The Virgo Cluster as a Node in Larger Structure Brent Tully
The Virgo Cluster as a Node in Larger Structure Brent Tully
The Virgo Cluster as a Node in Larger Structure Brent Tully
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Outl<strong>in</strong>e<br />
• Observational methods<br />
• Magnetic fields <strong>in</strong> spirals<br />
• Connection of magnetic fields and SF activity<br />
• Magnetism of dwarfs and irregular galaxies<br />
• Magnetic field evolution <strong>in</strong> merg<strong>in</strong>g galaxies<br />
• Conclusions and outlook<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
In collaboration with Ra<strong>in</strong>er Beck, Dom<strong>in</strong>ik Bomans, Robert Drzazga, George<br />
Heald, Wojciech Jurusik, LOFAR MKSP team
Magnetic field components<br />
Before (Beck 1996):<br />
B 2 total = B 2 regular + B 2 random<br />
(uniform)<br />
(turbulent)<br />
Now (Beck 2012):<br />
compression, shear (anisotr. turb.)<br />
B 2 total = B 2 coherent + B 2 anisotropic + B 2 random<br />
(regular)<br />
RM ∫ n e B coh║ dl<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
B 2 total = B 2 ordered + B 2 random<br />
I synchr<br />
PI B ord ┴<br />
Mean: 9μG 2 –5μG (Beck 2005)
New posibility – RM Synthesis<br />
More – George Heald’s talk<br />
Presents polarized <strong>in</strong>tensity <strong>as</strong> a function of Faraday depth<br />
Faraday depth:<br />
Only for Faraday screen =RM<br />
Multichannel radio observations of polarized signal are required<br />
– spectro-polarimetry<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
Burn 1966, <strong>Brent</strong>jens & de Bruyn 2005, Heald et al. 2009<br />
(application for SINGS galaxies), etc.
Other methods - examples<br />
SMC - optical starlight polarization<br />
M82 – <strong>in</strong>frared polarized emission<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
to LMC<br />
Starlight pol. B ┴ =1.6 G<br />
RM Bc ║ =-0.16 G<br />
Pan-Magellanic field()<br />
Mao et al. 2008, 2012<br />
Central radial field (superw<strong>in</strong>d)<br />
and superbubbles<br />
Greaves et al. 2000<br />
More from ALMA!
B structure <strong>in</strong> spirals<br />
• Regular (coherent) field - “mean-field” dynamo<br />
review: Beck 1996, 2012, Widrow 2002; MHD simul.: Gressel et al.<br />
2008, Han<strong>as</strong>z et al. 2009, Moss et al. 2012<br />
• Random field – small-scale (turbul.) dynamo e.g. Brandenburg and<br />
Ferrière 2006<br />
• Large-scale dynamo modes:<br />
Disk (top view)<br />
Halo (weaker) (side view)<br />
ASS<br />
BSS<br />
even (sym)<br />
(quadrupolar )<br />
odd (antisym)<br />
(dipolar)<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
• Dynamo modes of regular fields can be identified from the pattern of<br />
polarization angles and of RMs
B structure <strong>in</strong> spirals – M 51<br />
Spiral fields more or less parallel to<br />
the optical spiral arms<br />
PI VLA+Eff 6cm<br />
B-vectors+HST<br />
Fletcher et al. 2010<br />
RM 3-6cm<br />
B tot =20μG<br />
B ord =10μG<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
A large part (around 75%) of the strong polarised signal comes from<br />
anisotropic random magnetic fields! (compression <strong>in</strong> spiral density waves)
M51 model of regular field topology<br />
Fletcher et al. 2010<br />
axisymmetric<br />
bisymmetric<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
• Different dynamo modes <strong>in</strong> disk (ASS) and halo (BSS)<br />
• Field reversal between northern disk and <strong>in</strong>ner halo
NGC 253<br />
Nearly edge-on galaxy (78deg)<br />
Vertical field - an X-shaped pattern<br />
(common among edge-ons)<br />
Halo field compressed by expand<strong>in</strong>g g<strong>as</strong><br />
PI 6cm VLA+EFF + X, disk subtracted, Heesen et al. 2009<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012
NGC 4254<br />
B and ISM<br />
<strong>Virgo</strong> cluster<br />
spiral, weakly<br />
disturbed<br />
VLA+EFF<br />
4.86 GHz<br />
(6.3cm)<br />
B tot =16μG<br />
B ord =7μG<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
Chyży, Ehle & Beck 2007, A&A, 474, 415
