We present Multi Unit Spectroscopic Explorer (MUSE) observations of the gas-rich major merger BR1202−0725 at z ∼ 4.7, which constitutes one of the most overdense fields known in the early universe. ...We utilize these data in conjunction with existing Atacama Large Millimeter/submillimeter Array (ALMA) observations to compare and contrast the spatially resolved ionized- and cool-gas content of this system, which hosts a quasar (QSO), a submillimeter galaxy (SMG), the two known optical companion Ly emitters ("LAE 1" and "LAE 2"), and an additional companion discovered in this work "LAE 3" just 5″ to the north of the QSO. We find that QSO BR1202−0725 exhibits a large Ly halo, covering 55 pkpc on-sky at surface-brightness levels of SB ≥ 1 × 10−17 erg s−1 cm−2 arcsec−2. In contrast, the SMG, of similar far-infrared luminosity and star formation rate (SFR), does not exhibit such a Ly halo. The QSO's halo exhibits high velocity widths (∼1000 km s−1) but the gas motion is to some extent kinematically coupled with the previously observed C ii bridge between the QSO and the SMG. We note that the object known in the literature as LAE 2 shows no local peak of Ly emission, rather, its profile is more consistent with being part of the QSO's extended Ly halo. The properties of LAE 3 are typical of high-redshift LAEs; we measure FLy (LAE 3) = 0.24 0.03 × 10−16 erg s−1 cm−2, corresponding to SFRLy 5.0 0.5 M yr−1. The velocity width is Δv(LAE 3) 400 km s−1, and the equivalent width is EW0( , consistent with star formation being the primary driver of Ly emission. We also note a coherent absorption feature at ∼−400 km s−1 in spectra from at least three objects; the QSO, LAE 1, and LAE 2, which could imply the presence of an expanding neutral gas shell with an extent of at least 24 pkpc.
We present Atacama Large Millimeter/submillimeter Array observations of the dust continuum and C ii 158 m line emission from the z = 6.0695 Lyman-Break Galaxy (LBG) WMH5. These observations at 0 3 ...spatial resolution show a compact (∼3 kpc) main galaxy in dust and C ii emission, with a "tail" of emission extending to the east by about 5 kpc (in projection). The C ii tail is comprised predominantly of two distinct sub-components in velocity, separated from the core by ∼100 and 250 km s−1, with narrow intrinsic widths of about 80 km s−1, which we call "sub-galaxies." The sub-galaxies themselves are extended east-west by about 3 kpc in individual channel images. The C ii tail joins smoothly into the main galaxy velocity field. The C ii line to continuum ratios are comparable for the main and sub-galaxy positions, within a factor two. In addition, these ratios are comparable to LBGs. We conjecture that the WMH5 system represents the early formation of a galaxy through the accretion of smaller satellite galaxies, embedded in a smoother gas distribution, along a possibly filamentary structure. The results are consistent with current cosmological simulations of early galaxy formation and support the idea of very early enrichment with dust and heavy elements of the accreting material.
