TY - JOUR
T1 - Uncovering the orbit of the hercules dwarf galaxy
AU - Gregory, Alexandra L.
AU - Collins, Michelle L.M.
AU - Erkal, Denis
AU - Tollerud, Erik
AU - Delorme, Maxime
AU - Hill, Lewis
AU - Sand, David J.
AU - Strader, Jay
AU - Willman, Beth
N1 - Funding Information:
The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding Information:
The authors would like to thank Joshua Simon and Marla Geha for providing the Simon & Geha (2007) catalogue. We thank Justin Read and Michele De Leo for helpful discussions. Research by DJS is supported by NSF grants AST-1821967, 1821987, 1813708, 1813466, and 1908972. JS acknowledges support from the David and Lucile Packard Foundation.
Publisher Copyright:
2020 The Author(s)
PY - 2020
Y1 - 2020
N2 - We present new chemo-kinematics of the Hercules dwarf galaxy based on Keck II-DEIMOS spectroscopy. Our 21 confirmed members, including 9 newly confirmed members, have a systemic velocity of vHerc = 46.4 ± 1.3 km s−1 and a velocity dispersion σv,Herc = 4.4+−1142 km s−1, consistent with previous studies. From the strength of the Ca II triplet, we obtain a metallicity of [Fe/H] = −2.48 ± 0.19 dex and dispersion of σ[Fe/H] = 0.63+−001813 dex. This result is within 1σ of previous measurements, and makes Hercules a particularly metal-poor galaxy, placing it slightly below the standard mass–metallicity relation. Previous photometric and spectroscopic evidence suggests that Hercules is tidally disrupting and may be on a highly radial orbit. From our identified members, we measure no significant velocity gradient. By cross-matching with the second Gaia data release, we determine an uncertainty-weighted mean proper motion of μ∗α = μα cos(δ) = −0.153 ± 0.074 mas yr−1, μδ = −0.397 ± 0.063 mas yr−1. This proper motion is slightly misaligned with the elongation of Hercules, in contrast to models which suggest that any tidal debris should be well aligned with the orbital path. Future observations may resolve this tension.
AB - We present new chemo-kinematics of the Hercules dwarf galaxy based on Keck II-DEIMOS spectroscopy. Our 21 confirmed members, including 9 newly confirmed members, have a systemic velocity of vHerc = 46.4 ± 1.3 km s−1 and a velocity dispersion σv,Herc = 4.4+−1142 km s−1, consistent with previous studies. From the strength of the Ca II triplet, we obtain a metallicity of [Fe/H] = −2.48 ± 0.19 dex and dispersion of σ[Fe/H] = 0.63+−001813 dex. This result is within 1σ of previous measurements, and makes Hercules a particularly metal-poor galaxy, placing it slightly below the standard mass–metallicity relation. Previous photometric and spectroscopic evidence suggests that Hercules is tidally disrupting and may be on a highly radial orbit. From our identified members, we measure no significant velocity gradient. By cross-matching with the second Gaia data release, we determine an uncertainty-weighted mean proper motion of μ∗α = μα cos(δ) = −0.153 ± 0.074 mas yr−1, μδ = −0.397 ± 0.063 mas yr−1. This proper motion is slightly misaligned with the elongation of Hercules, in contrast to models which suggest that any tidal debris should be well aligned with the orbital path. Future observations may resolve this tension.
KW - Galaxies: dwarf
KW - Galaxies: evolution
KW - Galaxies: interactions
KW - Galaxies: kinematics and dynamics
KW - Local Group
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U2 - 10.1093/MNRAS/STAA1553
DO - 10.1093/MNRAS/STAA1553
M3 - Article
AN - SCOPUS:85094186913
VL - 496
SP - 1092
EP - 1104
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 2
ER -