Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-Faint Dwarf Galaxy in the Constellation Pegasus

Cerny, W.; Simon, J. D.; Li, T. S.; Drlica-Wagner, A.; Pace, A. B.; Martınez-Vazquez, C. E.; Riley, A. H.; Mutlu-Pakdil, B.; Mau, S.; Ferguson, P. S.; Erkal, D.; Munoz, R. R.; Bom, C. R.; Carlin, J. L.; Carollo, D.; Choi, Y.; Ji, A. P.; Martınez-Delgado, D.; Manwadkar, V.; Miller, A. E.; Noel, N. E. D.; Sakowska, J. D.; Sand, D. J.; Stringfellow, G. S.; Tollerud, E. J.; Vivas, A. K.; Carballo-Bello, J. A.; Hernandez-Lang, D.; James, D. J.; Castellon, J. L. Nilo; Olsen, K. A. G.; Zenteno, A.

doi:10.48550/arxiv.2203.11788

“…Throughout this analysis we will refer to the objects as dwarf spheroidal galaxies (dSphs) even though several objects do not have spectroscopic confirmation or have an ambiguous classification (e.g., Dra II, Sgr II, Tuc III). We do not include the recently discovered dSphs Eridanus IV and Pegasus IV as similar methods were used derive the systemic proper motion and only Pegasus IV has a line-of-sight velocity measurement (Cerny et al 2021(Cerny et al , 2022. We will refer to the dSphs by their shorted acronyms throughout the paper, which are listed in Table 1 along with their full names.…”

Section: Datamentioning

confidence: 99%

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

Pace

¹

,

Erkal

²

,

Li

³

2022

ApJ

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We combine Gaia early data release 3 astrometry with accurate photometry and utilize a probabilistic mixture model to measure the systemic proper motion of 52 dwarf spheroidal (dSph) satellite galaxies of the Milky Way (MW). For the 46 dSphs with literature line-of-sight velocities we compute orbits in both a MW and a combined MW + Large Magellanic Cloud (LMC) potential and identify Car II, Car III, Hor I, Hyi I, Phx II, and Ret II as likely LMC satellites. 40% of our dSph sample has a >25% change in pericenter and/or apocenter with the MW + LMC potential. For these orbits, we use a Monte Carlo sample for the observational uncertainties for each dSph and the uncertainties in the MW and LMC potentials. We predict that Ant II, Boo III, Cra II, Gru II, and Tuc III should be tidally disrupting by comparing each dSph's average density relative to the MW density at its pericenter. dSphs with large ellipticity (CVn I, Her, Tuc V, UMa I, UMa II, UMi, Wil 1) show a preference for their orbital direction to align with their major axis even for dSphs with large pericenters. We compare the dSph radial orbital phase to subhalos in MW-like N-body simulations and infer that there is not an excess of satellites near their pericenter. With projections of future Gaia data releases, we find that dSph's orbital precision will be limited by uncertainties in the distance and/or MW potential rather than in proper motion precision. Finally, we provide our membership catalogs to enable community follow-up.

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“…The faint end of the galaxy luminosity function is important for understanding dark matter and astrophysics on small scales (see, e.g., Bullock & Boylan-Kolchin 2017;Simon 2019, for recent reviews). In the Local Group, observations continue to find a variety of ultra-faint galaxies (for instance, most recently Mau et al 2020;Cerny et al 2021Cerny et al , 2022, while numerical simulations work out how stars form in the smallest dark matter subhalos of Milky Way-like systems (e.g., Brooks et al 2013;Sawala et al 2016;Wetzel et al 2016;Samuel et al 2020;Applebaum et al 2021;Engler et al 2021). Outside of the Local Group, faint dwarf galaxies are being identified in resolved stars (Chiboucas et al 2013;Crnojević et al 2014;Sand et al 2014;Crnojević et al 2016b;Carlin et al 2016;Toloba et al 2016;Smercina et al 2018;Bennet et al 2019;Crnojević et al 2019;Bennet et al 2020;Mutlu-Pakdil et al 2022), diffuse or semiresolved light (e.g., Bennet et al 2017;Carlsten et al 2020;Davis et al 2021), as well as spectroscopic surveys (Geha et al 2017;Mao et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D ≈ 1.4 Mpc*

