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Register a new userLyman Alpha line properties at $z simeq 3.78$ and their environmental dependence: a case study around a massive proto-cluster
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Ly$alpha$-emitting galaxies (LAEs) are easily detectable in the high-redshift Universe and are potentially efficient tracers of large scale structure at early epochs, as long as their observed properties do not strongly depend on environment. We investigate the luminosity and equivalent width functions of LAEs in the overdense field of a protocluster at redshift $z simeq 3.78$. Using a large sample of LAEs (many spectroscopically confirmed), we find that the Ly$alpha$ luminosity distribution is well-represented by a Schechter (1976) function with $log(L^{ast}/{rm erg s^{-1}}) = 43.26^{+0.20}_{-0.22}$ and $log(phi^{ast}/{rm Mpc^{-3}})=-3.40^{+0.03}_{-0.04}$ with $alpha=-1.5$. Fitting the equivalent width distribution as an exponential, we find a scale factor of $omega=79^{+15}_{-15}$ Angstroms. We also measured the Ly$alpha$ luminosity and equivalent width functions using the subset of LAEs lying within the densest cores of the protocluster, finding similar values for $L^*$ and $omega$. Hence, despite having a mean overdensity more than 2$times$ that of the general field, the shape of the Ly$alpha$ luminosity function and equivalent width distributions in the protocluster region are comparable to those measured in the field LAE population by other studies at similar redshift. While the observed Ly$alpha$ luminosities and equivalent widths show correlations with the UV continuum luminosity in this LAE sample, we find that these are likely due to selection biases and are consistent with no intrinsic correlations within the sample. This protocluster sample supports the strong evolutionary trend observed in the Ly$alpha$ escape fraction and suggest that lower redshift LAEs can be on average significantly more dusty that their counterparts at higher redshift.
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Reionization-era galaxies tend to exhibit weak Ly$alpha$ emission, likely reflecting attenuation from an increasingly neutral IGM. Recent observations have begun to reveal exceptions to this picture, with strong Ly$alpha$ emission now known in four of the most massive z=7$-$9 galaxies in the CANDELS fields, all of which also exhibit intense [OIII]$+$H$beta$ emission (EW$>$800 $mathrm{mathring{A}}$). To better understand why Ly$alpha$ is anonymously strong in a subset of massive z$simeq$7$-$9 galaxies, we have initiated an MMT/Binospec survey targeting a larger sample (N=22) of similarly luminous ($simeq$1$-$6 L$^{ast}_{mathrm{UV}}$) z$simeq$7 galaxies selected over very wide-area fields ($sim$3 deg$^2$). We confidently ($>$7$sigma$) detect Ly$alpha$ in 78% (7/9) of galaxies with strong [OIII]$+$H$beta$ emission (EW$>$800 $mathrm{mathring{A}}$) as opposed to only 8% (1/12) of galaxies with more moderate (EW=200$-$800 $mathrm{mathring{A}}$) [OIII]$+$H$beta$. We argue that the higher Ly$alpha$ EWs of the strong [OIII]$+$H$beta$ population likely reflect enhanced ionizing photon production efficiency owing to their large sSFRs ($gtrsim$30 Gyr$^{-1}$). We also find evidence that Ly$alpha$ transmission from massive galaxies declines less rapidly over $6<z<7$ than in low-mass lensed systems. In particular, our data suggest no strong evolution in Ly$alpha$ transmission, consistent with a picture wherein massive z$simeq$7 galaxies often reside in large ionized regions. We detect three closely-separated ($R$ = 1.7 physical Mpc) z$simeq$7 Ly$alpha$ emitters in our sample, conceivably tracing a large ionized structure that is consistent with this picture. We detect tentative evidence for an overdensity in this region, implying a large ionizing photon budget in the surrounding volume.
We discovered an over-density of H-alpha-emitting galaxies associated with a Planck compact source in the COSMOS field (PHzG237.0+42.5) through narrow-band imaging observations with Subaru/MOIRCS. This Planck-selected dusty proto-cluster at z=2.16 has 38 H-alpha emitters including six spectroscopically confirmed galaxies in the observed MOIRCS 4x7 field (corresponding to ~2.0x3.5~Mpc^2 in physical scale). We find that massive H-alpha emitters with log(M*/Msun)>10.5 are strongly clustered in the core of the proto-cluster (within ~300-kpc from the density peak of the H-alpha emitters). Most of the H-alpha emitters in this proto-cluster lie along the star-forming main sequence using H-alpha-based SFR estimates, whilst the cluster total SFR derived by integrating the H-alpha-based SFRs is an order of magnitude smaller than those estimated from Planck/Herschel FIR photometry. Our results suggest that H-alpha is a good observable for detecting moderately star-forming galaxies and tracing the large-scale environment in and around high-z dusty proto-clusters, but there is a possibility that a large fraction of star formation could be obscured by dust and undetected in H-alpha observations.
