Probing RM due to the IGMF with SKA

Transcription

1 Probing RM due to the IGMF with SKA Takuya Akahori Kagoshima University / SKA Organization Department of Physics and Astronomy, Graduate School of Science and Engineering Japan SKA Consortium / SKA Cosmic Magnetism SWG / ASKAP POSSUM With D. Ryu (UNIST), B.M. Gaensler (U.Toronto), et al. Origin, Evolution, and Sigunatures of Cosmological Magnetic Fields Stockholm

2 Wake-up Quiz RM grids in the SKA Era 2 # of extragalactic polarized sources per 1 sq. degree See e.g., Johnston-Hollitte, TA+ (2015) SKA Science Book 10,000? (SKA2) ~1 (VLA) ~30-100? (ASKAP) 300-1,000? (SKA1)

3 Contents 3 ALL INT DIG IGM ISM ERR v Observation of extragalactic linear polarization v Multiple contributions of Faraday rotation measures (RMs) along a line of signt (LOS) RM due to the Intergalactic magnetic field (IGMF) RMs due to others (INT, DIG, ISM, ERR) Methods to extract RM due to the IGMF Prospect of the Square Kilometre Array (SKA) Stockholm Origin, Evolution, and Sigunatures of Cosmological Magnetic Fields

4 1. Introduction Missing Baryon and the IGMF BigBang Cosmolgy Total baryon content in the Universe Observations galaxies clusters H I Lyα O VI Gas in filaments? 4 MOND? Seed inflation recombination reionization Early Universe Review: Ryu+11;Widrow+11 Seed shock instability Amplification compression, dynamo Large-Scale Structure Amp. comp., dynamo Seed shock instability Leakage winds, jets, ram pressure Galaxies v IGMF could be a probe of missing baryon v If µg in clusters à 1-10 ng in filaments? Dubois & Tessier 08 Ryu+08 Donnert+09

5 1. Introduction Observations of RM 5 Xu & Han (14) NVSS theirs redshift Oppermann, TA+ (15) v Lots of works! Extragalactic RM < 5-15 rad/m 2 Superclusters (Xu+06) & cluster radial profiles (Govoni+10) Latitude dependence (Schnitzeler 10) & probabilistic analysis (Oppermann, TA+15) using all-sly RM grids RM toward Galactic poles (Mao+10;Stil+11) RM as a function of redshift (Hammond+12; Xu & Han14) Relation between RM and MgII absorbers (Farnes+ 14ab) v Extraction of RM in filaments is not achieved yet

6 2. RM due to the IGMF Simulation of IGMF RM (local) IGMF model Ryu+08 v RM rms ~1.4 [rad/m 2 ] (T x = K) v l RM ~ several 100 h -1 [kpc] 6 Depth = 100 h -1 Mpc Log 10 RM [rad m -2 ] [h -1 Mpc] TA, Ryu (2010), ApJ, 723, 476

7 2. RM due to the IGMF Simulation of IGMF RM (z<5) z=0 z=5 Source distribution (Wilman+08) saturation of path length RM obs 1/(1+z) run average TA, Ryu (2011), ApJ, 738, 134 v Random walk & saturation v RM rms ~7-10 [rad/m 2 ] (T x = K) theoretical uncertainty could be a factor of several Galaxy Cluster Subtraction CLS: ALL grids (<1 Mpc of Tx>2 kev) TM7: ALL grids (T>10 7 ) TS8: ALL pixels (Tx*>10 7 & Sx*>10-8 ) TS0: ALL pixels (Tx*>10 7 & Sx*>10-10 ) T in [K], S in [erg/s/cm 2 /sr]

8 3. RM due to the ISM ISM RM toward Galactic Poles v Physically-consistent model of the random component n e0 : NE2001+ (Cordes, Lazio 02; Gaensler+08) T e : (Paladini+ 04) V rms : (Hill+ 08) B 0 : ABDQOPXNS (Sun+ 08, Sun, Reich 10; Giacinti+10; Jansson, Farrar 12; etc) Disk Spiral + Halo Toroidal + Vertical(Poloidal) + Direction + RMS velocity (ASS, BSS), (Dipole, Quadrupole), (Off, Poloidal, X-field), (NGP, SGP), (15km/s,30km/s) 8 Embed data of MHD turbulence Isothermal, compressible, saturation stage (Kim+99) M rms = 0.5,1,2,4, β 0 = 0.1,1,3,10, use closest one L box = 500 pc à L drive = 330 pc (Hill+08) à L int ~ 75 pc TA, Ryu, Kim, Gaensler (2013), ApJ, 767, 150

