J/ApJ/818/39 Hydra I wide-field imaging and spectroscopy obs. (Hargis+, 2016)
Evidence that Hydra I is a tidally disrupting Milky Way dwarf galaxy.
Hargis J.R., Kimmig B., Willman B., Caldwell N., Walker M.G., Strader J.,
Sand D.J., Grillmair C.J., Yoon J.H.
<Astrophys. J., 818, 39 (2016)>
=2016ApJ...818...39H 2016ApJ...818...39H (SIMBAD/NED BibCode)
ADC_Keywords: Radial velocities ; Abundances ; Photometry, ugriz
Keywords: galaxies: dwarf; Galaxy: halo; Galaxy: structure
Abstract:
The Eastern Banded Structure (EBS) and Hydra I halo overdensities are
very nearby (d∼10kpc) objects discovered in Sloan Digital Sky Survey
(SDSS) data. Previous studies of the region have shown that EBS and
Hydra I are spatially coincident, cold structures at the same
distance, suggesting that Hydra I may be the EBS's progenitor. We
combine new wide-field Dark Energy Camera (DECam) imaging and
MMT/Hectochelle spectroscopic observations of Hydra I with SDSS
archival spectroscopic observations to quantify Hydra I's present-day
chemodynamical properties, and to infer whether it originated as a
star cluster or dwarf galaxy. While previous work using shallow SDSS
imaging assumed a standard old, metal-poor stellar population, our
deeper DECam imaging reveals that Hydra I has a thin, well-defined
main sequence turnoff of intermediate age (∼5-6Gyr) and metallicity
([Fe/H]=-0.9dex). We measure statistically significant spreads in both
the iron and alpha-element abundances of σ[Fe/H]=0.13±0.02dex
and σ[α/Fe]=0.09±0.03dex, respectively, and place
upper limits on both the rotation and its proper motion. Hydra I's
intermediate age and [Fe/H] --as well as its low [α/Fe],
apparent [Fe/H] spread, and present-day low luminosity-- suggest that
its progenitor was a dwarf galaxy, which has subsequently lost more
than 99.99% of its stellar mass.
Description:
Observations of Hydra I were obtained on 2014 March 20-23 using the
DECam imager (ugri filters) installed on the CTIO Blanco 4m telescope.
We used MMT/Hectochelle to target stars throughout the Hydra I
overdensity. Spectroscopic observations were obtained over 7 nights
using the Hectochelle spectrograph on the 6.5m MMT (R∼38000).
We complemented our Hectochelle data with archival spectroscopy from
SDSS/SEGUE.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 54 29153 DECam photometry
table2.dat 64 411 Hectochelle/MMT spectroscopy
table3.dat 90 292 SDSS/SEGUE spectroscopy
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See also:
J/MNRAS/448/2717 : Resolved stellar spectra Bayesian analysis (Walker+, 2015)
J/AJ/149/53 : RVs of 12 Milky Way globular clusters (Kimmig+, 2015)
J/MNRAS/446/730 : VIJK photometry of Whiting 1 stars (Valcheva+, 2015)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJ/754/101 : Monoceros Overdensity deep imaging with Subaru (Conn+, 2012)
J/AJ/144/4 : Local Group dwarf galaxy properties (McConnachie+, 2012)
J/AJ/141/90 : SEGUE stellar parameter pipeline. V. (Lee+, 2011)
J/AJ/141/61 : Star clusters in M31. II. (Caldwell+, 2011)
J/ApJ/703/2177 : Metal-poor MS turnoff stars summary (Schlaufman+, 2009)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/AJ/136/2070 : SEGUE stellar parameter pipeline. III. (Allende Prieto+, 2008)
J/A+A/486/697 : Hydra I Cluster Catalogue (HCC) (Misgeld+, 2008)
J/A+A/459/423 : VI and [Fe/H] of Fornax dSph RGB stars (Battaglia+, 2006)
J/ApJS/85/249 : Surface Photometry of Hydra I Galaxies. I. (Hamabe 1993)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000) (1)
12- 19 F8.6 deg DEdeg Declination in decimal degrees (J2000) (1)
21- 26 F6.3 mag gmag [16.1/24.2] Calibrated g band magnitude (2)
28- 33 F6.4 mag e_gmag [0/0.6] The 1σ uncertainty in gmag
35- 40 F6.3 mag rmag [16.5/24] Calibrated r band magnitude (2)
42- 47 F6.4 mag e_rmag [0.001/0.4] The 1σ uncertainty in rmag
49- 54 F6.4 mag E(B-V) [0.02/0.07] The (B-V) color excess
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Note (1): DECam photometric point-source catalog of the EBS/Hydra I region
(see footprint in Figure 1).
