Publications


The radio galaxy population in the simba simulations

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 503 (2021) 3492-3509

N Thomas, R Davé, MJ Jarvis, D Anglés-Alcázar

<jats:title>ABSTRACT</jats:title> <jats:p>We examine the 1.4 GHz radio luminosities of galaxies arising from star formation and active galactic nuclei (AGNs) within the state-of-the-art cosmological hydrodynamic simulation Simba. Simba grows black holes via gravitational torque limited accretion from cold gas and Bondi accretion from hot gas, and employs AGN feedback including jets at low Eddington ratios. We define a population of radio loud AGNs (RLAGNs) based on the presence of ongoing jet feedback. Within RLAGN, we define high and low excitation radio galaxies (HERGs and LERGs) based on their dominant mode of black hole accretion: torque limited accretion representing feeding from a cold disc, or Bondi representing advection-dominated accretion from a hot medium. Simba predicts good agreement with the observed radio luminosity function (RLF) and its evolution, overall as well as separately for HERGs and LERGs. Quiescent galaxies with AGN-dominated radio flux dominate the RLF at $\gtrsim 10^{22-23}$ W Hz−1, while star formation dominates at lower radio powers. Overall, RLAGNs have higher black hole accretion rates and lower star formation rates than non-RLAGN at a given stellar mass or velocity dispersion, but have similar black hole masses. Simba predicts an LERG number density of 8.53 Mpc−3, ∼10× higher than for HERGs, broadly as observed. While LERGs dominate among most massive galaxies with the largest black holes and HERGs dominate at high specific star formation rates, they otherwise largely populate similar-sized dark matter haloes and have similar host galaxy properties. Simba thus predicts that deeper radio surveys will reveal an increasing overlap between the host galaxy demographics of HERGs and LERGs.</jats:p>


MIGHTEE: are giant radio galaxies more common than we thought?

Monthly Notices of the Royal Astronomical Society Oxford University Press 501 (2020) 3833-3845

J Delhaize, M Prescott, I Delvecchio, S White, C Hale, J Afonso, Y Ao, M Brienza, M Brüggen, J Collier, E Daddi, M Glowacki, N Maddox, L Morabito, I Prandoni, Z Randriamanakoto, S Sekhar, F An, N Adams, S Blyth, L Leeuw, L Marchetti, S Randriamampandry, O Smirnov, M Vaccari

We report the discovery of two new giant radio galaxies (GRGs) using the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey. Both GRGs were found within a ∼1 deg2 region inside the COSMOS field. They have redshifts of z = 0.1656 and z = 0.3363 and physical sizes of 2.4 and 2.0 Mpc, respectively. Only the cores of these GRGs were clearly visible in previous high-resolution Very Large Array observations, since the diffuse emission of the lobes was resolved out. However, the excellent sensitivity and uv coverage of the new MeerKAT telescope allowed this diffuse emission to be detected. The GRGs occupy an unpopulated region of radio power – size parameter space. Based on a recent estimate of the GRG number density, the probability of finding two or more GRGs with such large sizes at z < 0.4 in a ∼1 deg2 field is only 2.7 × 10−6, assuming Poisson statistics. This supports the hypothesis that the prevalence of GRGs has been significantly underestimated in the past due to limited sensitivity to low surface brightness emission. The two GRGs presented here may be the first of a new population to be revealed through surveys like MIGHTEE that provide exquisite sensitivity to diffuse, extended emission.


Predicting the observability of population III stars with ELT-HARMONI via the helium 1640 Å emission line

Monthly Notices of the Royal Astronomical Society Oxford University Press 501 (2021) 5517-5537

K Grisdale, N Thatte, J Devriendt, M Pereira Santaella, A Slyz, T Kimm, Y Dubois, S Yi

