arXiv subjects

Isabella Prandoni

Publications and source records attributed to Isabella Prandoni.

At least 55 records · Page 3Linked to original sources

arXiv2021

MIGHTEE-HI: The baryonic Tully-Fisher relation over the last billion years

Using a sample of 67 galaxies from the MIGHTEE Survey Early Science data we study the HI-based baryonic Tully-Fisher relation (bTFr), covering a period of $\sim$one billion years ($0 \leq z \leq 0.081 $). We consider the bTFr based on two different rotational velocity measures: the width of the global HI profile and $\rm V_{out}$, measured as the outermost rotational velocity from the resolved HI rotation curves. Both relations exhibit very low intrinsic scatter orthogonal to the best-fit relation ($σ_{\perp}=0.07\pm0.01$), comparable to the SPARC sample at $z \simeq 0$. The slopes of the relations are similar and consistent with the $ z \simeq 0$ studies ($3.66^{+0.35}_{-0.29}$ for $\rm W_{50}$ and $3.47^{+0.37}_{-0.30}$ for $\rm V_{out}$). We find no evidence that the bTFr has evolved over the last billion years, and all galaxies in our sample are consistent with the same relation independent of redshift and the rotational velocity measure. Our results set up a reference for all future studies of the HI-based bTFr as a function of redshift that will be conducted with the ongoing deep SKA pathfinders surveys.

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arXiv2021

The Evolutionary Map of the Universe Pilot Survey

We present the data and initial results from the first Pilot Survey of the Evolutionary Map of the Universe (EMU), observed at 944 MHz with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The survey covers 270 \sqdeg of an area covered by the Dark Energy Survey, reaching a depth of 25--30 \ujybm\ rms at a spatial resolution of $\sim$ 11--18 arcsec, resulting in a catalogue of $\sim$ 220,000 sources, of which $\sim$ 180,000 are single-component sources. Here we present the catalogue of single-component sources, together with (where available) optical and infrared cross-identifications, classifications, and redshifts. This survey explores a new region of parameter space compared to previous surveys. Specifically, the EMU Pilot Survey has a high density of sources, and also a high sensitivity to low surface-brightness emission. These properties result in the detection of types of sources that were rarely seen in or absent from previous surveys. We present some of these new results here.

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arXiv2020

New constraints on the 1.4 GHz source number counts and luminosity functions in the Lockman Hole field

We present a study of the 1173 sources brighter than $S_{1.4\,\rm GHz}= 120\,μ$Jy detected over an area of $\simeq 1.4\,\hbox{deg}^{2}$ in the Lockman Hole field. Exploiting the multi-band information available in this field for $\sim$79% of the sample, sources have been classified into radio loud (RL) active galactic nuclei (AGNs), star forming galaxies (SFGs) and radio quiet (RQ) AGNs, using a variety of diagnostics available in the literature. Exploiting the observed tight anti-correlations between IRAC band 1 or band 2 and the source redshift we could assign a redshift to 177 sources missing a spectroscopic measurement or a reliable photometric estimate. A Monte Carlo approach was used to take into account the spread around the mean relation. The derived differential number counts and luminosity functions at several redshifts of each population show a good consistency with models and with earlier estimates made using data from different surveys and applying different approaches. Our results confirm that below $\sim300\,μ$Jy SFGs$+$RQ AGNs overtake RL AGNs that dominate at brighter flux densities. We also confirm earlier indications of a similar evolution of RQ AGNs and SFGs. Finally, we discuss the angular correlation function of our sources and highlight its sensitivity to the criteria used for the classification.

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arXiv2020

The web of the Giant: spectroscopic confirmation of a Large Scale Structure around the z=6.31 quasar SDSS J1030+0524

