arXiv subjects

Spencer A. Stanford

Publications and source records attributed to Spencer A. Stanford.

At least 19 recordsLinked to original sources

arXiv2024

Spectroscopic confirmation of the galaxy clusters CARLA J0950+2743 at z=2.363, and CARLA-Ser J0950+2743 at z=2.243

Galaxy clusters, being the largest gravitationally bound structures in the Universe, are a powerful tool to study mass assembly at different epochs. At z$>$2 they give an unique opportunity to put solid constraints not only on dark matter halo growth, but also on the mechanisms of galaxy quenching and morphological transformation when the Universe was younger than 3.3 Gyr. However, the currently available sample of confirmed $z>2$ clusters remains very limited. We present the spectroscopic confirmation of the galaxy cluster CARLA J0950+2743 at $z=2.363\pm0.005$ and a new serendipitously discovered cluster, CARLA-Ser J0950+2743 at $z=2.243\pm0.008$ in the same region. We confirm eight star-forming galaxies in the first cluster, and five in the second by detecting [OII], [OIII] and $Hα$ emission lines. The analysis of a serendipitous X-ray observation of this field from Chandra reveals a counterpart with a total luminosity of $L_{0.5-5 keV} = 2.9\pm0.6\times10^{45}$ erg s$^{-1}$. Given the limited depth of the X-ray observations, we cannot distinguish the 1-D profile of the source from a PSF model, however, our statistical analysis of the 2-D profile favors an extended component that could be associated to a thermal contribution from the intra-cluster medium (ICM). If the extended X-ray emission is due to the hot ICM, the total dark matter mass for the two clusters would be $M_{200}=3.30 ^{+0.23}_{-0.26 (\mathrm{stat})}$ $^{+1.28}_{-0.96 (\mathrm{sys})} \times10^{14} M_{\odot}$. This makes our two clusters interesting targets for studies of the structure growth in the cosmological context. However, future investigations would require deeper high-resolution X-ray and spectroscopic observations.

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arXiv2023

The galaxy mass-size relation in CARLA clusters and proto-clusters at 1.4 < z < 2.8: larger cluster galaxy sizes

(Abridged) We study the galaxy mass-size relation in CARLA spectroscopically confirmed clusters at $1.4 10.5$ are systematically $\gtrsim 0.2-0.3~{\rm dex}$ larger than field ETGs. The passive ETG average size evolution is slower at $1<z<2$ when compared to the field. This could be explained by differences in the formation and early evolution of galaxies in haloes of a different mass. Strong compaction and gas dissipation in field galaxies, followed by a sequence of mergers may have also played a significant role in the field ETG evolution, but not in the evolution of cluster galaxies. Our passive ETG mass-size relation shows a tendency to flatten at $9.6<{\rm log}(M/M_{\odot})<10.5$, where the average size is $\mathrm{log}(R_e/\mathrm{kpc}) = 0.05 \pm 0.22$. This implies that galaxies in the low end of the mass-size relation do not evolve much from $z\sim 2$ to the present, and that their sizes evolve in a similar way in clusters and in the field. BCGs lie on the same mass-size relation as satellites, suggesting that their size evolution is not different at redshift z $\gtrsim$ 2. Half of the active ETGs ($\sim 30\%$ of the ETGs) follow the field passive galaxy mass-size relation, and the other half follow the field active galaxy mass-size relation. These galaxies likely went through a recent merger or neighbor galaxy interaction, and would most probably quench at a later epoch and increase the fraction of passive ETGs in clusters. We do not observe a large population of compact galaxies, as is observed in the field at these redshifts, implying that the galaxies in our clusters are not observed in an epoch close to their compaction.

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arXiv2022

Morphology-density Relation, Quenching, and Mergers in CARLA Clusters and Proto-Clusters at $1.4<z<2.8$

