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Millimeter Megamasers and AGN Feedback
Junzhi Wang
SHAO
Collaborators：Jiangshui Zhang(GZU), Yu Gao(PMO), ZhiyuZhang(ESO,PMO),
Di Li(NAOC), Min Fang(PMO), Yong Shi(NJU)
Outline
• Maser and Mega-maser
• Our research: 2 new mega-maser molecules
• Future prospects: high resolution observations
with JVLA and ALMA?
Astronomical Maser
• Mainly in star forming regions, evolved stars and
also Supernova remnants
• More than 10 molecules were found to have
maser emissions (OH, H2O, CH3OH, H2CO, SiO,
HCN, CH, NH3,etc.)
• Masers can be pumped by collision or radiation
• Masers can be used for astrophysical and
astrometry studies, such as BeSSeL project
Mega-masers
• Masers in galaxies had been found since 1970s
• Some of them are similar to that in the Milky Way
sources, and are just the collection of such maser
emissions
• Another type, the so-called mega-masers, with the
isotropic luminosity greater than 1 million times than
typical Galactic masers, and are not the simple
collection of millions of maser spots similar to that in
the Milky Way sources
• Such mega-masers are normally formed in extreme
conditions different to that in the Milky Way
History of Mega-masers
• First mega-maser：Water in NGC4945, 1975, nature
• OH in Arp220, 1982, ApJL, and H2CO in Arp220, 1986, ApJ
• Many searching projects of new mega-masers had been
done in past 30 years, mainly focus on class II CH3OH megamasers, without success
• Water mega-masers had been used to study the central
super massive black holes and to determine the Hubble
constant with the measurement of distances
• OH mega-masers had been used to study the starburst in
the central 100pc
• Few works on H2CO mega-maser
• For more information, see Lo (2005) ARA&A
What we have done
• 3mm observation toward the nearby type 2
Seyfert galaxy NGC 1068 with the IRAM 30m
telescope
• 27 hours observing time, Dec 2011, PI: Junzhi
Wang
• We detected SiO and CH3OH mega-maser
emissions, which increased the mega-maser
molecules from 3 to 5
NGC 1068
This composite image shows X-ray (red), optical (green), and
radio (blue) data credit: NASA/NRAO/NSF
SiO thermal emission in NGC 1068
Qiu et al. to be submitted
Usero et al. 2004
IRAM 30m
Dust continuum in NGC1068
The dash circle is the
beam of IRAM 30m
at 3mm
349GHz dust continuum emission observed with ALMA, provided by Santiago Garcia-Burillo
Observations
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Date: Dec 2011, 3 days
Observing mode: Wobboler switching
Backend: FTS
Receiver: EMIR
Observing band: 3mm (84-92 GHz)
Our results
Junzhi Wang, Jiangshui Zhang, Yu Gao, Zhi-Yu Zhang, Di Li, Min Fang, Yong Shi
Nature Communications，2014
They are real emission
• We checked them at 2 LO tunings and
detected them at both setups
• The entire spectrum at 3mm was at extreme
good performance, flat and stable baseline
• SiO J=2-1 (v=1) can also be seen at similar
velocity to that of v=3
Spectra of two LO tunings of SiO J=2-1
(v=3) for the 1125 km s-1 component
8 GHz frequency coverage spectrum at 3mm
They are masers
• The only on SiO J=2-1 (v=3) emission detected in the
Milky Way is maser emission instead of thermal
emission
• And the line widths of SiO J=2-1 (v=3) in NGC 1068 are
much less than the thermal lines, so it is reasonable to
assign them as masers
• CH3OH 5-1-40E line can be maser or thermal emission in
the Milky Way sources
• The detected CH3OH emission is more than 3 times of
that estimated from other millimeter CH3OH lines
detected with ALMA as thermal emission
• And the line profile is different to the thermal lines
They are mega-masers
• They are more luminous than one million
times of the typical Milky Way masers
• It is impossible to have more than one million
evolved stars with maser emissions near the
center of this galaxy (for SiO)
• And the velocity of CH3OH emission is
consistent with the jet maser of H2O, while
the velocities of SiO masers are similar to the
H2O disk maser
Possible origin of these two types of megamasers comparing with H2O maser
22GHz continuum
Spectrum of H2O maser
Gallimore et al. 2001 ApJ
Excitation conditions
• The upper level energy of SiO v=3 is about
3660K
• SiO molecules are needed: Shock or XDR?
• Pumping mechanism: collision or radiation?
• CH3OH: class I maser, collisional excitation
Future prospects
• Measuring the masses of central
• AGN feedback: from sub-pc (SiO) to ~100 pc
(CH3OH) scale
• Other applications
• High resolution high sensitivity observations,
especially with ALMA
• Single dish surveys: CH3OH mega-masers
(Millimeter and 834.285 MHz with FAST?)
• Millimeter VLBI including ALMA?
Searching such emission in other
galaxies
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NGC 4258 and NGC 3079
IRAM 30m, Dec 2012
Observing time: about 10 hours each source
Not detected
Thanks