| 1. |
- Berg, Danielle A., et al.
(author)
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The COS Legacy Archive Spectroscopy Survey (CLASSY) Treasury Atlas
- 2022
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In: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 261:2
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Journal article (peer-reviewed)abstract
- Far-ultraviolet (FUV; ∼1200–2000 Å) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. The launch of the James Webb Space Telescope will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before; however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of ample wavelength coverage, signal-to-noise, spectral-resolution, and sample diversity that has not yet been achieved by any FUV spectral database. We present the Cosmic Origins Spectrograph Legacy Spectroscopic Survey (CLASSY) treasury and its first high-level science product, the CLASSY atlas. CLASSY builds on the Hubble Space Telescope (HST) archive to construct the first high-quality (S/N1500 Å ≳ 5/resel), high-resolution (R ∼ 15,000) FUV spectral database of 45 nearby (0.002 < z < 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY sample covers a broad range of properties including stellar mass (6.2 < log M⋆(M⊙) < 10.1), star formation rate (−2.0 < log SFR (M⊙ yr−1) < +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization (0.5 < O32 < 38.0), reddening (0.02 < E(B − V) < 0.67), and nebular density (10 < ne (cm−3) < 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a sample that is consistent with the z ∼ 0 mass–metallicity relationship, but is offset to higher star formation rates by roughly 2 dex, similar to z ≳ 2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time.
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| 2. |
- Bridge, Joanna S., et al.
(author)
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The Ly alpha Reference Sample. VIII. Characterizing Ly alpha Scattering in Nearby Galaxies
- 2018
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 852:1
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Journal article (peer-reviewed)abstract
- We examine the dust geometry and Ly alpha scattering in the galaxies of the Lyman Alpha Reference Sample (LARS), a set of 14 nearby (0.02 < z < 0.2) Ly alpha-emitting and starbursting systems with Hubble Space Telescope Ly alpha, H alpha, and H beta imaging. We find that the global dust properties determined by line ratios are consistent with other studies, with some of the LARS galaxies exhibiting clumpy dust media, while others of them show significantly lower Ly alpha emission compared to their Balmer decrement. With the LARS imaging, we present Ly alpha/H alpha and H alpha/H beta maps with spatial resolutions as low as similar to 40 pc, and use these data to show that in most galaxies, the dust geometry is best modeled by three distinct regions: a central core where dust acts as a screen, an annulus where dust is distributed in clumps, and an outer envelope where Ly alpha photons only scatter. We show that the dust that affects the escape of Ly alpha is more restricted to the galaxies' central regions, while the larger Ly alpha halos are generated by scattering at large radii. We present an empirical modeling technique to quantify how much Ly alpha scatters in the halo, and find that this characteristic scattering distance correlates with the measured size of the Ly alpha halo. We note that there exists a slight anti-correlation between the scattering distance of Ly alpha and global dust properties.
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| 3. |
- Eide, Marius B., et al.
(author)
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Unlocking the Full Potential of Extragalactic Ly alpha through Its Polarization Properties
- 2018
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 856:2
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Journal article (peer-reviewed)abstract
- Ly alpha is a powerful astrophysical probe. Not only is it ubiquitous at high redshifts, it is also a resonant line, making Ly alpha photons scatter. This scattering process depends on the physical conditions of the gas through which Ly alpha propagates, and these conditions are imprinted on observables such as the Ly alpha spectrum and its surface brightness profile. In this work, we focus on a less-used observable capable of probing any scattering process: polarization. We implement the density matrix formalism of polarization into the Monte Carlo radiative transfer code tlac. This allows us to treat it as a quantum mechanical process where single photons develop and lose polarization from scatterings in arbitrary gas geometries. We explore static and expanding ellipsoids, biconical outflows, and clumpy multiphase media. We find that photons become increasingly polarized as they scatter and diffuse into the wings of the line profiles, making scattered Ly alpha polarized in general. The degree and orientation of Ly alpha polarization depends on the kinematics and distribution of the scattering H I gas. We find that it generally probes spatial or velocity space asymmetries and aligns itself tangentially to the emission source. We show that the mentioned observables, when studied separately, can leave similar signatures for different source models. We conclude by revealing how a joint analysis of the Ly alpha spectra, surface brightness profiles, and polarization can break these degeneracies and help us extract unique physical information on galaxies and their environments from their strongest, most prominent emission line.
