Feedback in Starburst Galaxies
description
Transcript of Feedback in Starburst Galaxies
![Page 1: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/1.jpg)
Feedback in Starburst Galaxies
Todd ThompsonPrinceton University
with Eliot Quataert, Norm Murray, & Eli Waxman
![Page 2: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/2.jpg)
Outline
• Goal: A model for the global structure of starbursts.
• Why starbursts? The physical conditions.
• Radiation pressure feedback.
• Magnetic fields, cosmic rays, & -rays.
![Page 3: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/3.jpg)
Kennicutt (1998)
Systematics of Star Formation
• Schmidt Law:
• ``Star-forming” galaxies:– Extended, few-kpc scales.– ~ billion year timescales.
• ``Starburst” galaxies:– Compact, 100’s pc scales.– 1-100 million year
timescales.
• Pressure: P ~ G g2
€
˙ Σ *∝ Σg7 / 5
Starbursts
Star-forming galaxies
![Page 4: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/4.jpg)
Kennicutt (1998)
Regulation & Feedback in Galaxies
• Low star formation efficiency:
Suggests feedback and/or regulation over a broad range of conditions.
• Q~1 observed in disks.(Martin & Kennicutt 2001)
• Stellar processes (?): Stellar winds, radiation, supernovae, HII regions, etc.
• Non-stellar processes (?): MRI. (Sellwood & Balbus 99;Piontek & Ostriker 04)
Starbursts
Star-forming galaxies
![Page 5: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/5.jpg)
Why Starbursts?
![Page 6: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/6.jpg)
NOAO
M82
M51
Arp 220
IRAS 19297-0406
NGC 253
![Page 7: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/7.jpg)
Backgrounds & Starbursts
Dole et al. (2006)
![Page 8: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/8.jpg)
Why Starbursts?• Starbursts & U/LIRGs
– lie on the same scaling relations with normal galaxies.
– constitute a large fraction of the IR background, the star-formation rate density at high z (also, -ray & MeV/TeV backgrounds).
– may be a key phase in the growth of super-massive black holes & spheroids.
– are connected physically to super-star clusters, starburst cores.
– have turbulent velocities v > 10 km/s.
• What do we want to know?– Constituents: radiation, gas/dust, magnetic fields, and cosmic rays.
– The origin and systematics of the scaling relations of galaxies.
![Page 9: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/9.jpg)
The Physical Conditions
Arp 220 (d ~ 80 Mpc):
• Two counter-rotating cores, ~100pc.• Circumbinary disk R~300pc.
gas ~ 5 g cm-2
n ~ 103-104 cm-3
• Mgas ~ 109 -1010 M
v ~ 100 km s-1
• LFIR ~ 21012 L
• LX ~ 3109 L
• tdyn ~ 106 n4-1/2 yr
Solomon, Sakamoto
300 pc
Beswick 2006; Mundell et al; Lonsdale et al
![Page 10: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/10.jpg)
Pressures• Accounting:
![Page 11: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/11.jpg)
What processes regulate Star Formation in ULIRGs?
• The standard lore: Energy injection by supernovae, stellar winds, HII regions (e.g., McKee & Ostriker ‘77). However, in a dense ISM, radiative losses are large: E n-1/4.
• Another Option: Radiation Pressure:
– Starburst photons absorbed & scattered by dust: UV ~ 100’s cm2/g.
– Dust is collisionally coupled to gas: ~ 0.01 pc a0.1 n3-1.
– Starbursts: optically thick to re-radiated IR : IR ~ gasIR > 1.
– Radiative diffusion: efficient coupling to cold, dusty component, most of the mass.
Scoville (2003) Thompson, Quataert, & Murray (2005)
![Page 12: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/12.jpg)
Radiation Pressure Supported Starbursts
• Radiative flux:
• Radiative diffusion:
• Radiation pressure:
• Obtain Eddington-limited starbursts:
![Page 13: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/13.jpg)
Some Predictions
• The “Schmidt”-law for optically-thick starbursts:
Higher implies more pressure support, which implies a lower star formation rate & efficiency.
Kennicutt (1998)€
˙ Σ *∝Σg
κ
€
˙ Σ *∝ Σg7 / 5
![Page 14: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/14.jpg)
The Rosseland Mean Opacity
• Sublimation: Tsub ~ 1000 K.
• Dust dominates T < 1000 K.
• At T < 200 K — in the Rayleigh limit — = 0T2.
