| 1. |
- Marques-Chaves, R., et al.
(författare)
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No correlation of the Lyman continuum escape fraction with spectral hardness
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 663
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Tidskriftsartikel (refereegranskat)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.
(författare)
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The Lyman alpha reference sample IV. Morphology at low and high redshift
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 576
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Tidskriftsartikel (refereegranskat)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.
(författare)
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MUSE- inspired view of the quasar Q2059-360, its Lyman alpha blob, and its neighborhood
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 604
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Tidskriftsartikel (refereegranskat)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.
(författare)
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The UV, Lyman alpha, and dark matter halo properties of high-redshift galaxies
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 450:2, s. 1279-1294
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 952:2
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Tidskriftsartikel (refereegranskat)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. |
- Pardy, Stephen A., et al.
(författare)
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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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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 794:2
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Rasekh, Armin, et al.
(författare)
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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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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 662
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Tidskriftsartikel (refereegranskat)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. |
- Xu, Xinfeng, et al.
(författare)
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Tracing Lyα and LyC Escape in Galaxies with Mg ıı Emission
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 933:2
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Tidskriftsartikel (refereegranskat)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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| 10. |
- Östlin, Göran, et al.
(författare)
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THE Ly alpha REFERENCE SAMPLE. I. SURVEY OUTLINE AND FIRST RESULTS FOR MARKARIAN 259
- 2014
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 797:1
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Tidskriftsartikel (refereegranskat)abstract
- The Ly alpha Reference Sample (LARS) is a substantial program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the detailed astrophysics of the visibility and strength of the Ly alpha line of neutral hydrogen. Ly alpha is the dominant spectral line in use for characterizing high-redshift (z) galaxies. This paper presents an overview of the survey, its selection function, and HST imaging observations. The sample was selected from the combined GALEX+Sloan Digital Sky Survey catalog at z = 0.028-0.19, in order to allow Ly alpha to be captured with combinations of long-pass filters in the Solar Blind Channel (SBC) of the Advanced Camera for Surveys (ACS) onboard HST. In addition, LARS utilizes H alpha and H beta narrowband and u, b, i broadband imaging with ACS and the Wide Field Camera 3 (WFC3). In order to study galaxies in which large numbers of Ly alpha photons are produced (whether or not they escape), we demanded an H alpha equivalent width W(H alpha) >= 100 angstrom. The final sample of 14 galaxies covers far-UV (FUV, lambda similar to 1500 angstrom) luminosities that overlap with those of high-z Ly alpha emitters (LAEs) and Lyman break galaxies (LBGs), making LARS a valid comparison sample. We present the reduction steps used to obtain the Ly alpha images, including our LARS eXtraction software (LaXs), which utilizes pixel-by-pixel spectral synthesis fitting of the energy distribution to determine and subtract the continuum at Ly alpha. We demonstrate that the use of SBC long-pass-filter combinations increase the signal-to-noise ratio by an order of magnitude compared to the nominal Ly alpha filter available in SBC. To exemplify the science potential of LARS, we also present some first results for a single galaxy, Mrk 259 (LARS #1). This irregular galaxy shows bright and extended (indicative of resonance scattering) but strongly asymmetric Ly alpha emission. Spectroscopy from the Cosmic Origins Spectrograph on board HST centered on the brightest UV knot shows a moderate outflow in the neutral interstellar medium (probed by low ionization stage absorption features) and Ly alpha emission with an asymmetric profile. Radiative transfer modeling is able to reproduce the essential features of the Ly alpha line profile and confirms the presence of an outflow. From the integrated photometry we measure an Ly alpha luminosity of L-Ly alpha= 1.3x10(42) erg s(-1) an equivalent width W(Ly alpha) = 45 angstrom and an FUV absolute magnitude M-FUV = -19.2 (AB). Mrk 259 would hence be detectable in high-z Ly alpha and LBG surveys. The total Ly alpha escape fraction is 12%. This number is higher than the low-z average, but similar to that at z > 4, demonstrating that LARS provides a valid comparison sample for high-z galaxy studies.
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