arXiv subjects

Jacinta Delhaize

Publications and source records attributed to Jacinta Delhaize.

At least 19 recordsLinked to original sources

arXiv2026

MIGHTEE: Discovery of a triple-double radio galaxy

Triple-double radio galaxies (TDRGs) are amongst the rarest subpopulations of radio galaxies (RGs). They are characterised by three pairs of radio lobes, where each pair of lobes represents an episode of nuclear activity. Such a feature makes them key objects that can be used to constrain the duty cycle of RGs. In this paper, we report the discovery of J022248\m060934, a new TDRG, hosted by a galaxy at a spectroscopic redshift of $z \approx$ 0.94. We have used the MIGHTEE-DR1 data set and MIGHTEE sub-band images as our main data. In total intensity, J022248\m060934 has a bright core and triple-double, edge-brightened-like peaks of radio emission. The polarimetry of the source reveals an inhomogeneous density of the hosting environment which is consistent with the more pronounced bending in its eastern lobes. The spectral index and curvature maps suggest an inverted core and an ultra-steepening of the spectrum towards the outer lobes which reinforce a recurrent nuclear activity. We perform individual spectral age fitting of the components of the source using the JP model and we found a lower limit total age of $\sim$16 Myr. We also derive a short inactive period between the active phases and a rapid duty cycle of 90 per cent for the first cycle of activity. Our spectral ageing analysis suggests that the triple-double structure in TDRGs is not the product of long quiescent periods, as deduced by previous works based on kinematic ages.

astro-ph.GA↗

arXiv2025

Probing the formation of megaparsec-scale giant radio galaxies II. Continuum & polarization behavior from MHD simulations

The persistence of radiative signatures in giant radio galaxies remains a frontier topic of research, with contemporary telescopes revealing intricate features that require investigation. This study aims to examine the emission characteristics of simulated GRGs, and correlate them with their underlying 3D dynamical properties. Sky-projected continuum and polarization maps at 1 GHz were computed from five 3D-RMHD simulations by integrating the synthesized emissivity data along the line of sight, with the integration path chosen to reflect the GRG evolution in the sky plane. The emissivities were derived from these RMHD simulations, featuring FR-I and FR-II jets injected from different locations of the large-scale environment. The jet-cocoon morphologies are strongly shaped by the triaxiality of the environment, resulting in features like wings and asymmetric cocoons, thereby making morphology a crucial indicator of GRG formation mechanisms. The decollimation of the bulk flow in GRG jets gives rise to intricate cocoon features, most notably filamentary structures-magnetically dominated threads with lifespans of a few Myr. High-jet-power cases frequently display enhanced emission zones at mid-cocoon distances (alongside warmspots around the jet-head), contradicting the interpretations of the GRG as a restarting source. In such cases, examining the lateral intensity variation of the cocoon may reveal the source's state, with a gradual decrease in emission suggesting a low-active stage. This study highlights that applying a simple radio power-jet power relation to a statistical GRG sample is unfeasible, as it depends on growth conditions of individual GRGs. Effects such as inverse-Compton CMB cooling and matter entrainment significantly impact the long-term emission persistence of GRGs. The diminishing fractional polarization with GRG evolution reflects increasing turbulence in the cocoon.

astro-ph.GA↗

arXiv2025

Investigating the influence of radio-faint AGN activity on the infrared-radio correlation of massive galaxies

