The First Billion Years

Spectral measurements of atomic and molecular lines embedded in the cosmic microwave background (CMB) have the potential to open entirely new probes of the early Universe. Two avenues are of great interest: 1) Spectral line deviations from the CMB blackbody spectrum will enable the study of hydrogen and helium recombination physics during and before the time of the surface of last scattering, and could provide the potential for game-changing discoveries by testing dark matter annihilation in the redshift range 6000> z > 1000, by allowing a test of the time-dependence of the fine-structure constant at a critical epoch, and by testing inflation models using an independent method. 2) Extension of CMB anisotropy measurements to detect unresolved spectral line emission from starforming galaxies during reionization (6 < z < 10) would directly delineate the large-scale structure of the galaxies responsible for reionizing the Universe and provide the only foreseeable measurements on scales sufficiently large to compare with upcoming observations of reionization by way of the redshifted hydrogen 21 cm line. CO, [C II], and Ly-a lines were investigated as promising targets. CO and [C II] line transitions emerged as particularly compelling. The two science objectives identified in the Program share some common core technological requirements based on the shared need for approximately 1000-element feed arrays followed by broadband, highresolution spectral correlators. The technical requirements lead to a roadmap for development of large feed arrays beginning with applications in a ground-based CO mapping instrument and leading to a spaceborne recombination-line all-sky spectrometer. The key technical issues include compact and light-weight integrated spectral dual-polarization inexpensive receiver modules, large high-resolution spectral correlators (analog and/or digital), and light-weight feeds. In parallel we recommend long-term investigations into high precision calibrators and calibration techniques that will be required for the recombination line instrument. A second roadmap addresses technical developments required for a 2-D spectroscopic instrument for [C II] mapping

The First Billion Years

Spectral measurements of atomic and molecular lines embedded in the cosmic microwave background (CMB) have the potential to open entirely new probes of the early Universe. Two avenues are of great interest: 1) Spectral line deviations from the CMB blackbody spectrum will enable the study of hydrogen and helium recombination physics during and before the time of the surface of last scattering, and could provide the potential for game-changing discoveries by testing dark matter annihilation in the redshift range 6000> z > 1000, by allowing a test of the time-dependence of the fine-structure constant at a critical epoch, and by testing inflation models using an independent method. 2) Extension of CMB anisotropy measurements to detect unresolved spectral line emission from starforming galaxies during reionization (6 < z < 10) would directly delineate the large-scale structure of the galaxies responsible for reionizing the Universe and provide the only foreseeable measurements on scales sufficiently large to compare with upcoming observations of reionization by way of the redshifted hydrogen 21 cm line. CO, [C II], and Ly-a lines were investigated as promising targets. CO and [C II] line transitions emerged as particularly compelling. The two science objectives identified in the Program share some common core technological requirements based on the shared need for approximately 1000-element feed arrays followed by broadband, highresolution spectral correlators. The technical requirements lead to a roadmap for development of large feed arrays beginning with applications in a ground-based CO mapping instrument and leading to a spaceborne recombination-line all-sky spectrometer. The key technical issues include compact and light-weight integrated spectral dual-polarization inexpensive receiver modules, large high-resolution spectral correlators (analog and/or digital), and light-weight feeds. In parallel we recommend long-term investigations into high precision calibrators and calibration techniques that will be required for the recombination line instrument. A second roadmap addresses technical developments required for a 2-D spectroscopic instrument for [C II] mapping

Understanding Galaxy Formation via Near-Infrared Surveys in the 2020s

A discussion of science cases in extragalactic astrophysics and galaxy formation that wide-area space-based infrared surveys will address in the 2020s. <p/

Hydrogen Epoch of Reionization Array (HERA)

The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to measure 21 cm emission from the primordial intergalactic medium (IGM) throughout cosmic reionization ($z=6-12$), and to explore earlier epochs of our Cosmic Dawn ($z\sim30$). During these epochs, early stars and black holes heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is designed to characterize the evolution of the 21 cm power spectrum to constrain the timing and morphology of reionization, the properties of the first galaxies, the evolution of large-scale structure, and the early sources of heating. The full HERA instrument will be a 350-element interferometer in South Africa consisting of 14-m parabolic dishes observing from 50 to 250 MHz. Currently, 19 dishes have been deployed on site and the next 18 are under construction. HERA has been designated as an SKA Precursor instrument. In this paper, we summarize HERA's scientific context and provide forecasts for its key science results. After reviewing the current state of the art in foreground mitigation, we use the delay-spectrum technique to motivate high-level performance requirements for the HERA instrument. Next, we present the HERA instrument design, along with the subsystem specifications that ensure that HERA meets its performance requirements. Finally, we summarize the schedule and status of the project. We conclude by suggesting that, given the realities of foreground contamination, current-generation 21 cm instruments are approaching their sensitivity limits. HERA is designed to bring both the sensitivity and the precision to deliver its primary science on the basis of proven foreground filtering techniques, while developing new subtraction techniques to unlock new capabilities. The result will be a major step toward realizing the widely recognized scientific potential of 21 cm cosmology.Comment: 26 pages, 24 figures, 2 table

The Herschel–ATLAS data release 2, Paper I. Submillimeter and far-infrared images of the South and North Galactic Poles: the largest Herschel survey of the extragalactic sky

We present the largest submillimeter images that have been made of the extragalactic sky. The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) is a survey of 660 deg2 with the PACS and SPIRE cameras in five photometric bands: 100, 160, 250, 350, and 500 μm. In this paper we present the images from our two largest fields, which account for ~75% of the survey. The first field is 180.1 deg2 in size, centered on the north Galactic pole (NGP), and the second is 317.6 deg2 in size, centered on the south Galactic pole. The NGP field serendipitously contains the Coma cluster. Over most (~80%) of the images, the pixel noise, including both instrumental noise and confusion noise, is approximately 3.6, and 3.5 mJy pix−1 at 100 and 160 μm, and 11.0, 11.1 and 12.3 mJy beam−1 at 250, 350 and 500 μm, respectively, but reaches lower values in some parts of the images. If a matched filter is applied to optimize point-source detection, our total 1σ map sensitivity is 5.7, 6.0, and 7.3 mJy at 250, 350, and 500 μm, respectively. We describe the results of an investigation of the noise properties of the images. We make the most precise estimate of confusion in SPIRE maps to date, finding values of 3.12 ± 0.07, 4.13 ± 0.02, and 4.45 ± 0.04 mJy beam−1 at 250, 350, and 500 μm in our un-convolved maps. For PACS we find an estimate of the confusion noise in our fast-parallel observations of 4.23 and 4.62 mJy beam−1 at 100 and 160 μm. Finally, we give recipes for using these images to carry out photometry, both for unresolved and extended sources

The new galaxy evolution paradigm revealed by the Herschel surveys

The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys, which presents a challenge for galaxy-evolution models. The Herschel surveys reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a a single Galaxy Sequence (GS) rather than a star-forming ‘main sequence’ and a separate region of ‘passive’ or ‘red-and-dead’ galaxies. The form of the GS is now clearer because far-infrared surveys such as the Herschel ATLAS pick up a population of optically-red star-forming galaxies that would have been classified as passive using most optical criteria. The space-density of this population is at least as high as the traditional star-forming population. By stacking spectra of H-ATLAS galaxies over the redshift range 0.001 < z < 0.4, we show that the galaxies responsible for the rapid low-redshift evolution have high stellar masses, high star-formation rates but, even several billion years in the past, old stellar populations— they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today. The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution. We propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population