Engineering topics

Walter, Fabian

Publications and source records attributed to Walter, Fabian.

At least 19 records

DOE OSTI2024

Measurements of the z > 5 Lyman-α forest flux autocorrelation functions from the extended XQR-30 data set

We present the first observational measurements of the Lyman-α (Ly α) forest flux autocorrelation functions in ten redshift bins from 5.1 ≤ z ≤ 6.0. We use a sample of 35 quasar sightlines at z > 5.7 from the extended XQR-30 data set; these data have signal-to-noise ratios of >20 per spectral pixel. We carefully account for systematic errors in continuum reconstruction, instrumentation, and contamination by damped Ly α systems. With these measurements, we introduce software tools to generate autocorrelation function measurements from any simulation. Our measurements of the smallest bin of the autocorrelation function increase with redshift when normalizing by the mean flux, $\langle{F}\rangle$. This increase may come from decreasing $\langle{F}\rangle$ or increasing mean free path of hydrogen-ionizing photons, λmfp. Recent work has shown that the autocorrelation function from simulations at z > 5 is sensitive to λmfp, a quantity that contains vital information on the ending of reionization. For an initial comparison, we show our autocorrelation measurements with simulation models for recently measured λmfp values and find good agreements. Further work in modelling and understanding the covariance matrices of the data is necessary to get robust measurements of λmfp from this data.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Random Forests as a Viable Method to Select and Discover High-redshift Quasars

We present a method of selecting quasars up to redshift ≈6 with random forests, a supervised machine-learning method, applied to Pan-STARRS1 and WISE data. We find that, thanks to the increasing set of known quasars, we can assemble a training set that enables supervised machine-learning algorithms to become a competitive alternative to other methods up to this redshift. We present a candidate set for the redshift range 4.8–6.3, which includes the region around z = 5.5 where selecting quasars is difficult due to their photometric similarity to red and brown dwarfs. We demonstrate that, under our survey restrictions, we can reach a high completeness (66% ± 7% below redshift 5.6/83{sub -9}{sup +6}% above redshift 5.6) while maintaining a high selection efficiency (78{sub -8}{sup +10}%/94{sub -8}{sup +5}%). Our selection efficiency is estimated via a novel method based on the different distributions of quasars and contaminants on the sky. The final catalog of 515 candidates includes 225 known quasars. We predict the candidate catalog to contain additional 148{sub -33}{sup +41} new quasars below redshift 5.6 and 45{sub -8}{sup +5} above, and we make the catalog publicly available. Spectroscopic follow-up observations of 37 candidates led us to discover 20 new high redshift quasars (18 at 4.6 ≤ z ≤ 5.5, 2 z ~ 5.7). These observations are consistent with our predictions on efficiency. We argue that random forests can lead to higher completeness because our candidate set contains a number of objects that would be rejected by common color cuts, including one of the newly discovered redshift 5.7 quasars.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Resolving the Radio Emission from the Quasar P172+18 at z = 6.82

We present high angular resolution imaging of the quasar PSO J172.3556+18.7734 at z = 6.82 with the Very Long Baseline Array (VLBA). This source currently holds the record of being the highest redshift radio-loud quasar. These observations reveal a dominant radio source with a flux density of 398.4 ± 61.4 μJy at 1.53 GHz, a deconvolved size of 9.9 × 3.5 mas (52.5 × 18.6 pc), and an intrinsic brightness temperature of (4.7 ± 0.7) × 10{sup 7} K. A weak unresolved radio extension from the main source is also detected at the ∼3.1σ level. The total flux density recovered with the VLBA at 1.53 GHz is consistent with that measured with the Very Large Array (VLA) at a similar frequency. The quasar is not detected at 4.67 GHz with the VLBA, suggesting a steep spectral index with a limit of α{sub 4.67}{sup 1.53}<−1.55. The quasar is also not detected with the VLBA at 7.67 GHz. The overall characteristics of the quasar suggest that it is a very young radio source similar to lower redshift gigahertz peaked spectrum radio sources, with an estimated kinematic age of ∼10{sup 3} yr. The VLA observations of this quasar revealed a second radio source in the field 23.″1 away. This radio source, which does not have an optical or IR counterpart, is not detected with the VLBA at any of the observed frequencies. Its nondetection at the lowest observed VLBA frequency suggests that it is resolved out, implying a size larger than ∼0.″17. It is thus likely situated at lower redshift than the quasar.