It is well-known that star-forming galaxies (SFGs) exhibit a tight correlation between their radio and infrared emissions, commonly referred to as the infrared-radio correlation (IRRC). Recent empirical studies have reported a dependence of the IRRC on the galaxy stellar mass, in which more massive galaxies tend to show lower infrared-to-radio ratios (qIR) with respect to less massive galaxies. One possible, yet unexplored, explanation is a residual contamination of the radio emission from active galactic nuclei (AGN), not captured through "radio-excess" diagnostics. To investigate this hypothesis, we aim to statistically quantify the contribution of AGN emission to the radio luminosities of SFGs located within the scatter of the IRRC. Our VLBA program "AGN-sCAN" has targeted 500 galaxies that follow the qIR distribution of the IRRC, i.e., with no prior evidence for radio-excess AGN emission based on low-resolution (~ arcsec) VLA radio imaging. Our VLBA 1.4 GHz observations reach a 5-sigma sensitivity limit of 25 microJy/beam, corresponding to a radio brightness temperature of Tb ~ 10^5 K. This classification serves as a robust AGN diagnostic, regardless of the host galaxy's star formation rate. We detect four VLBA sources in the deepest regions, which are also the faintest VLBI-detected AGN in SFGs to date. The effective AGN detection rate is 9%, when considering a control sample matched in mass and sensitivity, which is in good agreement with the extrapolation of previous radio AGN number counts. Despite the non-negligible AGN flux contamination (~ 30%) in our individual VLBA detections, we find that the peak of the qIR distribution is completely unaffected by this correction. We conclude that residual AGN contamination from non-radio-excess AGN is unlikely to be the primary driver of the M* - dependent IRRC.

astro-ph.GA↗

arXiv2025

MIGHTEE-HI: The direct detection of neutral hydrogen in galaxies at $z>0.25$

Atomic hydrogen constitutes the gas reservoir from which molecular gas and star formation in galaxies emerges. However, the weakness of the line means it has been difficult to directly detect in all but the very local Universe. Here we present results from the first search using the MeerKAT International Tiered Extragalactic Exploration (MIGHTEE) Survey for high-redshift ($z>0.25$) H{\sc i} emission from individual galaxies. By searching for 21-cm emission centered on the position and redshift of optically-selected emission-line galaxies we overcome difficulties that hinder untargeted searches. We detect 11 galaxies at $z>0.25$, forming the first sample of $z>0.25$ detections with an interferometer, with the highest redshift detection at $z = 0.3841$. We find they have much larger H{\sc i} masses than their low-redshift H{\sc i}-selected counterparts for a given stellar mass. This can be explained by the much larger cosmological volume probed at these high redshifts, and does not require any evolution of the H{\sc i} mass function. We make the first-ever measurement of the baryonic Tully-Fisher relation (bTFr) with H{\sc i} at $z>0.25$ and find consistency with the local bTFr, but with tentative evidence of a flattening in the relation at these redshifts for higher-mass objects. This may signify evolution, in line with predictions from hydrodynamic simulations, or that the molecular gas mass in these high-mass galaxies could be significant. This study paves the way for future studies of H{\sc i} beyond the local Universe, using both searches targeted at known objects and via pure H{\sc i} selection.

astro-ph.GA↗

arXiv2024

Looking At the Distant Universe with the MeerKAT Array: the HI Mass Function in the Local Universe

We present measurements of the neutral atomic hydrogen (HI) mass function (HIMF) and cosmic HI density ($\Omega_{\rm HI}$) at $0 \leq z \leq 0.088$ from the Looking at the Distant Universe with MeerKAT Array (LADUMA) survey. Using LADUMA Data Release 1 (DR1), we analyze the HIMF via a new "recovery matrix" (RM) method that we benchmark against a more traditional Modified Maximum Likelihood (MML) method. Our analysis, which implements a forward modeling approach, corrects for survey incompleteness and uses extensive synthetic source injections to ensure robust estimates of the HIMF parameters and their associated uncertainties. This new method tracks the recovery of sources in mass bins different from those in which they were injected and incorporates a Poisson likelihood in the forward modeling process, allowing it to correctly handle uncertainties in bins with few or no detections. The application of our analysis to a high-purity subsample of the LADUMA DR1 spectral line catalog in turn mitigates any possible biases that could result from the inconsistent treatment of synthetic and real sources. For the surveyed redshift range, the recovered Schechter function normalization, low-mass slope, and "knee" mass are $\phi_\ast = 3.56_{-1.92}^{+0.97} \times 10^{-3}$ Mpc$^{-3}$ dex$^{-1}$, $\alpha = -1.18_{-0.19}^{+0.08}$, and $\log(M_\ast/M_\odot) = 10.01_{-0.12}^{+0.31}$, respectively, which together imply a comoving cosmic HI density of $\Omega_{\rm HI}=3.09_{-0.47}^{+0.65}\times 10^{-4}$. Our results show consistency between RM and MML methods and with previous low-redshift studies, giving confidence that the cosmic volume probed by LADUMA, even at low redshifts, is not an outlier in terms of its HI content.

