J/ApJ/949/18 Stellar pop. in the central 0.5pc of the GC. III. (Jia+, 2023)
Stellar populations in the central 0.5pc of our Galaxy.
III. The dynamical substructures.
Jia S., Xu N., Lu J.R., Chu D.S., O'Neil K.K., Drechsler W.B.,
Hosek M.W.J., Sakai S., Do T., Ciurlo A., Gautam A.K., Ghez A.M.,
Becklin E., Morris M.R., Bentley R.O.
<Astrophys. J., 949, 18 (2023)>
=2023ApJ...949...18J 2023ApJ...949...18J
ADC_Keywords: Galactic center; Spectra, infrared; Radial velocities;
Proper motions; Photometry, infrared
Keywords: Astrometry ; Galactic center ; Infrared observatories ;
High angular resolution
Abstract:
We measure the 3D kinematic structures of the young stars within the
central 0.5pc of our Galactic Center using the 10m telescopes of the
W. M. Keck Observatory over a time span of 25yr. Using high-precision
measurements of positions on the sky and proper motions and radial
velocities from new observations and the literature, we constrain the
orbital parameters for each young star. Our results show two
statistically significant substructures: a clockwise stellar disk with
18 candidate stars, as has been proposed before, but with an improved
disk membership; and a second, almost edge-on plane of 10 candidate
stars oriented east-west on the sky that includes at least one IRS 13
star. We estimate the eccentricity distribution of each substructure
and find that the clockwise disk has =0.39 and the edge-on plane
has =0.68. We also perform simulations of each disk/plane with
incompleteness and spatially variable extinction to search for
asymmetry. Our results show that the clockwise stellar disk is
consistent with a uniform azimuthal distribution within the disk. The
edge-on plane has an asymmetry that cannot be explained by variable
extinction or incompleteness in the field. The orientation, asymmetric
stellar distribution, and high eccentricity of the edge-on plane
members suggest that this structure may be a stream associated with
the IRS 13 group. The complex dynamical structure of the young nuclear
cluster indicates that the star formation process involved complex gas
structures and dynamics and is inconsistent with a single massive
gaseous disk.
Description:
In this work, we included all spectroscopically identified young
(early-type) stars with well-measured radial velocities (RV) and
proper motions. To get a young star list with well-understood
completeness, we combined new Galactic Center OSIRIS Wide-field Survey
(GCOWS) observations with previous GCOWS observations
(Do+ 2013, J/ApJ/764/154) and with other spectral types from the
literature.
The GCOWS survey consists of observations with the Keck OSIRIS
spectrograph behind the laser-guide-star adaptive optics system on the
W. M. Keck Observatory. We obtained diffraction-limited,
medium-spectral-resolution (R∼4000) spectra with the Kn3 filter
(2.121-2.220um). We used two different plate scales: 35mas in the
central fields where the stellar densities are highest and 50mas for
the outer fields having relatively lower stellar density. Details on
the GCOWS survey are presented by Do+ (2009, J/ApJ/703/1323 & 2013).
In this work, we have added 13 new observations for 11 stars in the
south and north (magenta boxes in Figure 1). The new spectroscopic
observations spanned 2013-05-17 to 2019-07-08.
As described in Section 2.4, projected positions and proper motions on
the sky are derived from high-resolution infrared (IR) images obtained
over a 10-25yr time baseline. Depending on the distance from Sgr A*,
we either use observations from the 10m telescopes at the W. M. Keck
Observatory (WMKO) or the HST WFC3-IR instrument.
The HST data set consists of 10 epochs of observations centered on
SgrA* that were obtained between 2010 and 2020 in the F153M filter
(2010.5: GO 11671/PI Ghez, 2011.6: GO 11671/PI Ghez, 2012.6:
GO 12318/PI Ghez, 2014.1: GO 13049/PI Do, 2018.1: GO 15199, PI Do,
2019.2: GO 15498/PI Do, 2019.6: GO 16004/PI Do, 2019.7: GO 16004/PI Do
2019.8: GO 16004/PI Do, 2020.2: GO 15894/PI Do). While the HST spatial
resolution is ∼2.5 times lower than that achieved with the Keck
observations (FWHM∼0.17" versus FWHM∼0.06"), HST's FOV of 120"x120" is
much larger than can be realistically achieved with current AO systems.
