[Paper Review] Measuring Cosmic Density of Neutral Hydrogen via Stacking the DINGO-VLA Data

Qingxiang Chen, M. Meyer+14 more|arXiv (Cornell University)|Apr 16, 2021

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy97 references17 citations

TL;DR

This study measures the cosmic density of neutral hydrogen (ΩH I) at z ≈ 0.05 using a novel three-dimensional cubelet stacking method applied to DINGO-VLA 21 cm emission data from 3,622 galaxies. By stacking spatially resolved cubelets and deconvolving with a stacked point spread function, the method recovers a robust 30σ H i mass detection of (1.674 ± 0.183) × 10⁹ M⊙, yielding ΩH I = (0.377 ± 0.042) × 10⁻³, consistent with no significant evolution in H i content at low redshift.

ABSTRACT

We use the 21 cm emission line data from the DINGO-VLA project to study the atomic hydrogen gas H\,{ extsc i} of the Universe at redshifts $z<0.1$. Results are obtained using a stacking analysis, combining the H\,{ extsc i} signals from 3622 galaxies extracted from 267 VLA pointings in the G09 field of the Galaxy and Mass Assembly Survey (GAMA). Rather than using a traditional one-dimensional spectral stacking method, a three-dimensional cubelet stacking method is used to enable deconvolution and the accurate recovery of average galaxy fluxes from this high-resolution interferometric dataset. By probing down to galactic scales, this experiment also overcomes confusion corrections that have been necessary to include in previous single dish studies. After stacking and deconvolution, we obtain a $30\sigma$ H\,{ extsc i} mass measurement from the stacked spectrum, indicating an average H\,{ extsc i} mass of $M_{ m H\,{ extsc i}}=(1.674\pm 0.183) imes 10^{9}~{\Msun}$. The corresponding cosmic density of neutral atomic hydrogen is $\Omega_{ m H\,{ extsc i}}=(0.377\pm 0.042) imes 10^{-3}$ at redshift of $z=0.051$. These values are in good agreement with earlier results, implying there is no significant evolution of $\Omega_{ m H\,{ extsc i}}$ at lower redshifts.

Motivation & Objective

• To measure the cosmic density of neutral hydrogen (ΩH I) at low redshift (z < 0.1) using high-resolution interferometric 21 cm data.
• To overcome limitations of traditional spectral stacking in interferometric data, such as non-Gaussian beams and sidelobes from poor uv-coverage.
• To eliminate confusion corrections required in single-dish studies by resolving individual galaxies down to galactic scales.
• To test for cosmic evolution of H i content by measuring ΩH I at z ≈ 0.051 and comparing with higher-redshift results.
• To validate the new cubelet stacking method for future H i surveys with next-generation radio telescopes.

Proposed method

• Applies a three-dimensional cubelet stacking technique: extracts small spatial-spectral cubelets centered on known galaxy positions from VLA data.
• Uses a stacked point spread function (PSF) to deconvolve the stacked cubelets, enabling accurate recovery of average galaxy fluxes.
• Performs spectral extraction from the deconvolved stacked cube to obtain a high signal-to-noise spectrum.
• Employs a weighted stacking approach across 267 VLA pointings in the GAMA G09 field, covering 3,622 galaxies.
• Corrects for beam and sensitivity effects using the known PSF and noise characteristics of the DINGO-VLA dataset.
• Applies a deconvolution algorithm to recover fluxes from partially resolved sources, avoiding the need for confusion corrections.

Experimental results

Research questions

• RQ1 What is the cosmic density of neutral hydrogen (ΩH I) at z ≈ 0.051 using high-resolution interferometric data?
• RQ2 Does the H i content of galaxies show significant evolution between z ≈ 0.05 and higher redshifts (e.g., z > 2)?
• RQ3 Can the cubelet stacking method successfully recover average H i fluxes from interferometric data with poor uv-coverage and non-Gaussian beams?
• RQ4 How does the H i mass function and ΩH I derived from this method compare with previous single-dish and DLA-based measurements?
• RQ5 To what extent can this method be extended to probe H i evolution up to z ∼ 0.3 using the remaining DINGO-VLA data?

Key findings

• The stacked spectrum yields a 30σ detection of H i emission, corresponding to an average H i mass of (1.674 ± 0.183) × 10⁹ M⊙ per galaxy.
• The derived cosmic neutral hydrogen density is ΩH I = (0.377 ± 0.042) × 10⁻³ at z = 0.051, consistent with previous measurements.
• The result shows no significant evolution in ΩH I at low redshift, implying that the H i content of galaxies has remained relatively stable since z ≈ 0.05.
• The cubelet stacking method successfully mitigates beam and sidelobe effects from short VLA observations, enabling accurate flux recovery.
• The method avoids confusion corrections required in single-dish studies by resolving sources at galactic scales.
• The measurement is in excellent agreement with the hydrodynamical model of Davé et al. (2017), which predicts ΩH I ∝ (1 + z)⁰.⁷⁴, supporting its validity at low z.