Publications by Leah Morabito


LoTSS DR1: Double-double radio galaxies in the HETDEX field

ASTRONOMY & ASTROPHYSICS 622 (2019) ARTN A13

VH Mahatma, MJ Hardcastle, WL Williams, PN Best, JH Croston, K Duncan, B Mingo, R Morganti, M Brienza, RK Cochrane, G Gurkan, JJ Harwood, MJ Jarvis, M Jamrozy, N Jurlin, LK Morabito, HJA Rottgering, J Sabater, TW Shimwell, DJB Smith, A Shulevski, C Tasse


The origin of radio emission in broad absorption line quasars: Results from the LOFAR Two-metre Sky Survey

Astronomy and Astrophysics EDP Sciences 622 (2018) A15

L Morabito, J Matthews, P Best, G Gurkan, M Jarvis, I Prandoni, K Duncan, M Hardcastle, M Kunert-Bajraszewska, A Mechev, S Mooney, J Sabeter, H Rottgering, T Shimwell, D Smith, C Tasse, W Williams

We present a study of the low-frequency radio properties of broad absorption line quasars (BALQSOs) from the LOFAR Two-metre Sky-Survey Data Release 1 (LDR1). The value-added LDR1 catalogue contains Pan-STARRS counterparts, which we match with the Sloan Digital Sky Survey (SDSS) DR7 and DR12 quasar catalogues. We find that BALQSOs are twice as likely to be detected at 144 MHz than their non-BAL counterparts, and BALQSOs with low-ionisation species present in their spectra are three times more likely to be detected than those with only high-ionisation species. The BALQSO fraction at 144 MHz is constant with increasing radio luminosity, which is inconsistent with previous results at 1.4 GHz, indicating that observations at the different frequencies may be tracing different sources of radio emission. We cross-match radio sources between the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey and LDR1, which provides a bridge via the LDR1 Pan-STARRS counterparts to identify BALQSOs in SDSS. Consequently we expand the sample of BALQSOs detected in FIRST by a factor of three. The LDR1-detected BALQSOs in our sample are almost exclusively radio-quiet (log(R144 MHz) <2), with radio sizes at 144 MHz typically less than 200 kpc; these radio sizes tend to be larger than those at 1.4 GHz, suggesting more extended radio emission at low frequencies. We find that although the radio detection fraction increases with increasing balnicity index (BI), there is no correlation between BI and either low-frequency radio power or radio-loudness. This suggests that both radio emission and BI may be linked to the same underlying process, but are spatially distinct phenomena.


The environments of radio-loud AGN from the LOFAR Two-Metre Sky Survey (LoTSS)

ASTRONOMY & ASTROPHYSICS 622 (2019) ARTN A10

JH Croston, MJ Hardcastle, B Mingo, PN Best, J Sabater, TM Shimwell, WL Williams, KJ Duncan, HJA Rottgering, M Brienza, G Gurkan, J Ineson, GK Miley, LM Morabito, SP O'Sullivan, I Prandoni


Radio-loud AGN in the first LoTSS data release The lifetimes and environmental impact of jet-driven sources

ASTRONOMY & ASTROPHYSICS 622 (2019) ARTN A12

MJ Hardcastle, WL Williams, PN Best, JH Croston, KJ Duncan, HJA Rottgering, J Sabater, TW Shimwell, C Tasse, JR Callingham, RK Cochrane, F de Gasperin, G Gurkan, MJ Jarvis, V Mahatma, GK Miley, B Mingo, S Mooney, LK Morabito, SP O'Sullivan, I Prandoni, A Shulevski, DJB Smith


LoTSS DR1: Double-double radio galaxies in the HETDEX field

Astronomy and Astrophysics EDP Sciences (2019)

VH Mahatma, MJ Hardcastle, WL Williams, PN Best, JH Croston, K Duncan, B Mingo, R Morganti, M Brienza, RK Cochrane, G Gürkan, JJ Harwood, MJ Jarvis, M Jamrozy, N Jurlin, LK Morabito, HJA Röttgering, J Sabater, TW Shimwell, DJB Smith, A Shulevski, C Tasse