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| 4. |
- Hagstotz, Steffen, et al.
(author)
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Breaking cosmic degeneracies : Disentangling neutrinos and modified gravity with kinematic information
- 2019
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 629
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Journal article (peer-reviewed)abstract
- Searches for modified gravity in the large-scale structure try to detect the enhanced amplitude of density fluctuations caused by the fifth force present in many of these theories. Neutrinos, on the other hand, suppress structure growth below their free-streaming length. Both effects take place on comparable scales, and uncertainty in the neutrino mass leads to a degeneracy with modified gravity parameters for probes that are measuring the amplitude of the matter power spectrum. We explore the possibility to break the degeneracy between modified gravity and neutrino effects in the growth of structures by considering kinematic information related to either the growth rate on large scales or the virial velocities inside of collapsed structures. In order to study the degeneracy up to fully non-linear scales, we employ a suite of N-body simulations including both f (R) modified gravity and massive neutrinos. Our results indicate that velocity information provides an excellent tool to distinguish massive neutrinos from modified gravity. Models with different values of neutrino masses and modified gravity parameters possessing a comparable matter power spectrum at a given time have different growth rates. This leaves imprints in the velocity divergence, which is therefore better suited than the amplitude of density fluctuations to tell the models apart. In such models with a power spectrum comparable to ACDM today, the growth rate is strictly enhanced. We also find the velocity dispersion of virialised clusters to be well suited to constrain deviations from general relativity without being affected by the uncertainty in the sum of neutrino masses.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- Hayes, Matthew J., et al.
(author)
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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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| 8. |
- Hu, Weida, et al.
(author)
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CLASSY VII Lyα Profiles : The Structure and Kinematics of Neutral Gas and Implications for LyC Escape in Reionization-era Analogs
- 2023
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 956:1
-
Journal article (peer-reviewed)abstract
- Lyα line profiles are a powerful probe of interstellar medium (ISM) structure, outflow speed, and Lyman-continuum escape fraction. In this paper, we present the Lyα line profiles of the Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY, a sample rich in spectroscopic analogs of reionization-era galaxies. A large fraction of the spectra show a complex profile, consisting of a double-peaked Lyα emission profile in the bottom of a damped, Lyα absorption trough. Such profiles reveal an inhomogeneous ISM. We successfully fit the damped Lyα absorption and the Lyα emission profiles separately, but with complementary covering factors, a surprising result because this approach requires no Lyα exchange between high-NH i and low-NH i paths. The combined distribution of column densities is qualitatively similar to the bimodal distributions observed in numerical simulations. We find an inverse relation between Lyα peak separation and the [O iii]/[O ii] flux ratio, confirming that the covering fraction of Lyman-continuum-thin sightlines increases as the Lyα peak separation decreases. We combine measurements of Lyα peak separation and Lyα red peak asymmetry in a diagnostic diagram, which identifies six Lyman-continuum leakers in the COS Legacy Archive Spectrocopy SurveY (CLASSY) sample. We find a strong correlation between the Lyα trough velocity and the outflow velocity measured from interstellar absorption lines. We argue that greater vignetting of the blueshifted Lyα peak, relative to the redshifted peak, is the source of the well-known discrepancy between shell-model parameters and directly measured outflow properties. The CLASSY sample illustrates how scattering of Lyα photons outside the spectroscopic aperture reshapes Lyα profiles because the distances to these compact starbursts span a large range.
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| 9. |
- Matthee, Jorryt, et al.
