- ID:
- ivo://CDS.VizieR/J/AJ/138/1874
- Title:
- MOJAVE. VI. Kinematic analysis of blazar jets
- Short Name:
- J/AJ/138/1874
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss the jet kinematics of a complete flux-density-limited sample of 135 radio-loud active galactic nuclei (AGNs) resulting from a 13 year program to investigate the structure and evolution of parsec-scale jet phenomena. Our analysis is based on new 2cm Very Long Baseline Array (VLBA) images obtained between 2002 and 2007, but includes our previously published observations made at the same wavelength, and is supplemented by VLBA archive data. In all, we have used 2424 images spanning the years 1994-2007 to study and determine the motions of 526 separate jet features in 127 jets.
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- ID:
- ivo://CDS.VizieR/J/ApJ/798/134
- Title:
- MOJAVE. XII. Acceleration of blazar jets
- Short Name:
- J/ApJ/798/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the acceleration properties of 329 features in 95 blazar jets from the MOJAVE Very Long Baseline Array program. Nearly half the features and three-quarters of the jets show significant changes in speed and/or direction. In general, apparent speed changes are distinctly larger than changes in direction, indicating that changes in the Lorentz factors of jet features dominate the observed speed changes rather than bends along the line of sight. Observed accelerations tend to increase the speed of features near the jet base, <~10-20pc projected, and decrease their speed at longer distances. The range of apparent speeds at a fixed distance in an individual jet can span a factor of a few, indicating that shock properties and geometry may influence the apparent motions; however, we suggest that the broad trend of jet features increasing their speed near the origin is due to an overall acceleration of the jet flow out to deprojected distances of the order of 10^2^pc, beyond which the flow begins to decelerate or remains nearly constant in speed. We estimate intrinsic rates of change of the Lorentz factors in the galaxy frame of the order of {sdot}{Gamma}/{Gamma}~=10^-3^ to 10^-2^/yr, which can lead to total Lorentz factor changes of a factor of a few on the length scales observed here. Finally, we also find evidence for jet collimation at projected distances of <~10pc in the form of the non-radial motion and bending accelerations that tend to better align features with the inner jet.
- ID:
- ivo://CDS.VizieR/J/AJ/152/12
- Title:
- MOJAVE. XIII. New 15GHz observations on 1994-2013
- Short Name:
- J/AJ/152/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 1625 new 15GHz (2cm) VLBA images of 295 jets associated with active galactic nuclei (AGNs) from the MOJAVE and 2cm VLBA surveys, spanning observations between 1994 August 31 and 2013 August 20. For 274 AGNs with at least 5 VLBA epochs, we have analyzed the kinematics of 961 individual bright features in their parsec-scale jets. A total of 122 of these jets have not been previously analyzed by the MOJAVE program. In the case of 451 jet features that had at least 10 epochs, we also examined their kinematics for possible accelerations. At least half of the well-sampled features have non-radial and/or accelerating trajectories, indicating that non-ballistic motion is common in AGN jets. Since it is impossible to extrapolate any accelerations that occurred before our monitoring period, we could only determine reliable ejection dates for ~24% of those features that had significant proper motions. The distribution of maximum apparent jet speeds in all 295 AGNs measured by our program to date is peaked below 5c , with very few jets with apparent speeds above 30c . The fastest speed in our survey is ~50c , measured in the jet of the quasar PKS0805-07, and is indicative of a maximum jet Lorentz factor of ~50 in the parent population. An envelope in the maximum jet speed versus redshift distribution of our sample provides additional evidence of this upper limit to the speeds of radio-emitting regions in parsec-scale AGN jets. The Fermi-LAT-detected gamma-ray AGNs in our sample have, on average, higher jet speeds than non-LAT-detected AGNs, indicating a strong correlation between parsec-scale jet speed and the gamma-ray Doppler boosting factor. We have identified 11 moderate-redshift (z<0.35) AGNs with fast apparent speeds (>10c) that are strong candidates for future TeV gamma-ray detection. Of the five gamma-ray loud narrow-lined Seyfert I AGNs in our sample, three show highly superluminal jet motions, while the others have sub-luminal speeds. This indicates that some narrow-lined Seyfert I AGNs possess powerful jets with Lorentz factors in excess of 10, and viewing angles less than 10{deg}, consistent with those of typical BL Lac objects and flat-spectrum radio quasars.
