arXiv subjects

E. Momjian

Publications and source records attributed to E. Momjian.

At least 55 records · Page 3Linked to original sources

arXiv2018

Discovery of OH absorption from a galaxy at z~0.05: implications for large surveys with SKA pathfinders

We present the first detection of OH absorption in diffuse gas at $z>0$, along with another eight stringent limits on OH column densities for cold atomic gas in galaxies at $0 $13.6) to be $n_{\rm OH}$ = $0.008^{+0.018}_{-0.008}$ at $z\sim0.1$. Based on this we expect to detect 10$^{+20}_{-10}$ such OH absorbers from the MeerKAT Absorption Line Survey. Using HI 21-cm and OH 1667 MHz absorption lines detected towards Q0248+430, we estimate ($ΔF/F$) = (5.2$\pm$4.5)$\times 10^{-6}$, where $F \equiv g_p (α^2/μ)^{1.57}$, $α$ $-$ the fine structure constant, $μ$ $-$ the electron-proton mass ratio and $g_p$ $-$ the proton gyromagnetic ratio. This corresponds to $Δα/α$($z=0.0519$) = (1.7 $\pm$ 1.4)$\times 10^{-6}$, which is among the stringent constraints on the fractional variation of $α$.

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arXiv2018

A New Detection of Extragalactic Anomalous Microwave Emission in a Compact, Optically-Faint Region of NGC\,4725

We discuss the nature of a discrete, compact radio source (NGC 4725 B) located $\approx$1.9 kpc from the nucleus in the nearby star-forming galaxy NGC 4725, which we believe to be a new detection of extragalactic Anomalous Microwave Emission (AME). Based on detections at 3, 15, 22, 33, and 44 GHz, NGC 4725 B is a $μ$Jy radio source peaking at $\approx$33 GHz. While the source is not identified in $BVRI$ photometry, we detect counterparts in the mid-infrared $Spitzer$/IRAC bands (3.6, 4.5, 5.8, 8.0 $μ$m) that appear to be associated with dust emission in the central region of NGC 4725. Consequently, we conclude that NGC 4725 B is a new detection of AME, and very similar to a recent detection of AME in an outer-disk star-forming region in NGC 6946. We find that models of electric dipole emission from rapidly rotating ultra-small grains are able to reproduce the radio spectrum for reasonable interstellar medium conditions. Given the lack of an optical counterpart and the shape of the radio spectrum, NGC 4725 B appears consistent with a nascent star-forming region in which young ($\lesssim 3$ Myr) massive stars are still highly enshrouded by their natal cocoons of gas and dust with insufficient supernovae occurring to produce a measurable amount of synchrotron emission.

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arXiv2018

VLBA+GBT observations of the COSMOS field and radio source counts at 1.4 GHz

We present very long baseline interferometry (VLBI) observations of 179 radio sources in the COSMOS field with extremely high sensitivity using the Green Bank Telescope (GBT) together with the Very Long Baseline Array (VLBA) (VLBA+GBT) at 1.4 GHz, to explore the faint radio population in the flux density regime of tens of $μ$Jy. Here, the identification of active galactic nuclei (AGN) is based on the VLBI detection of the source, i.e., it is independent of X-ray or infrared properties. The milli-arcsecond resolution provided by the VLBI technique implies that the detected sources must be compact and have large brightness temperatures, and therefore they are most likely AGN (when the host galaxy is located at z$\geq$0.1). On the other hand, this technique allows us to only positively identify when a radio-active AGN is present, i.e., we cannot affirm that there is no AGN when the source is not detected. For this reason, the number of identified AGN using VLBI should be always treated as a lower limit. We present a catalogue containing the 35 radio sources detected with the VLBA+GBT, 10 of which were not previously detected using only the VLBA. We have constructed the radio source counts at 1.4 GHz using the samples of the VLBA and VLBA+GBT detected sources of the COSMOS field to determine a lower limit for the AGN contribution to the faint radio source population. We found an AGN contribution of >40-75% at flux density levels between 150 $μ$Jy and 1 mJy. This flux density range is characterised by the upturn of the Euclidean-normalised radio source counts, which implies a contribution of a new population. This result supports the idea that the sub-mJy radio population is composed of a significant fraction of radio-emitting AGN, rather than solely by star-forming galaxies, in agreement with previous studies.

