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 > or =, slanted3sigma or 23.1 mu Jy beam super(-1). This 3sigma limit corresponds to a rest-frame 1.4 GHz luminosity density limit of L sub(v), 1.4 GHz < 1.76 x 10 super(24) W Hz super(-1) for a spectral index of alpha = 0, and L sub(v), 1.4 GHz < 1.42 x 10 super(25) W Hz super(-1) for a spectral index of alpha = -1. The rest-frame 1.4 GHz luminosity limits are L sub(rad) < 6.43 x 10 super(6) L sub(middot in circle) and L sub(rad) < 5.20 x 10 super(7) L sub(middot in circle) for alpha = 0 and alpha = -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* sub(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 gap 6) quasars.
We studied the molecular gas properties of AzTEC/C159, a star-forming disk galaxy at z = 4.567, in order to better constrain the nature of the high-redshift end of the submillimeter-selected galaxy ...(SMG) population. We secured 12CO molecular line detections for the J = 2 →1 and J = 5 →4 transitions using the Karl G. Jansky Very Large Array (VLA) and the NOrthern Extended Millimeter Array (NOEMA) interferometer. The broad (FWHM ~ 750 km s−1) and tentative double-peaked profiles of the two 12CO lines are consistent with an extended molecular gas reservoir, which is distributed in a rotating disk, as previously revealed from CII 158 μm line observations. Based on the 12CO(2 →1) emission line, we derived L′CO=(3.4±0.6)×1010 K km s−1 pc2 $L'_{\rm{CO}}=(3.4\pm0.6)\times10^{10}\textrm{\,K\,km\,s}^{-1}\textrm{\,pc}^{2}$L′CO=(3.4±0.6)×1010 K km s−1 pc2 , which yields a molecular gas mass of MH2(αCO/4.3)=(1.5±0.3)×1011 M⊙ $M_{\textrm{H}_2} (\alpha_{\textrm{CO}}/4.3)=(1.5\pm0.3)\times 10^{11} \, M_{\odot}$MH2(αCO/4.3)=(1.5±0.3)×1011 M⊙ and unveils a gas-rich system with μgas(αCO/4.3)≡MH2/M⋆=3.3±0.7 $\mu_{\textrm{gas}}(\alpha_{\textrm{CO}}/4.3)\equiv M_{\textrm{H}_2}/M_{\star}=3.3\pm0.7$μgas(αCO/4.3)≡MH2/M⋆=3.3±0.7 . The extreme star formation efficiency of AzTEC/C159, parametrized by the ratio LIR/L′CO=(216±80) L⊙ (K km s−1 pc2)−1 $L_{\rm{IR}}/L'_{\rm{CO}}=(216\pm80)\, {L}_{\odot}\textrm{\,(K\,km\,s}^{-1}\textrm{\,pc}^{2})^{-1}$LIR/L′CO=(216±80) L⊙ (K km s−1 pc2)−1 , is comparable to merger-driven starbursts such as local ultra-luminous infrared galaxies and SMGs. Likewise, the 12CO(5 →4)/CO(2 →1) line brightness temperature ratio of r52 = 0.55 ± 0.15 is consistent with high-excitation conditions as observed in SMGs. Based on mass budget considerations, we constrained the value for the L′CO $L'_{\text{CO}}$L′CO – H2 mass conversion factor in AzTEC/C159, that is, αCO=3.9−1.3+2.7 M⊙ K−1 km−1 s pc−2 $\alpha_{\text{CO}}=3.9^{+2.7}_{-1.3}{\,M}_{\odot}\textrm{\,K}^{-1}\textrm{\,km}^{-1}\textrm{\,s\,pc}^{-2}$αCO=3.9−1.3+2.7 M⊙ K−1 km−1 s pc−2 , which is consistent with a self-gravitating molecular gas distribution as observed in local star-forming disk galaxies. Cold gas streams from cosmological filaments might be fueling a gravitationally unstable gas-rich disk in AzTEC/C159, which breaks into giant clumps and forms stars as efficiently as in merger-driven systems and generates high gas excitation. These results support the evolutionary connection between AzTEC/C159-like systems and massive quiescent disk galaxies at z ~ 2.