Sand

¹

,

Mutlu-Pakdil

²

,

Jones

³

et al. 2022

ApJL

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We report the discovery of Tucana B, an isolated ultra-faint dwarf galaxy at a distance of D = 1.4 Mpc. Tucana B was found during a search for ultra-faint satellite companions to the known dwarfs in the outskirts of the Local Group, although its sky position and distance indicate the nearest galaxy to be ∼500 kpc distant. Deep ground-based imaging resolves Tucana B into stars, and it displays a sparse red giant branch consistent with an old, metal-poor stellar population analogous to that seen in the ultra-faint dwarf galaxies of the Milky Way, albeit at fainter apparent magnitudes. Tucana B has a half-light radius of 80 ± 40 pc and an absolute magnitude of M V = − 6.9 − 0.6 + 0.5 mag ( L V = ( 5 − 2 + 4 ) × 10 4 L ⊙), which is again comparable to the Milky Way’s ultra-faint satellites. There is no evidence for a population of young stars, either in the optical color–magnitude diagram or in GALEX archival ultraviolet imaging, with the GALEX data indicating log ( SFR NUV / M ⊙ yr − 1 ) < − 5.4 for star formation on ≲100 Myr timescales. Given its isolation and physical properties, Tucana B may be a definitive example of an ultra-faint dwarf that has been quenched by reionization, providing strong confirmation of a key driver of galaxy formation and evolution at the lowest mass scales. It also signals a new era of ultra-faint dwarf galaxy discovery at the extreme edges of the Local Group.

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“…Over the last two decades, data from large digital sky surveys (e.g., the Sloan Digital Sky Survey (SDSS), the Dark Energy Survey (DES), and PanSTARRS) have led to an order-ofmagnitude increase in the number of known low surface brightness stellar systems in the vicinity (<200 kpc) of the Milky Way (e.g., Willman et al 2005aWillman et al , 2005bZucker et al 2006;Belokurov et al 2007;Walsh et al 2007;Willman 2010;Koposov et al 2015a;Laevens et al 2015aLaevens et al , 2015bBechtol et al 2015;Drlica-Wagner et al 2015Homma et al 2016Homma et al , 2018Mau et al 2020;Cerny et al 2021Cerny et al , 2022. One particularly intriguing class of faint systems, which were first detected in SDSS data over a decade ago (Willman et al 2005a(Willman et al , 2005b, are ultra-faint dwarf galaxies (UFDs).…”

Section: Introductionmentioning

confidence: 99%

Magellan/IMACS Spectroscopy of Grus I: A Low Metallicity Ultra-faint Dwarf Galaxy*

Chiti

¹

,

Simon

²

,

Frebel

³

et al. 2022

ApJ

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We present a chemodynamical study of the Grus I ultra-faint dwarf galaxy (UFD) from medium-resolution (R ∼ 11,000) Magellan/IMACS spectra of its individual member stars. We identify eight confirmed members of Grus I, based on their low metallicities and coherent radial velocities, and four candidate members for which only velocities are derived. In contrast to previous work, we find that Grus I has a very low mean metallicity of 〈[Fe/H]〉 = −2.62 ± 0.11 dex, making it one of the most metal-poor UFDs. Grus I has a systemic radial velocity of −143.5 ± 1.2 km s−1 and a velocity dispersion of σ rv = 2.5 − 0.8 + 1.3 km s−1, which results in a dynamical mass of M 1 / 2 ( r h ) = 8 − 4 + 12 × 10 5 M ⊙ and a mass-to-light ratio of M/L V = 440 − 250 + 650 M ⊙/L ⊙. Under the assumption of dynamical equilibrium, our analysis confirms that Grus I is a dark-matter-dominated UFD (M/L > 80 M ⊙/L ⊙). However, we do not resolve a metallicity dispersion (σ [Fe/H] < 0.44 dex). Our results indicate that Grus I is a fairly typical UFD with parameters that agree with mass–metallicity and metallicity-luminosity trends for faint galaxies. This agreement suggests that Grus I has not lost an especially significant amount of mass from tidal encounters with the Milky Way, in line with its orbital parameters. Intriguingly, Grus I has among the lowest central densities ( ρ 1 / 2 ∼ 3.5 − 2.1 + 5.7 × 10 7 M ⊙ kpc−3) of the UFDs that are not known to be tidally disrupting. Models of the formation and evolution of UFDs will need to explain the diversity of these central densities, in addition to any diversity in the outer regions of these relic galaxies.

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Pegasus IV: Discovery and Spectroscopic Confirmation of an Ultra-Faint Dwarf Galaxy in the Constellation Pegasus

Abstract: We report the discovery of Pegasus IV, an ultra-faint dwarf galaxy found in archival data from the Dark Energy Camera processed by the DECam Local Volume Exploration Survey. Pegasus IV is a compact, ultra-faint stellar system (r 1/2 = 41 +8 −6 pc; M V = −4.25 ± 0.2 mag) located at

Cited by 6 publications

References 100 publications

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

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

Tucana B: A Potentially Isolated and Quenched Ultra-faint Dwarf Galaxy at D ≈ 1.4 Mpc*

Magellan/IMACS Spectroscopy of Grus I: A Low Metallicity Ultra-faint Dwarf Galaxy*

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