To ensure that our final sample shares a common photometric system, we
adopt the Kp magnitude for each star from the deep wide mosaic image
analysis reported in Lu+ 2013ApJ...764..155L 2013ApJ...764..155L, which covers all
88 stars in our sample. We applied the full extinction map from
Schodel+ (2010A&A...511A..18S 2010A&A...511A..18S) to correct extinction with an average
value of Aks=2.7. See Section 2.5.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 24 88 Disk membership
table7.dat 100 149 RV summary
table8.dat 99 149 Proper-motion summary
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See also:
J/ApJ/643/1011 : Early-type stars in the center of the Galaxy (Paumard+, 2006)
J/ApJ/697/1741 : Warped disks of YSOs in Galactic center (Bartko+, 2009)
J/ApJ/703/1323 : Sp. of stars in the Galaxy's nuclear cluster (Do+ 2009)
J/A+A/502/91 : Proper motions of stars near SgrA* (Schoedel+, 2009)
J/ApJS/190/1 : A survey of stellar families (Raghavan+, 2010)
J/A+A/511/A18 : NIR observations of stars near SgrA* (Schoedel+, 2010)
J/other/Sci/337.444 : RV curves of Galactic massive O stars (Sana+, 2012)
J/ApJ/764/154 : Stellar populations in the central 0.5pc. I. (Do+, 2013)
J/ApJ/783/131 : Kinematic of stars in Galactic center (Yelda+, 2014)
J/A+A/584/A2 : KMOS view of the Galactic centre. I. (Feldmeier-Krause+, 2015)
J/ApJ/808/106 : NIR spectroscopic obs. in the Galactic Center (Stostad+, 2015)
J/ApJ/825/19 : Mass & radii for planets with Rp<4 (Wolfgang+, 2016)
J/A+A/610/A83 : GALACTICNUCLEUS: JHKs imaging survey (Nogueras-Lara+, 2018)
J/ApJ/873/65 : Keck/NIRC2 obs. of the Galactic Center (Sakai+, 2019)
J/AJ/159/63 : New AO obs. of exoplanets & BD companions (Bowler+, 2020)
J/ApJ/932/L6 : Young stars in the Galactic Center (von Fellenberg+, 2022)
J/ApJ/948/94 : Binary stars from long-term obs. of the GC (Chu+, 2023)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Star name
10- 13 F4.2 --- Pdisk1 [0/0.76] Disk1 probability membership (1)
15- 18 F4.2 --- PPlane2 [0/1] Plane2 probability membership (1)
20- 24 F5.3 --- SA [0/1.4] Solid angle measured at the contour
where the disk density drops to half of
the peak value (see Section 4.2)
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Note (1): The density map of normal vectors, L, shows two overdense regions,
indicating the presence of at least two distinct populations, each of
which consists of stars that share a common orbital plane (Figure 6).
We label the two peaks as Disk1 and Plane2;
see Section 5.1 for further explanations.
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Star name
12- 16 I5 km/s RVg [-1054/631]? RV measurement from our Galactic
Center OSIRIS Wide-field Survey (GCOWS)
database
18- 19 I2 km/s e_RVg [4/72]? RVg uncertainty
21 A1 --- f_RVg [*] *: stars with multiple measurements in
our database; only one measurement is shown
here
23- 28 F6.1 yr t0g [2002.4/2019.4]? Epoch, t0GCOWS
30- 32 A3 --- [PGM2006] ID from Paumard+ 2006, J/ApJ/643/1011 (P06)
34- 38 I5 km/s RVP06 [-1060/610]? RV measurements from P06
40- 42 I3 km/s e_RVP06 [20/150]? RVP06 uncertainty
44- 47 I4 km/s RVB09 [-557/536]? RV measurements from
Bartko+ 2009, J/ApJ/697/1741
49- 52 I4 km/s e_RVB09 [6/100]? RVB09 uncertainty
54- 57 I4 --- [FNS2015] [64/2233]? ID from Feldmeier-Krause+ 2015,
J/A+A/584/A2 (F15)
59- 62 I4 km/s RVF15 [-229/277]? RV measurements from F15
64- 67 I4 km/s e_RVF15 [-120/211]? RVF15 uncertainty
69- 72 I4 km/s RV [-542/536]? Final radial velocity used,
RVuse
74- 76 I3 km/s e_RV [2/211]? RV uncertainty
78- 80 A3 --- n_RV Note on RV
82- 86 A5 --- r_RV Reference(s) for final RVuse (1)