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arXiv2017

The Star Formation in Radio Survey: Jansky Very Large Array 33 GHz Observations of Nearby Galaxy Nuclei and Extranuclear Star-Forming Regions

We present 33 GHz imaging for 112 pointings towards galaxy nuclei and extranuclear star-forming regions at $\approx$2" resolution using the Karl G. Jansky Very Large Array (VLA) as part of the Star Formation in Radio Survey. A comparison with 33 GHz Robert C. Byrd Green Bank Telescope single-dish observations indicates that the interferometric VLA observations recover $78\pm4 %$ of the total flux density over 25" regions ($\approx$ kpc-scales) among all fields. On these scales, the emission being resolved out is most likely diffuse non-thermal synchrotron emission. Consequently, on the $\approx30-300$ pc scales sampled by our VLA observations, the bulk of the 33 GHz emission is recovered and primarily powered by free-free emission from discrete HII regions, making it an excellent tracer of massive star formation. Of the 225 discrete regions used for aperture photometry, 162 are extranuclear (i.e., having galactocentric radii $r_{\rm G} \geq 250$ pc) and detected at $>3σ$ significance at 33 GHz and in H$α$. Assuming a typical 33 GHz thermal fraction of 90 %, the ratio of optically-thin 33 GHz-to-uncorrected H$α$ star formation rates indicate a median extinction value on $\approx30-300$ pc scales of $A_{\rm Hα} \approx 1.26\pm0.09$ mag with an associated median absolute deviation of 0.87 mag. We find that 10 % of these sources are "highly embedded" (i.e., $A_{\rm Hα}\gtrsim3.3$ mag), suggesting that on average HII regions remain embedded for $\lesssim1$ Myr. Finally, we find the median 33 GHz continuum-to-H$α$ line flux ratio to be statistically larger within $r_{\rm G}<250$ pc relative the outer-disk regions by a factor of $1.82\pm0.39$, while the ratio of 33 GHz-to-24 $μ$m flux densities are lower by a factor of $0.45\pm0.08$, which may suggest increased extinction in the central regions.

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arXiv2017

The MeerKAT Absorption Line Survey (MALS)

Deep galaxy surveys have revealed that the global star formation rate (SFR) density in the Universe peaks at 1 < z < 2 and sharply declines towards z = 0. But a clear picture of the underlying processes, in particular the evolution of cold atomic (~100 K) and molecular gas phases, that drive such a strong evolution is yet to emerge. MALS is designed to use MeerKAT's L- and UHF-band receivers to carry out the most sensitive (N(HI)>10$^{19}$ cm$^{-2}$) dust-unbiased search of intervening HI 21-cm and OH 18-cm absorption lines at 0 < z < 2. This will provide reliable measurements of the evolution of cold atomic and molecular gas cross-sections of galaxies, and unravel the processes driving the steep evolution in the SFR density. The large sample of HI and OH absorbers obtained from the survey will (i) lead to tightest constraints on the fundamental constants of physics, and (ii) be ideally suited to probe the evolution of magnetic fields in disks of galaxies via Zeeman Splitting or Rotation Measure synthesis. The survey will also provide an unbiased census of HI and OH absorbers, i.e. cold gas associated with powerful AGNs (>10$^{24}$ W Hz$^{-1}$) at 0 < z < 2, and will simultaneously deliver a blind HI and OH emission line survey, and radio continuum survey. Here, we describe the MALS survey design, observing plan and the science issues to be addressed under various science themes.

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arXiv2017

The faint radio sky: VLBA observations of the COSMOS field

We study the faint radio population using wide-field very long baseline interferometry (VLBI) observations of 2865 known radio sources in the Cosmic Evolution Survey (COSMOS) field. The main objective of the project was to determine where active galactic nuclei (AGN) are present. The combination of number of sources, sensitivity, angular resolution and area covered by this project are unprecedented. We have detected 468 radio sources, expected to be AGNs, with the Very Long Baseline Array (VLBA) at 1.4 GHz. This is, to date, the largest sample assembled of VLBI detected sources in the sub-mJy regime. The input sample was taken from previous observations with the Very Large Array (VLA). We present the catalogue with additional multiwavelength information. We find a detection fraction of 20%, considering only those sources from the input catalogue which were in principle detectable with the VLBA (2361). As a function of redshift, we see no evolution of the detection fraction over the redshift range 0.5 1.5 we find that spiral galaxies become the most prevalent (48%). We demonstrate that wide-field VLBI observations, together with new calibration methods such as multi-source self-calibration and mosaicing, result in information which is difficult or impossible to obtain otherwise.

