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Craig Sarazin University of Virginia

Chandra Observations of Low Mass X-ray Binaries, ULXs, and Globular Clusters in Elliptical Galaxies. Craig Sarazin University of Virginia. Chandra Observations of Early Type Galaxies and Collaborators. NGC 4697 – E6 – Sarazin, Irwin, & Bregman 2000, 2001

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Craig Sarazin University of Virginia

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  1. Chandra Observations ofLow Mass X-ray Binaries,ULXs, and Globular Clustersin Elliptical Galaxies Craig Sarazin University of Virginia

  2. Chandra Observations of Early Type Galaxies and Collaborators NGC 4697 – E6 –Sarazin, Irwin, & Bregman 2000, 2001 NGC 4365 – E3 –Sivakoff, Sarazin, & Irwin 2003 NGC 4649 (M60) – E2 –Randall, Sarazin, & Irwin 2003 NGC 1553 - S0 – Blanton, Sarazin, & Irwin 2003 NGC 4382 (M80) – S0 –Sivakoff, Sarazin, & Irwin 2003 NGC 1291 – Sa bulge -Irwin, Sarazin, & Bregman 2002 NGC 1600 – E3 - Sivakoff, Sarazin, & Carlin 2003 NGC 533 – E3 – Carlin, Sarazin, & Sivakoff 2003

  3. Definition of ULXs Because of interest in connection to IMBHs, take a conservative definition: LX > 2 x 1039 erg/s, broad-band (0.3-10 keV) Macc≳ 20 M → not a stellar black hole or NS if Eddington limited (Irwin et al. 2004)

  4. NGC 4697 E6 Nearest optically luminous, X-ray faint elliptical

  5. Chandra X-ray Image of NGC 4697 ~ 90 % of X-ray flux resolved into point sources Most of X-rays from X-ray faint ellipticals = point sources

  6. Point SourcesLow Mass X-ray Binaries (LMXBs) Wavelet detection (CIAO WAVDETECT) Significance Threshold < 10-6 (< 1 spurious source per galaxy) Flux SNR > 3 s Limits ≳ 3 x 10-4 cts/sec ≳ 11 counts (LX ≳ 5 x 1037 ergs/sec) 50 – 300 LMXBs / galaxy (~10 BG sources)

  7. Total X-ray Spectrum of LMXBs LMXBs Hard Spectrum Bremsstrahlung kTbrem ~ 7 keV, or Power-law, G ~ 1.5 (Sarazin et al. 2000; Irwin et al. 2003)

  8. X-ray Spectra of Bright LMXBsin Early-Type Galaxies Exception: sources with 1039≤ LX ≤ 2 x 1039 have softer spectra (Irwin et al. 2003) High/soft state in BH binaries?

  9. X-ray “Colors” H21 = (M – S)/(M + S) H31 = (H – S)/(H + S) S = soft band counts, 0.3 – 1 keV M = medium band counts, 1 – 2 keV H = hard band counts, 2 – 10 keV

  10. X-ray Colors – NGC 4697 H31 H21

  11. X-ray Colors – NGC 4697 G = photon index 0.0 1.2 H31 2.0 3.2 H21

  12. X-ray Colors – NGC 4697 AGN? Supersoft sources LMXBs AGN? LMXB?

  13. Supersoft Sources 0 – 5 found per galaxy No X-rays hn  1 keV (see also Di Stefano et al., also quasi-soft sources) kTeff≈ 70 (40 – 100) eV LX = 1 – 4 x 1038 ergs/s (0.3 – 10 keV) Lbol ≈ 0.3 – 2 x 1039 ergs/s > LEdd (1.4 MWD) Not accreting WDs! Are E galaxy supersofts accreting, intermediate mass BHs?

  14. Variable Sources During Chandra observations ~ 10 hours Doing repeat Chandra observations (NGC 4697, 5 obs., t ~ min → 5 years)

  15. Spatial Distribution of LMXBs distribution LMXBs ≳ distribution stars

  16. Luminosity Function of LMXBs NGC 4697

  17. Broken Power-Law? broken power-law power-law fit by broken power-law (Sarazin et al. 2000)

  18. Broken Power-Law? Lb BHs? Mainly NSs? Lb≈ 3 x 1038 ergs/s ≈ LEddington (1.4 M NS)

  19. Cutoff Power-Law? Lcutoff≈ 1039 ergs/s ≈ LEdd (largest stellar BH) (Sivakoff et al. 2003; Jordan et al 2004)

  20. LMXBs and Globular Clusters (GCs) High fraction of LMXBs are in GCs 20 - 70% But, most areas of most galaxies lack GC catalogs (require HST observations) also, NGC 1399 (Angelini et al. 2001), NGC 4472 (Kundu et al. 2002), M87 (Jordan et al. 2004) o = LMXBs o = GC LMXBs NGC 4365