- ID:
- ivo://CDS.VizieR/J/AJ/146/120
- Title:
- MOJAVE. X. Parsec-scale kinematics of AGNs
- Short Name:
- J/AJ/146/120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the parsec-scale kinematics of 200 active galactic nucleus (AGN) jets based on 15GHz Very Long Baseline Array (VLBA) data obtained between 1994 August 31 and 2011 May 1. We present new VLBA 15 GHz images of these and 59 additional AGNs from the MOJAVE and 2cm Survey programs. Nearly all of the 60 most heavily observed jets show significant changes in their innermost position angle over a 12-16yr interval, ranging from 10{deg} to 150{deg} on the sky, corresponding to intrinsic variations of ~0.5{deg} to ~2{deg}. The BL Lac jets show smaller variations than quasars. Roughly half of the heavily observed jets show systematic position angle trends with time, and 20 show indications of oscillatory behavior. The time spans of the data sets are too short compared to the fitted periods (5-12yr), however, to reliably establish periodicity. The rapid changes and large jumps in position angle seen in many cases suggest that the superluminal AGN jet features occupy only a portion of the entire jet cross section and may be energized portions of thin instability structures within the jet. We have derived vector proper motions for 887 moving features in 200 jets having at least five VLBA epochs. For 557 well-sampled features, there are sufficient data to additionally study possible accelerations. We find that the moving features are generally non-ballistic, with 70% of the well-sampled features showing either significant accelerations or non-radial motions. Inward motions are rare (2% of all features), are slow (<0.1mas/yr), are more prevalent in BL Lac jets, and are typically found within 1mas of the unresolved core feature. There is a general trend of increasing apparent speed with distance down the jet for both radio galaxies and BL Lac objects. In most jets, the speeds of the features cluster around a characteristic value, yet there is a considerable dispersion in the distribution. Orientation variations within the jet cannot fully account for the dispersion, implying that the features have a range of Lorentz factor and/or pattern speed. Very slow pattern speed features are rare, comprising only 4% of the sample, and are more prevalent in radio galaxy and BL Lac jets. We confirm a previously reported upper envelope to the distribution of speed versus beamed luminosity for moving jet features. Below 10^26^W/Hz there is a fall-off in maximum speed with decreasing 15GHz radio luminosity. The general shape of the envelope implies that the most intrinsically powerful AGN jets have a wide range of Lorentz factors up to ~40, while intrinsically weak jets are only mildly relativistic.
- ID:
- ivo://CDS.VizieR/J/ApJ/874/43
- Title:
- MOJAVE. XVII. Parsec-scale jet kinematics of AGNs
- Short Name:
- J/ApJ/874/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a parsec-scale jet kinematics study of 409 bright radio-loud active galactic nuclei (AGNs) based on 15GHz Very Long Baseline Array (VLBA) data obtained between 1994 August 31 and 2016 December 26 as part of the 2cm VLBA survey and Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) programs. We tracked 1744 individual bright features in 382 jets over at least 5 epochs. A majority (59%) of the best-sampled jet features showed evidence of accelerated motion at the >3{sigma} level. Although most features within a jet typically have speeds within ~40% of a characteristic median value, we identified 55 features in 42 jets that had unusually slow pattern speeds, nearly all of which lie within 4pc (100pc deprojected) of the core feature. Our results, combined with other speeds from the literature, indicate a strong correlation between apparent jet speed and synchrotron peak frequency, with the highest jet speeds being found only in low-peaked AGNs. Using Monte Carlo simulations, we find best-fit parent population parameters for a complete sample of 174 quasars above 1.5Jy at 15GHz. Acceptable fits are found with a jet population that has a simple unbeamed power-law luminosity function incorporating pure luminosity evolution and a power-law Lorentz factor distribution ranging from 1.25 to 50 with slope -1.4+/-0.2. The parent jets of the brightest radio quasars have a space density of 261+/-19Gpc^-3^ and unbeamed 15GHz luminosities above ~10^24.5^W/Hz, consistent with FRII class radio galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/151
- Title:
- MOJAVE. XVI: parsec-scale AGN jet cores at 15GHz
- Short Name:
- J/ApJ/862/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the core linear polarization properties of 387 parsec-scale active galactic nuclei (AGNs) jets. Using 15GHz VLBA data, we revisit the conclusions of the first paper in this series with multiepoch measurements and more detailed analysis of a larger AGN sample that spans a broader range of synchrotron peak frequencies. Each AGN has been observed for at least five epochs between 1996 and 2017. We find that BL Lac objects have core electric vector position angles (EVPAs) that tend toward alignment with the local jet direction; compared to flat spectrum radio quasars, their EVPAs are also less variable over time. The AGN cores that are most fractionally polarized and least variable in polarization have EVPAs that are closely aligned with the local jet direction; they also have low variability in EVPA. These results support the popular model of a standing transverse shock at the base of the jet that collimates the jet magnetic field perpendicular to the jet direction, increasing the fractional polarization and leading to greater polarization stability over time. High-synchrotron-peaked BL Lac objects form a low luminosity, low fractional polarization population. The five narrow line Seyfert 1 galaxies in our sample have low fractional polarization and large EVPA-jet misalignments. Although AGNs detected at {gamma}-rays are thought to be more Doppler boosted than nondetected AGNs, we find no significant differences in fractional polarization based on detection by Fermi-LAT; the {gamma}-loud AGNs are, however, more variable in core EVPAs.
