Measuring the Universe with Galaxy Redshift Surveys

Galaxy Redshift surveys provide a three-dimensional map of the Universe. Three distinct processes that encode cosmological information in these maps, are commonly used to constrain models: (i) the comoving power spectrum shape depends on the physical properties of the early Universe, including the physical matter, baryon and neutrino densities, the inflation power spectrum and the degree of Gaussianity of density fluctuations; (ii) we can use the statistical clustering of galaxies as a standard ruler by matching it, or parts of it at different redshifts, and to the Cosmic Microwave Background (CMB); (iii) redshift-space distortions, anisotropic patterns caused by peculiar galaxy velocities, reveal structure growth. Following the design of my talk at the 1st Galileo–Xu Guangqi Meeting, I will use these proceedings to briefly review these experiments.

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Mapping the Cosmic Web with the largest all-sky surveys

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316009753 ◽

2014 ◽

Vol 11 (S308) ◽

pp. 143-148

Author(s):

Maciej Bilicki ◽

John A. Peacock ◽

Thomas H. Jarrett ◽

Michelle E. Cluver ◽

Louise Steward

Keyword(s):

Three Dimensional ◽

Optical Data ◽

Microwave Background ◽

Sky Surveys ◽

Photometric Redshift ◽

Redshift Surveys ◽

Cross Correlations ◽

Galaxy Redshift ◽

Celestial Sphere ◽

The Universe

AbstractOur view of the low-redshift Cosmic Web has been revolutionized by galaxy redshift surveys such as 6dFGS, SDSS and 2MRS. However, the trade-off between depth and angular coverage limits a systematic three-dimensional account of the entire sky beyond the Local Volume (z< 0.05). In order to reliably map the Universe to cosmologically significant depths over the full celestial sphere, one must draw on multiwavelength datasets and state-of-the-art photometric redshift techniques. We have undertaken a dedicated program of cross-matching the largest photometric all-sky surveys – 2MASS, WISE and SuperCOSMOS – to obtain accurate redshift estimates of millions of galaxies. The first outcome of these efforts – the 2MASS Photometric Redshift catalog (2MPZ, Bilickiet al. 2014a) – has been publicly released and includes almost 1 million galaxies with a mean redshift ofz=0.08. Here we summarize how this catalog was constructed and how using the WISE mid-infrared sample together with SuperCOSMOS optical data allows us to push to redshift shells ofz∼ 0.2 –0.3 on unprecedented angular scales. Our catalogs, with ∼ 20 million sources in total, provide access to cosmological volumes crucial for studies of local galaxy flows (clustering dipole, bulk flow) and cross-correlations with the cosmic microwave background such as the integrated Sachs-Wolfe effect or lensing studies.

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Darth Fader: Analysing galaxy spectra at low signal-to-noise

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314013581 ◽

2014 ◽

Vol 10 (S306) ◽

pp. 72-74

Author(s):

Adrienne Leonard ◽

Daniel P. Machado ◽

Filipe B. Abdalla ◽

Jean-Luc Starck

Keyword(s):

Spectral Lines ◽

Signal To Noise ◽

Automated Method ◽

Redshift Surveys ◽

Formation History ◽

The Galaxy ◽

History Of ◽

Galaxy Redshift ◽

The Universe

AbstractSpectroscopic redshift surveys are an incredibly valuable tool in cosmology, allowing us to trace the distribution of galaxies as a function of distance and, thus, trace the evolution of structure formation in the Universe. However, estimating the redshifts from spectra with low signal-to-noise is difficult, and such data are often either discarded or require human classification of spectral lines to obtain the galaxy redshift. Darth Fader offers an automated method for estimating the redshifts of galaxies in the low signal-to-noise regime. Using a sophisticated, wavelet-based technique, galaxy spectra can be separated into continuum, line and noise components, and the lines can then be cross-correlated with template spectra in order to estimate the redshifts. Cross-matching of the identified lines then allows for a cleaning of the resulting catalogue, effectively removing the vast majority of erroneous redshift estimates and resulting in a highly pure, highly accurate redshift catalogue. Darth Fader allows us to effectively use low signal-to-noise galaxy spectra, and dramatically reduces the number of human hours required to do this, allowing spectroscopic surveys to probe deeper into the formation history of the Universe.

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Evidence for cosmic acceleration with next-generation surveys: a model-independent approach

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa040 ◽

2020 ◽

Vol 499 (1) ◽

pp. L6-L10 ◽

Cited By ~ 2

Author(s):

Carlos A P Bengaly

Keyword(s):

Dark Energy Model ◽

Cosmic Acceleration ◽

Accelerated Expansion ◽

Redshift Surveys ◽

Model Independent ◽

Galaxy Redshift ◽

Hubble Parameters ◽

The Universe ◽

Lower Redshift ◽

A Current

ABSTRACT We quantify the evidence for cosmic acceleration using simulations of H(z) measurements from SKA- and Euclid-like surveys. We perform a non-parametric reconstruction of the Hubble parameters and its derivative to obtain the deceleration parameter q(z) using the Gaussian Processes method. This is a completely model-independent approach, so we can determine whether the Universe is undergoing accelerated expansion regardless of any assumption of a dark energy model. We find that Euclid-like and SKA-like band 1 surveys can probe cosmic acceleration at over 3 and 5σ confidence level, respectively. By combining them with an SKA-like band 2 survey, which reaches lower redshift ranges, the evidence for a current accelerated phase increases to over 7σ. This is a significant improvement from current H(z) measurements from cosmic chronometers and galaxy redshift surveys, showing that these surveys can underpin cosmic acceleration in a model-independent way.

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Large-Scale Flows in the Local Universe

Symposium - International Astronomical Union ◽

10.1017/s0074180900110058 ◽

1996 ◽

Vol 168 ◽

pp. 175-182 ◽

Cited By ~ 1

Author(s):

D.S. Mathewson ◽

V.L. Ford

Keyword(s):

Large Scale ◽

Velocity Measurements ◽

Local Universe ◽

Peculiar Velocities ◽

Redshift Surveys ◽

Density Maps ◽

The Universe ◽

Great Wall ◽

Great Attractor ◽

Streaming Flow

Peculiar velocity measurements of 2500 southern spiral galaxies show large-scale flows in the direction of the Hydra-Centaurus clusters which fully participate in the flow themselves. The flow is not uniform over this region and seems to be associated with the denser regions which participate in the flow of amplitude about 400km/s. In the less dense regions the flow is small or non-existent. This makes the flow quite asymmetric and inconsistent with that expected from large-scale, parallel streaming flow that includes all galaxies out to 6000km/s as previously thought. The flow cannot be modelled by a Great Attractor at 4300km/s or the Centaurus clusters at 3500km/s. Indeed, from the density maps derived from the redshift surveys of “optical” and IRAS galaxies, it is difficult to see how the mass concentrations can be responsible particularly as they themselves participate in the flow. These results bring into question the generally accepted reason for the peculiar velocities of galaxies that they arise solely as a consequence of infall into the dense regions of the universe. To the N. of the Great Attractor region, the flow increases and shows no sign of diminishing out to the redshift limit of 8000km/s in this direction. We may have detected flow in the nearest section of the Great Wall.

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