The Herschel Multi‐tiered Extragalactic Survey (HerMES) is a legacy programme designed to map a set of nested fields totalling ∼380 deg2. Fields range in size from 0.01 to ∼20 deg2, using the Herschel‐Spectral and Photometric Imaging Receiver (SPIRE) (at 250, 350 and 500 μm) and the Herschel‐Photodetector Array Camera and Spectrometer (PACS) (at 100 and 160 μm), with an additional wider component of 270 deg2 with SPIRE alone. These bands cover the peak of the redshifted thermal spectral energy distribution from interstellar dust and thus capture the reprocessed optical and ultraviolet radiation from star formation that has been absorbed by dust, and are critical for forming a complete multiwavelength understanding of galaxy formation and evolution. The survey will detect of the order of 100 000 galaxies at 5σ in some of the best‐studied fields in the sky. Additionally, HerMES is closely coordinated with the PACS Evolutionary Probe survey. Making maximum use of the full spectrum of ancillary data, from radio to X‐ray wavelengths, it is designed to facilitate redshift determination, rapidly identify unusual objects and understand the relationships between thermal emission from dust and other processes. Scientific questions HerMES will be used to answer include the total infrared emission of galaxies, the evolution of the luminosity function, the clustering properties of dusty galaxies and the properties of populations of galaxies which lie below the confusion limit through lensing and statistical techniques. This paper defines the survey observations and data products, outlines the primary scientific goals of the HerMES team, and reviews some of the early results.

Extragalactic background light (EBL) anisotropy traces variations in the total production of photons over cosmic history, and may contain faint, extended components missed in galaxy point source surveys. Infrared EBL fluctuations have been attributed to primordial galaxies and black holes at the epoch of reionization (EOR), or alternately, intra-halo light (IHL) from stars tidally stripped from their parent galaxies at low redshift. We report new EBL anisotropy measurements from a specialized sounding rocket experiment at 1.1 and 1.6 micrometers. The observed fluctuations exceed the amplitude from known galaxy populations, are inconsistent with EOR galaxies and black holes, and are largely explained by IHL emission. The measured fluctuations are associated with an EBL intensity that is comparable to the background from known galaxies measured through number counts, and therefore a substantial contribution to the energy contained in photons in the cosmos.At near-infrared wavelengths, where the large zodiacal light foreground complicates absolute photometry measurements, the extragalactic background light (EBL) may be best accessed by anisotropy measurements. On large angular scales, fluctuations are produced by the clustering of galaxies, which is driven by the underlying distribution of dark matter. EBL anisotropy measurements can probe emission from epoch of reionization (EOR) galaxies (1-3) and directcollapse black holes (4) that formed during the EOR before the universe was fully ionized by exploiting the distinctive Lyman cutoff feature in the rest-frame ultraviolet (UV), thus probing the UV luminosity density at high redshifts (5). However, large-scale fluctuations may also arise from the intrahalo light (IHL) created by stars stripped from their parent galaxies during tidal interactions (6) at redshift z < 3. A multi-wavelength fluctuation analysis can distinguish among these scenarios and constrain the EOR star formation rate.A search for such background components must carefully account for fluctuations produced 2 by known galaxy populations. Linear galaxy clustering is an important contribution to fluctuations on scales much larger than galaxies themselves. On fine scales, the variation in the number of galaxies produces predominantly Poissonian fluctuations, with an amplitude that depends on the luminosity distribution. Anisotropy measurements suppress foreground galaxy fluctuations by masking known galaxies from an external catalog.The first detections of infrared fluctuations in excess of the contribution from known galaxies with the Spitzer Space Telescope (7-9) were interpreted as arising from a population of faint first-light galaxies at z > 7. The Hubble Space Telescope was used at shorter wavelengths (10) to carry out a fluctuation study in a small deep field but did not report fluctuations in excess of known galaxy populations. Measurements with the AKARIsatellite (11) show excess fluctuations with a blue spectrum rapidly rising from 4.1μm to 2.4μm. Fluctuation measurements in a large survey fi...

