Hintze Centre for Astrophysical Surveys

Abstract:

We compare the CO(1-0) and Hα kinematics in 34 nearby galaxies, selected from the ALMaQUEST and EDGE-CALIFA surveys. We use 3D-Barolo, a 3D tilted-ring model, to derive the CO and Hα rotation curves. Before comparing rotation curves in the 34 nearby galaxies, we found systematics between the MaNGA and CALIFA data using eight MaNGA-CALIFA overlapping galaxies. We assume the rotation curves based on the MaNGA data are accurate and made the corresponding correction to the CALIFA data. Our result shows that ∼56% (19/34) of our galaxies present slower Hα rotation curves compared to the CO rotation curves, with a median value of 6.5 km s−1. The remaining galaxies (15/34) show consistent CO-Hα rotation velocity within uncertainties. As a result, the Hα rotation may underestimate the total dynamical mass by 6% for a circular velocity of 200 km s−1 (the median value in our sample). Furthermore, the difference in the velocity between the CO and Hα rotational velocity is found to correlate with the difference in velocity dispersion between CO and Hα, suggesting that gas pressure plays a role in the discrepancy in velocity. After incorporating the effect of pressure support due to the turbulent gas motion into our sample, the median value of the difference in the velocities decreases to 1.9 km s−1, which in turn reduces the underestimation of the dynamical mass to ∼2%. Finally, we also investigate the role that the extraplanar diffuse ionized gas plays in the discrepancy in the velocity of CO-Hα.

Abstract:

We study the nature of the faint radio source population detected in the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Early Science data in the COSMOS field, focusing on the properties of the radio-loud active galactic nuclei (AGNs). Using the extensive multiwavelength data available in the field, we are able to classify 88 per cent of the 5223 radio sources in the field with host galaxy identifications as AGNs (35 per cent) or star-forming galaxies (54 per cent). We select a sample of radio-loud AGNs with redshifts out to z ∼ 6 and radio luminosities 10²⁰ < L_1.4 GHz/W Hz⁻¹ < 10²⁷ and classify them as high-excitation and low-excitation radio galaxies (HERGs and LERGs). The classification catalogue is released with this work. We find no significant difference in the host galaxy properties of the HERGs and LERGs in our sample. In contrast to previous work, we find that the HERGs and LERGs have very similar Eddington-scaled accretion rates; in particular we identify a population of very slowly accreting AGNs that are formally classified as HERGs at these low radio luminosities, where separating into HERGs and LERGs possibly becomes redundant. We investigate how black hole mass affects jet power, and find that a black hole mass ≳ 10^7.8 M_⊙ is required to power a jet with mechanical power greater than the radiative luminosity of the AGN (L_mech/L_bol > 1). We discuss that both a high black hole mass and black hole spin may be necessary to launch and sustain a dominant radio jet.