A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III<sup>∗</sup>

Mutlu-Pakdil, Burçin; Sand, David J.; Carlin, Jeffrey L.; Spekkens, Kristine; Caldwell, Nelson; Crnojević, Denija; Hughes, Allison; Willman, Beth; Zaritsky, Dennis

doi:10.3847/1538-4357/aacd0e

Cited by 97 publications

(78 citation statements)

References 90 publications

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“…However, this does not mean that Sgr II cannot be a GC. There are GCs with Oo II characteristics similar to Sgr II in the inner halo (Clement et al 2001), andMutlu-Pakdil et al (2018) has further shown that its structural parameters are more consistent with extended GCs. Spectroscopic studies are eventually required to ascertain whether it is a galaxy or a star cluster, by investigating velocity and metallicity dispersions of the system and/or a possible presence of Na-O or Mg-Al anti-correlations shown only in GCs.…”

Section: Rr Lyrae Stars In the Field Of Sgr IImentioning

confidence: 91%

RR Lyrae Stars in the Field of Sagittarius II

Joo

Kyeong

Yang

et al. 2019

ApJ

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We present the detection of RR Lyrae variable stars in the field of the Sagittarius II (Sgr II) ultrafaint dwarf (UFD) galaxy. Using B, V time-series photometry obtained with the Korea Microlensing Telescope Network (KMTNet) 1.6 m telescope at CTIO and G-band data from Gaia Data Release 2 (DR2), we identified and characterized two ab -type and four c -type RR Lyrae variables. Five out of the six stars are clustered within three half-light radii (∼4. ′ 8) of the galaxy indicating their association with Sgr II, while the RRab star V4 is located ∼22 ′ from the galaxy center. By excluding V4, the high c -type fraction (0.8) and the period of the only RRab star V3 (P V 3 ≃ 0.666 days) suggest an Oosterhoff II (Oo II) classification for Sgr II. Located close to the locus of Oo II clusters in the periodamplitude diagram, V3 is similar to RRab stars in other UFDs having Oosterhoff-intermediate and Oo II properties. Sgr II is, however, more compact than usual UFDs, placed in between star clusters and dwarf galaxies in the size-luminosity plane, and therefore spectroscopic studies are eventually required to ascertain the true nature of this stellar system. We derive the metallicity ([Fe/H] RRab ≃ −2.1 ± 0.3) and heliocentric distance (∼64±3 kpc) of Sgr II from the RR Lyrae stars, and estimate its age (∼12 Gyr) based on our stellar population models. The Oosterhoff properties of UFDs can be explained with the evolution effect of RR Lyrae stars in the instability strip.

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Section: Rr Lyrae Stars In the Field Of Sgr IImentioning

confidence: 91%

RR Lyrae Stars in the Field of Sagittarius II

Joo

Kyeong

Yang

et al. 2019

ApJ

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“…We determine the distance modulus of Leo V by counting the number of stars consistent with the M92 fiducial, as described in Mutlu-Pakdil et al (2018, see also Walsh et al 2008. We assume a distance modulus of m − M = 14.62 mag for M92 as in Brown et al (2014), taking the mean of measurements from Paust et al (2007, 14.60 ± 0.09 mag), Del Principe et al (2005,14.62 ± 0.1 mag), and Sollima et al (2006, 14.65 ± 0.1 mag).…”

Section: Distance and Color-magnitude Diagrammentioning

confidence: 99%

Signatures of Tidal Disruption in Ultra-faint Dwarf Galaxies: A Combined HST, Gaia, and MMT/Hectochelle Study of Leo V

Mutlu-Pakdil¹,

Sand²,

Walker

et al. 2019

ApJ

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The ultra-faint dwarf galaxy Leo V has shown both photometric overdensities and kinematic members at large radii, along with a tentative kinematic gradient, suggesting that it may have undergone a close encounter with the Milky Way. We investigate these signs of disruption through a combination of i) high-precision photometry obtained with the Hubble Space Telescope (HST ), ii) two epochs of stellar spectra obtained with the Hectochelle Spectrograph on the MMT, and iii) measurements from the Gaia mission. Using the HST data, we examine one of the reported stream-like overdensities at large radii, and conclude that it is not a true stellar stream, but instead a clump of foreground stars and background galaxies. Our spectroscopic analysis shows that one known member star is likely a binary, and challenges the membership status of three others, including two distant candidates that had formerly provided evidence for overall stellar mass loss. We also find evidence that the proposed kinematic gradient across Leo V might be due to small number statistics. We update the systemic proper motion of Leo V, finding (µ α cos δ, µ δ ) = (0.009 ± 0.560, −0.777 ± 0.314) mas yr −1 , which is consistent with its reported orbit that did not put Leo V at risk of being disturbed by the Milky Way. These findings remove most of the observational clues that suggested Leo V was disrupting, however, we also find new plausible member stars, two of which are located > 5 half-light radii from the main body. These stars require further investigation. Therefore, the nature of Leo V still remains an open question.

