Hintze Centre for Astrophysical Surveys

Abstract:

This paper reports on the atomic hydrogen gas (H I) observations of the spiral galaxy NGC 1566 using the newly commissioned Australian Square Kilometre Array Pathfinder radio telescope. We measure an integrated H I flux density of 180.2 Jy km s−1 emanating from this galaxy, which translates to an H I mass of 1.94×1010M⊙ at an assumed distance of 21.3 Mpc. Our observations show that NGC 1566 has an asymmetric and mildly warped H I disc. The H I-to-stellar mass fraction (MHI/M∗) of NGC 1566 is 0.29, which is high in comparison with galaxies that have the same stellar mass (⁠1010.8 M⊙). We also derive the rotation curve of this galaxy to a radius of 50 kpc and fit different mass models to it. The NFW, Burkert, and pseudo-isothermal dark matter halo profiles fit the observed rotation curve reasonably well and recover dark matter fractions of 0.62, 0.58, and 0.66, respectively. Down to the column density sensitivity of our observations (⁠NHI=3.7×1019 cm−2), we detect no H I clouds connected to, or in the nearby vicinity of, the H I disc of NGC 1566 nor nearby interacting systems. We conclude that, based on a simple analytic model, ram pressure interactions with the IGM can affect the H I disc of NGC 1566 and is possibly the reason for the asymmetries seen in the H I morphology of NGC 1566.

Abstract:

We have observed the G23 field of the Galaxy AndMass Assembly (GAMA) survey using the Australian Square Kilometre Array Pathfinder (ASKAP) in its commissioning phase to validate the performance of the telescope and to characterise the detected galaxy populations. This observation covers ∼48 deg2 with synthesised beam of 32.7 arcsec by 17.8 arcsec at 936MHz, and ∼39 deg2 with synthesised beam of 15.8 arcsec by 12.0 arcsec at 1320MHz. At both frequencies, the root-mean-square (r.m.s.) noise is ∼0.1 mJy/beam. We combine these radio observations with the GAMA galaxy data, which includes spectroscopy of galaxies that are i-band selected with a magnitude limit of 19.2. Wide-field Infrared Survey Explorer (WISE) infrared (IR) photometry is used to determine which galaxies host an active galactic nucleus (AGN). In properties including source counts, mass distributions, and IR versus radio luminosity relation, the ASKAP-detected radio sources behave as expected. Radio galaxies have higher stellar mass and luminosity in IR, optical, and UV than other galaxies. We apply optical and IR AGN diagnostics and find that they disagree for ∼30% of the galaxies in our sample. We suggest possible causes for the disagreement. Some cases can be explained by optical extinction of the AGN, but for more than half of the cases we do not find a clear explanation. Radio sources aremore likely (∼6%) to have an AGN than radio quiet galaxies (∼1%), but the majority of AGN are not detected in radio at this sensitivity.