9 3. RM due to the ISM 2 nd order Structure Function 9 n-th order structure function (SF) v 900 deg 2 FOV toward N/S Galactic poles ß South Galactic Pole :Mao+ (10) WSRT+ACTA ー :Stil+ (11) NVSS(VLA) ß North Galactic Pole :Mao+ (10) WSRT+ACTA ー :Stil+ (11) NVSS(VLA) ß IGMF ー :σ RM ~ several [rad/m 2 ] gives flat S 2 at >0.2 with [rad 2 /m 4 ] (TA, Ryu 2011) ß ISM is small & steep! ー :σ RM ~ 2-5 [rad/m 2 ] gives steep S 2 with < 50 [rad 2 /m 4 ] (TA+13) TA, Ryu, Kim, Gaensler (2013), ApJ, 767, 150; Taylor, TA+ (2015) SKA science book

10 4. RM due to the DIG Depolarizing Intervening Galaxies v Source model as simple as possible 1 or 10 size uniform, α I = α P = -1, 100% pol. v DIG model TA Milky Way type v Observation Stokes Q, U RM given by the polarization angle gradient 10 1 ~ 2 kpc (z=0.1), 6 kpc (0.5), 8 kpc (1.0) TA, Farnes, O Sullivan, Sun, Takahashi, Gaensler in prep.

11 4. RM due to the DIG Monte-Carlo Simulations v 100 K realizations. In each realization, we randomely choose the inclination angle B configuration (ASS/ BSS, DT/QT, X/OFF), LOS offset from the GC v 1 (Core-type) DIG s RM < 2 rad/m 2 if z DIG > 1 v 10 (Lobe-type) DIG s RM < 2 rad/m 2 TA, Farnes, O Sullivan, Sun, Takahashi, Gaensler in prep. 11 L( MHz) S( MHz) à Ideal LOSs for exploring RM due to the IGMF

12 5. RM due to the INT Intrinsic RM need more studies 12 RM or RM rms [rad/m 2 ] at the observer frame à High-z QSOs might be good for exploring RM due to the IGMF RM INT,rms =10/(1+z) 2 Gray ALL RMs for NVSS 317 sources at b >75 (1.4GHz Taylor+09; Hammod+12) Black ALL-ERR (σ RM2 -σ ERR2 ) 1/2 for σ ERR =0, 10, 15 rad/m 2 Blue INT σ INT,0 *(1+z) -2 for σ INT,0 =10 rad/m 2 Red IGM σ IGM = 7 rad/m 2 up to z=5 (TS0 run, TA & Ryu 11) Green ISM σ ISM = 8.4 rad/m 2 (Schnitzeler 10) ß although 2-5 rad/m 2 (TA+ 13) TA, Gaensler, Ryu (2014a), ApJ, 790, 123

13 IGM map Akahori, Ryu 2011 INT random σ INT =σ INT,0 (1+z) -2 σ INT,0 =10 rad/m 2 DIG random, 50% MgII ISM map Akahori ERR ISM random map σ ERR =1 rad/m 2 6. Extracting RM due to the IGMF Statistical Approach ALL Map COM Map ICM filter INT filter DIG filter ISM filter ERR filter RRM map RRM map TA, Gaensler, Ryu (2014a), ApJ, 790, 123 Choose high-z sources σ INT (z=2) ~ 1 rad/m 2 Discard 50 % of sources they have large DIG RMs Cut large-scale component filtering scale at ~1-2 Assume sources have mean RM error ~1 rad/m 2 13 Remove clusters of galaxies X-ray brightness & temperature Chop! Green: ISM Red: IGM

14 6. Extracting RM due to the IGMF Extraction Simulations deg 2 FOV, South Galactic Pole, z>2 sources only ー IGM ー COM(ALL) ー RRM SKA1 (Survey) 100 RM/deg 2 ~a few µjy level SKA1 (Deep) 1000 RM/deg 2 ~100 njy level SKA2 (Deep) RM/deg 2 ~10 njy level Number under discussion (See Larry s talk & 3.1 of our memo) v Our selection criteria: ~86% of sources were discarded v 100 RM/deg 2 data may allow to extract σ IGM v 1000 RM/deg 2 data may allow to extract S 2,IGM down to ~0.1 TA, Gaensler, Ryu (2014a), ApJ, 790, 123

15 6. Extracting RM due to the IGMF Faraday Tomography 15 Ideal situations v Detect a RM gap between two FDFs Milky Way and Source (Strategy A) Source of Sources (Stretegy B) v Can we find such ideal situations? No depolarization, no MgII (A,B) On/Off-source observation (A,B) An angular separation < 0.1º is reasonable to regard that the two LOS go through the same foreground (B) IGMF, z=1.0 Gal. pole GMF IGMF, z=0.3 IGMF, z=0.1 TA, Kumazaki, Takahashi, Ryu (2014b), PASJ, 66, 65

16 6. Extracting RM due to the IGMF QU-fitting Results SKA1-SUR, 1 hr, 1 mjy source, RM IGMF = 5 rad/m 2, 3σ confidence ー MHz ー MHz ー MHz 16 Model FDF v IGMF RM of ~ several rad/m 2 could be detectable with the SKA (MID) Full frequency coverage is desirable. But if it is not feasible, going to lower frequencies would be better Govoni, TA+ (2014), SKA Science Assessment Document