We compare the physical and morphological properties of z ~ 2 Lyman-alpha emitting galaxies (LAEs) identified in the HETDEX Pilot Survey and narrow band studies with those of z ~ 2 optical emission line galaxies (oELGs) identified via HST WFC3 infrared grism spectroscopy. Both sets of galaxies extend over the same range in stellar mass (7.5 < logM < 10.5), size (0.5 < R < 3.0 kpc), and star-formation rate (~1 < SFR < 100). Remarkably, a comparison of the most commonly used physical and morphological parameters -- stellar mass, half-light radius, UV slope, star formation rate, ellipticity, nearest neighbor distance, star formation surface density, specific star formation rate, [O III] luminosity, and [O III] equivalent width -- reveals no statistically significant differences between the populations. This suggests that the processes and conditions which regulate the escape of Ly-alpha from a z ~ 2 star-forming galaxy do not depend on these quantities. In particular, the lack of dependence on the UV slope suggests that Ly-alpha emission is not being significantly modulated by diffuse dust in the interstellar medium. We develop a simple model of Ly-alpha emission that connects LAEs to all high-redshift star forming galaxies where the escape of Ly-alpha depends on the sightline through the galaxy. Using this model, we find that mean solid angle for Ly-alpha escape is 2.4+/-0.8 steradians; this value is consistent with those calculated from other studies.
We have discovered a 300kpc-wide giant Lya nebula centered on the massive galaxy group RO-1001 at z=2.91 in the COSMOS field. Keck Cosmic Web Imager observations reveal three cold gas filaments converging into the center of the potential well of its ~4x10^13Msun dark matter halo, hosting 1200Msun/yr of star formation as probed by ALMA and NOEMA observations. The nebula morphological and kinematics properties and the prevalence of blueshifted components in the Lya spectra are consistent with a scenario of gas accretion. The upper limits on AGN activity and overall energetics favor gravity as the primary Lya powering source and infall as the main source of gas flows to the system. Although interpretational difficulties remain, with outflows and likely also photoionization with ensuing recombination still playing a role, this finding provides arguably an ideal environment to quantitatively test models of cold gas accretion and galaxy feeding inside an actively star-forming massive halo at high redshift.
We present an extensive ALMA spectroscopic follow-up programme of the $z,{=},4.3$ structure SPT2349$-$56, one of the most actively star-forming proto-cluster cores known, to identify additional members using their [C{sc ii}] 158,$mu$m and mbox{CO(4--3)} lines. In addition to robustly detecting the 14 previously published galaxies in this structure, we identify a further 15 associated galaxies at $z,{=},4.3$, resolving 55$,{pm},$5,per cent of the 870-$mu$m flux density at 0.5,arcsec resolution compared to 21,arcsec single-dish data. These galaxies are distributed into a central core containing 23 galaxies extending out to 300,kpc in diameter, and a northern extension, offset from the core by 400,kpc, containing three galaxies. We discovered three additional galaxies in a red {it Herschel/}-SPIRE source 1.5,Mpc from the main structure, suggesting the existence of many other sources at the same redshift as SPT2349$-$56 that are not yet detected in the limited coverage of our data. An analysis of the velocity distribution of the central galaxies indicates that this region may be virialized with a mass of (9$pm$5)$,{times},$10$^{12}$,M$_{odot}$, while the two offset galaxy groups are about 30 and 60,per cent less massive and show significant velocity offsets from the central group. We calculate the [C{sc ii}] and far-infrared number counts, and find evidence for a break in the [C{sc ii}] luminosity function. We estimate the average SFR density within the region of SPT2349$-$56 containing single-dish emission (a proper diametre of 720,kpc), assuming spherical symmetry, to be roughly 4$,{times},10^4$,M$_{odot}$,yr$^{-1}$,Mpc$^{-3}$; this may be an order of magnitude greater than the most extreme examples seen in simulations.
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