Rolf Kudritzki SS 2015 12. Megamasers · Rolf Kudritzki SS 2015 16 3. Time dependence and observed...

Rolf Kudritzki SS 2015

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12. Megamasers Maser sources in the ISM of galaxies amplification of ISM molecular line radiation at microwave and radio wavelengths classical maser lines OH at λ = 18cm H2O at λ = 1.35cm Milky Way: - masers in immediate neighborhood of young stellar objects or circumstellar envelopes of evolved stars - isotropic luminosities up to 1 Lsun (integrated over all lines) or up to 0.1 Lsun in one line (example star formation region W49N)


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External Galaxies: - H2O maser in high density molecular gas located in circumnuclear disks within parsecs of AGN cores (Seyfert2, LINER, spirals, ellipticals) - OH maser within 100 pc of nuclear starburst regions - isotropic luminosities ~ 102 - 104 Lsun à 106 brighter than MW maser à Megamaser - archetype megamaser galaxy is NGC 4258 at 7.6 Mpc - most distant megamaser detected at red shift z = 0.66 (Barvainis & Antonucci, 2005, ApJ 628, L89) Megamaser are potential distance indicators in the Hubble flow key publications: K.Y. Lo, 2005, Annu.Rev.Astron.Astrophys. 43, 625 Herrnstein, J.R. et al., 1999, Nature 400, 539 Humphreys, E.M.L. et al., 2013, ApJ 775, 13


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Maser mechanism

most likely process: - collisional excitation from below (symbolic level a) to upper (symbolic) level b - spontaneous transitions from b downwards overpopulate level u relative to level l -  level inversion à line absorption coefficient negative < 0 à line emission exponentially amplified by stimulated emission

⌫ =h⌫

4⇡�(⌫)Blu

✓nl �

glgu

nu

◆

I0⌫ I⌫ = I0⌫e�

R L0 ⌫dL

note: exponent is positive exponential amplification

Rotational Transitions of H2O (An Asymmetric Top molecule)

616-523: λ = 1.35 cm

ν = 22.235 GHz

J K+K– E(616)/k = 640 K

© Fred Lo, 2011

MIA

PP 2

014

“Maser Galaxy” distance accurate to 3% Humphreys et al., 2013

NGC 4258 7.6 Mpc

New anchor galaxy of extragalactic distance scale using PLR of Cepheids Riess et al., 2011


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NGC 4258 – observations 1. spectrum at 1.35 cm of the central region

•  strong H2O emissions lines

•  three radial velocity systems vrad ~ -470 km/s (systemic velocity) and vrad ~ -470 ± 1000 km/s (blue and red shifted) •  for each systems many different components

•  obvious interpretation: we look almost edge on at a circumnuclear disk which is rotating with ~1000 km/s


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Strong nuclear water maser at 22 GHz

vsys&±&1000&kms31&

GBT&(Modjaz&et&al.&2005)&&MIAPP,&28&May&2014&

Humphreys, 2014, MIAPP WS NGC 4258 – spectrum at 1.35 cm


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Map structure of AGN disks < 1 pc from SMBH

MIAPP,&28&May&2014&

VLBA: Angular resolution = 200 µas (0.006 pc at ~ 7.0 Mpc)

Spectral resolution < 1 kms-1

2. VLBA imaging and spectroscopy of NGC 4258

Humphreys, 2014, MIAPP WS


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2. VLBA imaging and spectroscopy

•  individual masers resolved and vrad assigned to individual components

•  objects in front of AGN have vrad ~ -470 km/s (systemic velocity) the inclination angle relative to AGN is i ~ 82° •  objects at the edges have vrad ~ -470 ± 1000 km/s (blue and red

shifted) •  a rotating Keplerian disk provides a perfect fit to each individually

observed components of the three radial velocity systems with an accuracy better than 1%


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•  Insert the time seried

This Dataset: 18 epochs

1220&km&s31& 1650&km&s31&

Argon, Greenhill, Reid, Moran & Humphreys (2007) VLBA + VLA +EFLS

3525&km&s31& 3280&km&s31&

MIAPP,&28&May&2014&

1&mas&@&7.2&Mpc&!&0.04&pc&



11 Argon et al. (2007)

Red-shifted emission

MIAPP,&28&May&2014&



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Systemic Maser Emission

Argon&et&al.&(2007)&MIAPP,&28&May&2014&



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Blue-shifted Emission

Argon&et&al.&(2007)&MIAPP,&28&May&2014&



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0.15&pc&

Masers probe sub-pc portion of nuclear disk

MIAPP,&28&May&2014&Miyoshi&et&al.&(1995)&

Herrnstein&et&al.&(1999)&

Almost perfect Keplerian rotation

to ~ 1%

40&000&Rsch&


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more detailed discussion of model will follow later