Population III (Pop. III) stars, as of yet, have not been detected, however as we move into the era of extremely large telescopes this is likely to change. One likely tracer for Pop. III stars is the He IIλ1640 emission line, which will be detectable by the HARMONI spectrograph on the European Extremely Large Telescope (ELT) over a broad range of redshifts (2 ≤ z ≤ 14). By post-processing galaxies from the cosmological, AMR-hydrodynamical simulation NEWHORIZON with theoretical spectral energy distributions (SED) for Pop. III stars and radiative transfer (i.e. the Yggdrasil Models and CLOUDY look-up tables, respectively) we are able to compute the flux of He IIλ1640 for individual galaxies. From mock 10 h observations of these galaxies we show that HARMONI will be able to detect Pop. III stars in galaxies up to z ∼ 10 provided Pop. III stars have a top heavy initial mass function (IMF). Furthermore, we find that should Pop. III stars instead have an IMF similar to those of the Pop. I stars, the He IIλ1640 line would only be observable for galaxies with Pop. III stellar masses in excess of 107M⊙⁠, average stellar age <1Myr at z = 4. Finally, we are able to determine the minimal intrinsic flux required for HARMONI to detect Pop. III stars in a galaxy up to z = 10.


The Evolution of NGC 7465 as Revealed by Its Molecular Gas Properties

ASTROPHYSICAL JOURNAL 909 (2021) ARTN 98

LM Young, DS Meier, M Bureau, A Crocker, TA Davis, S Topal


The Horizon Run 5 cosmological hydrodynamical simulation: probing galaxy formation from kilo- to gigaparsec scales

Astrophysical Journal IOP Publishing 908 (2021) 11

J Lee, J Shin, ON Snaith, Y Kim, CG Few, J Devriendt, Y Dubois, LM Cox, SE Hong, O-K Kwon, C Park, C Pichon, J Kim, BK Gibson, C Park

Horizon Run 5 (HR5) is a cosmological hydrodynamical simulation that captures the properties of the universe on a Gpc scale while achieving a resolution of 1 kpc. Inside the simulation box, we zoom in on a high-resolution cuboid region with a volume of 1049 × 119 × 127 cMpc3. The subgrid physics chosen to model galaxy formation includes radiative heating/cooling, UV background, star formation, supernova feedback, chemical evolution tracking the enrichment of oxygen and iron, the growth of supermassive black holes, and feedback from active galactic nuclei in the form of a dual jet-heating mode. For this simulation, we implemented a hybrid MPI-OpenMP version of RAMSES, specifically targeted for modern many-core many-thread parallel architectures. In addition to the traditional simulation snapshots, lightcone data were generated on the fly. For the post-processing, we extended the friends-of-friend algorithm and developed a new galaxy finder PGalF to analyze the outputs of HR5. The simulation successfully reproduces observations, such as the cosmic star formation history and connectivity of galaxy distribution, We identify cosmological structures at a wide range of scales, from filaments with a length of several cMpc, to voids with a radius of ~ 100 cMpc. The simulation also indicates that hydrodynamical effects on small scales impact galaxy clustering up to very large scales near and beyond the baryonic acoustic oscillation scale. Hence, caution should be taken when using that scale as a cosmic standard ruler: one needs to carefully understand the corresponding biases. The simulation is expected to be an invaluable asset for the interpretation of upcoming deep surveys of the universe.


MIGHTEE-HI: The H I emission project of the MeerKAT MIGHTEE survey

Astronomy and Astrophysics EDP Sciences 646 (2021) A35

N Maddox, B Frank, A Ponomareva, M Jarvis, E Adams, R Davé, T Oosterloo, M Santos, S Blyth, M Glowacki, R Kraan-Korteweg, W Mulaudzi, B Namumba, I Prandoni, S Rajohnson, K Spekkens, N Adams, R Bowler, J Collier, I Heywood, S Sekhar, A Taylor

