Young X-ray source populations in M81 and other galaxies Andreas Zezas Harvard-Smithsonian Center for Astrophysics In collaboration with: K. Gazeas, J. Huchra, J. Gallagher, M. Mutchler, Z. Levay

X-ray source populations There is evidence for a common XLF describing different XRB populations (e.g. Grimm etal 2002) Theoretical population synthesis models indicate evolution of the populations and their XLFs (e.g. Belczynski etal 2002) Observational results show evidence for changes between HMXB and LMXB populations - but little is known about variations within each population. Star-forming galaxies address the evolution of HMXBs Spiral galaxies address the evolution of HMXBs and LMXBs.

Spiral galaxies There is strong evidence for changing populations in star-forming galaxies (arms, bulge, inter-arm regions) Grimm etal 2006 However, little is known about the properties of those X-ray sources. Soria & Wu 2002

M81 : A case study Nearby (3.6 Mpc) grand design spiral galaxy Detect the bulk of active X-ray binaries Identify optical counterparts Detect early type (OB) stars Resolve star-clusters, and measure structural parameters

M81 profile Gordon etal 2004 Prime target to study star-formation and its relation to X-ray binary populations Extensively studied Optical : several stellar generations (6- 600Myr, >1Gyr; e.g. Chandar etal 2001) Radio : Radio SNRs (Kaufman etal 1987) Infrared : Obscured star-formation (Gordon etal 2004, Willner etal 2004) X-rays : Deep exposures (PI D. Swartz) and monitoring campaign (PI D. Pooley) Several populations of X-ray sources Tennant etal 2000 Swartz etal 2003

Description of the Chandra observations 13 ACIS-S pointings (PI D. Pooley) Cover ~50% of D25 Exposure : ~10-15ksec Detection limit : ~10 37 erg/s in each pointing (2  % compl.) ~6  erg/s in combined exposure (4  % compl.)

Chandra observations : First results sources in each pointing 120 sources in coadded exposure (~35 backgr. sources)

A caveat Photometry on coadded exposures underestimates luminosity of faint sources Zezas etal 2007 Average Lx Coadded Lx

Chandra observations : First results XLFs do not vary Consistent with results from the Antennae and other star-forming galaxies

HST observations HST-ACS BVI imaging of entire galaxy Combination of P10540 (I-band; PI J. Huchra) and P10584 (BV-bands; PI A. Zezas) Total of 29 ACS fields (24+39 orbits) B,V-band exposure : 1200 sec (~27 mag at S/N=10) I-band exposure : 1650 sec (~27 mag at S/N=10) Goal : Detect all star-clusters, and bulk of OB stars

Bulge and inner disk

First results

Comparison with Chandra Chandra-HST astrometric registration : < 0.4” Very high chance coincidence rate Cross-corelate with different source types OB stars Giants /supergiants

Comparison with Chandra a ~ 0.75

Star-forming galaxies We find indication for different XLFs associated with different stellar populations NGC1569 NGC5253 NGC4214 Young Older Antennae Starburst sequence NGC 1569 NGC 4214 NGC 5253

Future plans Derive the spatially resolved star-formation history of M81 Classify X-ray sources, compare populations with local star- formation history Compare with predictions from X-ray binary population synthesis models (Belczynski etal, 2007) Compare properties of different X-ray source populations Compare results with other galaxies

Large scale structure OB associations, star-clusters, globular clusters HII regions Inner bulge dust lanes Background galaxies

Comparison with Chandra : XLFs of different source populations Select X-ray sources based on their position on the CMD Spatial distribution of OB sources, unidentified sources. XLF of source populations

Nuclear regionHII regions OB associations Background galaxies

First results : HST

Data analysis Data preparation (drizzle, cleaning etc) Astrometric registration with SDSS (0.3” rms) Detection limits : ~ 27 mag at S/N = 10 ~ 27.5 mag at S/N = 5 Covers the bulk of OB main sequence stars