Populations of X-ray sources Populations of X-ray sources in star-forming galaxies in star-forming galaxies Roberto Soria (MSSL) K Wu, A Kong, M Pakull, R Kilgard, D Swartz

Contents  ”ultra-luminous sources”  different physical classes of X-ray sources what they are and how to test the models case studies: M83, NGC300, M74, NGC 4449 multiwavelength comparisons  luminosity and colour distributions and what they tells us about the host galaxy  introduction why studying X-ray sources in other galaxies

Why studying X-ray sources in galaxies  understand the properties of individual X-ray sources  do statistical studies of X-ray source populations spectra, lightcurves, state transitions,... spatial distribution luminosity & color distribution different classes of compact objects  use discrete X-ray sources and diffuse emission as a tool to understand galactic activity and evolution

STAR FORMATION Stellar evolution PNe, SNe II, Ib/c Compact remnants HMXB, LMXB Cold gas Hot gas (shocks) Diffuse soft X-rays X-rays from accretion External triggers Internal triggers?

luminosity (count rate) distribution spatial distribution, multi-band comparisons/identification colour distributions for different classes of sources Basic steps: Distinguish different physical types of X-ray binaries, SNR, SNe Determine: Use X-ray sources as probes of galaxy structure and evolution

Cumulative luminosity distribution of the discrete X-ray sources in a galaxy N(>L) L “normal” spiral population Starburst/star-forming regions Ellipticals erg/s

Breaks in the luminosity distribution Luminosity functions in M83Luminosity functions in M81 Breaks/features in the luminosity function may depend on:  Eddington limit for the neutron stars distance indicator  ageing of the X-ray binary population (Wu 2001) galactic history indicator outside disk starburst nucleus

A look in detail: M83 (d ~ 4 Mpc)

10 arcsec

Super-soft source Wind / XRB? X-ray binary galactic nucleus SNR?

ULX X-ray pulsar

Starburst nucleus Spiral arms High abund of Ne, Mg, Si,S Low Fe/O, Fe/C High C/O ISM may be enriched by: winds from WR stars, core-collapse SNe T ~ 0.6 keV T ~ 0.4 keV

Identification of the X-ray sources: multiwavelength comparisons Chandra/ACISHST/WFPC2

HST/WFPC2 greyscale, Chandra contours

H  greyscale (SSO), Chandra contours ( keV)

V-band greyscale (VLT), 6 cm radio contours (VLA)

Colour-colour plot for bright M83 sources

Supersoft sources Soft sources (SNR +) X-ray binaries (BH, NS)

Candidate X-ray SNR are associated to brighter HII regions HHHH

H  greyscale (SSO), Chandra point sources

6 cm radio greyscale (VLA), Chandra point sources

many SNR in M83, fewer in M81...

...almost none in M31 Courtesy of S Trudolyubov et al, 2003 submitted

NGC 300 XMM OM image (UV filters)

NGC 300 XMM OM image (UV filters)

Optical SNRs Radio SNRs

Comparing samples of SNR radio  radio-identified SNR: dense HII regions core-collapse SNe (young population) optically  optically-identified SNR: low-density regions mostly Type Ia (old population) X-ray  X-ray SNR: both, but brighter when associated to radio SNR Radio + X-ray (+ optical) X-ray + optical erg/s L Core-collapse Type Ia

(Young) core-collapse X-ray SNe thermal spectrum:  thermal spectrum: emission from hot, shocked gas non-thermal spectrum:  non-thermal spectrum: dominated by synchrotron radiation (power-law spectrum) SN in NGC 4449 SN 1978k in NGC 1313

SN2002ap in M74 seen by XMM Colour distribution for M74

Thermal X-ray emission from SNe  High mass loss rate, low velocity wind, low velocity ejecta (< 30,000 km/s) L > ~ erg/s fr H S Hard X-rays first Soft X-rays later (weeks/months) Optically thick cool shell SN 1993J Type II

Thermal X-ray emission from SNe  Low mass loss rate, high velocity wind, low velocity ejecta (< 30,000 km/s) L ~ erg/s fr (H) S Hard X-rays negligible Soft X-rays always visible Optically thin cool shell SN 2002ap Type Ib/c

