| 1. |
- Uscanga, L., et al.
(författare)
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Evolution of the Outflow in the Water Fountain Source IRAS 18043-2116
- 2023
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 948:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the spectral and spatial evolution of H2O masers associated with the water fountain source IRAS 18043-2116, found in observations with the Nobeyama 45 m Telescope and the Australia Telescope Compact Array. We have found new highest-velocity components of the H2O masers (at the redshifted side V (LSR) similar or equal to 376 km s(-1) and at the blueshifted side V (LSR) similar or equal to -165 km s(-1)), and the resulting velocity spread of similar or equal to 540 km s(-1) breaks the speed record of fast jets/outflows in this type of sources. The locations of those components have offsets from the axis joining the two major maser clusters, indicating a large opening angle of the outflow (similar to 60 degrees). The evolution of the maser cluster separation of similar to 2.9 mas yr(-1) and the compact (similar to 0.'' 2) CO emission source mapped with the Atacama Large Millimeter-submillimeter Array suggest a very short (similar to 30 yr) timescale of the outflow. We also confirmed an increase in the flux density of the 22 GHz continuum source. The properties of the jet and the continuum sources and their possible evolution in the transition to the planetary nebula phase are further discussed.
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| 2. |
- Cheng, Yu, et al.
(författare)
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Gas Kinematics of the Massive Protocluster G286.21+0.17 Revealed by ALMA
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 894:2
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Tidskriftsartikel (refereegranskat)abstract
- We study the gas kinematics and dynamics of the massive protocluster G286.21+0.17 with the Atacama Large Millimeter/submillimeter Array using spectral lines of {equation presented}(3-2), and DCN(3-2). On the parsec clump scale, C18O emission appears highly filamentary around the systemic velocity, N2D+ and DCO+ are more closely associated with the dust continuum, and DCN is strongly concentrated toward the protocluster center, where no or only weak detection is seen for N2D and DCO+, possibly due to this region being at a relatively evolved evolutionary stage. Spectra of 76 continuum-defined dense cores, typically a few 1000 au in size, are analyzed to measure their centroid velocities and internal velocity dispersions. There are no statistically significant velocity offsets of the cores among the different dense gas tracers. Furthermore, the majority (71%) of the dense cores have subthermal velocity offsets with respect to their surrounding, lower-density C18O-emitting gas. Within the uncertainties, the dense cores in G286 show internal kinematics that are consistent with being in virial equilibrium. On clump scales, the core-to-core velocity dispersion is also similar to that required for virial equilibrium in the protocluster potential. However, the distribution in velocity of the cores is largely composed of two spatially distinct groups, which indicates that the dense molecular gas has not yet relaxed to virial equilibrium, perhaps due to there being recent/continuous infall into the system.
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| 3. |
- Russell, T. D., et al.
(författare)
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Disk-Jet Coupling in the 2017/2018 Outburst of the Galactic Black Hole Candidate X-Ray Binary MAXI J1535-571
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 883:2
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Tidskriftsartikel (refereegranskat)abstract
- MAXI J1535-571 is a Galactic black hole candidate X-ray binary that was discovered going into outburst in 2017 September. In this paper, we present comprehensive radio monitoring of this system using the Australia Telescope Compact Array, as well as the MeerKAT radio observatory, showing the evolution of the radio jet during its outburst. Our radio observations show the early rise and subsequent quenching of the compact jet as the outburst brightened and then evolved toward the soft state. We constrain the compact jet quenching factor to be more than 3.5 orders of magnitude. We also detected and tracked (for 303 days) a discrete, relativistically moving jet knot that was launched from the system. From the motion of the apparently superluminal knot, we constrain the jet inclination (at the time of ejection) and speed to = 0.69 c, respectively. Extrapolating its motion back in time, our results suggest that the jet knot was ejected close in time to the transition from the hard intermediate state to soft intermediate state. The launching event also occurred contemporaneously with a short increase in X-ray count rate, a rapid drop in the strength of the X-ray variability, and a change in the type-C quasi-periodic oscillation (QPO) frequency that occurs >2.5 days before the first appearance of a possible type-B QPO.
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| 4. |
- Bower, G. C., et al.
(författare)
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THE ALLEN TELESCOPE ARRAY Pi GHz SKY SURVEY. I. SURVEY DESCRIPTION AND STATIC CATALOG RESULTS FOR THE BOOTES FIELD
- 2010
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 725:2, s. 1792-1804
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Tidskriftsartikel (refereegranskat)abstract
- The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array. PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky with an emphasis on synoptic observations that measure the static and time-variable properties of the sky. During the 2.5 year campaign, PiGSS will twice observe similar to 250,000 radio sources in the 10,000 deg(2) region of the sky with b > 30 degrees to an rms sensitivity of similar to 1 mJy. Additionally, sub-regions of the sky will be observed multiple times to characterize variability on timescales of days to years. We present here observations of a 10 deg(2) region in the Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The PiGSS image was constructed from 75 daily observations distributed over a 4 month period and has an rms flux density between 200 and 250 mu Jy. This represents a deeper image by a factor of 4-8 than we will achieve over the entire 10,000 deg(2). We provide flux densities, source sizes, and spectral indices for the 425 sources detected in the image. We identify similar to 100 new flat-spectrum radio sources; we project that when completed PiGSS will identify 10(4) flat-spectrum sources. We identify one source that is a possible transient radio source. This survey provides new limits on faint radio transients and variables with characteristic durations of months.
