- ID:
- ivo://CDS.VizieR/J/ApJ/740/98
- Title:
- Synchroton peak for blazars and radio galaxies
- Short Name:
- J/ApJ/740/98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We revisit the concept of a blazar sequence that relates the synchrotron peak frequency ({nu}_peak_) in blazars with synchrotron peak luminosity (L_peak_, in {nu}L_{nu}_) using a large sample of radio-loud active galactic nuclei. We present observational evidence that the blazar sequence is formed from two populations in the synchrotron {nu}_peak_-L_peak_ plane, each forming an upper edge to an envelope of progressively misaligned blazars, and connecting to an adjacent group of radio galaxies having jets viewed at much larger angles to the line of sight. When binned by jet kinetic power (L_kin_; as measured through a scaling relationship with extended radio power), we find that radio core dominance decreases with decreasing synchrotron L_peak_, revealing that sources in the envelope are generally more misaligned. We find population-based evidence of velocity gradients in jets at low kinetic powers (~10^42^-10^44.5^erg/s), corresponding to Fanaroff-Riley (FR) I radio galaxies and most BL Lac objects. These low jet power "weak-jet" sources, thought to exhibit radiatively inefficient accretion, are distinguished from the population of non-decelerating, low synchrotron-peaking (LSP) blazars and FR II radio galaxies ("strong" jets) which are thought to exhibit radiatively efficient accretion. The two-population interpretation explains the apparent contradiction of the existence of highly core-dominated, low-power blazars at both low and high synchrotron peak frequencies, and further implies that most intermediate synchrotron peak sources are not intermediate in intrinsic jet power between LSP and high synchrotron-peaking (HSP) sources, but are more misaligned versions of HSP sources with similar jet powers.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/111/57
- Title:
- Synthetic absorption in star forming regions
- Short Name:
- J/A+AS/111/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectral evolutionary calculations have been employed in order to follow the behaviour of absorption lines in single-burst star forming regions. The model calculations are based on theoretical evolutionary tracks and model atmosphere stellar spectra at 5A resolution and they include the pre-main sequence phase. Three different metallicities have been considered; Z=0.001, 0.008 and 0.020, this range covers easily the one occupied by blue compact dwarf galaxies. This analysis focuses on the post-active burst phase and follows the evolution up to 15 million years after the episode of star formation has ceased, using an instantaneous burst of star formation. The absorption lines included are hydrogen, neutral and once ionized helium. Non-LTE absorption line profiles have been implemented to these lines, also at a 5A resolution. The equivalent widths and line profiles are studied as a function of lower and upper mass limits and slope of the mass function as well as the age. It is shown that the equivalent widths of the Balmer lines are increasing during the course of evolution, while the strength of the neutral and ionized helium lines decreases monotonically. Both the hydrogen and helium lines show high sensitivity to variations in the initial mass function (IMF). The Balmer line equivalent widths range from about 1.5 to 6.5A, depending on the IMF parameters used. As anticipated, these numbers are rather insensitive to the metallicity. Contrary to what has been claimed, the Balmer lines are prominent even if the lower mass limit is as high as 10M_{sun}_. It has been proposed that the weak hydrogen lines sometimes seen in starburst galaxies, often interpreted as evidence for a deficiency in low mass stars, could be due to the finite lifetimes of pre-main sequence stars. This analysis shows that it is very much dependent on the slope of the mass function. The equivalent width of the HeI-4471A line never exceeds 0.35A for any choice of the IMF parameters while the equivalent width of the HeII-4686A line reaches at the most 0.20A using the most top-heavy IMF. As expected, these numbers are only slightly dependent on the metallicity in the optical spectral region.
