Original article can be found at: http://www.iop.org/EJ/journal/1538-3881 Copyright American Astronomical Society. DOI: 10.1088/0004-6256/137/6/4670 [Full text of this article is not available in the UHRA]

HERACLES: The HERA CO-Line Extragalactic Survey

Author(s): Huang, L; Dey, A; Schlegel, DJ; Lang, D; Blum, R; Burleigh, K; Fan, X; Findlay, JR; Finkbeiner, D; Herrera, D; Juneau, S; Landriau, M; Levi, M; McGreer, I; Meisner, A; Myers, AD; Moustakas, J; Nugent, P; Patej, A; Schlafly, EF; Walker, AR; Valdes, F; Weaver, BA; Yeche, C; Zou, H; Zhou, X; Abareshi, B; Abbott, TMC; Abolfathi, B; Aguilera, C; Alam, S; Allen, L; Alvarez, A; Annis, J; Ansarinejad, B; Aubert, M; Beechert, J; Bell, EF; Benzvi, SY; Beutler, F; Bielby, RM; Bolton, AS; Briceno, C; Buckley-Geer, EJ; Butler, K; Calamida, A; Carlberg, RG; Carter, P; Casas, R; Castander, FJ; Choi, Y; Comparat, J; Cukanovaite, E; Delubac, T; Devries, K; Dey, S; Dhungana, G; Dickinson, M; Ding, Z; Donaldson, JB; Duan, Y; Duckworth, CJ; Eftekharzadeh, S; Eisenstein, DJ; Etourneau, T; Fagrelius, PA; Farihi, J; Fitzpatrick, M; Font-Ribera, A; Fulmer, L; Gansicke, BT; Gaztanaga, E; George, K; Gerdes, DW; A Gontcho, SG; Gorgoni, C; Green, G; Guy, J; Harmer, D; Hernandez, M; Honscheid, K; Huang, LW; James, DJ; Jannuzi, BT; Jiang, L | Abstract: © 2019. The American Astronomical Society. All rights reserved.. The DESI Legacy Imaging Surveys (http://legacysurvey.org/) are a combination of three public projects (the Dark Energy Camera Legacy Survey, the Beijing-Arizona Sky Survey, and the Mayall z-band Legacy Survey) that will jointly image ≈14,000 deg2 of the extragalactic sky visible from the northern hemisphere in three optical bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. The combined survey footprint is split into two contiguous areas by the Galactic plane. The optical imaging is conducted using a unique strategy of dynamically adjusting the exposure times and pointing selection during observing that results in a survey of nearly uniform depth. In addition to calibrated images, the project is delivering a catalog, constructed by using a probabilistic inference-based approach to estimate source shapes and brightnesses. The catalog includes photometry from the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12, and 22 μm) observed by the Wide-field Infrared Survey Explorer satellite during its full operational lifetime. The project plans two public data releases each year. All the software used to generate the catalogs is also released with the data. This paper provides an overview of the Legacy Surveys project.

Overview of the DESI Legacy Imaging Surveys

Neutral atomic hydrogen (HI) and molecular hydrogen (H2) play a primordial role in the cosmic evolution of galaxies. However, little is known about the co-evolution of these two gas phases. This discrepancy and the design of future telescopes like the SKA and ALMA require theoretical models of the joint evolution of HI and H2 in galaxies. This thesis starts with a phenomenological analysis of the H2/HI-ratios in a sample of 245 local galaxies. This analysis reveals a number of correlations between H2/HI-ratios and other galaxy properties, and we demonstrate that these correlations can be understood in terms of the microscopic relation between the H2/HI-ratio and the external gas pressure. We subsequently use this relation to derive an analytic model for the column densities of HI and H2 in arbitrary regular galaxies. As a second step, we apply the model for the column densities of HI and H2 to post-process approximately 3*10^7 virtual galaxies, whose cosmic evolution was simulated on the evolving dark matter skeleton output by the Millennium Simulation. The post-processing of these galaxies allows us to (i) split their total cold gas masses between HI, H2, and Helium, (ii) to assign realistic sizes to both the HI and H2-disks, and (iii) to evaluate the velocity profiles of HI and H2. The resulting hydrogen simulation successfully reproduces many local observations of HI and H2, such as mass functions (MFs), mass-diameter relations, and mass-velocity relations. A key prediction of this simulation is that the H2/HI-ratio of regular galaxies increases dramatically with redshift z, leading to a scaling of (1+z)^1.6 for the ratio between the cosmic space densities of H2 and HI. This prediction offers a unified explanation for (i) the weak evolution of the cosmic HI-density inferred from Lyman-alpha absorption against quasars, (ii) the large molecular masses detected in regular galaxies at z=1.5, and (iii) the recent cosmic decline in the density of star formation. As a third step, we introduce a heuristic model for the conversion of H2-masses into observable CO-line luminosities for galaxies at all redshifts. We apply this model to our hydrogen simulation in order to predict the luminosity functions of the first 10 rotational transitions of CO in galaxies at redshift z=0 to z=10. As a final step, we transform the simulated catalog of 3*10^7 evolving galaxies into a virtual observing cone, i.e. a catalog that lists the apparent HI and CO-line fluxes and corresponding line widths of millions of galaxies in a sky field with a comoving diameter of 500 Mpc/h. This catalog represents a tangible contribution towards the design and operation of future telescopes, such as the SKA and ALMA.