We produce simulations of the atomic CII line emission in large sky fields in order to determine the current and future prospects for mapping this line during the high redshift epoch of reionization. We calculate the CII line intensity, redshift evolution and spatial fluctuations using observational relations between CII emission and the galaxy star formation rate (SFR) over the frequency range 200 -300 GHz. We estimate an averaged intensity of I CII = (4 ± 2) × 10 2 Jy sr −1 in the redshift range z ∼ 5.3 − 8.5. Observations of the CII emission in this frequency range will suffer contamination from emission lines at lower redshifts, in particular CO rotational lines. Using simulations, we estimated the CO contamination to be I CO ≈ 10 3 Jy sr −1 (originating from galaxies at z < 2.5). Using detailed simulations of the CII and CO emission across a range of redshifts, we generate maps as a function of angle and frequency, fully taking into account this resolution and light cone effects. In order to reduce the foreground contamination we find that we should mask galaxies below redshifts ∼ 2.5 with a CO(J:2-1) to CO(J:6-5) line flux density higher than 5 × 10 −22 W m −2 or a AB magnitude lower than m K = 22. We estimate that the additional continuum contamination originating in emission from stars and in dust, free-free, free-bound and two photon emission in the ISM is of the order of 10 5 Jy sr −1 however it can be removed from observation due to the smooth evolution of this foreground with frequency. We also consider the possibility of cross correlating foreground lines with galaxy surveys in order to probe the intensity of the foregrounds. Finally, we discuss the expected constraints from two experiments capable of measuring the expected CII power spectrum. Subject headings: cosmology: theory -diffuse radiation -intergalactic medium -large scale structure of universe

Unresolved anisotropies of the cosmic near-infrared background radiation are expected to have contributions from the earliest galaxies during the epoch of reionization and from faint, dwarf galaxies at intermediate redshifts. Previous measurements were unable to pinpoint conclusively the dominant origin because they did not sample spatial scales that were sufficiently large to distinguish between these two possibilities. Here we report a measurement of the anisotropy power spectrum from subarcminute to one-degree angular scales, and find the clustering amplitude to be larger than predicted by the models based on the two existing explanations. As the shot-noise level of the power spectrum is consistent with that expected from faint galaxies, a new source population on the sky is not necessary to explain the observations. However, a physical mechanism that increases the clustering amplitude is needed. Motivated by recent results related to the extended stellar light profile in dark-matter haloes, we consider the possibility that the fluctuations originate from intrahalo stars of all galaxies. We find that the measured power spectrum can be explained by an intrahalo light fraction of 0.07 to 0.2 per cent relative to the total luminosity in dark-matter haloes of 10(9) to 10(12) solar masses at redshifts of about 1 to 4.

The atomic CII fine-structure line is one of the brightest lines in a typical star-forming galaxy spectrum with a luminosity ∼ 0.1% to 1% of the bolometric luminosity. It is potentially a reliable tracer of the dense gas distribution at high redshifts and could provide an additional probe to the era of reionization. By taking into account of the spontaneous, stimulated and collisional emission of the CII line, we calculate the spin temperature and the mean intensity as a function of the redshift. When averaged over a cosmologically large volume, we find that the CII emission from ionized carbon in individual galaxies is larger than the signal generated by carbon in the intergalactic medium (IGM). Assuming that the CII luminosity is proportional to the carbon mass in dark matter halos, we also compute the power spectrum of the CII line intensity at various redshifts. In order to avoid the contamination from CO rotational lines at low redshift when targeting a CII survey at high redshifts, we propose the cross-correlation of CII and 21-cm line emission from high redshifts. To explore the detectability of the CII signal from reionization, we also evaluate the expected errors on the CII power spectrum and CII-21 cm cross power spectrum based on the design of the future milimeter surveys. We note that the CII-21 cm cross power spectrum contains interesting features that captures physics during reionization, including the ionized bubble sizes and the mean ionization fraction, which are challenging to measure from 21-cm data alone. We propose an instrumental concept for the reionization CII experiment targeting the frequency range of ∼ 200 to 300 GHz with 1, 3 and 10 meter apertures and a bolometric spectrometer array with 64 independent spectral pixels with about 20,000 bolometers. Subject headings: cosmology: theory -diffuse radiation -intergalactic medium -large scale structure of universe

