Post on 20-Dec-2015
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X-ray Bright, Optically Normal Galaxies - XBONGS Forman, Anderson, Hickox,
Jones, Murray, Vikhlinin, Kenterand the Bootes Team
Bootes Survey9.3 sq. degrees with Chandra
4632 X-ray sources1600 optical spectra
NOAO Deep Wide Field SurveyAGES Optical Spectroscopic Survey
20,000 galaxy spectraKey to success is contiguous area and efficient spectroscopy with Hectospec
XBONGS - debated nature since Einstein Obs. (Elvis et al. 1981)
Dilution of optical AGN signature by galaxy light Absorption Radiatively inefficient accretion flow (little optical/UV)
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The XBootes Survey• 126 ACIS 5 ksec pointings
• Joint GTO (Murray) and GO (Jones) program
• 14h 32m +34 06’
• 4642 sources detected (>=2 cts)– 625 spurious
• 3293 sources detected (>=4 cts)– 22 spurious
• 42 extended sources (>=10 cts)
• fmin= 4(8)x10-15 erg cm-2 s-1 (0.5-7 keV)
• 98% sources 4 cts matched to NDWFS candidates (R26)
Murray et al. ApJ S 163, 2005
Kenter et al. ApJ S 163, 2005
Brand et al. ApJ, 2006
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Spectroscopy in Bootes
• MMT/Hectospec fiber spectrograph – 300 fibers– 6 A resolution, 4000-8000A
• Spectroscopy– Complete X-ray >4 cts and I<21.5 and galaxies I<19.5– 1,531 X-ray selected and ~19,000 galaxies
– 1175 Broad Line Galaxies– 50 Narrow Line Galaxies– 258 XBONGS
• Huge sample• 17% of total• 0 < z < 1
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Heterogeneous Class of Objects
From optical SED’s and morphology
• Red Ellipticals 60• Blue Ellipticals 84• Interacting 21• Spirals 9• “AGN” 12
(Fioc &Rocca-Volmerange 1997; Francis et al. 1991)
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XBONG Magnitude Distribution
XBONGBL (z<1) NL
XBONG counterparts similar to NL/BL AGNpossibly somewhat fainter than NL AGN
Argues against significant dilution of lines by underlying host galaxy for all of sample
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Luminosity Distributions
XBONGBL (z<1)NL
•200 XBONGs with Lx>1042 erg/s
•50% with Lx>1043 erg/s
•XBONG’s and NL AGN
•Similar Lx
•Similar Fx/FR
•Argues against dilution for all of
sample
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Merged X-ray Spectra
Type (90% error) and no absorption
Red Ellipticals 1.12-1.32
Blue Ellipticals 1.55-1.73
“AGN” 1.83-2.25
Interacting 1.28-1.56 (confirmed by hardness ratios)
Red ellipticals - for an assumed =1.9 power law
nH ~ 0.7-1.1 x 10 22 cm-2 (90% confidence)
• Some “types” absorbed, some not absorbed
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IRAC Color-Color Diagrams (following Stern et al.)
Z<0.15
0.15<Z<0.30
0.30<Z<0.45
0.45<Z<0.60
0.60<Z<0.75
0.75<Z<1.00
z<0.3 Dilution - about 30%; consistent with Georgantopoulos et al. dilution criterion
z>0.3 XBONGS concentrated under AGN wedge
XBONGS BL AGNNL AGN
Red Blue
BL AGN
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Radiatively Inefficient Accretion Flows (RIAF)
•At low accretion rates (Yuan & Narayan)- Optically thick disk is truncated at Rtrans
- Interior to Rtrans flow is RIAF (radiatively inefficient;
optically thin)- Observed in high state galactic black holes-X-rays from inverse Compton in RIAF-Little optical or UV since no disk at small radii- model requires L/Ledd < 0.03
•Test RIAF model with spheroidal sample of XBONGS
-Use optical luminosity as proxy for MBH (108-109 Msun)
- MBH yields Ledd
-Derive AGN LBOL from SED (Elvis et al.)
- For 46 XBONGS, LBOL /Ledd < 0.01
VIABLE MODEL - needs detailed SED’s
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Conclusions• Large XBONG sample
– 258 with redshifts to 1
– Variety of optical morphologies
• Origin of XBONG signature– Some dilution at low z (small fx/fR)
– Some absorption - esp. red ellipticals with nH~1022 cm-2
– Many sources show little (<1022 cm-2) absorption
– RIAF (radiatively inefficient accretion flow)
• Spheroidal sample has low Eddington ratio (Lbol/Ledd<0.01)
– Probably some BL Lac’s
XBONG’s are a heterogeneous class
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Future Work• Deeper & Wider
– Chandra and XMM-Newton
– Larger samples, better S/N
• X-ray spectra– Better models applied to ensemble of spectra
• Optical spectra for fainter sources– Probe to higher z
• Detailed analysis of optical spectra– Derive equivalent widths and line strength limits– Model NL galaxies, compare to XBONGS
• Derive SED’s for different classes to test e.g., RIAF models• Study local environment
– 20,000 galaxy redshifts– Measure local density, compare to other AGN classes
Remarkable class Promises new insights into accretion process