ALBERT

Description: Using the most recent measurements of the ultraviolet (UV) luminosity functions (LFs) and dust estimates of early galaxies, we derive updated dust-corrected star formation rate functions (SFRFs) at z  ~ 4–8, which we model to predict the evolution to higher redshifts, z  〉 8. We employ abundance matching techniques to calibrate a relation between galaxy star formation rate (SFR) and host halo mass M h by mapping the shape of the observed SFRFs at z  ~ 4–8 to that of the halo mass function. The resulting scaling law remains roughly constant over this redshift range. We apply the average SFR– M h relation to reproduce the observed SFR functions at 4 z 8 and also derive the expected UV LFs at higher redshifts. At z  ~ 9 and z  ~ 10 these model LFs are in excellent agreement with current observed estimates. Our predicted number densities and UV LFs at z  〉 10 indicate that James Webb Space Telescope will be able to detect galaxies out to z  ~ 15 with an extensive treasury sized program. We also derive the redshift evolution of the star formation rate density (SFRD) and associated reionization history by galaxies. Models which integrate down to the current HUDF12/XDF detection limit ( M UV  ~ –17.7 mag) result in a SFRD that declines as (1 +  z ) –10.4 ± 0.3 at high redshift and fail to reproduce the observed cosmic microwave background electron scattering optical depth, ~= 0.066, to within 1. On the other hand, we find that the inclusion of galaxies with SFRs well below the current detection limit ( M UV  〈 –5.7 mag) leads to a fully reionized universe by z  ~ 6.5 and an optical depth of ~= 0.054, consistent with the recently derived Planck value at the 1 level.

Description: Recent Spitzer /InfraRed Array Camera (IRAC) photometric observations have revealed that rest-frame optical emission lines contribute significantly to the broad-band fluxes of high-redshift galaxies. Specifically, in the narrow redshift range z  ~ 5.1–5.4 the [3.6]–[4.5] colour is expected to be very red, due to contamination of the 4.5 μm band by the dominant Hα line, while the 3.6 μm filter is free of nebular emission lines. We take advantage of new reductions of deep Spitzer /IRAC imaging over the Great Observatories Origins Deep Survey-North+South fields (Labbé et al. 2015 ) to obtain a clean measurement of the mean Hα equivalent width (EW) from the [3.6]–[4.5] colour in the redshift range z = 5.1–5.4. The selected sources either have measured spectroscopic redshifts (13 sources) or lie very confidently in the redshift range z = 5.1–5.4 based on the photometric redshift likelihood intervals (11 sources). Our z phot = 5.1–5.4 sample and z spec = 5.10–5.40 spectroscopic sample have a mean [3.6]–[4.5] colour of 0.31 ± 0.05 and 0.35 ± 0.07 mag, implying a rest-frame EW (Hα+[N ii ]+[S ii ]) of 665 ± 53 and 707 ± 74 Å, respectively, for sources in these samples. These values are consistent albeit slightly higher than derived by Stark et al. at z  ~ 4, suggesting an evolution to higher values of the Hα+[N ii ]+[S ii ] EW at z  〉 2. Using the 3.6 μm band, which is free of emission line contamination, we perform robust spectral energy distribution fitting and find a median specific star formation rate of sSFR = $17_{-5}^{+2}$ Gyr –1 , $7_{-2}^{+1}\times$ higher than at z  ~ 2. We find no strong correlation (〈2) between the Hα+[N ii ]+[S ii ] EW and the stellar mass of sources. Before the advent of JWST , improvements in these results will come through an expansion of current spectroscopic samples and deeper Spitzer /IRAC measurements.

Description: We show that a bursty model of star formation explains several puzzling observations of high-redshift galaxies. We begin by showing that because the observed star formation rate integrated over a Hubble time exceeds the observed stellar mass by an order of magnitude, the specific star formation rate requires a duty-cycle of ~10 per cent. We use the specific star formation rate to calibrate a merger-driven model of star formation regulated by supernova feedback, and reproduce the star formation rate density and stellar mass functions of galaxies at 4 z 7. The specific star formation rate is predicted not to evolve rapidly with either mass or redshift at z 4, consistent with observation. This is in contrast to expectations from hydrodynamical simulations where star formation closely follows accretion rate, and increases strongly towards high redshift. Bursty star formation explains the observation that there is not enough stellar mass at z  ~ 2–4 to account for all star formation observed. A duty-cycle of ~10 per cent implies that there could be 10 times the number of known high-redshift galaxies at fixed stellar mass that have not yet been detected through UV selection. We therefore predict the possible existence of an undetected population of UV-faint galaxies that accounts for most of the stellar mass density at z  ~ 4–8.

