Preprint typeset using L ATEX style emulateapj EVIDENCE FOR EXTENDED, OBSCURED STARBURSTS IN SUBMM GALAXIES
We compare high-resolution optical and radio imaging of 12 luminous submillimeter (submm) galaxie... more We compare high-resolution optical and radio imaging of 12 luminous submillimeter (submm) galaxies at a median z = 2.2 ± 0.2 observed with Hubble Space Telescope (HST) and the MERLIN and VLA radio interferometers at comparable spatial resolution, ∼ 0.3 ′ ′ ( ∼ 2kpc). The radio emission is used as a tracer of the likely far-infrared morphology of these dusty, luminous galaxies. In ∼30 % of the sample the radio emission appears unresolved at this spatial scale, suggesting that the power source is compact and may either be an obscured AGN or a compact nuclear starburst. However, in the majority of the galaxies, ∼70 % (8/12), we find that the radio emission is resolved by MERLIN/VLA on scales of ∼ 1 ′ ′ (∼10kpc). For these galaxies we also find that the radio morphologies are often broadly similar to their restframe UV emission traced by our HST imaging. To assess whether the radio emission may be extended on even larger scales, ≫ 1 ′ ′ , resolved out by the MERLIN+VLA synthesized image...
The Role of the EVN in our Understanding of High-redshift Star-formation Activity and Low-Luminosity AGN Systems through Integrated Imaging across Wide Spatial Scales
Monthly Notices of the Royal Astronomical Society, 2017
We present a deep survey of the Super-Cluster Assisted Shear Survey (SuperCLASS) supercluster-a r... more We present a deep survey of the Super-Cluster Assisted Shear Survey (SuperCLASS) supercluster-a region of sky known to contain five Abell clusters at redshift z ∼ 0.2-performed using the Arcminute Microkelvin Imager (AMI) Large Array (LA) at 15.5 GHz. Our survey covers an area of approximately 0.9 deg 2. We achieve a nominal sensitivity of 32.0 µJy beam −1 towards the field centre, finding 80 sources above a 5σ threshold. We derive the radio colourcolour distribution for sources common to three surveys that cover the field and identify three sources with strongly curved spectra-a high-frequency-peaked source and two GHz-peakedspectrum sources. The differential source count (i) agrees well with previous deep radio source counts, (ii) exhibits no evidence of an emerging population of star-forming galaxies, down to a limit of 0.24 mJy, and (iii) disagrees with some models of the 15 GHz source population. However, our source count is in agreement with recent work that provides an analytical correction to the source count from the Square Kilometre Array Design Study (SKADS) Simulated Sky, supporting the suggestion that this discrepancy is caused by an abundance of flat-spectrum galaxy cores as yet not included in source population models.
Monthly Notices of the Royal Astronomical Society, 2018
We have analysed a new high-resolution e-MERLIN 1.5 GHz radio continuum map together with HST and... more We have analysed a new high-resolution e-MERLIN 1.5 GHz radio continuum map together with HST and SDSS imaging of NGC 5322, an elliptical galaxy hosting radio jets, aiming to understand the galaxy's central structure and its connection to the nuclear activity. We decomposed the composite HST + SDSS surface brightness profile of the galaxy into an inner stellar disc, a spheroid, and an outer stellar halo. Past works showed that this embedded disc counter-rotates rapidly with respect to the spheroid. The HST images reveal an edge-on nuclear dust disc across the centre, aligned along the major-axis of the galaxy and nearly perpendicular to the radio jets. After careful masking of this dust disc, we find a central stellar mass deficit M def in the spheroid, scoured by SMBH binaries with final mass M BH such that M def /M BH ∼ 1.3-3.4. We propose a three-phase formation scenario for NGC 5322, where a few (2-7) 'dry' major mergers involving SMBHs built the spheroid with a depleted core. The cannibalism of a gas-rich satellite subsequently creates the faint counter-rotating disc and funnels gaseous material directly on to the AGN, powering the radio core with a brightness temperature of T B, core ∼ 4.5 × 10 7 K and the low-power radio jets (P jets ∼ 7.04 × 10 20 W Hz −1), which extend ∼1.6 kpc. The outer halo can later grow via minor mergers and the accretion of tidal debris. The low-luminosity AGN/jet-driven feedback may have quenched the late-time nuclear star formation promptly, which could otherwise have replenished the depleted core.
