J/MNRAS/512/4171 Fornax dSph star members study with GaiaEDR3 (Yang+, 2022)
An extended stellar halo discovered in the Fornax dwarf spheroidal using
Gaia EDR3.
Yang Y., Hammer F., Jiao Y., Pawlowski M.S.
<Mon. Not. R. Astron. Soc. 512, 4171-4184 (2022)>
=2022MNRAS.512.4171Y 2022MNRAS.512.4171Y (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, dwarf ; Galaxies, nearby ; Local group ; Stars, giant ;
Stars, G-type ; Stars, K-type ; Stars, M-type ; Positional data ;
Optical ; Photometry
Keywords: proper motions - galaxies: dwarf - galaxies: Local Group
Abstract:
We have studied the extent of the Red Giant Branch stellar population
in the Fornax dwarf spheroidal galaxy using the spatially extended and
homogeneous data set from Gaia EDR3. Our pre-selection of stars
belonging to Fornax is based on their proper motions, parallaxes, and
colour-magnitude diagram. The latter criteria provide a Fornax star
sample, which we further restrict by colour and magnitude to eliminate
contaminations due to either Milky Way stars or QSOs. The precision of
the data has been sufficient to reach extremely small contaminations
(0.02-0.3 per cent), allowing us to reach to a background level 12
magnitudes deeper than the central surface brightness of Fornax. We
discover a break in the density profile, which reveals the presence of
an additional component that extents 2.1 degree in radius, i.e. 5.4
kpc, and almost seven times the half-light radius of Fornax. The
extended new component represents 10 per cent of the stellar mass of
Fornax, and behaves like an extended halo. The absence of tidally
elongated features at such an unprecedented depth (equivalent to
37.94 ± 0.16 mag arcsec-2 in V-band) rules out a possible role of
tidal stripping. We instead suggest that Fornax is likely at first
infall, and has lost its gas very recently, which consequently leads
to a lack of gravity implying that residual stars have spherically
expanded to form the newly discovered stellar halo of Fornax.
Description:
In this paper, we present a case study on Fornax, using Gaia EDR3.
Thanks to its homogeneous coverage and data quality, we can explore
the data over a very large area. Both coverage and calibrations across
large field are difficulties for ground-based and mosaic-type
observations on dSphs. Our goal is to search possible faint structures
in the outskirts of Fornax using Gaia data.
The data is a chosen field of 20 by 20 degrees centred on Fornax. This
very large area, more than 30 times larger than Fornax in diameter
should be enough to reach and robustly determine the outskirts of
Fornax. We select Fornax candidate members by focusing our study on
RGB branch on CMDs , also we did a PM and a parallax selection (i.e
see section 4). These three selections give the SBASE in which we
seperate it in 3 final samples by adding Gmag and BP-RP criteria. We
present these giving stars lists in tables s0cand.dat, s1cand.dat and
s2cand.dat.
Next, as explained in the section 5.2, We derive and analyse the
radial surface-density profile for each three member candidate samples
by applying the same algorithm. The surface-density profil are
presented in tables s0dens.dat, s1dens.dat and s2dens.dat.
Objects:
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RA (ICRS) DE Designation(s)
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02 39 59.29 -34 26 56.9 NAME Fornax Dwarf Spheroidal = ESO 356-4
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
s0cand.dat 170 21359 *Fornax member candidates S0 final sample
s1cand.dat 170 12818 *Fornax member candidates S1 final sample
s2cand.dat 170 3883 *Fornax member candidates S2 final sample
s0dens.dat 127 193 Surface density profile of S0 final sample
s1dens.dat 127 158 Surface density profile of S1 final sample
s2dens.dat 127 113 Surface density profile of S2 final sample
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Note on s0cand.dat: S0 selection criteria are as
SBASE & (Gmag < 20 & (BP-RP) > 0.8) with SBASE defined as interection of
SPM, SRGB and SPLX (which stand for proper motion, RGB/CMD and parallax
selection), (i.e see section 4 Member star candidates).
Note on s1cand.dat: S1 selection criteria are as
SBASE & (Gmag < 20.8 & (BP-RP) > 1.1) with SBASE defined as interection of
SPM, SRGB and SPLX (which stand for proper motion, RGB/CMD and parallax
selection), (i.e see section 4 Member star candidates).
Note on s2cand.dat: S2 selection criteria are as
SBASE & (Gmag < 19.2 & (BP-RP) > 1.1) with SBASE defined as interection of
SPM, SRGB and SPLX (which stand for proper motion, RGB/CMD and parallax
selection), (i.e see section 4 Member star candidates).
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See also:
J/AJ/144/4 : Properties of dwarf galaxies in the Local Group
(McConnachie+, 2012)
J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018)
J/A+A/649/A7 : MC structure and properties (Gaia Collaboration+, 2021)
J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)
J/MNRAS/453/690 : Fornax VST ATLAS catalogue (Bate+, 2015)
J/A+A/459/423 : VI and [Fe/H] of Fornax dSph RGB stars (Battaglia+, 2006)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
Byte-by-byte Description of file: s0cand.dat s1cand.dat s2cand.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaEDR3 Id of sources in Gaia EDR3 (source_id)
21- 38 F18.15 deg RAdeg Right ascension (ICRS) at Ep=2016.0 from
Gaia EDR3 (ra)
40- 50 F11.9 deg e_RAdeg Error of RAdeg Gaia EDR3 (ra_error)
52- 70 F19.15 deg DEdeg Declination (ICRS) at Ep=2016.0 from
Gaia EDR3 (dec)
72- 82 F11.9 deg e_DEdeg Error of DEdeg Gaia EDR3 (dec_error)
84- 92 F9.6 mag Gmag G-band mean magnitude (Vega) from Gaia EDR3
(photgmean_mag)
94- 103 F10.8 mag BP-RP BP-RP colour from Gaia EDR3 (bp_rp)
105- 127 E23.17 --- x Recentered x position as described
cos(DEdeg)*sin(RAdeg-RAdegC) in the
equation 1 of section 3 Data (x)
129- 150 E22.17 --- y Recentered y position as described
sin(DEdeg)*cos(DEdegC) -
cos(DEdeg)*sin(DEdegC)*cos(RAdeg-RAdegC)
in the equation 1 of section 3 Data (y)
152- 170 F19.16 deg Rmaj Normalized ellipcial radius of each sources
useful to index elliptical annulus (rmajor)
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Byte-by-byte Description of file: s0dens.dat s1dens.dat s2dens.dat
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Bytes Format Units Label Explanations
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1- 18 F18.16 deg Rmean The mean radius of each elliptical annulus
Rmaj (xr)
20- 37 F18.16 deg Rmin The radius range lower band of each
elliptical annulus (xr1)
39- 57 F19.16 deg Rmax The radius range upper band of each
elliptical annulus (xr2)
59- 80 E22.16 arcmin-2 Sdens The surface number density of stars peer
arcmin2 area in stars/arcmin2 (density)
82- 103 E22.16 arcmin-2 e_Sdens Mean error of Sdens (density_error)
105- 123 F19.16 arcmin2 Area The area of each elliptical annulus (area)
125- 127 I3 ct Counts The raw counts of stars in each elliptical
annulus (counts)
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 17-Mar-2025