Galaxies in the XMMNewton and Chandra era

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Galaxies in the XMM-Newton and Chandra era

• Antonis Georgakakis
• Imperial College

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Outline

• Overview of galaxies at X-rays
• Emission components (e.g. XRBs, SNR, hot gas)
• Astrophysical significance
• Emission mechanisms
• Cosmological significance

X-ray Astronomy Summer School, Athens 2006
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Galaxies at optical Hubble sequence

• Ellipticals
• smooth profiles
• old stars
• Spirals
• spiral arms
• young stars
• Lenticulars
• smooth profile spiral structure
• Irregulars
• amorphous
• young stars

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Emission components

• X-ray binaries
• Supernovae remnants
• Hot gas
• Stellar coronae

Accretion of material from primary to compact
secondary (black hole or neutron star) infalling
material heats up to 106K giving off
X-rays Low-mass X-ray binaries primary mass
similar or lower to that of the Sun, slow
evolution High-mass X-ray binaries primary mass
gt3M?, fast evolution timescale Major contributor
to integrated X-ray emission of our Galaxy (50)
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Emission components

• X-ray binaries
• Supernovae remnants
• Hot gas
• Stellar coronae

Explosion produces shock wave that accelerates
electrons and heats up material X-rays due to
thermal, synchrotron and bremsstrahlung
radiation. However, small contribution to total
X-ray emission of Galaxy (lt1-2)
Cas-A, T5?106K
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Emission components

• X-ray binaries
• Supernovae remnants
• Hot gas
• Stellar coronae

Gas heated by SN explosions trapped in galaxy
potential well. Relativisitc electrons produce
X-rays by bremsstrahlung Major contribution to
total X-ray emission of galaxies (50-100)
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Emission components

• X-ray binaries
• Supernovae remnants
• Hot gas
• Stellar coronae

Like the Sun, most stars have atmosphere of hot
plasma (T106K) thermal X-ray emission
However, minor contribution to overall Galaxy
X-ray emission (lt1-2)
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Galaxies at X-rays does it worth it?

• X-rays represent a tiny fraction of the energy
  output of galaxies
• e.g. Arp 220
• most of the energy at the infrared
• X-rays 5dex lower flux!
• This is unlike AGN (e.g. NGC 5548) where X-rays a
  dominant component

LMC
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Galaxies at X-rays why important?

• Hot gas component
• Metal enrichment
• formation history of ellipticals
• Binary star population
• formation evolution
• link to star-formation

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Galaxies at X-rays why important?

• Hot gas component
• Metal enrichment
• formation history of ellipticals
• Binary star population
• formation evolution
• link to star-formation

Antennae
Credit NASA/CXC/SAO/G. Fabbiano et al.
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Galaxies at X-rays why important?
NGC 1700 merger remnant

• Hot gas component
• Metal enrichment
• formation history of ellipticals
• Binary star population
• formation evolution
• link to star-formation

Credit NASA/Ohio U./T.Statler et al.
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Galaxies at X-rays why important?
Credit NASA/UMass/Z.Li Q.D.Wang

• Hot gas component
• Metal enrichment
• formation history of ellipticals
• Binary star population
• formation evolution
• link to star-formation

Point sources (X-ray binaries) Diffuse hot gas
(106-107K)
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Galaxy gallery

• Point sources (mostly XRBs) follow spiral
  structure (link to star-formation)
• Ultra luminous X-ray sources 10-1000 X-ray power
  compared to typical X-ray binaries.
• Accretion on intermediate mass black holes,
  100-104M?.
• How such massive compact objects created?

Credit X-ray NASA/CXC/U. of Michigan/J.Liu et
al. Optical NOAO/AURA/NSF/T.Boroson
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Galaxy gallery
Antennae

• Galaxy fountains
• Bubble of warm (104K red) and hot (107K blue)
  gas blown out of the galaxy.
• SN explosions or AGN activity
• Metal enrichment of interstellar/intergalactic
  medium
• Regulation of SF/AGN activity by depleting fule
  (cold gas) from galaxy centres

NGC 3979 superwind
Credit NASA/CXC/STScI/U.North Carolina/G.Cecil
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Galaxy gallery

• Ellipticals
• X-rays dominated by diffuse emission
• Hot gas distribution inhomogeneous (unlike
  optical)
• Some stirring mechanism in operation possible
  periodic AGN activity

Credit X-ray NASA/CXC/U. Ohio/T.Statler
S.Diehl
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Summary I

• Galaxies are faint X-ray sources BUT
• X-rays unique diagnostic of galaxies
• the only observational tool to study stellar
  binaries
• direct census of metal enrichment
• information on galaxy formation/evolution

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Binary star orbits

• Roche lobes the volume around a star in a binary
  system in which, if you were to release a
  particle, it would fall back onto the surface of
  that star.
• L1 inner Lagrangian point where the gravity from
  the two stars is equal. Mass is transferred from
  one star to the other through L1.