We present the H I emission project within the MIGHTEE survey, currently being carried out with the newly commissioned MeerKAT radio telescope. This is one of the first deep, blind, medium-wide interferometric surveys for neutral hydrogen (H I) ever undertaken, extending our knowledge of H I emission to z = 0.6. The science goals of this medium-deep, medium-wide survey are extensive, including the evolution of the neutral gas content of galaxies over the past 5 billion years. Simulations predict nearly 3000 galaxies over 0 <  z <  0.4 will be detected directly in H I, with statistical detections extending to z = 0.6. The survey allows us to explore H I as a function of galaxy environment, with massive groups and galaxy clusters within the survey volume. Additionally, the area is large enough to contain as many as 50 local galaxies with H I mass < 108 M⊙, which allows us to study the low-mass galaxy population. The 20 deg2 main survey area is centred on fields with exceptional multi-wavelength ancillary data, with photometry ranging from optical through far-infrared wavelengths, supplemented with multiple spectroscopic campaigns. We describe here the survey design and the key science goals. We also show first results from the Early Science observations, including kinematic modelling of individual sources, along with the redshift, H I, and stellar mass ranges of the sample to date.


SDSS-IV MaNGA: Modeling the Spectral Line-spread Function to Subpercent Accuracy

ASTRONOMICAL JOURNAL 161 (2021) ARTN 52

DR Law, KB Westfall, MA Bershady, M Cappellari, R Yan, F Belfiore, D Bizyaev, JR Brownstein, Y Chen, B Cherinka, N Drory, D Lazarz, S Shetty


The role of mergers and interactions in driving the evolution of dwarf galaxies over cosmic time

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 500 (2021) 4937-4957

G Martin, R Jackson, S Kaviraj, H Choi, J Devriendt, Y Dubois, T Kimm, K Kraljic, S Peirani, C Pichon, M Volonteri, S Yi

&#xA9; 2020 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. Dwarf galaxies (M&#x2217; &lt; 109 M&#xB7;) are key drivers of mass assembly in high-mass galaxies, but relatively little is understood about the assembly of dwarf galaxies themselves. Using the NewHorizon cosmological simulation (&#x223C;40 pc spatial resolution), we investigate how mergers and fly-bys drive the mass assembly and structural evolution of around 1000 field and group dwarfs up to z = 0.5. We find that, while dwarf galaxies often exhibit disturbed morphologies (5 and 20 per cent are disturbed at z = 1 and z = 3 respectively), only a small proportion of the morphological disturbances seen in dwarf galaxies are driven by mergers at any redshift (for 109 M&#xB7;, mergers drive under 20 per cent morphological disturbances). They are instead primarily the result of interactions that do not end in a merger (e.g. fly-bys). Given the large fraction of apparently morphologically disturbed dwarf galaxies which are not, in fact, merging, this finding is particularly important to future studies identifying dwarf mergers and post-mergers morphologically at intermediate and high redshifts. Dwarfs typically undergo one major and one minor merger between z = 5 and z = 0.5, accounting for 10 per cent of their total stellar mass. Mergers can also drive moderate star formation enhancements at lower redshifts (3 or 4 times at z = 1), but this accounts for only a few per cent of stellar mass in the dwarf regime given their infrequency. Non-merger interactions drive significantly smaller star formation enhancements (around two times), but their preponderance relative to mergers means they account for around 10 per cent of stellar mass formed in the dwarf regime.


Bow-shocks, nova shells, disc winds and tilted discs: the Nova-Like V341 Ara Has It All

Monthly Notices of the Royal Astronomical Society Oxford University Press 501 (2021) 1951-1969

N Castro Segura, C Knigge, JA Acosta-Pulido, R Fender, A Ponomareva, D Williams

V341 Ara was recently recognized as one of the closest (d ≃ 150 pc) and brightest (V ≃ 10) nova-like cataclysmic variables. This unique system is surrounded by a bright emission nebula, likely to be the remnant of a recent nova eruption. Embedded within this nebula is a prominent bow shock, where the system’s accretion disc wind runs into its own nova shell. In order to establish its fundamental properties, we present the first comprehensive multiwavelength study of the system. Long-term photometry reveals quasi-periodic, super-orbital variations with a characteristic time-scale of 10–16 d and typical amplitude of ≃1 mag. High-cadence photometry from theTransiting Exoplanet Survey Satellite (TESS) reveals for the first time both the orbital period and a ‘negative superhump’ period. The latter is usually interpreted as the signature of a tilted accretion disc. We propose a recently developed disc instability model as a plausible explanation for the photometric behaviour. In our spectroscopic data, we clearly detect antiphased absorption and emission-line components. Their radial velocities suggest a high mass ratio, which in turn implies an unusually low white-dwarf mass. We also constrain the wind mass-loss rate of the system from the spatially resolved [O III] emission produced in the bow shock; this can be used to test and calibrate accretion disc wind models. We suggest a possible association between V341 Ara and a ‘guest star’ mentioned in Chinese historical records in AD 1240. If this marks the date of the system’s nova eruption, V341 Ara would be the oldest recovered nova of its class and an excellent laboratory for testing nova theory.