• Overall normalization is dependent on metallicity and the dust-to-gas ratio.
Semenov et al. (2003)
![Page 15: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/15.jpg)
Some Predictions• The “Schmidt”-law:
• When = 0T2:
no dependence on anything, but 0.
![Page 16: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/16.jpg)
Data from Condon et al. (1991)
ULIRGs are compact. Intrinsic size?
Appeal to radio size, hoping that the radio reliably traces the star formation.
A Characteristic Flux?
![Page 17: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/17.jpg)
Evidence for a Characteristic Flux?
Davies et al. (2006)
![Page 18: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/18.jpg)
Why Radiation Always Wins
• Schmidt law:• Flux:• Radiation pressure:
• Hydrostatic pressure:
• Critical surface density:
€
˙ Σ *∝ Σg7 / 5
€
˙ Σ *∝ Σg7 / 5
![Page 19: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/19.jpg)
Magnetic Fields & Cosmic Rays
![Page 20: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/20.jpg)
How do CR electrons cool?
Radio synchrotron from CR e-’s accelerated by SNe.
FIR traces star formation, massive stars, SNe.
“Calorimeter” theory: synchrotron cooling timescale shorter than the escape time:
tsynch < < tescape
(Völk‘89; generally unaccepted)
galaxy = CR beam dump
The FIR-Radio Correlation
Yun et al. (2001)
Starbursts
Star-Forming Galaxies
![Page 21: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/21.jpg)
Magnetic Fields & Cosmic Rays
• In the Milky Way, B~5-10G and
• In starburst galaxies, how do we estimate B?– “Minimum energy” (UB~UCR; Burbidge 1956): (~5-10G in MW).
Depends on the ratio [p/e] and on the injected CR spectral index.
– Magnetic energy density in equipartition with total hydrostatic pressure: (~5-10G in MW)
![Page 22: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/22.jpg)
Magnetic Fields
€
Bmin∝ (Lνrad /V )2 / 7
Conclusion:
Magnetic fields in star-forming galaxies are both minimum energy & equipartition.
and
€
B2 /8π ~ UCR
![Page 23: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/23.jpg)
Magnetic Fields
€
Bmin∝ (Lνrad /V )2 / 7
Conclusion:
Either
the minimum energy estimate is wrong,
or
magnetic fields are dynamically weak in starburst galaxies.
Thompson et al. (2006)
![Page 24: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/24.jpg)
UBmin/Uph measures the importance of synchrotron relative to IC cooling.
If Bmin is correct, IC dominates for starbursts.
This contradicts the linearity of the FIR-radio correlation.
Bmin Must Underestimate the True Field
UBmin /Uph
![Page 25: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/25.jpg)
Magnetic Fields & FIR-Radio Correlation
• In the limit of very strong cooling (the “calorimeter” limit):
• The observed Schmidt Law says that
• Therefore, in the limit of strong cooling:
€
˙ Σ *∝ Σg7 / 5
![Page 26: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/26.jpg)
Magnetic Fields
€
Bmin∝ (Lνrad /V )2 / 7
Conclusion:
If a fraction ~1% of 1051 ergs per SN goes to CR electrons, and they cool rapidly, the observed trend is reproduced.
Implies that B is in fact larger than Bmin.
Thompson et al. (2006)
![Page 27: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/27.jpg)
Magnetic Fields in Starbursts
• Observations thus imply rapid electron cooling.– Strong evidence for the calorimeter theory for the FIR-
radio correlation: tcool< < tescape.
• So, how big is B? – Well, B is big enough that the synchrotron cooling
timescale is << tesc. But, what is tesc?
Very uncertain:
Diffusion in MW tesc ~107.5 yrs. Maybe advection (winds!) in starbursts tesc ~105.5 yrs (?).
![Page 28: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/28.jpg)
Magnetic Fields in Starbursts• Argument/Problem:
– The strongest objection to the calorimeter theory for FIR-radio correlation: if synchrotron dominates cooling and tcool< < tesc, the radio spectral indices of starbursts at GHz should be steep “cooled” : F ~ - , with ~ 1-1.2.
– This is not observed. Spectral indices at GHz are ~constant & not steep: F ~ - , with ~ 0.7.
• Solution: – If CRs interact with matter at mean density & B~Beq, then
Ionization losses dominate for low-energy CRs, not high. This effect changes the expected slope of the radio spectrum at a characteristic frequency ~GHz.
