| 1. |
- Caruana, Joseph, et al.
(author)
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The MUSE-Wide survey : a measurement of the Ly alpha emitting fraction among z > 3 galaxies
- 2018
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 473:1, s. 30-37
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Journal article (peer-reviewed)abstract
- We present a measurement of the fraction of Lyman α (Ly α) emitters (XLy α) amongst HST continuum-selected galaxies at 3 < z < 6 with the Multi-Unit Spectroscopic Explorer (MUSE) on the VLT. Making use of the first 24 MUSE-Wide pointings in GOODS-South, each having an integration time of 1 h, we detect 100 Ly α emitters and find XLy α ≳ 0.5 for most of the redshift range covered, with 29 per cent of the Ly α sample exhibiting rest equivalent widths (rest-EWs) ≤ 15 Å. Adopting a range of rest-EW cuts (0–75 Å), we find no evidence of a dependence of XLy α on either redshift or ultraviolet luminosity.
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| 2. |
- Duval, Florent, et al.
(author)
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The Lyman alpha reference sample VI. Lyman alpha escape from the edge-on disk galaxy Mrk 1486
- 2016
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 587
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Journal article (peer-reviewed)abstract
- Context. Recent numerical simulations suggest that the strength of the Lyman alpha (Ly alpha) line of star-forming disk galaxies strongly depends on the inclination at which they are observed: from edge-on to face-on, we expect to see a change from a strongly attenuated Ly alpha line to a strong Ly alpha emission line.Aims. We aim to understand how a strong Ly alpha emission line is able to escape from the low-redshift highly inclined (edge-on) disk galaxy Mrk 1486 (z similar to 0.0338). To our knowledge, this work is the first observational study of Ly alpha transport inside an edge-on disk galaxy.Methods. Using a large set of HST imaging and spectroscopic data, we investigated the interstellar medium (ISM) structure and the dominant source of Ly alpha radiation inside Mrk 1486. Moreover, using a 3D Monte Carlo Ly alpha radiation transfer code, we studied the radiative transfer of Ly alpha and UV continuum photons inside a 3D geometry of neutral hydrogen (HI) and dust that models the ISM structure at the galaxy center. Our numerical simulations predicted the Ly alpha line profile that we then compared to the one observed in the HST/COS spectrum of Mrk 1486.Results. While a pronounced Ly alpha absorption line emerges from the disk of Mrk 1486, very extended Ly alpha structures are observed at large radii from the galaxy center: a large Ly alpha-halo and two very bright Ly alpha regions located slightly above and below the disk plane. The analysis of IFU H alpha spectroscopic data of Mrk 1486 indicates the presence of two bipolar outflowing halos of HI gas at the same location as these two bright Ly alpha regions. Comparing different diagnostic diagrams (such as [OIII](5007)/H beta versus [OI](6300)/H alpha) to photo-and shock-ionization models, we find that the Ly alpha production of Mrk 1486 is dominated by photoionization inside the galaxy disk. From this perspective, our numerical simulations succeed in reproducing the strength and shape of the observed Ly alpha emission line of Mrk 1486 by assuming a scenario in which the Ly alpha photons are produced inside the galaxy disk, travel along the outflowing halos, and scatter on cool HI materials toward the observer.Conclusions. Extended bipolar galactic winds are frequently observed from star-forming disk galaxies. Given the advantage Ly alpha photons take of such outflowing HI materials to easily escape from Mrk 1486, this mechanism may explain the origin of strong Ly alpha emission lines frequently observed from highly inclined galaxies at high-redshift. This therefore challenges the robustness of the expected viewing-angle effect on the Ly alpha properties of star-forming disk galaxies.
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| 3. |
- Feltre, Anna, et al.
