Examinando por Autor "Hughes, Thomas"

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  • Miniatura
    Ítem
    The atomic gas of star-forming galaxies at z~0.05 as revealed by the Five-hundred-meter Aperture Spherical Radio Telescope
    (European Southern Observatory, 2020) Ibar, Eduardo; Hughes, Thomas
    Context. We report new Hi observations of four z ∼ 0.05 VALES galaxies undertaken during the commissioning phase of the Fivehundred-meter Aperture Spherical Radio Telescope (FAST). Aims. FAST is the largest single-dish telescope in the world, with a 500 meter aperture and a 19-Beam receiver. Exploiting theunprecedented sensitivity provided by FAST, we aim to study the atomic gas content, via the Hi 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 Hi data provides crucial information to measure the gas mass and dynamics. Methods. As a pilot Hi galaxy survey, we targeted four local star-forming galaxies at z ∼ 0.05. In particular, one of them has already been detected in Hi 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 0.7mJy beam−1 at a 1.7 kms−1 velocity resolution within only 20 minutes ON-target integration time. Results. In this letter, we demonstrate the great capabilities of the FAST 19-beam receiver for pushing the detectability of the Hi emission line of extra-galactic sources. The Hi emission line detected by FAST shows good consistency with the previous Arecibo telescope ALFALFA results. Our observations are put in 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 Hi emission line profiles are similar. The dynamical mass estimated from the Hi 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 Hi 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.
  • Miniatura
    Ítem
    Cosmic evolution of molecular gas mass density from an empirical relationship between L1.4 GHz and L′CO
    (Royal Astronomical Society, 2020) Orellana Gonzalez, Gustavo; Ibar, Eduardo; Hughes, Thomas
    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.
  • Miniatura
    Ítem
    A kpc-scale resolved study of unobscured and obscured star-formation activity in normal galaxies at z = 1.5 and 2.2 from ALMA and HiZELS
    (Royal Astronomical Society, 2020) Cheng, Cheng; Ibar, Eduardo; Hughes, Thomas
    We present Atacama Large Millimeter/Submillimeter Array (ALMA) continuum observations of a sample of nine star-forming galaxies at redshifts 1.47 and 2.23 selected from the High-z Emission Line Survey (HiZELS). Four galaxies in our sample are detected at high significance by ALMA at a resolution of 0′′.25 at rest-frame 355 μm. Together with the previously observed H α emission, from adaptive optics-assisted integral-field-unit spectroscopy (∼0′′.15 resolution), and F606W and F140W imaging from the Hubble Space Telescope (∼0′′.2 resolution), we study the star formation activity, stellar and dust mass in these high-redshift galaxies at ∼kpc-scale resolution. We find that ALMA detection rates are higher for more massive galaxies (M* > 1010.5 M⊙) and higher [N II]/H α ratios (>0.25, a proxy for gas-phase metallicity). The dust extends out to a radius of 8 kpc, with a smooth structure, even for those galaxies presenting clumpy H α morphologies. The half-light radii (Rdust) derived for the detected galaxies are of the order ∼4.5 kpc, more than twice the size of submillimetre-selected galaxies at a similar redshift. Our global star formation rate estimates – from far-infrared and extinction-corrected H α luminosities – are in good agreement. However, the different morphologies of the different phases of the interstellar medium suggest complex extinction properties of the high-redshift normal galaxies.
  • Miniatura
    Ítem
    VALES VII. Molecular and ionized gas properties in the pressure balanced interstellar medium of starburst galaxies at z ∼ 0.15
    (European Southern Observatory, 2020) Ibar, Eduardo; Godoy, Nicolas; Cheng, Cheng; Hughes, Thomas
    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.