3703. Synthetic galaxy spectra
- ID:
- ivo://CDS.VizieR/J/A+A/538/A38
- Title:
- Synthetic galaxy spectra
- Short Name:
- J/A+A/538/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an optimized library of synthetic galaxy spectra that are to be used for the Gaia satellite observations of unresolved galaxies. These galaxy spectral templates are useful for the optimal performance of the unresolved galaxy classifier (UGC) software. The UGC will assign spectral classes to the observed unresolved galaxies by Gaia (classification) and estimate some of their intrinsic astrophysical parameters, which were used to create the synthetic library (parametrization). We present the new optimized synthetic library of galaxy spectra and the classification and parametrization results using the Gaia-simulated version of this library. To optimize our synthetic library, we applied the principal component analysis (PCA) method to our synthetic spectra and studied the influence of the star-formation rate parameters on the spectra, and how these agree with some typical characteristics of the galaxy spectral types. We used support vector machines (SVM) to classify and parametrize the optimal simulated spectra. The library of synthetic galaxy spectra was optimized. In this new set of synthetic spectra, overlaps in spectral energy distributions and colors are highly suppressed, while the results of UGC classification are improved.
- ID:
- ivo://CDS.VizieR/J/MNRAS/412/1070
- Title:
- Synthetic supernova extinction curves
- Short Name:
- J/MNRAS/412/1070
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We apply the supernova (SN) extinction curves to reproduce the observed properties of SST J1604+4304 which is a young infrared (IR) galaxy at z~1. The SN extinction curves used in this work were obtained from models of unmixed ejecta of Type II supernovae for the Salpeter initial mass function with a mass range from 8 to 30M_{sun}_ or 8 to 40M_{sun}_. The effect of dust distributions on the attenuation of starlight is investigated by performing the {chi}^2^ fitting method against various dust distributions. These are the commonly used uniform dust screen, the clumpy dust screen and the internal dust geometry. We add to these geometries three scattering properties, namely, no scattering, isotropic scattering and forward-only scattering. Judging from the {chi}^2^ values, we find that the uniform screen models with any scattering property provide good approximations to the real dust geometry.
- ID:
- ivo://CDS.VizieR/J/A+A/477/67
- Title:
- Systematic search for M31 novae from Schmidt plates
- Short Name:
- J/A+A/477/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper reports on the detection of optical novae in our neighbour galaxy M 31 based on digitized historical Tautenburg Schmidt plates. The accurate positions of the detected novae lead to a much larger database when searching for recurrent novae in M 31. We conducted a systematic search for novae on 306 digitized Tautenburg Schmidt plates covering a time span of 36 years from 1960 to 1996. From the database of both ~3x10^5^ light curves and >~10^6^ detections on only one plate per colour band, nova candidates were efficiently selected by automated algorithms and subsequently individually inspected by eye. We report the detection of 84 nova candidates.
- ID:
- ivo://CDS.VizieR/J/ApJ/639/724
- Title:
- Tadpole galaxies in the Hubble UDF
- Short Name:
- J/ApJ/639/724
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the Hubble Ultra Deep Field (HUDF, Cat. <II/258>) an abundance of galaxies is seen with a knot at one end plus an extended tail, resembling a tadpole. These "tadpole galaxies" appear dynamically unrelaxed - presumably in an early merging stage - where tidal interactions likely created the distorted knot-plus-tail morphology. Here we systematically select tadpole galaxies from the HUDF and study their properties as a function of their photometric redshifts.
- ID:
- ivo://CDS.VizieR/J/A+A/647/A138
- Title:
- Taffy system CO(1-0) datacube
- Short Name:
- J/A+A/647/A138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Taffy system (UGC 12914/15) consists of two massive spiral galaxies which had a head-on collision about 20Myr ago. New sensitive, high-resolution CO(1-0) observations of the Taffy system with the IRAM PdBI are presented. About 25% of the total interferometric CO luminosity stems from the bridge region. Assuming a Galactic N(H2)/ICO conversion factor for the galactic disks and a third of this value for the bridge gas, about 10% of the molecular gas mass is located in the bridge region. The giant HII region close to UGC 12915 is located at the northern edge of the high-surface brightness giant molecular cloud association (GMA), which has the highest velocity dispersion among the bridge GMAs. The bridge GMAs are clearly not virialized because of their high velocity dispersion. Three dynamical models are presented and while no single model reproduces all of the observed features, they are all present in at least one of the models. Most of the bridge gas detected in CO does not form stars. We suggest that turbulent adiabatic compression is responsible for the exceptionally high velocity dispersion of the molecular ISM and the suppression of star formation in the Taffy bridge. In this scenario the turbulent velocity dispersion of the largest eddies and turbulent substructures/clouds increase such that giant molecular clouds are no longer in global virial equilibrium. The increase of the virial parameter leads to a decrease of the star formation efficiency. Most of the low-surface density, CO-emitting gas will disperse without forming stars but some of the high-density gas will probably collapse and form dense star clusters, such as the luminous HII region close to UGC 12915. We suggest that globular clusters and super star clusters formed and still form through the gravitational collapse of gas previously compressed by turbulent adiabatic compression during galaxy interactions.
