[Paper Review] Study of galaxies in the Lynx-Cancer void. VI. HI-observations with the Nancay Radio Telescope

S. A. Pustilnik, Jean‐Michel Martin|HAL (Le Centre pour la Communication Scientifique Directe)|Aug 29, 2016

Galaxies: Formation, Evolution, Phenomena52 references6 citations

TL;DR

This study presents new HI observations of 45 galaxies in the Lynx-Cancer void using the Nancay Radio Telescope, significantly expanding the sample to 103 void galaxies. It finds that void galaxies are systematically gas-rich—on average 39% richer in HI mass relative to blue luminosity—compared to similar galaxies in denser Local Volume environments, providing strong evidence for slower evolution in low-density regions due to reduced external perturbations and lower metallicities.

ABSTRACT

Context. Void population consists mainly of late-type and low surface brightness (LSB) dwarf galaxies whose atomic hydrogen is the main component of their baryonic matter. Therefore, observations of void galaxy HI are mandatory in order to understand their evolution and dynamics. Aims. Our aim was to obtain integrated HI parameters for a fainter part of the nearby Lynx-Cancer void galaxy sample (total of 45 objects) with the Nancay Radio Telescope (NRT) and to conduct the comparative analysis of all the 103 void galaxies with known HI data with a sample of similar galaxies residing in denser environments of the Local Volume. Methods. For HI observations we used the NRT with its sensitive antenna/receiver system FORT and standard processing. The comparison of the void and control samples on the parameter M(HI)/L_B is conducted with the non-parametric method `The 2x2 Contingency Table test'. Results. We obtained new HI data for about 40% of the Lynx-Cancer galaxy sample. Along with data from the literature, we use these new data for further analysis of 103 void objects. The proxy of the evolutional parameter M(HI)/L_B of the void sample is compared with that of 82 galaxies of morphological types 8--10 residing in the Local Volume (LV) groups and aggregates. Conclusions. At the confidence level of P = 0.988, we conclude that for the same luminosity, these void galaxies are systematically gas-richer, on average by ~39%. This result is consistent with the authors' earlier conclusion on the smaller gas metallicities and evidence for the slower low-mass galaxy evolution in voids.

Motivation & Objective

• To obtain integrated HI parameters for fainter galaxies in the Lynx-Cancer void using the Nancay Radio Telescope.
• To compare the gas content of void galaxies with that of similar late-type galaxies in denser Local Volume environments.
• To test whether the void environment leads to slower evolution in low-mass galaxies, as suggested by prior studies on metallicity and morphology.
• To assess the statistical significance of differences in the HI-to-luminosity ratio (M(HI)/LB) between void and control samples.

Proposed method

• HI line observations were conducted using the Nancay Radio Telescope (NRT) with the FORT receiver system and standard data processing pipelines.
• The 2×2 contingency table test was applied to compare the distribution of M(HI)/LB ratios between the void sample (103 galaxies) and a control sample of 82 Local Volume group galaxies.
• Blue luminosity (LB) and HI mass (M(HI)) were derived from optical photometry and radio line data, respectively, to compute the gas fraction proxy M(HI)/LB.
• Galaxy samples were selected based on morphological types 8–10 (dwarf and low-surface-brightness galaxies) and distances within 20 Mpc to ensure completeness for faint objects.
• Statistical significance was evaluated using non-parametric testing to assess differences in gas content distribution.
• Linear regression was applied to the log(M(HI)/LB) vs. log(LB) relation to quantify the dependence of gas richness on luminosity across both samples.

Experimental results

Research questions

• RQ1 Is there a statistically significant difference in the HI mass-to-blue luminosity ratio (M(HI)/LB) between galaxies in the Lynx-Cancer void and those in denser Local Volume environments?
• RQ2 Do void galaxies exhibit systematically higher gas fractions than similar galaxies in higher-density regions, indicating slower evolutionary timescales?
• RQ3 How does the M(HI)/LB ratio vary with luminosity in void galaxies compared to control samples, and is the trend consistent with known down-sizing phenomena?
• RQ4 To what extent do the observed gas richness and low metallicities in void galaxies support the hypothesis of reduced external perturbations and delayed evolution?

Key findings

• The void galaxy sample shows a statistically significant excess in gas richness, with a 39% higher average M(HI)/LB ratio compared to Local Volume group galaxies at a confidence level of P = 0.988.
• The difference in gas content remains significant at P = 0.9956 when comparing void galaxies to Local Volume group galaxies outside the Virgo cluster region.
• The slope of the M(HI)/LB ∝ LB^k relation is –0.129 ± 0.054 for void galaxies and –0.208 ± 0.051 for Local Volume galaxies, with no significant difference between the two, suggesting a common underlying trend.
• The median M(HI)/LB ratio varies by a factor of ~4 across the luminosity range of ~3 magnitudes, indicating strong scatter in gas content even within the void sample.
• The observed gas richness is consistent with prior findings of lower gas-phase oxygen abundances (O/H) in void galaxies, reinforcing the hypothesis of slower evolution due to reduced environmental quenching.
• The broad distribution of M(HI)/LB, ranging from ~0.05 to ~28, indicates that multiple competing processes influence HI content in void galaxies, including internal feedback and accretion mechanisms.