Upper limits on the escape fraction of ionizing radiation from galaxies at 2 ≲ z < 6

In this work, we investigate upper limits on the global escape fraction of ionizing photons ($f_{\rm esc/global}^{\rm abs}$) from a sample of galaxies probed for Lyman-continuum (LyC) emission characterized as non-LyC and LyC leakers. We present a sample of 9 clean non-contaminated (by low redshift interlopers, CCD problems and internal reflections of the instrument) galaxies which do not show significant (&gt; 3σ) LyC flux between 880Å &lt;λrest &lt; 910Å. The 9 galaxy stacked spectrum reveals no significant LyC flux with an upper limit of $f_{\rm esc}^{\rm abs} \le 0.06$. In the next step of our analysis, we join all estimates of $f_{\rm esc}^{\rm abs}$ upper limits derived from different samples of 2 ≲ z &lt; 6 galaxies from the literature reported in last ∼20 years and include the sample presented in this work. We find the $f_{\rm esc}^{\rm abs}$ upper limit ≤ 0.084 for the galaxies recognized as non-LyC leakers. After including all known detections from literature $f_{\rm esc/global}^{\rm abs}$ upper limit ≤ 0.088 for all galaxies examined for LyC flux. Furthermore, $f_{\rm esc}^{\rm abs}$ upper limits for different groups of galaxies indicate that the strongest LyC emitters could be galaxies classified as Lyman alpha emitters. We also discuss the possible existence of a correlation among the observed flux density ratio $(F_{\nu }^{LyC}/F_{\nu }^{UV})_{\rm obs}$ and Lyman alpha equivalent width EW(Lyα), where we confirm the existence of moderately significant correlation among galaxies classified as non-LyC leakers.

Distinguishing AGN from starbursts as the origin of double-peaked Lyman-alpha emitters in the reionization era

We discuss the possible origin of the double-peaked profiles recently observed in Lyman-alpha emitters (LAEs) at the epoch of reionization (z ≳ 6.5) from obscured active galactic nuclei (AGN). In combining the extent of the Lyman-α near-zones estimated from the blue peak velocity offset in these galaxies, with the ionizing emissivity of quasars at z ≳ 6, we forecast the intrinsic UV and X-ray luminosities of the AGN needed to give rise to their double-peaked profiles. We also estimate the extent of the obscuration of the AGN by comparing their luminosities to those of similar quasar samples at these epochs. Future X-ray and radio observations, as well as those with the James Webb Space Telescope, will be valuable tools to test the AGN contribution to the intergalactic-scale ionization zones of high-redshift LAEs.

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

We present a study of the intersection between the populations of star forming galaxies selected as either Lyman break galaxies (LBGs) or Lyman-alpha emitters (LAEs) in the redshift range 2.9 − 6.7 and within the same volume of universe sampled by the Multi-Unit Spectroscopic Explorer (MUSE) behind the Hubble Frontier Fields lensing cluster A2744. We define three samples of star-forming galaxies: LBG galaxies with an LAE counterpart (92 galaxies), LBG galaxies without an LAE counterpart (408 galaxies), and LAE galaxies without an LBG counterpart (46 galaxies). All these galaxies are intrinsically faint because of the lensing nature of the sample (M1500 ≥ −20.5). The fraction of LAEs among all selected star-forming galaxies increases with redshift up to z ∼ 6 and decreases for higher redshifts, in agreement with previous findings. The evolution of LAE/LBG populations with UV magnitude and Lyα luminosity shows that the LAE selection is able to identify intrinsically UV faint galaxies with M1500 ≥ −15 that are typically missed in the deepest lensing photometric surveys. The LBG population seems to fairly represent the total population of star-forming galaxies down to M1500 ∼ −15. Galaxies with M1500 < −17 tend to have SFRLyα < SFRuv, whereas the opposite trend is observed within our sample for faint galaxies with M1500 > −17, including galaxies only detected by their Lyα emission, with a large scatter. These trends, previously observed in other samples of star-forming galaxies at high-z, are seen here for very faint M1500 ∼ −15 galaxies; that is, much fainter than in previous studies. The present results show no clear evidence for an intrinsic difference between the properties of the two populations selected as LBG and/or LAE. The observed trends could be explained by a combination of several phenomena, like the existence of different star-formation regimes, the dust content, the relative distribution and morphology of dust and stars, or the stellar populations.