astro-ph.GA↗

arXiv2024

Probing the Formation of Megaparsec-scale Giant Radio Galaxies (I): Dynamical Insights from MHD Simulations

Giant radio galaxies (GRGs), a minority among the extended-jetted population, form in a wide range of jet and environmental configurations, complicating the identification of the growth factors that facilitate their attainment of megaparsec scales. This study aims to numerically investigate the hypothesized formation mechanisms of GRGs extending $\gtrsim 1$ Mpc to assess their general applicability. We employ triaxial ambient medium settings to generate varying levels of jet frustration and simulate jets with low and high power from different locations in the environment, formulating five representations. The emergence of distinct giant phases in all five simulated scenarios suggests that GRGs may be more common than previously believed, a prediction to be verified with contemporary radio telescopes. We find that different combinations of jet morphology, power, and the evolutionary age of the formed structure hold the potential to elucidate different formation scenarios. The simulated lobes are overpressured, prompting further investigation into pressure profiles when jet activity ceases, potentially distinguishing between relic and active GRGs. We observed a potential phase transition in giant radio galaxies, marked by differences in lobe expansion speed and pressure variations compared to their smaller evolutionary phases. This suggests the need for further investigation across a broader parameter space to determine if GRGs fundamentally differ from smaller RGs. Axial ratio analysis reveals self-similar expansion in rapidly propagating jets, with notable deviations when the jet forms wider lobes. Overall, this study emphasizes that multiple growth factors at work can better elucidate the current-day population of GRGs, including scenarios e.g., growth of GRGs in dense environments, GRGs of several megaparsecs, GRG development in low-powered jets, and the formation of X-shaped GRGs.

astro-ph.GA↗

arXiv2023

MIGHTEE-\HI: Possible interactions with the galaxy NGC~895

The transformation and evolution of a galaxy is strongly influenced by interactions with its environment. Neutral hydrogen (\HI) is an excellent way to trace these interactions. Here, we present \HI\ observations of the spiral galaxy NGC~895, which was previously thought to be isolated. High-sensitivity \HI\ observations from the MeerKAT large survey project MIGHTEE reveal possible interaction features, such as extended spiral arms, and the two newly discovered \HI\ 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 $\mathrm{1.75 \pm 0.09 [M_{\odot}/yr]}$, 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 \HI\ and optical to reveal a more complete picture of galaxy environments.

astro-ph.GA↗

arXiv2022

MIGHTEE-HI: Evolution of HI scaling relations of star-forming galaxies at $z<0.5$

We present the first measurements of HI galaxy scaling relations from a blind survey at $z>0.15$. We perform spectral stacking of 9023 spectra of star-forming galaxies undetected in HI at $0.23<z<0.49$, extracted from MIGHTEE-HI Early Science datacubes, acquired with the MeerKAT radio telescope. We stack galaxies in bins of galaxy properties ($M_*$, SFR, and sSFR, with ${\rm sSFR}\equiv M_*/{\rm SFR}$), obtaining $\gtrsim 5\sigma$ detections in most cases, the strongest HI-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 $z_{\rm med}\sim 0.37$ to $z\sim 0$. In particular, low-$M_*$ galaxies ($\log_{10}(M_*/{\rm M_\odot})\sim 9$) experience a strong HI depletion ($\sim 0.5$ dex in $\log_{10}(M_{\rm HI}/{\rm M}_\odot)$), while massive galaxies ($\log_{10}(M_*/{\rm M_\odot})\sim 11$) keep their HI mass nearly unchanged. When looking at the star formation activity, highly star-forming galaxies evolve significantly in $M_{\rm HI}$ ($f_{\rm HI}$, where $f_{\rm HI}\equiv M_{\rm}/M_*$) 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 HI depletion during the last $\sim4$ Gyr, while massive galaxies have undergone a significant HI 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.