![Page 29: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/29.jpg)
Magnetic Fields in Starbursts
p=2.0
p=2.5
• Ionization losses flatten the radio spectra
• Ionization is important only if CRs interact with ISM of ~mean density.
• Prediction: spectral break ubiquitous at GHz ’s for all galaxies obeying FIR-radio.
• Because this only works if B~Beq, this is the best argument for B >> Bmin in starbursts.
Steeper
Flatter
![Page 30: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/30.jpg)
Summary• Observations indicate
– feedback is important, SF is inefficient, starbursts are dusty, disks have Q~1.
• Radiation pressure – can dominate feedback in the optically thick regions of starbursts.– yields qualitative change to Schmidt Law.– couples to the cold dusty component, most of the mass.– predict starburst structure: T, Teff, F, , , v, SFR/area, efficiency– are in good agreement with observations (local & high-z ULIRGs).
• Magnetic Fields in Starbursts– are larger than Bmin and probably ~ Beq.– are large enough that the “calorimeter” theory for FIR-radio is preferred.– are consistent with starburst radio spectral indices only if CRs interact with
ISM of mean density so that ionization/bremsstrahlung losses are important. -Ray Observations of Starbursts
– will constrain the ISM density seen by CR protons.– will constrain the energetics of CR acceleration. - Lastly, (CRp/CRe) ~ 10.
Thompson et al. (2005), (2006ab)
![Page 31: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/31.jpg)
The Present & The Future • Radiation pressure feedback:
– Embedded sources, porosity, transport, multi-phase ISM.
– The gravitational instability in radiation pressure dominated backgrounds.
– Starburst winds, scaling relations: Faber-Jackson, M-.
• Other mechanisms for feedback:– HII regions, stellar winds, supernovae, gravity.
• The starburst-AGN fueling connection.
• The FIR-radio correlation:– Test prediction of spectral breaks at GHz.
– Electron calorimetry in normal star-forming galaxies (?).
• Starbursts: what is the role of the secondary electron/positrons?
• Backgrounds: neutrino (MeV to >TeV), -ray, FIR, & radio.
• What is the energy density of cosmic rays in starburst galaxies?
![Page 32: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/32.jpg)
The End
![Page 33: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/33.jpg)
Constraining the Average Density “Seen” by Cosmic Rays
![Page 34: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/34.jpg)
-Rays from Starbursts• Assume SNe accelerate both CR protons & electrons.• The GeV protons collide with ambient gas:
• Proton-proton collisions produce
• If pp<< esc, then the starburst is a “proton calorimeter,” and all of the proton energy goes into ’s (1/3), e+,-’s (1/6), and ’s (1/2).
• What is esc? As for CR electrons, very uncertain.
Thompson et al. (2006)
![Page 35: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/35.jpg)
-Rays from Starbursts• Massive star formation IR emission Supernovae:
where is the fraction of 1051 ergs per supernova to CRp’s. This is a FIR--Ray correlation analogous to FIR-radio.
• How do we constrain ? Assume the e+,-’s from p-p cool via only synchrotron in the starburst:
• Observed FIR-radio correlation:Thompson et al. (2006)
![Page 36: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/36.jpg)
-Rays from Starbursts
€
Lν (GeV) ~ 10-5η 0.05LTIR
Arp 220
NGC 253
![Page 37: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/37.jpg)
-Rays from Starbursts• If GLAST sees a larger flux from NGC 253:
– Then > 0.05 more energy per SN to CR protons.
– Because from secondary electrons/positrons, another process (not synchrotron) must dominate CR electron cooling.
• If GLAST sees a smaller flux from NGC 253:– Either the CRs interact ISM below mean density, rapid escape,
– or, < 0.05 less energy per SN to CR protons.
– These options can in principle be distinguished by modeling the IC
and relativistic bremsstrahlung emission at -ray energies since the latter also depends on density.
€
Lν (GHz) ~ 3×10-6η 0.05LTIR
![Page 38: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/38.jpg)
The Diffuse -Ray Background• Massive star formation IR emission Supernovae.
+ star formation rate history of the universe.
+ the fraction of all star formation at high-z that occurs in “proton calorimeters” (high density).
• For an individual galaxy:
• For the history of star formation:
Thompson et al. (2006)
€
Lν (GeV) ~ 10-5η 0.05LTIR
![Page 39: Feedback in Starburst Galaxies](https://reader035.fdocuments.in/reader035/viewer/2022062315/56815168550346895dbf995c/html5/thumbnails/39.jpg)
The -Ray Background