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Heavily Obscured Supermassive Black Holes Ezequiel Treister Einstein Fellow IfA, Hawaii Collaborators: Meg Urry, Priya Natarajan, Carie Cardamone, Kevin Schawinski (Yale), Eric Gawiser (Rutgers), Dave Sanders (IfA) and the MUSYC team Credit: ESO/NASA, the AVO project and Paolo Padovani Active Galactic Nuclei (AGN) Black hole: 106-108 Msun Accretion disk: ~few light-days Torus: 105-107 Msun ~few parsec gas+dust geometry unknown Source of nuclear obscuration Urry & Padovani, 1995 AGN Emission mm far-IR near-IR Optical-UV X-rays Manners, 2002 Black hole–galaxy connection All (massive) galaxies have black holes Tight correlation of MBH with Common BH/SFR Evolution AGN feedback important Milky Way SMBH Mass: 4x106 Msun All (Massive) Galaxies have super-massive black holes Black hole–galaxy connection All (massive) galaxies have black holes Tight correlation of MBH with Common BH/SFR Evolution AGN feedback important MBH- Correlation Same relation for both active and non-active galaxies. : stellar velocity dispersion, measured in the central region. indicates stellar mass outside influence radius of BH. Greene & Ho, 2006 Black hole–galaxy connection All (massive) galaxies have black holes Tight correlation of MBH with Common BH/SFR Evolution AGN feedback important Common BH/Star Formation Evolution Redshift (z): receding velocity due to expansion of the Universe. z=1 z=2 ~50% of the age of the Universe, 7.7x109 light years. ~80% of the age of the Universe. Marconi et al. 2004 Black hole–galaxy connection All (massive) galaxies have black holes Tight correlation of MBH with Common BH/SFR Evolution AGN feedback important AGN Feedback No AGN With AGN Feedback Springel et al. 2005 QuickTime™ and a decompressor are needed to see this picture. Unobscured (naked) Quasar Obscured Quasar T~108years Hopkins et al. (2008) Obscured Accretion • Critical stage of BH-galaxy connection. • Occurs when galaxies form most of their stars. • Can represent up to 50% of matter accretion onto the central black hole. How do we know that? Credit: ESO/NASA, the AVO project and Paolo Padovani Observed X-ray “Background” Treister et al. 2009b Resolving the X-ray Background AGN in X-rays X-ray spectrum of unobscured AGN much softer than X-ray background. AGN in X-rays Photoelectric absorption affect mostly low energy emission making the observed spectrum look harder. AGN in X-rays Compton Thick AGN •Defined as obscured sources with NH>1024 cm-2. • Very hard to find (even in X-rays). • Observed locally and needed to explain the Xray background. • Number density highly uncertain. Increasing NH X-ray Background XRB well explained using a combination of obscured and unobscured AGN. •Setti & Woltjer 1989 •Madau et al. 1994 •Comastri et al. 1995 •Gilli et al. 1999,2001 •Treister & Urry 2005 •Gilli et al. 2007 •And others… Treister et al. 2009b Finding nearby obscured AGN Swift INTEGRAL Swift Sources ISDC Tueller et al. 2010 Deep INTEGRAL Survey (3 Msec) Significance Image, 20-50 keV Deep INTEGRAL Survey (3 Msec) Significance Image, 20-50 keV Deep INTEGRAL Survey (3 Msec) Significance Image, 20-50 keV Fraction of Heavily-Obscured AGN X-ray background does not constrain density of heavilyobscured AGN Direct detections of individual sources are required. Treister et al. 2009b How to find distant obscured AGN? Mid-IR Most of the absorbed energy is re-emitted at IR wavelengths. Sources with high ratios of IR (mostly AGN) to optical (stars) emission are good candidates to be obscured AGN. R-K=2.5log(fK/fR) Fiore et al. 2008, 2009; Treister et al. 2009 Stacking of non-Xrays Sources Soft (0.5-2 keV) Hard (2-8 keV) - ~4 detection in each band. - fsoft=2.1x10-17erg cm-2s-1. Fhard= 8x10-17erg cm-2s-1 - Sources can be detected individually in ~10 Msec. - Spectral slope shows a large fraction of heavily obscured AGN in this sample. Namely, ~90% obscured AGN and 10% starforming galaxies. Treister et al. ApJ 2009c X-Ray to Mid-IR Ratio Both X-rays and 12µm good tracers of AGN activity. ~100x lower ratio for X-ray undetected sources. Explained by NH~5x1024 to 1025cm-2 Treister et al. ApJ 2009c X-Ray to Mid-IR Ratio Ratio for sources with L12µm>1043erg/s (~80% of the sources) ~2-3x higher than star-forming galaxies Treister et al. ApJ 2009c Optical/Near-IR SED Fitting X-ray Undetected - Median stellar mass for X-ray detected sources ~4.6x1011 Msun. - For X-ray undetected source ~1011 Msun. X-ray Detected Evidence for significant recent star formation in most sources Treister et al. ApJ 2009c Heavily-Obscured AGN Space Density Systematic excess for Lx>1044erg/s sources relative to extrapolation of Compton-thin LF Strong evolution in number of sources from z=1.5 to 2.5. Consistent with heavilyobscured phase after merger? Treister et al. ApJ 2009c Obscured to Unobscured Quasar Ratio IR-selected Local ULIRGs Treister et al. submitted The Merger-Quasar Connection Obscured quasars are the product of the merger of two massive gas-rich galaxies. After a time t the quasar becomes unobscured. d 2 merger t N gal ( M min (z)) f gas(z) N obsc dtdN (z) NUnobsc NUnobsc(z) Treister et al. submitted The Merger-Quasar Connection t=9623 Myrs The obscured phase represents ~30% of total accretion onto supermassive black holes Treister et al. submitted The Future: NuSTAR Energy Range 6-80 keV Angular resolution 40” Field of View 12’x12’ Flux Limit ~2x10-14 in 1 Msec Launch Date August 2011 PI Fiona Harrison NuSTAR Observations NuSTAR will directly detect a large number of heavily-obscured AGN up to z~1-2. Summary • Obscured AGN are critical to understand galaxy evolution. • From the Swift and INTEGRAL experiments we are starting to understand the nearby obscured AGN population • Mid-IR selection finds large number of obscured AGN at larger distances. • Strong evolution in numbers up to z~3. • This could be evidence for a heavily obscured phase after quasar triggering. • NuSTAR will be critical in understanding the AGNGalaxy connection.