astro-ph.GA↗

arXiv2022

LADUMA: Discovery of a luminous OH megamaser at $z > 0.5$

In the local Universe, OH megamasers (OHMs) are detected almost exclusively in infrared-luminous galaxies, with a prevalence that increases with IR luminosity, suggesting that they trace gas-rich galaxy mergers. Given the proximity of the rest frequencies of OH and the hyperfine transition of neutral atomic hydrogen (HI), radio surveys to probe the cosmic evolution of HI in galaxies also offer exciting prospects for exploiting OHMs to probe the cosmic history of gas-rich mergers. Using observations for the Looking At the Distant Universe with the MeerKAT Array (LADUMA) deep HI survey, we report the first untargeted detection of an OHM at $z > 0.5$, LADUMA J033046.20$-$275518.1 (nicknamed "Nkalakatha"). The host system, WISEA J033046.26$-$275518.3, is an infrared-luminous radio galaxy whose optical redshift $z \approx 0.52$ confirms the MeerKAT emission line detection as OH at a redshift $z_{\rm OH} = 0.5225 \pm 0.0001$ rather than HI at lower redshift. The detected spectral line has 18.4$\sigma$ peak significance, a width of $459 \pm 59\,{\rm km\,s^{-1}}$, and an integrated luminosity of $(6.31 \pm 0.18\,{\rm [statistical]}\,\pm 0.31\,{\rm [systematic]}) \times 10^3\,L_\odot$, placing it among the most luminous OHMs known. The galaxy's far-infrared luminosity $L_{\rm FIR} = (1.576 \pm 0.013) \times 10^{12}\,L_\odot$ marks it as an ultra-luminous infrared galaxy; its ratio of OH and infrared luminosities is similar to those for lower-redshift OHMs. A comparison between optical and OH redshifts offers a slight indication of an OH outflow. This detection represents the first step towards a systematic exploitation of OHMs as a tracer of galaxy growth at high redshifts.

astro-ph.GA↗

arXiv2021

The XXL Survey: XLIII. The quasar radio loudness dichotomy exposed via radio luminosity functions obtained by combining results from COSMOS and XXL-S X-ray selected quasars

We studied a sample of 274 radio and X-ray selected quasars (XQSOs) detected in the COSMOS and XXL-S radio surveys at 3 GHz and 2.1 GHz, respectively. This sample was identified by adopting a conservative threshold in X-ray luminosity, Lx [2-10\ keV] >= 10^44 erg/s, selecting only the most powerful quasars. Using available multiwavelength data, we examined various criteria for the selection of radio-loud (RL) and radio-quiet (RQ) XQSOs, finding that the number of RL/RQ XQSOs changes significantly depending on the chosen criterion. This discrepancy arises due to the different criteria tracing different physical processes and due to our sample being selected from flux-limited radio and X-ray surveys. Another approach to study the origin of radio emission in XQSOs is via their radio luminosity function (RLF). We constructed the XQSO 1.4 GHz radio luminosity functions (RLFs) in six redshift bins at 0.5 <= z <= 3.7. The lower-1.4 GHz luminosity end shows a higher normalization than expected only from AGN contribution in all studied redshift bins. The found "bump" is mostly dominated by emission due to star-forming (SF) processes within the XQSO host galaxies. As expected, AGN-related radio emission dominates at the higher-luminosity end of RLF. The evolution of XQSO RLF was studied via combination of analytic forms from the literature to constrain the lower-luminosity "bump" and the higher-luminosity AGN part of the RLF. We defined two 1.4 GHz luminosity thresholds, L_th,SF and L_th,AGN, below and above which more than 80% of sources contributing to the RLF are dominated by SF and AGN-related activity, respectively. These thresholds evolve with redshift, most likely due to the strong evolution of SFRs of the XQSO host galaxies.

