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The Nancy Grace Roman Space Telescope, NASA's next flagship observatory, will redefine deep-field galaxy survey with a field of view two orders of magnitude larger than Hubble and an angular resolution of matching quality. These future deep-wide galaxy surveys necessitate new simulations to forecast their scientific output and to optimise survey strategies. In this work, we present five realizations of 2-deg^2 lightcones, containing a total of >25 million simulated galaxies with -16 < MUV < -25 spanning z ~ 0 to 10. This dataset enables a new set of experiments with the impacts of survey size on the derived galaxy formation and cosmological constraints. The intrinsic and observable galaxy properties are predicted using a well-established, physics-based semi-analytic modelling approach. We provide forecasts for number density, cosmic SFR, field-to-field variance, and angular two-point correlation functions, and demonstrate how the future wide-field surveys will be able to improve these measurements relative to current generation surveys. We also present a comparison between these lightcones and others that have been constructed with empirical models. The mock lightcones are designed to facilitate the exploration of multi-instrument synergies and connecting with current generation instruments and legacy surveys. In addition to Roman, we also provide photometry for a number of other instruments on upcoming facilities, including Euclid and Rubin, as well as the instruments that are part of many legacy surveys. Full object catalogues and data tables for the results presented in this work are made available through a web-based, interactive portal https://www.simonsfoundation.org/semi-analytic-forecasts., 25 pages, 16 figures. Accepted for publication in MNRAS

We report the discovery of 14 Lyman-alpha blobs (LABs) at z~0.3, existing at least 4-7 billion years later in the Universe than all other LABs known. Their optical diameters are 20-70 kpc, and GALEX data imply Ly-alpha luminosities of (0.4-6.3)x10^43 erg/s. Contrary to high-z LABs, they live in low-density areas. They are ionized by AGN, suggesting that cold accretion streams as a power source must deplete between z=2 and z=0.3. We also show that transient AGN naturally explain the ionization deficits observed in many LABs: Their Ly-alpha and X-ray fluxes decorrelate below 10^6 years because of the delayed escape of resonantly scattering Ly-alpha photons. High Ly-alpha luminosities do not require currently powerful AGN, independent of obscuration. Chandra X-ray data reveal intrinsically weak AGN, confirming the luminous optical nebulae as impressive ionization echoes. For the first time, we also report mid-infrared thermal echoes from the dusty tori. We conclude that the AGN have faded by 3-4 orders of magnitude within the last 10^(4-5) years, leaving fossil UV, optical and thermal radiation behind. The host galaxies belong to the group of previously discovered Green Bean galaxies (GBs). Gemini optical imaging reveals smooth spheres, mergers, spectacular outflows and ionization cones. Because of their proximity and high flux densities, GBs are perfect targets to study AGN feedback, mode switching and the Ly-alpha escape. The fully calibrated, coadded optical FITS images are publicly available., Comment: 36 pages, 27 figures. Accepted for publication in MNRAS 2016 July 21. The coadded gri FITS images are publicly available at https://zenodo.org/record/56059

Ly{\alpha} line EWs provide important clues to the physical nature of high redshift LAEs. However, measuring the Ly{\alpha} EW distribution of high-z narrowband selected LAEs can be hard because many sources do not have broadband photometry. We investigate the possible biases in measuring the intrinsic Ly{\alpha} EW distribution for a LAE sample at z $\sim$ 4.5 in the Extended CDFS. Only weak Malmquist-type bias in both the intrinsic Ly{\alpha} luminosity function and the Ly{\alpha} EW distribution were found. However, the observed EW distribution is severely biased if one only considers LAEs with detections in the continuum. Taking the broadband non-detections into account requires fitting the distribution of the broadband-to-narrowband ratio, which then gives a larger EW distribution scale length. Assuming an exponential form of the intrinsic Ly{\alpha} EW distribution dN/dEW = N exp(-EW/W$_0$), we obtain W$_0$ = 167+/-44A (uncorrected for IGM absorption of Ly{\alpha}). We discuss the likely range of IGM absorption effects in light of recent measurements of Ly{\alpha} line profiles and velocity offsets. Our data are consistent with Ly{\alpha} EW being independent of UV luminosity (i.e., we do not see evidence for the "Ando" effect). Our simulations also imply that broad-band images should be 0.5-1 magnitude deeper than narrowband images for an effective and reasonably complete LAE survey. Comparing with consistent measurements at other redshifts, we see a strong evolution in Ly{\alpha} EW distribution with redshift which goes as a power-law form of W$_0$ $\prop$(1+z)$^${\xi}, with {\xi} = 1.1$\pm$0.1 (0.6$\pm$0.1) if no IGM corrections are applied to the Ly{\alpha} line; or {\xi} = 1.7$\pm$0.1 (1.2$\pm$0.1) after applying a maximal IGM-absorption correction to Ly{\alpha} line) for an exponential (a gaussian) EW distribution from z = 0.3 to 6.5.