- ID:
- ivo://CDS.VizieR/J/A+A/569/A115
- Title:
- TANAMI monitoring of Centaurus A.
- Short Name:
- J/A+A/569/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Centaurus A (Cen A) is the closest radio-loud active galactic nucleus. Very Long Baseline Interferometry (VLBI) enables us to study the spectral and kinematic behavior of the radio jet-counterjet system on milliarcsecond scales, providing essential information for jet emission and propagation models. In the framework of the TANAMI monitoring, we investigate the kinematics and complex structure of Cen A on subparsec scales. We have been studying the evolution of the central parsec jet structure of Cen A for over 3.5-years. The proper motion analysis of individual jet components allows us to constrain jet formation and propagation and to test the proposed correlation of increased high-energy flux with jet ejection events. Cen A is an exceptional laboratory for such a detailed study because its proximity translates to unrivaled linear resolution, where one milliarcsecond corresponds to 0.018pc. As a target of the southern-hemisphere VLBI monitoring program TANAMI, observations of Cen A are done approximately every six months at 8.4GHz with the Australian Long Baseline Array (LBA) and associated telescopes in Antarctica, Chile, New Zealand, and South Africa, complemented by quasi-simultaneous 22.3GHz observations. The first seven epochs of high-resolution TANAMI VLBI observations at 8.4GHz of Cen A are presented, resolving the jet on (sub-)milliarcsecond scales. They show a differential motion of the subparsec scale jet with significantly higher component speeds farther downstream where the jet becomes optically thin. We determined apparent component speeds within a range of 0.1c to 0.3c and identified long-term stable features. In combination with the jet-to-counterjet ratio, we can constrain the angle to the line of sight to {theta}~12{deg}-45{deg}. The high-resolution kinematics are best explained by a spine-sheath structure supported by the downstream acceleration occurring where the jet becomes optically thin. On top of the underlying, continuous flow, TANAMI observations clearly resolve individual jet features. The flow appears to be interrupted by an obstacle causing a local decrease in surface brightness and circumfluent jet behavior. We propose a jet-star interaction scenario to explain this appearance. The comparison of jet ejection times to high X-ray flux phases yields a partial overlap of the onset of the X-ray emission and increasing jet activity, but the limited data do not support a robust correlation.
3709. TANAMI radio galaxies I
- ID:
- ivo://CDS.VizieR/J/A+A/627/A148
- Title:
- TANAMI radio galaxies I
- Short Name:
- J/A+A/627/A148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the framework of the TANAMI multi-wavelength and VLBI monitoring, we study the evolution of the parsec-scale radio emission in radio galaxies in the southern hemisphere and their relationship to the gamma-ray properties of the sources. Our study investigates systematically, for the first time, the relationship between the two energy regimes in radio galaxies. In this first paper, we focus on Fermi-LAT-detected sources. The TANAMI program monitors a large sample of radio-loud AGN at 8.4GHz and 22.3GHz with the Australian Long Baseline Array(LBA) and associated telescopes in Antarctica, Chile, New Zealand and South Africa. We perform a kinematic analysis for five gamma-ray detected radio galaxies using multi-epoch 8.4 GHz VLBI images, deriving limits on intrinsic jet parameters such as speed and viewing angle. We analyzed103 months of Fermi-LAT data in order to study possible connections between the gamma-ray properties and the pc-scale jets of Fermi-LAT-detected radio galaxies, both in terms of variability and average properties. We discuss the individual source results and draw preliminary conclusions on sample properties including published VLBI results from the MOJAVE survey, with a total of fifteen sources. We find that the first gamma-ray detection of Pictor A might be associated with the passage of a new VLBI component through the radio core, which appears to be a defining feature of high-energy emitting Fanaroff-Riley type II radio galaxies. For the peculiar AGN PKS 0521-36, we detect subluminal parsec-scale jet motions, and we confirm the presence of fast gamma-ray variability in the source down to timescales of 6 hours, which is not accompanied by variations in the VLBI jet. We robustly confirm the presence of significant superluminal motion, up to {beta}_app_~3, in the jet of the TeV radio galaxy PKS 0625-35. Our VLBI results constrain the jet viewing angle to be {theta}<53{deg}, allowing for the possibility of a closely aligned jet. Finally, by analyzing the first pc-scale multi-epoch images of the prototypical Compact Symmetric Object (CSO) PKS 1718-649, we place an upper limit on the separation speed between the two mini-lobes, which in turn allows us to derive a lower limit on the age of the source.Conclusions.We can draw some preliminary conclusions on the relationship between pc-scale jets and gamma-ray emission in radio galaxies, basedonFermi-LAT-detected sources with available multi-epoch VLBI measurements. We find that the VLBI core flux density correlates with the gamma-ray flux, as seen in blazars. On the other hand, the gamma-ray luminosity does not show any dependence on the core brightness temperature and core dominance, two common indicators of jet Doppler boosting. This seems to indicate that gamma-ray emission in radio galaxies is not driven by orientation-dependent effects, as in blazars, which is consistent with the unified model of jetted AGN.