(author)
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(Re)Solving reionization with Lyα : how bright Lyα Emitters account for the z ≈ 2–8 cosmic ionizing background
- 2022
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 512:4, s. 5960-5977
-
Journal article (peer-reviewed)abstract
- The cosmic ionizing emissivity from star-forming galaxies has long been anchored to UV luminosity functions. Here, we introduce an emissivity framework based on Lyα emitters (LAEs), which naturally hones in on the subset of galaxies responsible for the ionizing background due to the intimate connection between production and escape of Lyα and LyC photons. Using constraints on the escape fractions of bright LAEs (LLyα > 0.2L*) at z ≈ 2 obtained from resolved Lyα profiles, and arguing for their redshift-invariance, we show that: (i) quasars and LAEs together reproduce the relatively flat emissivity at z ≈ 2–6, which is non-trivial given the strong evolution in both the star formation density and quasar number density at these epochs and (ii) LAEs produce late and rapid reionization between z ≈ 6−9 under plausible assumptions. Within this framework, the >10 × rise in the UV population-averaged fesc between z ≈ 3–7 naturally arises due to the same phenomena that drive the growing LAE fraction with redshift. Generally, a LAE dominated emissivity yields a peak in the distribution of the ionizing budget with UV luminosity as reported in latest simulations. Using our adopted parameters (fesc=50 per cent, ξion = 1025.9 Hz erg−1 for half the bright LAEs), a highly ionizing minority of galaxies with MUV < −17 accounts for the entire ionizing budget from star-forming galaxies. Rapid flashes of LyC from such rare galaxies produce a ‘disco’ ionizing background. We conclude proposing tests to further develop our suggested Lyα-anchored formalism.
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| 10. |
- Matthee, Jorryt, et al.
(author)
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The X-SHOOTER Lyman α survey at z = 2 (XLS-z2) I : what makes a galaxy a Lyman α emitter?
- 2021
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 505:1, s. 1382-1412
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Journal article (peer-reviewed)abstract
- We present the first results from the X-SHOOTER Lyman α survey at z = 2 (XLS-z2). XLS-z2 is a deep spectroscopic survey of 35 Lyman α emitters (LAEs) utilizing ≈90 h of exposure time with Very Large Telescope/X-SHOOTER and covers rest-frame Ly α to H α emission with R ≈ 4000. We present the sample selection, the observations, and the data reduction. Systemic redshifts are measured from rest-frame optical lines for 33/35 sources. In the stacked spectrum, our LAEs are characterized by an interstellar medium with little dust, a low metallicity, and a high ionization state. The ionizing sources are young hot stars that power strong emission lines in the optical and high-ionization lines in the ultraviolet (UV). The LAEs exhibit clumpy UV morphologies and have outflowing kinematics with blueshifted Si ii absorption, a broad [O iii] component, and a red-skewed Ly α line. Typically, 30 per cent of the Ly α photons escape, of which one quarter on the blue side of the systemic velocity. A fraction of Ly α photons escape directly at the systemic suggesting clear channels enabling an ≈10 per cent escape of ionizing photons, consistent with an inference based on Mg ii. A combination of a low effective H i column density, a low dust content, and young starburst determines whether a star-forming galaxy is observed as an LAE. The first is possibly related to outflows and/or a fortunate viewing angle, while we find that the latter two in LAEs are typical for their stellar mass of 109 M⊙.
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| 11. |
- Naidu, Rohan P., et al.