  21. LMXBs and GC – Virgo Survey Lack of HST GC catalogs for nearby ellipticals HST Cycle 11 Large Project: ACS Virgo Cluster Survey (PI: Coté) → GCs Chandra Cycles 4 & 5 Virgo Cluster Survey HST Cycle 13 Fornax Cluster Survey (PI: Jordan) ~100 elllipticals with LMXBs and GC

  22. LMXBs and Globular Clusters (GCs) Fraction LMXBs in GCs ~ 20 - 70% Fraction of optical stars in GCs ~ 0.1 % Optical stars in GCs ~ 500 x more likely to be in LMXB than field stars (same true for Galaxy, M31) LMXBs made by stellar interactions in GCs (Clark 1975; Fabian et al. 1975; Hills 1976)

  23. Are All LMXBs Made in GCs? LX(LMXBs) ∝ Number of GCs (not galaxy luminosity) (Grindlay 1984; Sarazin et al. 2001; White et al. 2002; Irwin et al. 2003)

  24. Fraction LMXBs in GCs vs. Hubble Type Two populations: GC LMXBs and field LMXBs?

  25. LMXBs vs. GC Properties LMXBs prefer brighter GCs (Kundu et al. 2002; Sarazin et al. 2003) Probability of LMXB ∝ Lopt ∝ number of possible donor stars

  26. LMXBs vs. GC Properties (cont.) LMXBs prefer red GCs Due to: Younger GCs? More metal-rich GCs? More metal-rich(Kundu et al. 2003)

  27. LMXBs vs. GC Properties (cont.) LMXBs prefer dense GCs? M87 (Jordan et al. 2004) ProbX∝ n✳ N✳ / σ (not just N✳) ∝ rate of exchange or tidal interactions LMXBs made by stellar interactions in GCs

  28. LMXBs vs. GC Properties (cont.) No strong differences in X-ray properties of LMXB in GCs vs. field, but Luminous LMXBs avoid GCs? BH hard to retain in GCs? True in our Galaxy? (Portegies Zwart & McMillan 2000)

  29. Spatial Distribution of LMXBs and GCs In E galaxies, GCs are “missing” from inner regions Due to: didn’t form in inner regions? were destroyed in inner regions? Destroyed → leave stars behind LMXBs = detectable population from GCs Spatial distribution of LMXBs, GCs, and stars information on destruction of GCs, fraction of LMXBs made in GCs

  30. Do Early-Type GalaxiesContain ULXs? E/S0s have many sources with LX < 2 x 1039 erg/s (0.3-10 keV) (Colbert & Ptak 2002) but . . . N(LX > 2 x 1039 erg/s) ≈ N(BG sources) Density ≈ constant on sky (Irwin et al. 2004)

  31. Do Early-Type GalaxiesContain ULXs? No evidence for real ULXs in E/S0s ? (Irwin et al. 2004)

  32. Do Early-Type GalaxiesContain ULXs? NGC 720, NGC 1407: Distances poorly known, could be < 2 x 1039 some are BG AGN (Arp et al. 2004) NGC 1600: 21 ULXs, expect 10 BG sources (but cosmic variance?) NGC 1399: two ULXs in GCs, one marginal, multiple sources? NGC1600 (Sivakoff et al. 2004)

  33. Spiral Galaxy ULXs and Star Clusters Many ULXs in star forming galaxlies associated with young and intermediate age star clusters Examples: Antennae (Zezas, Fabbiano, et al., Clark et al.) M82-X7 in cluster MGC-11 (Kaaret et al. 2001) Are ULXs in or just near to young clusters? IMBHs or runaway binaries with lower mass BHs?

  34. Conclusions: LMXBs, ULXs, and GCs in X-ray Faint Ellipticals • Most of X-ray emission is from LMXBs, large populations hard integrated spectrum some supersoft sources → IMBHs • Luminosity function: “Eddington break” Lb or high luminosity cutoff BHs vs. NSs? Stellar BHs vs. IMBHs • High fraction of LMXBs in GCs fraction increases Hubble sequence Sp bulges → S0 → E → cD • No real ULXs in early-type galaxies? Associated with star formation only? • New window on stellar evolution in ellipticals 1st detections of NSs and stellar BHs in bright E’s Proof that Es once had many OB stars

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