arXiv subjects

T. Connor

Publications and source records attributed to T. Connor.

14 recordsLinked to original sources

arXiv2026

The most extreme high-z radio quasars in the eRASS:1 X-ray survey

We present the selection and identification of high-z radio quasars from a combination of X-ray (eROSITA All-Sky Survey), optical/NIR (DECam Local Volume Exploration), and radio (Rapid ASKAP Continuum Survey) surveys. After building a sample of 68 new high-z quasar candidates, we performed follow-up spectroscopic observations on 46 sources, confirming 39 to have redshifts z>3.5. For the subset of radio quasars at z>4, the 14 new sources identified here represent an increase of $\sim$65% in the known population of objects above the same flux limits in the same area. Using X-ray-to-optical relative intensity, we identified blazars in our sample, which we then used to compare the total number of z>4, X-ray selected blazars to the predictions of a fractional IC/CMB model previously proposed in the literature. Overall we find a relatively good agreement, even considering the potential biases in the redshift distribution from the incompleteness of the spectroscopic follow-up and the blazar classification criteria. The sources presented in this work represent a sample well suited for investigating the evolution of the most extreme systems in the early Universe, including their relativistic jets and accretion properties

astro-ph.GA↗

arXiv2026

Gaia GraL X.: The GraL catalogue of gravitationally lensed quasars Matched with \textit{Gaia} data, redshifts, and time delays

Determining the Hubble constant tension requires alternative strategies, and multiply imaged quasars, with their intermediate redshifts, can potentially be used in this regard. We provide a currently complete catalogue of spectroscopically confirmed lensed quasars with ESA/{\it Gaia} astrometry and photometry, as well as redshifts and time delays when available. In addition to the improved astrometry, the catalogue increases the number of lensed quasars by a factor of 1.5 (now 364, of which 277 are doubles and 87 are quads or triples) and significantly increases the number of lensing galaxies detected (now 218), which represents a major step forward. Redshifts are provided for 347 quasars and 188 deflectors. A completely new table of time delays, required for estimates of $H_0$, is presented, with 195 time delays from 73 systems. {\it Gaia} absolute astrometry is sub-milliarcsecond and covers the entire sky. Future {\it Gaia} data releases will provide long-term photometry, which should provide many more time delays. The catalogues as presented here enable machine-learning techniques to be trained and tested and subsequently applied to the {\it Gaia} data releases. Finally, we derive simple but homogeneous models of the 18 quadruply imaged quasars for which images of all four components are presented in {\it Gaia} DR3.}

astro-ph.GA↗

arXiv2025

Identifying tidal disruption events among radio transient galaxies

We present the optical and infrared properties of a sample of 24 radio transient sources discovered in the Very Large Array Sky Survey (VLASS). Previous studies of their radio emission showed that these sources resemble young gigahertz-peaked spectrum (GPS) radio sources, but are less powerful and characterized by low-power jets. The bursts of radio activity in most cases are likely due to intrinsic changes in the accretion processes. However, for a few sources in this sample, we cannot rule out the possibility that their radio variability results from a tidal disruption event (TDE). In this work, we extend our analysis to the optical and infrared regimes, confirming that our sample of radio transients is not homogeneous in terms of their optical and infrared properties either. The host galaxies of most of these sources are massive ellipticals with emission dominated by active galactic nuclei (AGN). They host supermassive black holes (SMBHs) with masses typical of radio-loud AGNs ($\rm >10^7\,M_{\odot}$), but exhibit very low accretion activity. In contrast, the sources for which a TDE origin is suspected are either pure star-forming galaxies or show significant ongoing star formation, similar to radio-selected optically-detected TDEs. Additionally, two of them exhibit infrared flares characteristic of TDEs, while the remaining sources do not display significant variability outside the radio regime. Moreover, the evolution of their radio brightness in the W3/radio diagnostic diagram, which we employ in our analysis, also sets our TDE candidates apart from the rest of the sample and resembles the radio variability seen in optically discovered TDEs with radio emission. Finally, based on our findings, we hypothesize that the mid-IR/radio relation can serve as a tool to distinguish between radio transients caused by TDEs and those originating from intrinsic AGN variability.

astro-ph.HE↗

arXiv2025

X-ray investigation of possible super-Eddington accretion in a radio-loud quasar at $z=6.13$

