Measuring Cosmic Distances with Quasars Main collaborators: K. - - PowerPoint PPT Presentation

Measuring Cosmic Distances with Quasars

Marianne Vestergaard

Dark Cosmology Centre, Copenhagen

Lund, February 5, 2013

Main collaborators:

• K. Denney & D. Watson,

plus students (DARK),

• A. King & T. Davis

(U. Queensland),

• M. Bentz (Georgia St.),
• B. Peterson (OSU)

13 Black hole Accretion Disk: gas, continuum emission (X-ray, UV, optical) (Accretion) Torus: Dust+Gas, IR emission Broad Emission Line Gas (“clouds”) Fast-moving gas Face-on Edge-on

Basic Quasar Structure

• Standard Candles

Quasars as Cosmic Distance Indicators

F = L 4!d 2

16 photons

New Standard candle: The “BLR size” of AGN

MBH = v2 R /G

13

Black Hole Virial Mass

BH Broad Emission Line Gas (“clouds”) Face-on Edge-on It takes time for light to travel to the BEL gas from the accretion disk We can measure this time delay (or distance) with variability studies RBLR= c τ Fast moving gas

• ionized by

photons from accretion disk Accretion Disk: gas, continuum emission (X-ray, UV, optical)

AGN Virial Mass Estimates

MBH = v2 RBLR/G

Delay, τ

FluxHβ Fluxcont

Continuum

Emission line

L1

L2

R1

R2

• Variability

Studies: RBLR=cτ

• Radius – Luminosity

Relation: τ t

t + τ

The Radius-Luminosity Relationship

• Physics behind the photo-ionization responsible for

broad line emission dictates R ~ L0.5

• This ‘nebular physics’ is well understood.
• Supported by recent calibrations from ‘lags’ = RBLR/c
• This implies: AGNs can be used as “standard candles” !!

Plot courtesy Misty Bentz

L2 > L1

R2 > R1

RBLR = cτ

L R

L(λ) = F(λ) 4π d2

d ¡~ ¡τ/F1/2 ¡ Quasars as Cosmic Distance Indicators

L1

L2

R1

R2

(Watson, Denney, Vestergaard, Davis, 2011, ApJ, 740, L49)

13

AGN Hubble Diagram: Recession Velocity vs Distance

Black holes as distance indicators

The SNe Hubble Diagram

What is the current status of SNe?

– 583 SNe – Standardizable light-curves – Corrections for host galaxy type, dust, photometric calibration, etc – z-binning?

Union2 SNe Compilation Amanullah et al. (2010) 569 SNe

The SNe Hubble Diagram

Union2 SNe Compilation Amanullah et al. (2010) Union2.1 SNe Compilation Suzuki et al. (2011)

What is the current status of SNe?

– 583 SNe – Standardizable light-curves – Corrections for host galaxy type, dust, photometric calibration, etc – z-binning? RMS is larger at z > 0.4 – this is where AGN can help

583 SNe

• SNe Results:

– Amanullah et al. 2010 (ApJ 716, 712) – Suzuki et al. 2012 (ApJ, 746, 85)

• They were 10 years

ago where we are now…

• Look how far they’ve

come!

• RMS ~ 0.2 mag

SNe Took a While to Catch on too.

Suzuki+ 2012 14 0.19±0.04

Amanullah et al. (2010)

The AGN Hubble Diagram

Reduce the Scatter:

– Misidentified Lags – Reddening/dust Corrections (e.g. Crenshaw ‘01) – Multiple measurements of individual objects RM Lag / AGN Flux0.5

Residuals (dex)

Residuals (mag) Redshift

Luminosity Distance (Mpc) All data: 1σ scatter = 0.5mag SNe: 1σ = 0.2 mag; Best data: 0.12 mag

(Watson, Denney, Vestergaard, Davis, 2011, ApJ, 740, L49)

Most recent update

• Improved flux errors + Galactic reddening (all data)
• Additional and improved corrections for host galaxy

light corrections

Bentz et al. 2013, ApJ, submitted Scatter: 0.13 dex

With the most recent updates, the RMS scatter is already only ~0.33 mag !! And we can do better.

Additional datapoints

Most recent update

Bentz et al. 2013, ApJ, submitted Scatter: 0.13 dex

A significant error is inaccurate distances to the nearby objects not in the Hubble flow. The good news: This is CORRECTABLE!

• Improved flux errors + Galactic reddening (all data)
• Additional and improved corrections for host galaxy

light corrections

Is the Cosmological Constant “constant”?

• Time dependence of w, w(z) = w0 + wa ( 1- (1 + z)-1)
• Best probed at high z
• AGNs have the clear

advantage here: — Exist at all z — Do not dim with time — Can be re-observed — Targets can be selected: ü At certain redshifts ü With minimal reddening ü With favorable properties (variability amplitude, strong lines)

The power of AGNs

The Potential Power of AGNs

W0 Wa W0

Marginalized over Ω(matter) With knowledge of Ω(matter)

Complementary to SNe, CMB, and BAO

Figure of Merit: W0 – Wa plane

As function of the maximum cut-off redshift of AGN sample

Factor 30 increase Factor 2 increase SNe BAO AGN

• incl. AGN

SNe+BAO+CMB alone

Summary

• We can determine the size of the broad line emitting

region R(BLR) near the black hole from light travel time

• delays. Traditionally, R is used for BH mass estimates.
• R(BLR) can be used to determine cosmological distances

because this size correlates tightly with the quasar nuclear luminosity: R ~ L0.5

• Scatter (~0.5mag) needs to be reduced (to < 0.2mag), but
• utlook is good for AGNs to help constrain w and

especially wa better than any other method to date. The current scatter is ~0.33 mag The power of AGNs (over SNe) is at z > 1

• If we apply the same resources to RM as has been to

SNe, we can take this far -> testing DE onset?