We present a spectroscopically confirmed sample of Lyman alpha emitting galaxies (LAEs) at z ~ 4.5 in the Extended Chandra Deep Field South (ECDFS), which we combine with a sample of z ~ 4.5 LAEs from the Large Area Lyman Alpha (LALA) survey to build a unified Lya luminosity function (LF). We spectroscopically observed 64 candidate LAEs in the ECDFS, confirming 46 objects as z~4.5 LAEs. We did not detect significant flux from neither C_iv 1549\AA\ nor the He_ii 1640\AA\ emission in individual LAE spectra, even with a coadded spectrum. With the coadded line ratio of He_ii to Lya constraining the Population III star formation rate (SFR) to be 2$\sigma$ significance, and the product $L^*\Phi^*$ differs by a factor of >3. Similar LF differences have been used to infer evolution in the neutral gas fraction in the intergalactic medium at z>6, yet here the difference is likely due to cosmic variance, given that the two samples are from adjoining line-of-sight volumes. Combining our new sample of LAEs with those from previous LALA narrowband surveys at z = 4.5, we obtain one of the best measured Lya LFs to date of L* = 42.83 $\pm$ 0.06 and $\Phi^*$ = -3.48 $\pm$ 0.09. We compare our new LF to others from the literature to study the evolution of the Lya luminosity density at 0 < z < 7. We find tentative evidence for evolution in the product $L^* \Phi^*$, which approximately tracks the cosmic SFR density, but since field-to-field and survey-to-survey variations are in some cases as large as the possible evolution, some caution is needed in interpreting this trend.

Rapid mass assembly, likely from mergers or smooth accretion, has been predicted to play a vital role in star-formation in high-redshift Lyman-alpha (Lya) emitters. Here we predict the major merger, minor merger, and smooth accreting Lya emitter fraction from z~3 to z~7 using a large dark matter simulation, and a simple physical model that is successful in reproducing many observations over this large redshift range. The central tenet of this model, different from many of the earlier models, is that the star-formation in Lya emitters is proportional to the mass accretion rate rather than the total halo mass. We find that at z~3, nearly 35% of the Lya emitters accrete their mass through major (3:1) mergers, and this fraction increases to about 50% at z~7. This imply that the star-formation in a large fraction of high-redshift Lya emitters is driven by mergers. While there is discrepancy between the model predictions and observed merger fractions, some of this difference (~15%) can be attributed to the mass-ratio used to define a merger in the simulation. We predict that future, deeper observations which use a 3:1 definition of major mergers will find >30% major merger fraction of Lya emitters at redshifts >3.

Recent results have shown that a substantial fraction of high-redshift Lyman alpha galaxies contain considerable amounts of dust. This implies that Lyman alpha galaxies are not primordial, as has been thought in the past. However, this dust has not been directly detected in emission; rather it has been inferred based on extinction estimates from rest-frame ultraviolet (UV) and optical observations. This can be tricky, as both dust and old stars redden galactic spectra at the wavelengths used to infer dust. Measuring dust emission directly from these galaxies is thus a more accurate way to estimate the total dust mass, giving us real physical information on the stellar populations and interstellar medium (ISM) enrichment. New generation instruments such as the Atacama Large Millimeter Array (ALMA) and Sub-Millimeter Array (SMA), should be able to detect dust emission from some of these galaxies in the sub-mm. Using measurements of the UV spectral slopes, we derive far-infrared flux predictions for of a sample of 23 z > 4 Lyman alpha galaxies. We find that in only a few hours, we can detect dust emission from 39 +/- 22% of our Lyman alpha galaxies. Comparing these results to those found from a sample of 21 Lyman break galaxies (LBGs), we find that LBGs are on average 60% more likely to be detected than Lyman alpha galaxies, implying that they are more dusty, and thus indicating an evolutionary difference between these objects. These observations will provide better constraints on dust in these galaxies than those derived from their UV and optical fluxes alone. Undeniable proof of dust in these galaxies could explain the larger than expected Lyman alpha equivalent widths seen in many Lyman alpha galaxies today., Accepted to MNRAS; 9 pages, 5 figures