Is There a Polarization Horizon?
Modern radio spectrometers make measurement of polarized intensity as a function of Faraday depth possible. I investigate the effect of depolarization along a model line of sight. I model sightlines with two components informed by observations: a warm ionized medium with a lognormal electron density...
| Main Author: | |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2018-11-01
|
| Series: | Galaxies |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2075-4434/6/4/129 |
| _version_ | 1819142716094676992 |
|---|---|
| author | Alex S. Hill |
| author_facet | Alex S. Hill |
| author_sort | Alex S. Hill |
| collection | DOAJ |
| description | Modern radio spectrometers make measurement of polarized intensity as a function of Faraday depth possible. I investigate the effect of depolarization along a model line of sight. I model sightlines with two components informed by observations: a warm ionized medium with a lognormal electron density distribution and a narrow, denser component simulating a spiral arm or H<span style="font-variant: small-caps;">ii</span> region, all with synchrotron-emitting gas mixed in. I then calculate the polarized intensity from 300⁻1800 MHz and calculate the resulting Faraday depth spectrum. The idealized synthetic observations show far more Faraday complexity than is observed in Global Magneto-Ionic Medium Survey observations. In a model with a very nearby H<span style="font-variant: small-caps;">ii</span> region observed at low frequencies, most of the effects of a “depolarization wall„ are evident: the H<span style="font-variant: small-caps;">ii</span> region depolarizes background emission, and less (but not zero) information from beyond the H<span style="font-variant: small-caps;">ii</span> region reaches the observer. In other cases, the effects are not so clear, as significant amounts of information reach the observer even through significant depolarization, and it is not clear that low-frequency observations sample largely different volumes of the interstellar medium than high-frequency observations. The observed Faraday depth can be randomized such that it does not always have any correlation with the true Faraday depth. |
| first_indexed | 2024-12-22T12:14:46Z |
| format | Article |
| id | doaj.art-d2c4f7b04a574ec885ab1446733bf48d |
| institution | Directory Open Access Journal |
| issn | 2075-4434 |
| language | English |
| last_indexed | 2024-12-22T12:14:46Z |
| publishDate | 2018-11-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Galaxies |
| spelling | doaj.art-d2c4f7b04a574ec885ab1446733bf48d2022-12-21T18:26:11ZengMDPI AGGalaxies2075-44342018-11-016412910.3390/galaxies6040129galaxies6040129Is There a Polarization Horizon?Alex S. Hill0Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, CanadaModern radio spectrometers make measurement of polarized intensity as a function of Faraday depth possible. I investigate the effect of depolarization along a model line of sight. I model sightlines with two components informed by observations: a warm ionized medium with a lognormal electron density distribution and a narrow, denser component simulating a spiral arm or H<span style="font-variant: small-caps;">ii</span> region, all with synchrotron-emitting gas mixed in. I then calculate the polarized intensity from 300⁻1800 MHz and calculate the resulting Faraday depth spectrum. The idealized synthetic observations show far more Faraday complexity than is observed in Global Magneto-Ionic Medium Survey observations. In a model with a very nearby H<span style="font-variant: small-caps;">ii</span> region observed at low frequencies, most of the effects of a “depolarization wall„ are evident: the H<span style="font-variant: small-caps;">ii</span> region depolarizes background emission, and less (but not zero) information from beyond the H<span style="font-variant: small-caps;">ii</span> region reaches the observer. In other cases, the effects are not so clear, as significant amounts of information reach the observer even through significant depolarization, and it is not clear that low-frequency observations sample largely different volumes of the interstellar medium than high-frequency observations. The observed Faraday depth can be randomized such that it does not always have any correlation with the true Faraday depth.https://www.mdpi.com/2075-4434/6/4/129techniques: radio polarizationISM: turbulenceISM: magnetic fields |
| spellingShingle | Alex S. Hill Is There a Polarization Horizon? Galaxies techniques: radio polarization ISM: turbulence ISM: magnetic fields |
| title | Is There a Polarization Horizon? |
| title_full | Is There a Polarization Horizon? |
| title_fullStr | Is There a Polarization Horizon? |
| title_full_unstemmed | Is There a Polarization Horizon? |
| title_short | Is There a Polarization Horizon? |
| title_sort | is there a polarization horizon |
| topic | techniques: radio polarization ISM: turbulence ISM: magnetic fields |
| url | https://www.mdpi.com/2075-4434/6/4/129 |
| work_keys_str_mv | AT alexshill isthereapolarizationhorizon |