Download Effects of Ram Pressure: NGC 4402

Intracluster Shocking of the ISM
in Virgo Spirals:
Modified FIR-Radio Relations
Eric J. Murphy
(Caltech)
The EVLA: Galaxies Through Cosmic Time
SPITSOV: Spitzer Survey of Virgo
Team: J. Kenney, E. Murphy, G. Helou, A. Abramson, I. Wong, J. Howell,
J. Van Gorkom, R. Beck, B. Vollmer , H. Crowl, A. Chung
 44 S0/a-Sm Virgo
Spirals
 Located throughout
cluster
 Range of HI & H
properties
 IRAC & MIPS
Imaging; x2 SINGS
integration
NGC 4254
NGC 4501
NGC 4330
NGC 4402
NGC 4522
NGC 4580
IRAC 3-color images: 3.6m blue; 4.5m green; 5.8 & 8.0m red
c/o Ivy Wong
FIR – Radio Correlation: How it works… well, kind of
(de Jong et al. 1985; Helou et al. 1985)
FIR
SNe
σ = .26
(L. Cowie)
synchrotron
 Driven by Massive Star Formation
 FIR – Dust heated by Massive stars
 mfp of dust heating UV photons ~100 pc
 Radio – CRe- accelerated by SNe in B-field
 CRe- diffuse ~1 kpc
Yun, Reddy, & Condon. (2001)
 Radio image is smoother version of FIR image
Image Smearing Analysis: (e.g. NGC 5194)
A
22cm Map
C
Φ
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Residuals between
Radio & Smeared
FIR Images
(Murphy et al. 2006a,b)
B: Best-fit Scale-length
Φ: Improvement
(~x2-3 on average)
B
A: l = 0.0 kpc
Smeared
70µm
Maps
B: l = 0.6 kpc
C: l = 3.0 kpc
Comparing FIR and Radio Morphologies:
e.g. NGC 4402
MIPS 70 μm
VLA 20 cm
Radio affected more than FIR:
– CRe-’s which diffuse far away from SF sites/mol. clouds easier to push
around by ICM wind
Use FIR image to predict radio distribution.
– Characterize ICM strength and direction: FIR/RC ratios sensitive to current RP!
Looking for Deviations from Expected
Radio Morphology
1. Smooth 70m map to optimally
reduce differences w/ radio disk

