H I Properties of Field Galaxies at $boldsymbol{zapprox 0.2}$-0.6: Insights into Declining Cosmic Star Formation
David DePalma, Neeraj Gupta, Hsiao-Wen Chen, Robert A. Simcoe, Sergei Balashev, Erin Boettcher, Sebastiano Cantalupo, Mandy C. Chen, Franc{c}oise Combes, Claude-Andr’e Faucher-Gigu`ere, Sean D. Johnson, Hans-Rainer Kl"ockner, Jens-Kristian Krogager, Jennifer I-Hsiu Li, Sebasti’an L’opez, Pasquier Noterdaeme, Patrick Petitjean, Zhijie Qu, Gwen C. Rudie, Joop Schaye, Fakhri Zahedy
arXiv:2510.03400v1 Announce Type: new
Abstract: We report statistically significant detection of H I 21-cm emission from intermediate-redshift ($zapprox0.2$-0.6) galaxies. By leveraging multi-sightline galaxy survey data from the Cosmic Ultraviolet Baryon Survey (CUBS) and deep radio observations from the MeerKAT Absorption Line Survey (MALS), we have established a sample of $approx6000$ spectroscopically identified galaxies in 11 distinct fields to constrain the neutral gas content at intermediate redshifts. The galaxies sample a broad range in stellar mass — $8lesssimlog{M_rm{star}/rm{M}_odot}lesssim11$ with a median of $langlelog{M_rm{star}/rm{M}_odot}rangle_rm{med}approx10$ — and a wide range in redshift — $0.24lesssim zlesssim0.63$ with a median of $langle zrangle_rm{med}=0.44$. Our detected emission-line signal exceeds $4,sigma$ significance in the stacked spectra of all subsamples, and the observed total H I 21-cm line flux translates to a H I mass $M_rm{H;I}approx10^{10}rm{M}_odot$. We find a high H I-to-stellar mass ratio of $M_mathrm{H;I}/M_rm{star}approx6$ for low-mass galaxies with $langlelog{M_rm{star}/rm{M}_odot}rangle approx9.3$ ($>3.7,sigma$). For galaxies with $langlelog{M_rm{star}/rm{M}_odot}rangleapprox10.6$, we find $M_mathrm{H;I}/M_rm{star}approx0.3$ ($>4.7,sigma$). Additionally, the redshift evolution of H I mass in both low- and high-mass field galaxies, inferred from the stacked emission-line signal, aligns well with the expectation from the cosmic star formation history. This suggests that the overall decline in the cosmic star formation activity across the general galaxy population may be connected to a decreasing supply of neutral hydrogen. Finally, our analysis has revealed significant 21-cm signals at distances greater than 75 kpc from these intermediate-redshift galaxies, indicating a substantial reservoir of H I gas in their extended surroundings.arXiv:2510.03400v1 Announce Type: new
Abstract: We report statistically significant detection of H I 21-cm emission from intermediate-redshift ($zapprox0.2$-0.6) galaxies. By leveraging multi-sightline galaxy survey data from the Cosmic Ultraviolet Baryon Survey (CUBS) and deep radio observations from the MeerKAT Absorption Line Survey (MALS), we have established a sample of $approx6000$ spectroscopically identified galaxies in 11 distinct fields to constrain the neutral gas content at intermediate redshifts. The galaxies sample a broad range in stellar mass — $8lesssimlog{M_rm{star}/rm{M}_odot}lesssim11$ with a median of $langlelog{M_rm{star}/rm{M}_odot}rangle_rm{med}approx10$ — and a wide range in redshift — $0.24lesssim zlesssim0.63$ with a median of $langle zrangle_rm{med}=0.44$. Our detected emission-line signal exceeds $4,sigma$ significance in the stacked spectra of all subsamples, and the observed total H I 21-cm line flux translates to a H I mass $M_rm{H;I}approx10^{10}rm{M}_odot$. We find a high H I-to-stellar mass ratio of $M_mathrm{H;I}/M_rm{star}approx6$ for low-mass galaxies with $langlelog{M_rm{star}/rm{M}_odot}rangle approx9.3$ ($>3.7,sigma$). For galaxies with $langlelog{M_rm{star}/rm{M}_odot}rangleapprox10.6$, we find $M_mathrm{H;I}/M_rm{star}approx0.3$ ($>4.7,sigma$). Additionally, the redshift evolution of H I mass in both low- and high-mass field galaxies, inferred from the stacked emission-line signal, aligns well with the expectation from the cosmic star formation history. This suggests that the overall decline in the cosmic star formation activity across the general galaxy population may be connected to a decreasing supply of neutral hydrogen. Finally, our analysis has revealed significant 21-cm signals at distances greater than 75 kpc from these intermediate-redshift galaxies, indicating a substantial reservoir of H I gas in their extended surroundings.