J/MNRAS/486/378 BHB stars reveal halo's metal-rich progenitor (Lancaster+, 2019)
The halo's ancient metal-rich progenitor revealed with BHB stars.
Lancaster L., Koposov S.E., Belokurov V., Evans N.W., Deason A.J.
<Mon. Not. R. Astron. Soc., 486, 378-389 (2019)>
=2019MNRAS.486..378L 2019MNRAS.486..378L (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, halo ; Stars, blue ; Stars, horizontal branch ;
Proper motions ; Radial velocities ; Stars, distances ;
Photometry, SDSS
Keywords: Galaxy: formation - Galaxy: halo - Galaxy: kinematics and dynamics
Abstract:
Using the data from the Sloan Digital Sky Survey and the Gaia
satellite, we assemble a pure sample of ∼3000 blue horizontal branch
(BHB) stars with 7D information, including positions, velocities, and
metallicities. We demonstrate that, as traced with BHBs, the Milky
Way's stellar halo is largely unmixed and cannot be well represented
with a conventional Gaussian velocity distribution. A single-component
model fails because the inner portions of the halo are swamped with
metal-rich tidal debris from an ancient, head-on collision, known as
the 'Gaia Sausage'. Motivated by the data, we build a flexible mixture
model that allows us to track the evolution of the halo make-up across
a wide range of radii. It is built from two components, one
representing the radially anisotropic Sausage stars with their lobed
velocity distribution, and the other representing a more metal-poor
and more isotropic component built up from minor mergers. We show that
inside 25kpc the 'Sausage' contributes at least 50 per cent of the
Galactic halo. The fraction of 'Sausage' stars diminishes sharply
beyond 30kpc, which is the long-established break radius of the
classical stellar halo.
Description:
We aim to measure the evolution of the velocity ellipsoid of the Milky
Way's stellar halo as a function of Galactocentric radius. To do this,
we need 3D kinematic information for a large sample of stars in the
stellar halo. We supplement the proper motion measurements of the Gaia
satellite (Gaia Collaboration 2018A&A...616A...1G 2018A&A...616A...1G, Cat. I/345) with
spectroscopic radial velocity and photometric distance relations for a
large sample of BHB stars.
Our initial sample consists of a catalogue of 4985 BHB stars compiled
by Xue et al. (2011ApJ...738...79X 2011ApJ...738...79X, Cat. J/ApJ/738/79). These stars
were selected using spectroscopic and photometric information from the
SEGUE-1, SEGUE-2, and older SDSS surveys and the data was publicly
released as part of SDSS DR8 (Aihara et al. 2011ApJS..193...29A 2011ApJS..193...29A, Cat.
V/139).
We provide a new catalogue of the BHB stars that we use in this study
with all of the information that we have derived here. We give a file
that use all of our selections to remove BS contaminants and stars
with poor spectroscopic or astrometric data (table bhball, 3680
sources), as well as a file that additionally removes the Sagittarius
stream (table bhbfilt, 3064 sources).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
bhball.dat 461 3680 Blue Horizontal Branch stars in the Stellar
Halo of the Milky Way
bhbfilt.dat 461 3064 Blue Horizontal Branch stars in the Stellar
Halo of the Milky Way (Sagittarius stream
removed)
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
V/139 : The SDSS Photometric Catalog, Release 8
(Adelman-McCarthy+, 2012)
J/ApJ/738/79 : SDSS-DR8 BHB stars in the Milky Way's halo (Xue+, 2011)
Byte-by-byte Description of file: bhball.dat bhbfilt.dat
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Bytes Format Units Label Explanations
