| 1. |
- Marques-Chaves, R., et al.
(author)
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No correlation of the Lyman continuum escape fraction with spectral hardness
- 2022
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 663
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Journal article (peer-reviewed)abstract
- The properties that govern the production and escape of hydrogen-ionizing photons (Lyman continuum, LyC; with energies > 13.6 eV) in star-forming galaxies are still poorly understood, but they are key to identifying and characterizing the sources that reionized the Universe. Here we empirically explore the relation between the hardness of ionizing radiation and the LyC leakage in a large sample of low-z star-forming galaxies from the recent Hubble Space Telescope Low-z Lyman Continuum Survey. Using Sloan Digital Sky Survey stacks and deep X-shooter observations, we investigate the hardness of the ionizing spectra (QHe+/QH) between 54.4 eV (He+) and 13.6 eV (H) from the optical recombination lines He II 4686 Å and Hβ 4861 Å for galaxies with LyC escape fractions spanning a wide range, fesc(LyC) ≃ 0−90%. We find that the observed intensity of He II/Hβ is primarily driven by variations in the metallicity, but is not correlated with LyC leakage. Both very strong (esc(LyC)> ≃ 0.5) and nonleakers (esc(LyC)> ≃ 0) present similar observed intensities of He II and Hβ at comparable metallicity, between ≃0.01 and ≃0.02 for 12 + log(O/H)> 8.0 and < 8.0, respectively. Our results demonstrate that QHe+/QH does not correlate with fesc(LyC), which implies that strong LyC emitters do not show harder ionizing spectra than nonleakers at similar metallicity.
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| 2. |
- Guaita, Lucia, et al.
(author)
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The Lyman alpha reference sample IV. Morphology at low and high redshift
- 2015
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 576
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Journal article (peer-reviewed)abstract
- Context. The transport of Ly alpha photons in galaxies is a complex process and the conditions under which Ly alpha photons manage to escape from certain galaxies is still under investigation. The Lyman alpha reference sample (LARS) is a sample of 14 local star-forming galaxies, designed to study Ly alpha in detail and relate it to rest-frame UV and optical emission. Aims. With the aim of identifying rest-frame UV and optical properties, which are typical of Ly alpha emitters (LAEs, galaxies with EW(Ly alpha) > 20 angstrom) at both low and high redshift, we investigated the morphological properties of the LARS galaxies, in particular the ones that exhibit intense Ly alpha radiation. Methods. We measured sizes and morphological parameters in the continuum, Ly alpha, and Ha images. We studied morphology by using the Gini coefficient vs. M20 and asymmetry vs. concentration diagrams. We then simulated LARS galaxies at z similar to 2 and 5.7, performing the same morphological measurements. We also investigated the detectability of LARS galaxies in current deep field observations. The subsample of LAEs within LARS (LARS-LAEs) was stacked to provide a comparison to stacking studies performed at high redshift. Results. LARS galaxies have continuum size, stellar mass, and rest-frame absolute magnitude typical of Lyman break analogues in the local Universe and also similar to 2 < z < 3 star-forming galaxies and massive LAEs. LARS optical morphology is consistent with the one of merging systems, and irregular or starburst galaxies. For the first time we quantify the morphology in Ly alpha images: even if a variety of intrinsic conditions of the interstellar medium can favour the escape of Ly alpha photons, LARS-LAEs appear small in the continuum, and their Ly alpha is compact. LARS galaxies tend to be more extended in Ly alpha than in the rest-frame UV. It means that Ly alpha photons escape by forming haloes around HII regions of LARS galaxies. Conclusions. The stack of LARS-LAE Ly alpha images is peaked in the centre, indicating that the conditions, which make a galaxy an LAE, tend to produce a concentrated surface brightness profile. On the other hand, the stack of all LARS galaxies is shallower and more extended. This can be caused by the variety of dust and HI amount and distribution, which produces a more complex, patchy, and extended profile, like the one observed for Lyman break galaxies that can contribute to the stack. We cannot identify a single morphological property that controls whether a galaxy emits a net positive Ly alpha flux. However, the LARS-LAEs have continuum properties consistent with merging systems.
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| 3. |
- North, P. L., et al.
