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Populations of X-ray sources in star-forming galaxies. Roberto Soria ( MSSL) K Wu, A Kong, M Pakull, R Kilgard , D Swartz. Contents. introduction why studying X-ray sources in other galaxies. luminosity and colour distributions

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slide1

Populations of X-ray sources

in star-forming galaxies

Roberto Soria (MSSL)

K Wu, A Kong, M Pakull, R Kilgard, D Swartz

slide2

Contents

  • introduction

why studying X-ray sources in other galaxies

  • luminosity and colour distributions

and what they tells us about the host galaxy

  • different physical classes of X-ray sources
  • case studies: M83, NGC300, M74, NGC 4449
  • multiwavelength comparisons
  • ”ultra-luminous sources”

what they are and how to test the models

slide3

Why studying X-ray sources in galaxies

  • use discrete X-ray sources and diffuse emission

as a tool to understand galactic activity and evolution

  • do statistical studies of X-ray source populations
  • spatial distribution
  • luminosity & color distribution
  • different classes of compact objects
  • understand the properties of individual X-ray sources

spectra, lightcurves, state transitions,...

slide4

External triggers

Internal triggers?

Cold gas

STAR FORMATION

Stellar evolution

PNe, SNe II, Ib/c

Hot gas (shocks)

Diffuse soft X-rays

Compact remnants

HMXB, LMXB

X-rays from accretion

slide5

Basic steps:

Determine:

  • luminosity (count rate) distribution
  • spatial distribution, multi-band comparisons/identification
  • colour distributions for different classes of sources

Distinguish different physical types of X-ray binaries, SNR, SNe

Use X-ray sources as probes of galaxy structure and evolution

slide6

Cumulative luminosity distribution

of the discrete X-ray sources in a galaxy

1036

1038

1040

N(>L)

erg/s

Starburst/star-forming regions

“normal” spiral population

Ellipticals

L

slide7

Breaks in the luminosity distribution

Luminosity functions in M83

Luminosity functions in M81

outside disk

outside disk

starburst nucleus

Breaks/features in the luminosity function may depend on:

  • Eddington limit for the neutron starsdistance indicator
  • ageing of the X-ray binary population(Wu 2001)

galactic history indicator

slide12

galactic nucleus

X-ray binary

Super-soft source

SNR?

Wind / XRB?

slide13

ULX

X-ray pulsar

slide14

T ~ 0.6 keV

Starburst nucleus

High abund of Ne, Mg, Si,S

Low Fe/O, Fe/C

High C/O

T ~ 0.4 keV

ISM may be enriched by:

winds from WR stars,

core-collapse SNe

Spiral arms

slide15

Identification of the X-ray sources:

multiwavelength comparisons

Chandra/ACIS

HST/WFPC2

slide19

Colour-colour plot

for bright M83 sources

slide20

X-ray binaries (BH, NS)

Soft sources (SNR +)

Supersoft sources

slide21

Candidate X-ray SNR are

associated to brighter HII regions

Ha

slide25

...almost none in M31

Courtesy of S Trudolyubov et al, 2003 submitted

slide26

NGC 300

XMM OM image

(UV filters)

slide27

NGC 300

XMM OM image

(UV filters)

slide28

Optical SNRs

Radio SNRs

slide33

Comparing samples of SNR

  • radio-identified SNR: dense HII regions

core-collapse SNe (young population)

  • optically-identified SNR: low-density regions

mostly Type Ia (old population)

  • X-ray SNR: both, but brighter when associated to radio SNR

Radio + X-ray (+ optical)

Core-collapse

L

X-ray + optical

1036erg/s

Type Ia

slide34

(Young) core-collapse X-ray SNe

SN in NGC 4449

  • thermal spectrum: emission from hot, shocked gas
  • non-thermal spectrum: dominated by synchrotron radiation (power-law spectrum)

SN 1978k in NGC 1313

slide35

Colour distribution for M74

SN2002ap in M74 seen by XMM

slide36

Thermal X-ray emission from SNe

Type II

  • High mass loss rate, low velocity wind,

SN 1993J

low velocity ejecta (< 30,000 km/s)

H

Hard X-rays first

Soft X-rays later

(weeks/months)

S

f

r

Optically thick

cool shell

L > ~ 1038erg/s

slide37

Thermal X-ray emission from SNe

Type Ib/c

  • Low mass loss rate, high velocity wind,

SN 2002ap

low velocity ejecta (< 30,000 km/s)

(H)

Hard X-rays negligible

Soft X-rays always visible

S

f

r

Optically thin

cool shell

L~1037erg/s

slide38

Thermal X-ray emission from SNe

Type Ib/c

  • Relativistic ejecta? (> 100,000 km/s?)

SN 1998bw

Hard X-rays, g-rays

(Hypernova?)