We present radio and X-ray observations of the recently discovered $z=6.13$ radio-powerful quasar RACS J032021.44$-$352104.1 using uGMRT, ATCA, LBA, and Chandra. The observed radio properties are in line with what is typically observed in high-$z$ radio quasars ($\alpha_{\rm r}=0.72\pm 0.02$ and L$_{\rm 1.4GHz}=5.8 \pm 0.9 \times 10^{26}$ W Hz$^{-1}$). Despite the relatively low X-ray flux observed $F_{\rm 0.5-7.0 keV}=2.3\pm0.5 \times 10^{-14}$ erg sec$^{-1}$ cm$^{-2}$, the intrinsic luminosity in the 2-10 keV rest frame is markedly high, $L_{\rm 2-10 keV}=1.8^{+1.1}_{-0.7} \times 10^{46}$ erg sec$^{-1}$, making RACS J032021.44$-$352104.1 one of the most luminous quasars currently known at $z>5.5$. The high X-ray luminosity is largely driven by an extrapolation to energies below the observable X-ray window with Chandra and the slope derived in the 0.5-7 keV band (or 3.5--50 keV in the rest-frame; $\Gamma_{\rm X}=3.3\pm0.4$). By analysing the overall spectral energy distribution of the quasar we found that the remarkably soft X-ray emission: (1) cannot be produced by relativistic jets, even when relativistic boosting is considered; and (2) is consistent with expectations for a super-Eddington accreting SMBH. If such a high accretion rate was confirmed, this source would be a unique laboratory to study high accretion in the early Universe and could help resolve some challenges inherent in early black hole growth paradigms.

astro-ph.GA↗

arXiv2025

High-$z$ radio Quasars in RACS I: Selection, identification, and multi-wavelength properties

Radio-bright, jetted quasars at $z>5$ serve as unique laboratories for studying supermassive black hole activity in the early Universe. In this work, we present a sample of high-$z$ jetted quasars selected from the combination of the radio Rapid ASKAP Continuum Survey (RACS) with deep wide-area optical/near-infrared surveys. From this cross-match we selected 45 new high-$z$ radio quasar candidates with S$_{888MHz}>1$ mJy and mag$z<21.3$ over an area of 16000deg$^2$. Using spectroscopic observations, we confirmed the high-$z$ nature of 24 new quasars, 13 at $4.5 5$. If we also consider similar, in terms of radio/optical fluxes and sky position, quasars at $z>5$ already reported in the literature, the overall $z>5$ RACS sample is composed by 33 powerful quasars, expected to be ~90% complete at mag$z<21.3$ and S$_{888MHz}>1$ mJy. Having rest-frame radio luminosities in the range $\nu L_{1.4GHz}=10^{41.5}-10^{44.4}$ erg s$^{-1}$, this sample contains the most extreme radio quasars currently known in the early Universe. We also present all X-ray and radio data currently available for the sample, including new, dedicated {\it Chandra}, uGMRT, MeerKAT and ATCA observations for a sub-set of the sources. from the modelling of their radio emission, either with a single power law or a broken power law, we found that these systems have a wide variety of spectral shapes with most quasars (22) having a flat radio emission (i.e., $-0.5<\alpha_{r}<0.5$). At the same time, the majority of the sources with X-ray coverage present a high-energy luminosity larger than the one expected from the X-ray corona only. Both the radio and X-ray properties of the high-$z$ RACS sample suggest that many of these sources have relativistic jets oriented close to our line of sight. (i.e., blazars) and can therefore be used to perform statistical studies on the entire jetted population at high redshift.