Cross-correlating radio continuum surveys and CMB lensing: constraining redshift distributions, galaxy bias and cosmology

Monthly Notices of the Royal Astronomical Society Oxford University Press (2021) stab046

D Alonso, M Jarvis, E Bellini

We measure the harmonic-space auto-power spectrum of the galaxy overdensity in the LOFAR Two-metre Sky Survey (LoTSS) First Data Release and its cross correlation with the map of the lensing convergence of the cosmic microwave background (CMB) from the Planck collaboration. We report a ∼5σ detection of the cross-correlation. We show that the combination of the clustering power spectrum and CMB lensing cross-correlation allows us to place constraints on the high-redshift tail of the redshift distribution, one of the largest sources of uncertainty in the use of continuum surveys for cosmology. Our analysis shows a preference for a broader redshift tail than that predicted by the photometric redshifts contained in the LoTSS value added catalog, as expected, and more compatible with predictions from simulations and spectroscopic data. Although the ability of CMB lensing to constrain the width and tail of the redshift distribution could also be valuable for the analysis of current and future photometric weak lensing surveys, we show that its performance relies strongly on the redshift evolution of the galaxy bias. Assuming the redshift distribution predicted by the Square Kilometre Array Design simulations, we use our measurements to place constraints on the linear bias of radio galaxies and the amplitude of matter inhomogeneities σ8, finding σ8=0.69+0.14−0.21 assuming the galaxy bias scales with the inverse of the linear growth factor, and σ8=0.79+0.17−0.32 assuming a constant bias.


The rapid transition from star formation to AGN-dominated rest-frame ultraviolet light at z ≃ 4

Monthly Notices of the Royal Astronomical Society Oxford University Press 502 (2021) 662-677

R Bowler, N Adams, M Jarvis, B Häußler

With the advent of deep optical-to-near-infrared extragalactic imaging on the degree scale, samples of high-redshift sources are being selected that contain both bright star-forming (SF) galaxies and faint active galactic nuclei (AGN). In this study, we investigate the transition between SF- and AGN-dominated systems at z ≃ 4 in the rest-frame ultraviolet (UV). We find a rapid transition to AGN-dominated sources brightward of MUV ≃ −23.2. The effect is observed in the rest-frame UV morphology and size–luminosity relation, where extended clumpy systems become point-source-dominated, and also in the available spectra for the sample. These results allow us to derive the rest-frame UV luminosity function (LF) for the SF- and AGN-dominated subsamples. We find the SF-dominated LF is best fit with a double power law, with a lensed Schechter function being unable to explain the existence of extremely luminous SF galaxies at MUV ≃ −23.5. If we identify AGN-dominated sources according to a point-source morphology criterion, we recover the relatively flat faint-end slope of the AGN LF determined in previous studies. If we instead separate the LF according to the current spectroscopic AGN fraction, we find a steeper faint-end slope of α = −1.83 ± 0.11. Using a simple model to predict the rest-frame AGN LF from the z = 4 galaxy LF, we find that the increasing impact of host galaxy light on the measured morphology of faint AGN can explain our observations.


