Broadband, radio spectro-polarimetric study of 100 radiative-mode and jet-mode AGN

We present the results from a broadband (1 to 3 GHz), spectro-polarimetry study of the integrated emission from 100 extragalactic radio sources with the ATCA, selected to be highly linearly polarized at 1.4 GHz. We use a general purpose, polarization model-fitting procedure that describes the Faraday rotation measure (RM) and intrinsic polarization structure of up to three distinct polarized emission regions or 'RM components' of a source. Overall, 37%/52%/11% of sources are best fit by one/two/three RM components. However, these fractions are dependent on the signal-to-noise ratio (S/N) in polarization (more RM components more likely at higher S/N). In general, our analysis shows that sources with high integrated degrees of polarization at 1.4 GHz have low Faraday depolarization, are typically dominated by a single RM component, have a steep spectral index, and a high intrinsic degree of polarization. After classifying our sample into radiative-mode and jet-mode AGN, we find no significant difference between the Faraday rotation or Faraday depolarization properties of jet-mode and radiative-mode AGN. However, there is a statistically significant difference in the intrinsic degree of polarization between the two types, with the jet-mode sources having more intrinsically ordered magnetic field structures than the radiative-mode sources. We also find a preferred perpendicular orientation of the intrinsic magnetic field structure of jet-mode AGN with respect to the jet direction, while no clear preference is found for the radiative-mode sources.Comment: 29 pages (including Appendix), 28 figures, 7 tables. Accepted for publication in MNRA

The Magnetic Field and Polarization Properties of Radio Galaxies in Different Accretion States

We use the integrated polarized radio emission at 1.4 GHz ($\Pi_{\rm 1.4\,GHz}$) from a large sample of AGN (796 sources at redshifts $z<0.7$) to study the large-scale magnetic field properties of radio galaxies in relation to the host galaxy accretion state. We find a fundamental difference in $\Pi_{\rm 1.4\,GHz}$ between radiative-mode AGN (i.e. high-excitation radio galaxies, HERGs, and radio-loud QSOs) and jet-mode AGN (i.e. low-excitation radio galaxies, LERGs). While LERGs can achieve a wide range of $\Pi_{\rm 1.4\,GHz}$ (up to $\sim$$30\%$), the HERGs and radio-loud QSOs are limited to $\Pi_{\rm 1.4\,GHz} \lesssim 15\%$. A difference in $\Pi_{\rm 1.4\,GHz}$ is also seen when the sample is divided at 0.5% of the total Eddington-scaled accretion rate, where the weakly accreting sources can attain higher values of $\Pi_{\rm 1.4\,GHz}$. We do not find any clear evidence that this is driven by intrinsic magnetic field differences of the different radio morphological classes. Instead, we attribute the differences in $\Pi_{\rm 1.4\,GHz}$ to the local environments of the radio sources, in terms of both the ambient gas density and the magnetoionic properties of this gas. Thus, not only are different large-scale gaseous environments potentially responsible for the different accretion states of HERGs and LERGs, we argue that the large-scale magnetised environments may also be important for the formation of powerful AGN jets. Upcoming high angular resolution and broadband radio polarization surveys will provide the high precision Faraday rotation measure and depolarization data required to robustly test this claim.Comment: 18 pages, 17 figures, accepted for publication in Ap

Interacting Large-Scale Magnetic Fields and Ionised Gas in the W50/SS433 System

The W50/SS433 system is an unusual Galactic outflow-driven object of debatable origin. We have used the Australia Telescope Compact Array (ATCA) to observe a new 198 pointing mosaic, covering $3^\circ \times 2^\circ$, and present the highest-sensitivity full-Stokes data of W50 to date using wide-field, wide-band imaging over a 2 GHz bandwidth centred at 2.1 GHz. We also present a complementary H$\alpha$ mosaic created using the Isaac Newton Telescope Photometric H$\alpha$ Survey of the Northern Galactic Plane (IPHAS). The magnetic structure of W50 is found to be consistent with the prevailing hypothesis that the nebula is a reanimated shell-like supernova remnant (SNR), that has been re-energised by the jets from SS433. We observe strong depolarization effects that correlate with diffuse H$\alpha$ emission, likely due to spatially-varying Faraday rotation measure (RM) fluctuations of $\ge48$ to 61 rad m$^{-2}$ on scales $\le4.5$ to 6 pc. We also report the discovery of numerous, faint, H$\alpha$ filaments that are unambiguously associated with the central region of W50. These thin filaments are suggestive of a SNR's shock emission, and almost all have a radio counterpart. Furthermore, an RM-gradient is detected across the central region of W50, which we interpret as a loop magnetic field with a symmetry axis offset by $\approx90^{\circ}$ to the east-west jet-alignment axis, and implying that the evolutionary processes of both the jets and the SNR must be coupled. A separate RM-gradient is associated with the termination shock in the Eastern ear, which we interpret as a ring-like field located where the shock of the jet interacts with the circumstellar medium. Future optical observations will be able to use the new H$\alpha$ filaments to probe the kinematics of the shell of W50, potentially allowing for a definitive experiment on W50's formation history.Comment: Submitted to MNRA