astro-ph.GA↗

arXiv2024

The host galaxies of radio-loud quasars at z>5 with ALMA

The interaction between radio-jets and quasar host galaxies plays a paramount role in quasar/galaxy co-evolution. However, very little has been known so far about this interaction at very high-z. Here, we present new Atacama Large Millimeter/submillimeter Array (ALMA) observations in Band 7 and Band 3 of six radio-loud quasars' host galaxies at $z > 5$. We recover [CII] 158 $\mu$m line and underlying dust continuum emission at $>2\sigma$ for five sources, while we obtain upper limits for the CO(6-5) emission line and continuum for the remaining source. At the spatial resolution of our observations ($\sim$1.0"-1.4"), we do not recover perturbed/extended morphologies or kinematics, signatures of potential mergers. These galaxies already host large quantities of gas, with [CII]-based star formation rates of $30-400 M_{\odot} $yr$^{-1}$. Building their radio/sub-mm spectral energy distributions (SEDs), we find that in at least four cases the 1mm continuum intensity arises from a combination of synchrotron and dust emission, with an initial estimation of synchrotron contribution at 300 GHz of $\gtrsim$10%. We compare the properties of the sources inspected here with a large collection of radio-quiet sources from the literature, as well as a sample of radio-loud quasars from previous studies, at comparable redshift. We recover a potential mild decrease in $L_{\rm [CII]}$ for the radio-loud sources, which might be due to a suppression of the cool gas emission due to the radio-jets. We do not find any [CII]-emitting companion galaxy candidate around the five radio-loud quasars observed in Band 7: given the depth of our dataset, this result is still consistent with that observed around radio-quiet quasars. Further higher-spatial resolution observations, over a larger frequency range, of high-z radio-loud quasars hosts will allow for a better understanding of the physics of such sources.

astro-ph.GA↗

arXiv2021

The Close AGN Reference Survey (CARS): No obvious signature of AGN feedback on star formation, but subtle trends

[Abridged] Active Galactic Nuclei (AGN) are thought to be responsible for the suppression of star formation in massive ~10$^{10}$ M$_\odot$ galaxies. While this process is a key feature in numerical simulations, it is not yet unambiguously confirmed in observational studies. Characterization of the star formation rate (SFR) in AGN host galaxies is challenging as AGN light contaminates most SFR tracers. We aim to obtain and compare SFR estimates from different tracers for AGN host galaxies in the Close AGN Reference Survey (CARS) to provide new observational insights. We construct integrated panchromatic spectral energy distributions (SED) to measure the FIR luminosity as a tracer for the recent (< 100 Myr) SFR. In addition, we use integral-field unit observation of the CARS targets to employ the H$\alpha$ luminosity decontaminated by AGN excitation as a proxy for the current (< 5 Myr) SFR. We find that significant differences in specific SFR of the AGN host galaxies as compared with the larger galaxy population disappear once cold gas mass, in addition to stellar mass, is used to predict the SFR. We identify individual galaxies with a significant difference in their SFR which can be related to a recent enhancement or decline in their SFR history that might be related to various processes including interactions, gas consumption, outflows and AGN feedback. AGN can occur in various stages of galaxy evolution which makes it difficult to relate the SFR solely to the impact of the AGN. We do not find any strong evidence for global positive or negative AGN feedback in the CARS sample. However, there is tentative evidence that 1) the relative orientation of the AGN engine with respect to the host galaxies might alter the efficiency of AGN feedback and 2) the recent SFH is an additional tool to identify rapid changes in galaxy growth driven by the AGN or other processes.

astro-ph.GA↗

arXiv2020

Stellar mass measurements in Abell 133 with Magellan / IMACS

We present the analysis of deep optical imaging of the galaxy cluster Abell 133 with the IMACS instrument on Magellan. Our multi-band photometry enables stellar mass measurements in the cluster member galaxies down to a mass limit of $M_\star=3\times10^8\,M_\odot$ ($\approx 0.1$ of the Large Magellanic Cloud stellar mass). We observe a clear difference in the spatial distribution of large and dwarf galaxies within the cluster. Modeling these galaxies populations separately, we can confidently track the distribution of stellar mass locked in the galaxies to the cluster's virial radius. The extended envelope of the cluster's brightest galaxy can be tracked to $\sim 200$ kpc. The central galaxy contributes $\sim 1/3$ of the the total cluster stellar mass within the radius $r_{500c}$.

astro-ph.GA↗

arXiv2019

The Close AGN Reference Survey (CARS). A massive multi-phase outflow impacting the edge-on galaxy HE1353-1917