Monthly Notices of the Royal Astronomical Society, 2010
From a combination of Multi-Element Radio-Linked Interferometer Network (MERLIN) and global Very ... more From a combination of Multi-Element Radio-Linked Interferometer Network (MERLIN) and global Very Long Baseline Interferometry (VLBI) observations of the starburst galaxy M82, images of 36 discrete sources at resolutions ranging from ∼3 to ∼80 mas at 1.7 GHz are presented. Of these 36 sources, 32 are identified as supernova remnants, two are H II regions and three remain unclassified. Sizes, flux densities and radio brightnesses are given for all of the detected sources. Additionally, global VLBI only data from this project are used to image four of the most compact radio sources. These data provide a fifth epoch of VLBI observations of these sources, covering a 19-yr time-line. In particular, the continued expansion of one of the youngest supernova remnants, 43.31+59.3, is discussed. The deceleration parameter is a power-law index used to represent the time evolution of the size of a supernova remnant. For the source 43.31+59.3, a lower limit to the deceleration parameter is calculated to be 0.53 ± 0.06, based on a lower limit of the age of this source.
Monthly Notices of the Royal Astronomical Society, 2006
We report the first observation of a transient relativistic jet from the canonical black hole can... more We report the first observation of a transient relativistic jet from the canonical black hole candidate, Cygnus X-1, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN). The jet was observed in only one of six epochs of MERLIN imaging of the source during a phase of repeated X-ray spectral transitions in 2004 Jan-Feb, and this epoch corresponded to the softest 1.5-12 keV X-ray spectrum. With only a single epoch revealing the jet, we cannot formally constrain its velocity. Nevertheless, several lines of reasoning suggest that the jet was probably launched 0.5-4.0 d before this brightening, corresponding to projected velocities of 0.2c v app 1.6c, and an intrinsic velocity of 0.3c. We also report the occurrence of a major radio flare from Cyg X-1, reaching a flux density of ∼120 mJy at 15 GHz, and yet not associated with any resolvable radio emission, despite a concerted effort with MERLIN. We discuss the resolved jet in terms of the recently proposed 'unified model' for the disc-jet coupling in black hole X-ray binaries, and tentatively identify the 'jet line' for Cyg X-1. The source is consistent with the model in the sense that a steady jet appears to persist initially when the X-ray spectrum starts softening, and that once the spectral softening is complete the core radio emission is suppressed and transient ejecta/shock observed. However, there are some anomalies, and Cyg X-1 clearly does not behave like a normal black hole transient in progressing to the canonical soft/thermal state once the ejection event has happened.
VLBI MERLIN and VLA Observations of the Blazar 1156+ 295-a Bending Relativistic Jet
Monthly Notices of …, 1990
... in 1978 December (referenced in Wills et al. 1983). ... A best linear fit to the motion gives... more ... in 1978 December (referenced in Wills et al. 1983). ... A best linear fit to the motion gives a velocity of 1 .1 5 mas yr ` which, at a redshift z = 0.729, translates into a superluminal velocity of 1 5 h ` c (throughout this paper we will assume H0 = lOOh km ` Mpc ` and q0 = 0.5). ...
We present results from 20 years of global VLBI imaging of the supernova remnants in Messier 82. ... more We present results from 20 years of global VLBI imaging of the supernova remnants in Messier 82. These observations, along with deep MERLIN 5 GHz observations, have traced the structural evolution of the most compact radio supernova remnants, measuring their source sizes, structures and expansion velocities. Additionally these observations constrain the rate at which these expanding shells are decelerating due to their interaction with the surrounding ISM.
Monthly Notices of the Royal Astronomical Society, 2004
As part of an ongoing radio supernova monitoring program, we have discovered a variable, compact ... more As part of an ongoing radio supernova monitoring program, we have discovered a variable, compact steep spectrum radio source ∼65 arcsec (∼4 kpc) from the centre of the starburst galaxy NGC 3310. If the source is at the distance of NGC 3310, then its 5 GHz luminosity is ∼ 3 × 10 19 W Hz −1. The source luminosity, together with its variability characteristics, compact structure (<17 mas) and its association with a group of Hii regions, leads us to propose that it is a previously uncatalogued type II radio supernova. A search of archival data also shows an associated X-ray source with a luminosity similar to known radio supernova.
