J/ApJ/857/145 MagLiteS Carina II and Carina III spectroscopy (Li+, 2018)
Ships passing in the night: spectroscopic analysis of two ultra-faint satellites
in the constellation Carina.
Li T.S., Simon J.D., Pace A.B., Torrealba G., Kuehn K., Drlica-Wagner A.,
Bechtol K., Vivas A.K., van der Marel R.P., Wood M., Yanny B., Belokurov V.,
Jethwa P., Zucker D.B., Lewis G., Kron R., Nidever D.L., Sanchez-Conde M.A.,
Ji A.P., Conn B.C., James D.J., Martin N.F., Martinez-Delgado D.,
Noel N.E.D.
<Astrophys. J., 857, 145 (2018)>
=2018ApJ...857..145L 2018ApJ...857..145L
ADC_Keywords: Galaxies, spectra; Radial velocities; Abundances, [Fe/H];
Equivalent widths; Photometry, ugriz
Keywords: dark matter; galaxies: dwarf;
galaxies: individual (Carina II, Carina III);
galaxies: stellar content; Local Group; stars: abundances
Abstract:
We present Magellan/IMACS, Anglo-Australian Telescope/AAOmega+2dF, and
Very Large Telescope/GIRAFFE+FLAMES spectroscopy of the Carina II
(CarII) and Carina III (CarIII) dwarf galaxy candidates, recently
discovered in the Magellanic Satellites Survey (MagLiteS). We identify
18 member stars in Car II, including two binaries with variable radial
velocities and two RR Lyrae stars. The other 14 members have a mean
heliocentric velocity vhel=477.2±1.2km/s and a velocity dispersion
of σv=3.4-0.8+1.2km/s. Assuming Car II is in dynamical
equilibrium, we derive a total mass within the half-light radius of
1.0-0.4+0.8x106M☉, indicating a mass-to-light ratio of
369-161+309M☉/L☉. From equivalent width measurements
of the calcium triplet lines of nine red giant branch (RGB) stars, we
derive a mean metallicity of [Fe/H]=-2.44±0.09 with dispersion
σ[Fe/H]=0.22-0.07+0.10. Considering both the kinematic and
chemical properties, we conclude that CarII is a dark-matter-dominated
dwarf galaxy. For CarIII, we identify four member stars, from which we
calculate a systemic velocity of vhel=284.6-3.1+3.4km/s. The
brightest RGB member of CarIII has a metallicity of [Fe/H]=-1.97±0.12.
Due to the small size of the Car III spectroscopic sample, we cannot
conclusively determine its nature. Although these two systems have the
smallest known physical separation (Δd∼10kpc) among Local Group
satellites, the large difference in their systemic velocities,
∼200km/s, indicates that they are unlikely to be a bound pair. One or
both systems are likely associated with the Large Magellanic Cloud
(LMC), and may remain LMC satellites today. No statistically
significant excess of γ-ray emission is found at the locations
of Car II and Car III in eight years of Fermi-LAT data.
Description:
We obtained multi-slit spectroscopy of Car II and Car III with the
IMACS spectrograph on the Magellan Baade telescope on 2017 January 24-25
(R∼11000; wavelength range of at least 7550-8750Å).
We observed Car II and Car III with the AAOmega Spectrograph, a
fiber-fed multi-object spectrograph on the 3.9m AAT at the Australian
Astronomical Observatory (AAO); spectral resolution of R=10000 and
wavelength coverage of 8400-8810Å for the red arm and R=1300 and
wavelength coverage of 3750-5750Å for the blue arm. Observations
with AAT/AAOmega+2dF were taken on 2017 January 23 and May 29 through
the service observing program, and on 2017 January 25 through
classical observing time.
In addition to MagLiteS photometry (see Drlica-Wagner+
2016ApJ...833L...5D 2016ApJ...833L...5D), we also used photometry from time-series
follow-up observations (to search for RR Lyrae stars) acquired with
DECam during Blanco 4m Director's Discretionary and engineering time.