[Abridged] We combine extensive spatially-resolved multi-wavelength observations, taken as part of the Close AGN Reference Survey (CARS), for the edge-on disc galaxy HE1353-1917 to characterize the impact of the AGN on its host galaxy via outflows and radiation. Multi-color broad-band photometry is combined with spatially-resolved optical, NIR and sub-mm and radio observations taken with VLT/MUSE, Gemini-N/NIFS, ALMA and the VLA to map the physical properties and kinematics of the multi-phase inter-stellar medium (ISM). We detect a biconical extended narrow-line region (ENLR) ionized by the luminous AGN oriented nearly parallel to the galaxy disc, extending out to at least 25kpc. The extra-planar gas originates from galactic fountains initiated by star formation processes in the disc, rather than an AGN outflow, as shown by the kinematics and the metallicity of the gas. Nevertheless, a fast multi-phase AGN-driven outflow with speeds up to 1000km/s is detected close to the nucleus at 1kpc distance. A radio jet, in connection with the AGN radiation field, is likely responsible for driving the outflow as confirmed by the energetics and the spatial alignment of the jet and multi-phase outflow. Evidence for negative AGN feedback suppressing the star formation rate (SFR) is mild and restricted to the central kpc. But while any SFR suppression must have happened recently, the outflow has the potential to greatly impact the future evolution of the galaxy disc due to its geometrical orientation. Our observations reveal that low-power radio jets can play a major role in driving fast multi-phase galaxy-scale outflows even in radio-quiet AGN. Since the outflow energetics for HE1353-1917 are consistent with literature scaling relations of AGN-driven outflows the contribution of radio jets as the driving mechanisms still needs to be systematically explored.

astro-ph.GA↗

arXiv2019

Powerful AGN jets and unbalanced cooling in the hot atmosphere of IC 4296

We present new Karl G. Jansky Very Large Array (VLA, 1.5 GHz) radio data for the giant elliptical galaxy IC 4296, supported by archival radio, X-ray (Chandra, XMM-Newton) and optical (SOAR, HST) observations. The galaxy hosts powerful radio jets piercing through the inner hot X-ray emitting atmosphere, depositing most of the energy into the ambient intra-cluster medium (ICM). Whereas the radio surface brightness of the A configuration image is consistent with a Fanaroff-Riley Class I (FR I) system, the D configuration image shows two bright, relative to the central region, large (~160 kpc diameter), well-defined lobes, previously reported by Killeen et al., at a projected distance r~>230 kpc. The XMM-Newton image reveals an X-ray cavity associated with one of the radio lobes. The total enthalpy of the radio lobes is ~7x10^59 erg and the mechanical power output of the jets is ~10^44 erg/s. The jets are mildly curved and possibly re-brightened by the relative motion of the galaxy and the ICM. The lobes display sharp edges, suggesting the presence of bow shocks, which would indicate that they are expanding supersonically. The central entropy and cooling time of the X-ray gas are unusually low and the nucleus hosts a warm H\alpha+[NII] nebula and a cold molecular CO disk. Because most of the energy of the jets is deposited far from the nucleus, the atmosphere of the galaxy continues to cool, apparently feeding the central supermassive black hole and powering the jet activity.

astro-ph.GA↗

arXiv2018

Cooling in the X-ray halo of the rotating, massive early-type galaxy NGC 7049

The relative importance of the physical processes shaping the thermodynamics of the hot gas permeating rotating, massive early-type galaxies is expected to be different from that in non-rotating systems. Here, we report the results of the analysis of XMM-Newton data for the massive, lenticular galaxy NGC 7049. The galaxy harbours a dusty disc of cool gas and is surrounded by an extended hot X-ray emitting gaseous atmosphere with unusually high central entropy. The hot gas in the plane of rotation of the cool dusty disc has a multi-temperature structure, consistent with ongoing cooling. We conclude that the rotational support of the hot gas is likely capable of altering the multiphase condensation regardless of the $t_{\rm cool}/t_{\rm ff}$ ratio, which is here relatively high, $\sim 40$. However, the measured ratio of cooling time and eddy turnover time around unity ($C$-ratio $\approx 1$) implies significant condensation, and at the same time, the constrained ratio of rotational velocity and the velocity dispersion (turbulent Taylor number) ${\rm Ta_t} > 1$ indicates that the condensing gas should follow non-radial orbits forming a disc instead of filaments. This is in agreement with hydrodynamical simulations of massive rotating galaxies predicting a similarly extended multiphase disc.

astro-ph.GA↗

arXiv2018

Thermodynamic properties, multiphase gas and AGN feedback in a large sample of giant ellipticals