Faint LAEs near z > 4.7 C iv absorbers revealed by MUSE*

We present the results from the search for Lyman Alpha emitters (LAEs) in the proximity of 11 C iv absorption systems at z &gt; 4.7 in the spectrum of the QSO J1030+0524, using data from MUSE. We have found multiple LAE candidates close to four C iv systems at $z_{\rm {{C\,{\small IV}}}}=4.94$–5.74 with $\log _{10}(N_{\rm{{C\,{\small IV}}}}[$cm−2]) &gt; 13.5. At z = 5–6, C iv systems with W$_0(\rm {{C\,{\small IV}}})&gt; 0.2$ Å seem more likely to have galaxies with Lyα emission within ρ &lt; 200 proper kpc (4/5 cases), than the C iv systems with W$_0(\rm {{C\,{\small IV}}})&lt;0.2$ Å (0/6 cases). The impact parameter of LAE-C iv systems with equivalent widths W0(C iv) &gt; 0.5 Å is in the range $11\, {\lesssim}\, \rho \, {\lesssim}\, 200$ proper kpc (pkpc). Furthermore, all candidates are in the luminosity range 0.18–1.15 L$^{\star }_{\rm{{Ly\alpha}}}(z=5.7)$, indicating that the environment of C iv systems within 200 pkpc is populated by the faint end of the Lyα luminosity function. We report a 0.28 L$^{\star }_{\rm {{Ly\alpha}}}$ galaxy at a separation of ρ = 11 pkpc from a strong C iv absorption ($\log _{10}(N_{\rm {{C\,{\small IV}}}}[$cm−2]) = 14.52) at $z_{\rm {{C\,{\small IV}}}}=5.72419$. The prevalence of sub-L$^{\star }_{\rm {{Ly\alpha}}}$ galaxies in the proximity of z &gt; 4.9 C iv systems suggest that the absorbing material is rather young, likely ejected in the recent past of the identified galaxies. The connection between faint LAEs and high-ionization absorption systems reported in this work, is potentially a consequence of the role of low mass galaxies in the early evolution of the circum-galactic and intergalactic media.

Web of the giant: Spectroscopic confirmation of a large-scale structure around the z = 6.31 quasar SDSS J1030+0524

We report on the spectroscopic confirmation of a large-scale structure around the luminous z = 6.31 quasi-stellar object (QSO) SDSS J1030+0524, powered by a one billion solar mass black hole. The structure is populated by at least six members, namely, four Lyman-break galaxies (LBGs), and two Lyman alpha emitters (LAEs). The four LBGs were identified among a sample of 21 i-band dropouts with zAB < 25.5 selected up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their redshifts were determined through multi-object spectroscopic observations at 8−10 m class telescopes lasting up to eight hours. The two LAEs were identified in a 6 h VLT/MUSE observation centered on the QSO. The redshifts of the six galaxies cover the range between 6.129−6.355. Assuming that the peculiar velocities are negligible, this range corresponds to radial separations of ±5 physical Mpc from the QSO, that is comparable to the projected scale of the observed LBG distribution on the sky. We conservatively estimate that this structure is significant at a level > 3.5σ and that the level of the galaxy overdensity is at least 1.5−2 within the large volume sampled (∼780 physical Mpc3). The spectral properties of the six member galaxies (Lyα strength and UV luminosity) are similar to those of field galaxies at similar redshifts. This is the first spectroscopic identification of a galaxy overdensity around a supermassive black hole in the first billion years of the Universe. Our finding lends support to the idea that the most distant and massive black holes form and grow within massive (>1012 M⊙) dark matter halos in large-scale structures and that the absence of earlier detections of such systems is likely due to observational limitations.

Are Ly α emitters segregated in protoclusters regions?

ABSTRACT The presence of neutral hydrogen in the interstellar medium (ISM) and intergalactic medium (IGM) induces radiative transfer (RT) effects on $\rm {Ly}\,\alpha$ photons that affect the observability of Lyman alpha emitters (LAEs). We use the galform semi-analytic model of galaxy formation and evolution to analyse how these effects shape the spatial distribution of LAEs with respect to $\rm {H}\,\alpha$ emitters (HAEs) around high-density regions at high redshift. We find that when a large sample of protoclusters is considered, HAEs showing also $\rm {Ly}\,\alpha$ emission (HAEs + LAEs) populate the same regions as those that do not display the $\rm {Ly}\,\alpha$ line at $z$ = 2.2. We compare against the protocluster USS1558-003, one of the most massive protoclusters located at $z$ = 2.53. Our results indicate that the strong depletion of HAEs + LAEs present in the high-density regions of USS1558-003 may be due to cosmic variance. We find that at $z$ = 2.2 and $z$ = 3.0, RT of the ISM produces a strong decline (30–50 per cent) of the clustering amplitude of HAEs + LAEs with respect to HAEs towards the protoclusters centre. At $z$ = 5.7, given the early evolutionary state of protoclusters and galaxies, the clustering of HAEs + LAEs has a smaller variation (10–20 per cent) towards the protoclusters centre. Depending on the equivalent width and luminosity criteria of the emission-line galaxy sample, the IGM can have a mild or a null effect on galaxy properties and clustering in high-density regions.