(Abridged) To understand if the morphology-density and passive-density relations are already established at z>1.5, we study galaxies in 16 confirmed clusters at $1.3<z<2.8$ from the CARLA survey. Our main finding is that the morphology-density and passive-density relations are already in place at $z\sim2$. The cluster at z = 2.8 shows a similar fraction of ETG as in the other clusters in its densest region. The cluster ETG and passive fractions depend on local environment and mildly on galaxy mass. They do not depend on global environment. At lower local densities, the CARLA clusters exhibit a lower ETG fraction than clusters at z = 1. This implies that the densest regions influence the morphology of galaxies first, with lower density local environments either taking longer or only influencing galaxy morphology at later cosmological times. Interestingly, we find evidence of high merger fractions in our clusters with respect to the field, but the merger fractions do not significantly depend on local environment. This suggests that merger remnants in the lowest density regions can reform disks fuelled by cold gas flows, but those in the highest density regions are cut-off from the gas supply and will become passive ETG. The percentages of active ETG, with respect to the total ETG population, are $21 \pm 6\%$ and $59 \pm 14\% $ at 1.35 < z <1.65 and 1.65 < z < 2.05, respectively, and about half of them are mergers or asymmetric in both redshift bins. All the spectroscopically confirmed CARLA clusters have properties consistent with clusters and proto-clusters. The differences between our results and those that find enhanced star formation and star-bursts in cluster cores at similar redshifts are probably due to the different sample selection criteria, which choose different environments that host galaxies with different accretion and pre-processing histories.

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arXiv2020

Massive molecular gas reservoir around the central AGN in the CARLA J1103+3449 cluster at z=1.44

Passive early-type galaxies dominate cluster cores at z $\lesssim$1.5. At higher redshift, cluster core galaxies are observed to have still on-going star-formation, fuelled by cold molecular gas. We measure the molecular gas reservoir of the central region around the radio-loud AGN in the cluster CARLA J1103+3449 at z=1.44 with NOEMA. The AGN synchrotron emission dominates the continuum emission at 94.48 GHz, and we measure its flux at the AGN position and at the position of two radio jets. Combining our measurements with published results over the range 4.71 GHz-94.5 GHz, we obtain a flat spectral index $α= 0.14 \pm 0.03$ for the AGN core emission, and a steeper index $α= 1.43 \pm 0.04$ and $α= 1.15 \pm 0.04$ at positions close to the western and eastern lobe, respectively. The total spectral index is $α= 0.92 \pm 0.02$ over the range 73.8 MHz-94.5 GHz. We detect two CO(2-1) emission lines, both blue-shifted with respect to the AGN. Their emission corresponds to two regions, ~17 kpc south-east and ~14 kpc south-west of the AGN, not associated with galaxies. In these two regions, we find a total massive molecular gas reservoir of $M_{gas}$ = 3.9 $\pm$ 0.4 $10^{10} M_{\odot}$, which dominates (~ 60%) the central total molecular gas reservoir. These results can be explained by massive cool gas flows in the center of the cluster. The AGN early-type host is not yet quenched; its star formation rate is consistent with being on the main sequence of star-forming galaxies in the field (SFR~30-140 $M_{\odot}$/yr), and the cluster core molecular gas reservoir is expected to feed the AGN and the host star-formation before quiescence. The other cluster confirmed members show star formation rates at ~2 $σ$ below the field main sequence at similar redshifts and do not have molecular gas masses larger than galaxies of similar stellar mass in the field.

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arXiv2020

The Massive and Distant Clusters of WISE Survey X: Initial Results from a Sunyaev-Zeldovich Effect Study of Massive Galaxy Clusters at z>1 using MUSTANG2 on the GBT

The properties of galaxy clusters as a function of redshift can be utilized as an important cosmological tool. We present initial results from a program of follow-up observations of the Sunyaev-Zeldovich effect (SZE) in high redshift galaxy clusters detected at infrared wavelengths in the Massive and Distant Clusters of WISE Survey (MaDCoWS). Using typical on-source integration times of 3-4 hours per cluster, MUSTANG2 on the Green Bank Telescope was able to measure strong detections of SZE decrements and statistically significant masses on 14 out of 16 targets. On the remaining two, weaker (3.7 sigma) detections of the SZE signal and strong upper limits on the masses were obtained. In this paper we present masses and pressure profiles of each target and outline the data analysis used to recover these quantities. Of the clusters with strong detections, three show significantly flatter pressure profiles while, from the MUSTANG2 data, five others show signs of disruption at their cores. However, outside of the cores of the clusters, we were unable to detect significant amounts of asymmetry. Finally, there are indications that the relationship between optical richness used by MaDCoWS and SZE-inferred mass may be significantly flatter than indicated in previous studies.

