J/ApJ/863/25 Deep Magellan/Megacam obs. of 4 MW satellites (Mutlu-Pakdil+, 2018)
A deeper look at the new Milky Way satellites: Sagittarius II, Reticulum II,
Phoenix II, and Tucana III.
Mutlu-Pakdil B., Sand D.J., Carlin J.L., Spekkens K., Caldwell N.,
Crnojevic D., Hughes A.K., Willman B., Zaritsky D.
<Astrophys. J., 863, 25 (2018)>
=2018ApJ...863...25M 2018ApJ...863...25M
ADC_Keywords: Galaxies, photometry; Optical; Extinction
Keywords: galaxies: dwarf ;
galaxies: individual (Sagittarius II, Reticulum II, Phoenix II,
Tucana II) ; galaxies: structure
Abstract:
We present deep Magellan/Megacam stellar photometry of four recently
discovered faint Milky Way satellites: Sagittarius II (Sgr II),
Reticulum II (Ret II), Phoenix II (Phe II), and Tucana III (Tuc III).
Our photometry reaches ∼2-3 magnitudes deeper than the discovery data,
allowing us to revisit the properties of these new objects (e.g.,
distance, structural properties, luminosity measurements, and signs of
tidal disturbance). The satellite color-magnitude diagrams show that
they are all old (∼13.5Gyr) and metal poor ([Fe/H]≲-2.2). Sgr II is
particularly interesting, as it sits in an intermediate position
between the loci of dwarf galaxies and globular clusters in the
size-luminosity plane. The ensemble of its structural parameters is
more consistent with a globular cluster classification, indicating
that Sgr II is the most extended globular cluster in its luminosity
range. The other three satellites land directly on the locus defined
by Milky Way ultra-faint dwarf galaxies of similar luminosity. Ret II
is the most elongated nearby dwarf galaxy currently known for its
luminosity range. Our structural parameters for Phe II and Tuc III
suggest that they are both dwarf galaxies. Tuc III is known to be
associated with a stellar stream, which is clearly visible in our
matched-filter stellar density map. The other satellites do not show
any clear evidence of tidal stripping in the form of extensions or
distortions. Finally, we also use archival HI data to place limits on
the gas content of each object.
Description:
We observed our targets with Megacam at the f/5 focus at the Magellan
Clay telescope in the g and r bands. The data were mostly taken during
a single run on 2015 October 12-13, and was supplemented by some
observations taken on 2017 October 17.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 58 61674 Sgr II photometry in the PS1 photometric system
table3.dat 58 36045 Ret II photometry in the DES photometric system
table4.dat 58 42564 Phe II photometry in the DES photometric system
table5.dat 58 57847 Tuc III photometry in the DES photometric system
table6.dat 123 4 Structural properties of the Milky Way satellites
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See also:
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+, 2016)
J/MNRAS/390/1437 : Stellar streams in Andromeda (M31) (Chapman+, 2008)
J/ApJ/704/898 : Photometry of the Hercules dwarf galaxy (Sand+, 2009)
J/ApJ/718/530 : Leo IV g- and r-band photometry (Sand+, 2010)
J/AJ/144/4 : Dwarf galaxies in the Local Group (McConnachie+, 2012)
J/ApJ/756/79 : Opt. photometry in 3 Local Group dwarf gal. (Sand+, 2012)
J/ApJ/809/146 : SDSS-DR8 isolated low-mass galaxies (Bradford+, 2015)
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/AJ/151/82 : The 4 brightest red giants in Ret 2 (Roederer+, 2016)
J/ApJ/838/83 : RVel, abundances & membership in TriII (Kirby+, 2017)
J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017)
J/A+A/620/A155 : Gaia proper motions of 7 UFD galaxies (Massari+, 2018)
J/AJ/157/12 : Star clusters, associations & cand. in the MW (Bica+, 2019)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Seq [0/61673] Sequential star number in Sgr II
7- 15 F9.5 deg RAdeg [297.9/298.4] Right Ascension (J2000)
17- 26 F10.6 deg DEdeg [-22.3/-21.8] Declination (J2000)
28- 32 F5.2 mag gmag [17.73/27.36] Clay/Megacam g band AB photometry (1)
34- 37 F4.2 mag e_gmag [0.0/0.54] Uncertainty in gmag
39- 42 F4.2 mag Ag [0.32/0.37] Extinction in the g band (2)
44- 48 F5.2 mag rmag [17.13/26.27] Clay/Megacam r AB band photometry (1)
50- 53 F4.2 mag e_rmag [0.0/0.54] Uncertainty in rmag
55- 58 F4.2 mag Ar [0.23/0.27] Extinction in the r band (2)
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Note (1): Calibrated by matching to the PS1 survey (Chambers+,
2016arXiv161205560C 2016arXiv161205560C; Flewelling+, 2016arXiv161205243F 2016arXiv161205243F;
Magnier+ 2016arXiv161205242M 2016arXiv161205242M) to fit a zeropoint and color term.