After the observations with AAT and Magellan, we also observed Car II
and Car III with the GIRAFFE+FLAMES spectrograph on the 8.2m Kueyen
telescope (UT2) based at the ESO-VLT through Director's Discretionary
time. On the night of 2017 February 26, one 2775s exposure was taken
under excellent seeing conditions; wavelength range from 8206 to
9400Å at a resolution of R∼6000.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 285 2 *Summary of properties of Carina II and Carina III
table4.dat 140 407 Velocity and metallicity measurements
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Note on table2.dat: All values reported here are from the 50th percentile of
the posterior probability distributions. The uncertainties are from the 16th
and 84th percentiles of the posterior probability distributions.
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See also:
J/AJ/108/1016 : Kinematics of local RR lyrae stars. I. (Layden, 1994)
J/ApJ/649/201 : Velocities & Washington photom. in Carina dSph (Munoz+, 2006)
J/AJ/131/2114 : Radial velocities in Fornax dSph (Walker+, 2006)
J/ApJ/663/960 : Radial velocities of Leo I stars (Sohn+, 2007)
J/AJ/136/1645 : Spectroscopy of bright QUEST RR Lyrae stars (Vivas+, 2008)
J/ApJ/694/L144 : Spectroscopic study of Leo V dSph (Walker+, 2009)
J/ApJ/710/1664 : BV photometry in Leo IV and Leo V dSphs (de Jong+, 2010)
J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJS/218/23 : Fermi LAT third source catalog (3FGL) (Acero+, 2015)
J/ApJ/799/86 : Isotropic diffuse gamma-ray emission (Ackermann+, 2015)
J/ApJ/801/74 : Dark matter profiles in dwarf gal. (Geringer-Sameth+, 2015)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/ApJ/829/108 : Kinematic data of Galactic globular clusters (Eadie+, 2016)
J/ApJ/817/41 : Abundances of 4 metal-poor red giants in BooII (Ji+, 2016)
J/ApJ/819/53 : Magellan/M2FS spectrosc. of Tucana 2 & Grus 1 (Walker+, 2016)
J/ApJ/838/83 : RVs, abundances & membership in TriII (Kirby+, 2017)
J/AJ/154/199 : Survey of the MAgellanic Stellar History (Nidever+, 2017)
J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Dwarf galaxy name
12- 19 F8.4 deg RAdeg [114.1/114.7] Right ascension (J2000) (1)
21- 26 F6.4 deg e_RAdeg [0.006/0.007] RAdeg uncertainty (1)
28- 35 F8.4 deg DEdeg [-58/-57.8] Declination (J2000) (1)
37- 42 F6.4 deg e_DEdeg [0.008/0.01] DEdeg uncertainty (1)
44- 48 F5.2 mag m-M [17.2/17.9] Distance modulus (1)
50- 53 F4.2 mag e_m-M [0.02/0.1] m-M uncertainty (1)
54 A1 --- f_m-M Flag on m-M (2)
56- 59 F4.1 kpc Dist [27.8/37.4] Heliocentric distance (1)
61- 63 F3.1 kpc e_Dist [0.4/0.6] Dist uncertainty (1)
64 A1 --- f_Dist Flag on Dist (2)
66- 69 F4.1 mag VMag [-4.5/-2.4] V-band absolute magnitude (1)
71- 73 F3.1 mag e_VMag [0.1/0.2] Vmag uncertainty (1)
75- 80 E6.2 Lsun LV [780/5400] V-band luminosity (1)
82- 87 E6.2 Lsun e_LV [130/500] Negative uncertainty in LV (1)
89- 94 E6.2 Lsun E_LV [160/500] Positive uncertainty in LV (1)
