of Lyα observations and extend its usefulness even further we need to understand exactly what kind of galaxies emit Lyα, and, by extension, which physical processes control its escape. Even though Lyα is relatively easy to detect at high redshift we cannot study the details of the escape process there, due to the lack of additional information about the emitting galaxies. In order to understand Lyα in detail then, we need to observe galaxies at much lower redshift where we can get more information. This is the main driver of the projects included in this thesis which focuses on furthering our understanding of Lyα using local universe observations. We find that Lyα escape is a strongly multivariate issue and that using simple machine learning techniques can both help us predict Lyα and determine what the main drivers of Lyα emission are. We present two studies focusing on multivariate prediction of both imaging and spectral observations of Lyα showing that it is, in general, possible to predict the total Lyα luminosity very well but that the equivalent width and the escape fraction still remain somewhat elusive. We show that the primary variables controlling of Lyα seem to be the production rate of Lyα photons and the ionization state of the surrounding gas. We also study the spatial distribution of extended Lyα halo emission in an effort to determine how important spatial scattering of Lyα is and whether the properties of halos change between low and high redshift. We find that halos at low redshift are remarkably consistent with high redshift results but that the extended emission most likely is not solely due to scattering of Lyα photons produced in the central galaxy but is also produced by faint stellar components at large radii, something not demonstrated before.Lastly, we present a database of Lyα spectral profiles and use that dataset to examine the evolution of Lyα spectra as a function of redshift. The profiles show clear trends, with blueshifted emission becoming markedly less prominent at high redshifts. Using a prescription for the expected attenuation of the intergalactic medium, we show that the evolution in the profiles is consistent with the intrinsic line shape not evolving between redshift 0 and redshift 6. We also present work analyzing correlations of Lyα with both stellar population and nebular gas properties in extensive detail shedding further light on what properties makes a galaxy a Lyα emitter.
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| 14. |
- Sirressi, Mattia, et al.
(author)
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Haro 11-Untying the knots of the nuclear starburst
- 2022
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 510:4, s. 4819-4836
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Journal article (peer-reviewed)abstract
- Star formation is a clustered process that regulates the structure and evolution of galaxies. We investigate this process in the dwarf galaxy Haro 11, forming stars in three knots (A, B, and C). The exquisite resolution of HST imaging allows us to resolve the starburst into tens of bright star clusters. We derive masses between 105 and 107 M and ages younger than 20 Myr, using photometric modelling. We observe that the clustered star formation has propagated from knot C (the oldest) through knot A (in between) towards knot B (the youngest). We use aperture-matched ultraviolet and optical spectroscopy (HST + MUSE) to independently study the stellar populations of Haro 11 and determine the physical properties of the stellar populations and their feedback in 1-kpc diameter regions. We discuss these results in light of the properties of the ionized gas within the knots. We interpret the broad blue-shifted components of the optical emission lines as outflowing gas (vmax ∼ 400 km/s). The strongest outflow is detected in knot A with a mass rate of M˙ out ∼ 10 M/yr, 10 times higher than the star formation in the same region. Knot B hosts a young and not fully developed outflow, whereas knot C has likely been already evacuated. Because Haro 11 has properties similar to high-redshift unresolved galaxies, our work can additionally aid the understanding of star formation at high redshift, a window that will be opened by upcoming facilities.
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| 15. |
- Östlin, Göran, et al.
(author)
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The Source of Leaking Ionizing Photons from Haro11 : Clues from HST/COS Spectroscopy of Knots A, B, and C
- 2021
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 912:2
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Journal article (peer-reviewed)abstract
- Understanding the escape of ionizing (Lyman continuum) photons from galaxies is vital for determining how galaxies contributed to reionization in the early universe. While directly detecting the Lyman continuum from high-redshift galaxies is impossible due to the intergalactic medium, low-redshift galaxies in principle offer this possibility but require observations from space. The first local galaxy for which Lyman continuum escape was found is Haro 11, a luminous blue compact galaxy at z = 0.02, where observations with the FUSE satellite revealed an escape fraction of 3.3%. However, the FUSE aperture covers the entire galaxy, and it is not clear from where the Lyman continuum is leaking out. Here we utilize Hubble Space Telescope/Cosmic Origins Spectrograph spectroscopy in the wavelength range 1100-1700 angstrom of the three knots (A, B, and C) of Haro 11 to study the presence of Ly alpha emission and the properties of intervening gas. We find that all knots have bright Ly alpha emission. UV absorption lines, originating in the neutral interstellar medium, as well as lines probing the ionized medium, are seen extending to blueshifted velocities of 500 km s(-1) in all three knots, demonstrating the presence of an outflowing multiphase medium. We find that knots A and B have large covering fractions of neutral gas, making LyC escape along these sightlines improbable, while knot C has a much lower covering fraction (less than or similar to 50%). Knot C also has the the highest Ly alpha escape fraction, and we conclude that it is the most likely source of the escaping Lyman continuum detected in Haro 11.
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