Description: We present a detailed analysis of an individual case of gravitational lensing of a z  ~ 8 Lyman-break galaxy (LBG) in a blank field, identified in Hubble Space Telescope imaging obtained as part of the Brightest of Reionizing Galaxies survey. To investigate the close proximity of the bright ( m AB  = 25.8) Y 098 -dropout to a small group of foreground galaxies, we obtained deep spectroscopy of the dropout and two foreground galaxies using VLT/X-Shooter. We detect H α, H β, [O  iii ] and [O  ii ] emission in the brightest two foreground galaxies (unresolved at the natural seeing of 0.8 arcsec), placing the pair at z  = 1.327. We can rule out emission lines contributing all of the observed broad-band flux in H 160 band at 70, allowing us to exclude the z  ~ 8 candidate as a low-redshift interloper with broad-band photometry dominated by strong emission lines. The foreground galaxy pair lies at the peak of the luminosity, redshift and separation distributions for deflectors of strongly lensed z  ~ 8 objects, and we make a marginal detection of a demagnified secondary image in the deepest ( J 125 ) filter. We show that the configuration can be accurately modelled by a singular isothermal ellipsoidal deflector and a Sérsic source magnified by a factor of μ = 4.3 ± 0.2. The reconstructed source in the best-fitting model is consistent with luminosities and morphologies of z  ~ 8 LBGs in the literature. The lens model yields a group mass of 9.62 ± 0.31  x  10 11 M and a stellar mass-to-light ratio for the brightest deflector galaxy of $M_{\star }/L_{B}=2.3^{+0.8}_{-0.6} \,\mathrm{M}_{{\odot }}/\mathrm{L}_{{\odot }}$ within its effective radius. The foreground galaxies’ redshifts would make this one of the few strong lensing deflectors discovered at z  〉 1. Deeper imaging would allow for confirmation of the existence of the secondary image and elongation in the primary image, verifying multiple imaging and producing more robust estimations of the image magnifications.

Description: Measurements of the UV-continuum slopes β provide valuable information on the physical properties of galaxies forming in the early universe, probing the dust reddening, age, metal content, and even the escape fraction. While constraints on these slopes generally become more challenging at higher redshifts as the UV-continuum shifts out of the Hubble Space Telescope bands (particularly at z 〉 7), such a characterization actually becomes abruptly easier for galaxies in the redshift window z = 9.5–10.5 due to the Spitzer /Infrared Array Camera 3.6 μm-band probing the rest-UV continuum and the long wavelength baseline between this Spitzer band and the Hubble H f 160 w band. Higher S/N constraints on β are possible at z  ~ 10 than at z = 8. Here, we take advantage of this opportunity and five recently discovered bright z = 9.5–10.5 galaxies to present the first measurements of the mean β for a multi-object sample of galaxy candidates at z  ~ 10. We find the measured β obs 's of these candidates are –2.1 ± 0.3 ± 0.2 (random and systematic), only slightly bluer than the measured β's (β obs –1.7) at 3.5 〈 z 〈 7.5 for galaxies of similar luminosities. Small increases in the stellar ages, metallicities, and dust content of the galaxy population from z  ~ 10 to z  ~ 7 could easily explain the apparent evolution in β.

Description: Using Hubble data, including new grism spectra, Oesch et al. recently identified GN-z11, an M UV  = –21.1 galaxy at z  = 11.1 (just 400 Myr after the big bang). With an estimated stellar mass of ~10 9  M , this galaxy is surprisingly bright and massive, raising questions as to how such an extreme object could form so early in the Universe. Using meraxes , a semi-analytic galaxy-formation model developed as part of the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulations (DRAGONS) programme, we investigate the potential formation mechanisms and eventual fate of GN-z11. The volume of our simulation is comparable to that of the discovery observations and possesses two analogue galaxies of similar luminosity to this remarkably bright system. Existing in the two most massive subhaloes at z  = 11.1 ( M vir  = 1.4  x  10 11  M and 6.7  x  10 10  M ), our model analogues show excellent agreement with all available observationally derived properties of GN-z11. Although they are relatively rare outliers from the full galaxy population at high- z , they are no longer the most massive or brightest systems by z  = 5. Furthermore, we find that both objects possess relatively smooth, but extremely rapid mass growth histories with consistently high star formation rates and UV luminosities at z  〉 11, indicating that their brightness is not a transient, merger-driven feature. Our model results suggest that future wide-field surveys with the James Webb Space Telescope may be able to detect the progenitors of GN-z11 analogues out to z  ~ 13–14, pushing the frontiers of galaxy-formation observations to the early phases of cosmic reionization and providing a valuable glimpse of the first galaxies to reionize the Universe on large scales.