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| 5. |
- Croft, S., et al.
(författare)
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THE ALLEN TELESCOPE ARRAY TWENTY-CENTIMETER SURVEY-A 690 DEG(2), 12 EPOCH RADIO DATA SET. I. CATALOG AND LONG-DURATION TRANSIENT STATISTICS
- 2010
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 719:1, s. 45-58
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Tidskriftsartikel (refereegranskat)abstract
- We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a multi-epoch (12 visits), 690 deg(2) radio image and catalog at 1.4 GHz. The survey is designed to detect rare, very bright transients as well as to verify the capabilities of the ATA to form large mosaics. The combined image using data from all 12 ATATS epochs has rms noise sigma = 3.94 mJy beam(-1) and dynamic range 180, with a circular beam of 150 '' FWHM. It contains 4408 sources to a limiting sensitivity of 5 sigma = 20 mJy beam(-1). We compare the catalog generated from this 12 epoch combined image to the NRAO VLA Sky Survey (NVSS), a legacy survey at the same frequency, and find that we can measure source positions to better than similar to 20 ''. For sources above the ATATS completeness limit, the median flux density is 97% of the median value for matched NVSS sources, indicative of an accurate overall flux calibration. We examine the effects of source confusion due to the effects of differing resolution between ATATS and NVSS on our ability to compare flux densities. We detect no transients at flux densities greater than 40 mJy in comparison with NVSS and place a 2 sigma upper limit of 0.004 deg(-2) on the transient rate for such sources. These results suggest that the greater than or similar to 1 Jy transients reported by Matsumara et al. may not be true transients, but rather variable sources at their flux density threshold.
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| 6. |
- Behrens, E., et al.
(författare)
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Tracing Interstellar Heating: An ALCHEMI Measurement of the HCN Isomers in NGC 253
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 939:2
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Tidskriftsartikel (refereegranskat)abstract
- We analyze HCN and HNC emission in the nearby starburst galaxy NGC 253 to investigate its effectiveness in tracing heating processes associated with star formation. This study uses multiple HCN and HNC rotational transitions observed using the Atacama Large Millimeter/submillimeter Array via the ALCHEMI Large Program. To understand the conditions and associated heating mechanisms within NGC 253's dense gas, we employ Bayesian nested sampling techniques applied to chemical and radiative transfer models, which are constrained using our HCN and HNC measurements. We find that the volume density n H 2 and cosmic-ray ionization rate (CRIR) ζ are enhanced by about an order of magnitude in the galaxy’s central regions as compared to those further from the nucleus. In NGC 253's central giant molecular clouds (GMCs), where observed HCN/HNC abundance ratios are the lowest, n ∼ 105.5 cm−3 and ζ ∼ 10−12 s−1 (greater than 104 times the average Galactic rate). We find a positive correlation in the association of both density and CRIR with the number of star formation-related heating sources (supernova remnants, H ii regions, and super hot cores) located in each GMC, as well as a correlation between CRIRs and supernova rates. Additionally, we see an anticorrelation between the HCN/HNC ratio and CRIR, indicating that this ratio will be lower in regions where ζ is higher. Though previous studies suggested HCN and HNC may reveal strong mechanical heating processes in NGC 253's CMZ, we find cosmic-ray heating dominates the heating budget, and mechanical heating does not play a significant role in the HCN and HNC chemistry.
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| 7. |
- Bhat, Harshitha K., et al.
(författare)
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Influence of Jets on [O iii] Extensions in Green Pea/Bean Galaxies
- 2024
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 960:2
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Tidskriftsartikel (refereegranskat)abstract
- We present a study investigating the influence of jets on galaxies exhibiting strong [O iii]λ5007 emission, known as Green Peas and Green Beans. Our sample comprised 12 nearby sources (z ∼ 0.04-0.1, six with jets and six without jets) with high [O iii] luminosity (L ∼ 1040 erg s−1), selected from a radio-selected galaxy sample observed with the Sloan Digital Sky Survey and Radio Sky at Twenty-centimeters survey. We perform Large Binocular Telescope-Multi-Object Double Spectrograph long-slit spectroscopy at two position angles for each galaxy: one aligned with the jet direction and another perpendicular to it. By tracing the [O iii] emission along these slits, we aimed to assess the extension of the narrow line region and examine the impact of jets. Surprisingly, our analysis revealed no preferred direction for the extension of the [O iii] emission, indicating that jets have a limited influence on the extended emission line regions (EELRs). This also suggests the possibility of missed detection of conical-shaped EELRs aligned with the jets, attributable to our slit orientations. Furthermore, we compared the extension of [O ii] emission, which traces star-forming regions, with that of [O iii]. We observed a significant difference, with [O ii] exhibiting a considerably greater extension along the galactic plane. This suggests a stronger association of [O ii] emission with stellar processes.
