The atomic gas of star-forming galaxies at z ∼ 0.05 as revealed by the Five-hundred-meter Aperture Spherical Radio Telescope
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.
Astronomy and Astrophysics
- Pub Date:
- June 2020
- galaxies: evolution;
- galaxies: ISM;
- galaxies: star formation;
- galaxies: starburst;
- radio lines: galaxies;
- Astrophysics - Astrophysics of Galaxies
- 5 pages, 3 figures, 2 appendix, A&