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The continuous histogram shows the distribution of NVSS peak flux densities for the magnitude-limited sample of 2471 SDSS QSOs brighter than mr = +18.5 in the redshift range 1.8 < z < 2.5. The dotted histogram (colored blue in the online version) indicates the distribution of NVSS peak flux densities at "blank sky" positions one degree north of the QSOs, and it is well fit by a Gaussian of mean 〈Sp〉 = −0.014 ± 0.009 mJy beam−1 and rms σ = 0.459 ± 0.009 mJy beam−1 (dotted curve, colored blue in the online version). The dashed curve (colored green in the online version) is the distribution predicted by extrapolating the flux-density distribution of NVSS sources powered primarily by AGNs to lower luminosities, and the continuous black curve represents the distribution predicted by our best-fit model extremely luminous star-forming host galaxies may contribute significantly to the radio emission of high-redshift QSOs.
Source publication
We used the 1.4 GHz NVSS to study radio sources in two color-selected QSO samples: a volume-limited sample of 1313 QSOs defined by M
i < –23 in the redshift range 0.2 < z < 0.45 and a magnitude-limited sample of 2471 QSOs with m
r ≤ 18.5 and 1.8 < z < 2.5. About 10% were detected above the 2.4 mJy NVSS catalog limit and are powered primarily by act...
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Citations
... Other authors (e.g. Mahony et al. 2012 ;Condon et al. 2013 ;Zwart et al. 2015 ) point out several limitations of stacking such as the Figure 6. The distributions of the flux density S ν, peak (top) and 5 GHz rest frame luminosity L ν, 5 GHz (middle row) computed from our 1-2 GHz continuum images at the optical positions of the z > 6 quasars. ...
Quasars at redshifts z > 6 are an excellent probe of the formation and evolution of supermassive black holes in the early Universe. The population of radio-luminous quasars is of particular interest, as such quasars could potentially be used to study the neutral intergalactic medium during cosmic reionization via H i 21 cm absorption studies. However, the lack of deep radio observations of z > 6 quasars leaves the population poorly constrained, and suitable candidates for an H i 21 cm absorption study have yet to be found. In this work, we present Jansky Very Large Array (VLA) 1–2 GHz radio continuum observations of 138 quasars at redshifts 6.0 ≤ z < 7.6. We detect the radio continuum emission of the z = 6.1 quasar J1034−1425, with a 1.6 GHz flux density of $170\pm 36\, \mu$Jy. This quasar is radio-quiet with radio-loudness, R ≡ f5 GHz/fν, 4400 Å = 2.4 ± 0.5. In addition, we detect seven other quasars at z > 6, which have previously been characterized in the literature at these frequencies. Using the full sample, we estimate the radio-loud fraction to be $3.8^{+6.2}_{-2.4}\ \hbox{per cent}$, where the uncertainties are 95 per cent confidence intervals. This is lower than recent estimates of the radio-loud fraction in the literature, but is still marginally consistent with no redshift evolution of the radio-loud fraction. We explore the undetected quasar population by stacking their continuum images at their optical positions and obtain a median stacked flux density of 13.8 ± 3.9 µJy and luminosity of log L5 GHz/(W Hz−1) = 24.2 ± 0.1.
... About 5 per cent-10 per cent of these optically selected sources are found to emit strongly in the radio band, likely due to the presence of relativistic jets (Urry & P ado vani 1995 ), while the remaining 90 per cent are only weak radio sources, whose emission could be purely a result of star formation (SF, e.g. Kimball et al. 2011 ;Condon et al. 2013 ;Kellermann et al. 2016 ). This division into radio-loud (RL) and radio-quiet (RQ) quasars raises the question of whether these two types of objects represent physically distinct populations or different evolutionary stages of a single one. ...