We present a study of the thermal structure of the hot X-ray emitting atmospheres for a sample of 49 nearby X-ray and optically bright elliptical galaxies using {\it Chandra} X-ray data. We focus on the connection between the properties of the hot X-ray emitting gas and the cooler H$\alpha$+[NII] emitting phase, and the possible role of the latter in the AGN (Active Galactic Nuclei) feedback cycle. We do not find evident correlations between the H$\alpha$+[NII] emission and global properties such as X-ray luminosity, mass of hot gas, and gas mass fraction. We find that the presence of H$\alpha$+[NII] emission is more likely in systems with higher densities, lower entropies, shorter cooling times, shallower entropy profiles, lower values of min($t_{\rm cool}/t_{\rm ff}$), and disturbed X-ray morphologies (linked to turbulent motions). However, we see no clear separations in the observables obtained for galaxies with and without optical emission line nebulae. The AGN jet powers of the galaxies with X-ray cavities show hint of a possible weak positive correlation with their H$\alpha$+[NII] luminosities. This correlation and the observed trends in the thermodynamic properties may result from chaotic cold accretion (CCA) powering AGN jets, as seen in some high-resolution hydrodynamic simulations.

astro-ph.GA↗

arXiv2018

Chandra X-rays from the redshift 7.54 quasar ULAS J1342+0928

We present a 45 ks Chandra observation of the quasar ULAS J1342+0928 at z=7.54. We detect 14.0^{+4.8}_{-3.7} counts from the quasar in the observed-frame energy range 0.5-7.0 keV (6-sigma detection), representing the most distant non-transient astronomical source identified in X-rays to date. The present data are sufficient only to infer rough constraints on the spectral parameters. We find an X-ray hardness ratio of HR = -0.51^{+0.26}_{-0.28} between the 0.5-2.0 keV and 2.0-7.0 keV ranges and derive a power-law photon index of Gamma = 1.95^{+0.55}_{-0.53}. Assuming a typical value for high-redshift quasars of Gamma = 1.9, ULAS J1342+0928 has a 2-10 keV rest-frame X-ray luminosity of L_{2-10} = 11.6^{+4.3}_{-3.5} x 10^{44} erg/s. Its X-ray-to-optical power-law slope is alpha_{OX}=-1.67^{+0.16}_{-0.10}, consistent with the general trend indicating that the X-ray emission in the most bolometrically powerful quasars is weaker relative to their optical emission.

astro-ph.GA↗

arXiv2013

The origin of cold gas in giant elliptical galaxies and its role in fueling radio-mode AGN feedback

We present a multi-wavelength study of the interstellar medium in eight nearby, X-ray and optically bright, giant elliptical galaxies. Using Herschel PACS, we map the cold gas in the lines of [CII], [OI], and [OIb]. Additionally, we present Ha+[NII] imaging of warm ionized gas with the SOAR telescope, and a study of the hot X-ray emitting plasma with Chandra. All systems with extended Ha emission in our sample (6/8 galaxies) display significant [CII] line emission indicating the presence of cold gas. This emission is co-spatial with the Ha+[NII] emitting nebulae and the lowest entropy X-ray emitting plasma. The entropy profiles of the hot galactic atmospheres show a clear dichotomy, with the systems displaying extended emission line nebulae having lower entropies beyond r~1 kpc than the cold-gas-poor systems. We show that while the hot atmospheres of the cold-gas-poor galaxies are thermally stable outside of their innermost cores, the atmospheres of the cold-gas-rich systems are prone to cooling instabilities. This result indicates that the cold gas is produced chiefly by thermally unstable cooling from the hot phase. We show that cooling instabilities may develop more easily in rotating systems and discuss an alternative condition for thermal instability for this case. The hot atmospheres of cold-gas-rich galaxies display disturbed morphologies indicating that the accretion of clumpy multiphase gas in these systems may result in variable power output of the AGN jets, potentially triggering sporadic, larger outbursts. In the two cold-gas-poor, X-ray morphologically relaxed galaxies of our sample, NGC 1399 and NGC 4472, powerful AGN outbursts may have destroyed or removed most of the cold gas from the cores, allowing the jets to propagate and deposit most of their energy further out, increasing the entropy of the hot galactic atmospheres and leaving their cores relatively undisturbed.

astro-ph.CO↗