We present a search for the C II 158 {mu}m fine structure line (a main cooling line of the interstellar medium) and the underlying far-infrared (FIR) continuum in three high-redshift (6.6 < z < 8.2) ...star-forming galaxies using the IRAM Plateau de Bure Interferometer. We targeted two Ly{alpha}-selected galaxies (Ly{alpha} emitters, LAEs) with moderate UV-based star formation rates (SFRs {approx} 20 M{sub Sun} yr{sup -1}; Himiko at z = 6.6 and IOK-1 at z = 7.0) and a gamma-ray burst (GRB) host galaxy (GRB 090423 at z {approx} 8.2). Based on our 3{sigma} rest-frame FIR continuum limits, previous (rest-frame) UV continuum measurements and spectral energy distribution (SED) fitting, we rule out SED shapes similar to highly obscured galaxies (e.g., Arp 220, M 82) and less extreme dust-rich nearby spiral galaxies (e.g., M 51) for the LAEs. Conservatively assuming an SED shape typical of local spiral galaxies we derive upper limits for the FIR-based star formation rates (SFRs) of {approx}70 M{sub Sun} yr{sup -1}, {approx}50 M{sub Sun} yr{sup -1}, and {approx}40 M{sub Sun} yr{sup -1} for Himiko, IOK-1, and GRB 090423, respectively. For the LAEs these limits are only a factor {approx}3 higher than the published UV-based SFRs (uncorrected for extinction). This indicates that the dust obscuration in the z > 6 LAEs studied here is lower by a factor of a few than what has recently been found in some LAEs at lower redshift (2 < z < 3.5) with similar UV-based SFRs. A low obscuration in our z > 6 LAE sample is consistent with recent rest-frame UV studies of z {approx} 7 Lyman break galaxies.
Abstract
We report results from a deep Jansky Very Large Array (JVLA) search for 12CO J = 1-0 line emission from galaxies in a candidate galaxy cluster at z ∼ 1.55 in the COSMOS field. We target four ...galaxies with optical spectroscopic redshifts in the range z = 1.47-1.59, consistent with the likely redshift for the candidate galaxy cluster. Two of these four galaxies, ID 51613 and ID 51813, are nominally detected in CO 1-0 line emission at the 3-4σ level. We find CO luminosities of (2.42 ± 0.58) × 1010 K km s−1 pc2 and (1.26 ± 0.38) × 1010 K km s−1 pc2, respectively. Taking advantage from the clustering and expanded 2-GHz bandwidth of the JVLA, we perform a search for emission lines in the proximity of optical sources within the field of view of our observations (60 arcsec). We limit our search to galaxies with K
S < 23.5 (AB) and z
phot = 1.2-1.8. We find two bright optical galaxies, ID 51207 and ID 51380, to be associated with significant emission line peaks (>4σ) in the data cube, which we identify with the CO 1-0 line emission. To test the reliability of the line peaks found, we performed a parallel search for line peaks using a Bayesian inference method. Both CO line emitting candidates are identified with probabilities of 13 per cent and 72 per cent that there are line emitting sources in each case, respectively. Monte Carlo simulations show that such associations are statistically significant, with probabilities of chance association of 3.5 per cent and 10.7 per cent for ID 51207 and ID 51380, respectively. Modelling of their optical/IR spectral energy distributions indicates that the CO detected galaxies and candidates have stellar masses and star formation rates in the range (0.3-1.1) × 1011 M⊙ and 60-160 M⊙ yr−1, with star formation efficiencies comparable to that found in other star-forming galaxies at similar redshifts. By comparing the space density of CO emitters derived from our observations with the space density derived from previous CO detections at z ∼ 1.5, and with semi-analytic predictions for the CO luminosity function, we suggest that the latter tend to underestimate the number of CO galaxies detected at high redshift. Finally, we argue about the benefits of future searches for molecular gas line emission in clustered fields with upcoming submillimetre/radio facilities.
ABSTRACT
We present a deep, new 1200‐μm survey of the ELAIS N2 and Lockman Hole fields using the Max‐Planck Millimeter Bolometer array (MAMBO). The areas surveyed are 160 arcmin2 in ELAIS N2 and 197 ...arcmin2 in the Lockman Hole, covering the entire Submillimetre Common User Bolometer Array (SCUBA) 8‐mJy survey. In total, 27 (44) sources have been detected at a significance ≥4.0σ (≥3.5σ). The primary goals of the survey were to investigate the reliability of (sub)millimetre galaxy (SMG) samples, to analyse SMGs using flux ratios sensitive to redshift at z > 3, and to search for ‘SCUBA drop‐outs’, i.e. galaxies at z≫ 3. We present the 1200‐μm number counts and find tentative evidence of a fall at bright flux levels. Employing parametric models for the evolution of the local 60‐μm IRAS luminosity function, we are able to account simultaneously for the 1200‐ and 850‐μm counts, suggesting that the MAMBO and SCUBA sources trace the same underlying population of high‐redshift, dust‐enshrouded galaxies. From a nearest‐neighbour clustering analysis, we find tentative evidence that the most significant MAMBO sources come in pairs, typically separated by ∼23 arcsec. Our MAMBO observations unambiguously confirm around half of the SCUBA sources. In a robust subsample of 13 SMGs detected by both MAMBO and SCUBA at a significance ≥3.5σ, only one has no radio counterpart. Furthermore, the distribution of 850/1200‐μm flux density ratios for this subsample is consistent with the spectroscopic redshift distribution of radio‐detected SMGs. Finally, we have searched for evidence of a high‐redshift tail of SMGs amongst the 18 MAMBO sources that are not detected by SCUBA. Although we cannot rule out that some of them are SCUBA drop‐outs at z≫ 3, their overall 850‐to‐1200 μm flux distribution is statistically indistinguishable from that of the 13 SMGS which were robustly identified by both MAMBO and SCUBA.