We report on the spectroscopic confirmation of a large scale structure around the luminous, z=6.31 QSO SDSS~J1030+0524, that is powered by a billion solar mass black hole. The structure is populated by at least six members, four Lyman Break Galaxies (LBGs) and two Lyman Alpha Emitters (LAEs). The four LBGs have been identified among a sample of 21 i-band dropouts with z{AB}<25.5 selected up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their redshifts have been determined through up to 8hr-long multi-object spectroscopic observations at 8-10m class telescopes. The two LAEs have been identified in a 6hr VLT/MUSE observation centered on the QSO. The redshifts of the six galaxies cover the range 6.129-6.355. Assuming that peculiar velocities are negligible, this range corresponds to radial separations of +/-5 physical Mpc from the QSO, that is comparable to the projected scale of the observed LBG distribution on the sky. We conservatively estimate that this structure is significant at >3.5 sigma level, and that the level of the galaxy overdensity is at least 1.5-2 within the large volume sampled (~780 physical Mpc^3). The spectral properties of the six member galaxies (Lyalpha strength and UV luminosity) are similar to those of field galaxies at similar redshifts. This is the first spectroscopic identification of a galaxy overdensity around a super-massive black hole in the first billion years of the Universe. Our finding lends support to the idea that the most distant and massive black holes form and grow within massive (>10^{12} Msun) dark matter halos in large scale structures, and that the absence of earlier detections of such systems was likely due to observational limitations.

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arXiv2019

Rotation Measure synthesis applied on synthetic SKA images of galaxy clusters

Future observations with next generation radio telescopes will help us to understand the presence and the evolution of magnetic fields in galaxy clusters through the determination of the so-called Rotation Measure (RM). In this work, we applied the RM-synthesis technique on synthetic SKA1-MID radio images of a pair of merging galaxy clusters, measured between 950 and 1750 MHz with a resolution of 10 arcsec and a thermal noise of 0.1$μ$Jy/beam. The results of our RM-synthesis analysis are compared to the simulations' input parameters. We study two cases: one with radio haloes at the cluster centres, and another without. We found that the information obtained with the RM-synthesis is in general agreement with the input information. Some discrepancies are however present. We characterise them in this work, with the final goal of determining the potential impact of SKA1-MID on the study of cluster magnetic fields.

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arXiv2019

The AGN fuelling/feedback cycle in nearby radio galaxies II. Kinematics of the molecular gas

This is the second paper of a series exploring the multi-component (stars, warm and cold gas and radio jets) properties of a sample of eleven nearby low excitation radio galaxies (LERGs), with the aim of better understanding the AGN fuelling/feedback cycle in these objects. Here we present a study of the molecular gas kinematics of six sample galaxies detected in $^{12}$CO(2-1) with ALMA. In all cases, our modelling suggests that the bulk of the gas in the observed (sub-)kpc CO discs is in ordered rotation. Nevertheless, low-level distortions are ubiquitous, indicating that the molecular gas is not fully relaxed into the host galaxy potential. The majority of the discs, however, are only marginally resolved, preventing us from drawing strong conclusions. NGC 3557 and NGC 3100 are special cases. The features observed in the CO velocity curve of NGC 3557 allow us to estimate a super-massive black hole (SMBH) mass of $(7.10\pm0.02)\times10^{8}$ M$_{\odot}$, in agreement with expectations from the M$_{\rm SMBH}- σ_{*}$ relation. The rotation pattern of NGC 3100 shows distortions that appear to be consistent with the presence of both a position angle and inclination warp. Non-negligible radial motions are also found in the plane of the CO disc, likely consistent with streaming motions associated with the spiral pattern found in the inner regions of the disc. The dominant radial motions are likely to be inflows, supporting a scenario in which the cold gas is contributing to the fuelling of the AGN.

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arXiv2019

Feedback from low-luminosity radio galaxies: B2 0258+35

Low-luminosity radio-loud active galactic nuclei (AGN) are of importance in studies concerning feedback from radio AGN since a dominant fraction of AGN belong to this class. We report high-resolution Very Large Array (VLA) and European VLBI Network (EVN) observations of HI-21cm absorption from a young, compact steep-spectrum radio source, B2 0258+35, nested in the early-type galaxy NGC 1167, which contains a 160 kpc HI disc. Our VLA and EVN HI absorption observations, modelling, and comparison with molecular gas data suggest that the cold gas in the centre of NGC 1167 is very turbulent (with a velocity dispersion of ~ 90 km/s) and that this turbulence is induced by the interaction of the jets with the interstellar medium (ISM). Furthermore, the ionised gas in the galaxy shows evidence of shock heating at a few kpc from the radio source. These findings support the results from numerical simulations of radio jets expanding into a clumpy gas disc, which predict that the radio jets in this case percolate through the gas disc and drive shocks into the ISM at distances much larger than their physical extent. These results expand the number of low-luminosity radio sources found to impact the surrounding medium, thereby highlighting the possible relevance of these AGN for feedback.

