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J/AJ/113/634 The survival of Sagittarius dwarf galaxy (Ibata+ 1997)
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The Kinematics, Orbit, and Survival of the Sagittarius Dwarf Spheroidal Galaxy
Ibata R.A., Wyse R.F.G., Gilmore G., Irwin M.J., Suntzeff N.B.
<Astron. J. 113, 634 (1997)>
=1997AJ....113..634I
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ADC_Keywords: Galaxies, photometry ; Radial velocities
Abstract:
The Sagittarius dwarf spheroidal galaxy, the closest satellite galaxy
of the Milky Way, has survived for many orbits about the Galaxy.
Extent numerical calculations modeled this galaxy as a system with a
centrally-concentrated mass profile, following the light, and found
that it should lose more than one-half of its mass every 2-4 orbits
and be completely disrupted long before now. Apparently the
Sagittarius dwarf spheroidal, and by implication other dSph galaxies,
do not have a centrally-concentrated profile for their dark matter. We
develop a model in which the stars of the Sgr dwarf are embedded in a
constant-density dark matter halo, representing the core of a
tidally-limited system, and show that this is consistent with its
survival. We present new photometric and kinematic observations of the
Sagittarius dwarf spheroidal and show these data are consistent with
this explanation for the continued existence of this galaxy. The
Sagittarius dwarf is being tidally distorted and is tidally limited,
but is not disrupted as yet. The corresponding minimum total mass is
10^9^M_{sun}_, while the central mass to visual light ratio is ~50 in
Solar units. Our new photographic photometry allows the detection of
main-sequence stars of the Sagittarius dwarf over an area of
22x8{deg}. The Sagittarius dwarf is prolate, with axis ratios ~3:1:1.
For an adopted distance of 16+/-2kpc from the Galactic center on the
opposite side of the Galaxy to the Sun, the major axis is >~9kpc long
and is aligned approximately normal to the plane of the Milky Way
Galaxy, roughly following the coordinate line l=5{deg}. The central
velocity dispersion of giant stars which are members of the
Sagittarius dwarf is 11.4+/-0.7 km/s and is consistent with being
constant over the face of the galaxy. The gradient in mean
line-of-sight velocity with position along the major axis, dv/db, is
~0km/s/degree in the central regions and increases in amplitude to
dv/db=-3km/s/degree over the outermost three degrees for which we have
data. A first measurement of the proper motion of the Sagittarius
dwarf determines the component of its space velocity parallel to its
major axis to be 250+/-90km/s, directed towards the Galactic Plane. We
model these kinematic data to determine the orbit of the Sagittarius
dwarf. Our best fit model has an orbital period of <~1Gyr and has the
Sagittarius dwarf spheroidal close to perigalacticon. This period is
shorter, by about a factor of >~10, than the age of the bulk of its
stellar population.
(Copyright) 1997 American Astronomical Society.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.tex 100 25 AASTeX version of table1
table2a 52 231 Radial velocity data from 1994 AAT run
table2a.tex 91 256 AASTeX version of table2a
table2b 67 272 Radial velocity data from 1994 CTIO run
table2b.tex 109 300 AASTeX version of table2b
table3 52 12 Mean velocities and velocity dispersions in the
observed Sgr fields
table3.tex 83 33 AASTeX version of table3
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Table1: Physical parameters of the globular clusters of the Sagittarius dwarf
spheroidal
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Cluster ra (1950) dec (1950) [Fe/H] RVGal (km/s) T (Gyr) M_V_
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M54 18 51 51.2 -30 32 34 -1.55 +/-0.10 172 +/-1 -10.0
Ter 7 19 14 26.2 -34 44 54 -0.4 -->-1 186 +/-4 9--12 -6.0
Ter 8 19 38 30.3 -34 07 05 -1.99 +/-0.08 158 +/-8 16--19 -5.0
Arp 2 19 25 33.9 -30 27 26 -1.70 +/-0.11 154 +/-10 13--14 -5.3
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Byte-by-byte Description of file: table2a
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension 1950
4- 5 I2 min RAm Right ascension 1950
7- 11 F5.2 s RAs Right ascension 1950
14 A1 --- DE- Sign declination (always blank)
15- 16 I2 deg DEd Declination 1950
18- 19 I2 arcmin DEm Declination 1950
21- 24 F4.1 arcsec DEs Declination 1950
26- 32 F7.2 mag Rmag R magnitude
34- 39 F6.2 mag B(J)-R B_J_- R color
41- 48 F8.0 km/s HRV Heliocentric radial velocity
52 A1 --- CTIO [yn] 'y' if observed in CTIO run, else 'n'
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Byte-by-byte Description of file: table2b
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension 1950
4- 5 I2 min RAm Right ascension 1950
7- 11 F5.2 s RAs Right ascension 1950
14 A1 --- DE- Sign declination (always blank)
15- 16 I2 deg DEd Declination 1950
18- 19 I2 arcmin DEm DecDeclination 1950
21- 24 F4.1 arcsec DEs DecDeclination 1950
26- 32 F7.2 mag Rmag R magnitude
34- 39 F6.2 mag B(J)-R B_J_ - R color
41- 48 F8.0 km/s HRV Heliocentric radial velocity
50- 56 F7.2 --- R(TR) Tonry-Davis cross-correlation R value
58- 63 F6.2 km/s dV ?=99.99 Delta V value
67 A1 --- AAT [yn] 'y' if observed in AAT run, else 'n'
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Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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1- 2 A2 --- Field Field designation
4- 7 A4 --- Instr Instrument
9- 13 F5.3 deg GLON Galactic longitude
15- 21 F7.3 deg GLAT Galactic latitude
23- 29 F7.3 km/s <RVGal> Mean galactocentric radial velocity
31- 35 F5.3 km/s e_<RVGal> rms uncertainty on <RVGal>
37- 42 F6.3 km/s sigmaV Velocity dispersion
44- 48 F5.3 km/s e_sigmaV rms uncertainty on sigmaV
50- 52 I3 --- Nstar Nunber of stars
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Origin: AAS CD-ROM series, Volume 8, 1997 Lee Brotzman [ADS] 04-Apr-1997
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(End) [CDS] 03-Jul-1997