ORCID Profile
0000-0002-6085-5073
Current Organisation
The University of Texas at Austin
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Publisher: EDP Sciences
Date: 09-2020
DOI: 10.1051/0004-6361/202038133
Abstract: We investigated the ultraviolet (UV) spectral properties of faint Lyman- α emitters (LAEs) in the redshift range 2.9 ≤ z ≤ 4.6, and we provide material to prepare future observations of the faint Universe. We used data from the MUSE Hubble Ultra Deep Survey to construct mean rest-frame spectra of continuum-faint (median M UV of −18 and down to M UV of −16), low stellar mass (median value of 10 8.4 M ⊙ and down to 10 7 M ⊙ ) LAEs at redshift z ≳ 3. We computed various averaged spectra of LAEs, subs led on the basis of their observational (e.g., Ly α strength, UV magnitude and spectral slope) and physical (e.g., stellar mass and star-formation rate) properties. We searched for UV spectral features other than Ly α , such as higher ionization nebular emission lines and absorption features. We successfully observed the O III ] λ 1666 and [C III ] λ 1907+C III ] λ 1909 collisionally excited emission lines and the He II λ 1640 recombination feature, as well as the resonant C IV λ λ 1548,1551 doublet either in emission or P-Cygni. We compared the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the LAEs. In particular, the mean spectra of LAEs with larger Ly α equivalent widths, fainter UV magnitudes, bluer UV spectral slopes, and lower stellar masses show the strongest nebular emission. The line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in in idual spectra of z 2 galaxies. This suggests that weak UV features are likely ubiquitous in high z , low-mass, and faint LAEs. We publicly released the stacked spectra, as they can serve as empirical templates for the design of future observations, such as those with the James Webb Space Telescope and the Extremely Large Telescope.
Publisher: EDP Sciences
Date: 03-2022
DOI: 10.1051/0004-6361/202141900
Abstract: Context. The hydrogen Lyman α line is often the only measurable feature in optical spectra of high-redshift galaxies. Its shape and strength are influenced by radiative transfer processes and the properties of the underlying stellar population. High equivalent widths of several hundred Å are especially hard to explain by models and could point towards unusual stellar populations, for ex le with low metallicities, young stellar ages, and a top-heavy initial mass function. Other aspects influencing equivalent widths are the morphology of the galaxy and its gas properties. Aims. The aim of this study is to better understand the connection between the Lyman α rest-frame equivalent width (EW 0 ) and spectral properties as well as ultraviolet (UV) continuum morphology by obtaining reliable EW 0 histograms for a statistical s le of galaxies and by assessing the fraction of objects with large equivalent widths. Methods. We used integral field spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE) combined with broad-band data from the Hubble Space Telescope (HST) to measure EW 0 . We analysed the emission lines of 1920 Lyman α emitters (LAEs) detected in the full MUSE-Wide (one hour exposure time) and MUSE-Deep (ten hour exposure time) surveys and found UV continuum counterparts in archival HST data. We fitted the UV continuum photometric images using the Galfit software to gain morphological information on the rest-UV emission and fitted the spectra obtained from MUSE to determine the double peak fraction, asymmetry, full-width at half maximum, and flux of the Lyman α line. Results. The two surveys show different histograms of Lyman α EW 0 . In MUSE-Wide, 20% of objects have EW 0 240 Å, while this fraction is only 11% in MUSE-Deep and ≈16% for the full s le. This includes objects without HST continuum counterparts (one-third of our s le), for which we give lower limits for EW 0 . The object with the highest securely measured EW 0 has EW 0 = 589 ± 193 Å (the highest lower limit being EW 0 = 4464 Å). We investigate the connection between EW 0 and Lyman α spectral or UV continuum morphological properties. Conclusions. The survey depth has to be taken into account when studying EW 0 distributions. We find that in general, high EW 0 objects can have a wide range of spectral and UV morphological properties, which might reflect that the underlying causes for high EW 0 values are equally varied.