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arXiv2019

The AGN fuelling/feedback cycle in nearby radio galaxies - I. ALMA observations and early results

This is the first paper of a series exploring the multi-frequency properties of a sample of eleven nearby low excitation radio galaxies (LERGs) in the southern sky. We are conducting an extensive study of different galaxy components (stars, warm and cold gas, radio jets) with the aim of improving our understanding of the AGN fuelling/feedback cycle in LERGs. We present ALMA Band 6 $^{12}$CO(2-1) and continuum observations of nine sources. Continuum emission from the radio cores was detected in all objects. Six sources also show mm emission from jets on kpc/sub-kpc scales. The jet structures are very similar at mm and cm wavelengths. We conclude that synchrotron emission associated with the radio jets dominates the continuum spectra up to 230 GHz. The $^{12}$CO(2-1) line was detected in emission in six out of nine objects, with molecular gas masses ranging from $2 \times 10^{7}$ to $2 \times 10^{10}$ M$_{\rm \odot}$. The CO detections show disc-like structures on scales from $\approx$0.2 to $\approx$10 kpc. In one case (NGC 3100) the CO disc presents some asymmetries and is disrupted in the direction of the northern radio jet, indicating a possible jet/disc interaction. In IC 4296, CO is detected in absorption against the radio core, as well as in emission. In four of the six galaxies with CO detections, the gas rotation axes are roughly parallel to the radio jets in projection; the remaining two cases show large misalignments. In those objects where optical imaging is available, dust and CO appear to be co-spatial.

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arXiv2018

LoTSS/HETDEX: Optical quasars I. Low-frequency radio properties of optically selected quasars

The radio-loud/radio-quiet (RL/RQ) dichotomy in quasars is still an open question. Although it is thought that accretion onto supermassive black holes in the centre the host galaxies of quasars is responsible for some radio continuum emission, there is still a debate as to whether star formation or active galactic nuclei (AGN) activity dominate the radio continuum luminosity. To date, radio emission in quasars has been investigated almost exclusively using high-frequency observations in which the Doppler boosting might have an important effect on the measured radio luminosity, whereas extended structures, best observed at low radio frequencies, are not affected by the Doppler enhancement. We used a sample of quasars selected by their optical spectra in conjunction with sensitive and high-resolution low-frequency radio data provided by the LOw Frequency ARray (LOFAR) as part of the LOFAR Two-Metre Sky Survey (LoTSS) to investigate their radio properties using the radio loudness parameter ($\mathcal{R} = \frac{L_{\mathrm{144-MHz}}}{L_{\mathrm{i\,band}}}$). The examination of the radio continuum emission and RL/RQ dichotomy in quasars exhibits that quasars show a wide continuum of radio properties (i.e. no clear bimodality in the distribution of $\mathcal{R}$). Radio continuum emission at low frequencies in low-luminosity quasars is consistent with being dominated by star formation. We see a significant albeit weak dependency of $\mathcal{R}$ on the source nuclear parameters. For the first time, we are able to resolve radio morphologies of a considerable number of quasars. All these crucial results highlight the impact of the deep and high-resolution low-frequency radio surveys that foreshadow the compelling science cases for the Square Kilometre Array (SKA).

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arXiv2018

Science with an ngVLA: Radio Jet-ISM Feedback on Sub-galactic Scales

Energetic feedback by active galactic nuclei (AGNs) plays an important evolutionary role in the regulation of star formation (SF) 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. Given its unique combination of frequency range, angular resolution, and sensitivity, the ngVLA will serve as a transformational new tool in our understanding of how radio jets affect their surroundings. By combining broadband continuum data with measurements of the cold gas content and kinematics, the ngVLA will quantify the energetic impact of radio jets hosted by gas-rich galaxies as the jets interact with the star-forming gas reservoirs of their hosts.

