Populations of X-ray sources in star-forming galaxies

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

2. 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

3. 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,...

4. 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

5. 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

6. 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

7. 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

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

11. 10 arcsec

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

13. ULX X-ray pulsar

14. 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

15. Identification of the X-ray sources: multiwavelength comparisons Chandra/ACIS HST/WFPC2

16. HST/WFPC2 greyscale, Chandra contours

17. Ha greyscale (SSO), Chandra contours (0.3--8 keV)

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

19. Colour-colour plot for bright M83 sources

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

21. Candidate X-ray SNR are associated to brighter HII regions Ha

22. Ha greyscale (SSO), Chandra point sources

23. 6 cm radio greyscale (VLA), Chandra point sources

24. many SNR in M83, fewer in M81...

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

26. NGC 300 XMM OM image (UV filters)

27. NGC 300 XMM OM image (UV filters)

28. Optical SNRs Radio SNRs

33. 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

34. (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

35. Colour distribution for M74 SN2002ap in M74 seen by XMM

36. 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

37. 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

38. 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

39. 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

40. “Ultra-luminous” sources Emitted luminosity > Eddington limit for M = 7 Msun 2 x1038 1039 1040 Neutron stars Black holes SNR Black holes SNR ”ULX”

41. NGC 4449

42. X-7 X-1

43. X-7

44. X-1 1 arcsec

45. X-1: diskbb (Tcol~ 0.6keV) + pow(G~ 2.6) X-7:pow(G~ 2.1)

46. 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)

47. 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

48. 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

49. 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

50. 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?