A Possible Detection of Ionized Gas Orbiting around an IMBH embeddedin the Galactic Center IRS13E Complex; The Second Galactic Center Black Hole?
M. Tsuboi, Y. Kitamura (ISAS/JAXA), T. Tsutsumi (NRAO), K. Uehara (U.Tokyo), M. Miyoshi (NAOJ), R.
Miyawaki (J.F.Oberlin Univ.), and A. Miyazaki (JSF/NAOJ)

Please see Tsuboi et al. APJL, 850, id. L5, (2017)

29”.0

IRS13NICRS Declination29”.2ε29”.4

CXOGC
J174539.7-290029

αE4IRS13E
E329”.629”.8E5E230”.030”.230”.4340GHz cont.

-29 00’30”.6hmss

17 45 39 .86

39 .82s39 .78s

39 .74ICRS Right Ascension
Figure 2Close-up continuum map of IRS13E at 340 GHz. The
angular resolutions using “uniform weighting” is 0”.10X0”.09.

aICRS Declination

IRS13E3

H30a
340GHz cont.

b

H30α (-400, 400)
340GHz cont.

IRS13E

Angular offset from IRS13E3 (arcsec)

IRS13N

Figure 2 shows the close-up continuum map of theIRS13E complex at 340 GHz. The IRS13E complex isresolved into a group of compact objects in the map.
Most of these are the IR identified objects (e.g.,Maillard et al. 2004 ; Schödel et al. 2005 ; Paumard et al.
2006), including IRS13E3 which is a main member of
the IRS13E complex but an ionized gas blob (Fritz et al.
2010). The angular sizes of these objects are estimatedby the 2D Gaussian fit. The beam-deconvolved angularsize of IRS13E3 is derived to be 0.”102 x 0.”090,
corresponding to the physical size of 800 au x 700 au at
the Galactic Center distance. Because the spectra ofIRS13E3 is flat, the emission is an optically thin free–
free emission and the sign of dust thermal emission isnot clear.

B0.5

IRS13N

A0.0

H30αIRS13EDA-0.5-1.0

A-1.5

BC-2.0A-2.5-3.0-600-400200-2000
LSRK radio velocity (km/s)

400600ICRS Right Ascension
Figure 3Position–velocity diagram of H30a recombination line. The velocity width toward IRS13E3 is very large, up to 650 km/s.
The IRS 13E complex is connected to the southern extended component by a curved ridge. The ionized gas can be described bya Keplerian Oribit (broken curve).

16NE

1W

16NW
16C

16SE2

SgrA*34W

13N

16SW

raB

13E
Magnetar

AFNWNW

33N
2133E
AFNW

9NW
9W

nFWHM

EaretsmAr

AF

H30α mom.0
7E210W

734E
16NE
1W

SgrA*34W

x
16SE2

rm

340GHz

34E

nA

δ

3E

ther28”.87

Nor

We observed the continuum emission of Sgr A* and the Mini-spirals at 340 GHz as an ALMA Cy.3
program (2015.1.01080.S. PI M.Tsuboi). The angular resolutions using “natural weighting" and “uniformweighting” are 0”.14X0”.13 and 0”.10X0”.09, respectively. The sensitivities are 0.10 and 0.18 mJy/beam,respectively. Sgr A* and the Mini-spirals are clearly detected at 340 GHz in figure 1 (upper panel). The flux
density of Sgr A*is = 2.8 Jy at 340 GHz.
We analyzed the DDT observation toward the Galactic Center with ALMA, which was released in theautumn of 2016 (2015. A.00021.S). Figure 1(lower panel) shows Integrated intensity (moment 0) mapof the H30a recombination line. The angular resolutions is 0”.41X0”.30 using “natural weighting”. The
recombination line emission associated with Sgr A* is not detected. Famous IR objects are detected in thecontinuum map. Most of them are WR stars except for IRS7, which is a cool star. Some clusters areprominent both in the maps, for example, IRS13E and IRS21.

7E2

10W

rm

Consequently, a very fascinating possibility is that the detected ionized gas is
rotating around an IMBH embedded in the IRS13E complex.

340GHz cont.

nAtherNor

The Galactic Center is the nuclear region of the nearest spiral galaxy, the Milky Way, andcontains the supermassive black hole with M ~ 4x106 M☉, Sagittarius A*(Sgr A*) . One of thebasic questions about the Galactic Center is whether or not Sgr A* is the only “massive” blackhole in the region.
The IRS13E complex is a very intriguing IR object that contains a large dark mass comparable
to the mass of an intermediate mass black hole ( IMBH) from the proper motions of the main
member stars. However, the existence of the IMBH remains controversial. There are someobjections to accepting the existence of the IMBH.
In this study, we detected ionized gas with a very large velocity width (DVFWZI ~ 650 km s−1)
and a very compact size (r ~ 400 au) in the complex using ALMA. We also found an extended
component connecting with the compact ionized gas. The properties suggest that this is an
ionized gas streamer on the Keplerian orbit with high eccentricity. The enclosed mass isestimated to be M ~ 6x104 M☉ by the analysis of the orbit. The mass does not conflict with theupper limit mass of the IMBH around Sgr A*, which is derived by the long-term astrometry
with VLBA. In addition, the object probably has an X-ray counterpart.

13N

raB

13E
33N2133E9NW
9WrAnFWHM

Eamrets

Figure 1upper panel: Continuum map of Sgr A region at 340 GHz. The
angular resolutions is 0”.14X0”.13. lower panel: Integrated intensity(moment 0) map of the H30a recombination. The angular resolutions
is 0”.41X0”.30.

Figure 3 shows the position–velocity diagram of theH30a recombination line. The velocity width toward
IRS13E3 is very large, up to 650 km/s. The IRS 13E
complex is connected to the southern extended
component by a curved ridge. The ionized gas can bedescribed by a Keplerian Oribit (broken curve).
From the Keplarian orbit, the semi-major axis,eccentricity, orbital period and enclosed mass are
estimated to be a~1.5x1017 cm,; e~0.97, T~4000 yr, andMIRS13E ~ 6x104 M☉, respectively. The enclosed mass is aslarge as 1% of Sgr A* mass, MIRS13E~ MSgrA*x10-2.
The ionized gas mass is estimated to be M~6X10-3 M☉
assuming the electron temperature of Te~1x104 K(Tsuboi+2017). If the efficiency is assumed to be 1% as aconservative value, the mass accretion rate, dM/dt~1x10-8, would be comparable to the mass accretion rateof Sgr A* (10-9~10-6 Mo/yr, e.g. Genzel 2010).
The positional difference between the peak positionsof the integrated H30a recombination line and X-ray
continuum emission (CXOJ174539.7-290029; 0.5-7 keV)
is Da =0.35”, Dd =0.03”. This difference is as small as thepositional accuracy of these. These positions areidentical. This object has a X-ray Counterpart.
Using VLBA, the position of Sgr A* had been monitor
for 15 years (Reid&Brunthaler 2004). The positionchange vertical to the galactic plane was as small as
0.4mas/yr, the upper limit mass of the IMBH is ~10^4Mo
at the physical distance of 10^3~10^5 AU. Our result is
consistent with this upper limit mass.

This object is probably an IMBH
4with 10 Mo.