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X-ray binaries accretion

• Transfer of mass occur via
• Roche-lobe overflow through L1. An accretion disk
  is formed.
• capture of the stellar wind of the primary. An
  accretion disk may form.

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X-ray binaries accretion

• Spherical accretion radiation pressure cannot
  exceed gravitational pull.
• Upper limit in luminosity, LEddington. Scales
  with mass of accreting source.

LEddington 1.3?1038 (M/M?) erg/s
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X-ray binary luminosities

• X-ray binaries typically have LXltlt1038erg/s
• LMXRBs
• Flat distribution at faint-end
• max luminosities 1038-1039erg/s.
• HMXRBs
• Power-law distribution
• Max LX 1040erg/s, i.e. brighter than the Milky
  Way!!!

Gilfanov 2004
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Ultra-Luminous X-ray Sources
M74

• Massive stellar source, M100M?, intermediate
  mass black holes
• Non-spherical accretion
• Collimated emission, i.e. in a funnel.

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X-ray binaries accretion
L2?r2?T4, TBB( L / 2?r2? )1/4, Assuming the
Eddinghton limit kTBB6.7?(M/M?)
(R/km)-21/4 Using typical values for accreting
sources NS 1.4M?, R10km ?kTBB2keV WD 3M?,
R5000km ?kTBB0.1keV BH R2GM/c2
?kTBB1keV(M/M?)-1/4

• Black-body temperature, TBB typical temperature
  of the source if it radiated as black body.
• For typical values of compact accreting sources
  (white dwarfs, neutron stars and black holes)
  black body radiation peaks at the X-ray regime.

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X-ray binary spectra

• Complex X-ray spectra
• Power-law component with G1-2 (hot corona
  Compton scattering)
• Black-body component at soft energies (lt1keV
  accretion disk)
• Also variability, high/low states, absorption etc

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X-ray binary lifetimes
Evolution timescale time it takes for the star
to radiate the energy produced by H?He
thermonuclear reactions tlifeMc2/L, where M
mass of the star and L its luminosity. Empirical
relation between stellar mass and
luminosity LM3.5, combining the two
tlifeM?2.5, 1M? tlife1010yr 10M? tlife107yr
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X-ray binary lifetimes
Evolution timescale time it takes for the star
to radiate the energy produced by H?He
thermonuclear reactions tlifeMc2/L, where M
mass of the star and L its luminosity. Empirical
relation between stellar mass and
luminosity LM3.5, combining the two
tlifeM?2.5, 1M? tlife1010yr 10M? tlife107yr

• HMXRBs
• primary massive star (gt2M?)
• short-lived (107yr)
• measure instantaneous star-formation rate
• LMXRBs
• primary low-mass star (1M?)
• long lived (109yr)
• measure star-formation integrated over the
  lifetime of the galaxy, i.e. total stellar mass.

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Summary II

• X-ray binaries X-ray emission via accretion on a
  compact object
• HMXRBs short-lived, luminous, linked to
  star-formation
• LMXRBs long-lived, less luminous, linked to
  stellar mass

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Hot gas

• Gas origin
• mass ejected by old stars
• gas falling back on the galaxy
• Gas heating mechanism
• shock heating
• Supernovae
• AGN feedback?

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Hot gas Bremsstrahlung

• Bremsstrahlung or braking radiation emitted by a
  charged particle when accelerating in electric
  field.
• In the case of X-rays, e- in Coulomb collision
  charge of Z protons
• The resulting spectrum is flat with an upper
  cutoff wcut, related to the interaction time, Dt
  v/b, or interaction frequency w 1/Dt b/v

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Hot gas thermal Bremsstrahlung

• In astrophysically interesting cases, electrons
  have velocity distribution.
• In the case of plasma with uniform temperature T,
  Maxwell distribution
• Thermal Bremsstrahlung falls off exponentially at
  high energies
• Hot gas is radiatively cooling via Bremsstrahlung
  ?T0.5 and ?np
• e.g. ellipticals np0.1cm-3 and T107K
• tcool3?108yr (cooling problem)
• spirals np0.1cm-3 and T106K
• tcool8?107yr

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X-ray spectra of galaxies

• Elliptical galaxy NGC 4649
• Two temperature hot gas components
• T8?106 2?107K
• 85 of LX
• Power-law, G1.8
• stellar sources (e.g. binaries)
• 15 of the luminosity

Randall et al. 2006
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X-ray spectra of galaxies

• Starburst galaxy NGC 3310
• Two temperature hot gas components
• T3?106 7?106K
• 25 of the 0.3-10keV LX
• Power-law, G1.8
• stellar sources (e.g. binaries)
• 75 of the 0.3-10keV luminosity

Jenkins et al. 2004
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X-ray emission and star-formation

• Linear relation between X-ray luminosity and
  star-formation indicators (e.g. far-infrared
  luminosity) for spirals.
• X-ray emission can be used as a census of the
  star-formation rate (SFR) in late type galaxies.
• X-ray/SFR correlation is driven by short-lived
  HMXRB population

Ranalli et al. 2003
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X-ray emission and star-formation
Grimm et al. 2003

• X-ray binary luminosity function (i.e. number of
  sources with luminosity LX) for galaxies with
  SFRs in the range0.1-50M?yr-1.

