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Register a new userA Planck-selected dusty proto-cluster at z=2.16 associated with a strong over-density of massive H$alpha$ emitting galaxies
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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.
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Bright Ly-$alpha$ blobs (LABs) --- extended nebulae with sizes of $sim$100kpc and Ly-$alpha$ luminosities of $sim$10$^{44}$erg s$^{-1}$ --- often reside in overdensities of compact Ly-$alpha$ emitters (LAEs) that may be galaxy protoclusters. The number density, variance, and internal kinematics of LABs suggest that they themselves trace group-like halos. Here we test this hierarchical picture, presenting deep, wide-field Ly-$alpha$ narrowband imaging of a 1$^circ$ $times$ 0.5$^circ$ region around a LAB pair at $z$ = 2.3 discovered previously by a blind survey. We find 183 Ly-$alpha$ emitters, including the original LAB pair and three new LABs with Ly-$alpha$ luminosities of (0.9--1.3)$times$10$^{43}$erg s$^{-1}$ and isophotal areas of 16--24 arcsec$^2$. Using the LAEs as tracers and a new kernel density estimation method, we discover a large-scale overdensity (Bo{o}tes J1430+3522) with a surface density contrast of $delta_{Sigma}$ = 2.7, a volume density contrast of $delta$ $sim$ 10.4, and a projected diameter of $approx$ 20 comoving Mpc. Comparing with cosmological simulations, we conclude that this LAE overdensity will evolve into a present-day Coma-like cluster with $log{(M/M_odot)}$ $sim$ $15.1pm0.2$. In this and three other wide-field LAE surveys re-analyzed here, the extents and peak amplitudes of the largest LAE overdensities are similar, not increasing with survey size, implying that they were indeed the largest structures then and do evolve into rich clusters today. Intriguingly, LABs favor the outskirts of the densest LAE concentrations, i.e., intermediate LAE overdensities of $delta_Sigma = 1 - 2$. We speculate that these LABs mark infalling proto-groups being accreted by the more massive protocluster.
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.
We compare galaxy scaling relations as a function of environment at $zsim2$ with our ZFIRE survey where we have measured H$alpha$ fluxes for 90 star-forming galaxies selected from a mass-limited [$log(M_{star}/M_{odot})>9$] sample based on ZFOURGE. The cluster galaxies (37) are part of a confirmed system at z=2.095 and the field galaxies (53) are at $1.9<z<2.4$; all are in the COSMOS legacy field. There is no statistical difference between H$alpha$-emitting cluster and field populations when comparing their star formation rate (SFR), stellar mass ($M_{star}$), galaxy size ($r_{eff}$), SFR surface density [$Sigma$(H$alpha_{star}$)], and stellar age distributions. The only difference is that at fixed stellar mass, the H$alpha$-emitting cluster galaxies are $log(r_{eff})sim0.1$ larger than in the field. Approximately 19% of the H$alpha$-emitters in the cluster and 26% in the field are IR-luminous ($L_{IR}>2times10^{11} L_{odot}$). Because the LIRGs in our combined sample are $sim5$ times more massive than the low-IR galaxies, their radii are $sim70$% larger. To track stellar growth, we separate galaxies into those that lie above, on, and below the H$alpha$ star-forming main sequence (SFMS) using $Delta$SFR$(M_{star})=pm0.2$ dex. Galaxies above the SFMS (starbursts) tend to have higher H$alpha$ SFR surface densities and younger light-weighted stellar ages compared to galaxies below the SFMS. Our results indicate that starbursts (+SFMS) in the cluster and field at $zsim2$ are growing their stellar cores. Lastly, we compare to the (SFR-$M_{star}$) relation from RHAPSODY cluster simulations and find the predicted slope is nominally consistent with the observations. However, the predicted cluster SFRs tend to be too low by a factor of $sim2$ which seems to be a common problem for simulations across environment.
We present a study of ~100 high redshift (z~2-4) extremely strong damped Lyman-alpha systems (ESDLA, with N(HI)>0.5x10^22 cm^-2) detected in quasar spectra from the Baryon Oscillation Spectroscopic Survey SDSS-III DR11. We study the neutral hydrogen, metal, and dust content of this elusive population of absorbers and confirm our previous finding that the high column density end of the N(HI) frequency distribution has a relatively shallow slope with power-law index -3.6, similar to what is seen from 21-cm maps in nearby galaxies. The stacked absorption spectrum indicates a typical metallicity ~1/20th solar, similar to the mean metallicity of the overall DLA population. The relatively small velocity extent of the low-ionisation lines suggests that ESDLAs do not arise from large-scale flows of neutral gas. The high column densities involved are in turn more similar to what is seen in DLAs associated with gamma-ray burst afterglows (GRB-DLAs), which are known to occur close to star forming regions. This indicates that ESDLAs arise from lines of sight passing at very small impact parameters from the host galaxy, as observed in nearby galaxies. This is also supported by simple theoretical considerations and recent high-z hydrodynamical simulations. We strongly substantiate this picture by the first statistical detection of Lya emission with <L>~(0.6+/-0.2)x10^42 erg/s in the core of ESDLAs (corresponding to about 0.1 L* at z~2-3), obtained through stacking the fibre spectra (of radius 1 corresponding to ~8 kpc at z~2.5). [truncated]
Dusty, star-forming galaxies have a critical role in the formation and evolution of massive galaxies in the Universe. Using deep far-infrared imaging in the range 100-500um obtained with the Herschel telescope, we investigate the dust-obscured star formation in the galaxy cluster XDCP J0044.0-2033 at z=1.58, the most massive cluster at z >1.5, with a measured mass M200= 4.7x10$^{14}$ Msun. We perform an analysis of the spectral energy distributions (SEDs) of 12 cluster members (5 spectroscopically confirmed) detected with >3$sigma$ significance in the PACS maps, all ULIRGs. The individual star formation rates (SFRs) lie in the range 155-824 Ms/yr, with dust temperatures of 24$pm$35 K. We measure a strikingly high amount of star formation (SF) in the cluster core, SFR (< 250 kpc) > 1875$pm$158 Ms/yr, 4x higher than the amount of star formation in the cluster outskirts. This scenario is unprecedented in a galaxy cluster, showing for the first time a reversal of the SF-density relation at z~1.6 in a massive cluster.
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