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arXiv2018

EoR Foregrounds: the Faint Extragalactic Radio Sky

A wealth of new data from upgraded and new radio interferometers are rapidly improving and transforming our understanding of the faint extra-galactic radio sky. Indeed the mounting statistics at sub-mJy and uJy flux levels is finally allowing us to get stringent observational constraints on the faint radio population and on the modeling of its the various components. In this paper I will provide a brief overview of the latest results in areas that are potentially important for an accurate treatment of extra-galactic foregrounds in experiments designed to probe the Epoch of Reionization.

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arXiv2018

An ngVLA Wide Area AGN Survey

The next generation Very Large Array (ngVLA) will have unprecedented sensitivities and mapping speeds at $1-8$ GHz. We discuss how the active galactic nuclei (AGN) community can benefit from a wide-area, medium depth ngVLA survey. We propose a 10 deg$^2$ survey in the Stripe 82 field using the 8 GHz band with an rms depth of $1\,μ$Jy beam$^{-1}$. We will detect $\sim$130,000 galaxies, including radio-quiet AGN out to $z\sim7$. We can measure the luminosity and space density evolution of radio-quiet and radio-loud AGN. We can also measure AGN evolution through clustering of both populations using cross-correlation functions. A wide area ngVLA survey will benefit from existing multiwavelength AGN populations, particularly in the Stripe 82 field, as well as new information from next-generation optical and infrared survey instruments such as LSST and WFIRST.

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arXiv2018

Revolutionizing Our Understanding of AGN Feedback and its Importance to Galaxy Evolution in the Era of the Next Generation Very Large Array

Energetic feedback by Active Galactic Nuclei (AGNs) plays an important evolutionary role in the regulation of star formation (SF) 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 km) 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 multi-wavelength 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 pc to a few kpc 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.

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arXiv2018

LOFAR/H-ATLAS: The low-frequency radio luminosity - star-formation rate relation

Radio emission is a key indicator of star-formation activity in galaxies, but the radio luminosity-star formation relation has to date been studied almost exclusively at frequencies of 1.4 GHz or above. At lower radio frequencies the effects of thermal radio emission are greatly reduced, and so we would expect the radio emission observed to be completely dominated by synchrotron radiation from supernova-generated cosmic rays. As part of the LOFAR Surveys Key Science project, the Herschel-ATLAS NGP field has been surveyed with LOFAR at an effective frequency of 150 MHz. We select a sample from the MPA-JHU catalogue of SDSS galaxies in this area: the combination of Herschel, optical and mid-infrared data enable us to derive star-formation rates (SFRs) for our sources using spectral energy distribution fitting, allowing a detailed study of the low-frequency radio luminosity--star-formation relation in the nearby Universe. For those objects selected as star-forming galaxies (SFGs) using optical emission line diagnostics, we find a tight relationship between the 150 MHz radio luminosity ($L_{150}$) and SFR. Interestingly, we find that a single power-law relationship between $L_{150}$ and SFR is not a good description of all SFGs: a broken power law model provides a better fit. This may indicate an additional mechanism for the generation of radio-emitting cosmic rays. Also, at given SFR, the radio luminosity depends on the stellar mass of the galaxy. Objects which were not classified as SFGs have higher 150-MHz radio luminosity than would be expected given their SFR, implying an important role for low-level active galactic nucleus activity.

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arXiv2017

The eMERGE Survey I: Very Large Array 5.5 GHz observations of the GOODS-North Field

We present new observations of the GOODS-N field obtained at 5.5 GHz with the Karl G. Jansky Very Large Array (VLA). The central region of the field was imaged to a median r.m.s. of 3 microJy/beam with a resolution of 0.5 arcsec. From a 14-arcmin diameter region we extracted a sample of 94 radio sources with signal-to-noise ratio greater than 5. Near-IR identifications are available for about 88 percent of the radio sources. We used different multi-band diagnostics to separate active galactic nuclei (AGN), both radiatively efficient and inefficient, from star-forming galaxies. From our analysis, we find that about 80 percent of our radio-selected sample is AGN-dominated, with the fraction raising to 92 percent when considering only the radio sources with redshift >1.5. This large fraction of AGN-dominated radio sources at very low flux densities (the median flux density at 5.5 GHz is 42 microJy), where star-forming galaxies are expected to dominate, is somewhat surprising and at odds with other results. Our interpretation is that both the frequency and angular resolution of our radio observations strongly select against radio sources whose brightness distribution is diffuse on scale of several kpc. Indeed, we find that the median angular sizes of the AGN-dominated sources is around 0.2-0.3 arcsec against 0.8 arcsec for star-forming galaxies. This highlights the key role that high frequency radio observations can play in pinpointing AGN-driven radio emission at microJy levels. This work is part of the eMERGE legacy project.

