J/ApJ/875/77 Proper motions of MW satellites with Gaia & DES (Pace+, 2019) ================================================================================ Proper motions of Milky Way ultra-faint satellites with Gaia DR2 x DES DR1. Pace A.B., Li T.S. =2019ApJ...875...77P ================================================================================ ADC_Keywords: Galaxies, photometry; Proper motions; Photometry, VRI; Stars, normal Keywords: galaxies: dwarf ; galaxies: kinematics and dynamics ; Local Group ; proper motions ; stars: kinematics and dynamics Abstract: We present a new, probabilistic method for determining the systemic proper motions of Milky Way (MW) ultra-faint satellites in the Dark Energy Survey (DES). We utilize the superb photometry from the first public data release (DR1) of the DES to select candidate members and cross-match them with the proper motions from the Gaia DR2. We model the candidate members with a mixture model (satellite and MW) in spatial and proper motion space. This method does not require prior knowledge of satellite membership and can successfully determine the tangential motion of 13 DES satellites. With our method, we present measurements of the following satellites: Columba I, Eridanus III, Grus II, Phoenix II, Pictor I, Reticulum III, and Tucana IV. This is the first systemic proper motion measurement for several of these satellites, and the majority lack extensive spectroscopic follow-up studies. We compare these to the predictions of Large Magellanic Cloud satellites and the vast polar structure. With the high-precision DES photometry, we conclude that most of the newly identified member stars are very metal-poor ([Fe/H]<=-2), similar to other ultra-faint dwarf galaxies, while Reticulum III is likely more metal-rich. We also find potential members in the following satellites that might indicate their overall proper motion: Cetus II, Kim 2, and Horologium II. However, due to the small number of members in each satellite, spectroscopic follow-up observations are necessary to determine the systemic proper motion in these satellites. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1.dat 104 20 Properties of the DES satellites table4.dat 118 399 Proper motion members from the likelihood fit with membership probability p_i_>0.1 -------------------------------------------------------------------------------- See also: II/357 : The Dark Energy Survey (DES): Data Release 1 (Abbott+, 2018) I/345 : Gaia DR2 (Gaia Collaboration, 2018) J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012) J/ApJ/770/16 : Spectroscopic members of Segue 2 galaxy (Kirby+, 2013) J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013) J/ApJ/803/63 : gr photometry of stars in Kim 2 (Kim+, 2015) J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015) J/ApJ/808/108 : M2FS stellar spectroscopy of Reticulum 2 (Walker+, 2015) J/ApJ/819/53 : Magellan/M2FS spectrosc. of Tucana 2 & Grus 1 (Walker+, 2016) J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017) J/ApJ/857/74 : Abundances of 7 new member stars in Tucana II (Chiti+, 2018) J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018) J/ApJ/866/22 : Spectroscopic analysis of Tuc III stream (Li+, 2018) J/ApJ/857/145 : MagLiteS Carina II and Carina III spectroscopy (Li+, 2018) J/A+A/620/A155 : Gaia proper motions of 7 UFD galaxies (Massari+, 2018) J/ApJ/863/25 : Deep Magellan obs. of 4 MW satellites (Mutlu-Pakdil+, 2018) J/ApJ/852/99 : Abundances of 3 metal-poor stars in Hor I (Nagasawa+, 2018) J/ApJ/863/89 : Gaia PMs of stars in ultra-faint MW satellites (Simon, 2018) J/A+A/623/A129 : New satellites of the LMC search (Fritz+, 2019) Byte-by-byte Description of file: table1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 14 A14 --- Name Satellite name 16 A1 --- f_Name [ab] Flag on Name (1) 18- 25 F8.4 deg RAdeg Right ascension in decimal degrees (J2000) 27- 34 F8.4 deg DEdeg Declination in