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| 8. |
- Casey, Caitlin M., et al.
(författare)
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Physical Characterization of an Unlensed, Dusty Star-forming Galaxy at z = 5.85
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 887:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a physical characterization of MM J100026.36+021527.9 (a.k.a. "Mambo-9"), a dusty star-forming galaxy (DSFG) at z = 5.850 ± 0.001. This is the highest-redshift unlensed DSFG (and fourth most distant overall) found to date and is the first source identified in a new 2 mm blank-field map in the COSMOS field. Though identified in prior samples of DSFGs at 850 μm to 1.2 mm with unknown redshift, the detection at 2 mm prompted further follow-up as it indicated a much higher probability that the source was likely to sit at z > 4. Deep observations from the Atacama Large Millimeter and submillimeter Array (ALMA) presented here confirm the redshift through the secure detection of 12CO(J = 6→5) and p-H2O (21,1 → 20,2). Mambo-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M o˙ yr-1 and 220 M o˙ yr-1, total molecular hydrogen gas mass of (1.7 ± 0.4) × 1011 M o˙, dust mass of (1.3 ± 0.3) × 109 M o˙, and stellar mass of (3.2-1.5+1.0) × 109 M o˙. The total halo mass, (3.3 ± 0.8) × 1012 M o˙, is predicted to exceed 1015 M o˙ by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in τ depl = 40-80 Myr, converting its large molecular gas reservoir (gas fraction of 96-2+1) into stars. Mambo-9 evaded firm spectroscopic identification for a decade, following a pattern that has emerged for some of the highest-redshift DSFGs found. And yet, the systematic identification of unlensed DSFGs like Mambo-9 is key to measuring the global contribution of obscured star formation to the star formation rate density at z ⪆ 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times (≲1 Gyr).
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| 9. |
- Eatough, Ralph P., et al.
(författare)
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Verification of Radiative Transfer Schemes for the EHT
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 897:2
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Tidskriftsartikel (refereegranskat)abstract
- The Event Horizon Telescope (EHT) Collaboration has recently produced the first resolved images of the central supermassive black hole in the giant elliptical galaxy M87. Here we report on tests of the consistency and accuracy of the general relativistic radiative transfer codes used within the collaboration to model M87∗ and Sgr A∗. We compare and evaluate (1) deflection angles for equatorial null geodesics in a Kerr spacetime; (2) images calculated from a series of simple, parameterized matter distributions in the Kerr metric using simplified emissivities and absorptivities; (3) for a subset of codes, images calculated from general relativistic magnetohydrodynamics simulations using different realistic synchrotron emissivities and absorptivities; (4) observables for the 2017 configuration of EHT, including visibility amplitudes and closure phases. The error in total flux is of order 1% when the codes are run with production numerical parameters. The dominant source of discrepancies for small camera distances is the location and detailed setup of the software "camera"that each code uses to produce synthetic images. We find that when numerical parameters are suitably chosen and the camera is sufficiently far away the images converge and that for given transfer coefficients, numerical uncertainties are unlikely to limit parameter estimation for the current generation of EHT observations. The purpose of this paper is to describe a verification and comparison of EHT radiative transfer codes. It is not to verify EHT models more generally.
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| 10. |
- Fan, Lulu, et al.
(författare)
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ALMA Reveals a Gas-rich, Maximum Starburst in the Hyperluminous, Dust-obscured Quasar W0533-3401 at z similar to 2.9
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 887:1
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Tidskriftsartikel (refereegranskat)abstract
- We present ALMA observations and multiwavelength spectral energy distribution analysis in a Wide-field Infrared Survey Explorer-selected, hyperluminous dust-obscured quasar W0533-3401 at z = 2.9. We derive the physical properties of each of its components, such as molecular gas, stars, dust, and the central supermassive black hole (SMBH). Both the dust continuum at 3 mm and the CO (3-2) line are detected. The derived molecular gas mass M-gas = 8.4 x 10(10) M-circle dot and its fraction f(gas) = 0.7 suggest that W0533-3401 is gas-rich. The star formation rate (SFR) has been estimated to be similar to 3000-7000M(circle dot) yr(-1) by using different methods. The high values of SFR and specific SFR suggest that W0533-3401 is a maximum starburst. The corresponding gas depletion timescales are very short (t(depl) similar to 12-28 Myr). The CO (3-2) emission line is marginally resolved and has a velocity gradient, which is possibly due to a rotating gas disk, gas outflow, or merger. Finally, we infer the black hole mass growth rate of W0533-3401 ((M)over dot(BH) = 49 M-circle dot yr(-1)), which suggests a rapid growth of the central SMBH. The observed black hole to stellar mass ratio M-BH/M-* of W0533-3401, which is dependent on the adopted Eddington ratio, is over one order of magnitude higher than the local value, and is evolving toward the evolutionary trend of unobscured quasars. Our results are consistent with the scenario that W0533-3401, with both a gas-rich maximum starburst and a rapid black hole growth, is experiencing a short transition phase toward an unobscured quasar.
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