i.e. predicted radio map
2. Create ratio map
 obs./mod. radio
3. Identify pixels significantly
deviant w.r.t. S/N of map &
internal dispersion of disk
 Excess regions
NGC 4402
NGC 4254
Ratio maps
 Pix > 1.3
 Deficit regions are detected
 Pix < 0.50
4. Quantify severity of deficit by
defining:
Deficit regions
Radio Continuum Deficit/Excess Regions
HI contours overlaid
– 6/10 galaxies: we detect
deficit regions (pix < 0.50)
 Each shows additional
evidence of ram pressure
effect
Radio Deficits located opposite
synchrotron tails & excess regions:
- associated with ICM wind
NGC 4522: A well studied case for ram
pressure stripping:
Leading
edge
ICM wind
(Murphy et al. 2008 (arXiv:0812:2922)
Polarized RC
on HI
Evidence of Ongoing
Pressure
(Vollmer et al. 2004)
Has only 25% of normal HI (HI def =0.6)
HI truncated in disk at 0.3R25
extraplanar HI (40% of total) on only one side of disk
Polarized Radio Continuum:
A Diagnostic of Ram Pressure
Pol. + 6cm on Def.
Pol. on HI
Leading
edge
Leading
edge
NGC 4402
ICM wind
NGC 4501
ICM wind
 Magnetic field Vectors aligned parallel with ICM-ISM working surface
 Evidence of polarized ridges arising from ram pressure in a number of
galaxies having radio deficit regions (e.g. N4254, N4388; Vollmer et al. 2008)
Such studies will benefit significantly from improved EVLA capabilities!
NGC 4522: Comparison of RC Deficits with
SPX & POL data:
(SPX & POL data from Vollmer et al. 2004)
Flat Spectral Index:
Re-acceleration
Just Interior to
Deficit Region
High Polarization:
B-field shear/
compression
Deficit region caused by ICM ram pressure (consistent for other galaxies).
Moderate RC
 CR electrons being re-accelerated by ICM driven shocklets:
enhancement
 B-field compressed and sheared:
- moderate local RC enhancement; shear stretches B-field resulting in tails.
Deficit vs. Time Since Peak Pressure
(Large deficit)
(Small deficit)
 tquench:
Time since peak
pressure from stellar
population studies of
Crowl & Kenney
2008.
 Agree with gas
stripping simulation
of Vollmer et al.
 100 - 300 Myr
 x5 decrease in peak
Pram
 Similar change in
radio deficit region!
Deficit region is a good indicator of the strength of the
CURRENT ram pressure!
Severity of Deficit vs. q
<q>
Low q
High q
 q’s generally low
compared to field
galaxies (x2 – 3 )
 Miller & Owen
(2001)
 Reddy & Yun
(2004)
 q sensitive to
strength of ICM
pressure?
q ~ log(FIR/Radio)
• Galaxies with large LOCAL radio deficits have GLOBAL radio
enhancements relative to the FIR!
Excess Radio: CR Reacceleration by ICM
Shocks?
 ICM driven shocks:
RC deficit on 6cm RC and
B-field Vectors
 Compress & Shear B-field
 Explains Polarized RC
 Re-accelerate CRe’s
B-field
sheared
Synchrotron
Tail
 Explains flat Radio SPX &
large-scale gradient
 Shocks run through thin disk
quickly
 shock ~ 20 - 40 Myr
 Excess global RC?
 For typical Virgo parameters: ~311% of KE from shock must be
given to CR’s to have doubled
RC emission.
 Clearly, shocks have enough
energy to explain low q!
B-field mildly
ICM Driven compressed
ICM Wind Shocklets
Currently, this is our preferred picture
General Conclusions
 Distribution of radio/FIR ratios w/in cluster galaxies thought to be
experiencing ICM-ISM effects differ systematically from field
galaxies:
 radio/FIR ratios low along edges in direction of ICM wind due to a deficit of
radio emission
 FIR-radio correlation within cluster galaxies appears sensitive to
effects of ram pressure
 Large local radio deficits => Low global FIR/radio ratios
 Preferred picture: CRe- reacceleration by ICM driven shocks
 Radio deficits inversely correlated with time since peak pressure as
inferred from stellar population studies and gas stripping models
 The radio deficits may be a powerful diagnostic to quantify ongoing ICM
wind direction and strength of current ram pressure!
 Plasma pressure estimates agree with expected ram pressure strengths
KINGFISH:
(Key Insights on Nearby Galaxies: A Far-Infrared Study with Herschel)





PI’s. R. Kennicutt (EU); D. Calzetti (US)
526 hr approved Herschel OTKP
Will build upon success of SINGS
61 nearby galaxies
2 Observational Components:
 Imaging:
 6 bands from 70 - 500m (5 - 35”)
 Spectroscopic Imaging:
 55 nuclear & 50 extra-nuclear star-forming regions
 Principle atomic ISM cooling lines
([OI]63mm, [OIII]88mm, [NII]122,205mm, [CII]158mm)
 SINGS + New Ancillary Data:
 Spitzer, optical + H, NIR, WSRT 22cm, THINGS
(HI), BIMA-SONG (CO), IRAM-HERA (CO),
CARMA (CO), Nobeyama (CO), SCUBA2 (submm), multi-frequency radio lacking!!!
KINGFISHER:
(KINGFISH - Emission in Radio)
 BIG THINKING for the EVLA
 PI’s: E.J Murphy & E. Schinnerer
 3 - component program
e.g. NGC 6946
 Global spectral indices
 ~5 bands: GBT + Effelsberg
 Multi-frequency imaging of
SINGS/KINGFISH
spectroscopically targeted starforming regions
 GBT + EVLA
 RRL’s as well? -- GBT Pilot Project
SINGS+KINGFISH e-nucs
 Complete multi-frequency imaging
of 1 (or 2?) very nearby galaxies SINGS+KINGFISH Radial Strip
Proposed (Pilot) GBT RRL + 30 GHz
 GBT + EVLA