Polarized point sources in the LOFAR Two-meter Sky Survey: A preliminary catalog

The polarization properties of radio sources at very low frequencies (h45m–15h30m right ascension, 45°–57° declination, 570 square degrees). We have produced a catalog of 92 polarized radio sources at 150 MHz at 4.′3 resolution and 1 mJy rms sensitivity, which is the largest catalog of polarized sources at such low frequencies. We estimate a lower limit to the polarized source surface density at 150 MHz, with our resolution and sensitivity, of 1 source per 6.2 square degrees. We find that our Faraday depth measurements are in agreement with previous measurements and have significantly smaller errors. Most of our sources show significant depolarization compared to 1.4 GHz, but there is a small population of sources with low depolarization indicating that their polarized emission is highly localized in Faraday depth. We predict that an extension of this work to the full LOTSS data would detect at least 3400 polarized sources using the same methods, and probably considerably more with improved data processing

Using Climate Data to Understand the Response by Wildlife and Fisheries

Montana’s water supply varies from about 40 to 160 percent average. This is due to a large variability in the mountain snowpack, spring and summer precipitation and temperature. Nearly all of these parameters that determine the runoff will impact fish and wildlife throughout the year. Time of various climatic events in Montana, such as when snowpack starts to accumulate, when it reaches it season’s maximum, when it melts out, winter temperatures, when streams reach their annual peak flow, and when plants break dormancy (spring green-up), forage production, whether or not there is fall green-up and the time of fall green-up all have had a historical variation spanning about eight weeks. In addition, there is annual variation in climatic conditions across the state. Wildlife and fisheries managers need to take this variability into account when managing wildlife. Tools to help assess the potential variability and timing of various climatic, hydrologic and phenological parameters will be presented. Using observed climatic and hydrologic data collected over the past 100 years can be further interpreted to help understand and predict the response and effects on fish and wildlife. Relating these responses to these parameters provide better relationships than by using calendar dates

Climatic Data for Wildlife Research and Management

There is generally a poor correlation between climatic variables at lower elevations and higher elevations. It is imperative that this relationship be understood when evaluating climatic effects on species that move from lower to higher elevation during different seasons. It is also important that valley climatic conditions are not used to define relationship of species that occupy higher elevations. Using data from NRCS SNOTEL (SNOw TELemetry) sites and NWS climatic stations can help define climatic conditions at locations occupied by concerned species.  Daily data is generally more useful than monthly or seasonal averages. There are approximately 90 SNOTEL sites across Montana that typically report daily SWE (snow water equivalent), precipitation, maximum, minimum and average temperatures yeararound and data is available in real-time. SWE can be related to travel, soil temperature, forage production and availability, migration and predator-prey relationships.  Some SNOTEL sites also report snow depth. NWS stations typically report daily precipitation, maximum and minimum temperature but data for most stations is reported monthly.  SWE can be estimated for NWS sites where daily air temperature, snow depth and precipitation are reported. Precipitation can be related to forage production, soil moisture and fall green-up. Maximum, minimum and average daily temperature can be related to forage production, phenology, the day plants break dormancy, fall green-up, critical temperatures for animals. Annual variability as well as elevational variability can be used to refine data to each area of interest.  Some examples of the relationships described above will be presented

The Influence of Snow on Ground Temperatures

Snow influences temperatures within the snowpack and soil temperatures.  Air temperatures may be well below freezing but temperatures within the snowpack and at soil surface will be near 0 0C (32 0F). When there is fall green-up and snow covers the vegetation before cold temperatures occur (less than – 5 0C or 23 0F), the native forage may stay green into January. With soil surface temperatures near freezing under snow packs that exceed about one meter, organisms can survive extremely cold winter air temperatures. Air temperatures can affect snow consistency as the seasons snowpack is being deposited which can affect foraging and animal movement. Relationships between air temperature, snow temperature and soil temperatures will be presented