Vir A<br />
1.2 Mpc<br />
NGC 4254<br />
PI 4.86 GHz
Magnetic field<br />
components - SFR<br />
B tot ΣSFR 0.180.01<br />
<strong>The</strong> radio-IR correlation is due to the<br />
turbulent field<br />
B ord<br />
B ran ΣSFR 0.260.01
Similar relations NGC 6946<br />
Tabatabaei et al. (2012 subm.)<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
<strong>The</strong> orig<strong>in</strong> of the ordered magnetic field can be<br />
l<strong>in</strong>ked to the dynamo effect on galactic scales (e.g.<br />
Beck et al. 1990, 1996) and is not correlated with<br />
SFR (e.g. Chyży 2008; Krause 2009; Fletcher et al.<br />
2011).<br />
More: Marita Krause talk
Are dwarf galaxies different<br />
IC10, m<strong>as</strong>sive<br />
starburst, local equivalent of BCG<br />
Unlike spirals small dwarf<br />
irregulars have no spiral fields<br />
Weak fields: mean B≤4μG<br />
IC10 – B tot ~10μG<br />
exceptionally strong<br />
IC10 - only small-scale<br />
dynamo<br />
Dwarfs follow radio-FIR<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
0.2 kpc<br />
________<br />
VLA 4.6 GHz + Halpha, Chyzy et al. 2005<br />
Can they magnetize IGM<br />
How far out do the magnetic<br />
fields extend <br />
(Kronberg et al. 1999, 2001,<br />
2006, Bertone et al. 2006,<br />
Donnert et al. 2009, Samui et<br />
al. 2009)
Synchrotron envelopes<br />
IC10 – VLA observations<br />
VLA 21cm, Chyzy <strong>in</strong> prep<br />
6cm, EVLA, Heesen et al. 2012<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
Can LOFAR or WSRT detect larger<br />
synchrotron envelope at lower frequencies<br />
Soon: RM Synthesis at 330 MHz WSRT
NGC 2976<br />
● Dynamically simple, bulgeless<br />
● Pure-disk object (Simon et al. 2003)<br />
● Disk - 6kpc<br />
● low HI m<strong>as</strong>s (1.5 10^8 Ms)<br />
● In the periphery of M81/M82 group<br />
Large-scale dynamo<br />
Optical<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
Chynoweth 2008<br />
HI
PI + B-vectors<br />
RM Synthesis WSRT 1.5 GHz<br />
VLA 1.43 GHz<br />
Drzazga et al. reanalysis of WSRT data (Heald et al. 2009)<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
●<br />
●<br />
Both methods give similar results<br />
magnetic fields escap<strong>in</strong>g <strong>in</strong>to <strong>in</strong>tergalactic space,<br />
far away from the group centre<br />
Drzazga et al. <strong>in</strong> prep.
NGC 2976<br />
Faraday depth<br />
(RM)<br />
<strong>The</strong> same <strong>as</strong> for the Milky<br />
Way (Faraday screen)<br />
RM = -36 rad/m 2<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
• No thermal electrons<br />
• No regular (large-scale dynamo) field <strong>in</strong> the halo<br />
(no large-scale dynamo – below dynamo threhshold, strong anisotropic<br />
fields!)
Contrary c<strong>as</strong>e M81<br />
First (prelim<strong>in</strong>ary)<br />
RM Synthesis at 330 MHz WSRT<br />
rms close to confusion limit <strong>in</strong> TP<br />
Drzazga et al. <strong>in</strong> prep.<br />
M81<br />
• Only the Milky Way is visible<br />
• No polarised emission from M81<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
• Can we observe polarized emission<br />
from external galaxies at such long<br />
wavelengths
How magnetic fields evolve <strong>in</strong> merg<strong>in</strong>g galaxies<br />
<strong>The</strong> Toomre sequence + Br<strong>as</strong>s<strong>in</strong>gton et al. 2007<br />
+ object available from VLA archive<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
In total 24 galaxies (16 <strong>in</strong>teract<strong>in</strong>g systems)<br />
Drzazga, Chyży, Jurusik , Wiórkiewicz 2011
<strong>The</strong> Taffy and <strong>The</strong> Taffy2<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
Radio bridges discovered by Condon et al. 2002<br />
In the bridge: Btot = 16μG, Breg = 10μG<br />
Nearly head-on collision<br />
occurred about 10^7 years<br />
ago <strong>in</strong> the Taffy and 5x10^7<br />
years ago <strong>in</strong> the Taffy2
<strong>The</strong> radio (6cm) – FIR(60μm) correlation<br />
<strong>The</strong> slope for the normal<br />
