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Studies of the faint X-ray source populations in the SMC University of Crete, Greece

Studies of the faint X-ray source populations in the SMC University of Crete, Greece Harvard-Smithsonian Center for Astrophysics Vallia Antoniou In collaboration with: Andreas Zezas (CfA), Despina Hatzidimitriou (UoC). 2nd nearest star-forming galaxy (~60kpc)

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Studies of the faint X-ray source populations in the SMC University of Crete, Greece

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  1. Studies of the faintX-ray source populations in the SMC University of Crete, Greece Harvard-Smithsonian Center for Astrophysics Vallia Antoniou In collaboration with: Andreas Zezas (CfA), Despina Hatzidimitriou (UoC)

  2. 2nd nearest star-forming galaxy (~60kpc) • Low interstellar absorption • Well determined • metallicity (Z~0.2Z◉) • stellar populations (e.g. Harris & Zaritsky, 2004; Gardiner & Hatzidimitriou, 1992) • young (~ 8-30Myr): in the center • intermediate (< 500Myr): drop rapidly in larger distances • old (~ 2-10Gyr): in a fairly regular spheroid extending to the • outer regions of the SMC NGC 362 Galactic Foreground Cluster Why do we observe the Small Magellanic Cloud? Why do we observe the Small Magellanic Cloud ? 47 Tuc N E Anglo-Australian Observatory/Royal Obs.Edinburgh (UK Schmidt plates by David Malin)

  3. XRBs in the SMC • large population of HMXBs Be-XRBs: most numerous sub-class • population associated with recent SF • Classification of different type of sources (e.g. Be/SG - XRBs) understand the connection between SF and XRB formation • Number statistics of these different classes • Luminosity functions study the faint end of the luminosity distribution of XRBs & compare it with the LF of other galaxies

  4. Chandra observations XMM-Newton observations X-ray study of the SMC FIELD 2 FIELD 3 FIELD 5 FIELD 1 FIELD 7 FIELD 6 FIELD 6 FIELD 4 FIELD 3 FIELD 5

  5. 122 sources (@ 3 level) • Lx ~ 4 x 1033 erg s-1 (0.7-10keV) (Zezas et al., in prep.) • 15 pulsars in our fields 3 (out of 15) detected in our survey (Edge et al., 2004) Chandra observations FIELD 3 FIELD 5 FIELD 7 FIELD 6 FIELD 4

  6. 144 sources (@ 3 level) • Lx ~ 3.4 x 1033 erg s-1 (0.5-12keV) (Antoniou et al., in prep.) • 3 pulsars in our fields : 1 detected also in our survey 1 detected without pulsations (Lx ~ 3.2 x 1034 erg s-1) 1 not detected at all XMM-Newton observations NO detections in XMM Field-5 due to high background (1 SSS; Orio et al. 2007) FIELD 2 FIELD 6 FIELD 1 FIELD 3 FIELD 5 Online compilation of SXPs (Coe; last update: June 2007)

  7. 0.01 0.01 0.01 0.01 0.01 Harris & Zaritsky, 2004 42 Myr 42 Myr SFH of our Chandra fields 422Myr 422Myr FIELD 3 FIELD 5 FIELD 7 42 Myr 27 Myr FIELD 6 168Myr 422Myr FIELD 4 42 Myr 422Myr 6.7Myr

  8. 668 Myr 11 Myr 0.01 0.01 0.01 0.01 67 Myr 422Myr SFH of our XMM-Newton fields 67 Myr FIELD 2 17Myr FIELD 1 FIELD 6 FIELD 3 Harris & Zaritsky, 2004

