J/ApJ/916/81 Grus I and Indus II deep DES photometry (Cantu+, 2021)
A deeper look at DES dwarf galaxy candidates: Grus I and Indus II.
Cantu S.A., Pace A.B., Marshall J., Strigari L.E., Crnojevic D., Simon J.D.,
Drlica-Wagner A., Bechtol K., Martinez-Vazquez C.E., Santiago B., Amara A.,
Stringer K.M., Diehl H.T., Aguena M., Allam S., Avila S., Brooks D.,
Carnero Rosell A., Carrasco Kind M., Carretero J., Costanzi M.,
Da Costa L.N., De Vicente J., Desai S., Doel P., Eifler T.F., Everett S.,
Frieman J., Garcia-Bellido J., Gaztanaga E., Gruen D., Gruendl R.A.,
Gschwend J., Gutierrez G., Hinton S.R., Hollowood D.L., Honscheid K.,
James D.J., Kuehn K., Maia M.A.G., Menanteau F., Miquel R., Palmese A.,
Paz-Chinchon F., Plazas A.A., Sanchez E., Scarpine V., Schubnell M.,
Serrano S., Sevilla-Noarbe I., Smith M., Soares-Santos M., Suchyta E.,
Swanson M.E.C., Tarle G., Walker A.R., Wilkinson R.D.,
The DES Collaboration.
<Astrophys. J., 916, 81 (2021)>
=2021ApJ...916...81C 2021ApJ...916...81C
ADC_Keywords: Galaxies, photometry; Optical; Surveys
Keywords: Dwarf galaxies ; Astronomy data analysis ; Photometry ;
Galaxy properties ; Bayesian statistics
Abstract:
We present deep g- and r-band Magellan/Megacam photometry of two dwarf
galaxy candidates discovered in the Dark Energy Survey (DES), Grus I
and Indus II (DES J2038-4609). For the case of Grus I, we resolved the
main sequence turn-off (MSTO) and ∼2 mags below it. The MSTO can be
seen at g0∼24 with a photometric uncertainty of 0.03mag. We show
Grus I to be consistent with an old, metal-poor (∼13.3Gyr, [Fe/H]~-1.9)
dwarf galaxy. We derive updated distance and structural parameters for
Grus I using this deep, uniform, wide-field data set. We find an
azimuthally-averaged halflight radius more than two times larger
(∼151+21-31pc; ∼4.16'-0.74+0.54) and an absolute V-band
magnitude ~-4.1 that is ∼1 magnitude brighter than previous studies.
We obtain updated distance, ellipticity, and centroid parameters that
are in agreement with other studies within uncertainties. Although our
photometry of Indus II is ∼2-3 magnitudes deeper than the DES Y1
public release, we find no coherent stellar population at its reported
location. The original detection was located in an incomplete region
of sky in the DES Y2Q1 data set and was flagged due to potential blue
horizontal branch member stars. The best-fit isochrone parameters are
physically inconsistent with both dwarf galaxies and globular
clusters. We conclude that Indus II is likely a false positive,
flagged due to a chance alignment of stars along the line of sight.
Description:
We observed Indus II and Grus I over four nights in 2017 April with
the Megacam instrument at the f/5 focus of the 6.5m Magellan Clay
telescope. The data were binned 2x2 resulting in a pixel scale of
0.16".
We used DES photometry to transform Megacam instrumental magnitudes to
DES standard magnitudes. See Section 2.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
22 56 42 -50 09 47 Grus I = NAME Grus I
20 38 52 -46 09 35 Indus II = NAME Indus II
----------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 51 6743 The final calibrated stellar catalog for Grus I
table4.dat 51 5520 The final calibrated stellar catalog for Indus II
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See also:
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
II/371 : The Dark Energy Survey (DES): Data Release 2 (Abbott+, 2021)
J/MNRAS/380/281 : Faint galactic satellites sp. survey (Martin+, 2007)
J/ApJ/756/79 : Opt. photometry in 3 Local Group dwarf galaxies (Sand+, 2012)
J/ApJ/819/53 : Magellan/M2FS sp. of Tucana 2 and Grus 1 (Walker+, 2016)
J/ApJ/866/22 : Spectroscopic analysis of Tuc III stream (Li+, 2018)
J/ApJ/860/65 : MegaCam survey of outer halo satellites. I. (Munoz+, 2018)
J/ApJ/863/25 : Magellan/Megacam obs. of 4 MW satellites (Mutlu-Pakdil+, 2018)
J/ApJ/870/83 : Abundances in ultra-faint dwarf gal. GruI & TriII (Ji+, 2019)
J/ApJ/893/47 : MW satellite census. I. DES & PS1 (Drlica-Wagner+, 2020)
J/ApJ/913/53 : Gas content of dwarf gal. within 2Mpc of MW (Putman+, 2021)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 9 I9 --- ID [67/122349592] Stellar identifier
11- 17 F7.3 deg RAdeg [343.85/344.51] Right Ascension (J2000)
19- 25 F7.3 deg DEdeg [-50.37/-49.95] Declination (J2000)
27- 32 F6.3 mag gmag [15.58/27] Apparent DES g band magnitude
34- 38 F5.3 mag e_gmag [0/0.3] Uncertainty in gmag
40- 45 F6.3 mag rmag [15.17/26.67] Apparent DES r band magnitude
47- 51 F5.3 mag e_rmag [0/0.3] Uncertainty in rmag
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 I9 --- ID [6/174663982] Stellar identifier
11- 17 F7.3 deg RAdeg [309.41/310.02] Right Ascension (J2000)
19- 25 F7.3 deg DEdeg [-46.37/-45.95] Declination (J2000)
27- 32 F6.3 mag gmag [15.18/27.08] Apparent DES g band magnitude
34- 38 F5.3 mag e_gmag [0/0.3] Uncertainty in gmag
40- 45 F6.3 mag rmag [14.75/27.07] Apparent DES r band magnitude
47- 51 F5.3 mag e_rmag [0/0.3] Uncertainty in rmag
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 29-Nov-2022