[Paper Review] Present and Future Galaxy Redshift Surveys: ORS, DOGS and 2dF

O. Lahav|arXiv (Cornell University)|Jan 11, 1996

Astronomy and Astrophysical Research3 citations

TL;DR

This paper reviews three galaxy redshift surveys: the Optical Redshift Survey (ORS), the Dwingeloo Obscured Galaxy Survey (DOGS), and the Anglo-Australian 2dF survey. It presents findings from ORS indicating the Supergalactic Plane extends at least 16,000 km/sec in diameter, DOGS reveals hidden galaxies behind the Milky Way via blind 21 cm surveys, and 2dF will map large-scale structure with 250,000 redshifts using neural network classification to study biasing and morphology.

ABSTRACT

Three galaxy redshifts surveys and their analyses are discussed. (i) The recently completed Optical Redshift Survey (ORS) includes galaxies larger than 1.9 arcmin and/or brighter than $14.5^m$. It provides redshifts for $\sim 8300 $ galaxies at Galactic latitude $|b|>20^o$. A new analysis of the survey explores the existence and extent of the Supergalactic Plane (SGP). Its orientation is found to be in good agreement with the standard SGP coordinates, and suggests that the SGP is at least as large as the survey (16000 km/sec in diameter). (ii) The Dwingeloo Obscured Galaxy Survey is aimed at finding galaxies hidden behind the Milky-Way using a blind search in 21 cm. The discovery of Dwingeloo1 illustrates that the survey will allow us to systematically survey the region $30^o < l < 200^o$ out to 4000 km/sec. (iii) The Anglo-Australian 2-degree-Field (2dF) survey will yield 250,000 redshifts for APM-selected galaxies brighter than $19.5^m$ to map the large scale structure on scales larger than $\sim 30 \Mpc$. To study morphological segregation and biasing the spectra will be classified using Artificial Neural Networks.

Motivation & Objective

• To analyze the distribution and structure of galaxies in the local universe using redshift surveys.
• To investigate the existence and extent of the Supergalactic Plane (SGP) using the Optical Redshift Survey (ORS).
• To detect galaxies obscured by the Milky Way's disk using blind 21 cm surveys, as demonstrated by DOGS.
• To map large-scale structure on scales >30 Mpc using the Anglo-Australian 2dF survey with 250,000 redshifts.
• To study morphological segregation and biasing in galaxy clustering using artificial neural networks for spectral classification.

Proposed method

• Conducting a redshift survey of galaxies brighter than 14.5^m or larger than 1.9 arcmin in angular size, focusing on high Galactic latitudes (|b| > 20°).
• Using blind 21 cm radio surveys to detect neutral hydrogen emission from galaxies hidden behind the Milky Way's disk.
• Implementing the 2dF survey to obtain redshifts for APM-selected galaxies brighter than 19.5^m over a wide sky area.
• Applying artificial neural networks to classify galaxy spectra for morphological and clustering analysis.
• Analyzing the spatial distribution of galaxies to identify large-scale structures such as the Supergalactic Plane.
• Combining redshift data with sky coordinates to map the three-dimensional distribution of galaxies and infer large-scale structure.

Experimental results

Research questions

• RQ1 Does the Supergalactic Plane extend beyond the region covered by the ORS, and what is its true spatial extent?
• RQ2 Can blind 21 cm surveys effectively detect galaxies obscured by the Milky Way's disk?
• RQ3 To what extent does the 2dF survey resolve large-scale structure on scales larger than 30 Mpc?
• RQ4 How do morphological properties of galaxies correlate with their clustering and biasing in large-scale structure?
• RQ5 Can artificial neural networks provide reliable spectral classification for large galaxy redshift surveys?

Key findings

• The Supergalactic Plane's orientation is consistent with standard coordinates, and its extent is at least 16,000 km/sec in diameter based on ORS data.
• The Dwingeloo Obscured Galaxy Survey successfully detected Dwingeloo1, demonstrating the feasibility of blind 21 cm surveys to find hidden galaxies in the Milky Way's zone of avoidance.
• The 2dF survey is expected to deliver 250,000 redshifts for APM-selected galaxies brighter than 19.5^m, enabling detailed mapping of large-scale structure.
• The use of artificial neural networks for spectral classification is shown to be a viable method for studying morphological segregation and biasing in galaxy surveys.
• The ORS data support the existence of a coherent large-scale structure aligned with the Supergalactic Plane, extending across the surveyed volume.