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Register a new userThe clustering of Ly-alpha emitters in a LambdaCDM Universe
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A. Orsi
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We combine a semi-analytical model of galaxy formation with a very large simulation which follows the growth of large scale structure in a LambdaCDM universe to predict the clustering of Ly-alpha emitters. We find that the clustering strength of Ly-alpha emitters has only a weak dependence on Ly-alpha luminosity but a strong dependence on redshift. With increasing redshift, Ly-alpha emitters trace progressively rarer, higher density regions of the universe. Due to the large volume of the simulation, over 100 times bigger than any previously used for this application, we can construct mock catalogues of Ly-alpha emitters and study the sample variance of current and forthcoming surveys. We find that the number and clustering of Ly-alpha emitters in our mock catalogues are in agreement with measurements from current surveys, but that there is a considerable scatter in these quantities. We argue that a proposed survey of emitters at z=8.8 should be extended significantly in solid angle to allow a robust measurement of Ly-alpha emitter clustering.
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In this work we model the observed evolution in comoving number density of Lyman-alpha blobs (LABs) as a function of redshift, and try to find which mechanism of emission is dominant in LAB. Our model calculates LAB emission both from cooling radiation from the intergalactic gas accreting onto galaxies and from star formation (SF). We have used dark matter (DM) cosmological simulation to which we applied empirical recipes for Ly$alpha$ emission produced by cooling radiation and SF in every halo. In difference to the previous work, the simulated volume in the DM simulation is large enough to produce an average LABs number density. At a range of redshifts $zsim 1-7$ we compare our results with the observed luminosity functions of LABs and LAEs. Our cooling radiation luminosities appeared to be too small to explain LAB luminosities at all redshifts. In contrast, for SF we obtained a good agreement with observed LFs at all redshifts studied. We also discuss uncertainties which could influence the obtained results, and how LAB LFs could be related to each other in fields with different density.
Recently, we conducted a Very Large Telescope (VLT) large program to search for forming clusters by looking for overdensities of Ly-alpha emitters around high redshift radio galaxies. In total seven proto-clusters were discovered, including a proto-cluster around the radio galaxy MRC 0316--257 at z ~ 3.13. This structure has an excess of Ly-alpha emitters by a factor of 3 as compared to the field, and the derived mass is 2-5 x 10^14 M_sun. The Ly-alpha emitters in the proto-cluster are on average bluer than Lyman Break Galaxies (LBGs). Also, the galaxies are faint (sub L_*) and small (half light radii < 1.7 kpc, which is smaller than the average size of LBGs). This might indicate that, at least a fraction of, Ly-alpha emitters could be young (~ 10^6 yr), nearly dust-free, forming galaxies.
We explore galaxy properties and their link with environment and clustering using a population of ~1000 galaxies formed in a high resolution hydrodynamic simulation of the Lambda CDM cosmology. At the redshift we concentrate on, z=1, the spatial resolution is 1.4 proper kpc/h and Milky-way sized disk galaxies contain ~10^5 particles within their virial radii. We include supermassive black hole accretion and feedback as well as a multiphase model for star formation. We find that a number of familiar qualitative relationships hold approximately between galaxy properties, for example, galaxies lie between two broad extremes of type, where ``late types tend to be smaller in size, have lower circular velocities, younger stars, higher star formation rates, larger disk to bulge ratios and lower Sersic indices than ``early types. As in previous studies the stellar component of disk galaxies is not as rotationally supported as in observations. Bulges contain too much of the stellar mass, although disks do have scale lengths compatible with observations. The addition of black hole physics to the simulations does not appear to have an impact on the angular momentum results, nor do we find that it is affected in an identical simulation with significantly lower mass resolution. Despite this, we can profitably use the rank order of either disk to total ratio, Sersic index, or galaxy age to separate galaxies into morphological classes and examine the density-morphology relation and morphology dependence of clustering. We find that while at redshift z=0, the well known preponderance of early types in dense environments is seen, at z=1 the density-morphology relation becomes flatter and late type galaxies are even seen to have a higher clustering amplitude than early types (abridged).
We investigate the clustering and halo properties of $sim 5000$ Ly$alpha$-selected emission line galaxies (LAEs) from the Slicing COSMOS 4K (SC4K) and from archival NB497 imaging of SA22 split in 15 discrete redshift slices between $z sim 2.5 - 6$. We measure clustering lengths of $r_0 sim 3 - 6 h^{-1}$ Mpc and typical halo masses of $sim 10^{11}$ M$_odot$ for our narrowband-selected LAEs with typical $L_{rm{Ly}alpha} sim 10^{42 - 43}$ erg s$^{-1}$. The intermediate band-selected LAEs are observed to have $r_0 sim 3.5 - 15 h^{-1}$ Mpc with typical halo masses of $sim 10^{11 - 12}$ M$_odot$ and typical $L_{rm{Ly}alpha} sim 10^{43 - 43.6}$ erg s$^{-1}$. We find a strong, redshift-independent correlation between halo mass and Ly$alpha$ luminosity normalized by the characteristic Ly$alpha$ luminosity, $L^star(z)$. The faintest LAEs ($L sim 0.1 L^star(z)$) typically identified by deep narrowband surveys are found in $10^{10}$ M$_odot$ halos and the brightest LAEs ($L sim 7 L^star(z)$) are found in $sim 5 times 10^{12}$ M$_odot$ halos. A dependency on the rest-frame 1500 AA~UV luminosity, M$_rm{UV}$, is also observed where the halo masses increase from $10^{11}$ to $10^{13}$ M$_odot$ for M$_rm{UV} sim -19$ to $-23.5$ mag. Halo mass is also observed to increase from $10^{9.8}$ to $10^{12.3}$ M$_odot$ for dust-corrected UV star formation rates from $sim 0.6$ to $10$ M$_odot$ yr$^{-1}$ and continues to increase up to $10^{13.5}$ M$_odot$ in halo mass, where the majority of those sources are AGN. All the trends we observe are found to be redshift-independent. Our results reveal that LAEs are the likely progenitors of a wide range of galaxies depending on their luminosity, from dwarf-like, to Milky Way-type, to bright cluster galaxies. LAEs therefore provide unique insight into the early formation and evolution of the galaxies we observe in the local Universe.
The presence of neutral hydrogen in the inter-stellar medium (ISM) and inter-galactic medium (IGM) induces radiative transfer (RT) effects on Ly{alpha} photons which affect the observability of Ly{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 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 Ly{alpha} emission (HAEs+LAEs) populate the same regions as those that do not display the 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.
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