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arXiv2020

Measuring the total infrared light from galaxy clusters at z=0.5-1.6: connecting stellar populations to dusty star formation

Massive galaxy clusters undergo strong evolution from z~1.6 to z~0.5, with overdense environments at high-z characterized by abundant dust-obscured star formation and stellar mass growth which rapidly give way to widespread quenching. Data spanning the near- to far-infrared (IR) spectrum can directly trace this transformation; however, such studies have largely been limited to the massive galaxy end of cluster populations. In this work, we present ``total light" stacking techniques spanning 3.4-500μm aimed at revealing the total cluster IR emission, including low mass members and potential intracluster dust. We detail our procedures for WISE, Spitzer, and Herschel imaging, including corrections to recover the total stacked emission in the case of high fractions of detected galaxies. We apply our stacking techniques to 232 well-studied massive (log M200/Msun~13.8) clusters across multiple z bins, recovering extended cluster emission at all wavelengths, typically at >5sigma. We measure the averaged near- to far-IR radial profiles and SEDs, quantifying the total stellar and dust content. The near-IR radial profiles are well described by an NFW model with a high (c~7) concentration parameter. Dust emission is similarly concentrated, albeit suppressed at small radii (r<0.2Mpc). The measured SEDs lack warm dust, consistent with the colder SEDs expected for low mass galaxies. We derive total stellar masses consistent with the theoretical Mhalo-M_star relation and specific-star formation rates that evolve strongly with redshift, echoing that of massive (log Mstar/Msun>10) cluster galaxies. Separating out the massive galaxy population reveals that the majority of cluster far-IR emission (~70-80%) is provided by the low mass constituents, which differs from field galaxies. This effect may be a combination of mass-dependent quenching and excess dust in low mass cluster galaxies.

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arXiv2020

The Massive and Distant Clusters of WISE Survey: SZ effect Verification with the Atacama Compact Array -- Localization and Cluster Analysis

The Massive and Distant Clusters of WISE Survey (MaDCoWS) provides a catalog of high-redshift ($0.7\lesssim z\lesssim 1.5$) infrared-selected galaxy clusters. However, the verification of the ionized intracluster medium, indicative of a collapsed and nearly virialized system, is made challenging by the high redshifts of the sample members. The main goal of this work is to test the capabilities of the Atacama Compact Array (ACA; also known as the Morita Array) Band 3 observations, centered at about 97.5 GHz, to provide robust validation of cluster detections via the thermal Sunyaev-Zeldovich (SZ) effect. Using a pilot sample that comprises ten MaDCoWS galaxy clusters, accessible to ACA and representative of the median sample richness, we infer the masses of the selected galaxy clusters and respective detection significance by means of a Bayesian analysis of the interferometric data. Our test of the "Verification with the ACA - Localization and Cluster Analysis" (VACA LoCA) program demonstrates that the ACA can robustly confirm the presence of the virialized intracluster medium in galaxy clusters previously identified in full-sky surveys. In particular, we obtain a significant detection of the SZ effect for seven out of the ten VACA LoCA clusters. We note that this result is independent of the assumed pressure profile. However, the limited angular dynamic range of the ACA in Band 3 alone, short observational integration times, and possible contamination from unresolved sources limit the detailed characterization of the cluster properties and the inference of the cluster masses within scales appropriate for the robust calibration of mass-richness scaling relations.

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arXiv2019

The Massive and Distant Clusters of WISE Survey VII: The Environments and Properties of Radio Galaxies in Clusters at z~1

We present the results from a study with NSF's Karl G. Jansky Very Large Array (VLA) to determine the radio morphologies of extended radio sources and the properties of their host galaxies in 50 massive galaxy clusters at z~1. We find a majority of the radio morphologies to be Fanaroff-Riley (FR) type IIs. By analyzing the infrared counterparts of the radio sources, we find that ~40% of the host galaxies are the candidate brightest cluster galaxy (BCG) and ~83% are consistent with being one of the top six most massive galaxies in the cluster. We investigate the role of environmental factors on the radio-loud AGN population by examining correlations between environmental and radio-galaxy properties. We find that the highest stellar mass hosts ($M_{*} \gtrsim$ 4$\times 10^{11} M_{\odot}$) are confined to the cluster center and host compact jets. There is evidence for an increase in the size of the jets with cluster-centric radius, which may be attributed to the decreased ICM pressure confinement with increasing radius. Besides this correlation, there are no other significant correlations between the properties of the radio-AGN (luminosity, morphology, or size) and environmental properties (cluster richness and location within the cluster). The fact that there are more AGN in the cluster environment than the field at this epoch, combined with the lack of strong correlation between galaxy and environmental properties, argues that the cluster environment fosters radio activity but does not solely drive the evolution of these sources at this redshift.

