Absolute	  proper	  mo-on	  measurement	  of	  water	  maser	  source	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  	  toward	  Sgr	  D	  HII	  region	  with	  VERA	
Daisuke	  Sakai,	  Mareki	  Honma,	  Tomoaki	  Oyama,	  Takumi	  Nagayama,	  Hideyuki	  Kobayashi	
Sgr D HII region is one of the radio sources toward the Galactic Center region. Galactic longitude of this source is
l=1.14deg. Line-of-sight velocity of thermal molecular line associated with this source is -16 km/s, which is prohibited in flat
rotation at positive galactic longitude. Narrowness of the molecular line width(~4-5 km/s) seems to avoid this source locating in
Galactic Center, because typical line width in Galactic Center region is 20-30 km/s. These facts make determination of distancefor this source difficult.
We have conducted astrometric observations for 22 GHz water maser source associated with Sgr D HII region with VERA.
We obtained absolute proper motion for this source, and the measured motion implies this source locating in near side relative
to the Galactic Center. By considering the measured absolute proper motion, we constrained the location of this source onnear 3 kpc arm or near central molecular zone(CMZ).	

Introduc-on	

Results	
Proper-es	  of	  Sgr	  D	  region	  SNR	  region	

Radio	  con-nuum	  image	  of	  Sgr	  D	  region	  from	  Mahringer	  et	  al.	  (1999)	  	30

-8

20-10

10-12-14

0-16-10-18-20

1 mas/yr

80

60

40
20
R.A. offset (mas)0-20・Red	  shiF	  component	  on	  east	  side	  ・Blue	  shiF	  component	  on	  west	  side	  ・Projected	  scale	  is	  about	  160	  AU	  assuming	  8	  kpc	  ・Typical	  internal	  mo-on	  is	  1	  mas/yr	  	  	  	  	  	  -­‐	  This	  corresponds	  to	  38	  km/s	  at	  8	  kpc.	  	  Absolute	  proper	  mo-on	
2	  GalacEc	  Center?	  	  or	  	  Disk?	  	  	

Sgr D

(a)	

1(b)	

0-2

-2

Offset (mas)Decl. offset (mas)

0.6

-4-6

0.4

-4-6

0-0.2
-0.6

-10-0.8

-10
0-2

-4-6

2008 2009 2010 2011 2012-1
2008 2009 2010 2011 2012

YearYear

R.A. offset (mas)(a) Projected	  absolute	  mo-on	  (b)	  Time	  versus	  R.A.	  and	  Dec.	  oﬀset	  (c)	  R.A.	  mo-on	  subtracted	  with	  the	  absolute	  proper	  mo-on	Parallax	  Fieng	  results	

VERA	  array(Mizusawa,	  Iriki,	  Ogasawara,	  	  and	  Ishigakijima)	

Fi4ed	  value	

Error	

Parallax	

0.181	  mas	0.076	  mas	Distance	

5.525	  kpc	-­‐1.634/+3.999	  kpc	  RA	  mo-on	-­‐1.739	  mas/yr	

0.045	  mas/yr	

Dec	  mo-on	-­‐2.832	  mas/yr	

0.395	  masyr	

Tabular	  2.	  UVW	  values	  for	  sources	  within	  4	  kpc	  radius	  	  	  	Is	  Sgr	  D	  H	  II	  region	  in	  GC	  or	  Disk?	
Sanna	  et	  al.	  2014	Reid	  et	  al.	  2009	
Sanna+14

0.2-0.4-8-8Array	  :	  VERA	  Target	  line	  :	  22	  GHz	  water	  maser	  Velocity	  resolu-on	  :	  0.42	  km/s	  Epochs	  :	  13	  epochs(2008-­‐2011)	  Mode	  :	  2-­‐beam	  	  	  	  	  	  -­‐	  A-­‐beam	  Sgr	  D	  	  	  	  	  -­‐	  B-­‐beam	  J1745-­‐2820	  	  	  	  	  	  	  	  	  	  posi-on	  reference	  source	  (c)	0.8

0Observa-ons	

Sgr D

-22

Internal	  proper	  mo-on	  of	  Sgr	  D	  maser	  spots.	  
Spots	  detected	  for	  3	  epochs	  are	  selected.	

Measuring	  parallax	  and	  absolute	  proper	  mo-on	  with	  VLBI	  observa-on	  can	  constrain	  the	  loca-on	  of	  Sgr	  D	  HII	  region.	  	

Discussion	

-20160	  AU@8	  kpc	-30

Our	  result	

Sgr D

Disk case
Sgr D
G0.09.62+00.19
G010.47+00.02
G10.62-00.38
G012.02-00.03
G023.44-00.18
G023.70-00.19
GC caseSgr D
Sgr B2R (kpc)
3
3.4
1.6
3.6
2.1
3.8
3.7

UGC (km s−1 )
-49.6
-36.1
30.3
-60.8
25.5
4.7
51.4

VGC (km s−1 )
75.4
191.9
121.7
228.2
215.0225.4
167.1

WGC (km s−1 )
7.3
-10.1
18.2
8.1
1.5
2.0
4.6

0.3
0.1

-23.9
-17.7

141.0
105.4

11.7
-38.0

Sgr B2200 km s-1

Measured	  mo-ons	  for	  several	  maser	  sources	  in	  inner-­‐Galaxy	  	  are	  superposed	  on	  the	  schema-c	  view	  of	  the	  Galaxy.	  	

LSR velocity (km/s)

Decl. offset (mas)Sgr	  D	  region	  consists	  of:	  	  	  	  	  ・H	  II	  region	  	  	  	  	  ・SNR	  region	  Galac-c	  longitude:	  	  	  	  	  	  l	  =	  1.14	  deg	  Line-­‐of-­‐sight	  velocity:	  	  	  	  	  V	  =	  -­‐16	  km/s	  at	  CS	  lines	  Velocity	  width:	  	  	  	  	  σ	  =	  4-­‐5	  km/s	  	  	  	  	  	  22	  GHz	  water	  maser	  is	  associated	  with	  Sgr	  D	  HII	  region.	  	  	  	  	  Sgr	  D	  HII	  region	  is	  one	  of	  the	  most	  intense	  radio	  con-nuum	  source	  in	  GC.	  Distance	  to	  this	  source	  has	  not	  been	  determined	  yet.	  

Offset (mas)H	  II	  region	

One-­‐beam	  mapping	

Disk	  case	  (R=3	  kpc)	  :	  VGC	  for	  Sgr	  D	  is	  less	  than	  a	  half	  those	  of	  other	  sources.	  
GC	  case	  (R=0.3	  kpc):	  VGC	  is	  similar	  to	  that	  for	  Sgr	  B2.	  	  This	  result	  seems	  to	  indicate	  that	  Sgr	  D	  is	  located	  in	  GC	  rather	  than	  Disk.	  	  	  	  →	  We	  have	  to	  increase	  the	  number	  of	  sources	  for	  GC	  region	  to	  conﬁrm	  it.