(author)
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MUSE- inspired view of the quasar Q2059-360, its Lyman alpha blob, and its neighborhood
- 2017
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 604
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Journal article (peer-reviewed)abstract
- The radio-quiet quasar Q2059-360 at redshift z = 3 : 08 is known to be close to a small Lyman ff blob (LAB) and to be absorbed by a proximate damped Ly ff (PDLA) system. Here, we present the Multi Unit Spectroscopic Explorer (MUSE) integral field spectroscopy follow-up of this quasi-stellar object (QSO). Our primary goal is to characterize this LAB in detail by mapping it both spatially and spectrally using the Ly ff line, and by looking for high-ionization lines to constrain the emission mechanism. Combining the high sensitivity of the MUSE integral field spectrograph mounted on the Yepun telescope at ESO-VLT with the natural coronagraph provided by the PDLA, we map the LAB down to the QSO position, after robust subtraction of QSO light in the spectral domain. In addition to confirming earlier results for the small bright component of the LAB, we unveil a faint filamentary emission protruding to the south over about 80 pkpc (physical kpc); this results in a total size of about 120 pkpc. We derive the velocity field of the LAB (assuming no transfer effects) and map the Ly ff line width. Upper limits are set to the flux of the N v lambda 1238 1242, C iv lambda 1548 1551, Heii lambda 1640, and C i i i] lambda 1548 1551 lines. We have discovered two probable Ly alpha emitters at the same redshift as the LAB and at projected distances of 265 kpc and 207 kpc from the QSO; their Ly alpha luminosities might well be enhanced by the QSO radiation. We also find an emission line galaxy at z = 0 : 33 near the line of sight to the QSO. This LAB shares the same general characteristics as the 17 others surrounding radio-quiet QSOs presented previously. However, there are indications that it may be centered on the PDLA galaxy rather than on the QSO.
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| 4. |
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| 5. |
- Garel, T., et al.
(author)
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The UV, Lyman alpha, and dark matter halo properties of high-redshift galaxies
- 2015
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 450:2, s. 1279-1294
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Journal article (peer-reviewed)abstract
- We explore the properties of high-redshift Lyman alpha emitters (LAEs), and their link with the Lyman-break galaxy (LBG) population, using a semi-analytic model of galaxy formation that takes into account resonant scattering of Ly alpha photons in gas outflows. We can reasonably reproduce the abundances of LAEs and LBGs from z approximate to 3 to 7, as well as most UV luminosity functions (LFs) of LAEs. The stronger dust attenuation for (resonant) Ly alpha photons compared to UV continuum photons in bright LBGs provides a natural interpretation to the increase of the LAE fraction in LBG samples, X-LAE, towards fainter magnitudes. The redshift evolution of XLAE seems however very sensitive to UV magnitudes limits and equivalent width (EW) cuts. In spite of the apparent good match between the statistical properties predicted by the model and the observations, we find that the tail of the Lya EW distribution (EW greater than or similar to 100 angstrom) cannot be explained by our model, and we need to invoke additional mechanisms. We find that LAEs and LBGs span a very similar dynamical range, but bright LAEs are similar to 4 times rarer than LBGs in massive haloes. Moreover, massive haloes mainly contain weak LAEs in our model, which might introduce a bias towards low-mass haloes in surveys which select sources with high-EW cuts. Overall, our results are consistent with the idea that LAEs and LBGs make a very similar galaxy population. Their apparent differences seem mainly due to EW selections, UV detection limits, and a decreasing Lya to UV escape fraction ratio in high star formation rate galaxies.
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| 6. |
- Gazagnes, Simon, et al.