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arXiv2019

The Contribution of Galaxies to the $3.4\,\mathrm{μm}$ Cosmic Infrared Background as Measured Using WISE

The study of the extragalactic background light (EBL) in the optical and near infrared has received a lot of attention in the last decade, especially near a wavelength of $λ\approx 3.4\operatorname{μm}$, with remaining tension among different techniques for estimating the background. In this paper we present a measurement of the contribution of galaxies to the EBL at $3.4\operatorname{μm}$ that is based on the measurement of the luminosity function (LF) in Lake et al. (2018) and the mean spectral energy distribution of galaxies in Lake & Wright (2016). The mean and standard deviation of our most reliable Bayesian posterior chain gives a $3.4\operatorname{μm}$ background of $I_ν= 9.0\pm0.5 \operatorname{kJy} \operatorname{sr}^{-1}$ ($νI_ν= 8.0\pm0.4 \operatorname{nW} \operatorname{m}^{-2} \operatorname{sr}^{-1} e\operatorname{-fold}^{-1}$), with systematic uncertainties unlikely to be greater than $2\operatorname{kJy} \operatorname{sr}^{-1}$. This result is higher than most previous efforts to measure the contribution of galaxies to the $3.4\operatorname{μm}$ EBL, but is consistent with the upper limits placed by blazars and the most recent direct measurements of the total $3.4\operatorname{μm}$ EBL.

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arXiv2018

The Massive and Distant Clusters of WISE Survey V: Extended Radio Sources in Massive Galaxy Clusters at z~1

We present the results from a pilot study with the Karl G. Jansky Very Large Array (JVLA) to determine the radio morphologies of extended radio sources and the properties of their host-galaxies in 10 massive galaxy clusters at z~1, an epoch in which clusters are assembling rapidly. These clusters are drawn from a parent sample of WISE-selected galaxy clusters that were cross-correlated with the VLA Faint Images of the Radio Sky at Twenty-Centimeters survey (FIRST) to identify extended radio sources within 1$^{\prime}$ of the cluster centers. Out of the ten targeted sources, six are FR II sources, one is an FR I source, and three sources have undetermined morphologies. Eight radio sources have associated Spitzer data, 75% presenting infrared counterparts. A majority of these counterparts are consistent with being massive galaxies. The angular extent of the FR sources exhibits a strong correlation with the cluster-centric radius, which warrants further investigation with a larger sample.

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arXiv2017

Calibrating the Planck Cluster Mass Scale with Cluster Velocity Dispersions

We measure the Planck cluster mass bias using dynamical mass measurements based on velocity dispersions of a subsample of 17 Planck-detected clusters. The velocity dispersions were calculated using redshifts determined from spectra obtained at Gemini observatory with the GMOS multi-object spectrograph. We correct our estimates for effects due to finite aperture, Eddington bias and correlated scatter between velocity dispersion and the Planck mass proxy. The result for the mass bias parameter, $(1-b)$, depends on the value of the galaxy velocity bias $b_v$ adopted from simulations: $(1-b)=(0.51\pm0.09) b_v^3$. Using a velocity bias of $b_v=1.08$ from Munari et al., we obtain $(1-b)=0.64\pm 0.11$, i.e, an error of 17% on the mass bias measurement with 17 clusters. This mass bias value is consistent with most previous weak lensing determinations. It lies within $1σ$ of the value needed to reconcile the Planck cluster counts with the Planck primary CMB constraints. We emphasize that uncertainty in the velocity bias severely hampers precision measurements of the mass bias using velocity dispersions. On the other hand, when we fix the Planck mass bias using the constraints from Penna-Lima et al., based on weak lensing measurements, we obtain a positive velocity bias $b_v \gtrsim 0.9$ at $3σ$.