The Cosmic Evolution of Atomic and Molecular Hydrogen in Galaxies

We present The H I Nearby Galaxy Survey (THINGS), a high spectral (≤5.2 km s–1) and spatial (~6'') resolution survey of H I emission in 34 nearby galaxies obtained using the NRAO Very Large Array (VLA). The overarching scientific goal of THINGS is to investigate fundamental characteristics of the interstellar medium (ISM) related to galaxy morphology, star formation, and mass distribution across the Hubble sequence. Unique characteristics of the THINGS database are the homogeneous sensitivity as well as spatial and velocity resolution of the H I data, which is at the limit of what can be achieved with the VLA for a significant number of galaxies. A sample of 34 objects at distances 2 D 15 Mpc (resulting in linear resolutions of ~100 to 500 pc) are targeted in THINGS, covering a wide range of star formation rates (~10–3 to 6 M ☉ yr–1), total H I masses M HI (0.01 to 14 × 109 M ☉), absolute luminosities M B (–11.5 to –21.7 mag), and metallicities (7.5 to 9.2 in units of 12+log[O/H]). We describe the setup of the VLA observations, the data reduction procedures, and the creation of the final THINGS data products. We present an atlas of the integrated H I maps, the velocity fields, the second moment (velocity dispersion) maps and individual channel maps of each THINGS galaxy. The THINGS data products are made publicly available through a dedicated webpage. Accompanying THINGS papers (in this issue of the Astronomical Journal) address issues such as the small-scale structure of the ISM, the (dark) matter distribution in THINGS galaxies, and the processes leading to star formation.

THINGS: The HI Nearby Galaxy Survey

The peculiar velocity field offers a unique way to probe dark matter density field on large scales at low redshifts. In this work, we have compiled a new sample of 465 peculiar velocities from low redshift $(z < 0.067)$ Type Ia supernovae. We compare the reconstructed velocity field derived from the 2M++ galaxy redshift compilation to the supernovae, the SFI++ and the 2MTF Tully-Fisher distance catalogues. We used a forward method to jointly infer the distances and the velocities of distance indicators by comparing the observations to the reconstruction. Comparison of the reconstructed peculiar velocity fields to observations allows us to infer the cosmological parameter combination $f\sigma_8$, and the bulk flow velocity arising from outside the survey volume. The residual bulk flow arising from outside the 2M++ volume is inferred to be $171^{+11}_{-11}$ km s$^{-1}$ in the direction $l=301^{\circ} \pm 4^{\circ}$ and $b=0^{\circ} \pm 3^{\circ}$. We obtain $f\sigma_{8} = 0.400 \pm 0.017$, equivalent to $S_8 \approx \sigma_8(\Omega_m/0.3)^{0.55}=0.776\pm0.033$, which corresponds to an approximately $ 4\%\,$ statistical uncertainty on the value of $f\sigma_8$. Our inferred value is consistent with other low redshift results in the literature.

Cosmic flows in the nearby Universe: new peculiar velocities from SNe and cosmological constraints

The Widefield ASKAP L-band Legacy All-sky Blind surveY (wallaby) is a next-generation survey of neutral hydrogen (H i) in the Local Universe. It uses the widefield, high-resolution capability of the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of 36 \times12-m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia. wallaby aims to survey three-quarters of the sky (-90^{\circ} < \delta< +30^{\circ}) to a redshift of z \lesssim0.26, and generate spectral line image cubes at ∼30 arcsec resolution and ∼1.6 mJy beam$^{−1}$ per 4 km s$^{−1}$ channel sensitivity. ASKAP’s instantaneous field of view at 1.4 GHz, delivered by the PAF’s 36 beams, is about 30 sq deg. At an integrated signal-to-noise ratio of five, wallaby is expected to detect around half a million galaxies with a mean redshift of z \sim0.05 (∼200 Mpc). The scientific goals of wallaby include: (a) a census of gas-rich galaxies in the vicinity of the Local Group; (b) a study of the H i properties of galaxies, groups and clusters, in particular the influence of the environment on galaxy evolution; and (c) the refinement of cosmological parameters using the spatial and redshift distribution of low-bias gas-rich galaxies. For context we provide an overview of recent and planned large-scale H i surveys. Combined with existing and new multi-wavelength sky surveys, wallaby will enable an exciting new generation of panchromatic studies of the Local Universe. — First results from the wallaby pilot survey are revealed, with initial data products publicly available in the CSIRO ASKAP Science Data Archive (CASDA).

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D. H. Jones

Papers

WALLABY – an SKA Pathfinder H i survey