We analyze data from the Hydrogen Epoch of Reionization Array (HERA). This is the third in a series of papers on the closure phase delay spectrum technique designed to detect the H i 21 cm emission ...from cosmic reionization. We present the details of the data and models employed in the power spectral analysis and discuss limitations to the process. We compare images and visibility spectra made with HERA data to parallel quantities generated from sky models based on the Galactic and Extra-Galactic All-Sky MWA (GLEAM) survey, incorporating the HERA telescope model. We find reasonable agreement between images made from HERA data with those generated from the models, down to the confusion level. For the visibility spectra, there is broad agreement between model and data across the full band of ∼80 MHz. However, models with only GLEAM sources do not reproduce a roughly sinusoidal spectral structure at the tens of percent level seen in the observed visibility spectra on scales of ∼10 MHz on 29 m baselines. We find that this structure is likely due to diffuse Galactic emission, predominantly the Galactic plane, filling the far sidelobes of the antenna primary beam. We show that our current knowledge of the frequency dependence of the diffuse sky radio emission, and the primary beam at large zenith angles, is inadequate to provide an accurate reproduction of the diffuse structure in the models. We discuss some implications arising due to this missing structure in the models, in terms of calibration, and in the search for the H i 21 cm signal, as well as possible mitigation techniques.
We report the detection of the CO J = 1-0 emission line in three near-infrared selected star-forming galaxies at z {approx} 1.5 with the Very Large Array and the Green Bank Telescope. These ...observations directly trace the bulk of molecular gas in these galaxies. We find H{sub 2} gas masses of 8.3 {+-} 1.9 x 10{sup 10} M {sub sun}, 5.6 {+-} 1.4 x 10{sup 10} M{sub sun}, and 1.23 {+-} 0.34 x 10{sup 11} M{sub sun} for BzK-4171, BzK-21000, and BzK-16000, respectively, assuming a conversion {alpha}{sub CO} = 3.6 M {sub sun} (K km s{sup -1} pc{sup 2}){sup -1}. We combined our observations with previous CO 2-1 detections of these galaxies to study the properties of their molecular gas. We find brightness temperature ratios between the CO 2-1 and CO 1-0 emission lines of 0.80{sup +0.35}{sub -0.22}, 1.22{sup +0.61}{sub -0.36}, and 0.41{sup +0.23}{sub -0.13} for BzK-4171, BzK-21000, and BzK-16000, respectively. At the depth of our observations it is not possible to discern between thermodynamic equilibrium or sub-thermal excitation of the molecular gas at J = 2. However, the low temperature ratio found for BzK-16000 suggests sub-thermal excitation of CO already at J = 2. For BzK-21000, a large velocity gradient model of its CO emission confirms previous results of the low excitation of the molecular gas at J = 3. From a stacked map of the CO 1-0 images, we measure a CO 2-1 to CO 1-0 brightness temperature ratio of 0.92{sup +0.28}{sub -0.19}. This suggests that, on average, the gas in these galaxies is thermalized up to J = 2, has star formation efficiencies of {approx}100 L {sub sun} (K km s{sup -1} pc{sup 2}){sup -1}, and gas consumption timescales of {approx}0.4 Gyr, unlike submillimeter galaxies and quasi-stellar objects at high redshifts.
Imaging and spectroscopy with the Very Large Telescope have revealed 20 Lyα emitters within a projected distance of 1.3 Mpc and 600 km s-1 of the luminous radio galaxy TN J1338-1942 at z=4.1. ...Compared to the field density of Lyα emitters, this implies an overdensity on the order of 15. The structure has a projected size of at least 2.7×1.8 Mpc and a velocity dispersion of 325 km s-1, which makes it the most distant structure known. Using the galaxy overdensity and assuming a bias parameter b=3-5, the mass is estimated to be ~1015 Msolar. The radio galaxy itself is surrounded by an uniquely asymmetric Lyα halo. Taken together with our previous data on PKS 1138-262 at z~2.16, these results suggest that luminous radio sources are excellent tracers of high-density regions in the early universe, which evolve into present-day clusters. The statistics of bright radio sources and of concentrations in the Lyman break galaxy population are consistent with the picture that each of those concentrations harbors an active or passive luminous radio source. Based on observations carried out at the European Southern Observatory, Paranal, Chile; program LP167.A-0409.