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arXiv2014

The Galaxy Cluster Mid-Infrared Luminosity Function at 1.3<z<3.2

We present 4.5 μm luminosity functions for galaxies identified in 178 candidate galaxy clusters at 1.3 < z < 3.2. The clusters were identified as Spitzer/IRAC color-selected overdensities in the Clusters Around Radio-Loud AGN (CARLA) project, which imaged 421 powerful radio-loud AGN at z > 1.3. The luminosity functions are derived for different redshift and richness bins, and the IRAC imaging reaches depths of m*+2, allowing us to measure the faint end slopes of the luminosity functions. We find that α = -1 describes the luminosity function very well in all redshifts bins and does not evolve significantly. This provides evidence that the rate at which the low mass galaxy population grows through star formation, gets quenched and is replenished by in-falling field galaxies does not have a major net effect on the shape of the luminosity function. Our measurements for m* are consistent with passive evolution models and high formation redshifts z_f ~ 3. We find a slight trend towards fainter m* for the richest clusters, implying that the most massive clusters in our sample could contain older stellar populations, yet another example of cosmic downsizing. Modelling shows that a contribution of a star-forming population of up to 40% cannot be ruled out. This value, found from our targeted survey, is significantly lower than the values found for slightly lower redshift, z ~ 1, clusters found in wide-field surveys. The results are consistent with cosmic downsizing, as the clusters studied here were all found in the vicinity of radio-loud AGNs -- which have proven to be preferentially located in massive dark matter halos in the richest environments at high redshift -- they may therefore be older and more evolved systems than the general protocluster population.

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arXiv2012

The Faint End of the Cluster Galaxy Luminosity Function at High Redshift

We measure the faint end slope of the galaxy luminosity function (LF) for cluster galaxies at 1<z<1.5 using Spitzer IRAC data. We investigate whether this slope, alpha, differs from that of the field LF at these redshifts, and with the cluster LF at low redshifts. The latter is of particular interest as low-luminosity galaxies are expected to undergo significant evolution. We use seven high-redshift spectroscopically confirmed galaxy clusters drawn from the IRAC Shallow Cluster Survey to measure the cluster galaxy LF down to depths of M* + 3 (3.6 microns) and M* + 2.5 (4.5 microns). The summed LF at our median cluster redshift (z=1.35) is well fit by a Schechter distribution with alpha[3.6] = -0.97 +/- 0.14 and alpha[4.5] = -0.91 +/- 0.28, consistent with a flat faint end slope and is in agreement with measurements of the field LF in similar bands at these redshifts. A comparison to alpha in low-redshift clusters finds no statistically significant evidence of evolution. Combined with past studies which show that M* is passively evolving out to z~1.3, this means that the shape of the cluster LF is largely in place by z~1.3. This suggests that the processes that govern the build up of the mass of low-mass cluster galaxies have no net effect on the faint end slope of the cluster LF at z<1.3.

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arXiv2012

Spitzer Photometry of WISE-Selected Brown Dwarf and Hyper-Luminous Infrared Galaxy Candidates

We present Spitzer 3.6 and 4.5 $μ$m photometry and positions for a sample of 1510 brown dwarf candidates identified by the WISE all-sky survey. Of these, 166 have been spectroscopically classified as objects with spectral types M(1), L(7), T(146), and Y(12); Sixteen other objects are non-(sub)stellar in nature. The remainder are most likely distant L and T dwarfs lacking spectroscopic verification, other Y dwarf candidates still awaiting follow-up, and assorted other objects whose Spitzer photometry reveals them to be background sources. We present a catalog of Spitzer photometry for all astrophysical sources identified in these fields and use this catalog to identify 7 fainter (4.5 $μ$m $\sim$ 17.0 mag) brown dwarf candidates, which are possibly wide-field companions to the original WISE sources. To test this hypothesis, we use a sample of 919 Spitzer observations around WISE-selected high-redshift hyper-luminous infrared galaxy (HyLIRG) candidates. For this control sample we find another 6 brown dwarf candidates, suggesting that the 7 companion candidates are not physically associated. In fact, only one of these 7 Spitzer brown dwarf candidates has a photometric distance estimate consistent with being a companion to the WISE brown dwarf candidate. Other than this there is no evidence for any widely separated ($>$ 20 AU) ultra-cool binaries. As an adjunct to this paper, we make available a source catalog of $\sim$ 7.33 $\times 10^5$ objects detected in all of these Spitzer follow-up fields for use by the astronomical community. The complete catalog includes the Spitzer 3.6 and 4.5 $μ$m photometry, along with positionally matched $B$ and $R$ photometry from USNO-B; $J$, $H$, and $K_s$ photometry from 2MASS; and $W1$, $W2$, $W3$, and $W4$ photometry from the WISE all-sky catalog.

