Letter to the Editor

The atomic gas of star-forming galaxies at z ∼ 0.05 as revealed by the Five-hundred-meter Aperture Spherical Radio Telescope

¹ Chinese Academy of Sciences South America Center for Astronomy, National Astronomical Observatories, CAS, Beijing 100101, PR China
e-mail: chengcheng@nao.cas.cn
² National Astronomical Observatories, Chinese Academy of Sciences (NAOC), 20A Datun Road, Chaoyang District, Beijing 100101, PR China
³ CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
⁴ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
⁵ Kavli Institute for Astronomy and Astrophysics, Peking University, 5 Yiheyuan Road, Haidian District, Beijing 100871, PR China
⁶ Department of Astronomy, School of Physics, Peking University, Beijing 100871, PR China
⁷ Departamento de Astronomía (DAS), Universidad de Chile, Casilla 36, Santiago, Chile
⁸ Departamento de Matemática y Física Aplicadas, Universidad Católica de la Santísima Concepción, Alonso de Ribera 2850, Concepción, Chile
⁹ Departamento de Astronomía, Universidad de Concepción, Casilla 160, Concepción, Chile
¹⁰ CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei 230026, PR China
¹¹ School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, PR China

Received: 23 May 2020
Accepted: 8 June 2020

Abstract

Context. We report new H I observations of four z ∼ 0.05 VALES galaxies undertaken during the commissioning phase of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST).

Aims. FAST is the largest single-dish telescope in the world, with a 500 m aperture and a 19-Beam receiver. Exploiting the unprecedented sensitivity provided by FAST, we aim to study the atomic gas content, via the H I 21 cm emission line, in low-z star formation galaxies taken from the Valparaíso ALMA/APEX Line Emission Survey (VALES). Together with previous Atacama Large Millimeter/submillimeter Array (ALMA) CO(J = 1−0) observations, the H I data provides crucial information to measure the gas mass and dynamics.

Methods. As a pilot H I galaxy survey, we targeted four local star-forming galaxies at z ∼ 0.05. In particular, one of them has already been detected in H I by the Arecibo Legacy Fast ALFA survey (ALFALFA), allowing a careful comparison. We use an ON-OFF observing approach that allowed us to reach an rms of 0.7 mJy beam⁻¹ at a 1.7 km s⁻¹ velocity resolution within only 20 min ON-target integration time.

Results. In this Letter, we demonstrate the extraordinary capability of the FAST 19-beam receiver to push the detectability of the H I emission line of extra-galactic sources. The H I emission line detected by FAST shows good consistency with the previous Arecibo telescope ALFALFA results. Our observations are put into context with previous multi-wavelength data to reveal the physical properties of these low-z galaxies. We find that the CO(J = 1−0) and H I emission line profiles are similar. The dynamical mass estimated from the H I data is an order of magnitude higher than the baryon mass and the dynamical mass derived from the CO observations, implying that the mass probed by dynamics of H I is dominated by the dark matter halo. In one case, a target shows an excess of CO(J = 1−0) in the line centre, which can be explained by an enhanced CO(J = 1−0) emission induced by a nuclear starburst showing high-velocity dispersion.