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arXiv2017

A 33 GHz Survey of Local Major Mergers: Estimating the Sizes of the Energetically Dominant Regions from High Resolution Measurements of the Radio Continuum

We present Very Large Array observations of the 33 GHz radio continuum emission from 22 local ultraluminous and luminous infrared (IR) galaxies (U/LIRGs). These observations have spatial (angular) resolutions of 30--720 pc (0.07"-0.67") in a part of the spectrum that is likely to be optically thin. This allows us to estimate the size of the energetically dominant regions. We find half-light radii from 30 pc to 1.7 kpc. The 33 GHz flux density correlates well with the IR emission, and we take these sizes as indicative of the size of the region that produces most of the energy. Combining our 33 GHz sizes with unresolved measurements, we estimate the IR luminosity and star formation rate per area, and the molecular gas surface and volume densities. These quantities span a wide range (4 dex) and include some of the highest values measured for any galaxy (e.g., $\mathrm{Σ_{SFR}^{33GHz} \leq 10^{4.1} M_{\odot} yr^{-1} kpc^{-2}}$). At least $13$ sources appear Compton thick ($\mathrm{N_{H}^{33GHz} \geq 10^{24} cm^{-2}}$). Consistent with previous work, contrasting these data with observations of normal disk galaxies suggests a nonlinear and likely multi-valued relation between SFR and molecular gas surface density, though this result depends on the adopted CO-to-H$_{2}$ conversion factor and the assumption that our 33 GHz sizes apply to the gas. 11 sources appear to exceed the luminosity surface density predicted for starbursts supported by radiation pressure and supernovae feedback, however we note the need for more detailed observations of the inner disk structure. U/LIRGs with higher surface brightness exhibit stronger [{\sc Cii}] 158$μ$m deficits, consistent with the suggestion that high energy densities drive this phenomenon.

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arXiv2016

The Zeeman Effect in the 44 GHz Class I Methanol Maser Line toward DR21(OH)

We report the detection of the Zeeman effect in the 44 GHz Class I methanol maser line toward the star forming region DR21(OH). In a 219 Jy/beam maser centered at an LSR velocity of 0.83 km s$^{-1}$, we find a 20-$σ$ detection of $zB_{\text{los}} = 53.5 \pm 2.7$ Hz. If 44 GHz methanol masers are excited at $n \sim 10^{7-8}$ cm$^{-3}$, then the $B~vs.~n^{1/2}$ relation would imply from comparison with Zeeman effect detections in the CN($1-0$) line toward DR21(OH) that magnetic fields traced by 44 GHz methanol masers in DR21(OH) should be $\sim$10 mG. Together with our detected $zB_{\text{los}} = 53.5$ Hz, this would imply that the value of the 44 GHz methanol Zeeman splitting factor $z$ is $\sim$5 Hz mG$^{-1}$. Such small values of $z$ would not be a surprise, as the methanol molecule is non paramagnetic, like H$_2$O. Empirical attempts to determine $z$, as demonstrated, are important because currently there are no laboratory measurements or theoretically calculated values of $z$ for the 44 GHz methanol transition. Data from observations of a larger number of sources are needed to make such empirical determinations robust.

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arXiv2016

HI 21-cm absorption survey of quasar-galaxy pairs: Distribution of cold gas around z<0.4 galaxies

We present the results from our survey of HI 21-cm absorption, using GMRT, VLA and WSRT, in a sample of 55 z<0.4 galaxies towards radio sources with impact parameters (b) in the range ~0-35 kpc. In our primary sample (defined for statistical analyses) of 40 quasar-galaxy-pairs (QGPs), probed by 45 sightlines, we have found seven HI 21-cm absorption detections, two of which are reported here for the first time. Combining our primary sample with measurements having similar optical depth sensitivity ($\intτdv$ <= 0.3 km/s) from the literature, we find a weak anti-correlation (rank correlation coefficient = -0.20 at 2.42sigma level) between $\intτdv$ and b, consistent with previous literature results. The covering factor of HI 21-cm absorbers (C_21) is estimated to be 0.24 (+0.12/-0.08) at b <= 15 kpc and 0.06 (+0.09/-0.04) at b = 15-35 kpc. $\intτdv$ and C_21 show similar declining trend with radial distance along the galaxy's major axis and distances scaled with the effective HI radius. There is also tentative indication that most of the HI 21-cm absorbers could be co-planar with the extended HI discs. No significant dependence of $\intτdv$ and C_21 on galaxy luminosity, stellar mass, colour and star formation rate is found, though the HI 21-cm absorbing gas cross-section may be larger for the luminous galaxies. The higher detection rate (by a factor of ~4) of HI 21-cm absorption in z<1 DLAs compared to the QGPs indicates towards small covering factor and patchy distribution of cold gas clouds around low-z galaxies.

