The MUSE Hubble Ultra Deep Field Survey

Abstract

Context. The Lyα emitter (LAE) fraction, X LAE , is a potentially powerful probe of the evolution of the intergalactic neutral hydrogen gas fraction. However, uncertainties in the measurement of X LAE are still debated. Aims. Thanks to deep data obtained with the integral field spectrograph MUSE (Multi-Unit Spectroscopic Explorer), we can measure the evolution of the LAE fraction homogeneously over a wide redshift range of z ≈ 3-6 for UV-faint galaxies (down to UV magnitudes of M 1500 ≈ −17.75). This is significantly fainter than in former studies (M 1500 ≤ −18.75), and allows us to probe the bulk of the population of high-redshift star-forming galaxies. Methods. We construct a UV-complete photometric-redshift sample following UV luminosity functions and measure the Lyα emission with MUSE using the latest (second) data release from the MUSE Hubble Ultra Deep Field Survey. Results. We derive the redshift evolution of X LAE for M 1500 ∈ [−21.75; −17.75] for the first time with a equivalent width range EW(Lyα) ≥ 65 Å and find low values of X LAE 30% at z 6. The best fit linear relation is X LAE = 0.07 +0.06 −0.03 z − 0.22 +0.12 −0.24 . For M 1500 ∈ [−20.25; −18.75] and EW(Lyα) ≥ 25 Å, our X LAE values are consistent with those in the literature within 1σ at z 5, but our median values are systematically lower than reported values over the whole redshift range. In addition, we do not find a significant dependence of X LAE on M 1500 for EW(Lyα) ≥ 50 Å at z ≈ 3-4, in contrast with previous work. The differences in X LAE mainly arise from selection biases for Lyman Break Galaxies (LBGs) in the literature: UV-faint LBGs are more easily selected if they have strong Lyα emission, hence X LAE is biased towards higher values when those samples are used. Conclusions. Our results suggest either a lower increase of X LAE towards z ≈ 6 than previously suggested, or even a turnover of X LAE at z ≈ 5.5, which may be the signature of a late or patchy reionization process. We compared our results with predictions from a cosmological galaxy evolution model. We find that a model with a bursty star formation (SF) can reproduce our observed LAE fractions much better than models where SF is a smooth function of time.

The size and pervasiveness of Ly α–UV spatial offsets in star-forming galaxies at z ∼ 6

“…The confluence of these two effects appears to lead to a picture where the fraction of LAEs increases from z ∼ 0 until the edge of the reionization era (z ∼ 6) and then begins to drop precipitously at higher redshifts. Such a trend is indeed observed when the fraction of LAEs or derivative Lyα quantities have been used to probe the physical conditions during the reionization epoch, with such studies pointing to evidence of an increasingly neutral medium at z ∼ > 6 (e.g., Ota et al 2008;Fontana et al 2010;Pentericci et al 2011Pentericci et al , 2018bOno et al 2012;Treu et al 2013;Schenker et al 2014;Tilvi et al 2014;Hu et al 2017;Zheng et al 2017;Hoag et al 2019b;Mason et al 2018Mason et al , 2019Fuller et al 2020, though see, e.g., De Barros et al 2017;Caruana et al 2018;Kusakabe et al 2020 for a slightly different view). The fractional amount of Lyα estimated to escape starforming galaxies can also be used to place constraints on internal galaxy physics (e.g., Dijkstra et al 2011;Hayes et al 2011;De Barros et al 2017;Sobral et al 2018) and the measured velocity difference between the Lyα feature and the systemic velocity as well as the Lyα line profile can be used to constrain kinematic models of such galaxies (e.g., Dawson et al 2002;Westra et al 2005;Sawicki et al 2008;Verhamme et al 2008Verhamme et al , 2015Steidel et al 2010;Dijkstra 2014;Guaita et al 2017;Marchi et al 2019;Cassata et al 2020).…”

ALMA Lensing Cluster Survey: Bright [C ii] 158 μm Lines from a Multiply Imaged Sub-L ⋆ Galaxy at z = 6.0719

“…While high-redshift galaxies with Lyα spectroscopic redshifts show weak [C II] lines at a given star formation rate (Carniani et al 2018;Harikane et al 2018Harikane et al , 2020; but see Schaerer et al 2020), a recent study by Smit et al (2018) indicates that galaxies with no strong Lyα line may emit a strong [C II] line. Since the fraction of Lyα emitters (LAEs; e.g., equivalent width of Lyα > 25 Å) is less than 30% among star-forming galaxies with M UV ∼ −21.5 mag at z > 6 (e.g., Stark et al 2011;Treu et al 2013;Tilvi et al 2014;De Barros et al 2017;Pentericci et al 2018;Kusakabe et al 2020), follow-up observations of only those galaxies with secure Lyα lines will systematically miss a majority of the representative population at z > 6. An ALMA blind line survey is one possible solution, but novel [C II] line emitters z > 6…”

MUSE observations towards the lensing cluster A2744: Intersection between the LBG and LAE populations at z ∼ 3–7

“…On one hand, two-step surveys based on LAEs spectroscopically identified among photometrically pre-selected LBG populations are likely missing LAEs with the faintest continuum counterparts or exhibiting extended and/or ex-centered Lyα emission. On the other hand, Lyα emission is also likely to affect broad-band photometry used in the LBG pre-selection as well as the UV detection limit, as discussed in Kusakabe et al (2020). On the contrary, Arrabal Haro et al (2018) used the 25 medium bands of the SHARDS survey to select both the LBG and LAE populations.…”

“…Nevertheless, observations of LBGs and LAEs are rarely carried out in the same volume of universe because of observational limitations. Recent pioneering studies have started to address this issue in blank fields, such as for example Arrabal Haro et al (2018) using the SHARDS survey of the GOODS-N field which is a deep-imaging survey using 25 medium band filters, or Inami et al (2017) Hashimoto et al (2017), Maseda et al (2018), and Kusakabe et al (2020), all based on ultra-deep integral field units (IFU) data for the Hubble Ultra Deep Field (HUDF) from MUSE (the Multi-Unit Spectroscopic Explorer; Bacon et al 2010Bacon et al , 2017.…”