Publisher: Springer Science and Business Media LLC
Date: 30-10-2018
DOI: 10.1038/S41586-018-0664-3
Abstract: Change history: In this Letter, author M. Akhlaghi should be associated with affiliation (2) rather than (3). This error has been corrected online.
Publisher: EDP Sciences
Date: 10-2021
DOI: 10.1051/0004-6361/202140876
Abstract: Rest-frame ultraviolet (UV) emission lines probe electron densities, gas-phase abundances, metallicities, and ionization parameters of the emitting star-forming galaxies and their environments. The strongest main UV emission line, Ly α , has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Ly α emission becomes increasingly challenging at z ≳ 6 when the neutral hydrogen fraction of the circumgalactic and intergalactic media increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large s le of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxies’ physical properties and their Ly α emission. The s le of 2052 emission line sources with 1.5 z 6.4 was collected from integral field data from the MUSE-Wide and MUSE-Deep surveys taken as part of Guaranteed Time Observations. The objects were selected through untargeted source detection (i.e., no preselection of sources as in dedicated spectroscopic c aigns) in the three-dimensional MUSE data cubes. We searched optimally extracted one-dimensional spectra of the full s le for UV emission features via emission line template matching, resulting in a s le of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Ly α ) UV emission lines increases with survey depth, and that the emission line strength of He II λ 1640 Å, [O III ] λ 1661 + O III ] λ 1666, and [Si III ] λ 1883 + Si III ] λ 1892 correlate with the strength of [C III ] λ 1907 + C III ] λ 1909. The rest-frame equivalent width (EW 0 ) of [C III ] λ 1907 + C III ] λ 1909 is found to be roughly 0.22 ± 0.18 of EW 0 (Ly α ). We measured the velocity offsets of resonant emission lines with respect to systemic tracers. For C IV λ 1548 + C IV λ 1551 we find that Δ v C IV ≲ 250 km s −1 , whereas Δ v Ly α falls in the range of 250−500 km s −1 which is in agreement with previous results from the literature. The electron density n e measured from [Si III ] λ 1883 + Si III ] λ 1892 and [C III ] λ 1907 + C III ] λ 1909 line flux ratios is generally 10 5 cm −3 and the gas-phase abundance is below solar at 12 + log 10 (O/H)≈8. Lastly, we used “PhotoIonization Model Probability Density Functions” to infer physical parameters of the full s le and in idual systems based on photoionization model parameter grids and observational constraints from our UV emission line searches. This reveals that the UV line emitters generally have ionization parameter log 10 (U) ≈ −2.5 and metal mass fractions that scatter around Z ≈ 10 −2 , that is Z ≈ 0.66 Z ⊙ . Value-added catalogs of the full s le of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper.
Publisher: Oxford University Press (OUP)
Date: 22-08-2020
Abstract: CR7 is among the most luminous Ly α emitters (LAEs) known at z = 6.6 and consists of at least three UV components that are surrounded by Ly α emission. Previous studies have suggested that it may host an extreme ionizing source. Here, we present deep integral field spectroscopy of CR7 with VLT/Multi Unit Spectroscopic Explorer (MUSE). We measure extended emission with a similar halo scale length as typical LAEs at z ≈ 5. CR7’s Ly α halo is clearly elongated along the direction connecting the multiple components, likely tracing the underlying gas distribution. The Ly α emission originates almost exclusively from the brightest UV component, but we also identify a faint kinematically distinct Ly α emitting region nearby a fainter component. Combined with new near-infrared data, the MUSE data show that the rest-frame Ly α equivalent width (EW) is ≈100 Å. This is a factor 4 higher than the EW measured in low-redshift analogues with carefully matched Ly α profiles (and thus arguably H i column density), but this EW can plausibly be explained by star formation. Alternative scenarios requiring active galactic nucleus (AGN) powering are also disfavoured by the narrower and steeper Ly α spectrum and much smaller IR to UV ratio compared to obscured AGN in other Ly α blobs. CR7’s Ly α emission, while extremely luminous, resembles the emission in more common LAEs at lower redshifts very well and is likely powered by a young metal-poor starburst.
