Extending αOX Studies to Include the Numerous Low-

to-Moderate Luminosity AGNs

Aaron SteffenThe Pennsylvania State University

November 6th, 2006

Collaborators

Iskra StratevaMPE

Niel BrandtPSU

David AlexanderDurham, U.K.

Franz BauerColumbia

Anton KoekemoerSTScI

Bret LehmerPSU

Don SchneiderPSU

Cristian VignaliINAF - Bologna

Extended Chandra Deep Field - South (E-CDF-S; Lehmer et al. 2005)

Four contiguous 250 ks ACIS-I exposures centered on the 1Ms CDF-S

COMBO-17 (Wolf et al. 2004)Optically selected AGNs using 5 Broad-band

and 12 Medium-band filters

Project Motivation● Extend αOX studies to include the low-to-moderate luminosity AGNs that numerically dominate the AGN population.

● Break the luminosity - redshift degeneracy present in flux-limited samples.

● Compile a large, homogeneous AGN sample and use both parametric and non-parametric statistical tests to determine if αOX evolves with cosmic time.

Sobolewska, Siemiginowska & Zycki (2004)

Richards et al. (2006)

● UV emission from a thermalized thin accretion disk.

● X-ray emission from inverse-Compton scattering off of energetic electrons in optically thin corona.

● Radio jets and intrinsic absorption can affect the measurement of the intrinsic X-ray/UV emission.

Relation Between UV and X-ray Emission in AGN

Sample#

srcs# X-ray

Detected

Strateva et al. (2006)

Seyfert 1s 25a 25 (100%)

SDSS / ROSAT 155126

(81%)

High-z 36 32 (89%)

Steffen et al. (2006)

BQS / ROSAT 46 45 (98%)

COMBO-17 / E-CDF-S

52 47 (90%)

High-z 19 32 (89%)

Total 333293

(88%)

Sample#

srcs# X-ray

Detected

Strateva et al. (2006)

Seyfert 1s 25a 25 (100%)

SDSS / ROSAT 155126

(81%)

High-z 36 32 (89%)

Steffen et al. (2006)

BQS / ROSAT 46 45 (98%)

COMBO-17 / E-CDF-S

52 47 (90%)

High-z 19 32 (89%)

Sample#

srcs# X-ray

Detected

Strateva et al. (2006)

Seyfert 1s 25a 25 (100%)

SDSS / ROSAT 155126

(81%)

High-z 36 32 (89%)

Breaking the L-z Degeneracy

Comparing LUV and LX vs. redshift

Our sample spans 5 (4) orders of magnitude in LUV (LX).

X-ray vs. Optical Luminosity

OLS Bisector yields:

Non-parametric

Kendall’s partial τ = 0.519 (15σ)

Evidence for a non-linear relation

Dependance of αOX on log(LUV)

Non-parametric Kendall’s

partial τ = −0.377 (14σ)

No Evidence for Evolution

ParametricNon-Parametric

Kendall’s Partial τ = −0.031 (1.3σ)

Comparison with Earlier Studies

AT86

W94 S05 S06

Number of Sources

154 343 228 333

% X-rayDetected

61% 52% 86% 88%

Radio Loud or BALs?

Yes Yes No No

Future Studies: Including the Most Luminous AGNs

Sample#

srcs# X-ray

Detected

Strateva et al. (2006)

Seyfert 1s 25a 25 (100%)

SDSS / ROSAT 155126

(81%)

High-z 36 32 (89%)

Steffen et al. (2006)

BQS / ROSAT 46 45 (98%)

COMBO-17 / E-CDF-S

52 47 (90%)

High-z 19 32 (89%)

Total 333293

(88%)

Sample#

srcs# X-ray

Detected

Strateva et al. (2006)

Seyfert 1s 25a 25 (100%)

SDSS / ROSAT 155126

(81%)

High-z 36 32 (89%)

Steffen et al. (2006)

BQS / ROSAT 46 45 (98%)

COMBO-17 / E-CDF-S

52 47 (90%)

High-z 19 18 (89%)

Just et al. (2007)

SDSS / Chandra 3030

(100%)

High-z 19 14 (74%)

Total 382337

(88%)

Still no Evidence for Cosmic Evolution

Are the COMBO-17 selected AGNs the Faint Extension of the SDSS

Population?

COMBO-17 αOX Distrbution