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

Plateau de Bure High-z Blue Sequence Survey 2 (PHIBSS2): Search for Secondary Sources, CO Luminosity Functions in the Field, and the Evolution of Molecular Gas Density through Cosmic Time

We report on the results of a search for serendipitous sources in CO emission in 110 cubes targeting CO(2 − 1), CO(3 − 2), and CO(6 − 5) at z ∼ 1–2 from the second Plateau de Bure High-z Blue Sequence Survey (PHIBSS2). The PHIBSS2 observations were part of a 4 yr legacy program at the IRAM Plateau de Bure Interferometer aimed at studying early galaxy evolution from the perspective of molecular gas reservoirs. We present a catalog of 67 candidate secondary sources from this search, with 45 of the 110 data cubes showing sources in addition to the primary target that appear to be field detections, unrelated to the central sources. This catalog includes redshifts, line widths, and fluxes, as well as an estimation of their reliability based on their false-positive probability. We perform a search in the 3D Hubble Space Telescope/CANDELS catalogs for the secondary CO detections and tentatively find that ∼64% of these have optical counterparts, which we use to constrain their redshifts. Finally, we use our catalog of candidate CO detections to derive the CO(2 − 1), CO(3 − 2), CO(4 − 3), CO(5 − 4), and CO(6 − 5) luminosity functions over a range of redshifts, as well as the molecular gas mass density evolution. Despite the different methodology, these results are in very good agreement with previous observational constraints derived from blind searches in deep fields. They provide an example of the type of “deep-field” science that can be carried out with targeted observations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Quantitative Constraints on the Reionization History from the IGM Damping Wing Signature in Two Quasars at z > 7

During reionization, neutral hydrogen in the intergalactic medium (IGM) imprints a damping wing absorption feature on the spectrum of high-redshift quasars. A detection of this signature provides compelling evidence for a significantly neutral universe, and enables measurements of the hydrogen neutral fraction x HI (z) at that epoch. Obtaining reliable quantitative constraints from this technique, however, is challenging due to stochasticity induced by the patchy inside-out topology of reionization, degeneracies with quasar lifetime, and the unknown unabsorbed quasar spectrum close to rest-frame Lyα. Here, we combine a large-volume semi-numerical simulation of reionization topology with 1D radiative transfer through high-resolution hydrodynamical simulations of the high-redshift universe to construct models of quasar transmission spectra during reionization. Our state-of-the-art approach captures the distribution of damping wing strengths in biased quasar halos that should have reionized earlier, as well as the erosion of neutral gas in the quasar environment caused by its own ionizing radiation. Combining this detailed model with our new technique for predicting the quasar continuum and its associated uncertainty, we introduce a Bayesian statistical method to jointly constrain the neutral fraction of the universe and the quasar lifetime from individual quasar spectra. We apply this methodology to the spectra of the two quasars with the highest redshifts known, ULAS J1120+0641 and ULAS J1342+0928, and measure volume-averaged neutral fractions {x HI }(Z = 7.09) = 0.48 $+0.26\atop{-0.26}$and {x HI }(Z = 7.54) = 0.60 $+0.20\atop{-0.23}$ (posterior medians and 68% credible intervals) when marginalized over quasar lifetimes of 10 3 ≤ t q ≤ 10 8 yr.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Smooth H i Low Column Density Outskirts in Nearby Galaxies

