Prof. Matt Jarvis

Abstract:

The transformation and evolution of a galaxy is strongly influenced by interactions with its environment. Neutral hydrogen (H i) is an excellent way to trace these interactions. Here, we present H i observations of the spiral galaxy NGC 895, which was previously thought to be isolated. High-sensitivity H i observations from the MeerKAT large survey project MIGHTEE reveal possible interaction features, such as extended spiral arms and the two newly discovered H i companions, that drive us to change the narrative that it is an isolated galaxy. We combine these observations with deep optical images from the Hyper Suprime Camera to show an absence of tidal debris between NGC 895 and its companions. We do find an excess of light in the outer parts of the companion galaxy MGTH_J022138.1-052631, which could be an indication of external perturbation and thus possible sign of interactions. Our analysis shows that NGC 895 is an actively star-forming galaxy with a SFR of 1.75 ± 0.09[M⊙/yr], a value typical for high-stellar mass galaxies on the star-forming main sequence. It is reasonable to state that different mechanisms may have contributed to the observed features in NGC 895, and this emphasizes the need to revisit the target with more detailed observations. Our work shows the high potential and synergy of using state-of-the-art data in both H i and optical to reveal a more complete picture of galaxy environments.

Abstract:

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable ‘mini’ integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366−959 nm at R ∼ 5000, or two shorter ranges at R ∼ 20 000. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy’s origins by completing Gaia’s phase-space information, providing metallicities to its limiting magnitude for ∼3 million stars and detailed abundances for ∼1.5 million brighter field and open-cluster stars; (ii) survey ∼0.4 million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey ∼400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in z < 0.5 cluster galaxies; (vi) survey stellar populations and kinematics in ∼25 000 field galaxies at 0.3 ≲ z ≲ 0.7; (vii) study the cosmic evolution of accretion and star formation using >1 million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at z > 2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.

Abstract:

We present deep 1.4 GHz source counts from ∼5 deg2 of the continuum Early Science data release of the MeerKAT International Gigahertz Tiered Extragalactic Exploration (MIGHTEE) survey down to S1.4GHz ∼15 μJy. Using observations over two extragalactic fields (COSMOS and XMM-LSS), we provide a comprehensive investigation into correcting the incompleteness of the raw source counts within the survey to understand the true underlying source count population. We use a variety of simulations that account for: errors in source detection and characterisation, clustering, and variations in the assumed source model used to simulate sources within the field and characterise source count incompleteness. We present these deep source count distributions and use them to investigate the contribution of extragalactic sources to the sky background temperature at 1.4 GHz using a relatively large sky area. We then use the wealth of ancillary data covering a subset of the COSMOS field to investigate the specific contributions from both active galactic nuclei (AGN) and star forming galaxies (SFGs) to the source counts and sky background temperature. We find, similar to previous deep studies, that we are unable to reconcile the sky temperature observed by the ARCADE 2 experiment. We show that AGN provide the majority contribution to the sky temperature contribution from radio sources, but the relative contribution of SFGs rises sharply below 1 mJy, reaching an approximate 15-25 per cent contribution to the total sky background temperature (Tb ∼100 mK) at ∼15 μJy.

Abstract:

We present the first measurements of H i galaxy scaling relations from a blind survey at z > 0.15. We perform spectral stacking of 9023 spectra of star-forming galaxies undetected in H i at 0.23 < z < 0.49, extracted from MIGHTEE-H i Early Science data cubes, acquired with the MeerKAT radio telescope. We stack galaxies in bins of galaxy properties (stellar mass M *, star formation rateSFR, and specific star formation rate sSFR, with sSFR ≡ M */SFR), obtaining ≳5σ detections in most cases, the strongest H i-stacking detections to date in this redshift range. With these detections, we are able to measure scaling relations in the probed redshift interval, finding evidence for a moderate evolution from the median redshift of our sample z med ∼ 0.37 to z ∼ 0. In particular, low-M * galaxies ( log 10 ( M * / M ⊙ ) ∼ 9 ) experience a strong H i depletion (∼0.5 dex in log 10 ( M H I / M ⊙ ) ), while massive galaxies ( log 10 ( M * / M ⊙ ) ∼ 11 ) keep their H i mass nearly unchanged. When looking at the star formation activity, highly star-forming galaxies evolve significantly in M H I (f H I, where f H I ≡ M H I/M *) at fixed SFR (sSFR), while at the lowest probed SFR (sSFR) the scaling relations show no evolution. These findings suggest a scenario in which low-M * galaxies have experienced a strong H i depletion during the last ∼5 Gyr, while massive galaxies have undergone a significant H i replenishment through some accretion mechanism, possibly minor mergers. Interestingly, our results are in good agreement with the predictions of the simba simulation. We conclude that this work sets novel important observational constraints on galaxy scaling relations.

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.