Observations of the radio galaxy MRC 0316–257 at $z = 3.13$ and the surrounding field are presented. Using narrow- and broad-band imaging obtained with the VLT, 77 candidate Lyα emitters with a ...rest-frame equivalent width of >15 Å were selected in a ∼7´$\,\times\,7$´ field around the radio galaxy. Spectroscopy of 40 candidate emitters resulted in the discovery of 33 emission line galaxies of which 31 are Lyα emitters with redshifts similar to that of the radio galaxy, while the remaining two galaxies turned out to be $\ion{O}{ii}$ emitters. The Lyα profiles have widths (FWHM) in the range of 120–800 km s-1, with a median of 260 km s-1. Where the signal-to-noise was large enough, the Lyα profiles were found to be asymmetric, with apparent absorption troughs blueward of the profile peaks, indicative of absorption along the line of sight of an $\ion{H}{i}$ mass of at least $2 \times 10^2 {-} 5 \times 10^4$ M$_{\odot}$. Besides that of the radio galaxy and one of the emitters that is a QSO, the continuum of the emitters is faint, with luminosities ranging from 1.3 L* to <0.03 L*. The colors of the confirmed emitters are, on average, very blue. The median UV continuum slope is $\beta = -1.76$, bluer than the average slope of LBGs with Lyα emission ($\beta \sim -1.09$). A large fraction of the confirmed emitters (∼2/3) have colors consistent with that of dust-free starburst galaxies. Observations with the Advanced Camera for Surveys on the Hubble Space Telescope show that the emitters that were detected in the ACS image have a range of different morphologies. Four Lyα emitters (∼25%) were unresolved with upper limits on their half light radii of $r_{\rm h} < 0.6-1.3$ kpc, three objects (∼19%) show multiple clumps of emission, as does the radio galaxy, and the rest (∼56%) are single, resolved objects with $r_{\rm h} < 1.5$ kpc. A comparison with the sizes of Lyman break galaxies at $z \sim 3$ suggests that the Lyα emitters are on average smaller than LBGs. The average star formation rate of the Lyα emitters is 2.6 M$_{\odot}\;{\rm yr}^{-1}$ as measured by the Lyα emission line or <3.9 M$_{\odot}\;{\rm yr}^{-1}$ as measured by the UV continuum. The properties of the Lyα galaxies (faint, blue and small) are consistent with young star forming galaxies which are still nearly dust free. The volume density of Lyα emitting galaxies in the field around MRC 0316–257 is a factor of $3.3^{+0.5}_{-0.4}$ larger compared with the density of field Lyα emitters at that redshift. The velocity distribution of the spectroscopically confirmed emitters has a dispersion of 640 km s-1, corresponding to a FWHM of 1510 km s-1, which is substantially smaller than the width of the narrow-band filter (${\it FWHM} \sim 3500$ km s-1). The peak of the velocity distribution is located within 200 km s-1 of the redshift of the radio galaxy. We conclude that the confirmed Lyα emitters are members of a protocluster of galaxies at $z \sim 3.13$. The size of the protocluster is unconstrained and is larger than $3.3 \times 3.3$ Mpc2. The mass of this structure is estimated to be >$3{-}6 \times 10^{14}$ M$_{\odot}$ and could be the progenitor of a cluster of galaxies similar to e.g. the Virgo cluster.
ABSTRACT We present Karl G Jansky Very Large Array observations of CO( ) line emission and rest-frame 250 GHz continuum emission of the Hyper-Luminous IR Galaxies (HyLIRGs) BRI 1202-0725 (z = 4.69) ...and BRI 1335-0417 (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 BRI 1202-0725, 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 Ly emitting galaxies in the group. Line emission from the SMG shows an east-west extension of about 0 6. For Ly -2, the CO emission is detected at the same velocity as C ii and N ii, indicating a total gas mass ∼4.0 × 1010 M . The CO emission from BRI 1335-0417 peaks at the nominal quasar position, with a prominent northern extension (∼1″, a possible tidal feature). The gas depletion timescales are ∼107 years for the three HyLIRGs, consistent with extreme starbursts, while that of Ly -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 via gas-rich mergers in the early universe.
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