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arXiv2016

New Constraints on the Molecular Gas in the Prototypical HyLIRGs BRI1202-0725 & BRI1335-0417

We present Karl G Jansky Very Large Array (VLA) observations of CO(2-1) line emission and rest-frame 250GHz continuum emission of the Hyper-Luminous IR Galaxies (HyLIRGs) BRI1202-0725 (z=4.69) and BRI1335-0417 (z=4.41), with an angular resolution as high as 0.15". Our low order CO observations delineate the cool molecular gas, the fuel for star formation in the systems, in unprecedented detail. For BRI1202-0725, line emission is seen from both extreme starburst galaxies: the quasar host and the optically obscured submm galaxy (SMG), in addition to one of the Lyman-alpha emitting galaxies in the group. Line emission from the SMG shows an east-west extension of about 0.6". For Lyalpha-2, the CO emission is detected at the same velocity as [CII] and [NII], indicating a total gas mass ~4.0*10^10 solar masses. The CO emission from BRI1335-0417 peaks at the nominal quasar position, with a prominent northern extension (~1", a possible tidal feature). The gas depletion timescales are ~10^7 years for the three HyLIRGs, consistent with extreme starbursts, while that of Lyalpha-2 may be consistent with main sequence galaxies. We interpret these sources as major star formation episodes in the formation of massive galaxies and supermassive black holes (SMBHs) via gas rich mergers in the early Universe.

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arXiv2015

The Arecibo Galaxy Environment Survey IX: The Isolated Galaxy Sample

We have used the Arecibo L-band Feed Array to map three regions, each of 5 square degrees, around the isolated galaxies NGC 1156, UGC 2082, and NGC 5523. In the vicinity of these galaxies we have detected two dwarf companions: one near UGC 2082, previously discovered by ALFALFA, and one near NGC 1156, discovered by this project and reported in an earlier paper. This is significantly fewer than the 15.4 $^{+1.7}_{-1.5}$ that would be expected from the field HI mass function from ALFALFA or the 8.9 $\pm$ 1.2 expected if the HI mass function from the Local Group applied in these regions. The number of dwarf companions detected is, however, consistent with a flat or declining HI mass function as seen by a previous, shallower, HI search for companions to isolated galaxies.We attribute this difference in Hi mass functions to the different environments in which they are measured. This agrees with the general observation that lower ratios of dwarf to giant galaxies are found in lower density environments.

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arXiv2015

HI 21cm emission from the sub-damped Lyman-alpha absorber at z=0.0063 towards PG1216+069

We present HI 21cm emission observations of the z ~ 0.00632 sub-damped Lyman-alpha absorber (sub-DLA) towards PG1216+069 made using the Arecibo Telescope and the Very Large Array (VLA). The Arecibo 21cm spectrum corresponds to an HI mass of ~ 3.2x10^7 solar masses, two orders of magnitude smaller than that of a typical spiral galaxy. This is surprising since in the local Universe the cross-section for absorption at high HI column densities is expected to be dominated by spirals. The 21cm emission detected in the VLA spectral cube has a low signal-to-noise ratio, and represents only half the total flux seen at Arecibo. Emission from three other sources is detected in the VLA observations, with only one of these sources having an optical counterpart. This group of HI sources appears to be part of complex "W", believed to lie in the background of the Virgo cluster. While several HI cloud complexes have been found in and around the Virgo cluster, it is unclear whether the ram pressure and galaxy harassment processes that are believed to be responsible for the creation of such clouds in a cluster environment are relevant at the location of this cloud complex. The extremely low metallicity of the gas, ~ 1/40 solar, also makes it unlikely that the sub-DLA consists of material that has been stripped from a galaxy. Thus, while our results have significantly improved our understanding of the host of this sub-DLA, the origin of the gas cloud remains a mystery