3710. TANAMI radio galaxies II
- ID:
- ivo://CDS.VizieR/J/A+A/641/A152
- Title:
- TANAMI radio galaxies II
- Short Name:
- J/A+A/641/A152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper in our series studying the evolution of parsec-scale radio emission in radio galaxies in the southern hemisphere. Following our study of the radio and high-energy properties of gamma-ray-emitting sources, here we investigate the kinematic and spectral properties of the parsec-scale jets of radio galaxies that have not yet been detected by the Fermi Large Area Telescope (Fermi-LAT) instrument on board NASA's Fermi Gamma-ray Space Telescope. For many sources, these results represent the first milliarcsecond resolution information in the literature. These studies were conducted within the framework of the Tracking Active Nuclei with Austral Milliarcsecond Interferometry (TANAMI) monitoring program and in the context of high-energy gamma-ray observations from Fermi-LAT. We take advantage of the regular 8.4GHz and 22.3GHz Very Long Baseline Interferometry (VLBI) observations provided by the TANAMI monitoring program, and explore the kinematic properties of six gamma-ray-faint radio galaxies. We complement this with ~8.5 years of Fermi-LAT data, deriving updated upper limits on the gamma-ray emission from this subsample of TANAMI radio galaxies. We include publicly available VLBI kinematics of gamma-ray-quiet radio galaxies monitored by the MOJAVE program and perform a consistent Fermi-LAT analysis. We combine these results with those from our previous paper to construct the largest sample of radio galaxies with combined VLBI and gamma-ray measurements to date. The connection between parsec-scale jet emission and high-energy properties in the misaligned jets of radio galaxies is explored. We report for the first time evidence of superluminal motion up to beta_app_=3.6 in the jet of the gamma-ray-faint radio galaxy PKS 2153-69. We find a clear trend of higher apparent speed as a function of distance from the jet core, which indicates that the jet is still being accelerated on scales of tens of parsecs, or ~10^5^R_{sun}_, corresponding to the end of the collimation and acceleration zone in nearby radio galaxies. We find evidence of subluminal apparent motion in the jets of PKS 1258-321 and IC 4296, and no measurable apparent motion for PKS 1549-79, PKS 1733-565 and PKS 2027-308. For all these sources, TANAMI provides the first multi-epoch kinematic analysis on parsec scales. We then compare the VLBI properties of gamma-ray-detected and undetected radio galaxies, and find that the two populations show a significantly different distribution of median core flux density, and, possibly, of median core brightness temperature. In terms of correlation between VLBI and gamma-ray properties, we find a significant correlation between median core flux density and gamma-ray flux, but no correlation with typical Doppler boosting indicators such as median core brightness temperature and core dominance. Our study suggests that high-energy emission from radio galaxies is related to parsec-scale radio emission from the inner jet, but is not driven by Doppler boosting effects, in contrast to the situation in their blazar counterparts. This implies that gamma-ray loudness does not necessarily reflect a higher prevalence of boosting effects.