88 A1 --- WR Wolf-Rayet star?
90- 100 A11 --- Data The available data for each star (2)
--------------------------------------------------------------------------------
Note (1): Reference as follows:
1 = our GCOWS database,
2 = P06 (Paumard+ 2006, J/ApJ/643/1011),
3 = B09 (Bartko+ 2009, J/ApJ/697/1741),
4 = F15 (Feldmeier-Krause+ 2015, J/A+A/584/A2),
5 = Z20 (Zhu+ 2020ApJ...897..135Z 2020ApJ...897..135Z)
Note (2): The available data for each star as follows:
RV = radial velocity (see Section 2.1)
C = spectral completeness (see Section 2.3)
PM = proper motion (see Section 2.4)
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Byte-by-byte Description of file: table8.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Star name
12- 15 F4.1 mag Kpmag [9.1/16.2] Kp band magnitude
17- 20 F4.1 mag Kpmag0 [9.2/16.7] Extinction-corrected Kp band
magnitude to Aks=2.7
22- 28 F7.2 km/s/yr aR [-168/21.3]? αR parameter (1)
30- 34 F5.2 km/s/yr e_aR [0.08/18]? aR uncertainty
36- 42 F7.3 arcsec x0 [-11/12]? x0 parameter
44- 50 F7.5 arcsec e_x0 [1e-05/0.007]? x0 uncertainty
52- 58 F7.3 arcsec y0 [-11.6/12.3]? y0 parameter
60- 66 F7.5 arcsec e_y0 [2e-05/0.1]? y0 uncertainty
68- 73 F6.2 mas/yr vx [-14.01/32.4]? vx parameter
75- 78 F4.2 mas/yr e_vx [0.01/2.2]? vx uncertainty
80- 85 F6.2 mas/yr vy [-29/16.1]? vy parameter
87- 90 F4.2 mas/yr e_vy [0.01/2.3]? vy uncertainty
92- 97 F6.1 yr t0 [2002.2/2015.5]? Epoch
99 I1 --- Source [1/3]? Reference for the final
proper motion (2)
--------------------------------------------------------------------------------
Note (1): The absolute value of the line-of-sight distance |z| between the star
and Sgr A* can be calculated from the following equation if aR is
known:
aR=-(GMtot(r)R/r3),r=(R2+z2)0.5
Here, r is the 3D distance and R is the 2D projected sky-plane
distance from Sgr A*, where r2=R2+z2. We note that there is a
sign ambiguity in the line-of-sight distance.
See Section 3.1
Note (2): Reference for the final proper motion as follows:
1 = central 10"x10" region of the GC (approximately centered on Sgr A*) has
been monitored with diffraction-limited, near-IR imaging cameras at
WMKO since 1995
2 = maser mosaic of shallow Keck IR images covering a 22"x22" FOV as
described in Sakai+ (2019, J/ApJ/873/65). The astrometric uncertainties
in this mosaicked data set are typically larger than in the central
10" data, because of the shorter time baseline and lower S/N.
3 = HST WFC3-IR instrument
See Section 2.4.
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History:
From electronic version of the journal
References:
Do et al. Paper I. 2013ApJ...764..154D 2013ApJ...764..154D Cat. J/ApJ/764/154
Lu et al. Paper II. 2013ApJ...764..155L 2013ApJ...764..155L
(End) Emmanuelle Perret [CDS] 13-May-2025