(author)
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The synchrony of production and escape : half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50 per cent
- 2022
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 510:3, s. 4582-4607
-
Journal article (peer-reviewed)abstract
- The ionizing photon escape fraction [Lyman continuum (LyC) fesc] of star-forming galaxies is the single greatest unknown in the reionization budget. Stochastic sightline effects prohibit the direct separation of LyC leakers from non-leakers at significant redshifts. Here we circumvent this uncertainty by inferring fesc using resolved (R > 4000) Lyman α (Lyα) profiles from the X-SHOOTER Lyα survey at z = 2 (XLS-z2). With empirically motivated criteria, we use Lyα profiles to select leakers (fesc>20 per centfesc>20 per cent) and non-leakers (fesc<5 per centfesc<5 per cent) from a representative sample of >0.2L* Lyman α emitters (LAEs). We use median stacked spectra of these subsets over λrest ≈ 1000–8000 Å to investigate the conditions for LyC fesc. Our stacks show similar mass, metallicity, MUV, and βUV. We find the following differences between leakers versus non-leakers: (i) strong nebular C IV and He II emission versus non-detections; (ii) [O III]/[O II] ≈ 8.5 versus ≈3; (iii) Hα/Hβ indicating no dust versus E(B − V) ≈ 0.3; (iv) Mg II emission close to the systemic velocity versus redshifted, optically thick Mg II; and (v) Lyα fesc of ≈50 per cent≈50 per cent versus ≈10 per cent≈10 per cent. The extreme equivalent widths (EWs) in leakers ([O III]+Hβ≈1100Hβ≈1100 Å rest frame) constrain the characteristic time-scale of LyC escape to ≈3–10 Myr bursts when short-lived stars with the hardest ionizing spectra shine. The defining traits of leakers – extremely ionizing stellar populations, low column densities, a dust-free, high-ionization state interstellar medium (ISM) – occur simultaneously in the fesc>20 per centfesc>20 per cent stack, suggesting they are causally connected, and motivating why indicators like [O III]/[O II] may suffice to constrain fesc at z > 6 with the James Webb Space Telescope (JWST). The leakers comprise half of our sample, have a median LyCfesc≈50 per centfesc≈50 per cent (conservative range: 20−55 per cent20−55 per cent), and an ionizing production efficiency log(ξion/Hz erg−1)≈25.9log(ξion/Hz erg−1)≈25.9 (conservative range: 25.7–25.9). These results show LAEs – the type of galaxies rare at z ≈ 2, but that become the norm at higher redshift – are highly efficient ionizers, with extreme ξion and prolific fesc occurring in sync.
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| 12. |
- 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
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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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| 13. |
- 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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| 14. |
- 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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| 15. |
- Xu, Xinfeng, et al.
(author)
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Tracing Lyα and LyC Escape in Galaxies with Mg ıı Emission
- 2022
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 933:2
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Journal article (peer-reviewed)abstract
- Star-forming galaxies are considered the likeliest source of the H i ionizing Lyman continuum (LyC) photons that reionized the intergalactic medium at high redshifts. However, above z ≳ 6, the neutral intergalactic medium prevents direct observations of LyC. Therefore, recent years have seen the development of indirect indicators for LyC that can be calibrated at lower redshifts and applied in the epoch of reionization. Emission from the Mg ıı λλ2796, 2803 doublet has been proposed as a promising LyC proxy. In this paper, we present new Hubble Space Telescope/Cosmic Origins Spectrograph observations for eight LyC emitter candidates, selected to have strong Mg ii emission lines. We securely detect LyC emission in 50% (4/8) of the galaxies with 2σ significance. This high detection rate suggests that strong Mg ii emitters might be more likely to leak LyC than similar galaxies without strong Mg ıı. Using photoionization models, we constrain the escape fraction of Mg ii as ∼15%–60%. We confirm that the escape fraction of Mg ıı correlates tightly with that of Lyα, which we interpret as an indication that the escape fraction of both species is controlled by resonant scattering in the same low column density gas. Furthermore, we show that the combination of the Mg ıı emission and dust attenuation can be used to estimate the escape fraction of LyC statistically. These findings confirm that Mg ıı emission can be adopted to estimate the escape fraction of Lyα and LyC in local star-forming galaxies and may serve as a useful indirect indicator at the epoch of reionization.
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| 16. |
- 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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