galaxy sample is 0.98<br />
+/- 0.04.<br />
Tidal <strong>in</strong>teraction does<br />
not alter the correlation<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012
Evolution of magnetic fields <strong>in</strong> <strong>in</strong>teract<strong>in</strong>g<br />
galaxies<br />
• Major enhancement of<br />
SF and magnetic energy<br />
occurs at the stage of<br />
nuclear coalescence.<br />
• After that the process of<br />
generation of magnetic<br />
fields is term<strong>in</strong>ated.<br />
• Agreement with the<br />
evolution of the SFE<br />
(Georgakakis et al. 2000)<br />
• <strong>The</strong> strongest evolution<br />
is observed for nuclear<br />
regions<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
How magnetic fields evolve across the Hubble time
Conclusions and outlook<br />
M51 – well def<strong>in</strong>ed spiral fields but a large part is anisotropic. Different structures<br />
of the toroidal field <strong>in</strong> the disk and <strong>in</strong>ner halo.<br />
How important are anisotropic fields <strong>in</strong> galaxies<br />
Edge-on galaxy NGC253 shows X-shaped structure <strong>in</strong> halo.<br />
What is the orig<strong>in</strong> of X-shaped fields<br />
Dwarf galaxies show weak magnetic fields (≤4μG), without spiral patterns, show<br />
similar B-ΣSFR correlation <strong>as</strong> observed across NGC4254 and NGC6946.<br />
IC10 - dwarf with a large radio envelope.<br />
What is the full extent of synchrotron halo of galaxies<br />
NGC2976 - magnetized outflows at the periphery of M81/M82 group.<br />
At 330 MHz Milky Way is very bright.<br />
Are galaxies completely depolarized at long wavelengths<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
Magnetic fields evolve <strong>in</strong> merg<strong>in</strong>g galaxies: 3x stronger fields at the coalescence.<br />
How magnetic fields evolve across the Hubble time
Waller et al. 2001<br />
R<strong>in</strong>ged<br />
galaxy<br />
NGC 4736<br />
Early type Sab<br />
opt<br />
R<strong>in</strong>ged morphology – <strong>in</strong>ner<br />
L<strong>in</strong>dblad resonance of the<br />
galactic oval (accumulation of<br />
g<strong>as</strong> trigger star formation)<br />
No dist<strong>in</strong>ct spiral arms<br />
Magnetic fields<br />
UV
NGC 4736<br />
radio contours at 8.5 GHz (VLA+EFF)<br />
<strong>in</strong>frared 24 m – colors (SPITZER)<br />
8”x8” (200pc x 200pc)
Polarized <strong>in</strong>tensity 8.5 GHz<br />
+ B (of PP) + Hα image<br />
NGC 4736<br />
B tot 30 G<br />
B reg 13 G<br />
rms=6μJy<br />
MF are<br />
cross<strong>in</strong>g the<br />
r<strong>in</strong>g!<br />
Srong action<br />
of the largescale<br />
dynamo<br />
Pitch angle<br />
35 o<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
Chyży and Buta 2008, ApJLetters, 677, 17
<strong>The</strong> radio (11cm)<br />
– FIR(60μm)<br />
correlation<br />
(dwarfs<br />
and spiral galaxies)<br />
Low-m<strong>as</strong>s dwarf<br />
galaxies follow a<br />
trend determ<strong>in</strong>ed<br />
for high surface<br />
brightness spirals<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012
Dwarfs of the Local Group<br />
• Weak fields: mean B≤4μG<br />
IC10 – 10μG exceptionally strong<br />
• B correlates ma<strong>in</strong>ly with ΣSFR or Σρ<br />
B ΣSFR 0.280.04<br />
K. Chyży<br />
GA IAU<br />
Beij<strong>in</strong>g<br />
22.08.2012<br />
Effelsberg 2.6, 4.8 GHz, Chyży et al. 2011<br />
4,0<br />
Low-m<strong>as</strong>s dwarf<br />
galaxies follow a<br />
trend determ<strong>in</strong>ed for<br />
high surface<br />
brightness spirals:<br />
similar physical<br />
conditions for star<br />
formation,<br />
magnetic field, and<br />
cosmic-ray generation<br />
processes <strong>as</strong><br />
the m<strong>as</strong>sive spirals
What LOFAR can see<br />
NGC4631, WSRT 327 MHz map by<br />
Hummel & Dettmar 1990<br />
NGC 4631 LOFAR 131-162MHz -77SBs,<br />
51’’ x 37’’, levs 3.3mJy x (3,6,9,15,20, 30)<br />
Wojciech Jurusik, LOFAR MKSP team<br />
Very soon sufficient sensitivity!<br />
1.4 GHz, VLA, Krause & Beck 2002
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