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arXiv2016

Infrared-Faint Radio Sources in the SERVS deep fields: Pinpointing AGNs at high redshift

Infrared-Faint Radio Sources (IFRS) represent an unexpected class of objects relatively bright at radio wavelength, but unusually faint at infrared (IR) and optical wavelengths. A recent and extensive campaign on the radio-brightest IFRSs (S_{1.4GHz} >= 10 mJy) has provided evidence that most of them (if not all) contain an AGN. Still uncertain is the nature of the radio-faintest ones (S_{1.4GHz} <= 1 mJy). The scope of this paper is to assess the nature of the radio-faintest IFRSs, testing their classification and improving the knowledge of their IR properties making use of the most sensitive IR survey available so far: the Spitzer Extragalactic Representative Volume Survey (SERVS). We also explore how the criteria of IFRSs can be fine-tuned to pinpoint radio-loud AGNs at very high redshift (z > 4). We analysed a number of IFRS samples identified in SERVS fields, including a new sample (21 sources) extracted from the Lockman Hole. 3.6 and 4.5 mum IR counterparts of the 64 sources located in the SERVS fields were searched for, and, when detected, their IR properties were studied. We compared the radio/IR properties of the IR-detected IFRSs with those expected for a number of known classes of objects. We found that they are mostly consistent with a mixture of high-redshift (z >= 3) radio-loud AGNs. The faintest ones (S_{1.4GHz} ~ 100 muJy), however, could be also associated with nearer (z ~ 2) dust-enshrouded star-burst galaxies. We also argue that, while IFRSs with radio-to-IR ratios > 500 can very efficiently pinpoint radio-loud AGNs at redshift 2 < z < 4, lower radio-to-IR ratios (~ 100--200) are expected for higher redshift radio-loud AGNs.

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arXiv2016

Compact radio cores in radio-quiet AGNs

The mechanism of radio emission in radio-quiet (RQ) active galactic nuclei (AGN) is still debated and might arise from the central AGN, from star formation activity in the host, or from either of these sources. A direct detection of compact and bright radio cores embedded in sources that are classified as RQ can unambiguously determine whether a central AGN significantly contributes to the radio emission. We search for compact, high-surface-brightness radio cores in RQ AGNs that are caused unambiguously by AGN activity. We used the Australian Long Baseline Array to search for compact radio cores in four RQ AGNs located in the Extended Chandra Deep Field South (ECDFS). We also targeted four radio-loud (RL) AGNs as a control sample. We detected compact and bright radio cores in two AGNs that are classified as RQ and in one that is classified as RL. Two RL AGNs were not imaged because the quality of the observations was too poor. We report on a first direct evidence of radio cores in RQ AGNs at cosmological redshifts. Our detections show that some of the sources that are classified as RQ contain an active AGN that can contribute significantly (about 50% or more) to the total radio emission.

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arXiv2016

Dying radio galaxies in the LOFAR Lockman Hole

After the jets have switched off, radio galaxies undergo a fading phase which is often named the dying phase. The luminosity evolution of the remnant plasma during this period is still poorly constrained because of the paucity of objects detected. Using the new 150-MHz deep LOFAR observations of the well-known extragalactic field the Lockman Hole, we performed a systematic search of dying radio sources aiming to provide good statistics on their detection and properties. To avoid selection biases towards any specific class of dying sources we used both morphological and spectral selection criteria. To do this we combined the LOFAR data with publicly available surveys at other frequencies as well as dedicated deep observations. Our preliminary results, show that the fraction of candidate dying radio sources is < 6-8% of the entire radio source population and is dominated by steep spectrum sources. By comparing these observational results with statistical modelling of the radio sky population we will be able to constrain the main mechanisms contributing to the dying radio galaxy luminosity evolution.

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