Uncovering the orbit of the hercules dwarf galaxy

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>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 $\sigma _{v,\mathrm{Herc}}=4.4^{+1.4}_{-1.2}$ 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 $\sigma _{\rm {[Fe/H]}}= 0.63^{+0.18}_{-0.13}$ 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 $\mu _{\alpha }^*=\mu _{\alpha }\cos (\delta)=-0.153\pm {0.074}$ 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.</jats:p>

Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies

“…to check we are correctly identifying known dSph members and MW foreground stars) and to identify the most promising targets for future followup. Here we consider a candidate 3 We have also compared our proper motion results to previous Gaia DR2 results (Torrealba et Fritz et al 2019;Fu et al 2019;Walker et al 2019;Longeard et al 2018;Simon et al 2021Simon et al , 2020Gregory et al 2020;Mutlu-Pakdil et al 2019;Longeard et al 2020;Massari et al 2018;Chiti et al 2021;Pace et al 2020) and to non-Gaia proper motion measurements (Piatek et al 2003;Walker et al 2008;Pryor et al 2015;Casetti-Dinescu & Girard 2016;Sohn et al 2017;Piatek et al 2002;Dinescu et al 2004;Piatek et al 2007;Méndez et al 2011;Sohn et al 2013;Lépine et al 2011;Piatek et al 2016Piatek et al , 2006Fritz et al 2018b;Casetti-Dinescu et al 2018;Piatek et al 2005).…”

Gaia early DR3 systemic motions of Local Group dwarf galaxies and orbital properties with a massive Large Magellanic Cloud

“…In this section, we compare our systemic PMs determinations with those in the literature. These were obtained with Gaia DR2 data (Gaia Collaboration et al 2018b;Simon 2018;Simon et al 2020;Fritz et al 2018Fritz et al , 2019Carlin & Sand 2018a;Massari & Helmi 2018;Kallivayalil et al 2018;Pace & Li 2019;Pace et al 2020;Carlin & Sand 2018b;McConnachie & Venn 2020a;Longeard et al 2018Longeard et al , 2020Mau et al 2020;Cerny et al 2020;Chakrabarti et al 2019;Gregory et al 2020;Mutlu-Pakdil et al 2019), eGDR3 (McConnachie & Venn 2020bVasiliev & Baumgardt 2021;Jenkins et al 2020;Martínez-García et al 2021;Li et al 2021a), with HST (Piatek et al 2003, 2005Pryor et al 2015;Piatek et al 2016;Sohn et al 2013Sohn et al , 2017 and VLBI (Brunthaler et al 2005). For the HST measurements, we ignore older determinations, when newer ones from the same group are available.…”

Gaia early DR3 systemic motions of Local Group dwarf galaxies and orbital properties with a massive Large Magellanic Cloud

“…In this section, we compare our systemic PMs determinations with those in the literature. These were obtained with Gaia DR2 data (Gaia Collaboration 2018b;Simon et al 2020;Fritz et al 2018aFritz et al , 2019Massari & Helmi 2018;Kallivayalil et al 2018;Pace & Li 2019;Pace et al 2020;Fu et al 2019;McConnachie & Venn 2020a;Longeard et al 2018Longeard et al , 2020Torrealba et al 2019;Mau et al 2020;Cerny et al 2021;Chakrabarti et al 2019;Gregory et al 2020;Mutlu-Pakdil et al 2019), eDR3 (McConnachie & Venn 2020bVasiliev & Baumgardt 2021;Jenkins et al 2021;Martínez-García et al 2021;Li et al 2021a;Ji et al 2021), with HST (Piatek et al 2003(Piatek et al , 2005(Piatek et al , 2006(Piatek et al , 2007(Piatek et al , 2016Pryor et al 2015;Sohn et al 2013Sohn et al , 2017 and VLBI (Brunthaler et al 2005). For the HST measurements, we ignore older determinations, when newer ones from the same group are available.…”