Note (2): The photometric data have been corrected for Galactic extinction
(see Section 2.1) using the listed values of E(B-V). We provide
photometry only for stars with g-r<1 due to the photometric
calibration method employed in this study. Point-source selection
was performed using the DAOPHOT CHI and SHARP parameters.
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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- 10 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000) (1)
12- 19 F8.6 deg DEdeg Declination in decimal degrees (J2000) (1)
21- 26 F6.2 km/s HRV [-98/293] Heliocentric radial velocity (2)
28- 31 F4.2 km/s e_HRV [0.3/2.1] The 1σ uncertainty in HRV (2)
33- 38 F6.3 mag gmag [17/21.13] Calibrated g band magnitude (G1)
40- 44 F5.3 mag e_gmag [0.003/0.02] The 1σ uncertainty in gmag
46- 51 F6.3 mag rmag [16.51/20.76] Calibrated r band magnitude (G1)
53- 57 F5.3 mag e_rmag [0.002/0.02] The 1σ uncertainty in rmag
59- 64 F6.4 mag E(B-V) [0.03/0.06] The (B-V) color excess
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Note (1): Hectochelle/MMT catalog of all 411 stars passing the spectroscopic
quality control cuts and located within the SDSS CMD filter shown
in Figure 2a.
Note (2): HRV and uncertainties were derived using the method described
in Section 2.2. Only a subset of these spectra were used in our
analysis of Hydra I (see Section 3.1).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000) (1)
12- 19 F8.6 deg DEdeg Declination in decimal degrees (J2000) (1)
21- 27 F7.2 km/s HRV [-147/299] Heliocentric radial velocity (2)
29- 33 F5.2 km/s e_HRV [0.4/15] The 1σ uncertainty in HRV
35- 39 F5.2 [-] [Fe/H] [-2.9/0.2] Log Fe/H abundance ratio (2)
41- 45 F5.3 [-] e_[Fe/H] [0.001/0.3] The 1σ uncertainty in [Fe/H]
47- 51 F5.2 [-] [a/Fe] [-0.05/0.6] Log α/Fe abundance ratio (2)
53- 57 F5.3 [-] e_[a/Fe] [0.002/0.05] The 1σ uncertainty in [a/Fe]
59- 64 F6.3 mag gmag [15.56/20.5] Calibrated g band magnitude (G1)
66- 70 F5.3 mag e_gmag [0.003/0.02] The 1σ uncertainty in gmag
72- 77 F6.3 mag rmag [14.98/20.1] Calibrated r band magnitude (G1)
79- 83 F5.3 mag e_rmag [0.002/0.04] The 1σ uncertainty in rmag
85- 90 F6.4 mag E(B-V) [0.02/0.06] The (B-V) color excess
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Note (1): SDSS/SEGUE catalog of all 292 stars located in the Hydra I region
and within the SDSS CMD filter shown in Figure 2a.
Note (2): All spectroscopic parameters were taken from the SSPP pipeline. Only
a subset of these spectra were used in our analysis of Hydra I
(see Section 3.1).
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Global note:
Note (G1): The photometric data have been corrected for Galactic extinction
(see Section 2.1) using the listed values of E(B-V).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 26-Apr-2016