Double-double radio galaxies (DDRGs) represent a short but unique phase in the life-cycle of some of the most powerful radio-loud active galactic nuclei (RLAGN). These galaxies display large-scale remnant radio plasma in the intergalactic medium left behind by a past episode of active galactic nuclei (AGN) activity, and meanwhile, the radio jets have restarted in a new episode. The knowledge of what causes the jets to switch off and restart is crucial to our understanding of galaxy evolution, while it is important to know if DDRGs form a host galaxy dichotomy relative to RLAGN. We utilised the LOFAR Two-Metre Sky Survey DR1, using a visual identification method to compile a sample of morphologically selected candidate DDRGs, showing two pairs of radio lobes. To confirm the restarted nature in each of the candidate sources, we obtained follow-up observations with the VLA at higher resolution to observe the inner lobes or restarted jets, the confirmation of which created a robust sample of 33 DDRGs. We created a comparison sample of 777 RLAGN from the DR1 catalogue, and compared the optical and infrared magnitudes and colours of their host galaxies. We find that there is no statistically significant difference in the brightness of the host galaxies between double-doubles and single-cycle RLAGN. The DDRG and RLAGN samples also have similar distributions in WISE mid-infrared colours, indicating similar ages of stellar populations and dust levels in the hosts of DDRGs. We conclude that DDRGs and 'normal' RLAGN are hosted by galaxies of the same type, and that DDRG activity is simply a normal part of the life cycle of RLAGN. Restarted jets, particularly for the class of low-excitation radio galaxies, rather than being a product of a particular event in the life of a host galaxy, must instead be caused by smaller scale changes, such as in the accretion system surrounding the black hole.


LOFAR observations of the XMM-LSS field

Astronomy and Astrophysics EDP Sciences (2019)

CL Hale, W Williams, MJ Jarvis, MJ Hardcastle, LK Morabito, TW Shimwell, C Tasse, PN Best, JJ Harwood, I Heywood, I Prandoni, HJA Röttgering, J Sabater, DJB Smith, RJV Weeren

We present observations of the XMM Large-Scale Structure (XMM-LSS) field observed with the LOw Frequency ARray (LOFAR) at 120-168 MHz. Centred at a J2000 declination of $-4.5^{\circ}$, this is a challenging field to observe with LOFAR because of its low elevation with respect to the array. The low elevation of this field reduces the effective collecting area of the telescope, thereby reducing sensitivity. This low elevation also causes the primary beam to be elongated in the north-south direction, which can introduce side lobes in the synthesised beam in this direction. However the XMM-LSS field is a key field to study because of the wealth of ancillary information, encompassing most of the electromagnetic spectrum. The field was observed for a total of 12 hours from three four-hour LOFAR tracks using the Dutch array. The final image presented encompasses $\sim 27$ deg$^2$, which is the region of the observations with a $>$50\% primary beam response. Once combined, the observations reach a central rms of 280 $\mu$Jy beam$^{-1}$ at 144 MHz and have an angular resolution of $7.5 \times \ 8.5$". We present our catalogue of detected sources and investigate how our observations compare to previous radio observations. This includes investigating the flux scale calibration of these observations compared to previous measurements, the implied spectral indices of the sources, the observed source counts and corrections to obtain the true source counts, and finally the clustering of the observed radio sources.