astro-ph.GA↗

arXiv2021

Measuring Cosmic Density of Neutral Hydrogen via Stacking the DINGO-VLA Data

We use the 21 cm emission line data from the DINGO-VLA project to study the atomic hydrogen gas H\,{\textsc i} of the Universe at redshifts $z<0.1$. Results are obtained using a stacking analysis, combining the H\,{\textsc i} signals from 3622 galaxies extracted from 267 VLA pointings in the G09 field of the Galaxy and Mass Assembly Survey (GAMA). Rather than using a traditional one-dimensional spectral stacking method, a three-dimensional cubelet stacking method is used to enable deconvolution and the accurate recovery of average galaxy fluxes from this high-resolution interferometric dataset. By probing down to galactic scales, this experiment also overcomes confusion corrections that have been necessary to include in previous single dish studies. After stacking and deconvolution, we obtain a $30σ$ H\,{\textsc i} mass measurement from the stacked spectrum, indicating an average H\,{\textsc i} mass of $M_{\rm H\,{\textsc i}}=(1.674\pm 0.183)\times 10^{9}~{\Msun}$. The corresponding cosmic density of neutral atomic hydrogen is $Ω_{\rm H\,{\textsc i}}=(0.377\pm 0.042)\times 10^{-3}$ at redshift of $z=0.051$. These values are in good agreement with earlier results, implying there is no significant evolution of $Ω_{\rm H\,{\textsc i}}$ at lower redshifts.

astro-ph.GA↗

arXiv2021

The non-linear infrared-radio correlation of low-z galaxies: implications for redshift evolution, a new radio SFR recipe, and how to minimize selection bias

The infrared-radio correlation (IRRC) underpins many commonly used radio luminosity-star formation rate (SFR) calibrations. In preparation for the new generation of radio surveys we revisit the IRRC of low-$z$ galaxies by (a) drawing on the best currently available IR and 1.4 GHz radio photometry, plus ancillary data over the widest possible area, and (b) carefully assessing potential systematics. We compile a catalogue of $\sim$9,500 z $<$ 0.2 galaxies and derive their 1.4 GHz radio ($L_{\mathrm{1.4}}$), total IR, and monochromatic IR luminosities in up to seven bands, allowing us to parameterize the wavelength-dependence of monochromatic IRRCs from 22-500 $μ$m. For the first time for low-$z$ samples, we quantify how poorly matched IR and radio survey depths bias measured median IR/radio ratios, $\overline{q}_{\mathrm{TIR}}$, and discuss the level of biasing expected for low-z IRRC studies in ASKAP/MeerKAT fields. For our subset of $\sim$2,000 high-confidence star-forming galaxies we find a median $\overline{q}_{\mathrm{TIR}}$ of 2.54 (scatter: 0.17 dex). We show that $\overline{q}_{\mathrm{TIR}}$ correlates with $L_{\mathrm{1.4}}$, implying a non-linear IRRC with slope 1.11$\pm$0.01. Our new $L_{\mathrm{1.4}}$-SFR calibration, which incorporates this non-linearity, reproduces SFRs from panchromatic SED fits substantially better than previous IRRC-based recipes. Finally, we match the evolutionary slope of recently measured $\overline{q}_{\mathrm{TIR}}$-redshift trends without having to invoke redshift evolution of the IRRC. In this framework, the redshift evolution of $\overline{q}_{\mathrm{TIR}}$ reported at GHz frequencies in the literature is the consequence of a partial, redshift-dependent sampling of a non-linear IRRC obeyed by low-$z$ {\it and} distant galaxies.

astro-ph.GA↗

arXiv2018

The VLA-COSMOS 3 GHz Large Project: Star formation properties and radio luminosity functions of AGN with moderate-to-high radiative luminosities out to $z\sim6$