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arXiv2015

Circumnuclear and infalling HI gas in a merging galaxy pair at z=0.123

Using long-slit optical spectra obtained with the 2-m telescope at IUCAA Girawali Observatory, we show that the radio source J094221.98+062335.2 (z=0.123) is associated with a galaxy pair undergoing a major merger. Its companion is a normal star-forming galaxy infalling with a velocity of 185 km/s at a projected separation of 4.8 kpc. Using the Westerbork Synthesis Radio Telescope (WSRT) and Giant Metrewave Radio Telescope (GMRT) we detect a strong HI 21-cm absorption at the systemic redshift of the radio galaxy with N(HI)~9x10^21 cm^{-2} for an assumed spin-temperature of 100 K. Such a strong HI 21-cm absorption is rare and has been seen only in a few compact radio sources associated with similar merging galaxy pairs. Milliarcsecond resolution Very Long Baseline Array (VLBA) observations resolve the radio source into a compact symmetric object with the hotspot separation of 89 pc. The 21-cm absorption is detected in the VLBA spectra towards both the radio lobes albeit with a strong optical depth gradient. We show that the strong 21-cm absorption is consistent with it being arising from a clumpy circumnuclear disk/torus. We also detect two weaker absorption lines redshifted with respect to the radio source in the WSRT/GMRT spectrum. They probably represent cold (i.e. T< 10^4 K) HI gas falling into the radio source. The presence of high concentration of HI gas in the circumnuclear regions and signature of infalling cold gas allows us to conjecture that the young radio source may have been triggered by the gas infall due to the ongoing merger.

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arXiv2015

A Semi-automatic Search for Giant Radio Galaxy Candidates and their Radio-Optical Follow-up

We present results of a search for giant radio galaxies (GRGs) with a projected largest linear size in excess of 1 Mpc. We designed a computational algorithm to identify contiguous emission regions, large and elongated enough to serve as GRG candidates, and applied it to the entire 1.4-GHz NRAO VLA Sky survey (NVSS). In a subsequent visual inspection of 1000 such regions we discovered 15 new GRGs, as well as many other candidate GRGs, some of them previously reported, for which no redshift was known. Our follow-up spectroscopy of 25 of the brighter hosts using two 2.1-m telescopes in Mexico, and four fainter hosts with the 10.4-m Gran Telescopio Canarias (GTC), yielded another 24 GRGs. We also obtained higher-resolution radio images with the Karl G. Jansky Very Large Array for GRG candidates with inconclusive radio structures in NVSS.

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arXiv2015

Cold parsec-scale gas in a zabs~0.1 sub-DLA with disparate H2 and 21-cm absorption

We present a detailed analysis of a H2-bearing metal-rich sub-damped Lyman-alpha system at zabs = 0.10115 towards the radio-loud quasar J0441-4313, at a projected separation of ~7.6 kpc from a star-forming galaxy. The H2, C I and Na I absorption are much stronger in the redder of the two components seen in the Hubble Space Telescope / Cosmic Origins Spectrograph spectrum. The best single component fit to the strong H2 component gives log N(H2) = 16.61 +/- 0.05. However, possible hidden saturation in the medium resolution spectrum can allow for log N(H2) to be as high as 18.9. The rotational excitation temperature of H2 in this component is 133 +33/-22 K. Photoionization models suggest 30-80% of the total N(H I) is associated with the strong H2 component, that has a density <= 100 cm^-3 and is subject to a radiation field that is <= 0.5 times the Galactic mean field. The Very Large Baseline Array 1.4 GHz continuum image of the radio source contains only 27% of the arcsecond scale emission. Using a previously published spectrum, no 21-cm absorption is found to be associated with the strong H2 component. This suggests that either the N(H I) associated with this component is <= 50% of the total N(H I) or the gas covering factor is <= 0.27. This is consistent with the results of the photoionization model that uses UV radiation due to stars in the associated galaxy. The 21-cm absorption previously reported from the weaker H2 component suggests a spin temperature of <= 90 K, at odds with the weakness of H2, C I and Na I absorption in this component. From the inferred physical and chemical conditions, we suggest that the gas may be tracing a recent metal-rich outflow from the host-galaxy.

