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Rolf Kudritzki SS 2017
1
10. 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)
Rolf Kudritzki SS 2017
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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
Rolf Kudritzki SS 2017
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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
Rolf Kudritzki SS 2017
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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
Rolf Kudritzki SS 2015
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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
Rolf Kudritzki SS 2015
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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
Rolf Kudritzki SS 2017
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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%
Rolf Kudritzki SS 2015
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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&
Humphreys, 2014, MIAPP WS
Rolf Kudritzki SS 2015
11 Argon et al. (2007)
Red-shifted emission
MIAPP,&28&May&2014&
Humphreys, 2014, MIAPP WS
Rolf Kudritzki SS 2015
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Systemic Maser Emission
Argon&et&al.&(2007)&MIAPP,&28&May&2014&
Humphreys, 2014, MIAPP WS
Rolf Kudritzki SS 2015
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Blue-shifted Emission
Argon&et&al.&(2007)&MIAPP,&28&May&2014&
Humphreys, 2014, MIAPP WS
Rolf Kudritzki SS 2015
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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&
Rolf Kudritzki SS 2017
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more detailed discussion of model will follow later
Rolf Kudritzki SS 2017
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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
Rolf Kudritzki SS 2017
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vrad drift km/s/yr
Herrnstein et al., 1999
dvraddt
= a = 9.3
Rolf Kudritzki SS 2017
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position drift mas/yr d⇥
dt= 31.5
Rolf Kudritzki SS 2017
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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(�)
Rolf Kudritzki SS 2017
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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)
�vrad vth ⇡ 1km/s
�lcI⌫ = I0⌫e
�R �lc0 ⌫dl
�⌫ = ⌫0�vrad
c �⌫th = ⌫0
vthc
Rolf Kudritzki SS 2017
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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)
Rolf Kudritzki SS 2017
22
(R+ dR)2 = (Rcos(�))2 + (Rsin(�) + dl)2
(2)
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…
dR = dl
✓sin(�) +
dl
2R
◆
sin(d�)
dl
=sin(⇡2 + �)
R+ dR
=cos(�)
R+ dR
2RdR ⇡ 2Rsin(�)dl + dl2
Rolf Kudritzki SS 2017
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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(�)
Rolf Kudritzki SS 2017
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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 close to 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
Rolf Kudritzki SS 2015
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�lc�l0
Rolf Kudritzki SS 2017
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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)
Rolf Kudritzki SS 2015
27
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&
Humphreys, 2014, MIAPP WS
Rolf Kudritzki SS 2017
28
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
Rolf Kudritzki SS 2017
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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
Rolf Kudritzki SS 2017
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fit residuals smaller than 1%!!
Humphreys, 2014, MIAPP WS
Rolf Kudritzki SS 2017
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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 .
Rolf Kudritzki SS 2015
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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.&
Humphreys, 2014, MIAPP WS
Search for Megamasers in the Hubble Flow
Rolf Kudritzki SS 2015
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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&
Humphreys, 2014, MIAPP WS
Goal:
The Megamaser in UGC 3789
Braatz & Gugliucci 2008; Reid et al. 2009, 2013
© Fred Lo, 2011
Rolf Kudritzki SS 2015
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UGC&3789&
MIAPP,&28&May&2014&
Reid&et&al.&(2013)&
Humphreys, 2014, MIAPP WS
Rolf Kudritzki SS 2015
36
UGC&3789&
MIAPP,&28&May&2014&
D=&49.6&±&5.1&Mpc&H0&=&68.9&±&7.1&kms31Mpc31&
10%&
Reid&et&al.&(2013)&
Humphreys, 2014, MIAPP WS
NGC 6264
37
Discovery: Kondratko et al. 2006 Map: Kuo et al. 2011
© Fred Lo, 2011
Rolf Kudritzki SS 2015
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NGC 6264 Kuo et al. (2013)
MIAPP,&28&May&2014&
D=144±19&Mpc&H0=68±9&kms31Mpc31&
&&&&&&&&&&&&&13%&&
Humphreys, 2014, MIAPP WS
MCP: Angular Diameter Distance Scale
39
Cepheids DistanceLadder
0Mpc 100Mpc 150Mpc
NGC
4258
UGC
3789
NGC
6323
IC2560
NGC
1194
J0437+2456
Mrk1419
LargestS
tructures
One geometric method covers all scales out to the Hubble flow and the largest structures
NGC
6264
NGC
2273
50Mpc
ESO558-G009
NGC
5765b
© Fred Lo, 2011
Rolf Kudritzki SS 2015
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Challenge of Distant Maser Galaxies
MIAPP,&28&May&2014&
NGC&4258&
NGC&6323&
Henkel et al. (2012)
Humphreys, 2014, MIAPP WS
Rolf Kudritzki SS 2015
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