... Some studies find that SF is enough (e.g. Kimball et al. 2011 ;Condon et al. 2013 ), whilst others argue that it must come from AGN, in the form of small-scale jets, AGN-driven winds or disc coronal activity (e.g. Laor & Behar 2008 ;Zakamska et al. 2016 ;White et al. 2015 ;Symeonidis et al. 2016 ;White et al. 2017 ;Morabito et al. 2022 ). ...
We use new 144 MHz observations over 5634 deg2 from the LOFAR Two-metre Sky Survey (LoTSS) to compile the largest sample of uniformly-selected, spectroscopically-confirmed quasars from the 14th data release of the Sloan Digital Sky Survey (SDSS-DR14). Using the classical definition of radio-loudness, R = log (L1.4GHz/Li), we identify 3,697 radio-loud (RL) and 111,132 radio-quiet (RQ) sources at 0.6 < z < 3.4. To study their properties, we develop a new rest-frame spectral stacking algorithm, designed with forthcoming massively-multiplexed spectroscopic surveys in mind, and use it to create high signal-to-noise composite spectra of each class, matched in redshift and absolute i-band magnitude. We show that RL quasars have redder continuum and enhanced [O ii] emission than their RQ counterparts. These results persist when additionally matching in black hole mass, suggesting that this parameter is not the defining factor in making a QSO radio-loud. We find that these features are not gradually varying as a function of radio-loudness but are maintained even when probing deeper into the RQ population, indicating that a clear-cut division in radio-loudness is not apparent. Upon examining the star formation rates (SFRs) inferred from the [O ii] emission line, with the contribution from AGN removed using the [Ne v] line, we find that RL quasars have a significant excess of star-formation relative to RQ quasars out to z = 1.9 at least. Given our findings, we suggest that radio-loud sources either preferably reside in gas-rich systems with rapidly-spinning black holes, or represent an earlier obscured phase of QSO evolution.
... The radio emission from the host can be either non-thermal synchrotron radiation produced by relativistic electrons accelerated by supernovae (e.g. Condon et al. 2013 ) or thermal free-free emission in H II regions ionized by massiv e stars (e.g. P anessa et al. 2019 ). ...
In this work, we revisit the relationship between [O III] line width w90 (as the indicator of AGN outflow velocity) and the radio emission in RQQs by employing a large sample of Type I quasars (∼37, 000) selected from the Sloan Digital Sky Survey (SDSS) Data Release Sixteen. By median stacking the radio images (to include the dominant fraction of individually radio non-detected RQQs) of Karl G. Jansky Very Large Array (VLA) Sky Survey (VLASS) for subsamples of RQQs with different w90, our study demonstrates that, the correlation between w90 and radio emission in our SDSS RQQs is significant, and remains solid after controlling the effects of black hole mass, quasar luminosity, Eddington ratio and redshift. This intrinsic link supports that the [O III] outflows in quasars, most likely resulted from wide-angled sub-relativistic quasar winds launched from the accretion disc, could make a dominant contribution to radio emission in the general RQQs. Alternatively, the correlation may be attributed to low-power jets in RQQs if they are ubiquitous and could efficiently enhance the [O III] width through interacting with the ISM. Meanwhile, the star-formation rates traced by the flux ratio of [Ne V]/[O II] emission lines display no dependence on w90 after controlling the effects of black hole mass, quasar luminosity, Eddington ratio and redshift. This suggests that the stronger radio emission in RQQs with larger w90 could not be attributed to outflow enhanced (positive feedback) star formation in the hosts. However, this also indicates the outflows, though exhibiting robust correlation with radio power, produce neither positive nor negative feedback to the star formation in their hosts.
... On the other hand, multiple authors claim no clear division between AGNs based on their radio loudness (e.g. Cirasuolo et al. 2003a , b ;Balokovi ć et al. 2012 ;Condon et al. 2013 ;G ürkan et al. 2019 ;Macfarlane et al. 2021 ), as the apparent dichotomy is introduced by observational and mathematical biases. ...