Systematic effects in LOFAR data: A unified calibration strategy

ASTRONOMY & ASTROPHYSICS 622 (2019) ARTN A5

F de Gasperin, TJ Dijkema, A Drabent, M Mevius, D Rafferty, R van Weeren, M Brueggen, JR Callingham, KL Emig, G Heald, HT Intema, LK Morabito, AR Offringa, R Oonk, E Orru, H Rottgering, J Sabater, T Shimwell, A Shulevski, W Williams


LoTSS/HETDEX: Disentangling star formation and AGN activity in gravitationally lensed radio-quiet quasars

ASTRONOMY & ASTROPHYSICS 622 (2019) ARTN A18

HR Stacey, JP McKean, NJ Jackson, PN Best, GC Rivera, JR Callingham, KJ Duncan, G Gurkan, MJ Hardcastle, M Iacobelli, AP Mechev, LK Morabito, I Prandoni, HJA Rottgering, J Sabater, TW Shimwell, C Tasse, WL Williams


A kpc-scale star forming disk surrounding nuclei with shocked outflows (erratum)

ASTRONOMY & ASTROPHYSICS 613 (2018)

E Varenius, JE Conway, I Marti-Vidal, S Aalto, L Barcos-Munoz, S Konig, MA Perez-Torres, AT Deller, J Moldon, JS Gallagher, TM Yoast-Hull, C Horellou, LK Morabito, A Alberdi, N Jackson, R Beswick, TD Carozzi, O Wucknitz, N Ramirez-Olivencia


Revolutionizing our understanding of AGN feedback and its importance to galaxy evolution in the era of the next generation Very Large Array

Astrophysical Journal American Astronomical Society 859 (2018) 23

K Nyland, JJ Harwood, DD Mukherjee, L Morabito, E al.

Energetic feedback by active galactic nuclei (AGNs) plays an important evolutionary role in the regulation of star formation on galactic scales. However, the effects of this feedback as a function of redshift and galaxy properties such as mass, environment, and cold gas content remain poorly understood. The broad frequency coverage (1 to 116 GHz), high sensitivity (up to ten times higher than the Karl G. Jansky Very Large Array), and superb angular resolution (maximum baselines of at least a few hundred kilometers) of the proposed next-generation Very Large Array (ngVLA) are uniquely poised to revolutionize our understanding of AGNs and their role in galaxy evolution. Here, we provide an overview of the science related to AGN feedback that will be possible in the ngVLA era and present new continuum ngVLA imaging simulations of resolved radio jets spanning a wide range of intrinsic extents. We also consider key computational challenges and discuss exciting opportunities for multiwavelength synergy with other next-generation instruments, such as the Square Kilometer Array and the James Webb Space Telescope. The unique combination of high-resolution, large collecting area, and wide frequency range will enable significant advancements in our understanding of the effects of jet-driven feedback on sub-galactic scales, particularly for sources with extents of a few parsec to a few kiloparsec, such as young and/or lower-power radio AGNs, AGNs hosted by low-mass galaxies, radio jets that are interacting strongly with the interstellar medium of the host galaxy, and AGNs at high redshift.


LOFAR-Bootes: properties of high- and low-excitation radio galaxies at 0.5 < z < 2.0

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 475 (2018) 3429-3452

WL Williams, GC Rivera, PN Best, MJ Hardcastle, HJA Rottgering, KJ Duncan, F de Gasperin, MJ Jarvis, GK Miley, EK Mahony, LK Morabito, DM Nisbet, I Prandoni, DJB Smith, C Tasse, GJ White


Investigating the cause of the $α\,$-$\,z$ relation

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (2018)

LK Morabito, JJ Harwood

The correlation between radio spectral index and redshift has long been used to identify high redshift radio galaxies, but its cause is unknown. Traditional explanations invoke either $(i)$ intrinsic relations between spectral index and power, $(ii)$ environmental differences at high redshift, or $(iii)$ higher inverse Compton losses due to the increased photon energy density of the cosmic microwave background. In this paper we investigate whether the increased inverse Compton losses alone can cause the observed spectral index - redshift correlation by using spectral modelling of nearby radio galaxies to simulate high redshift equivalents. We then apply selection effects and directly compare the simulated radio galaxy sample with an observed sample with sufficient redshift coverage. We find excellent agreement between the two, implying that inverse Compton losses and selection effects alone can largely reproduce the observed spectral index - redshift correlation.


