VALES V: a kinematic analysis of the molecular gas content in H -ATLAS galaxies at z ∼ 0.03–0.35 using ALMA

Godoy

et al. 2020

A&A

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Context. Spatially resolved observations of the ionized and molecular gas are critical for understanding the physical processes that govern the interstellar medium (ISM) in galaxies. The observation of starburst systems is also important as they present extreme gas conditions that may help to test different ISM models. However, matched resolution imaging at ∼kpc scales for both ISM gas phases are usually scarce, and the ISM properties of starbursts still remain poorly understood. Aims. We aim to study the morpho-kinematic properties of the ionized and molecular gas in three dusty starburst galaxies at z = 0.12−0.17 to explore the relation between molecular ISM gas phase dynamics and the star-formation activity. Methods. We employ two-dimensional dynamical modelling to analyse Atacama Large Millimeter/submillimiter Array CO(1–0) and seeing-limited Spectrograph for INtegral Field Observations in the Near Infrared Paschen-α (Paα) observations, tracing the molecular and ionized gas morpho-kinematics at ∼kpc-scales. We use a dynamical mass model, which accounts for beam-smearing effects, to constrain the CO-to-H2 conversion factor and estimate the molecular gas mass content. Results. One starburst galaxy shows irregular morphology, which may indicate a major merger, while the other two systems show disc-like morpho-kinematics. The two disc-like starbursts show molecular gas velocity dispersion values comparable with those seen in local luminous and ultra luminous infrared galaxies but in an ISM with molecular gas fraction and surface density values in the range of the estimates reported for local star-forming galaxies. We find that these molecular gas velocity dispersion values can be explained by assuming vertical pressure equilibrium. We also find that the star-formation activity, traced by the Paα emission line, is well correlated with the molecular gas content, suggesting an enhanced star-formation efficiency and depletion times of the order of ∼0.1−1 Gyr. We find that the star-formation rate surface density (ΣSFR) correlates with the ISM pressure set by self-gravity (Pgrav) following a power law with an exponent close to 0.8. Conclusions. In dusty disc-like starburst galaxies, our data support the scenario in which the molecular gas velocity dispersion values are driven by the ISM pressure set by self-gravity and are responsible for maintaining the vertical pressure balance. The correlation between ΣSFR and Pgrav suggests that, in these dusty starbursts galaxies, the star-formation activity arises as a consequence of the ISM pressure balance.

Section: Introductionmentioning

confidence: 55%

Section: Alma Observationsmentioning

confidence: 99%

Section: Comparison With Previous Vales Workmentioning

confidence: 99%

See 1 more Smart Citation

Vales

Molina

Godoy

et al. 2020

A&A

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“…In Molina et al (2019), we presented a dynamical analysis of 39 VALES galaxies using the spatial extension of the CO(J = 1 − 0) emission. For the three Hi detected galaxies in this latter work, the dynamical study shows that the CO rotation curves are still increasing or are just about to turn to flat rotation curve with the radius (see the Appendix A of Molina et al 2019). While comparing the Hi and CO(J = 1 − 0) emission line spectra, we find that the CO(J = 1−0) line profiles in Fig.…”

Section: Dynamical Massesmentioning

confidence: 99%

“…On the other hand, our previous work also derived the dynamical mass within 2 × r 1/2CO from CO velocity map (Molina et al 2019), where the half light CO radius (r 1/2CO ) is about 4 kpc. We list the M CO dyn in Table 2 and we can see good consistency between the M CO dyn and the baryon mass.…”

Section: Dynamical Massesmentioning

confidence: 99%

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

Cheng

Molina

et al. 2020

A&A

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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.

Cosmic evolution of molecular gas mass density from an empirical relationship between L1.4 GHz and L′CO

Orellana-González

Monthly Notices of the Royal Astronomical Society

Leiton

et al. 2020

Historically, GHz radio emission has been used extensively to characterize the star-formation activity in galaxies. In this work, we look for empirical relationships amongst the radio luminosity, the infrared luminosity, and the CO-based molecular gas mass. We assemble a sample of 278 nearby galaxies with measurements of radio continuum and total infrared emission, and the 12CO J = 1–0 emission line. We find a correlation between the radio continuum and the CO emission line (with a scatter of 0.36 dex), in a large sample of different kinds of galaxies. Making use of this correlation, we explore the evolution of the molecular gas mass function and the cosmological molecular gas mass density in six redshift bins up to z = 1.5. These results agree with previous semi-analytic predictions and direct measurements: the cosmic molecular gas density increases up to z = 1.5. In addition, we find a single plane across five orders of magnitude for the explored luminosities, with a scatter of 0.27 dex. These correlations are sufficiently robust to be used for samples where no CO measurements exist.