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“…Their close proximity provides the possibility of detailed comparison between their observed properties and predictions from the concordance cosmology. Well-known discrepancies include the 'missing satellite' problem, where orders of magnitude more substructures are identified in the ΛCDM simulations than the number of observed satellite galaxies (Kauffmann et al 1993;Moore et al 1999;Klypin et al 1999;Mutlu-Pakdil et al 2018;Newton et al 2018), the 'too-bigto-fail' problem, that is, the most luminous observed satellites do not seem to live in the most massive dark subhalos expected from cosmological simulations, which however are 'too big to fail' at forming stars (Strigari et al 2010;Boylan-Kolchin et al 2011), the 'core-cusp' problem, where halos are less cuspy than the ΛCDM predictions (Simon et al 2005;Navarro et al 2010), and the 'planes of satellites' problem, where the observed satellite galaxies are distributed on a much thinner plane (Lynden-Bell 1982;Metz et al 2009;Pawlowski et al 2012;Ibata et al 2013) than substructures predicted by the ΛCDM model. Some of these discrepancies can be alleviated by reducing the expected host halo mass, for example, having fewer (massive) substructures in less-massive halos so that both the 'missing-satellite' problem and the 'too-big-tofail' problem could be less severe (Wang et al 2012;Cautun et al 2014a).…”

Section: Introductionmentioning

confidence: 99%

Local Group Analogs in ΛCDM Cosmological Simulations

Zhai

Guo

Zhao

et al. 2020

ApJ

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We use semi-analytic galaxy catalogs based on two high-resolution cosmological N-body simulations, Millennium-WMAP7 and Millennium-II, to investigate the formation of the Local Group (LG) analogs. Unlike previous studies, we use the observed stellar masses to select the LG member (Milky Way (MW) and M31) analogs, and then impose constrains using the observed separation, isolation, and kinematics of the two main member galaxies. By comparing radial and low-ellipticity orbits between the MW and M31, we find higher tangential velocity results in higher total mass, which are 4.4 +2.4 −1.5 ×10 12 M and 6.6 +2.7 −1.5 ×10 12 M for radial and low-ellipticity orbits. The orbits also influence the individual mass distribution of MW and M31 analogs. For radial orbits, the typical host halo masses of the MW and M31 are 1.5 +1.4 −0.7 ×10 12 M and 2.5 +1.3 −1.1 ×10 12 M ; for low-ellipticity orbits, the masses are 2.5 +2.2 −1.4 ×10 12 M and 3.8 +2.8 −1.8 ×10 12 M . The LG is located primarily in filaments with tails extending toward higher densities up to δ ∼ 4.5. The dark matter velocity anisotropy parameters β of both the MW and M31 analogs are close to zero in the center, increasing to 0.2-0.3 at 50-80 kpc and decreasing slowly outward. The slope is much flatter than computed from the MW satellites, and the amplitude is smaller than traced by halo stars. Values of β from different tracers agree at ∼120 kpc where β ∼ 0.2. We also find that model predictions agree broadly with observations in the radial distribution and luminosity function of satellites around the MW and M31.

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A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III^∗

Cited by 97 publications

References 90 publications

RR Lyrae Stars in the Field of Sagittarius II

RR Lyrae Stars in the Field of Sagittarius II

Signatures of Tidal Disruption in Ultra-faint Dwarf Galaxies: A Combined HST, Gaia, and MMT/Hectochelle Study of Leo V

Local Group Analogs in ΛCDM Cosmological Simulations

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A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III∗

Cited by 97 publications

References 90 publications

RR Lyrae Stars in the Field of Sagittarius II

RR Lyrae Stars in the Field of Sagittarius II

Signatures of Tidal Disruption in Ultra-faint Dwarf Galaxies: A Combined HST, Gaia, and MMT/Hectochelle Study of Leo V

Local Group Analogs in ΛCDM Cosmological Simulations

Contact Info

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Resources

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A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III^∗