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CYBERSKA
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Hi all,
Here is a first cut at characterizing core cosmic magnetism science goals in the SKA1 era. It is based on the submission from a few individuals over the past few days, folded in with my own thoughts. So to some degree this reflects my own bias and is meant as a starting point only. Please critique, let's start the debate
There is of course are wide range of polarization science that could be done, since magnetic fields are pervasive and important on most astrophysical processes. However, I suggest we keep the number of big picture science areas smallish. I propose three below.
1) Detection and Characterization of the magnetic cosmic web
2) Magnetism and galaxy evolution
a) central black holes and their environments
b) formation and evolution of coherent fields in disks
c) relation to and role in cosmic star formation history
d) global galaxy energetics and interaction with the intergalactic environment
3) Magnetic fields and Galaxy cluster formation and evolution through relics and haloes
Key observations for each (glossing over tremendous technical challenges)
1) a) the wide-area survey, which will need ?? RM precision (1 Rad/m2 ?)
b) SKA-mid deep wide-band surveys for very dense grid of high precision RMs to sample small angular scales
c) complemented by very sensitive intermediate angular resolution measures of diffuse emission at low frequency (SKA-low?)
2) a) wide-band spectro-polarimetry of SKA-survey to measure Faraday rotation and depolarization over wide range of bandwidth for large samples of AGN
b) deep fields to measure polarization of large samples of objects well below a microJy.
c) high fidelity images of large samples of radio galaxies from SKA-Survey
3) a) high surface-brightness sensitivity imaging with sensitivity to emission up to arcminute scale? Survey mode? Or targeted?
Final question: Is there a strong Milky Way science driver? The SKA-Survey grid will probe the Galactic sky and create the next generation all-sky RM map. What are the key science areas for Galactic science? Do we need sensitivity to diffuse emission on scales larger than a degree? This would drive the need of single dish. What is the science driver for this? Do we need a next generation GMIMS? What science results?
cheers
Russ
Comments
I agree to push the three sciences.
About final question, I think it is very important to mention that understanding Milky Way magnetic field is vital as foreground to address a couple of key sciences in the 21th century astrophysics and cosmology: "CMB polarization" which is a direct and concrete evidence to prove the inflation theory, "Epoch of Reionization" which is a precious record telling us when and how the first stars and first galaxies were formed, and "Origin of Ultra-High Energy Cosmic Rays" which is a longstanding unknown of our universe. These topics could be strond drivers to study Milky Way magnetic field. - Takuya
Hi Russ,
I'll think through this carefully, but this sounds like an excellent first pass. There is lots to do on the Milky Way, but I'm not sure if it should be a science driver.
cheers
Bryan
Hi Takuya,
I agree that CMB polarization is high profile science. But I am not sure the Galactic polarized foreground, if you are talking about diffuse emission, is best addressed by the SKA. A well-calibrated large single dish would be better. As an array, the SKA will miss the low spatial frequencies so will not alone sample the diffuse foregrounds with high fidelity.
Dear Russ, I am saying about modeling Galactic magnetic fields and modeling Galactic synchrotron emissions, for which studies with SKA (probably using RM grids of pulsars and extragalactic sources) woud be quite powerful compared with studies in any other frequencies... - Takuya
From Frederica,
I'm wondering if both scientific cases 1) and 2) indicated by Russ in the cyberSKA portal (i.e. cosmic web and galaxies) can be studied with the same wide-band spectro-polarimetry survey (e.g. with SKA1-survey), avoiding in this way a survey with SKA1-mid. If this is possible, I would leave SKA1-mid and SKA1-low for deep pointed observations on specific regions of the sky.
Regarding point 3) (clusters of galaxies), I suggest to use the spectro-polarimetry survey to investigate the RM of radio galaxies in the background of clusters and deep pointed observations with SKA1-mid and SKA1-low to investigate radio halos and relics.
Frederica: I was not my intention to recommend a wide-area survey with SKA1-mid, as this would be redundant with SKA-survey However SKA-mid is needed in 2) I think for complementary deep field surveys over broad bands reaching well below 1 microJy to allow detection of polarized emission and FR synthesis from large samples of normal galaxies to significant redshift.
Hi Russ,
Even though the Milky Way may not be a separate science driver, I would not want to omit its presence in the current science driver 2) Magnetism and galaxy evolution. SagA* and its surroundings would be a prima example of 2a), while 2c) would include the role of magnetic fields in Galactic star formation, synchrotron jets from young stellar objects, maser polarization probing circumstellar magnetic fields etc.
It's hard to predict now whether we'll need a next-generation GMIMS without knowing yet what the current-generation GMIMS will find. One reason for an SKA-GMIMS would be an increase in Faraday depth resolution from the current 3.6 rad/m2 for GMIMS to 0.2 rad/m2 for an SKA-low down to 70 MHz. I believe that that will help significantly with the 'magnetism in star formation' theme for galactic studies. A single dish survey would be needed for studies of depolarization (for fractional polarization) of diffuse emission, but I am not sure of a key science driver here.
Cheers,
Marijke