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Suprime-Cam Variability Survey for Faint AGN

This study explores variability-selected faint AGN using Subaru and XMM-Newton deep surveys, focusing on the optical and X-ray variability properties of these objects. The aim is to understand the statistical properties and potentially discover unexpected phenomena in these AGN.

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Suprime-Cam Variability Survey for Faint AGN

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  1. Suprime-Cam Variability Survey for Faint AGN Tomoki Morokuma (NAOJ) w/ Subaru/XMM-Newton Deep Survey (SXDS) Team Subaru Deep Field (SDF) Team Supernova Cosmology Project (SCP) Based on … - Morokuma et al. 2008a, ApJ, in press, astro-ph/0712.3108 - Morokuma et al. 2008b, ApJ, in press, astro-ph/0712.3106 Subaru Users' Meeting

  2. Menu • Introduction - optical variability surveys for AGN • Data & Method for Variability Detections - Subaru/XMM-Newton Deep Survey (SXDS): optical & X-ray • Results • X-ray undetected optically variable AGN • High-redshift (z~4) low-luminosity quasar • Summary Subaru Users' Meeting

  3. Introduction • Variability Study • One of the most interesting observational windows. • many <4m optical telescopes are doing variability surveys. • CFHT LS (SNLS), Pan-STARRS, SkyMapper, … • Some of 8-10m telescopes/HST are also doing variability studies by dividing data for ultra-deep surveys (HDF, UDF, SDF, SXDS, …). • Many kinds of opticallyvariable objects in the universe. • supernova, GRB afterglows • variable stars • AGN: • anti-correlation between AGN luminosity and variability amplitude (e.g. Vanden Berk+2004). • if we want to search faint AGN, host contaminations are NOT negligible.  color classifications become difficult. • microlensing events • moving objects Subaru Users' Meeting

  4. AGN Variability Surveys • HST/WFPC2, ACS studies (Sarajedini+2006, Cohen+2006) • - Comparable depths (deeper) • - small number statistics • multi-wavelength data available • found many variable AGN without X-ray detections, but not examined in detail. shallow This parameter space (wide-field & deep AGN variability survey) has NOT been statistically explored yet. ~ several tens objects • Our aim: • understand properties of variability-selected faint AGN statistically and in detail. • may find unexpected phenomena!? Future projects deep narrow wide Subaru Users' Meeting

  5. Subaru/XMM-Newton Deep Field (SXDF) • X-ray (XMM-Newton/EPIC, 50-100ks, Ueda+2007, Akiyama+2007) • 1e-15 erg s-1 cm-2 @0.5-2.0keV • 3e-15 erg s-1 cm-2 @2.0-10.0keV • MIR (Spitzer/IRAC) • 3.6μm-band ~ 22.0mag • optical (Subaru/Suprime-Cam, Furusawa+2008) • B(28.2mag),V(27.2mag),R(27.6mag), i(27.5mag),z(26.5mag) • optical variability (Subaru/Suprime-Cam, Morokuma+2007) • multi-epoch 8-10 times during 2002~2005 • Timescale: 1 day -- 3 years • iAB~26mag (each epoch) • iAB,vari~25.5mag (variable component=difference of flux among epochs Δf=|f1-f2|) Suprime-Cam 5 fields XMM-Newton 7 pointings (02h18m00s, -05:00:00) in J2000 (l,b)=(169o,-60o) Subaru Users' Meeting

  6. Variability Detection search reference subtraction - Simple photometry does not work because it is difficult to measure flux of extended objects precisely (the measurement depends on image depth). - Variable objects are usually point sources. Image subtraction method (Alard & Lupton 1998, Alard 2000) • 1,040 variable objects over 0.918 deg2 • ~580 AGN / deg2 Subaru Users' Meeting

  7. AGN samples optical variability X-ray 122 (9) <z>=1.32 89 (35) <z>=1.82 238 (36) <z>=1.48 Subaru Users' Meeting

  8. AGN samples optical variability X-ray 122 (9) <z>=1.32 89 (35) <z>=1.82 238 (36) <z>=1.48 Subaru Users' Meeting

  9. X-ray & optical variability detection of AGN X-ray detection limit Optical variability detection limit

  10. Variability selected AGN are type-1. X-ray detected Variability UNdetected X-ray detected Variability detected hard = obscured X-ray hardness ratio soft = unobscured X-ray flux Variability-selected AGN are mainly type-1. Subaru Users' Meeting

  11. AGN samples optical variability X-ray obscured (type-2) unobscured (type-1) unobscured? (type-1?) 122 (9) <z>=1.32 89 (35) <z>=1.82 238 (36) <z>=1.48 Subaru Users' Meeting

  12. Properties of variability-selected AGN X-ray detected Variability detected X-ray UNdetected Variability detected Constant ratios (1,0.1,0.01) between x and y axis. total magnitude including host galaxy differential flux betweem maximum and minimum in magnitude unit. faint variable component ~ faint AGN clearly different distributions Subaru Users' Meeting

  13. Images and Light Curves • faint variable components (AGN) in bright galaxies (e.g.Totani+2005) • flare-like variability? Radiatively inefficient accretion flow (RIAF)? • Similar to local LINER variability? (Maoz+2006) • ~10^8-9Mo SMBHs • early-type galaxies at zphoto~0.5 • ending phases of mass accretion • 5-10% of luminous galaxies at the same redshifts show such variability  several tens % in total!? (unknown variability detection completeness) reference subtraction 3 years • Next steps to reveal nature of this kind of low-luminosity AGN… • HST imaging • Deep spectroscopy (maybe stacking analysis necessary) Subaru Users' Meeting

  14. High-Redshift Low-Luminosity Quasars • “Dropout” selects not only quasars but also LBGs. • If we go fainter, comparable number densities • variability is a strong tool to discriminate quasars from LBGs variable stars galaxies at z<3.6 R-i B-R • 5 B-dropout i-band variable objects in the SXDF • 3 of them spectroscopically observed & identified as real quasars at z~4 Subaru Users' Meeting

  15. Faint-end of z~4 quasar luminosity function i=22-25mag 8-10 times over 3 years z=4.2-4.8 (COMBO-17) z=2 (2QZ) • Make much more statistical sample w/ HSC • variability in redder band  higher-z • Assuming variability dependence on wavelength (Vanden Berk+2004), time dilation effects are not so large. z=4.25, 4.75 (SDSS) Subaru Users' Meeting

  16. Summary • We have carried out the first statistical survey for optically faint variable objects using Suprime-Cam in ~ 1 deg2 (SXDF). • successfully found ~1000 variable objects. • Optical-variability-selected AGN: • - mainly type-1 AGN. • some of them are not detected in X-ray and are faint AGN in bright elliptical galaxies at z~0.5. • We showed optical variability are an efficient tool for low-luminosity quasars even at high-redshift.  much wider-field survey w/ HSC Subaru Users' Meeting

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