The Far-Infrared Radio Correlation at low radio frequency with LOFAR/H-ATLAS

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 480 (2018) 5625-5644

SC Read, DJB Smith, G Guerkan, MJ Hardcastle, WL Williams, PN Best, E Brinks, G Calistro-Rivera, KT Chyzy, K Duncan, L Dunne, MJ Jarvis, LK Morabito, I Prandoni, HJA Rottgering, J Sabater, S Viaene


LOFAR MSSS: Discovery of a 2.56 Mpc giant radio galaxy associated with a disturbed galaxy group

Astronomy & Astrophysics EDP Sciences 601 (2017) A25-

D Carbone, JH Croston, JS Farnes, JJ Harwood, V Heesen, A Horneffer, AJ van der Horst, M Iacobelli, E Orrú, R Paladino, M Pandey-Pommier, M Pietka, R Pizzo, L Pratley, CJ Riseley, HJA Rottgering, A Rowlinson, J Sabater, K Sendlinger, SS Sridhar, C Tasse, S van Velzen, RJ van Weeren, MW Wise

We report on the discovery in the LOFAR Multifrequency Snapshot Sky Survey (MSSS) of a giant radio galaxy (GRG) with a projected size of 2.56 ± 0.07 Mpc projected on the sky. It is associated with the galaxy triplet UGC 9555, within which one is identified as a broad-line galaxy in the Sloan Digital Sky Survey (SDSS) at a redshift of 0.05453 ± 1 × 10-5, and with a velocity dispersion of 215.86 ± 6.34 km s-1. From archival radio observations we see that this galaxy hosts a compact flat-spectrum radio source, and we conclude that it is the active galactic nucleus (AGN) responsiblefor generating the radio lobes. The radio luminosity distribution of the jets, and the broad-line classification of the host AGN, indicate this GRG is orientated well out of the plane of the sky, making its physical size one of the largest known for any GRG. Analysis of the infrared data suggests that the host is a lenticular type galaxy with a large stellar mass (log M/Mo = 11.56 ± 0.12), and a moderate star formation rate (1.2 ± 0.3 Mo/year). Spatially smoothing the SDSS images shows the system around UGC 9555 to be significantly disturbed, with a prominent extension to the south-east. Overall, the evidence suggests this host galaxy has undergone one or more recent moderate merger events and is also experiencing tidal interactions with surrounding galaxies, which have caused the star formation and provided the supply of gas to trigger and fuel the Mpc-scale radio lobes.


Low-frequency Carbon Radio Recombination Lines. II. The Diffuse Interstellar Medium

The Astrophysical Journal 837 (2017) 142-142

F Salgado, LK Morabito, JBR Oonk, P Salas, MC Toribio, HJA Röttgering, AGGM Tielens


Low-frequency Carbon Radio Recombination Lines. I. Calculations of Departure Coefficients

The Astrophysical Journal 837 (2017) 141-141

F Salgado, LK Morabito, JBR Oonk, P Salas, MC Toribio, HJA Röttgering, AGGM Tielens


Carbon and hydrogen radio recombination lines from the cold clouds towards Cassiopeia A

Monthly Notices of the Royal Astronomical Society 465 (2017) 1066-1088

JBR Oonk, RJ van Weeren, P Salas, F Salgado, LK Morabito, MC Toribio, AGGM Tielens, HJA Röttgering


The CALYMHA survey: Lyα luminosity function and global escape fraction of Lyα photons at z  = 2.23

Monthly Notices of the Royal Astronomical Society 466 (2017) 1242-1258

D Sobral, J Matthee, P Best, A Stroe, H Röttgering, I Oteo, I Smail, L Morabito, A Paulino-Afonso


The LOFAR window on star-forming galaxies and AGNs – curved radio SEDs and IR–radio correlation at 0

Monthly Notices of the Royal Astronomical Society Oxford University Press 469 (2017) 3468-3488