96- 99 F4.2 arcmin r1/2 [3.7/8.7] Half-light radius (1)
101-104 F4.2 arcmin e_r1/2 [0.7/1] r1/2 uncertainty (1)
106-107 I2 pc r1/2pc [30/91] Half-light radius in parsecs (1)
109 I1 pc e_r1/2pc [8/9] r1/2pc uncertainty (1)
111-114 F4.2 --- ell [0.34/0.55] Ellipticity, 1-b/a (1)
116-119 F4.2 --- e_ell [0.07/0.18] ell uncertainty (1)
121-123 I3 deg PA [150/170] Position angle, N to E (1)
125-126 I2 deg e_PA [9/14] PA uncertainty (1)
128-129 I2 --- Nm [4/14] Number of members
130 A1 --- f_Nm Flag on Nm (2)
132-136 F5.1 km/s HRV [284.6/477.2] Heliocentric velocity
138-140 F3.1 km/s e_HRV [1.2/3.1] Negative uncertainty in HRV
142-144 F3.1 km/s E_HRV [1.2/3.4] Positive uncertainty in HRV
146-148 I3 km/s VGSR [42/235] Galactic standard of rest
velocity
150-152 F3.1 km/s sigma [3.4/5.6] Dispersion velocity
154-156 F3.1 km/s e_sigma [0.8/2.1] Negative uncertainty on sigma
158-160 F3.1 km/s E_sigma [1.2/4.3] Positive uncertainty on sigma
161 A1 --- f_sigma Flag on sigma (2)
163-168 E6.2 Msun Mhalf [1e+06]? Dynamical mass
170-175 E6.2 Msun e_Mhalf [400000]? Negative uncertainty on Mhalf
177-182 E6.2 Msun E_Mhalf [800000]? Positive uncertainty on Mhalf
184-186 I3 Msun/Lsun M/LV [369]? Mass-to-light ratio
188-190 I3 Msun/Lsun e_M/LV [161]? Negative uncertainty on M/LV
192-194 I3 Msun/Lsun E_M/LV [309]? Positive uncertainty on M/LV
196-198 F3.1 km/s/arcmin dv/dx [0]? dν/dξ value
200-202 F3.1 km/s/arcmin e_dv/dx [0.3]? dv/dx uncertainty
204-208 F5.2 --- Metal [-2.5/-1.9] Mean metallicity
209 A1 --- f_Metal Flag on Metal (2)
211-214 F4.2 --- e_Metal [0.09]? Metal uncertainty
216-219 F4.2 --- dMet [0.22]? Metallicity dispersion (dex)
221-224 F4.2 --- e_dMet [0.07]? Negative uncertainty on dMet
226-229 F4.2 --- E_dMet [0.1]? Positive uncertainty on dMet
231-234 F4.1 GeV2/cm5 logJ0.1 [17.9/19.9] 0.1° J-factor (3)
236-238 F3.1 GeV2/cm5 e_logJ0.1 [0.5/0.9] Negative uncertainty in logJ0.1
240-242 F3.1 GeV2/cm5 E_logJ0.1 [0.6/1] Positive uncertainty in logJ0.1
243 A1 --- f_logJ0.1 Flag on logJ0.1 (2)
245-248 F4.1 GeV2/cm5 logJ0.5 [18.2/20.2] 0.5° J-factor (3)
250-252 F3.1 GeV2/cm5 e_logJ0.5 [0.5/0.9] Negative uncertainty in logJ0.5
254-256 F3.1 GeV2/cm5 E_logJ0.5 [0.5/1] Positive uncertainty in logJ0.5
257 A1 --- f_logJ0.5 Flag on logJ0.5 (2)
259-262 F4.1 GeV2/cm5 logD0.1 [16.9/17.8] 0.1° D-factor (3)
264-266 F3.1 GeV2/cm5 e_logD0.1 [0.3/0.5] Negative uncertainty in logD0.1
268-270 F3.1 GeV2/cm5 E_logD0.1 [0.3/0.5] Positive uncertainty in logD0.1
271 A1 --- f_logD0.1 Flag on logD0.1 (2)
273-276 F4.1 GeV2/cm5 logD0.5 [18/18.8] 0.5° D-factor (3)
278-280 F3.1 GeV2/cm5 e_logD0.5 [0.4/0.7] Negative uncertainty in logD0.5
282-284 F3.1 GeV2/cm5 E_logD0.5 [0.4/0.6] Positive uncertainty in logD0.5
285 A1 --- f_logD0.5 Flag on logD0.5 (2)
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Note (1): Data taken or derived from Paper I (Torrealba+ 2018MNRAS.475.5085T 2018MNRAS.475.5085T).