We present a study of the formation of clustered, massive galaxies at large look-back times via spectroscopic imaging of CO in the unique GN20 proto-cluster at z = 4.05. Existing observations show ...that this is a dense concentration of gas-rich, very active star forming galaxies, including multiple bright submillimeter galaxies (SMGs). Using deep, high-resolution Karl G. Jansky Very Large Array CO(2-1) observations, we image the molecular gas with a resolution of ~1 kpc just 1.6 Gyr after the big bang. The SMGs GN20.2a and GN20.2b have deconvolved sizes of ~5 kpc x 3 kpc and ~8 kpc x 5 kpc (Gaussian FWHM) in CO(2-1), respectively, and we measure gas surface densities up to ~12,700/1700 x (sin i) (alpha sub(CO)/0.8) M sub(middot in circle) pc super(-2) for GN20.2a/GN20.2b in the highest-resolution maps. Dynamical mass estimates allow us to constrain the CO-to-H sub(2) conversion factor to alpha sub(CO) = 1.7 + or - 0.8 M sub(middot in circle) (K km s super(-1) pc super(2)) super(-1) for GN20.2a and alpha sub(CO) = 1.1+ or - super(1.5) sub(1.1) M sub(middot in circle) (K km s super(-1) pc super(2)) super(-1) for GN20.2b. We measure significant offsets (0".5-1") between the CO and optical emission, indicating either dust obscuration on scales of tens of kiloparsecs or that the emission originates from distinct galaxies. CO spectral line energy distributions imply physical conditions comparable to other SMGs and reveal further evidence that GN20.2a and GN20.2b are in different merging stages. We carry out a targeted search for CO emission from the 14 known B-band Lyman break galaxies (LBGs) in the field, tentatively detecting CO in a previously undetected LBG and placing 3sigma upper limits on the CO luminosities of those that may lie within our bandpass. A blind search for emission-line sources down to a 5sigma limiting CO luminosity of L' sub(CO(2-1)) = 8 x 10 super(9) K km s super(-1) pc super(2) and covering Deltaz = 0.0273 (~20 comoving Mpc) produces no other strong contenders associated with the proto-cluster.
We present detections of the CO(J = 1–0) emission line in a sample of four massive star-forming galaxies at z ∼ 1.5–2.2 obtained with the Karl G. Jansky Very Large Array. Combining these observations ...with previous CO(2–1) and CO(3–2) detections of these galaxies, we study the excitation properties of the molecular gas in our sample sources. We find an average line brightness temperature ratios of R
21 = 0.70 ± 0.16 and R
31 = 0.50 ± 0.29, based on measurements for three and two galaxies, respectively. These results provide additional support to previous indications of sub-thermal gas excitation for the CO(3–2) line with a typically assumed line ratio R
31 ∼ 0.5. For one of our targets, BzK-21000, we present spatially resolved CO line maps. At the resolution of 0.18 arcsec (1.5 kpc), most of the emission is resolved out except for some clumpy structure. From this, we attempt to identify molecular gas clumps in the data cube, finding four possible candidates. We estimate that <40 per cent of the molecular gas is confined to giant clumps (∼1.5 kpc in size), and thus most of the gas could be distributed in small fainter clouds or in fairly diffuse extended regions of lower brightness temperatures than our sensitivity limit.
We present ALMA observations of cold dust and molecular gas in four high-luminosity, heavily reddened (AV ~ 2.5-6 mag) type 1 quasars at z ~ 2.5 with virial ..., to test whether dusty, massive ...quasars represent the evolutionary link between submillimetre-bright galaxies and unobscured quasars. All four quasars are detected in both the dust continuum and in the super( 12)CO(3-2) line. The mean dust mass is ... assuming a typical high-redshift quasar spectral energy distribution (T = 41 K, beta = 1.95 or T = 47 K, beta = 1.6). The implied star formation rates are very high -- ... in all cases. Gas masses estimated from the CO line luminosities cover ... and the gas depletion time-scales are very short -- ~5-20 Myr. A range of gas-to-dust ratios is observed in the sample. We resolve the molecular gas in one quasar -- ULASJ2315+0143 (z = 2.561) -- which shows a strong velocity gradient over ~20 kpc. The velocity field is consistent with a rotationally supported gas disc but other scenarios, e.g. mergers, cannot be ruled out at the current resolution of these data. In another quasar -- ULASJ1234+0907 (z = 2.503) -- we detected molecular line emission from two millimetre-bright galaxies within 200 kpc of the quasar, suggesting that this quasar resides in a significant overdensity. The high detection rate of both cold dust and molecular gas in these sources, suggests that reddened quasars could correspond to an early phase in massive galaxy formation associated with large gas reservoirs and significant star formation. (ProQuest: ... denotes formulae/symbols omitted.)