We report the discovery of a gravitationally lensed hyperluminous infrared galaxy (L_IR~10^13 L_s... more We report the discovery of a gravitationally lensed hyperluminous infrared galaxy (L_IR~10^13 L_sun) with strong radio emission (L_1.4GHz~10^25 W/Hz) at z=2.553. The source was identified in the citizen science project SpaceWarps through the visual inspection of tens of thousands of iJKs colour composite images of Luminous Red Galaxies (LRGs), groups and clusters of galaxies and quasars. Appearing as a partial Einstein ring (r_e~3") around an LRG at z=0.2, the galaxy is extremely bright in the sub-millimetre for a cosmological source, with the thermal dust emission approaching 1 Jy at peak. The redshift of the lensed galaxy is determined through the detection of the CO(3-2) molecular emission line with the Large Millimetre Telescope's Redshift Search Receiver and through [OIII] and H-alpha line detections in the near-infrared from Subaru/IRCS. We have resolved the radio emission with high resolution (300-400 mas) eMERLIN L-band and JVLA C-band imaging. These observations ar...
Monthly Notices of the Royal Astronomical Society, 2008
The results of an extremely deep, 8-d long observation of the central kpc of the nearby starburst... more The results of an extremely deep, 8-d long observation of the central kpc of the nearby starburst galaxy M82 using Multi-Element Radio Linked Interferometer Network (MERLIN) at 5 GHz are presented. The 17 μJy beam −1 rms noise level in the naturally weighted image makes it the most sensitive high-resolution radio image of M82 made to date. Over 50 discrete sources are detected, the majority of which are supernova remnants, but with 13 identified as H II regions. Sizes, flux densities and radio brightnesses are given for all of the detected sources, which are all well resolved with a majority showing shell or partial shell structures. Those sources within the sample which are supernova remnants have diameters ranging from 0.3 to 6.7 pc, with a mean size of 2.9 pc. From a comparison with previous MERLIN 5-GHz observations made in 1992 July, which gives a 9.75-yr timeline, it has been possible to measure the expansion velocities of 10 of the more compact sources, eight of which have not been measured before. These derived expansion velocities range between 2200 and 10 500 km s −1 .
High Resolution Studies of mJy and μJy Radio Sources
Symposium - International Astronomical Union, 2001
VLBI observations can now be used to examine the milliarcsecond properties of mJy and sub-mJy rad... more VLBI observations can now be used to examine the milliarcsecond properties of mJy and sub-mJy radio sources. Here we describe a snapshot survey of compact mJy sources selected from the FIRST survey and the first EVN observations of a 6 arcmin square field centred on the Hubble Deep Field. At the few mJy level, a significant number of steep-spectrum sources appear to be very young low-luminosity radio galaxies. Older and fainter examples of this type of source are seen in the HDF, and are detected by the EVN. The VLBI observations of the HDF support the view that at least one of the putative distant, dusty starbursts harbours an AGN.
High Resolution Studies of mJy and μJy Radio Sources
Symposium - International Astronomical Union, 2001
VLBI observations can now be used to examine the milliarcsecond properties of mJy and sub-mJy rad... more VLBI observations can now be used to examine the milliarcsecond properties of mJy and sub-mJy radio sources. Here we describe a snapshot survey of compact mJy sources selected from the FIRST survey and the first EVN observations of a 6 arcmin square field centred on the Hubble Deep Field. At the few mJy level, a significant number of steep-spectrum sources appear to be very young low-luminosity radio galaxies. Older and fainter examples of this type of source are seen in the HDF, and are detected by the EVN. The VLBI observations of the HDF support the view that at least one of the putative distant, dusty starbursts harbours an AGN.
The SUrvey for Pulsars and Extragalactic Radio Bursts – II. New FRB discoveries and their follow-up
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Papers by T. Muxlow