The low column density gas at the outskirts of galaxies as traced by the 21 cm hydrogen line emission (H i) represents the interface between galaxies and the intergalactic medium, i.e., where galaxies are believed to get their supply of gas to fuel future episodes of star formation. Photoionization models predict a break in the radial profiles of H i at a column density of ∼5 × 10{sup 19} cm{sup −2} due to the lack of self-shielding against extragalactic ionizing photons. To investigate the prevalence of such breaks in galactic disks and to characterize what determines the potential edge of the H i disks, we study the azimuthally averaged H i column density profiles of 17 nearby galaxies from the H i Nearby Galaxy Survey and supplemented in two cases with published Hydrogen Accretion in LOcal GAlaxieS data. To detect potential faint H i emission that would otherwise be undetected using conventional moment map analysis, we line up individual profiles to the same reference velocity and average them azimuthally to derive stacked radial profiles. To do so, we use model velocity fields created from a simple extrapolation of the rotation curves to align the profiles in velocity at radii beyond the extent probed with the sensitivity of traditional integrated H i maps. With this method, we improve our sensitivity to outer-disk H i emission by up to an order of magnitude. Except for a few disturbed galaxies, none show evidence of a sudden change in the slope of the H i radial profiles: the alleged signature of ionization by the extragalactic background.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

H i Kinematics along the Minor Axis of M82

M82 is one of the best-studied starburst galaxies in the local universe, and is consequently a benchmark for researching star formation feedback at both low and high redshift. We introduce new VLA H i observations that reveal the cold gas kinematics along the minor axis in unprecedented detail. This includes the detection of H i up to 10 kpc along the minor axis toward the south and beyond 5 kpc to the north. A surprising aspect of these observations is that the line-of-sight H i velocity decreases substantially from about 120 to $50\,\mathrm{km}\,{{\rm{s}}}^{-1}$ from 1.5 to 10 kpc off the midplane. The velocity profile is not consistent with the H i gas cooling from the hot wind. We determine that the velocity decrease is substantially greater than the deceleration expected from gravitational forces alone. If the H i consists of a continuous population of cold clouds, some additional drag force must be present, and the magnitude of the drag force places a joint constraint on the ratio of the ambient medium to the typical cloud size and density. We also demonstrate that the H i kinematics are inconsistent with a simple conical outflow centered on the nucleus, but instead require the more widespread launch of the H i over the ~1 kpc extent of the starburst region. Regardless of the launch mechanism for the H i gas, the observed velocity decrease along the minor axis is sufficiently great that the H i may not escape the halo of M82. The inferred H i outflow rate at 10 kpc off the midplane is much less than 1 ${M}_{\odot }$ yr–1.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

An 800-million-solar-mass black hole in a significantly neutral Universe at a redshift of 7.5

Quasars are the most luminous non-transient objects known and as a result they enable studies of the Universe at the earliest cosmic epochs. Despite extensive efforts, however, the quasar ULAS J1120 + 0641 at redshift z = 7.09 has remained the only one known at z > 7 for more than half a decade. Here we report observations of the quasar ULAS J134208.10 + 092838.61 (hereafter J1342 + 0928) at redshift z = 7.54. This quasar has a bolometric luminosity of 4 × 10 13 times the luminosity of the Sun and a black-hole mass of 8 × 10 8 solar masses. The existence of this supermassive black hole when the Universe was only 690 million years old—just five per cent of its current age—reinforces models of early black-hole growth that allow black holes with initial masses of more than about 104 solar masses or episodic hyper-Eddington accretion. We see strong evidence of absorption of the spectrum of the quasar redwards of the Lyman α emission line (the Gunn–Peterson damping wing), as would be expected if a significant amount (more than 10 per cent) of the hydrogen in the intergalactic medium surrounding J1342 + 0928 is neutral. We derive such a significant fraction of neutral hydrogen, although the exact fraction depends on the modelling. However, even in our most conservative analysis we find a fraction of more than 0.33 (0.11) at 68 per cent (95 per cent) probability, indicating that we are probing well within the reionization epoch of the Universe.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Deep CO(1–0) Observations of z = 1.62 Cluster Galaxies with Substantial Molecular Gas Reservoirs and Normal Star Formation Efficiencies