We report the appearance of a new radio source at a projected offset of 460 pc from the nucleus of Cygnus A. The flux density of the source (which we designate Cygnus A-2) rose from an upper limit of ...<0.5 mJy in 1989 to 4 mJy in 2016 ( = 8.5 GHz), but is currently not varying by more than a few percent per year. The radio luminosity of the source is comparable to the most luminous known supernovae, it is compact in Very Long Baseline Array observations down to a scale of 4 pc, and it is coincident with a near-infrared point source seen in pre-existing adaptive optics and HST observations. The most likely interpretation of this source is that it represents a secondary supermassive black hole in a close orbit around the Cygnus A primary, though an exotic supernova model cannot be ruled out. The gravitational influence of a secondary SMBH at this location may have played an important role in triggering the rapid accretion that has powered the Cygnus A radio jet over the past 107 years.
ABSTRACT We present a search for C ii line and dust continuum emission from optical dropout galaxies at z > 6 using ASPECS, our Atacama Large Millimeter submillimeter Array Spectroscopic Survey in ...the Hubble Ultra-deep Field (UDF). Our observations, which cover the frequency range of 212-272 GHz, encompass approximately the range of 6 < z < 8 for C ii line emission and reach a limiting luminosity of LC ii ∼ (1.6-2.5) × 108 L . We identify 14 C ii line emitting candidates in this redshift range with significances >4.5 , two of which correspond to blind detections with no optical counterparts. At this significance level, our statistical analysis shows that about 60% of our candidates are expected to be spurious. For one of our blindly selected C ii line candidates, we tentatively detect the CO(6-5) line in our parallel 3 mm line scan. None of the line candidates are individually detected in the 1.2 mm continuum. A stack of all C ii candidates results in a tentative detection with S1.2 mm = 14 5 Jy. This implies a dust-obscured star-formation rate (SFR) of (3 1) M yr−1. We find that the two highest-SFR objects have candidate C ii lines with luminosities that are consistent with the low-redshift LC ii versus SFR relation. The other candidates have significantly higher C ii luminosities than expected from their UV-based SFR. At the current sensitivity, it is unclear whether the majority of these sources are intrinsically bright C ii emitters, or spurious sources. If only one of our line candidates was real (a scenario greatly favored by our statistical analysis), we find a source density for C ii emitters at 6 < z < 8 that is significantly higher than predicted by current models and some extrapolations from galaxies in the local universe.
We present a high-resolution (down to 0.''18), multi-transition imaging study of the molecular gas in the z = 4.05 submillimeter galaxy GN20. GN20 is one of the most luminous starburst galaxy known ...at z>4, and is a member of a rich proto-cluster of galaxies at z = 4.05 in GOODS-North. We have observed the CO 1-0 and 2-1 emission with the Very Large Array (VLA), the CO 6-5 emission with the Plateau de Bure Interferometer, and the 5-4 emission with Combined Array for Research in Millimeter Astronomy. The H{sub 2} mass derived from the CO 1-0 emission is 1.3 x 10{sup 11}({alpha}/0.8) M{sub sun}. High-resolution imaging of CO 2-1 shows emission distributed over a large area, appearing as partial ring, or disk, of {approx}10 kpc diameter. The integrated CO excitation is higher than found in the inner disk of the Milky Way, but lower than that seen in high-redshift quasar host galaxies and low-redshift starburst nuclei. The CO 4-3 integrated line strength is more than a factor of 2 lower than expected for thermal excitation. The excitation can be modeled with two gas components: a diffuse, lower excitation component with a radius {approx}4.5 kpc and a filling factor {approx}0.5, and a more compact, higher excitation component (radius {approx}2.5 kpc, filling factor {approx}0.13). The lower excitation component contains at least half the molecular gas mass of the system, depending on the relative conversion factor. The VLA CO 2-1 image at 0.''2 resolution shows resolved, clumpy structure, with a few brighter clumps with intrinsic sizes {approx}2 kpc. The velocity field determined from the CO 6-5 emission is consistent with a rotating disk with a rotation velocity of {approx}570 km s{sup -1} (using an inclination angle of 45{sup 0}), from which we derive a dynamical mass of 3 x 10{sup 11} M{sub sun} within about 4 kpc radius. The star formation distribution, as derived from imaging of the radio synchrotron and dust continuum, is on a similar scale as the molecular gas distribution. The molecular gas and star formation are offset by {approx}1'' from the Hubble Space Telescope I-band emission, implying that the regions of most intense star formation are highly dust obscured on a scale of {approx}10 kpc. The large spatial extent and ordered rotation of this object suggests that this is not a major merger, but rather a clumpy disk accreting gas rapidly in minor mergers or smoothly from the proto-intracluster medium. Qualitatively, the kinematic and structural properties of GN20 compare well to the most rapid star formers fed primarily by cold accretion in cosmological hydrodynamic simulations. Conversely, if GN20 is a major, gas-rich merger, then some process has managed to ensure that the star formation and molecular gas distribution has not been focused into one or two compact regions.