decimal degrees (J2000) 36- 41 F6.3 arcmin ah [0.2/13] Semimajor half-light radius (a_h_) 43- 46 F4.2 --- ell [0.12/0.7]? Ellipticity {epsilon} 48- 50 I3 deg PA [4/164]? Position angle {theta} 52- 56 F5.1 kpc Dist [23.8/366] Heliocentric distance 58- 62 F5.2 mag VMag [-7.1/0] V-band absolute magnitude 64- 67 A4 --- Ref Reference(s) (2) 69- 72 A4 --- ID Abbreviated ID as given in Table 4; column added by CDS 74- 78 F5.2 mas/yr pmRA [-1.1/2.4]? Systemic proper motion in {alpha}cos{delta} direction (from Table 3) 80- 83 F4.2 mas/yr e_pmRA [0.04/0.4]? Negative uncertainty in pmRA 85- 88 F4.2 mas/yr E_pmRA [0.04/0.5]? Positive uncertainty in pmRA 90- 94 F5.2 mas/yr pmDE [-1.8/0.2]? Systemic proper motion in {delta} direction (from Table 3) 96- 99 F4.2 mas/yr e_pmDE [0.04/0.8]? Negative uncertainty in pmDE 101-104 F4.2 mas/yr E_pmDE [0.04/0.7]? Positive uncertainty in pmDE -------------------------------------------------------------------------------- Note (1): Flag as follows: a = Kim 2 also referred to as Indus I. b = For Columba I, we note that two probable members are likely to be more metal-rich stars. We therefore also calculated the proper motions with five members, which gives {mu}_{alpha}cos{delta}_=0.08+/-0.21, {mu}_{delta}_=-0.11+/-0.28mas/yr. See details in Sections 4.2 and 4.3. Note (2): References as follows: 1 = Drlica-Wagner et al. (2015ApJ...813..109D); 2 = Carlin et al. (2017AJ....154..267C); 3 = Crnojevic et al. (2016ApJ...824L..14C); 4 = Conn et al. (2018ApJ...852...68C); 5 = Koposov et al. (2015ApJ...805..130K); 6 = Kim & Jerjen (2015ApJ...808L..39K); 7 = Kim et al. (2015, J/ApJ/803/63); 8 = Mutlu-Pakdil et al. (2018, J/ApJ/863/25); 9 = Luque et al. (2017MNRAS.468...97L). -------------------------------------------------------------------------------- Byte-by-byte Description of file: table4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 A4 --- ID Dwarf galaxy identifier 6- 14 I9 --- CoadID [71227237/618443422] DES DR1 identifier (1) 16- 34 I19 --- Gaia Gaia DR2 identifier 36- 45 F10.6 deg RAdeg Gaia DR2 right ascension (ICRS) at Ep=2015.5 47- 56 F10.6 deg DEdeg [-61.4/-17.3] Gaia DR2 declination (ICRS) at Ep=2015.5 58- 63 F6.3 mag gmag0avg [16/21.6] Dereddened weighted average g band (AB) magnitude (2) 65- 70 F6.3 mag rmag0avg [15.3/20.9] Dereddened weighted average r band (AB) magnitude (2) 72- 77 F6.3 mag imag0avg [15/21.2] Dereddened weighted average i band (AB) magnitude (2) 79- 84 F6.3 mag Gmag [15.4/21] Apparent Gaia band magnitude (3) 86- 91 F6.3 mas/yr pmRA [-6.7/9.8] Proper motion along RA times cosDE 93- 97 F5.3 mas/yr e_pmRA [0.04/4.6] Uncertainty in pmRA 99-104 F6.3 mas/yr pmDE [-7.7/6.5] Proper motion along DE 106-110 F5.3 mas/yr e_pmDE [0.05/4.8] Uncertainty in pmDE 112-115 F4.2 --- Pi [0.1/1] Membership probability 117-118 I2 --- MP [-1/1]? Metallicity assessment (4) -------------------------------------------------------------------------------- Note (1): DES IDs are from COADD_OBJECT_ID column in DES DR1 (II/357). Note (2): The magnitudes are reddening corrected weighted average photometry (WAVG_MAG_PSF_DERED) from DES DR1 catalog (II/357). Note (3): From Gaia DR2 catalog without reddening correction. Note (4): To assess the metallicity of the star based on its location in the color-color diagram (see Section 4.2 for details). Code as follows: -1 = blue stars with g-r<0.35 without a metallicity assessment; 1 = stars with g-r>0.35 and a location on color-color diagram above the empirical stellar locus, indicating that they are possible metal-poor stars and therefore likely to be members of a ultra-faint satellite (243 occurrences). 0 = stars with g-r>0.35 and a location on color-color diagram below the empirical stellar locus, indicating that they are possible metal-rich stars and therefore likely to be non-members of a ultra-faint satellite. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Emmanuelle Perret [CDS] 04-Sep-2020