(author)
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The MUSE Hubble Ultra Deep Field Survey XII. Mg II emission and absorption in star-forming galaxies
- 2018
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 617
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Journal article (peer-reviewed)abstract
- The physical origin of the near-ultraviolet Mg II emission remains an underexplored domain, unlike more typical emission lines that are detected in the spectra of star-forming galaxies. We explore the nebular and physical properties of a sample of 381 galaxies between 0.70 < z < 2.34 drawn from the MUSE Hubble Ultra Deep Survey. The spectra of these galaxies show a wide variety of profiles of the Mg II lambda lambda 2796, 2803 resonant doublet, from absorption to emission. We present a study on the main drivers for the detection of Mg II emission in galaxy spectra. By exploiting photoionization models, we verified that the emission-line ratios observed in galaxies with Mg II in emission are consistent with nebular emission from HII regions. From a simultaneous analysis of MUSE spectra and ancillary Hubble Space Telescope information through spectral energy distribution fitting, we find that galaxies with Mg II in emission have lower stellar masses, smaller sizes, bluer spectral slopes, and lower optical depth than those with absorption. This leads us to suggest that Mg II emission is a potential tracer of physical conditions that are not merely related to those of the ionized gas. We show that these differences in Mg II emission and absorption can be explained in terms of a higher dust and neutral gas content in the interstellar medium (ISM) of galaxies showing Mg II in absorption, which confirms the extreme sensitivity of Mg II to the presence of the neutral ISM. We conclude with an analogy between the Mg II doublet and the Ly alpha line that lies in their resonant nature. Further investigations with current and future facilities, including the James Webb Space Telescope, are promising because the detection of Mg II emission and its potential connection with Ly alpha could provide new insights into the ISM content in the early Universe.
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| 4. |
- Herenz, Edmund Christian, et al.
(author)
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The Lyman alpha reference sample VII. Spatially resolved H alpha kinematics
- 2016
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 587
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Journal article (peer-reviewed)abstract
- We present integral field spectroscopic observations with the Potsdam Multi-Aperture Spectrophotometer of all 14 galaxies in the z similar to 0.1 Lyman Alpha Reference Sample (LARS). We produce 2D line-of-sight velocity maps and velocity dispersion maps from the Balmer alpha (H alpha) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Ly alpha radiation field. We show our kinematic maps that are spatially registered onto the Hubble Space Telescope H alpha and Lyman alpha (Ly alpha) images. We can conjecture a causal connection between spatially resolved H alpha kinematics and Ly alpha photometry for individual galaxies, however, no general trend can be established for the whole sample. Furthermore, we compute the intrinsic velocity dispersion sigma(0), the shearing velocity v(shear), and the v(shear)/sigma(0) ratio from our kinematic maps. In general LARS galaxies are characterised by high intrinsic velocity dispersions (54 km s(-1) median) and low shearing velocities (65 km s(-1) median). The v(shear/sigma 0) values range from 0.5 to 3.2 with an average of 1.5. It is noteworthy that five galaxies of the sample are dispersion-dominated systems with v(shear)/sigma(0) < 1, and are thus kinematically similar to turbulent star-forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Ly alpha properties, we find that dispersion-dominated systems show higher Ly alpha equivalent widths and higher Ly alpha escape fractions than systems with v(shear)/sigma(0) > 1. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Ly alpha radiation.
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| 5. |
- Leclercq, Floriane, et al.
(author)
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The MUSE &ITHubble&IT Ultra Deep Field Survey VIII. Extended Lyman-alpha haloes around high-&ITz&IT star-forming galaxies
- 2017
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 608
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Journal article (peer-reviewed)abstract
- We report the detection of extended Ly alpha haloes around 145 individual star-forming galaxies at redshifts 3 <= z <= 6 in the Hubble Ultra Deep Field observed with the Multi-Unit Spectroscopic Explorer (MUSE) at ESO-VLT. Our sample consists of continuum-faint (-15 >= M-UV >= -22) Ly alpha emitters (LAEs). Using a 2D, two-component (continuum-like and halo) decomposition of Ly alpha emission assuming circular exponential distributions, we measure scale lengths and luminosities of Ly alpha haloes. We find that 80% of our objects having reliable Ly alpha halo measurements show Ly alpha emission that is significantly more extended than the UV continuum detected by HST (by a factor approximate to 4 to >20). The median exponential scale length of the Ly alpha haloes in our sample is approximate to 4.5 kpc with a few haloes exceeding 10 kpc. By comparing the maximal detected extent of the Ly alpha emission with the predicted dark matter halo virial radii of simulated galaxies, we show that the detected Ly alpha emission of our selected sample of Ly alpha emitters probes a significant portion of the cold circum-galactic medium of these galaxies (>50% in average). This result therefore shows that there must be significant HI reservoirs in the circum-galactic medium and reinforces the idea that Ly alpha haloes are ubiquitous around high-redshift Ly alpha emitting galaxies. Our characterization of the Ly alpha haloes indicates that the majority of the Ly alpha flux comes from the halo (approximate to 65%) and that their scale lengths seem to be linked to the UV properties of the galaxies (sizes and magnitudes). We do not observe a significant Ly alpha halo size evolution with redshift, although our sample for z > 5 is very small. We also explore the diversity of the Ly alpha line profiles in our sample and we find that the Ly alpha lines cover a large range of full width at half maximum (FWHM) from 118 to 512 km s(-1). While the FWHM does not seem to be correlated to the Ly alpha scale length, most compact Ly alpha haloes and those that are not detected with high significance tend to have narrower Ly alpha profiles (<350 km s(-1)). Finally, we investigate the origin of the extended Ly alpha emission but we conclude that our data do not allow us to disentangle the possible processes, i.e. scattering from star-forming regions, fluorescence, cooling radiation from cold gas accretion, and emission from satellite galaxies.