  9. Optical study of the SMC • OGLE-II survey (Optical Gravitational Lensing Experiment; Udalski et al., 1998) • BVI photometric data for ~2.2M stars (down to B~20, V~20.5, I~20mag; ~80% completeness at these limits) • Astrometric accuracy ~0.7”, photometric errors <0.01mag • Coverage of our Chandra survey ~70%, XMM-Newton survey <40% • MCPS survey (Magellanic Clouds Photometric Survey; Zaritsky et al., 2002) • UBVI photometric data for ~5M stars (significant incompleteness below V~20) • Less accurate astrometric & photometric solutions in crowded fields than OGLE-II • Coverage of our Chandra/XMM-Newton surveys ~100%

  10. 15.5 Myr 27.5 Myr 49.0 Myr 87.1 Myr 154.9 Myr 275.4 Myr Optical counterparts of our Chandra sources The most likely optical counterpart (113 Chandra sources): • 9 without counterpart • 42 with single counterpart • 62 with multiple matches …with 89 not previously known!!! Chance coincidence probability for bright sources ~ 19% (Vo < 18.5, (B-V)o < -0.11) • 10 new candidate Be-XRBs • 2 new candidate HMXBs • consistent results with previous classifications in all cases of overlap (18 in total; all Be-XRBs) Antoniou et al., in prep

  11. Optical counterparts of our XMM-Newton sources The most likely optical counterpart (133 XMM-Newton sources): • 11 without counterpart • 43 with single counterpart • 79 with multiple matches Chance coincidence probability for bright sources ~ 2% (Vo < 18.5, (B-V)o < -0.11) Antoniou et al., in prep

  12. The largest existing sample of Be-XRB optical spectra • Obtained ~100 excellent quality spectra with the 2dF spectrograph (AAT) • First results confirmed all of the Be-XRB tentative classifications based on the CMD • 52 Be-XRBs (Chandra sources) have high quality optical spectra Hatzidimitriou et aL., in prep. • Total number of Be-XRBs in our Chandra fields = 57 (52 spectroscopic + 5 photometric classification)

  13. Number of Be-XRBs in each Chandra field FIELD 3 FIELD 5 FIELD 7 FIELD 6 FIELD 4 Compilation of Be-XRBs (Liu et al. 2005) + our new Be-XRBs (Antoniou et al., in prep.)

  14. Number of Be-XRBs in each XMM-Newton field FIELD 2 FIELD 1 FIELD 6 FIELD 3 Compilation of Be-XRBs (Liu et al. 2005) + our new Be-XRBs (Antoniou et al., in prep.)

  15. Normalizing the XRB population to the SFR • Study the Be-XRBs with respect to their related stellar populations • N(Be-XRBs)/N(OB) • Minimize age effects or variations due to SFR differences for populations of different ages • * our candidate SMC Be-XRBs + compilation of MCs HMXBs • (Liu et al. 2005) • * OB stars from MCPS • (Zaritsky et al. 2001)

  16. McSwain & Gies, 2005 X-ray source populations as a function of age

  17. Comparison with the Milky Way • sample of Be-XRBs (Lx 1034erg/s, within 10kpc of the Sun) : - compilations of MCs & MW HMXBs (Liu et al. 2005, 2006) - our candidate SMC Be-XRBs • OB stars : - Chandra fields (MCPS; Zaritsky et al. 2001) - Galactic (Reed 2001) • Be-XRBs ~2 times more common in the SMC when compared to the MW There is still a residual excess that can NOT be accounted for by the difference in the SF rate Difference in solar & SMC metallicity (0.2Z): Dray 2006 predict a factor of ~3 higher numbers

  18. We present the largest census of Be-XRBs in the SMC so far based on a combination of Chandra, XMM-Newton, and optical data • Find a peak of Be-XRBs at ages of ~ 40-60 Myr, and possible evidence for variation within this age range • Find an excess of Be-XRBs in the SMC with respect to the MW In the future: • Extend the analysis to lower luminosities using the Chandra deep observations • IMACS - Magellan analysis: * Identify optical counterparts for currently unidentified sources * Derive accurate SFH • Follow-up spectroscopically the candidate counterparts without spectra Identify the counterparts for most of the X-ray sources and probe the connection with the SFH of the SMC in more detail Summary

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