... This implies that AGNs in the stacked sample, even though they are close to the faint end of the LF, generally exceed the radio powers of 10 22-23 W Hz −1 characteristic for star formation in starburst galaxies (e.g. Condon et al. 1991 ;Kharb et al. 2006 ;Alexandroff et al. 2012 ;Condon et al. 2013 ), thus belong to the intermediate-luminosity population (e.g. Best et al. 2005 ;Smol či ć et al. 2017b ;Shobhana et al. 2023 ) at both frequency bands. ...
... radio emission mechanism in the sub-mJy sources is AGN activity (e.g. Condon et al. 2013 ;Jarvis et al. 2021 ). ...
Using empty-field ‘Quick Look’ images from the first two epochs of the VLA Sky Survey (VLASS) observations, centred on the positions of ∼3700 individually radio-non-detected active galactic nuclei (AGNs) at z ≥ 4, we performed image stacking analysis to examine the sub-mJy emission at 3 GHz. We found characteristic monochromatic radio powers of Pchar = (2–13) × 1024 W Hz−1, indicating that AGN-related radio emission is widespread in the sample. The signal-to-noise ratios of the redshift-binned median stacked maps are between 4–6, and we expect that with the inclusion of the yet to be completed third-epoch VLASS observations, the detection limit defined as signal-to-noise ratio SNR ≥ 6 could be reached, and the redshift dependence can be determined. To obtain information on the general spectral properties of the faint radio emission in high-redshift AGNs, we confined the sample to ∼3000 objects covered by both the VLASS and the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey. We found that the flux densities from the median stacked maps show a characteristic spectral index of α* = −0.30 ± 0.15, which is in agreement with the median spectral index of the radio-detected z ≥ 4 AGNs from our high-redshift AGN catalogue. The three-band mid-infrared colour–colour diagram based on Wide-field Infrared Survey Explorer observations provides further support regarding the AGN contribution to the radio emission in the sub-mJy sample.
... Alternatively star formation driven outflows and quasar winds that shock the ISM may be responsible for producing the observed radio emission and correlation with outflow properties (e.g. Condon et al. 2013;Nims et al. 2015;Zakamska et al. 2016;Hwang et al. 2018;Panessa et al. 2019). ...
We present a comprehensive study of the molecular gas properties of 17 Type 2 quasars at z < 0.2 from the Quasar Feedback Survey (L$_{\rm [O~{\small III}]}$ > 1042.1 $\rm ergs^{-1}$), selected by their high [O iii] luminosities and displaying a large diversity of radio jet properties, but dominated by LIRG-like galaxies. With these data, we are able to investigate the impact of AGN and AGN feedback mechanisms on the global molecular interstellar medium. Using APEX and ALMA ACA observations, we measure the total molecular gas content using the CO(1-0) emission and homogeneously sample the CO spectral line energy distributions (SLEDs), observing CO transitions (Jup = 1, 2, 3, 6, 7). We observe high r21 ratios (r21 = L’CO(2-1)/L’CO(1-0)) with a median r21 = 1.06, similar to local (U)LIRGs (with r21 ∼ 1) and higher than normal star-forming galaxies (with r21 ∼ 0.65). Despite the high r21 values, for the 7 targets with the required data we find low excitation in CO(6-5) & CO(7-6) (r61 and r62 < 0.6 in all but one target), unlike high redshift quasars in the literature, which are far more luminous and show higher line ratios. The ionised gas traced by [O iii] exhibit systematically higher velocities than the molecular gas traced by CO. We conclude that any effects of quasar feedback (e.g. via outflows and radio jets) do not have a significant instantaneous impact on the global molecular gas content and excitation and we suggest that it only occurs on more localised scales.
... In addition, the brightness temperature of a radio source is an indicator that distinguishes between star formation and AGN. While the brightness temperatures of star-forming galaxies do not exceed 10 5 K (Condon 1992 ;Condon et al. 2013 ), the brightness temperatures of AGN-related radio emission typically exceeds 10 8 K, especially in VLBI observations (e.g. Blundell & Beasley 1998 ;Ulvestad, Antonucci & Barvainis 2005 ;Alhosani et al. 2022 ;Wang et al. 2023a ). ...