We explore the properties of the submillijansky radio population at 20 cm by applying a newly developed optical color-based method to separate star- forming (SF) from active galactic nucleus (AGN) ...galaxies at intermediate redshifts. Although optical rest-frame colors are used, our separation method is shown to be efficient and not biased against dusty starburst galaxies. This classification method has been calibrated and tested on a local radio- selected optical sample. Given accurate multiband photometry and redshifts, it carries the potential to be generally applicable to any galaxy sample where SF and AGN galaxies are the two dominant populations. In order to quantify the properties of the submillijansky radio population, we have analyzed image2,400 radio sources, detected at 20 cm in the VLA-COSMOS survey; 90% of these have submillijansky flux densities. We classify the objects into (1) star candidates, (2) quasi-stellar objects, (3) AGN, (4) SF, and (5) high-redshift galaxies. We find, for the composition of the submillijansky radio population, that SF galaxies are not the dominant population at submillijansky flux levels, as previously often assumed, but that they make up an approximately constant fraction of 30%-40% in the flux density range of image50 muJy to 0.7 mJy. In summary, based on the entire VLA-COSMOS radio population at 20 cm, we find that the radio population at these flux densities is a mixture of roughly 30%-40% of SF and 50%-60% of AGN galaxies, with a minor contribution (image10%) of QSOs.
We make use of the deep Karl G. Jansky Very Large Array (VLA) COSMOS radio observations at 3 GHz to infer radio luminosity functions of star-forming galaxies up to redshifts of z ~ 5 based on ...approximately 6000 detections with reliable optical counterparts. This is currently the largest radio-selected sample available out to z ~ 5 across an area of 2 square degrees with a sensitivity of rms ≈ 2.3 μJy beam-1. By fixing the faint and bright end shape of the radio luminosity function to the local values, we find a strong redshift trend that can be fitted with a pure luminosity evolution L1.4 GHz ∝ (1 + z)(3.16 ± 0.2)−(0.32 ± 0.07)z. We estimate star formation rates (SFRs) from our radio luminosities using an infrared (IR)-radio correlation that is redshift dependent. By integrating the parametric fits of the evolved luminosity function we calculate the cosmic SFR density (SFRD) history since z ~ 5. Our data suggest that the SFRD history peaks between 2 < z < 3 and that the ultraluminous infrared galaxies (100 M⊙ yr-1 < SFR < 1000 M⊙ yr-1) contribute up to ~25% to the total SFRD in the same redshift range. Hyperluminous infrared galaxies (SFR > 1000 M⊙ yr-1) contribute an additional ≲2% in the entire observed redshift range. We find evidence of a potential underestimation of SFRD based on ultraviolet (UV) rest-frame observations of Lyman break galaxies at high redshifts (z ≳ 4) on the order of 15–20%, owing to appreciable star formation in highly dust-obscured galaxies, which might remain undetected in such UV observations.
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