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Register a new userResolved UV and [CII] structures of luminous galaxies within the epoch of reionisation
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We present new deep ALMA and HST/WFC3 observations of MASOSA and VR7, two luminous Ly$alpha$ emitters (LAEs) at $z=6.5$, for which the UV continuum level differ by a factor four. No IR dust continuum emission is detected in either, indicating little amounts of obscured star formation and/or high dust temperatures. MASOSA, with a UV luminosity M$_{1500}=-20.9$, compact size and very high Ly$alpha$ EW$_{0}approx145$ A, is undetected in [CII] to a limit of L$_{rm [CII]}<2.2times10^7$ L$_{odot}$ implying a metallicity $Zlesssim0.07 Z_{odot}$. Intriguingly, our HST data indicates a red UV slope $beta=-1.1pm0.7$, at odds with the low dust content. VR7, which is a bright (M$_{1500}=-22.4$) galaxy with moderate color ($beta=-1.4pm0.3$) and Ly$alpha$ EW$_0 = 34$ A, is clearly detected in [CII] emission (S/N=15). VR7s rest-frame UV morphology can be described by two components separated by $approx1.5$ kpc and is globally more compact than the [CII] emission. The global [CII]-UV ratio indicates $Zapprox0.2 Z_{odot}$, but there are large variations in the UV-[CII] ratio on kpc scales. We also identify diffuse, possibly outflowing, [CII]-emitting gas at $approx 100$ km s$^{-1}$ with respect to the peak. VR7 appears assembling its components at a slightly more evolved stage than other luminous LAEs, with outflows already shaping its direct environment at $zsim7$. Our results further indicate that the global [CII]-UV relation steepens at SFR $<30$ M$_{odot}$ yr$^{-1}$, naturally explaining why the [CII]-UV ratio is anti-correlated with Ly$alpha$ EW in many, but not all, observed LAEs.
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Small galaxies are thought to be the main contributors to the ionising budget of the Universe before reionisation was complete. There have been a number of numerical studies trying to quantify their ionising efficiency through the escape fraction $f_{esc}$. While there is a clear trend that $f_{esc}$ is higher for smaller haloes, there is a large scatter in the distribution of $f_{esc}$ for a single halo mass. We propose that this is due to the intrinsic burstiness of star formation in low mass galaxies. We performed high resolution radiative hydrodynamics simulations with Ramses-RT to model the evolution of three galaxies and their ionising efficiency. We found that the variability of $f_{esc}$ follows that of the star formation rate. We then discuss the consequences of this variability on the observability of such galaxies by JWST.
We present the photometric properties of galaxies in the First Light and Reionisation Epoch Simulations (FLARES). The simulations trace the evolution of galaxies in a range of overdensities through the Epoch of Reionistion (EoR). With a novel weighting scheme we combine these overdensities, extending significantly the dynamic range of observed composite distribution functions compared to periodic simulation boxes. FLARES predicts a significantly larger number of intrinsically bright galaxies, which can be explained through a simple model linking dust-attenuation to the metal content of the interstellar medium, using a line-of-sight (LOS) extinction model. With this model we present the photometric properties of the FLARES galaxies for $z in [5,10]$. We show that the ultraviolet (UV) luminosity function (LF) matches the observations at all redshifts. The function is fit by Schechter and double power-law forms, with the latter being favoured at these redshifts by the FLARES composite UV LF. We also present predictions for the UV continuum slope as well as the attenuation in the UV. The impact of environment on the UV LF is also explored, with the brightest galaxies forming in the densest environments. We then present the line luminosity and equivalent widths of some prominent nebular emission lines arising from the galaxies, finding rough agreement with available observations. We also look at the relative contribution of obscured and unobscured star formation, finding comparable contributions at these redshifts.