X-ray binary luminosity function scaled by the
SFR of the galaxy. The number of binaries in is
proportional to the SFR N(LXgt2?1038)2.9?SFRM?y
r-1
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Summary III

• X-ray binaries dominate X-ray emission in spirals
  (star-formation indicator)
• Hot gas dominates X-ray emission from early-type
  galaxies

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Georgakakis et al. 2006a, bGeorgantopoulos et
al. 2005
X-ray selected galaxies and cosmology

• Up to now X-ray properties of galaxies in the
  local Universe (i.e. 20Mpc7?107ly)
• Chandra and XMM the first X-ray selected galaxy
  samples outside the local Universe
• Chandra XMM-Newton wide-angle shallow surveys
  find galaxies at z0.1 (400Mpc the Universe was
  10 its present age)
• Chandra Deep Fields identify galaxies to z1
  (7?103Mpc the Universe was 50 its present age)
  
• Study how the X-ray properties of galaxies change
  with time, i.e. evolution to z1

z 0.07
Needles in the Haystack Survey
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X-ray selected galaxies and cosmology

• Up to now X-ray properties of galaxies in the
  local Universe (i.e. 20Mpc7?107ly)
• Chandra and XMM the first X-ray selected galaxy
  samples outside the local Universe
• Chandra XMM-Newton wide-angle shallow surveys
  find galaxies at z0.1 (400Mpc the Universe was
  10 its present age)
• Chandra Deep Fields identify galaxies to z1
  (7?103Mpc the Universe was 50 its present age)
  
• Study how the X-ray properties of galaxies change
  with time, i.e. evolution to z1

z 0.298
Hornschemeier et al. 2003
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Ghosh White 2001
Starforming galaxies at X-ray wavelengths

• Star-formation evolution studies at X-rays
• Least biased by dust (gt2keV)
• Unlike estimators at other wavelengths, includes
  information from low-mass stars (e.g. LMXRBs)
• information on the evolution timescales of HMXRB
  LMXRBs

SFR
X-rays
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Galaxy evolution
2dFGRS

• Luminosity function F(L,z)
• number of galaxies per unit volume with
  luminosity L?LdL
• i.e. F(L,z)dLdV number of galaxies with
  luminosity L at redshift z
• Schechter form for the LF
• F(L) f? (L/L?)a ? exp(?L/L?)

dV
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Galaxy evolution

• Count sources to a given flux limit S.

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Galaxy evolution

• Count sources to a given flux limit S.
• Use local LF to predict number assuming different
  evolution histories, e.g. LX?(1z)p

No evolution model
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Galaxy evolution

• Count sources to a given flux limit S.
• Use local LF to predict number assuming different
  evolution histories, e.g. LX?(1z)p

Evolution (1z)2.4
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Summary IV

• X-ray emission of spirals star-formation
  indicator
• X-rays provide information on the cosmological
  evolution of galaxies
• Star-formation evolution free from dust-induced
  biases.
• Future missions, e.g. XEUS (?100 XMM)
• Star-formation evolution to z2 (imaging)
• Metal enrichment out to z1 (spectroscopy)
• X-ray binary population evolution z1
  (spectroscopy)

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Thank you for your attention!
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Galaxies at optical Hubble sequence

• Ellipticals
• smooth profiles
• old stars
• Spirals
• spiral arms
• young stars
• Lenticulars
• smooth profile spiral structure
• Irregulars
• amorphous
• young stars

M87
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Galaxies at optical Hubble sequence

• Ellipticals
• smooth profiles
• old stars
• Spirals
• spiral arms
• young stars
• Lenticulars
• smooth profile spiral structure
• Irregulars
• amorphous
• young stars

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Galaxies at optical Hubble sequence

• Ellipticals
• smooth profiles
• old stars
• Spirals
• spiral arms
• young stars
• Lenticulars
• smooth profile spiral structure
• Irregulars
• amorphous
• young stars

M102
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Galaxies at optical Hubble sequence

• Ellipticals
• smooth profiles
• old stars
• Spirals
• spiral arms
• young stars
• Lenticulars
• smooth profile spiral structure
• Irregulars
• amorphous
• young stars

LMC