Publisher: EDP Sciences
Date: 04-2022
DOI: 10.1051/0004-6361/202142302
Abstract: Hydrogen Ly α haloes (LAHs) are commonly used as a tracer of the circumgalactic medium (CGM) at high redshifts. In this work, we aim to explore the existence of Ly α haloes around in idual UV-selected galaxies, rather than around Ly α emitters (LAEs), at high redshifts. Our s le was continuum-selected with F 775 W ≤ 27.5, and spectroscopic redshifts were assigned or constrained for all the sources thanks to the deepest (100- to 140-h) existing Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) data with adaptive optics. The final s le includes 21 galaxies that are purely F 775 W -magnitude selected within the redshift range z ≈ 2.9 − 4.4 and within a UV magnitude range −20 ≤ M 1500 ≤ −18, thus avoiding any bias toward LAEs. We tested whether galaxy’s Ly α emission is significantly more extended than the MUSE PSF-convolved continuum component. We find 17 LAHs and four non-LAHs. We report the first in idual detections of extended Ly α emission around non-LAEs. The Ly α halo fraction is thus as high as 81.0 −11.2 +10.3 %, which is close to that for LAEs at z = 3 − 6 in the literature. This implies that UV-selected galaxies generally have a large amount of hydrogen in their CGM. We derived the mean surface brightness (SB) profile for our LAHs with cosmic dimming corrections and find that Ly α emission extends to 5.4 arcsec (≃40 physical kpc at the midpoint redshift z = 3.6) above the typical 1 σ SB limit. The incidence rate of surrounding gas detected in Ly α per one-dimensional line of sight per unit redshift, d n /d z , is estimated to be 0.76 −0.09 +0.09 for galaxies with M 1500 ≤ −18 mag at z ≃ 3.7. Assuming that Ly α emission and absorption arise in the same gas, this suggests, based on abundance matching, that LAHs trace the same gas as d ed Ly α systems (DLAs) and sub-DLAs.
Publisher: EDP Sciences
Date: 03-2021
DOI: 10.1051/0004-6361/202039887
Abstract: We report the discovery of diffuse extended Ly α emission from redshift 3.1 to 4.5, tracing cosmic web filaments on scales of 2.5−4 cMpc. These structures have been observed in overdensities of Ly α emitters in the MUSE Extremely Deep Field, a 140 h deep MUSE observation located in the Hubble Ultra-Deep Field. Among the 22 overdense regions identified, five are likely to harbor very extended Ly α emission at high significance with an average surface brightness of 5 × 10 −20 erg s −1 cm −2 arcsec −2 . Remarkably, 70% of the total Ly α luminosity from these filaments comes from beyond the circumgalactic medium of any identified Ly α emitter. Fluorescent Ly α emission powered by the cosmic UV background can only account for less than 34% of this emission at z ≈ 3 and for not more than 10% at higher redshift. We find that the bulk of this diffuse emission can be reproduced by the unresolved Ly α emission of a large population of ultra low-luminosity Ly α emitters ( 10 40 erg s −1 ), provided that the faint end of the Ly α luminosity function is steep ( α ⪅ −1.8), it extends down to luminosities lower than 10 38 − 10 37 erg s −1 , and the clustering of these Ly α emitters is significant (filling factor 1/6). If these Ly α emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates 10 −4 M ⊙ yr −1 . These observations provide the first detection of the cosmic web in Ly α emission in typical filamentary environments and the first observational clue indicating the existence of a large population of ultra low-luminosity Ly α emitters at high redshift.
Publisher: Springer Science and Business Media LLC
Date: 10-2018
DOI: 10.1038/S41586-018-0564-6
Abstract: Galaxies are surrounded by large reservoirs of gas, mostly hydrogen, that are fed by inflows from the intergalactic medium and by outflows from galactic winds. Absorption-line measurements along the lines of sight to bright and rare background quasars indicate that this circumgalactic medium extends far beyond the starlight seen in galaxies, but very little is known about its spatial distribution. The Lyman-α transition of atomic hydrogen at a wavelength of 121.6 nanometres is an important tracer of warm (about 10
No related grants have been discovered for Floriane Leclercq.