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3. Time dependence and observed rotational motion

•  the individual components of the vrad ~ -470 km/s system in front of the AGN show a common change with time in vrad and position

•  average accelleration km/s/yr •  average change of impact parameter position mas/yr •  the ± 1000 km/s components at the edges do not show such a drift

•  this can be perfectly understood as the result of Keplerian rotation

d⇥

dt= 31.5

dvraddt

= a = 9.3


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vrad drift km/s/yr

Herrnstein et al., 1999

dvraddt

= a = 9.3


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position drift mas/yr d⇥

dt= 31.5


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4. A simple model thin rotating Keplerian disk -  AGN with mass M at center -  maser at angle φ, radius R -  projected angular distance of maser from center (impact parameter) is Θ -  D is distance of galaxy to observer -  projected linear distance of maser from the center is Keplerian velocity observed radial velocity

cos(�) =D⇥

R

vrot

=

✓2G

M

R

◆ 12

v

rad

= cos(�)vrot

D⇥ = Rcos(�)


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5. Likelihood to detect masers at φ = 0° and 90°

dl

for strong maser amplification one needs a long light path along which Doppler shifts of photons through differential rotational velocity are smaller than a thermal line width or The longest coherence lengths are obtained for φ = 90° (no Doppler shifts) and φ = 0° (smallest gradient of vrad along light path)

�⌫ = ⌫0�vrad

c �⌫th = ⌫0

�vthc

�vrad vth ⇡ 1km/s

�lcI⌫ = I0⌫e

�R �lc0 ⌫dl


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calculation of maser coherence length �lc

v

rad

= cos(�)vrot

dv

rad

dl

= cos(�)dv

rot

dl

+ v

rot

dcos(�)

dl

|dvrad

|dl

= v

rot

✓sin(�)(

d�

dl

) +1

2Rcos(�)

dR

dl

◆

dvrot

dl= �1

2vrot

1

R

dR

dl

dcos(�)

dl

= �sin(�)d�

dl

vrot

=

✓2G

M

R

◆ 12

(1)


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(R+ dR)2 = (Rcos(�))2 + (Rsin(�) + dl)2

2RdR = 2Rsin(�)dl + dl2

dR ⇡ dl

✓sin(�) +

dl

2R

◆(2)

sin(d�)

dl

=sin(⇡2 + �)

R+ dr

=cos(�)

R+ dr

d� ⇡ cos(�)

R

dl

applying the law of sines and noting that the angle between vrot and vrad is φ

(3)

combining (2) and (3) with (1) we obtain…


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|dvrad

|dl

=1

R

v

rot

cos(�)

✓3

2sin(�) +

dl

4R

◆or

(4)

for the tangential angle φ = 0° we obtain from (4) and we then re-write (4) as �l0 = 2R

✓�v

rad

vrot

◆ 12

4R2�v

rad

v

rot

= �l

c

cos(�)

✓4R

3

2sin(�) +�l

c

◆

(6)

which has the solution

✓�l

c

�l0

◆2

+ 3

✓v

rot

�v

rad

◆ 12

sin(�)�l

c

�l0� 1

cos(�)= 0

�l

c

�l0= �3

2

✓v

rot

�v

rad

◆ 12

sin(�) +

s9

4

v

rot

�v

rad

sin

2(�) +1

cos(�)


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�l

c

�l0= �3

2

✓v

rot

�v

rad

◆ 12

sin(�) +

s9

4

v

rot

�v

rad

sin

2(�) +1

cos(�)

with vrot ≈ 1000 km/s and Δvrad ≈ 1 km/s the solution varies dramatically as soon as sin(φ) ≠ 0, as shown in the figure on the next page. is different from zero only at φ = 0° and 90°. For vrot ≈ 1000 km/s and Δvrad ≈ 1 km/s we have . For R = 0.2 pc this corresponds to 3.7 1016 cm. This explains why we see masers mostly at φ = 0° and 90°.