The Chinese Space Station Optical Survey (CSS-OS) is a planned full sky survey operated by the Chinese Space Station Telescope (CSST). It can simultaneously perform the photometric imaging and spectroscopic slitless surveys, and will probe weak and strong gravitational lensing, galaxy clustering, individual galaxies and galaxy clusters, active galactic nucleus (AGNs), and so on. It aims to explore the properties of dark matter and dark energy and other important cosmological problems. In this work, we focus on two main CSS-OS scientific goals, i.e. the weak gravitational lensing (WL) and galaxy clustering surveys. We generate the mock CSS-OS data based on the observational COSMOS and zCOSMOS catalogs. We investigate the constraints on the cosmological parameters from the CSS-OS using the Markov Chain Monte Carlo (MCMC) method. The intrinsic alignments, galaxy bias, velocity dispersion, and systematics from instrumental effects in the CSST WL and galaxy clustering surveys are also included, and their impacts on the constraint results are discussed. We find that the CSS-OS can improve the constraints on the cosmological parameters by a factor of a few (even one order of magnitude in the optimistic case), compared to the current WL and galaxy clustering surveys. The constraints can be further enhanced when performing joint analysis with the WL, galaxy clustering, and galaxy-galaxy lensing data. Therefore, the CSS-OS is expected to be a powerful survey for exploring the Universe. Since some assumptions may be still optimistic and simple, it is possible that the results from the real survey could be worse. We will study these issues in details with the help of simulations in the future.

We calculate the absolute intensity and anisotropies of the Lyman-α radiation field present during the epoch of reionization. We consider emission from both galaxies and the intergalactic medium (IGM) and take into account the main contributions to the production of Lyman-α photons: recombinations, collisions, continuum emission from galaxies and scattering of Lyman-n photons in the IGM. We find that the emission from individual galaxies dominates over the IGM with a total Lyman-α intensity (times frequency) of about (1.43 − 3.57) × 10 −8 erg s −1 cm −2 sr −1 at a redshift of 7. This intensity level is low so it is unlikely that the Lyman-α background during reionization can be established by an experiment aiming at an absolute background light measurement. Instead we consider Lyman-α intensity mapping with the aim of measuring the anisotropy power spectrum which has rms fluctuations at the level of 1 × 10 −16 [erg s −1 cm −2 sr −1 ] 2 at a few Mpc scales. These anisotropies could be measured with a spectrometer at near-IR wavelengths from 0.9 to 1.4 µm with fields in the order of 0.5 to 1 sq. degrees. We recommend that existing ground-based programs using narrow band filters also pursue intensity fluctuations to study statistics on the spatial distribution of faint Lyman-α emitters. We also discuss the cross-correlation signal with 21 cm experiments that probe HI in the IGM during reionization. A dedicated sub-orbital or space-based Lyman-α intensity mapping experiment could provide a viable complimentary approach to probe reionization, when compared to 21 cm experiments, and is likely within experimental reach.

We propose observations of the molecular gas distribution during the era of reionization. At z ∼ 6 to 8, 12 CO(J = 1 − 0) line intensity results in a mean brightness temperature of about 0.5 µK with rms fluctuations of 0.1 µK at 1 to 10 Mpc spatial scales, corresponding to 30 arcminute angular scales. This intensity fluctuations can be mapped with an interferometer, similar to existing and planned 21-cm background experiments, but operating at ∼ 12 to 17 GHz. We discuss the feasibility of detecting the cross-correlation between HI and CO molecular gas since such a cross-correlation has the advantage that it will be independent of systematics and most foregrounds in each of the 21-cm and CO(1 − 0) line experiments. Additional instruments tuned to higher-order transitions of the CO molecule or an instrument operating with high spectral resolution at mmwavelengths targeting 158 µm CII could further improve the reionization studies with molecular gas. The combined 21-cm and CO line observations has the potential to establish the relative distribution of gas in the inter-galactic medium and molecular gas that are clumped in individual first-light galaxies that are closely connected to the formation of massive stars in these galaxies.