Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userAre Ly{alpha} emitters segregated in protoclusters regions?
67
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
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.
Ly$alpha$ emission is a standard tracer of starburst galaxies at high redshift. However, a number of local Ly$alpha$ emitters (LAEs) are X-ray sources, suggesting a possible origin of Ly$alpha$ photons other than young, hot stars, and which may be active at much later ages relative to the parent starburst. Resolved, nearby LAEs offer the opportunity to discriminate between diffuse X-ray emission arising from supernova-heated gas, high-mass X-ray binaries (HMXBs), or low-luminosity active galactic nuclei (LLAGN). We examine archival X-ray imaging from Chandra and XMM-Newton for 11 galaxies with spatially resolved Ly$alpha$ imaging to determine the luminosity, morphology, and spectral hardness of the X-ray sources. The data are consistent with 9 of the 12, bright Ly$alpha$ sources being driven by luminous, $10^{40}$ erg s$^{-1}$ X-ray sources. Half of the 8 Chandra sources are unresolved. The data suggest that nuclear activity, whether from LLAGN or nuclear starbursts, may play an important role in Ly$alpha$ emission. Our results also suggest a significant link between Ly$alpha$ emission and HMXBs, ULXs, and/or LLAGN, which would imply that Ly$alpha$ may be generated over timescales 1 - 2 orders of magnitude longer than produced by photoionization from OB stars. This highlights a critical need to quantify the relative contributions of different sources across cosmic time, to interpret Ly$alpha$ observations and the resulting properties of distant galaxies.
In this series of lectures, I review our observational understanding of high-$z$ Ly$alpha$ emitters (LAEs) and relevant scientific topics. Since the discovery of LAEs in the late 1990s, more than ten (one) thousand(s) of LAEs have been identified photometrically (spectroscopically) at $zsim 0$ to $zsim 10$. These large samples of LAEs are useful to address two major astrophysical issues, galaxy formation and cosmic reionization. Statistical studies have revealed the general picture of LAEs physical properties: young stellar populations, remarkable luminosity function evolutions, compact morphologies, highly ionized inter-stellar media (ISM) with low metal/dust contents, low masses of dark-matter halos. Typical LAEs represent low-mass high-$z$ galaxies, high-$z$ analogs of dwarf galaxies, some of which are thought to be candidates of population III galaxies. These observational studies have also pinpointed rare bright Ly$alpha$ sources extended over $sim 10-100$ kpc, dubbed Ly$alpha$ blobs, whose physical origins are under debate. LAEs are used as probes of cosmic reionization history through the Ly$alpha$ damping wing absorption given by the neutral hydrogen of the inter-galactic medium (IGM), which complement the cosmic microwave background radiation and 21cm observations. The low-mass and highly-ionized population of LAEs can be major sources of cosmic reionization. The budget of ionizing photons for cosmic reionization has been constrained, although there remain large observational uncertainties in the parameters. Beyond galaxy formation and cosmic reionization, several new usages of LAEs for science frontiers have been suggested such as the distribution of {sc Hi} gas in the circum-galactic medium and filaments of large-scale structures. On-going programs and future telescope projects, such as JWST, ELTs, and SKA, will push the horizons of the science frontiers.
We present a novel method to investigate cosmic reionization, using joint spectral information on high redshift Lyman Alpha Emitters (LAE) and quasars (QSOs). Although LAEs have been proposed as reionization probes, their use is hampered by the fact their Ly{alpha} line is damped not only by intergalactic HI but also internally by dust. Our method allows to overcome such degeneracy. First, we carefully calibrate a reionization simulation with QSO absorption line experiments. Then we identify LAEs in two simulation boxes at z=5.7 and z=6.6 and we build synthetic images/spectra of a prototypical LAE. At redshift 5.7, we find that the Ly{alpha} transmissivity (T_LAE) ~ 0.25, almost independent of the halo mass. This constancy arises from the conspiracy of two effects: (i) the intrinsic Ly{alpha} line width and (ii) the infall peculiar velocity. At higher redshift, z=6.6, where the transmissivity is instead largely set by the local HI abundance and LAE transmissivity consequently increases with halo mass from 0.15 to 0.3. Although outflows are present, they are efficiently pressure-confined by infall in a small region around the LAE; hence they only marginally affect transmissivity. Finally, we cast LOS originating from background QSOs passing through foreground LAEs at different impact parameters, and compute the quasar transmissivity (T_QSO). At smaller impact parameters, d < 1 cMpc, a positive correlation between T_QSO and halo mass is found at z = 5.7, which tends to become less pronounced (i.e. flatter) at larger distances. By cross-correlating T_LAE and T_QSO, we can obtain a HI density estimate unaffected by dust. At z= 5.7, the cross-correlation is relatively weak,whereas at z = 6.6 we find a clear positive correlation. We conclude by briefly discussing the perspectives for the application of the method to existing and forthcoming data.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