Thermal X-ray emission from SNe  Relativistic ejecta? (> 100,000 km/s?) fr H,  S Hard X-rays,  rays (Hypernova?) Type Ib/c SN 1998bw

Thermal X-ray emission from SNe  Relativistic ejecta? (> 100,000 km/s?) f H,  Hard X-rays,  rays (Hypernova?) Type Ib/c SN 1998bw

“Ultra-luminous” sources 2 x Neutron stars Black holes SNR Black holes SNR ”ULX” Emitted luminosity > Eddington limit for M = 7 M sun

NGC 4449

X-7 X-1

X-7

1 arcsec X-1

~ 0.6 X-1: diskbb (T col ~ 0.6 keV) ~ 2.6) + pow (  ~ 2.6) ~ 2.1) X-7: pow (  ~ 2.1)

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 populationsVery 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)

X-ray spectrum? Most are fitted by diskbb with scattering ~~ 1 T T col = f T eff where f ~ 1.5 – 3; T col ~ 1 keV Others are fitted by a simple power-law T col = 1.1 keV, L x = 2.7 x erg/s X-6 in M 81 (Swartz et al 2002) ~ 0.07 ~ Some are “super-soft”, T ~ 0.07 keV, L bol ~ erg/s A few can be identified as SNR

Three possibilities for accreting ULX M > 10 M sun, L < L edd IMBH ~~ M ~ 10 M sun, L >~ L edd ~~ M <~ 10 M sun, L <~ L edd beamed Problem not settled yet, need better observations Super-E

Intermediate-mass BH: how to form them? 1...and how to observe them? Optical counterparts, lightcurves, accretion disk lines obtain mass function  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 M sun  sinks to the cluster centre  SN  IMBH? (eg, Ebisuzaki et al 2001)

“Super-Eddington” sources (not really) 2 L edd = (4  cG) M /  = (M/M sun ) (0.40/  F rad (L=L edd ) = F grav Thomson scattering opacity Effective opacity for clumpy medium < for homogeneous medium Shaviv 1998 Witt & Gordon 1996 Isichenko 1992 (“percolation theory”) Accretion disks around BH (Begelman 2002) Classical novae (Shaviv 2001) Wolf-Rayet, supergiant stars,  Car (Shaviv 2000) Dust scattering in clumpy ISM (WG96) Super-soft sources? AGN? Starburst galaxies? Where to observe this? Look out for winds

Non-isotropic emission: how to beam it? 3...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) Thermal-timescale mass transfer phase? high mass transfer rate beaming? Analogy with Galactic microquasars/microblazars (King et al 2001) (Fabrika et al 2000)

New pieces of the ULX puzzle Colours/spectra, time variability, spatial distribution consistent with normal X-ray binaries 1

New pieces of the ULX puzzle Most ULXs are in interacting/merging galaxies (Swartz et al 2003) 2 Many ULXs are in low-metallicity environments (see Pakull’s work) 3 Tidal interactions  higher star formation Weaker stellar wind  higher mass of the BH remnant 4 ULXs in star-forming galaxies are young objects Optical counterparts are O stars, OB associations

M81 group (many ULXs)

NGC 4449 (2 ULXs)

Most likely explanation for ULXs? a M sun BH accreting from an O star via Roche-lobe overflow Work in progress by Podsiadlowski, Heger, Langer, etc ~ L x <~ L edd L x =  M c 2

Most likely explanation for ULXs? a M sun BH accreting from an O star via Roche-lobe overflow (LMXB)  NS or BH accreting from a low-mass star via Roche-lobe overflow (LMXB) (HMXB)  NS or BH accreting from a high-mass star via stellar wind (HMXB) (ULX + LMC X-4)  NS or BH accreting from a high-mass star via Roche-lobe overflow (ULX + LMC X-4) Three classes of X-ray binaries?

Statistical studies of X-ray populations (XRB, SNR, SSS, ULX) Star-formation in nearby galaxies Studies of individual sources Groups of galaxies X-ray studies of high-redshift galaxies