H, g

S

f

r

slide39

Thermal X-ray emission from SNe

Type Ib/c

  • Relativistic ejecta? (> 100,000 km/s?)

SN 1998bw

Hard X-rays, g-rays

(Hypernova?)

H, g

f

slide40

“Ultra-luminous” sources

Emitted luminosity > Eddington limit for M = 7 Msun

2 x1038

1039

1040

Neutron stars

Black holes

SNR

Black holes

SNR

”ULX”

slide42

X-7

X-1

slide44

X-1

1 arcsec

slide45

X-1: diskbb (Tcol~ 0.6keV)

+ pow(G~ 2.6)

X-7:pow(G~ 2.1)

slide46

Where are they?

Found in 20% of spiral galaxies

40% of ellipticals (7 in Fornax A, 6 in NGC 1553)

most tidally-disrupted starburst (10 in Antennae)

Very old populations

Very young populations

Variability?

All are persistent

Most variable by a factor of a few (over hours/yrs)

Long duty cycle? If so, how many quiescent sources?

State transitions?

Some similarities with Galactic BH (Roberts et al 2000)

slide47

X-ray spectrum?

Most are fitted by diskbb with scattering

T Tcol = f Teff where f ~1.5 – 3; Tcol~ 1keV

X-6 in M 81 (Swartz et al 2002)

Tcol= 1.1keV, Lx = 2.7 x 1039 erg/s

Others are fitted by a simple power-law

Some are “super-soft”, T ~ 0.07keV, Lbol~ 1039 erg/s

A few can be identified as SNR

slide48

Three possibilities for accreting ULX

M > 10 Msun , L < Ledd

IMBH

M ~ 10 Msun , L >~ Ledd

Super-E

M <~ 10 Msun , L <~ Ledd

beamed

Problem not settled yet, need better observations

slide49

1

Intermediate-mass BH: how to form them?

  • primordial (see eg Rees)

feeding -- from a molecular cloud? (Grindlay)

-- by capturing a companion?

  • in globular clusters from SN explosion of very massive stars?

(from merging of many smaller BH?)

NO. Ineffective because of slingshot effect

  • in super star clusters ( = young globular clusters?)

from merging of many stars  star of 500 Msun

 sinks to the cluster centre  SN  IMBH?

(eg, Ebisuzaki et al 2001)

...and how to observe them?

Optical counterparts, lightcurves, accretion disk lines

obtain mass function

slide50

2

“Super-Eddington” sources (not really)

Frad (L=Ledd) = Fgrav

Ledd = (4pcG) M / k = 1.3 1038 (M/Msun ) (0.40/k)

Thomson scattering opacity

Effective opacity for clumpy medium < for homogeneous medium

Shaviv 1998

Witt & Gordon 1996

Isichenko 1992 (“percolation theory”)

Where to observe this?

Look out for winds

Accretion disks around BH (Begelman 2002)

Classical novae (Shaviv 2001)

Wolf-Rayet, supergiant stars, h Car (Shaviv 2000)

Dust scattering in clumpy ISM (WG96)

Super-soft sources? AGN? Starburst galaxies?

slide51

3

Non-isotropic emission:

how to beam it?

(King et al 2001)

(Fabrika et al 2000)

Thermal-timescale mass transfer phase?

high mass transfer rate beaming?

Analogy with Galactic microquasars/microblazars

...and how to verify if it is beamed?

Optical (narrow-band) observations of X-ray ionized nebulae around ULX

can tell us whether X-ray source is beamed

(Pakull & Mirioni 2002)

slide52

New pieces of the ULX puzzle

Colours/spectra, time variability, spatial distribution

consistent with normal X-ray binaries

1

slide53

New pieces of the ULX puzzle

2

Most ULXs are in interacting/merging galaxies

(Swartz et al 2003)

Tidal interactions  higher star formation

3

ULXs in star-forming galaxies are young objects

Optical counterparts are O stars, OB associations

4

Many ULXs are in low-metallicity environments

(see Pakull’s work)

Weaker stellar wind  higher mass of the BH remnant

slide56

Most likely explanation for ULXs?

a 30-50 MsunBH accreting from an O star

via Roche-lobe overflow

Lx <~ Ledd

Lx = h M c2

Work in progress by Podsiadlowski, Heger, Langer, etc

slide57

Most likely explanation for ULXs?

a 30-50 MsunBH accreting from an O star

via Roche-lobe overflow

Three classes of X-ray binaries?

  • NS or BH accreting from a low-mass star via Roche-lobe overflow (LMXB)
  • NS or BH accreting from a high-mass star via stellar wind (HMXB)
  • NS or BH accreting from a high-mass star via Roche-lobe overflow (ULX + LMC X-4)
slide58

Statistical studies

of X-ray populations

(XRB, SNR, SSS, ULX)

Groups of galaxies

Star-formation

in nearby galaxies

Studies of individual sources

X-ray studies of

high-redshift galaxies

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