This study uses multifrequency very long baseline interferometry (VLBI) to study the radio emission from 10 radio-quiet quasars (RQQs) and four radio-loud quasars (RLQs). The diverse morphologies, radio spectra, and brightness temperatures observed in the VLBI images of these RQQs, together with the variability in their GHz spectra and VLBI flux densities, shed light on the origins of their nuclear radio emission. The total radio emission of RQQs appears to originate from non-thermal synchrotron radiation due to a combination of active galactic nuclei and star formation activities. However, our data suggest that the VLBI-detected radio emission from these RQQs is primarily associated with compact jets or corona, with extended emissions such as star formation and large-scale jets being resolved by the high resolution of the VLBI images. Wind emission models are not in complete agreement the VLBI observations. Unlike RLQs, where the parsec-scale radio emission is dominated by a relativistically boosted core, the radio cores of RQQs are either not dominant or are mixed with significant jet emission. RQQs with compact cores or core-jet structures typically have more pronounced variability, with flat or inverted spectra, whereas jet-dominated RQQs have steep spectra and unremarkable variability. Future high-resolution observations of more RQQs could help to determine the fraction of different emission sources and their associated physical mechanisms.
... In addition, the brightness temperature of a radio source is an indicator that distinguishes between star formation and AGN. While the brightness temperatures of star-forming galaxies do not exceed 10 5 K (Condon 1992;Condon et al. 2013), the brightness temperatures of AGN-related radio emission typically exceeds 10 8 K, especially in VLBI observations (e.g. Blundell & Beasley 1998;Ulvestad et al. 2005;Alhosani et al. 2022;Wang et al. 2023a). ...
This study uses multi-frequency Very Long Baseline Interferometry (VLBI) to study the radio emission from 10 radio-quiet quasars (RQQs) and four radio-loud quasars (RLQs). The diverse morphologies, radio spectra, and brightness temperatures observed in the VLBI images of these RQQs, together with the variability in their GHz spectra and VLBI flux densities, shed light on the origins of their nuclear radio emission. The total radio emission of RQQs appears to originate from non-thermal synchrotron radiation due to a combination of active galactic nuclei and star formation activities. However, our data suggest that the VLBI-detected radio emission from these RQQs is primarily associated with compact jets or corona, with extended emissions such as star formation and large-scale jets being resolved by the high resolution of the VLBI images. Wind emission models are not in complete agreement the VLBI observations. Unlike RLQs, where the parsec-scale radio emission is dominated by a relativistically boosted core, the radio cores of RQQs are either not dominant or are mixed with significant jet emission. RQQs with compact cores or core-jet structures typically have more pronounced variability, with flat or inverted spectra, whereas jet-dominated RQQs have steep spectra and unremarkable variability. Future high-resolution observations of more RQQs could help to determine the fraction of different emission sources and their associated physical mechanisms.
... AGN activity and enhanced SF are often related. The SF radio emission (Bell 2003) may be responsible for the bulk of the radio emission observed in RQQ ★ E-mail: sina.chen@campus.technion.ac.il (Kimball et al. 2011;Condon et al. 2013;Zakamska et al. 2016). If so, the radio emission would be predominantly optically thin synchrotron radiation ( < −0.5), and its radio morphology would be similar to other tracers of SF (e.g. ...
