Predictions for ASKAP Neutral Hydrogen Surveys (1208.5592v3)

Abstract: The Australian Square Kilometer Array Pathfinder (ASKAP) will revolutionise our knowledge of gas-rich galaxies in the Universe. Here we present predictions for two proposed extragalactic ASKAP neutral hydrogen (HI) emission-line surveys, based on semi-analytic models applied to cosmological N-body simulations. The ASKAP HI All-Sky Survey, known as WALLABY, is a shallow 3 Pi survey (z = 0 - 0.26) which will probe the mass and dynamics of over 600,000 galaxies. A much deeper small-area HI survey, called DINGO, aims to trace the evolution of HI from z = 0 - 0.43, a cosmological volume of 40 million Mpc^3, detecting potentially 100,000 galaxies. The high-sensitivity 30 antenna ASKAP core (diameter ~2 km) will provide an angular resolution of 30 arcsec (at z=0). Our simulations show that the majority of galaxies detected in WALLABY (87.5%) will be resolved. About 5000 galaxies will be well resolved, i.e. more than five beams (2.5 arcmin) across the major axis, enabling kinematic studies of their gaseous disks. This number would rise to 160,000 galaxies if all 36 ASKAP antennas could be used; the additional six antennas provide baselines up to 6 km, resulting in an angular resolution of 10 arcsec. For DINGO this increased resolution is highly desirable to minimise source confusion; reducing confusion rates from a maximum of 10% of sources at the survey edge to 3%. We estimate that the sources detected by WALLABY and DINGO will span four orders of magnitude in total halo mass (from 10^{11} to 10^{15} Msol) and nearly seven orders of magnitude in stellar mass (from 10^{5} to 10^{12} Msol), allowing us to investigate the process of galaxy formation across the last four billion years.

• The paper employs semi-analytic models with N-body simulations to forecast up to 600,000 galaxy detections for WALLABY and 100,000 for DINGO.
• It demonstrates that most WALLABY-detected galaxies will be spatially resolved, offering detailed insights into halo and stellar mass distributions over four billion years.
• The study highlights the synergy with optical surveys like GAMA, suggesting that stacking HI signals can reduce source confusion and extend detection limits.

Predictions for ASKAP Neutral Hydrogen Surveys

The paper "Predictions for ASKAP Neutral Hydrogen Surveys" by A. R. Duffy et al. presents a comprehensive analysis of the prospective capabilities of the Australian Square Kilometer Array Pathfinder (ASKAP) in conducting extragalactic neutral hydrogen (HI) emission-line surveys. The research focuses on two specific surveys: the wide-area shallow survey WALLABY and the deep but narrow survey DINGO. These surveys are intended to enhance our understanding of the distribution and dynamics of gas-rich galaxies across the Universe.

The WALLABY survey aims to scan approximately 75% of the sky up to a redshift of 0.26, detecting around 600,000 galaxies. In contrast, the DINGO survey seeks to explore a smaller area yet reach a redshift of 0.43, aiming to trace the evolution of HI in approximately 100,000 galaxies. The paper employs semi-analytic models applied to cosmological N-body simulations to predict the outcomes of these surveys, providing detailed expectations of galaxy detection numbers, resolution capabilities, and the surveys' ability to resolve gaseous disks.

ASKAP, featuring an advanced 36-antenna array, allows for significant observational capabilities, with a particular focus on its high sensitivity core that achieves an angular resolution of up to 30 arcseconds. The research highlights that most galaxies detected through WALLABY will be resolved, while the DINGO survey, with its deeper exploration, necessitates an angular resolution enhancement to minimize source confusion.

The implications of these surveys are profound. ASKAP's detections are expected to range over four orders of magnitude in halo mass and nearly seven orders in stellar mass. This range allows for an extensive investigation into the processes of galaxy formation and evolution over the last four billion years. Furthermore, the paper suggests that resolving such a wide array of masses and configurations will provide insights into the kinematic properties of galaxies, which is crucial for understanding dark matter distributions and galaxy formation theories.

In terms of synergy with optical surveys, the research explores the potential for stacking HI signals at given optical spectroscopic redshifts, particularly within overlapping fields, such as those used by the Galaxy And Mass Assembly (GAMA) survey. Such collaborative efforts can extend the effective limits of HI detections, improving our understanding of the stellar and gas mass build-up within galaxies.

The authors acknowledge the challenges associated with large-area HI surveys, particularly in differentiating between overlapping sources. By utilizing detailed models of galaxy distribution and clustering, the paper rigorously estimates the confusion rates across different redshift slices. It demonstrates how advanced imaging techniques, like creating high-resolution "postage stamp" images, can help alleviate these challenges by ensuring robust galaxy detection and characterization.

The paper concludes by discussing the expected outcomes of the proposed ASKAP surveys and the valuable dataset they will provide to the astronomical community. The anticipation is that these surveys will form a significant step forward in extragalactic astronomy, allowing for the direct observation and analysis of gas content in galaxies and offering new constraints on models of galaxy evolution.

Future developments will likely see further refinements in the theoretical models used to plan these surveys, as well as continued improvements in telescope technology and data processing capabilities. These advancements will enhance the resolution, sensitivity, and overall scientific yield of neutral hydrogen observations, providing an even deeper understanding of the Universe.