Note (2): MW extinction derived on a star by star basis using the Schlegel+
(1998ApJ...500..525S 1998ApJ...500..525S) reddening maps and coefficients of 3.172
and 2.271 for PS1 g and r.
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Byte-by-byte Description of file: table[345].dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Seq [0/57846] Sequential star number
7- 15 F9.5 deg RAdeg Right Ascension (J2000)
17- 26 F10.6 deg DEdeg Declination (J2000)
28- 32 F5.2 mag gmag [16.3/27.1] Clay/Megacam g band AB photometry (1)
34- 37 F4.2 mag e_gmag [0/0.6] Uncertainty in gmag
39- 42 F4.2 mag Ag [0.03/0.06] Extinction in the g band (2)
44- 48 F5.2 mag rmag [15.5/26.1] Clay/Megacam r band AB photometry (1)
50- 53 F4.2 mag e_rmag [0/0.5] Uncertainty in rmag
55- 58 F4.2 mag Ar [0.02/0.04] Extinction in the r band (2)
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Note (1): Calibrated by matching to the DES DR1 catalog (DES Collaboration,
2018arXiv180103181A 2018arXiv180103181A) to fit a zeropoint and color term.
Note (2): MW extinction derived on a star by star basis using the Schlegel+
(1998ApJ...500..525S 1998ApJ...500..525S) reddening maps and coefficients of 3.172
and 2.271 for DES g and r.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Name of the MW satellite
9- 10 I2 h RAh Hour of right ascension (J2000)
12- 13 I2 min RAm Minute of right ascension (J2000)
15- 19 F5.2 s RAs Second of right ascension (J2000)
21- 24 F4.1 s e_RAs [3/36.7] RA uncertainty
26 A1 --- DE- [-] Sign of declination (J2000)
27- 28 I2 deg DEd [22/59] Degree of declination (J2000)
30- 31 I2 arcmin DEm Arcminute of declination (J2000)
33- 37 F5.2 arcsec DEs Arcsecond of declination (J2000)
39- 42 F4.1 arcsec e_DEs [2.2/26] DE uncertainty
44- 47 F4.1 mag m-M [16.8/19.6] Distance modulus
49- 51 F3.1 mag e_m-M [0.1/0.2] m-M uncertainty
53- 56 F4.2 mag E(B-V) [0.01/0.2] Color excess
58- 61 F4.1 kpc Dist [22.9/84.1] Distance
63- 65 F3.1 kpc e_Dist [0.9/8] Dist uncertainty
67- 70 I4 --- N* [162/1502] Number of stars brighter than
r=24mag (1)
72- 75 F4.1 mag VMag [-5.2/-1.3] Absolute V-band magnitude
77- 79 F3.1 mag e_VMag [0.1/0.4] VMag uncertainty
81- 83 F3.1 arcmin rh [1.5/6.3] Half-light radius in arcmin
85- 87 F3.1 arcmin e_rh [0.1/1.2] rh uncertainty
89- 90 I2 pc rhpc [32/58] Half-light radius in pc
92 I1 pc e_rhpc [1/8] rhpc uncertainty
94 A1 --- l_e Limit flag on e
95- 97 F3.1 --- e [0.1/0.6] Ellipticity
99-101 F3.1 --- e_e [0.1]? e uncertainty
103-105 I3 deg PA [25/156]? Position angle
106 A1 --- f_PA u: unconstrained
108-109 I2 deg e_PA [2/38]? PA uncertainty
111-114 F4.1 GeV2/cm5 logJ [18.2/19.2] 0.5° J-factor
116-119 I4 Msun MHI [210/1400] 5σ upper limit on
the HI mass
121-123 F3.1 Msun/Lsun M/L [0.2/2] MHI to LV ratio
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Note (1): N* is the number of stars brighter than r=24mag selected by
the best-fit isochrone for each object.
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Nomenclature note:
Stars are <[MSC2018] Sgr II NNNNN>, <[MSC2018] Ret II NNNNN>,
<[MSC2018] Phe II NNNNN> or <MSC2018] Tuc III NNNNN> in Simbad
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 02-Aug-2019