The origin of the radio emission in radio-quiet quasars (RQQ) is not established yet. We present new VLBA observations at 1.6 and 4.9 GHz of ten RQQ (nine detected), which together with published earlier observations of eight RQQ (five detected), forms a representative sample of 18 RQQ drawn from the Palomar-Green sample of low z (< 0.5) AGN. The spectral slope of the integrated emission extends from very steep (alpha < -1.98) to strongly inverted (alpha = +2.18), and the slopes of nine of the 14 objects are flat (alpha > -0.5). Most objects have an unresolved flat-spectrum core, which coincides with the optical Gaia position. The extended emission is generally steep-spectrum, has a low brightness temperature (< 10^7 K), and is displaced from the optical core (the Gaia position) by ~ 5-100 pc. The VLBA core flux is tightly correlated with the X-ray flux, and follows a radio to X-ray luminosity relation of log L_R/L_X = -6, for all objects with a black hole mass log M_BH/M_Sun < 8.5. The flatness of the core emission implies a compact source size (< 0.1 pc), which likely originates from the accretion disk corona. The mas-scale extended emission is optically thin and of clumpy structure, and is likely produced by an outflow from the center. Radio observations at higher frequencies can further test the accretion disk coronal emission interpretation for the core emission in RQQ.
... In the paper Rakshit et al. (2020) were provided the logarithmic black hole mass (8.658600 ± 0.027332), and logarithmic Eddington ratio (-0.853556), both calculated based on Hβ, Mg II and C IV lines. Absolute i band magnitude is -24.134 from (Condon et al. 2013). The spectral index difference of 0.006 is given in paper (Krawczyk et al. 2015). ...
Here we present the first optical photometric monitoring results of a sample of twelve newly discovered blazars from the ICRF - Gaia CRF astrometric link. The observations were performed from April 2013 until August 2019 using eight telescopes located in Europe. For a robust test for the brightness and colour variability, we use Abbe criterion and F-test. Moreover, linear fittings are performed to investigate the relation in the colour-magnitude variations of the blazars. Variability was confirmed in the case of 10 sources; two sources, 1429+249 and 1556+335 seem to be possibly variable. Three sources (1034+574, 1722+119, and 1741+597) have displayed large amplitude brightness change of more than one magnitude. We found that the seven sources displayed bluer-when-brighter variations, and one source showed redder-when-brighter variations. We briefly explain the various AGN emission models which can explain our results.
... The excess of measured flux at radio wavelengths suggests that we are seeing AGN emission in addition to synchrotron emission from star formation. 37 This is in line with current models of QSO evolution, which suggest that coexistence of dust-obscured star formation and AGN activity is typical of most QSOs (e.g., Condon et al. 2013;Stacey et al. 2018). We can explain the mismatch in the HST-derived and radio/submillimeter-derived A/B flux ratios if the radio emission consists of a combination of point-like AGN emission and star-formation-related emission. ...
We present the discovery of a gravitationally lensed dust-reddened QSO at z = 2.517, identified in a survey for QSOs by infrared selection. Hubble Space Telescope imaging reveals a quadruply lensed system in a cusp configuration, with a maximum image separation of ∼1.″8. We find that, compared to the central image of the cusp, the neighboring brightest image is anomalous by a factor of ∼7–10, which is the largest flux anomaly measured to date in a lensed QSO. Incorporating high-resolution Very Large Array radio imaging and submillimeter imaging with the Atacama Large Millimeter/submillimeter Array, we conclude that a low-mass perturber is the most likely explanation for the anomaly. The optical through near-infrared spectrum reveals that the QSO is moderately reddened with E ( B − V ) ≃ 0.7–0.9. We see an upturn in the ultraviolet spectrum due to ∼1% of the intrinsic emission being leaked back into the line of sight, which suggests that the reddening is intrinsic and not due to the lens. The QSO may have an Eddington ratio as high as L / L Edd ≈ 0.2. Consistent with previous red QSO samples, this source exhibits outflows in its spectrum, as well as morphological properties suggestive of it being in a merger-driven transitional phase. We find a host galaxy stellar mass of log M ⋆ / M ⊙ = 11.4 , which is higher than the local M BH versus M ⋆ relation but consistent with other high-redshift QSOs. When demagnified, this QSO is at the knee of the luminosity function, allowing for the detailed study of a more typical moderate-luminosity infrared-selected QSO at high redshift.