We present Herschel/PACS observations of extended [CII]157.7{mu}m line emission detected on ~ 1 - 10 kpc scales in 60 local luminous infrared galaxies (LIRGs) from the Great Observatories All-sky LIRG Survey (GOALS). We find that most of the extra-nuclear emission show [CII]/FIR ratios >~ 4 x 10^-3, larger than the mean ratio seen in the nuclei, and similar to those found in the extended disks of normal star-forming galaxies and the diffuse inter-stellar medium (ISM) of our Galaxy. The [CII] deficits found in the most luminous local LIRGs are therefore restricted to their nuclei. There is a trend for LIRGs with warmer nuclei to show larger differences between their nuclear and extra-nuclear [CII]/FIR ratios. We find an anti-correlation between [CII]/FIR and the luminosity surface density, {Sigma}_IR, for the extended emission in the spatially-resolved galaxies. However, there is an offset between this trend and that found for the LIRG nuclei. We use this offset to derive a beam filling-factor for the star-forming regions within the LIRG disks of ~ 6 % relative to their nuclei. We confront the observed trend to photo-dissociation region (PDR) models and find that the slope of the correlation is much shallower than the model predictions. Finally, we compare the correlation found between [CII]/FIR and {Sigma}_IR with measurements of high-redshift starbursting IR-luminous galaxies.
We present [CII] 158um measurements from over 15,000 resolved regions within 54 nearby galaxies of the KINGFISH program to investigate the so-called [CII] line cooling deficit long known to occur in galaxies with different luminosities. The [CII]/TIR ratio ranges from above 1% to below 0.1% in the sample, with a mean value of 0.48+-0.21%. We find that the surface density of 24um emission dominates this trend, with [CII]/TIR dropping as nuInu{24um} increases. Deviations from this overall decline are correlated with changes in the gas phase metal abundance, with higher metallicity associated with deeper deficits at a fixed surface brightness. We supplement the local sample with resolved [CII] measurements from nearby luminous infrared galaxies and high redshift sources from z=1.8-6.4, and find that star formation rate density drives a continuous trend of deepening [CII] deficit across six orders of magnitude in SFRD. The tightness of this correlation suggests that an approximate star formation rate density can be estimated directly from global measurements of [CII]/TIR, and a relation is provided to do so. Several low-luminosity AGN hosts in the sample show additional and significant central suppression of [CII]/TIR, but these deficit enhancements occur not in those AGN with the highest X-ray luminosities, but instead those with the highest central starlight intensities. Taken together, these results demonstrate that the [CII] cooling line deficit in galaxies likely arises from local physical phenomena in interstellar gas.
The HI gas content is a key ingredient in galaxy evolution, the study of which has been limited to moderate cosmological distances for individual galaxies due to the weakness of the hyperfine HI 21-cm transition. Here we present a new approach that allows us to infer the HI gas mass $M_{rm HI}$ of individual galaxies up to $zapprox 6$, based on a direct measurement of the [CII]-to-HI conversion factor in star-forming galaxies at $zgtrsim 2$ using $gamma$-ray burst afterglows. By compiling recent [CII]-158 $mu$m emission line measurements we quantify the evolution of the HI content in galaxies through cosmic time. We find that the HI mass starts to exceed the stellar mass $M_star$ at $zgtrsim 1$, and increases as a function of redshift. The HI fraction of the total baryonic mass increases from around $20%$ at $z = 0$ to about $60%$ at $zsim 6$. We further uncover a universal relation between the HI gas fraction $M_{rm HI}/M_star$ and the gas-phase metallicity, which seems to hold from $zapprox 6$ to $z=0$. The majority of galaxies at $z>2$ are observed to have HI depletion times, $t_{rm dep,HI} = M_{rm HI}/{rm SFR}$, less than $approx 2$ Gyr, substantially shorter than for $zsim 0$ galaxies. Finally, we use the [CII]-to-HI conversion factor to determine the cosmic mass density of HI in galaxies, $rho_{rm HI}$, at three distinct epochs: $zapprox 0$, $zapprox 2$, and $zsim 4-6$. These measurements are consistent with previous estimates based on 21-cm HI observations in the local Universe and with damped Lyman-$alpha$ absorbers (DLAs) at $zgtrsim 2$, suggesting an overall decrease by a factor of $approx 5$ in $rho_{rm HI}(z)$ from the end of the reionization epoch to the present.
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