We study a sample of 1,604 moderate-to-high radiative luminosity active galactic nuclei (HLAGN) selected at 3 GHz within the VLA-COSMOS 3 GHz Large Project. These were classified by combining multiple AGN diagnostics: X-ray data, mid-infrared data and broad-band spectral energy distribution fitting. We decompose the total radio 1.4 GHz luminosity ($\mathrm{L_{1.4\ GHz,TOT}}$) into the emission originating from star formation and AGN activity by measuring the excess in $\mathrm{L_{1.4\ GHz,TOT}}$ relative to the infrared-radio correlation of star-forming galaxies. To quantify the excess, for each source we calculate the AGN fraction ($\mathrm{f_{AGN}}$), the fractional contribution of AGN activity to $\mathrm{L_{1.4\ GHz,TOT}}$. The majority of the HLAGN, $(68.0\pm1.5)\%$, are dominated by star-forming processes ($f_{AGN}\leq0.5$), while $(32.0\pm1.5)\%$ are dominated by AGN-related radio emission ($0.5 0$).

astro-ph.GA↗

arXiv2018

The XXL Survey : XXVI. Optical and near-infrared identifications of the ATCA 2.1 GHz radio sources in the XXL-S Field

In this paper we present the optical, near-infrared (NIR) and X-ray identifications of the 6287 radio sources detected in the 2.1 GHz deep radio survey down to a median rms of ~ 41microJy/beam obtained with the Australia Telescope Compact Array (ATCA) in the XXL-S field. The goal of this paper is to provide a multi wavelength catalogue of the counterparts of the radio sources to be used in further studies. For the optical and NIR identification of the radio sources, we used the likelihood ratio (LR) technique, slightly modified in order to take into account the presence of a large number of relatively bright counterparts close to the radio sources. This procedure led to the identification of optical/NIR counterparts for 4770 different radio sources (~77% of the whole radio sample), 414 of which also have an X-ray counterpart. This fraction of identification is in agreement with previous radio-optical association studies at a similar optical magnitude depth, but is relatively low in comparison to recent work conducted in other radio fields using deeper optical and NIR data. The analysis of optical and NIR properties of radio sources shows that, regardless of the radio flux limit of a radio survey, the nature of the identified sources is strongly dependent on the depth of the optical/NIR used in the identification process. Only with deep enough optical/NIR data will we be able to identify a significant fraction of radio sources with red (z_{DEC}-K) counterparts whose radio emission is dominated by nuclear activity rather than starburst activity.

astro-ph.GA↗

arXiv2018

The XXL Survey: XXXI. Classification and host galaxy properties of 2.1 GHz ATCA XXL-S radio sources

The classification of the host galaxies of the radio sources in the 25 deg$^2$ ultimate XMM extragalactic survey south field (XXL-S) is presented. XXL-S was surveyed at 2.1 GHz with the Australia Telescope Compact Array (ATCA) and is thus far the largest area radio survey conducted down to rms flux densities of $σ\sim 41$ $μ$Jy beam$^{-1}$. Of the 6287 radio sources in XXL-S, 4758 (75.7%) were cross-matched to an optical counterpart using the likelihood ratio technique. There are 1110 spectroscopic redshifts and 3648 photometric redshifts available for the counterparts, of which 99.4% exist out to $z \sim 4$. A number of multiwavelength diagnostics, including X-ray luminosities, mid-infrared colours, spectral energy distribution fits, radio luminosities, and optical emission lines and colours, were used to classify the sources into three types: low-excitation radio galaxies (LERGs), high-excitation radio galaxies (HERGs), and star-forming galaxies (SFGs). The final sample contains 1729 LERGs (36.3%), 1159 radio-loud HERGs (24.4%), 296 radio-quiet HERGs (6.2%), 558 SFGs (11.7%), and 1016 unclassified sources (21.4%). The LERGs tend to exist in the most massive galaxies with low star formation rates and redder colours, whereas the HERGs and SFGs exist in galaxies of lower mass, higher star formation rates, and bluer colours. The fraction of blue host galaxies is higher for radio-quiet HERGs than for radio-loud HERGs. LERGs and radio-loud HERGs are found at all radio luminosities, but radio-loud HERGs tend to be more radio luminous than LERGs at a given redshift. These results are consistent with the emerging picture in which LERGs exist in the most massive quiescent galaxies typically found in clusters with hot X-ray halos and HERGs are associated with ongoing star formation in their host galaxies via the accretion of cold gas.