Other values are derived using the measurements in this paper.
Note (2): Flag as follows:
b = The distance derived from RR Lyrae in Paper I
(Torrealba+ 2018MNRAS.475.5085T 2018MNRAS.475.5085T) is listed here as the heliocentric
distance of Car II and is used throughout the paper. For other
quantities, parameters derived from the CMD fit are used instead.
c = There are 18 spectroscopic members but only the 14 non-variable stars
are used for kinematic analysis.
d = Note that the velocity dispersion and the J-factor for Car III is
calculated based on only four spectroscopic members. We caution against
the use of this calculation as the classification of Car III is remain
unclear.
e = Note that this is the metallicity of the brightest member in Car III and
not the mean metallicity of the system.
Note (3): The J-factor is the line-of-sight integral of the dark matter density
squared: J(θ)=∫(ρDM2dΩdl). The D-factor is
the linear analog: D(θ)=∫(ρDMdΩdl). Here,
ρDM is the dark matter density and the integral is performed
over a solid angle ΔΩ with radius θ.
See section 4.3.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- --- [MAGLITES]
9- 27 A19 --- MagLiteS Original MAGLITES identifier
(JHHMMSS.ss+DDMMSS.s)
29- 37 F9.5 deg RAdeg [113.2/115] Right Ascension (J2000)
39- 47 F9.5 deg DEdeg [-58.4/-57.3] Declination (J2000)
49- 53 F5.2 mag g0mag [14.6/20.3] Dereddened DECam g band
magnitude (1)
55- 59 F5.2 mag r0mag [13.9/20] Dereddened DECam r band magnitude (1)
61- 78 A18 --- Inst Instrument/Masks used
80- 86 F7.1 d MJD [57777.7/57902.4] Modified Julian Date;
JD-2400000.5
88- 92 F5.1 --- S/N [3.2/110.8] Spectra signal-to-noise
94- 99 F6.2 km/s HRV [-21.5/499] Heliocentric radial velocity
101-105 F5.2 km/s e_HRV [0.5/15] Uncertainty in HRV
107-113 F7.2 0.1nm EW [1.7/5.2]?=9999 Equivalent width,
calcium triplet, in Angstrom units
115-121 F7.2 0.1nm e_EW [0.2/0.9]?=9999 Uncertainty in EW
123-130 F8.2 [Sun] [Fe/H] [-2.8/-1.9]?=99999 Metallicity
132-138 F7.2 [Sun] e_[Fe/H] [0.1/0.5]?=9999 Uncertainty in [Fe/H]
140-140 I1 --- Mm [0/3]? Membership (2)
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Note (1): Quoted magnitudes represent the weighted-average PSF magnitude derived
from the original MagLiteS survey rather than the photometry from
time-series follow-up observations that were used to search for RR
Lyrae stars. The photometry provided here is the dereddened photometry
using the extinction map from Schlegel et al. (1998ApJ...500..525S 1998ApJ...500..525S).
Note (2): Membership code as follows:
2 = Carina II members;
3 = Carina III members;
0 = Non-members.
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History:
From electronic version of the journal
References:
Torrealba et al. Paper I. 2018MNRAS.475.5085T 2018MNRAS.475.5085T
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Mar-2019