J/MNRAS/488/2743 Giant Galactic dwarf satellite in Gaia DR2 (Torrealba+, 2019)
The hidden giant: discovery of an enormous Galactic dwarf satellite in Gaia DR2.
Torrealba G., Belokurov V., Koposov S.E., Li T.S., Walker M.G.,
Sanders J.L., Geringer-Sameth A., Zucker D.B., Kuehn K., Evans N.W.,
Dehnen W.
<Mon. Not. R. Astron. Soc., 488, 2743-2766 (2019)>
=2019MNRAS.488.2743T 2019MNRAS.488.2743T (SIMBAD/NED BibCode)
ADC_Keywords: Stars, halo ; Positional data ; Radial velocities ;
Proper motions ; Effective temperatures ; Abundances, [Fe/H] ;
Optical
Keywords: Galaxy: halo - galaxies: dwarf - galaxies: individual: Antlia 2 Dwarf
Abstract:
We report the discovery of a Milky Way satellite in the constellation
of Antlia. The Antlia 2 dwarf galaxy is located behind the Galactic
disc at a latitude of b∼11° and spans 1.26°, which corresponds
to ∼2.9kpc at its distance of 130kpc. While similar in spatial extent
to the Large Magellanic Cloud, Antlia 2 is orders of magnitude fainter
at MV=-9mag, making it by far the lowest surface brightness system
known (at ∼31.9mag/arcsec2), ∼100 times more diffuse than the
so-called ultra diffuse galaxies. The satellite was identified using a
combination of astrometry, photometry, and variability data from Gaia
Data Release 2, and its nature confirmed with deep archival DECam
imaging, which revealed a conspicuous BHB signal. We have also
obtained follow-up spectroscopy using AAOmega on the AAT, identifying
159 member stars, and we used them to measure the dwarf's systemic
velocity, 290.9±0.5km/s, its velocity dispersion, 5.7±1.1km/s, and
mean metallicity, [Fe/H]=-1.4. From these properties we conclude that
Antlia 2 inhabits one of the least dense dark matter (DM) haloes
probed to date. Dynamical modelling and tidal-disruption simulations
suggest that a combination of a cored DM profile and strong tidal
stripping may explain the observed properties of this satellite. The
origin of this core may be consistent with aggressive feedback, or may
even require alternatives to cold dark matter (such as ultra-light
bosons).
Description:
We have presented the discovery of a new dwarf satellite galaxy of the
Milky Way, Antlia 2. Originally detected in Gaia DR2 data using a
combination of RRL (Holl et al. 2018A&A...618A..30H 2018A&A...618A..30H), proper motions,
parallaxes and shallow broad-band photometry, this new satellite is
also confirmed using deeper archival DECam imaging as well as AAT2dF+
AAOmega follow-up spectroscopy. The CMD of the Antlia 2 dwarf boasts a
broad and well-populated RGB as well as a prominent BHB sequence,
which we use as a standard candle. The resulting dwarf's distance
modulus is m-M=20.6, which is consistent with the location of the RGB,
giving an independent confirmation of the BHB distance. In addition,
there are possibly three associated RRL stars, lying in front of the
dwarf along the line of sight. These likely represent the near side of
an extended cloud of tidal debris originating from Antlia 2. The
angular half-light radius of the new dwarf is ∼1.3°, which
translates into a gigantic physical size of ∼2.8kpc, on par with the
measurements of the largest satellite of the MW, the LMC, but with a
luminosity some ∼4000 times fainter.
