Low-amplitude clustering in low-redshift 21-cm intensity maps cross-correlated with 2dF galaxy densities

C. J. Anderson, N. J. Luciw, Y. -C. Li, C. Y. Kuo, J. Yadav, K. W. Masui, T. -C. Chang, X. Chen, N. Oppermann, Y. -W. Liao, U. -L. Pen, D. C. Price, L. Staveley-Smith, E. R. Switzer, P. T. Timbie, L. Wolz

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We report results from 21-cm intensity maps acquired from the Parkes radio telescope and cross-correlatedwith galaxy maps from the 2dF galaxy survey. The data span the redshift range 0.057 <z <0.098 and cover approximately 1300 deg(2) over two long fields. Cross-correlation is detected at a significance of 5.7 sigma. The amplitude of the cross-power spectrum is low relative to the expected dark matter power spectrum, assuming a neutral hydrogen (H-I) bias andmass density equal to measurements from the ALFALFA survey. The decrement is pronounced and statistically significant at small scales. At k similar to 1.5 h Mpc(-1), the cross-power spectrum is more than a factor of 6 lower than expected, with a significance of 15.3 sigma. This decrement indicates a lack of clustering of neutral hydrogen (H-I), a small correlation coefficient between optical galaxies and H-I, or some combination of the two. Separating 2dF into red and blue galaxies, we find that red galaxies are much more weakly correlated with H-I on k similar to 1.5 h Mpc(-1) scales, suggesting that H-I is more associated with blue star-forming galaxies and tends to avoid red galaxies.

Original languageEnglish
Pages (from-to)3382-3392
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - May 2018

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