ORCID Profile
0000-0002-9809-6631
Current Organisation
Australian National University
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Publisher: American Astronomical Society
Date: 10-2022
Abstract: The distribution of LIGO black hole binaries (BBH) shows an intermediate-mass range consistent with the Salpeter initial mass function (IMF) in black hole formation by core-collapse supernovae, subject to preserving binary association. They are effectively parameterized by the mean mass μ with a Pearson correlation coefficient of r = 0.93 ± 0.06 of secondary to primary masses with a mean mass ratio of q ¯ ≃ 0.67 , q = M 2 / M 1 , consistent with the paucity of intermediate-mass X-ray binaries. The mass function of LIGO BBHs is well approximated by a broken power law with a tail μ ≳ 31.4 M ⊙ in the mean binary mass μ = M 1 + M 2 / 2 . Its power-law index of α B , true = 4.77 ± 0.73 inferred from the tail of the observed mass function is found to approach the upper bound 2 α S = 4.7 of the uncorrelated binary IMF, defined by the Salpeter index α S = 2.35 of the IMF of stars. The observed low scatter in BBH mass ratio q evidences equalizing mass transfer in binary evolution prior to BBH formation. At the progenitor redshift z ′ , furthermore, the power-law index satisfies α B ′ α B in a flat ΛCDM background cosmology. The bound α B , true ′ ≲ 2 α S hereby precludes early formation at arbitrarily high redshifts z ′ ≫ 1 , which may be made more precise and robust with extended BBH surveys from upcoming LIGO O4-5 observations.
Publisher: Oxford University Press (OUP)
Date: 28-11-2023
Abstract: We examine the H i gas kinematics of galaxy pairs in two clusters and a group using Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot survey observations. We compare the H i properties of galaxy pair candidates in the Hydra I and Norma clusters, and the NGC 4636 group, with those of non-paired control galaxies selected in the same fields. We perform H i profile decomposition of the s le galaxies using a tool, baygaud, which allows us to deblend a line-of-sight velocity profile with an optimal number of Gaussian components. We construct H i superprofiles of the s le galaxies via stacking of their line profiles after aligning the central velocities. We fit a double Gaussian model to the superprofiles and classify them as kinematically narrow and broad components with respect to their velocity dispersions. Additionally, we investigate the gravitational instability of H i gas discs of the s le galaxies using Toomre Q parameters and H i morphological disturbances. We investigate the effect of the cluster environment on the H i properties of galaxy pairs by iding the cluster environment into three subcluster regions (i.e. outskirts, infalling, and central regions). We find that the denser cluster environment (i.e. infalling and central regions) is likely to impact the H i gas properties of galaxies in a way of decreasing the litude of the kinematically narrow H i gas ($M_{\\rm {narrow}}^{\\rm {H\\, \\small {\\rm I}}}$/$M_{\\rm {total}}^{\\rm {H\\, \\small {\\rm I}}}$), and increasing the Toomre Q values of the infalling and central galaxies. This tendency is likely to be more enhanced for galaxy pairs in the cluster environment.
Publisher: American Astronomical Society
Date: 05-08-2022
Abstract: We present H i gas kinematics and star formation activities of NGC 6822, a dwarf galaxy located in the Local Group at a distance of ∼490 kpc. We perform profile decomposition of line-of-sight velocity profiles of the H i data cube (42.4″ × 12.0″ spatial, corresponding to ∼100 pc 1.6 km s −1 spectral) taken with the Australia Telescope Compact Array. For this, we use a new tool, the so-called baygaud , which is based on Bayesian analysis techniques, allowing us to decompose a line-of-sight velocity profile into an optimal number of Gaussian components in a quantitative manner. We classify the decomposed H i gas components of NGC 6822 into cool-bulk, warm-bulk, cool-non-bulk, and warm-non-bulk motions with respect to their centroid velocities and velocity dispersions. We correlate their gas surface densities with corresponding star formation rate densities derived using both the GALEX far-ultraviolet and WISE 22 μ m data to examine the resolved Kennicutt–Schmidt (K-S) law for NGC 6822. Of the decomposed H i gas components, the cool-bulk component is likely to better follow the linear extension of the K-S law for molecular hydrogen (H 2 ) at low gas surface densities where H i is not saturated.
No related grants have been discovered for Hye-Jin Park.