We present an extremely deep CO(1–0) observation of a confirmed z = 1.62 galaxy cluster. We detect two spectroscopically confirmed cluster members in CO(1–0) with signal-to-noise ratio >5. Both galaxies have log(M{sub ⋆}/M{sub ⊙}) > 11 and are gas rich, with M{sub mol}/(M{sub ⋆}+M{sub mol}) ∼ 0.17–0.45. One of these galaxies lies on the star formation rate (SFR)–M{sub ⋆} sequence, while the other lies an order of magnitude below. We compare the cluster galaxies to other SFR-selected galaxies with CO measurements and find that they have CO luminosities consistent with expectations given their infrared luminosities. We also find that they have gas fractions and star formation efficiencies (SFE) comparable to what is expected from published field galaxy scaling relations. The galaxies are compact in their stellar light distribution, at the extreme end for all high-redshift star-forming galaxies. However, their SFE is consistent with other field galaxies at comparable compactness. This is similar to two other sources selected in a blind CO survey of the HDF-N. Despite living in a highly quenched protocluster core, the molecular gas properties of these two galaxies, one of which may be in the process of quenching, appear entirely consistent with field scaling relations between the molecular gas content, stellar mass, star formation rate, and redshift. We speculate that these cluster galaxies cannot have any further substantive gas accretion if they are to become members of the dominant passive population in z<1 clusters.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Mapping the Lyα Emission around a z ∼ 6.6 QSO with MUSE: Extended Emission and a Companion at a Close Separation

We utilize the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope to search for extended Lyα emission around the z ∼ 6.6 QSO J0305−3150. After carefully subtracting the point spread function, we reach a nominal 5σ surface-brightness limit of SB{sub 5σ} = 1.9 × 10{sup −18} erg s{sup −1} cm{sup −2} arcsec{sup −2} over a 1 arcsec{sup 2} aperture, collapsing five wavelength slices centered at the expected location of the redshifted Lyα emission (i.e., at 9256 Å). Current data suggest the presence (5σ accounting for systematics) of a Lyα nebula that extends for 9 kpc around the QSO. This emission is displaced and redshifted by 155 km s{sup −1} with respect to the location of the QSO host galaxy traced by the [C II] 158 μm emission line. The total luminosity is L(Lyα) = (3.0 ± 0.4) × 10{sup 42} erg s{sup −1}. Our analysis suggests that this emission is unlikely to rise from optically thick clouds illuminated by the ionizing radiation of the QSO. It is more plausible that the Lyα emission is due to the fluorescence of the highly ionized optically thin gas. This scenario implies a high hydrogen volume density of n{sub H}∼6 cm{sup −3}. In addition, we detect a Lyα emitter (LAE) in the immediate vicinity of the QSO, i.e., with a projected separation of ∼12.5 kpc and a line-of-sight velocity difference of 560 km s{sup −1}. The luminosity of the LAE is L(Lyα) = (2.1 ± 0.2) × 10{sup 42} erg s{sup −1} and its inferred star-formation rate is SFR ∼ 1.3 M {sub ⊙} yr{sup −1}. The probability of finding such a close LAE is one order of magnitude above the expectations based on the QSO–galaxy cross-correlation function. This discovery is in agreement with a scenario where dissipative interactions favor the rapid build-up of supermassive black holes at early cosmic times.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

A Spatially Resolved Study of Cold Dust, Molecular Gas, H ii Regions, and Stars in the z = 2.12 Submillimeter Galaxy ALESS67.1