Description: The [C II] 158 μm line is one of the strongest IR emission lines, which has been shown to trace the star formation rate (SFR) of galaxies in the nearby Universe, and up to z ∼ 2. Whether this is also the case at higher redshift and in the early Universe remains debated. The ALPINE survey, which targeted 118 star-forming galaxies at 4.4 〈  z 〈  5.9, provides a new opportunity to examine this question with the first statistical dataset. Using the ALPINE data and earlier measurements from the literature, we examine the relation between the [C II] luminosity and the SFR over the entire redshift range from z ∼ 4 − 8. ALPINE galaxies, which are both detected in [C II] and in dust continuum, show good agreement with the local L([CII])–SFR relation. Galaxies undetected in the continuum by ALMA are found to be over-luminous in [C II] when the UV SFR is used. After accounting for dust-obscured star formation, by an amount of SFR(IR) ≈ SFR(UV) on average, which results from two different stacking methods and SED fitting, the ALPINE galaxies show an L([CII])–SFR relation comparable to the local one. When [C II] non-detections are taken into account, the slope may be marginally steeper at high-z, although this is still somewhat uncertain. When compared homogeneously, the z 〉  6 [C II] measurements (detections and upper limits) do not behave very differently to the z ∼ 4 − 6 data. We find a weak dependence of L([CII])/SFR on the Lyα equivalent width. Finally, we find that the ratio L([CII])/LIR ∼ (1 − 3) × 10−3 for the ALPINE sources, comparable to that of “normal” galaxies at lower redshift. Our analysis, which includes the largest sample (∼150 galaxies) of [C II] measurements at z 〉 4 available so far, suggests no or little evolution of the [C II]–SFR relation over the last 13 Gyr of cosmic time.

Description: Context. The Hubble Frontier Fields offer an exceptionally deep window into the high-redshift universe, covering a substantially larger area than the Hubble Ultra-Deep field at low magnification and probing 1–2 mag deeper in exceptional high-magnification regions. This unique parameter space, coupled with the exceptional multi-wavelength ancillary data, can facilitate for useful insights into distant galaxy populations. Aims. We aim to leverage Atacama Large Millimetre Array (ALMA) band 6 (≈263 GHz) mosaics in the central portions of five Frontier Fields to characterize the infrared (IR) properties of 1582 ultraviolet (UV)-selected Lyman-Break Galaxies (LBGs) at redshifts of z ∼ 2–8. We investigated individual and stacked fluxes and IR excess (IRX) values of the LBG sample as functions of stellar mass (M⋆), redshift, UV luminosity and slope β, and lensing magnification. Methods. LBG samples were derived from color-selection and photometric redshift estimation with Hubble Space Telescope photometry. Spectral energy distributions -templates were fit to obtain luminosities, stellar masses, and star formation rates for the LBG candidates. We obtained individual IR flux and IRX estimates, as well as stacked averages, using both ALMA images and u–v visibilities. Results. Two (2) LBG candidates were individually detected above a significance of 4.1-σ, while stacked samples of the remaining LBG candidates yielded no significant detections. We investigated our detections and upper limits in the context of the IRX–M⋆ and IRX–β relations, probing at least one dex lower in stellar mass than past studies have done. Our upper limits exclude substantial portions of parameter space and they are sufficiently deep in a handful of cases to create mild tension with the typically assumed attenuation and consensus relations. We observe a clear and smooth trend between M⋆ and β, which extends to low masses and blue (low) β values, consistent with expectations from previous works.

Description: High-resolution multi-wavelength photometry is crucial to explore the spatial distribution of star formation in galaxies and understand how these evolve. To this aim, in this paper we exploit the deep, multi-wavelength Hubble Space Telescope (HST) data available in the central parts of the Great Observatories Origins Deep Survey (GOODS) fields and study the distribution of star formation activity and mass in galaxies located at different positions with respect to the main sequence (MS) of star-forming galaxies. Our sample consists of galaxies with stellar mass ≥109.5 M⊙ in the redshift range 0.2 ≤ z ≤ 1.2. Exploiting 10-band photometry from the UV to the near-infrared at HST resolution, we derived spatially resolved maps of galaxy properties, such as stellar mass and star formation rate and specific star formation rate, with a resolution of ∼0.16 arcsec. We find that the star formation activity is centrally enhanced in galaxies above the MS and centrally suppressed below the MS, with quiescent galaxies (1 dex below the MS) characterised by the highest suppression. The specific star formation rate in the outer region does not show systematic trends of enhancement or suppression above or below the MS. The distribution of mass in MS galaxies indicates that bulges grow when galaxies are still on the MS relation. Galaxies below the MS are more bulge-dominated with respect to MS counterparts at fixed stellar mass, while galaxies in the upper envelope are more extended and have Sérsic indices that are always smaller than or comparable to their MS counterparts. The suppression of star formation activity in the central region of galaxies below the MS hints at inside-out quenching, as star formation is still ongoing in the outer regions.