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| 6. |
- Rivera-Thorsen, Thöger E., et al.
(author)
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THE LYMAN ALPHA REFERENCE SAMPLE. V. THE IMPACT OF NEUTRAL ISM KINEMATICS ANDGEOMETRY ON Lyα ESCAPE
- 2015
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 805:14
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Journal article (peer-reviewed)abstract
- We present high-resolution far-UV spectroscopy of the 14 galaxies of the Lyα Reference Sample; a sample of strongly star-forming galaxies at low redshifts (0.028 < z < 0.18). We compare the derived properties to global properties derived from multi-band imaging and 21 cm H i interferometry and single-dish observations, as well as archival optical SDSS spectra. Besides the Lyα line, the spectra contain a number of metal absorption features allowing us to probe the kinematics of the neutral ISM and evaluate the optical depth and and covering fraction of the neutral medium as a function of line of sight velocity. Furthermore, we show how this, in combination with the precise determination of systemic velocity and good Lyα spectra, can be used to distinguish a model in which separate clumps together fully cover the background source, from the "picket fence" model named by Heckman et al. We find that no one single effect dominates in governing Lyα radiative transfer and escape. Lyα escape in our sample coincides with a maximum velocity-binned covering fraction of 0.9 and bulk outflow velocities of 50 km s−1, although a number of galaxies show these characteristics and yet little or no Lyα escape. We find that Lyα peak velocities, where available, are not consistent with a strong backscattered component, but rather with a simpler model of an intrinsic emission line overlaid by a blueshifted absorption profile from the outflowing wind. Finally, we find a strong anticorrelation between Hα equivalent width and maximum velocity-binned covering factor, and propose a heuristic explanatory model.
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| 7. |
- Verhamme, Anne, et al.
(author)
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Using Lyman-alpha to detect galaxies that leak Lyman continuum
- 2015
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 578
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Journal article (peer-reviewed)abstract
- Aims. We propose to infer the output of the ionising continuum-leaking properties of galaxies based upon their Ly alpha line profiles. Methods. We carried out Ly alpha radiation transfer calculations in two models of H II regions. These models are porous to ionising continuum escape: 1) we define Lyman-continuum (LyC) optically thin star clusters, in which massive stars produce enough ionising photons to keep the surrounding interstellar medium transparent to the ionising continuum, in other words, almost totally ionised; and 2) we define riddled ionisation-bounded media that are surrounded by neutral interstellar medium, but have holes, which results in a covering fraction lower than unity. Results. The Ly alpha spectra that emerge from these configurations have distinctive features: 1) a classical asymmetric redshifted profile in the first case, but with a small shift of the profile maximum compared to the systemic redshift (v(peak) <= 150 km s(-1)); 2) a main peak at the systemic redshift in the second case (v(peak) = 0), with a non-zero Ly alpha flux bluewards of the systemic redshift as a consequence. If in a galaxy that leaks ionising photons the Ly alpha component that emerges from the leaking star cluster(s) is assumed to dominate the total Ly alpha spectrum, the Ly alpha shape may be used as a pre-selection tool for detecting LyC-leaking galaxies in objects with high spectral resolution Ly alpha spectra (R >= 4000). Our predictions are corroborated by examination of a sample of ten local starbursts with high-resolution HST/COS Ly alpha spectra that are known in the literature as LyC leakers or leaking candidates. Conclusions. Observations of Ly alpha profiles at high resolution are expected to show definite signatures revealing the escape of Lyman-continuum photons from star-forming galaxies.
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