We present detailed studies of a z = 2.12 submillimeter galaxy, ALESS67.1, using sub-arcsecond resolution ALMA, adaptive optics-aided VLT/SINFONI, and Hubble Space Telescope (HST)/CANDELS data to investigate the kinematics and spatial distributions of dust emission (870 μm continuum), {sup 12}CO(J = 3–2), strong optical emission lines, and visible stars. Dynamical modeling of the optical emission lines suggests that ALESS67.1 is not a pure rotating disk but a merger, consistent with the apparent tidal features revealed in the HST imaging. Our sub-arcsecond resolution data set allows us to measure half-light radii for all the tracers, and we find a factor of 4–6 smaller sizes in dust continuum compared to all the other tracers, including {sup 12}CO; also, ultraviolet (UV) and Hα emission are significantly offset from the dust continuum. The spatial mismatch between the UV continuum and the cold dust and gas reservoir supports the explanation that geometrical effects are responsible for the offset of the dusty galaxy on the IRX–β diagram. Using a dynamical method we derive an α{sub CO}=1.8±1.0, consistent with other submillimeter galaxies (SMGs) that also have resolved CO and dust measurements. Assuming a single α{sub CO} value we also derive resolved gas and star formation rate surface densities, and find that the core region of the galaxy (≲5 kpc) follows the trend of mergers on the Schmidt–Kennicutt relationship, whereas the outskirts (≳5 kpc) lie on the locus of normal star-forming galaxies, suggesting different star formation efficiencies within one galaxy. Our results caution against using single size or morphology for different tracers of the star formation activity and gas content of galaxies, and therefore argue the need to use spatially resolved, multi-wavelength observations to interpret the properties of SMGs, and perhaps even for z>1 galaxies in general.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Molecular Gas in Three z ∼ 7 Quasar Host Galaxies

We present ALMA band 3 observations of the CO(6–5), CO(7–6), and [C i] 369 μm emission lines in three of the highest-redshift quasar host galaxies at 6.6 2″, or ≳14 kpc) CO emission in all three quasar hosts. In two sources, we detect the continuum emission around 400 μm (rest-frame), and in one source we detect [C i] at low significance. We derive molecular gas reservoirs of (1–3) × 10{sup 10} M{sub ⊙} in the quasar hosts, i.e., approximately only 10 times the mass of their central supermassive black holes. The extrapolated [C ii]-to-CO(1–0) luminosity ratio is 2500–4200, consistent with measurements in galaxies at lower redshift. The detection of the [C i] line in one quasar host galaxy and the limit on the [C i] emission in the other two hosts enables a first characterization of the physical properties of the interstellar medium in z ∼ 7 quasar hosts. In the sources, the derived global CO/[C ii]/[C i] line ratios are consistent with expectations from photodissociation regions, but not X-ray-dominated regions. This suggest that quantities derived from the molecular gas and dust emission are related to ongoing star-formation activity in the quasar hosts, providing further evidence that the quasar hosts studied here harbor intense starbursts in addition to their active nucleus.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Gas Dynamics of a Luminous z = 6.13 Quasar ULAS J1319+0950 Revealed by ALMA High-resolution Observations

We present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum and [C ii] 158 μm fine structure line emission toward a far-infrared-luminous quasar, ULAS J131911.29+095051.4 at z = 6.13, and combine the new Cycle 1 data with ALMA Cycle 0 data. The combined data have an angular resolution of ∼0.″3, and resolve both the dust continuum and the [C ii] line emission on a few kiloparsec scales. The [C ii] line emission is more irregular than that of the dust continuum emission, which suggests different distributions between the dust and the [C ii]-emitting gas. The combined data confirm the [C ii] velocity gradient that we had previously detected in a lower-resolution ALMA image from the Cycle 0 data alone. We apply a tilted ring model to the [C ii] velocity map to obtain a rotation curve, and constrain the circular velocity to be 427 ± 55 km s{sup −1} at a radius of 3.2 kpc with an inclination angle of 34°. We measure the dynamical mass within the 3.2 kpc region to be 13.4{sub −5.3}{sup +7.8} × 10{sup 10} M{sub ⊙}. This yields a black-hole and host galaxy mass ratio of 0.020{sub −0.007}{sup +0.013}, which is about 4{sub −2}{sup +3} times higher than that of the present-day M{sub BH}/M{sub bulge} ratio. This suggests that the supermassive black hole grows the bulk of its mass before the formation of most of the stellar mass in this quasar host galaxy in the early universe.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