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arXiv2011

Optical Spectroscopic Survey of High Latitude WISE Selected Sources

We report on the results of an optical spectroscopic survey at high Galactic latitude (b\geq30°) of a sample of WISE-selected targets, grouped by WISE W1 (λ_eff = 3.4 \mum) flux, which we use to characterize the sources WISE detected. We observed 762 targets in 10 disjoint fields centered on ultra-luminous infrared galaxy (ULIRG) candidates using the DEIMOS spectrograph on Keck II. We find 0.30 \pm 0.02 galaxies arcmin^-2 with a median redshift of z=0.33 \pm 0.01 for the sample with W1 \geq 120 \muJy. The foreground stellar densities in our survey range from 0.23 \pm 0.07 arcmin^(-2) to 1.1 \pm 0.1 arcmin^(-2) for the same sample. We obtained spectra that produced science grade redshifts for \geq 90% of our targets for sources with W1 flux \geq 120 \muJy that also had i-band flux \geq 18 \muJy. We used for targeting very preliminary data reductions available to the team in August of 2010. Our results therefore present a conservative estimate of what is possible to achieve using WISE's Preliminary Data Release for the study of field galaxies.

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arXiv2011

A WISE View of Star Formation in Local Galaxy Clusters

We present results from a systematic study of star formation in local galaxy clusters using 22 micron data from the Wide-field Infrared Survey Explorer (WISE). The 69 systems in our sample are drawn from the Cluster Infall Regions Survey (CIRS), and all have robust mass determinations. The all-sky WISE data enables us to quantify the amount of star formation, as traced by 22 micron, as a function of radius well beyond R200, and investigate the dependence of total star formation rate upon cluster mass. We find that the fraction of star-forming galaxies increases with cluster radius but remains below the field value even at 3 R200. We also find that there is no strong correlation between the mass-normalized total specific star formation rate and cluster mass, indicating that the mass of the host cluster does not strongly influence the total star formation rate of cluster members.

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arXiv2011

WISE Discovery of Low Metallicity Blue Compact Dwarf Galaxies

We report two new low metallicity blue compact dwarf galaxies (BCDs), WISEP J080103.93+264053.9 (hereafter W0801+26) and WISEP J170233.53+180306.4 (hereafter W1702+18), discovered using the Wide-field Infrared Survey Explorer (WISE). We identified these two BCDs from their extremely red colors at mid-infrared wavelengths, and obtained follow-up optical spectroscopy using the Low Resolution Imaging Spectrometer on Keck I. The mid-infrared properties of these two sources are similar to the well studied, extremely low metallicity galaxy SBS 0335-052E. We determine metallicities of 12 + log(O/H) = 7.75 and 7.63 for W0801+26 and W1702+18, respectively, placing them amongst a very small group of very metal deficient galaxies (Z < 1/10 Zsun). Their > 300 Angstrom Hbeta equivalent widths, similar to SBS 0335-052E, imply the existence of young (< 5 Myr) star forming regions. We measure star formation rates of 2.6 and 10.9 Msun/yr for W0801+26 and W1702+18, respectively. These BCDs, showing recent star formation activity in extremely low metallicity environments, provide new laboratories for studying star formation in extreme conditions and are low-redshift analogs of the first generation of galaxies to form in the universe. Using the all-sky WISE survey, we discuss a new method to identify similar star forming, low metallicity BCDs.

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arXiv2011

Discovery of a Radio-Selected z ~ 6 Quasar

We present the discovery of only the second radio-selected, z ~ 6 quasar. We identified SDSS J222843.54+011032.2 (z=5.95) by matching the optical detections of the deep Sloan Digital Sky Survey (SDSS) Stripe 82 with their radio counterparts in the Stripe82 VLA Survey. We also matched the Canadian-France-Hawaiian Telescope Legacy Survey Wide (CFHTLS Wide) with the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey but have yet to find any z ~ 6 quasars in this survey area. The discovered quasar is optically-faint, z = 22.3 and M_{1450} ~ -24.5, but radio-bright, with a flux density of f$_{1.4GHz, peak}$ = 0.31mJy and a radio-loudness of R ~ 1100 (where R = f_{5GHz}/f_{2500}). The i-z color of the discovered quasar places it outside the color selection criteria for existing optical surveys. We conclude by discussing the need for deeper wide-area radio surveys in the context of high-redshift quasars.

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