(author)
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Interpreting the Si ii and C ii Line Spectra from the COS Legacy Archive Spectroscopic SurveY Using a Virtual Galaxy from a High-resolution Radiation-hydrodynamic Simulation
- 2023
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 952:2
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Journal article (peer-reviewed)abstract
- Observations of low-ionization state metal lines provide crucial insights into the interstellar medium (ISM) of galaxies, yet, disentangling the physical processes responsible for the emerging line profiles is difficult. This work investigates how mock spectra generated using a single galaxy in a radiation-hydrodynamical simulation can help us interpret observations of a real galaxy. We create 22,500 C ii and Si ii spectra from the virtual galaxy at different times and through multiple lines of sight and compare them with the 45 observations of low-redshift star-forming galaxies from the COS Legacy Spectroscopic SurveY (classy). We find that the mock profiles provide accurate replicates of the observations of 38 galaxies with a broad range of stellar masses (106–109M⊙) and metallicities (0.02–0.55 Z⊙). Additionally, we highlight that aperture losses explain the weakness of the fluorescent emission in several classy spectra and must be accounted for when comparing simulations to observations. Overall, we show that the evolution of a single simulated galaxy can produce a large diversity of spectra whose properties are representative of galaxies of comparable or smaller masses. Building upon these results, we explore the origin of the continuum, residual flux, and fluorescent emission in the simulation. We find that these different spectral features all emerge from distinct regions in the galaxy's ISM, and their characteristics can vary as a function of the viewing angle. While these outcomes challenge simplified interpretations of down-the-barrel spectra, our results indicate that high-resolution simulations provide an optimal framework to interpret these observations.
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| 7. |
- North, P., et al.
(author)
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Polarimetry of the Lyα envelope of the radio-quiet quasar SDSS J124020.91+145535.6
- 2024
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 684
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Journal article (peer-reviewed)abstract
- The radio quiet quasar SDSS J1240+1455 lies at a redshift of z = 3.11, is surrounded by a Lyα blob (LAB), and is absorbed by a proximate damped Lyα system. In order to better define the morphology of the blob and determine its emission mechanism, we gathered deep narrow-band images isolating the Lyα line of this object in linearly polarized light. We provide a deep intensity image of the blob, showing a filamentary structure extending up to 16″ (or 122 physical kpc) in diameter. No significant polarization signal could be extracted from the data, but 95% probability upper limits were defined through simulations. They vary between ∼3% in the central 0.75″ disk (after subtraction of the unpolarized quasar continuum) and ∼10% in the 3.8 − 5.5″ annulus. The low polarization suggests that the Lyα photons are emitted mostly in situ, by recombination and de-excitation in a gas largely ionized by the quasar ultraviolet light, rather than by a central source and scattered subsequently by neutral hydrogen gas. This blob shows no detectable polarization signal, contrary to LAB1, a brighter and more extended blob that is not related to the nearby active galactic nucleus (AGN) in any obvious way, and where a significant polarization signal of about 18% was detected.
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| 8. |
- Pardy, Stephen A., et al.
(author)
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THE LYMAN ALPHA REFERENCE SAMPLE. III. PROPERTIES OF THE NEUTRAL ISM FROM GBT AND VLA OBSERVATIONS
- 2014
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 794:2
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Journal article (peer-reviewed)abstract
- We present new Hi imaging and spectroscopy of the 14 UV-selected star-forming galaxies in the Lyman Alpha Reference Sample (LARS), aimed for a detailed study of the processes governing the production, propagation, and escape of Ly alpha photons. New Hi spectroscopy, obtained with the 100 m Green Bank Telescope (GBT), robustly detects the Hi spectral line in 11 of the 14 observed LARS galaxies (although the profiles of two of the galaxies are likely confused by other sources within the GBT beam); the three highest redshift galaxies are not detected at our current sensitivity limits. The GBT profiles are used to derive fundamental Hi line properties of the LARS galaxies. We also present new pilot Hi spectral line imaging of five of the LARS galaxies obtained with the Karl G. Jansky Very Large Array (VLA). This imaging localizes the Hi gas and provides a measurement of the total Hi mass in each galaxy. In one system, LARS 03 (UGC 8335 or Arp 238), VLA observations reveal an enormous tidal structure that extends over 160 kpc from the main interacting systems and that contains >10(9) M-circle dot of Hi. We compare various Hi properties with global Ly alpha quantities derived from Hubble Space Telescope measurements. The measurements of the Ly alpha escape fraction are coupled with the new direct measurements of Hi mass and significantly disturbed Hi velocities. Our robustly detected sample reveals tentative correlations between the total Hi mass and linewidth, and key Ly alpha tracers. Further, on global scales, these data support a complex coupling between Ly alpha propagation and the Hi properties of the surrounding medium.
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| 9. |
- 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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| 10. |
- 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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