The Compact, ∼1 kpc Host Galaxy of a Quasar at a Redshift of 7.1

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C ii] fine-structure line and the underlying far-infrared (FIR) dust continuum emission in J1120+0641, the most distant quasar currently known (z=7.1). We also present observations targeting the CO(2–1), CO(7–6), and [C i] 369 μm lines in the same source obtained at the Very Large Array and Plateau de Bure Interferometer. We find a [C ii] line flux of F{sub [CII]}=1.11±0.10 Jy km s{sup −1} and a continuum flux density of S{sub 227GHz}=0.53±0.04 mJy beam{sup −1}, consistent with previous unresolved measurements. No other source is detected in continuum or [C ii] emission in the field covered by ALMA (∼ 25″). At the resolution of our ALMA observations (0.″23, or 1.2 kpc, a factor of ∼70 smaller beam area compared to previous measurements), we find that the majority of the emission is very compact: a high fraction (∼80%) of the total line and continuum flux is associated with a region 1–1.5 kpc in diameter. The remaining ∼20% of the emission is distributed over a larger area with radius ≲4 kpc. The [C ii] emission does not exhibit ordered motion on kiloparsec scales: applying the virial theorem yields an upper limit on the dynamical mass of the host galaxy of (4.3±0.9)×10{sup 10} M{sub ⊙}, only ∼20 × higher than the central black hole (BH). The other targeted lines (CO(2–1), CO(7–6), and [C i]) are not detected, but the limits of the line ratios with respect to the [C ii] emission imply that the heating in the quasar host is dominated by star formation, and not by the accreting BH. The star formation rate (SFR) implied by the FIR continuum is 105–340 M{sub ⊙} yr{sup −1}, with a resulting SFR surface density of ∼100–350 M{sub ⊙} yr{sup −1} kpc{sup −2}, well below the value for Eddington-accretion-limited star formation.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

ALMA Resolves the Nuclear Disks of Arp 220

We present 90 mas (37 pc) resolution ALMA imaging of Arp 220 in the CO (1-0) line and continuum at λ=2.6 mm. The internal gas distribution and kinematics of both galactic nuclei are well resolved for the first time. In the west nucleus, the major gas and dust emission extends out to 0.″2 radius (74 pc); the central resolution element shows a strong peak in the dust emission but a factor of 3 dip in the CO line emission. In this nucleus, the dust is apparently optically thick (τ{sub 2.6mm}∼1) at λ=2.6 mm with a dust brightness temperature of ∼147 K. The column of interstellar matter at this nucleus is N{sub H2}⩾2×10{sup 26} cm{sup −2}, corresponding to ∼900 gr cm{sup −2}. The east nucleus is more elongated with radial extent 0.″3 or ∼111 pc. The derived kinematics of the nuclear disks provide a good fit to the line profiles, yielding the emissivity distributions, the rotation curves, and velocity dispersions. In the west nucleus, there is evidence of a central Keplerian component requiring a central mass of 8 × 10{sup 8} M{sub ⊙}. The intrinsic widths of the emission lines are Δv(FWHM)=250 (west) and 120 (east) km s{sup −1}. Given the very short dissipation timescales for turbulence (≲10{sup 5} years), we suggest that the line widths may be due to semicoherent motions within the nuclear disks. The symmetry of the nuclear disk structures is impressive, implying the merger timescale is significantly longer than the rotation period of the disks.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Dense Molecular Gas Tracers in the Outflow of the Starburst Galaxy NGC 253