17 7. The SKA Project SKA Phase 1 (SKA1) v Const , Eealy Sci , Full Sci v Cost ~650 M, Operation ~50M /yr 17 + SKA1-LOW AUS Log-Peri. ~130, x 256PL B max ~65-80 km SKA1-MID RSA 15m SKA Dish m MeerKAT 64 B max ~150 km ASKAP AUS 12m ASKAP Dish 36 Phased Array Feed (PAF)

18 7. The SKA Project SKA Phase 2 (SKA2) v Concept 2016-, Design 2018-, Const , Sci v Cost >1500 M, Operation ~150 M /yr? 18 + SKA2-LFAA AUS Log-Peri. ~1,000,000 B max ~3000 km SKA2-DISH RSA 15m SKA Dish ~2500 B max ~3000 km, PAF or Wide Band Single Pixel Feed (WBSPF) SKA2-MFAA RSA Dense Phased Aperture Array 250

19 7. The SKA Project Sensitivity SKA1 LOW MID B max (B core ) 11 ( a few ) 0.2 (2 ) Reference frequency 110 MHz 1670 MHz Continuum sensitivity 4.12 µjy/hr -1/2 (250 MHz) 0.72 µjy/hr -1/2 (770 MHz) Line sensitivity 206 µjy/hr -1/2 (100 khz) 63 µjy/hr -1/2 (100 khz) v Re-baselined LOW: 50% cut MID: 30% cut v Pol. purity LOW < 45dB ~ 0.003% MID < 40 db ~ 0.01% 19

20 7. The SKA Project Sensitivity (# of sources) # of polarized sources per degree SKA2 Gal FRI FRII LOW 4xLOW MID 10xMID 5xMID # of pulsars 20 Keane SKA1-3 POSSUM # of core antennae NVSS Polarized intensity [log mjy] Taylor, TA+ (2015) SKA Science Book v pol. sources/deg 2 4 µjy/beam (1 hr) and 2 resolution (Johnston-Hollitt+15) v 9000 PSRs MSPs and 7000 PSRs MSPs SKA1-MID and LOW, respectively, all sky, 10 min pointings (Keane+15)

21 7. The SKA Project Angular resolution Angular resolution of SKA SKA2 21 SKA1-LOW ( MHz) 1 SKA1-SUR ( MHz) SKA1-MID ( ) SKA1-MID ( ) 1 maximum baseline [km] 3000 v Maximum Baseline (B max ) LOW km (SKA1), 3000 km (SKA2) MID 150 km (SKA1), 3000 km (SKA2) v Nominal (core) Baseline (B nom ) several km (TBD) à the best (nominal) sensitivity is obtained at ~10 times worse resolutions (larger spatial scales) v Resolution 1/ frequency Govoni, TA+ (2014), SKA Science Assessment Document

22 7. The SKA Project Image Quality 22 Maximum angular scale SKA1-LOW ( MHz) SKA1-MID ( ) SKA1-MID ( ) 1 1 minimum baseline [m] v Minumum Baseline LOW = 43 m à TBD? MID = 23 m v Max. ang. scale 1/freq. Govoni, TA+ (2014), SKA Science Assessment Document MHz FOV deg MID 1.37/(GHz) 2

23 7. The SKA Project Frequency Coverage 23 LOFAR WSRT GMRT GMIMS* S-PASS* GALFACTS* JVLA ATCA ASKAP SKA1 SKA2 λ 2 coverage λ 2 [m 2 ] λ 2 [m 2 ] RM [rad/m 2 ] *single dish GMIMS (DRAO, Parkes, Effelsberg) S-PASS (Parkes), GALFACTS (Arecibo) Beck+12 facility band frequency (MHz) SKA1-LOW SKA1-MID PAF WBSPF A B MID band 3 & 4 will be not implemented under the 650 M cost cap

24 INT DIG IGM ISM Summary v IGM: σ RM ~ several rad/m 2 through filaments up to z=5, scales If B ~ 10 ng à 1 ng (e.g. Vazza+14), σ RM <~ 1 rad/m 2 v ISM: σ RM ~ 2-5 rad/m 2 toward Galactic poles, > 1 If the disk field 2 µg à 4 µg, σ RM < ~10 rad/m 2 Stratified media? Impact on vertical fields (average RM) v DIG: σ RM ~ 1-2 rad/m 2 if z>1 or extended (10 ) INT Depolarization vs. evolution of galaxies (e.g. Beck+12) v INT: σ RM ~ 10/(1+z) 2 rad/m 2 à ~1 rad/m z=2 Depolarization vs. evolution of AGN We will develop a model in 2016FY v RM grids and Faraday Tomography: IGMF RM of several rad/m 2 could be detactable in ideal LOSs We need to estabilish source selection criteria & test it v SKA Project: Awesome! 10 M polarized sources & 10 K pulsars in mid 2020!! 24