- ID:
- ivo://CDS.VizieR/J/ApJS/234/12
- Title:
- MOJAVE XV. VLBA 15GHz obs. of AGN jets 1996-2016
- Short Name:
- J/ApJS/234/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 5321 mas-resolution total intensity and linear polarization maps of 437 active galactic nuclei (AGNs) obtained with the VLBA at 15GHz as part of the MOJAVE survey, and also from the NRAO data archive. The former is a long-term program to study the structure and evolution of powerful parsec-scale outflows associated with AGNs. The targeted AGNs are drawn from several flux-limited radio and {gamma}-ray samples, and all have correlated VLBA flux densities greater than ~50mJy at 15GHz. Approximately 80% of these AGNs are associated with {gamma}-ray sources detected by the Fermi LAT instrument. The vast majority were observed with the VLBA on 5-15 occasions between 1996 January 19 and 2016 December 26, at intervals ranging from a month to several years, with the most typical sampling interval being six months. A detailed analysis of the linear and circular polarization evolutions of these AGN jets is presented in the other papers in this series.
- ID:
- ivo://CDS.VizieR/J/ApJ/705/144
- Title:
- Molecular and atomic gas in the LMC. II.
- Short Name:
- J/ApJ/705/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare the CO (J=1-0) and HI emission in the Large Magellanic Cloud in three dimensions, i.e., including a velocity axis in addition to the two spatial axes, with the aim of elucidating the physical connection between giant molecular clouds (GMCs) and their surrounding HI gas. The CO(J=1-0) data set is from the second NANTEN CO survey (Fukui et al. 2008, Cat. J/ApJS/178/56) and the HI data set is from the merged Australia Telescope Compact Array (ATCA) and Parkes Telescope surveys (Kim et al. 2003ApJS..148..473K).
- ID:
- ivo://CDS.VizieR/J/ApJ/872/121
- Title:
- Molecular cloud cores in the GC 50km/s cloud
- Short Name:
- J/ApJ/872/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic center 50km/s molecular cloud (50MC) is the most remarkable molecular cloud in the Sagittarius A region. This cloud is a candidate for the massive star formation induced by cloud-cloud collision (CCC) with a collision velocity of ~30km/s that is estimated from the velocity dispersion. We observed the whole of the 50MC with a high angular resolution (~2.0"x1.4") in Atacama Large Millimeter/submillimeter Array cycle 1 in the H^13^CO^+^ J=1-0 and C^34^S J=2-1 emission lines. We identified 241 and 129 bound cores with a virial parameter of less than 2, which are thought to be gravitationally bound, in the H^13^CO^+^ and C^34^S maps using the clumpfind algorithm, respectively. In the CCC region, the bound H^13^CO^+^ and C^34^S cores are 119 and 82, whose masses are 68% and 76% of those in the whole 50MC, respectively. The distribution of the core number and column densities in the CCC are biased to larger densities than those in the non-CCC region. The distributions indicate that the CCC compresses the molecular gas and increases the number of the dense bound cores. Additionally, the massive bound cores with masses of >3000M_{sun}_ exist only in the CCC region, although the slope of the core mass function (CMF) in the CCC region is not different from that in the non-CCC region. We conclude that the compression by the CCC efficiently formed massive bound cores even if the slope of the CMF is not changed so much by the CCC.
- ID:
- ivo://CDS.VizieR/J/ApJS/184/1
- Title:
- Molecular clouds in the LMC by NANTEN. II.
- Short Name:
- J/ApJS/184/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We studied star formation activities in the molecular clouds in the Large Magellanic Cloud. We have utilized the second catalog of 272 molecular clouds obtained by NANTEN (4m radio telescope of Nagoya University at Las Campanas Observatory, Chile) to compare the cloud distribution with signatures of massive star formation including stellar clusters, and optical and radio HII regions. We find that the molecular clouds are classified into three types according to the activities of massive star formation: Type I shows no signature of massive star formation; Type II is associated with relatively small HII region(s); and Type III with both HII region(s) and young stellar cluster(s). The radio continuum sources were used to confirm that Type I giant molecular clouds (GMCs) do not host optically hidden HII regions. These signatures of massive star formation show a good spatial correlation with the molecular clouds in the sense that they are located within ~100pc of the molecular clouds.