We present a detailed study of a molecular outflow feature in the nearby starburst galaxy NGC 253 using ALMA. We find that this feature is clearly associated with the edge of NGC 253's prominent ionized outflow, has a projected length of ∼300 pc, with a width of ∼50 pc, and a velocity dispersion of ∼40 km s{sup −1}, which is consistent with an ejection from the disk about 1 Myr ago. The kinematics of the molecular gas in this feature can be interpreted (albeit not uniquely) as accelerating at a rate of 1 km s{sup −1} pc{sup −1}. In this scenario, the gas is approaching an escape velocity at the last measured point. Strikingly, bright tracers of dense molecular gas (HCN, CN, HCO{sup +}, CS) are also detected in the molecular outflow: we measure an HCN(1–0)/CO(1–0) line ratio of ∼1/10 in the outflow, similar to that in the central starburst region of NGC 253 and other starburst galaxies. By contrast, the HCN/CO line ratio in the NGC 253 disk is significantly lower (∼1/30), similar to other nearby galaxy disks. This strongly suggests that the streamer gas originates from the starburst, and that its physical state does not change significantly over timescales of ∼1 Myr during its entrainment in the outflow. Simple calculations indicate that radiation pressure is not the main mechanism for driving the outflow. The presence of such dense material in molecular outflows needs to be accounted for in simulations of galactic outflows.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Milliarcsecond Imaging of the Radio Emission from the Quasar with the Most Massive Black Hole at Reionization

We report Very Long Baseline Array (VLBA) observations of the 1.5 GHz radio continuum emission of the z = 6.326 quasar SDSS J010013.02+280225.8 (hereafter J0100+2802). J0100+2802 is by far the most optically luminous and is a radio-quiet quasar with the most massive black hole known at z > 6. The VLBA observations have a synthesized beam size of 12.10 mas ×5.36 mas (FWHM), and detected the radio continuum emission from this object with a peak surface brightness of 64.6 ± 9.0 μ Jy beam{sup −1} and a total flux density of 88 ± 19 μ Jy. The position of the radio peak is consistent with that from SDSS in the optical and Chandra in the X-ray. The radio source is marginally resolved by the VLBA observations. A 2D Gaussian fit to the image constrains the source size to (7.1 ± 3.5) mas × (3.1 ± 1.7) mas. This corresponds to a physical scale of (40 ± 20) pc × (18 ± 10) pc. We estimate the intrinsic brightness temperature of the VLBA source to be T {sub B} = (1.6 ± 1.2) × 10{sup 7} K. This is significantly higher than the maximum value in normal star-forming galaxies, indicating an active galactic nucleus (AGN) origin for the radio continuum emission. However, it is also significantly lower than the brightness temperatures found in highest-redshift radio-loud quasars. J0100+2802 provides a unique example for studying the radio activity in optically luminous and radio-quiet AGNs in the early universe. Further observations at multiple radio frequencies will accurately measure the spectral index and address the dominant radiation mechanism of the radio emission.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

High-resolution observations of molecular lines in ARP 220: kinematics, morphology, and limits on the applicability of the ammonia thermometer

We observe Arp 220, the nearest ultra-luminous infrared galaxy, over 4 GHz in the K and Ka bands, providing constraints for the kinematics and morphology, and identifying molecular species on scales resolving both nuclei (0.″6 or 230 pc). We detect multiple molecular species, including hydroxyl (OH {sup 2}Π{sub 3/2}J=9/2F=4−4;5−5) in both cores, and tentatively detect H{sub 2}O(6{sub 15}-5{sub 23}) at ∼21.84 GHz in both nuclei, indicating the likely presence of maser emission. The observed frequency range also contains metastable ammonia transitions from (J, K) = (1, 1)–(5, 5), as well as the (9, 9) inversion line; together, they are a well-known thermometer of dense molecular gas. Furthermore, the non-metastable (4, 2) and (10, 9), and possibly the (3, 1), lines are also detected. We apply a standard temperature analysis to Arp 220; however, the analysis is complicated in that standard local thermal equilibrium (LTE) assumptions do not hold. There are indications that a substantial fraction of ammonia could be in the non-metastable transitions, as opposed to only the metastable ones. Thus, the non-metastable transitions could be essential to constraining the temperature. We compare all of these data to ALMA observations of this source, confirming the outflow previously observed by other tracers in both nuclei.

79 ASTRONOMY AND ASTROPHYSICS↗