J/ApJ/738/79 SDSS-DR8 BHB stars in the Milky Way's halo (Xue+, 2011)
Quantifying kinematic substructure in the Milky Way's stellar halo.
Xue X.-X., Rix H.-W., Yanny B., Beers T.C., Bell E.F., Zhao G.,
Bullock J.S., Johnston K.V., Morrison H., Rockosi C., Koposov S.E.,
Kang X., Liu C., Luo A., Lee Y.S., Weaver B.A.
<Astrophys. J., 738, 79 (2011)>
=2011ApJ...738...79X 2011ApJ...738...79X
ADC_Keywords: Milky Way ; Photometry, SDSS ; Radial velocities ;
Stars, horizontal branch ; Stars, halo
Keywords: galaxies: individual (Milky Way) - Galaxy: halo - Galaxy: structure -
stars: horizontal-branch - stars: kinematics and dynamics
Abstract:
We present and analyze the positions, distances, and radial velocities
for over 4000 blue horizontal-branch (BHB) stars in the Milky Way's
halo, drawn from SDSS DR8. We search for position-velocity
substructure in these data, a signature of the hierarchical assembly
of the stellar halo. Using a cumulative "close pair distribution"
as a statistic in the four-dimensional space of sky position,
distance, and velocity, we quantify the presence of position-velocity
substructure at high statistical significance among the BHB stars:
pairs of BHB stars that are close in position on the sky tend to have
more similar distances and radial velocities compared to a random
sampling of these overall distributions. We make analogous mock
observations of 11 numerical halo formation simulations, in which the
stellar halo is entirely composed of disrupted satellite debris, and
find a level of substructure comparable to that seen in the actually
observed BHB star sample. This result quantitatively confirms the
hierarchical build-up of the stellar halo through a signature in phase
(position-velocity) space. In detail, the structure present in the BHB
stars is somewhat less prominent than that seen in most simulated
halos, quite possibly because BHB stars represent an older
sub-population. BHB stars located beyond 20kpc from the Galactic
center exhibit stronger substructure than at rgc<20kpc.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 167 4985 *List of 4985 blue horizontal-branch (BHB) stars
selected from SDSS DR8
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Note on table1.dat: BHB stars are classified by combination of D0.2 and
fm method and the scale width vs. shape method (see section 2). The
parameters are:
D0.2 = width of the Balmer line at 20% below the local continuum
fm = flux relative to the continuum at the line core,
b,c = parameters of the Sersic profile
y=1.0-a*exp[-((|λ-λ0|)/b)c]
(see Sirko et al. 2004, Cat. J/AJ/127/899;
Xue et al. 2008, Cat. J/ApJ/684/1143).
The Balmer-line profile cuts used are:
* for the Hδ line: D0.2≤29Å, fm≤0.35
* for the Hγ line: 0.75≤cγ≤1.25,
7Å≤bγ≤10.8-26.5(cγ-1.08)2
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See also:
II/306 : The SDSS Photometric Catalog, Release 8 (Adelman-McCarthy+, 2011)
J/A+A/522/A88 : Photometric identification of BHB stars (Smith+, 2010)
J/AJ/140/1694 : Abundances of non-variable red and blue HB stars (For+, 2010)
J/AJ/137/3198 : New samples of BHB stars in the Milky Way (Kinman+, 2009)
J/AJ/135/564 : Photometry and spectroscopy of BHB candidates (Brown+, 2008)
J/ApJ/684/1143 : BHB candidates in the Milky Way (Xue+, 2008)
J/AJ/130/1097 : Century Survey Galactic Halo Project BHB stars (Brown+, 2005)
J/AJ/127/899 : Blue HB stars in SDSS (Sirko+, 2004)
J/MNRAS/352/285 : u(bj)r + BV photometry of blue HB stars (Clewley+, 2004)
J/A+AS/109/171 : Blue horizontal branch stars catalog (Flynn+, 1995)
J/AJ/108/1722 : Blue horizontal branch stars (Kinman+ 1994)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Plate SDSS-DR8 plate
5 A1 --- --- [-]
6- 10 I5 --- MJD SDSS modified Julian date
11 A1 --- --- [-]
12- 14 I3 --- Fiber SDSS-DR8 fiber
17- 26 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
29- 38 F10.6 deg DEdeg Declination in decimal degrees (J2000)
41- 50 F10.6 deg GLON [0.02/359.85] Galactic longitude
53- 62 F10.6 deg GLAT [-81.32/88.37] Galactic latitude
65- 69 F5.2 mag gmag [12.6/20.1] Extinction-corrected g band magnitude
73- 76 F4.2 mag u-g (u-g) color index after extinction correction
79- 83 F5.2 mag g-r (g-r) color index after extinction correction
86- 90 F5.2 0.1nm D0.2 Hδ line width at 20% below local continuum
94- 97 F4.2 -- fm Hδ line flux relative to continuum
at line core
101-104 F4.2 -- cHg The c of Hγ line
107-111 F5.2 0.1nm bHg The b of Hγ line
115-118 F4.1 kpc d [2.3/77.1] Distance to the Sun (1)
122-125 F4.1 kpc r Distance to the Galactic center (1)
128-132 F5.1 kpc x Galactocentric x-position (1)
135-139 F5.1 kpc y Galactocentric y-position (1)
142-146 F5.1 kpc z Galactocentric z-postiion (1)
148-153 F6.1 km/s HRV [-476.2/456.4] Heliocentic radial velocity
155-160 F6.1 km/s e_HRV [0.9/22.5] Error in HRV
162-167 F6.1 km/s Vgal Galactocentric radial velocity (1)
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Note (1): Distances are derived from the magnitudes and colors as in
Xue et al. 2008, Cat. J/ApJ/684/1143. The positions (x,y,z) are
given in the Galactic Standard of Rest frame (R☉=8.0kpc);
velocities assume a Local Standard of Rest velocity of 220km/s
and a Solar motion of (+10.0,+5.2,+7.2)km/s. The distance r is
sqrt(x2+y2+z2).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 15-Jan-2013