The VANDELS survey: a strong correlation between Ly α equivalent width and stellar metallicity at 3 ≤ z ≤ 5

ABSTRACT We present the results of a new study investigating the relationship between observed Ly α equivalent width (Wλ(Ly α)) and the metallicity of the ionizing stellar population ( Z⋆) for a sample of 768 star-forming galaxies at 3 ≤ z ≤ 5 drawn from the VANDELS survey. Dividing our sample into quartiles of rest-frame Wλ(Ly α) across the range $-58 \,\rm {\mathring{\rm A}} \lesssim$Wλ(Ly α) $\lesssim 110 \,\rm {\mathring{\rm A}}$, we determine Z⋆ from full spectral fitting of composite far-ultraviolet spectra and find a clear anticorrelation between Wλ(Ly α) and Z⋆. Our results indicate that Z⋆ decreases by a factor ≳ 3 between the lowest Wλ(Ly α) quartile (〈Wλ(Ly α)$\rangle =-18\,\rm {\mathring{\rm A}}$) and the highest Wλ(Ly α) quartile (〈Wλ(Ly α)$\rangle =24\,\rm {\mathring{\rm A}}$). Similarly, galaxies typically defined as Lyman alpha emitters (LAEs; Wλ(Ly α) $\gt 20\,\rm {\mathring{\rm A}}$) are, on average, metal poor with respect to the non-LAE galaxy population (Wλ(Ly α) $\le 20\,\rm {\mathring{\rm A}}$) with Z⋆non-LAE ≳ 2 × Z⋆LAE. Finally, based on the best-fitting stellar models, we estimate that the increasing strength of the stellar ionizing spectrum towards lower Z⋆ is responsible for ${\simeq}15{-}25{{\ \rm per\ cent}}$ of the observed variation in Wλ(Ly α) across our sample, with the remaining contribution (${\simeq}75{-}85{{\ \rm per\ cent}}$) being due to a decrease in the H i/dust covering fractions in low- Z⋆ galaxies.

Differences and similarities of stellar populations in LAEs and LBGs at z ∼ 3.4−6.8

ABSTRACT Lyman alpha emitters (LAEs) and Lyman break galaxies (LBGs) represent the most common groups of star-forming galaxies at high z, and the differences between their inherent stellar populations (SPs) are a key factor in understanding early galaxy formation and evolution. We have run a set of SP burst-like models for a sample of 1558 sources at 3.4 &lt; z &lt; 6.8 from the Survey for High-z Absorption Red and Dead Sources (SHARDS) over the GOODS-N field. This work focuses on the differences between the three different observational subfamilies of our sample: LAE–LBGs, no-Ly α LBGs, and pure LAEs. Single and double SP synthetic spectra were used to model the spectral energy distributions, adopting a Bayesian information criterion to analyze under which situations a second SP is required. We find that the sources are well modelled using a single SP in $\sim 79{{\ \rm per\ cent}}$ of the cases. The best models suggest that pure LAEs are typically young low-mass galaxies ($t\sim 26^{+41}_{-25}$ Myr; $M_{\mathrm{star}}\sim 5.6^{+12.0}_{-5.5}\times 10^{8}\ M_{\odot }$), undergoing one of their first bursts of star formation. On the other hand, no-Ly α LBGs require older SPs (t ∼ 71 ± 12 Myr), and they are substantially more massive (Mstar ∼ 3.5 ± 1.1 × 109 M⊙). LAE–LBGs appear as the subgroup that more frequently needs the addition of a second SP, representing an old and massive galaxy caught in a strong recent star-forming episode. The relative number of sources found from each subfamily at each z supports an evolutionary scenario from pure LAEs and single SP LAE–LBGs to more massive LBGs. Stellar mass functions are also derived, finding an increase of M* with cosmic time and a possible steepening of the low-mass slope from z ∼ 6 to z ∼ 5 with no significant change to z ∼ 4. Additionally, we have derived the SFR–Mstar relation, finding an $\mathrm{SFR}\propto M_{\mathrm{star}}^{\beta }$ behaviour with negligible evolution from z ∼ 4 to z ∼ 6.