Objects:
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RA (ICRS) DE Designation(s)
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09 35 32.83 -36 46 02.2 Antlia II = NAME Antlia II Dwarf Galaxy
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 248 1 Properties of the Antlia 2 dwarf
table2.dat 70 221 Results from the spectroscopic modelling
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Dwarf galaxy name
10- 17 F8.4 deg RAdeg Right ascension (J2000)
19- 22 F4.2 deg e_RAdeg Error on RAdeg
24- 31 F8.4 deg DEdeg Declination (J2000)
33- 36 F4.2 deg e_DEdeg Error on DEdeg
38- 45 F8.4 deg GLON Galactic longitude
47- 50 F4.2 deg e_GLON Error on GLON
52- 58 F7.4 deg GLAT Galactic latitude
60- 63 F4.2 deg e_GLAT Error on GLAT
65- 68 F4.1 mag m-M Distance modulus
70- 73 F4.2 mag e_m-M Error on m-M
75- 77 I3 kpc Dist Distance from the sun
79 I1 kpc e_Dist Error on Dist
81- 84 F4.2 deg rhdeg Half-light radius in degrees
86- 89 F4.2 deg e_rhdeg Error on rhdeg
91- 94 I4 pc rhpc Half-light radius in parsecs
96- 98 I3 pc e_rhpc Error on rhpc
100-103 F4.2 --- 1-b/a One minus the axial ratio b/a
105-108 F4.2 --- e_1-b/a Error on 1-b/a
110-112 I3 deg PA Position angle
114 I1 deg e_PA Error on PA
116-120 F5.2 mag VMAG Absolute V magnitude
122-125 F4.2 mag e_VMAG Error on VMAG
127-130 F4.1 mag/arcsec2 murh Surface brightness within r<rh
132-134 F3.1 mag/arcsec2 e_murh Error on murh
136-140 F5.2 [-] [Fe/H] Iron to hydrogen abundance ratio
142-145 F4.2 [-] e_[Fe/H] Error on [Fe/H]
147-150 F4.2 [-] sig[Fe/H] Standard deviation of [Fe/H]
152-155 F4.2 [-] e_sig[Fe/H] Error on sig[Fe/H]
157-161 F5.1 km/s HRV Heliocentric radial velocity
163-165 F3.1 km/s e_HRV Error on HRV
167-170 F4.1 km/s RVgsr Radial velocity in the galactic system
of rest
172-174 F3.1 km/s e_RVgsr Error on RVgsr
176 A1 --- f_RVgsr [b] Flag on RVgsr (1)
178-181 F4.2 km/s sigRV Global velocity dispersion
183-186 F4.2 km/s e_sigRV Error on sigRV
188-193 F6.3 mas/yr pmRA Proper motion on right ascension
195-199 F5.3 mas/yr e_pmRA Error on pmRA
201 A1 --- f_pmRA [a] Flag on pmRA (2)
203-207 F5.3 mas/yr pmDE Proper motion in declination
209-213 F5.3 mas/yr e_pmDE Error on pmDE
215 A1 --- f_pmDE [a] Flag on pmDE (2)
217-219 F3.1 10+7Msun Mrh Galaxy Mass within rh
221-223 F3.1 10+7Msun e_Mrh Error on Mrh
225-228 F4.1 10+7Msun M1.8rh Galaxy Mass within 1.8rh
230-232 F3.1 10+7Msun e_M1.8rh Error on M1.8rh
234-236 F3.1 10+5Msun M* Total stellar mass
238-240 F3.1 10+5Msun e_M* Error on M*
242-244 I3 Msun/Lsun M/L Mass to luminosity ratio
246-248 I3 Msun/Lsun e_M/L Error on M/L
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Note (1): Flag as follows:
b = Does not consider systematic uncertainties
Note (2): Flag as follows:
a = Does not consider LSR uncertainties
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Star identifier (Antlia2_NNN)
13- 20 F8.4 deg RAdeg Right ascension (J2000)
22- 29 F8.4 deg DEdeg Declination (J2000)
31- 35 F5.1 km/s HRV Heliocentric radial velocity
37- 40 F4.1 km/s e_HRV Error on HRV
42- 46 F5.2 [-] [Fe/H] Iron to hydrogen abundance ratio
48- 51 F4.2 [-] e_[Fe/H] Error on [Fe/H]
53- 56 F4.2 [cm/s2] logg Surface gravity
58- 61 F4.2 [cm/s2] e_logg Error on logg
63- 66 I4 K Teff Effective temperature
68- 70 I3 K e_Teff Error on Teff
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 08-Dec-2022