�lc�l0

�l0 = 0.06R


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�lc�l0


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6. Discussion of the model and distance

cos(�) =D⇥

R

v

rad

= cos(�)vrot

vrot

=

✓2G

M

R

◆ 12

in front of AGN with φ ≈ 90° we see the systemic components which have slightly different cos φ according to their different Θ. à linear behaviour in vrad vs impact parameter figure. obviously, the components are at roughly the same radius. The average slope b can be measured from this figure

vrad

=D

Rvrot

⇥

b =D

Rvrot (7)


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0.15&pc&

Masers probe sub-pc portion of nuclear disk

MIAPP,&28&May&2014&Miyoshi&et&al.&(1995)&

Herrnstein&et&al.&(1999)&

Almost perfect Keplerian rotation

to ~ 1%

40&000&Rsch&



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for these components we can also use the observed drifts in vrad and Θ

dv

rad

dt

= a = v

rot

d

dt

cos(�) = �v

rot

sin(�)d�

dt

the sin(φ) factor explains why no drift at φ = 0°. For φ ~ 90°, sin(φ) ~ 1 and with we obtain (8) the spatial drift is the change of with time and for φ ~ 90°, sin(φ) ~ 1 (9). The measurements (7), (8), (9) already yield R, D, vrot from the systemic components.

�(t) = !t ! =vrot

R

a =v2rot

R

⇥ =R

D

cos(�)

d⇥

dt= �R

Dsin(�)

d�

dt= �R

Dsin(�)

vrot

R

d⇥

dt=

vrot

D


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In addition, we can use the vrad shifted components at φ ~ 0° and 180° . We start again with using we obtain (10) this is the fit curve in the vrad vs impact parameter figure. all vrad shifted maser components are on one curve à same cos φ for all. Following section 5. we adopt φ = 0° and 180° . (10) yields M/D which can be used for distance together with (7), (8), (9).

v

rad

= cos(�)vrot

cos(�) =D⇥

R

vrot

=

✓2G

M

R

◆ 12

1

R

=cos(�)

D⇥

vrad = cos(�)32

✓2G

M

D

◆ 12 1

⇥12


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fit residuals smaller than 1%!!



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first detailed distance determination by Herrnstein, J.R. et al., 1999, Nature 400, 539 gave D = 7.2 ± 0.5 Mpc Improved data with longer time base line and refined fitting algorithms assuming a warped confocal elliptical disk and differential precession by Humphreys, E.M.L. et al., 2013, ApJ 775, 13 resulted in D = 7.6 ± 0.17 ± 0.15 Mpc fitting systematic errors This is a 3% accuracy and the most accurate distance to a galaxy outside the Local Group. The mass of the AGN black hole is (4.0 ± 0.09) �107 Msun .


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2. Megamaser Cosmology Project (MCP)

&NRAO&Key&Project&(PI:&Braatz)#to&determine&H0&by&measuring&geometric&distances&with&an&accuracy&of&~10%&to&

~10&galaxies&in&the&Hubble&Flow&&

MIAPP,&28&May&2014&

Braatz,&Condon,&ConstanUn,&Greene,&Hao,&Henkel,&Impellizzeri,&Kuo,&Lo,&Reid,&et&al.&


Search for Megamasers in the Hubble Flow


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Direct H0 Measurement •  Water masers in AGN have been detected well into

the Hubble Flow –  distances out to ~200 Mpc

•  Direct estimation of H0

•  Systematic uncertainties in individual disk models not likely to be correlated – Uncertainty in H0 scales as σH0/H0≈N-0.5(σD/D)

•  Broad distribution on sky needed to reduce impact of large scale flows –  Even after correction from models of cosmic velocity field

MIAPP,&28&May&2014&


Goal:


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UGC&3789&

MIAPP,&28&May&2014&

Reid&et&al.&(2013)&



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UGC&3789&

MIAPP,&28&May&2014&

D=&49.6&±&5.1&Mpc&H0&=&68.9&±&7.1&kms31Mpc31&

10%&

Reid&et&al.&(2013)&



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NGC 6264 Kuo et al. (2013)

MIAPP,&28&May&2014&

D=144±19&Mpc&H0=68±9&kms31Mpc31&

&&&&&&&&&&&&&13%&&


MCP: Angular Diameter Distance Scale

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Cepheids Distance Ladder

0 Mpc 100 Mpc 150 Mpc

NGC

4258

UGC

3789

NGC

6323

IC 2560

NGC

1194

J0437+2456

Mrk 1419

Largest S

tructures

One geometric method covers all scales out to the Hubble flow and the largest structures

NGC

6264

NGC

2273

50 Mpc

ESO 558-‐G009

NGC

5765b

© Fred Lo, 2011


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Challenge of Distant Maser Galaxies

MIAPP,&28&May&2014&

NGC&4258&

NGC&6323&

Henkel et al. (2012)



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Rolf Kudritzki SS 2015 12. Megamasers · Rolf Kudritzki SS 2015 16 3. Time dependence and observed...

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