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1- 11 F11.7 deg RAdeg Right ascension (ICRS) Ep=2015.5 (1)
13- 21 F9.7 mas e_RAdeg Error on RAdeg (1)
23- 33 F11.7 deg DEdeg Declination (ICRS) Ep=2015.5 (1)
35- 43 F9.7 mas e_DEdeg Error on DEdeg (1)
45- 52 F8.4 mas/yr pmRA Proper motion in right ascension
(pmRA*cosDE) (1)
54- 59 F6.4 mas/yr e_pmRA Error on pmRA
61- 68 F8.4 mas/yr pmDE Proper motion in declination (1)
70- 75 F6.4 mas/yr e_pmDE Error on pmDE
77- 85 F9.6 --- pmRApmDEcor Correlation between pmRA and pmDE (1)
87- 92 F6.1 km/s RV Heliocentric radial velocity (2)
94- 97 F4.1 km/s e_RV Error on RV (2)
99-105 F7.5 [kpc] logDist Logarithm of the heliocentric distance
to the star (4)
107-113 F7.5 [kpc] e_logDist Error on logDist (4)
115-124 F10.7 [Sun] [Fe/H] Iron to hydrogen abundance ratio
relative to solar (3)
126-134 F9.7 [Sun] e_[Fe/H] Error on [Fe/H] (3)
136-142 F7.4 mag umag SDSS PSF magnitude in u-band (3)
144-149 F6.4 mag e_umag Error on umag (3)
151-157 F7.4 mag gmag SDSS PSF magnitude in g-band (3)
159-164 F6.4 mag e_gmag Error on gmag (3)
166-172 F7.4 mag rmag SDSS PSF magnitude in r-band (3)
174-179 F6.4 mag e_rmag Error on rmag (3)
181-186 F6.4 mag Au Dust extinction in the u-band (3)
188-193 F6.4 mag Ag Dust extinction in the g-band (3)
195-200 F6.4 mag Ar Dust extinction in the r-band (3)
202-206 F5.2 0.1nm bHg Line width of the Hγ line of the
star (2)
208-211 F4.2 --- cHg Line shape of the Hγ line of the
star (2)
213-220 F8.6 mas epsi Astrometric excess noise from
Gaia DR2 (1)
222-230 F9.6 --- sepsi Astrometric excess noise
significance (1)
232-239 F8.5 mas plx Parallax (1)
241-247 F7.5 mas e_plx Error on plx (1)
249-257 F9.6 --- pmRAplxcor Correlation between pmRA and plx (1)
259-267 F9.6 --- pmDEplxcor Correlation between pmDE and plx (1)
269-276 F8.5 kpc Rgal Galactocentric radial distance (4)
278-286 F9.6 kpc2 varRgal Variance in the measurement of Rgal (4)
288-295 F8.3 km/s Vlon Galactocentric longitudinal velocity (4)
297-309 F13.6 km2/s2 varVlon Variance in the measurement of Vlon (4)
311-318 F8.3 km/s Vlat Galactocentric latitudinal velocity (4)
320-332 F13.6 km2/s2 varVlat Variance in the measurement of Vlat (4)
334-341 F8.3 km/s RVgal Galactocentric radial velocity (4)
343-352 F10.5 km2/s2 RVgalvar Variance in the measurement of RVgal (4)
354-362 F9.4 kpc.km/s RgalVloncov Covariance between Rgal and Vlon (4)
364-371 F8.4 kpc.km/s RgalVlatcov Covariance between Rgal and Vlat (4)
373-381 F9.5 kpc.km/s RgalRVgalcov Covariance between Rgal and RVgal (4)
383-390 F8.1 km2/s2 VlonVlatcov Covariance between Vlon and Vlat (4)
392-399 F8.1 km2/s2 VlonRVgalcov Covariance between Vlon and RVgal (4)
401-408 F8.1 km2/s2 VlatRVgalcov Covariance between Vlat and RVgal (4)
410-417 F8.3 km/s VRA Physical space velocity in the direction
of increasing right ascension (4)
419-430 F12.5 km2/s2 VRAvar Variance in the measurement of VRA (4)
432-439 F8.3 km/s VDE Physical space velocity in the direction
of increasing declination (4)
441-452 F12.5 km2/s2 vDEvar Variance in the measurement of VDE (4)
454-461 F8.1 km2/s2 VRAVDEcov Covariance between VRA and VDE (4)
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Note (1): Values taken from Gaia DR2 (Gaia Collaboration 2018A&A...616A...1G 2018A&A...616A...1G,
Cat. I/345)
Note (2): Values taken from Xue et al. (2011ApJ...738...79X 2011ApJ...738...79X, Cat. J/ApJ/738/79)
Note (3): Values taken from SDSS DR8 (Aihara et al. 2011ApJS..193...29A 2011ApJS..193...29A,
Cat. V/139)
Note (4): Values derived in this work
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 14-Oct-2022