Physical explanation for the galaxy distribution on the (lambda(R), epsilon) and (V/sigma, epsilon) diagrams or for the limit on orbital anisotropy

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 500 (2021)

B Wang, M Cappellari, Y Peng


Accretion and star formation in 'radio-quiet' quasars

Proceedings of the International Astronomical Union (2021) 204-208

SV White, MJ Jarvis, E Kalfountzou, MJ Hardcastle, A Verma, JM Cao Orjales, J Stevens

© The Author(s), 2021. Published by Cambridge University Press on behalf of International Astronomical Union. Radio observations allow us to identify a wide range of active galactic nuclei (AGN), which play a significant role in the evolution of galaxies. Amongst AGN at low radio-luminosities is the 'radio-quiet' quasar (RQQ) population, but how they contribute to the total radio emission is under debate, with previous studies arguing that it is predominantly through star formation. In this talk, SVW summarised the results of recent papers on RQQs, including the use of far-infrared data to disentangle the radio emission from the AGN and that from star formation. This provides evidence that black-hole accretion, instead, dominates the radio emission in RQQs. In addition, we find that this accretion-related emission is correlated with the optical luminosity of the quasar, whilst a weaker luminosity-dependence is evident for the radio emission connected with star formation. What remains unclear is the process by which this accretion-related emission is produced. Understanding this for RQQs will then allow us to investigate how this type of AGN influences its surroundings. Such studies have important implications for modelling AGN feedback, and for determining the accretion and star-formation histories of the Universe.


MOSAIC: the high multiplex and multi-IFU spectrograph for the ELT

Proceedings of SPIE - International Society for Optical Engineering Society of Photo-optical Instrumentation Engineers 11447 (2020)

G Dalton, R Sánchez-Janssen, F Hammer, S Morris, J-G Cuby, L Kaper, M Steinmetz, J Afonso, B Barbuy, M Rodrigues, I Lewis, E Bergin, C Evans

MOSAIC is the planned multi-object spectrograph for the 39m Extremely Large Telescope (ELT). Conceived as a multi-purpose instrument, it offers both high multiplex and multi-IFU capabilities at a range of intermediate to high spectral resolving powers in the visible and the near-infrared. MOSAIC will enable unique spectroscopic surveys of the faintest sources, from the oldest stars in the Galaxy and beyond to the first populations of galaxies that completed the reionisation of the Universe–while simultaneously opening up a wide discovery space. In this contribution we present the status of the instrument ahead of Phase B, showcasing the key science cases as well as introducing the updated set of top level requirements and the adopted architecture. The high readiness level will allow MOSAIC to soon enter the construction phase, with the goal to provide the ELT community with a world-class MOS capability as soon as possible after the telescope first light.


New prime focus rotator system for the WHT

Proceedings of SPIE Society of Photo-optical Instrumentation Engineers 11445 (2020) 114454S

G Dalton


Integration and early testing of WEAVE: the next-generation spectroscopy facility for the William Herschel Telescope

Proceedings of SPIE Society of Photo-optical Instrumentation Engineers 11447 (2020) 1144714

G Dalton, S Trager, DC Abrams, I Lewis, S Jin, A Molaeinezhad, E Schallig, S Hughes, M Brock, D Terrett

We present an update on the overall integration progress of the WEAVE next-generation spectroscopy facility for the William Herschel Telescope (WHT), now scheduled for first light in early-2021, with almost all components now arrived at the observatory. We also present a summary of the current planning behind the 5-year initial phase of survey operations, and some detailed end-to-end science simulations that have been implemented to evaluate the final on-sky performance after data processing. WEAVE will provide optical ground-based follow up of ground-based (LOFAR) and space-based (Gaia) surveys. WEAVE is a multi-object and multi-IFU facility utilizing a new 2-degree prime focus field of view at the WHT, with a buffered pick-and-place positioner system hosting 1000 multi-object (MOS) fibres, 20 mini integral field units, or a single large IFU for each observation. The fibres are fed to a single (dual-beam) spectrograph, with total of 16k spectral pixels, located within the WHT GHRIL enclosure on the telescope Nasmyth platform, supporting observations at R~5000 over the full 370-1000nm wavelength range in a single exposure, or a high resolution mode with limited coverage in each arm at R~20000.