astro-ph.GA↗

arXiv2018

The XXL Survey: XXIX. GMRT 610 MHz continuum observations

We present the 25 square-degree GMRT-XXL-N 610 MHz radio continuum survey, conducted at 50~cm wavelength with the Giant Metrewave Radio Telescope (GMRT) towards the XXL Northern field (XXL-N). We combined previously published observations of the XMM-Large Scale Structure (XMM-LSS) field, located in the central part of XXL-N, with newly conducted observations towards the remaining XXL-N area, and imaged the combined data-set using the Source Peeling and Atmospheric Modeling ({\sc SPAM}) pipeline. The final mosaic encompasses a total area of $30.4$ square degrees, with ${\rm rms}<150~μ$Jy/beam over 60\% of the area. The ${\rm rms}$ achieved in the inner 9.6 square degree area, enclosing the XMM-LSS field, is about $200~μ$Jy/beam, while that over the outer 12.66 square degree area (which excludes the noisy edges) is about $45~μ$Jy/beam. The resolution of the final mosaic is 6.5 arcsec. We present a catalogue of 5\,434 sources detected at $\geq7\times {\rm rms}$. We verify, and correct the reliability of, the catalog in terms of astrometry, flux, and false detection rate. Making use of the (to date) deepest radio continuum survey over a relatively large (2 square degree) field, complete at the flux levels probed by the GMRT-XXL-N survey, we also assess the survey's incompleteness as a function of flux density. The radio continuum sensitivity reached over a large field with a wealth of multi-wavelength data available makes the GMRT-XXL-N 610 MHz survey an important asset for studying the physical properties, environments and cosmic evolution of radio sources, in particular radio-selected active galactic nuclei (AGN).

astro-ph.GA↗

arXiv2018

Average radio spectral energy distribution of highly star-forming galaxies

The infrared-radio correlation (IRRC) offers a way to assess star formation from radio emission. Multiple studies found the IRRC to decrease with increasing redshift. This may in part be due to the lack of knowledge about the possible radio spectral energy distributions (SEDs) of star-forming galaxies. We constrain the radio SED of a complete sample of highly star-forming galaxies ($SFR>100\,\mathrm{M_{\odot}}/\,\mathrm{yr}$) based on the VLA-COSMOS $1.4\,\mathrm{GHz}$ Joint and $3\,\mathrm{GHz}$ Large Project catalogs. We reduce archival GMRT $325\,\mathrm{MHz}$ and $610\,\mathrm{MHz}$ observations, broadening the rest-frame frequency range to $0.3-15\,\mathrm{GHz}$. Employing survival analysis and fitting a double power law SED, we find that the slope steepens from a spectral index of $α_1=0.51\pm 0.04$ below $4.5\,\mathrm{GHz}$ to $α_2=0.98\pm0.07$ above $4.5\,\mathrm{GHz}.$ Our results suggest that the use of a K-correction assuming a single power-law radio SED for star forming galaxies is likely not the root cause of the IRRC trend.

astro-ph.GA↗

arXiv2017

Cosmic evolution of AGN with moderate-to-high radiative luminosity in the COSMOS field

We study the moderate-to-high radiative luminosity active galactic nuclei (HLAGN) within the VLA-COSMOS 3 GHz Large Project. The survey covers 2.6 square degrees centered on the COSMOS field with a 1$σ$ sensitivity of 2.3 $\mathrm{μJy}$/beam across the field. This provides the simultaneously largest and deepest radio continuum survey available to date with exquisite multi-wavelength coverage. The survey yields 10,830 radio sources with signal-to-noise ratios $\geq$5. A subsample of 1,604 HLAGN is analyzed here. These were selected via a combination of X-ray luminosity and mid-infrared colors. We derive luminosity functions for these AGN and constrain their cosmic evolution out to a redshift of $z\sim6$, for the first time decomposing the star formation and AGN contributions to the radio continuum emission in the AGN. We study the evolution of number density and luminosity density finding a peak at $z\sim1.5$ followed by a decrease out to a redshift $z\sim6$.

astro-ph.GA↗