G Calistro Rivera, WL Williams, MJ Hardcastle, K Duncan, HJA Röttgering, PN Best, M Brüggen, KT Chyży, CJ Conselice, F de Gasperin, D Engels, G Gürkan, HT Intema, M Jarvis, EK Mahony, GK Miley, LK Morabito, I Prandoni, J Sabater, DJB Smith, C Tasse, PP van der Werf, GJ White

We present a study of the low-frequency radio properties of star-forming (SF) galaxies and active galactic nuclei (AGNs) up to redshift z = 2.5. The new spectral window probed by the Low Frequency Array (LOFAR) allows us to reconstruct the radio continuum emission from 150 MHz to 1.4 GHz to an unprecedented depth for a radio-selected sample of 1542 galaxies in ∼ 7 deg2 of the LOFAR Boötes field. Using the extensive multiwavelength data set available in Boötes and detailed modelling of the far-infrared to ultraviolet spectral energy distribution (SED), we are able to separate the star formation (N = 758) and the AGN (N = 784) dominated populations. We study the shape of the radio SEDs and their evolution across cosmic time and find significant differences in the spectral curvature between the SF galaxy and AGN populations. While the radio spectra of SF galaxies exhibit a weak but statistically significant flattening, AGN SEDs show a clear trend to become steeper towards lower frequencies. No evolution of the spectral curvature as a function of redshift is found for SF galaxies or AGNs. We investigate the redshift evolution of the infrared–radio correlation for SF galaxies and find that the ratio of total infrared to 1.4-GHz radio luminosities decreases with increasing redshift: q1.4 GHz = (2.45 ± 0.04) (1 + z)−0.15 ± 0.03. Similarly, q150 MHz shows a redshift evolution following q150 GHz = (1.72 ± 0.04) (1 + z)−0.22 ± 0.05. Calibration of the 150 MHz radio luminosity as a star formation rate tracer suggests that a single power-law extrapolation from q1.4 GHz is not an accurate approximation at all redshifts.


Investigating the Unification of LOFAR-detected powerful AGN in the Boötes Field

Monthly Notices of the Royal Astronomical Society Oxford University Press 469 (2017) 1883-1896

LK Morabito, WL Williams, KJ Duncan, HJA Röttgering, G Miley, A Saxena, P Barthel, PN Best, M Bruggen, G Brunetti, KT Chyży, D Engels, MJ Hardcastle, JJ Harwood, MJ Jarvis, EK Mahony, I Prandoni, TW Shimwell, A Shulevski, C Tasse

Low radio frequency surveys are important for testing unified models of radio-loud quasars and radio galaxies. Intrinsically similar sources that are randomly oriented on the sky will have different projected linear sizes. Measuring the projected linear sizes of these sources provides an indication of their orientation. Steep-spectrum isotropic radio emission allows for orientation-free sample selection at low radio frequencies. We use a new radio survey of the Boötes field at 150 MHz made with the Low-Frequency Array (LOFAR) to select a sample of radio sources. We identify 60 radio sources with powers P &gt; 10<sup>25.5</sup>  W Hz<sup>−1,</sup> at 150 MHz using cross-matched multiwavelength information from the AGN and Galaxy Evolution Survey, which provides spectroscopic redshifts and photometric identification of 16 quasars and 44 radio galaxies. When considering the radio spectral slope only, we find that radio sources with steep spectra have projected linear sizes that are on average 4.4 ± 1.4 larger than those with flat spectra. The projected linear sizes of radio galaxies are on average 3.1 ± 1.0 larger than those of quasars (2.0 ± 0.3 after correcting for redshift evolution). Combining these results with three previous surveys, we find that the projected linear sizes of radio galaxies and quasars depend on redshift but not on power. The projected linear size ratio does not correlate with either parameter. The LOFAR data are consistent within the uncertainties with theoretical predictions of the correlation between the quasar fraction and linear size ratio, based on an orientation-based unification scheme.

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