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arXiv2014

Galaxies in HI 21-cm absorption at z<3.5

We present recent results from our searches of 21-cm absorption using GBT, GMRT, VLBA and WSRT to trace the evolution of cold gas in galaxies. Using ~130 sight lines with 21-cm absorption measurements, we find that within the measurement uncertainty, the 21-cm detection rate in strong MgII systems is constant over 0.5 2 DLAs with both 21-cm and H$_2$ (another tracer of cold gas) absorption measurements, we report two new H$_2$ detections and find that in 8/13 cases neither 21-cm nor H$_2$ is detected. This confirms that the HI gas in z>2 DLAs is predominantly warm. Interestingly, there are two cases where 21-cm absorption is not detected despite the presence of H$_2$ with evidence for the presence of cold gas. This can be explained if H$_2$ components seen in DLA are compact (<15 pc) and contain <10% of the total N(HI). We briefly discuss results from our ongoing survey to identify 21-cm absorbers at low-z to establish connection between 21-cm absorbers and galaxies, and constrain the extent of absorbing gas.

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arXiv2013

The spin temperature of high-redshift damped Lyman-$α$ systems

We report results from a programme aimed at investigating the temperature of neutral gas in high-redshift damped Lyman-$α$ absorbers (DLAs). This involved (1) HI 21cm absorption studies of a large DLA sample, (2) VLBI studies to measure the low-frequency quasar core fractions, and (3) optical/ultraviolet spectroscopy to determine DLA metallicities and velocity widths. Including literature data, our sample consists of 37 DLAs with estimates of the spin temperature $T_s$ and the covering factor. We find a strong $4σ$) difference between the $T_s$ distributions in high-z (z>2.4) and low-z (z<2.4) DLA samples. The high-z sample contains more systems with high $T_s$ values, $\gtrsim 1000$ K. The $T_s$ distributions in DLAs and the Galaxy are also clearly (~$6σ$) different, with more high-$T_s$ sightlines in DLAs than in the Milky Way. The high $T_s$ values in the high-z DLAs of our sample arise due to low fractions of the cold neutral medium. For 29 DLAs with metallicity [Z/H] estimates, we confirm the presence of an anti-correlation between $T_s$ and [Z/H], at $3.5σ$ significance via a non-parametric Kendall-tau test. This result was obtained with the assumption that the DLA covering factor is equal to the core fraction. Monte Carlo simulations show that the significance of the result is only marginally decreased if the covering factor and the core fraction are uncorrelated, or if there is a random error in the inferred covering factor. We also find evidence for redshift evolution in DLA $T_s$ values even for the z>1 sub-sample. Since z>1 DLAs have angular diameter distances comparable to or larger than those of the background quasars, they have similar efficiency in covering the quasars. Low covering factors in high-z DLAs thus cannot account for the observed redshift evolution in spin temperatures. (Abstract abridged.)

astro-ph.CO↗

arXiv2013

The Highest Redshift Quasar at $z=7.085$: A Radio Quiet Source

We present 1-2 GHz Very Large Array A-configuration continuum observations on the highest redshift quasar known to date, the $z=7.085$ quasar ULAS J112001.48+064124.3. The results show no radio continuum emission at the optical position of the quasar or its vicinity at a level of $\geq 3σ$ or $23.1 μ$Jy beam$^{-1}$. This $3σ$ limit corresponds to a rest frame 1.4 GHz luminosity density limit of $L_{ν,1.4\,GHz} < 1.76 \times 10^{24}$ W Hz$^{-1}$ for a spectral index of $α=0$, and $L_{ν,1.4\,GHz} < 1.42 \times 10^{25}$ W Hz$^{-1}$ for a spectral index of $α=-1$. The rest-frame 1.4 GHz luminosity limits are $L_{rad} < 6.43 \times 10^6 L_{\odot}$ and $L_{\rm rad} < 5.20 \times 10^7 L_{\odot}$ for $α=0$ and $α=-1$, respectively. The derived limits for the ratio of the rest frame 1.4 GHz luminosity density to the $B$-band optical luminosity density are $R\rlap{}_{1.4}^{*} < 0.53$ and $< 4.30$ for the above noted spectral indices, respectively. Given our upper limits on the radio continuum emission and the radio-to-optical luminosity ratio, we conclude that this quasar is radio-quiet and located at the low end of the radio quiet distribution of high redshift ($z \gtrsim 6$) quasars.

astro-ph.CO↗