Fibre links for the WEAVE instrument: the making of

Society of Photo-optical Instrumentation Engineers (2020) 114502F
Part of a series from Proceedings of SPIE

S Mignot, P Bonifacio, G Fasola, G Dalton, I Lewis

The WEAVE instrument nearing completion for the William Herschel Telescope is a fiber-fed spectrograph operating in three different modes. Two comprise deployable fibers at the prime focus for point-like objects and small integral field units (IFU), the third is a large IFU placed at the center of the field. Three distinct fiber systems support these modes and route the photons to the spectrograph located on the Nasmyth platform 33m away: the first features 960+940 fibers and is duplicated to allow configuring the fibers on one plate while observation is carried out on the other, the second has 20 hexagonal IFUs featuring 37 fibers each, the third is a large array of 609 fibers with twice the former’s diameter. The large number of fibers and the diversity of their instantiation have made procurement of the parts and assembly of the custom cables a challenge. They involve project partners in France, the UK and the Netherlands and industrial partners in France, Canada, the USA and China to combine know-how and compress the schedule by parallelizing assembly of the cables. Besides the complex management that this induces, it has called for revising the fibers’ handling to relax tolerances and for a rigorous assessment of the conformity of the products. This paper tells the story of the making of the fiber links, presents the overall organization of the procurement and assembly chains together with the inspection and testing allowing for assessing the conformance of the hardware delivered.


Final assembly, metrology, and testing of the WEAVE fibre positioner

Proceedings of SPIE Society of Photo-optical Instrumentation Engineers 11447 (2020)

S Hughes, E Schallig, I Lewis, G Dalton, D Terrett, DC Abrams, S Trager, M Brock, G Bishop, K Middleton, P Bonifacio, A Vallenari, E Carrasco, A Aguerri

WEAVE is the new wide-field spectroscopy facility for the prime focus of the William Herschel Telescope at La Palma, Spain. Its fibre positioner is essential for the accurate placement of the spectrograph’s 960 fibre multiplex. We provide an overview of the final assembly and metrology of the fibre positioner, and results of lab commissioning of its robot gantries. A completely new z-gantry for each positioner robot was acquired, with measurements showing a marked improvement in positioning repeatability. We also present the first results of the configuration soft ng, and discuss the metrology procedures that must be repeated after the positioner’s arrival at the observatory.


HARMONI: First light spectroscopy for the ELT: final design and assembly plan of the spectrographs

Ground-based and Airborne Instrumentation for Astronomy VIII SPIE (2020)

Z Ozer, H Schnetler, FT Bagci, M Booth, M Brock, N Cann, JI Capone, J Chao Ortiz, G Dalton, N Dobson, T Foster, A Hidalgo Valadez, J Kariuki, I Lewis, A Lowe, J Lynn, M Rodrigues, I Tosh, F Clarke, M Tecza, N Thatte


Dual effects of ram pressure on star formation in multiphase disk galaxies with strong stellar feedback

Astrophysical Journal IOP Science 905 (2020) 31

J Lee, T Kimm, H Katz, J Rosdahl, J Devriendt, A Slyz

We investigate the impact of ram pressure stripping due to the intracluster medium (ICM) on star-forming disk galaxies with a multiphase interstellar medium maintained by strong stellar feedback. We carry out radiation-hydrodynamic simulations of an isolated disk galaxy embedded in a 1011 M ⊙ dark matter halo with various ICM winds mimicking the cluster outskirts (moderate) and the central environment (strong). We find that both star formation quenching and triggering occur in ram pressure–stripped galaxies, depending on the strength of the winds. H i and H2 in the outer galactic disk are significantly stripped in the presence of moderate winds, whereas turbulent pressure provides support against ram pressure in the central region, where star formation is active. Moderate ICM winds facilitate gas collapse, increasing the total star formation rates by ~40% when the wind is oriented face-on or by ~80% when it is edge-on. In contrast, strong winds rapidly blow away neutral and molecular hydrogen gas from the galaxy, suppressing star formation by a factor of 2 within ~200 Myr. Dense gas clumps with n H gsim 10 M ⊙ pc−2 are easily identified in extraplanar regions, but no significant young stellar populations are found in such clumps. In our attempts to enhance radiative cooling by adopting a colder ICM of T = 106 K, only a few additional stars are formed in the tail region, even if the amount of newly cooled gas increases by an order of magnitude.

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