On the absence of backsplash analogues to NGC 3109 in the ΛCDM framework

Abstract The dwarf galaxy NGC 3109 is receding 105 km/s faster than expected in a ΛCDM timing argument analysis of the Local Group and external galaxy groups within 8 Mpc. If this few-body model accurately represents long-range interactions in ΛCDM, this high velocity suggests that NGC 3109 is a backsplash galaxy that was once within the virial radius of the Milky Way and was slingshot out of it. Here, we use the Illustris TNG300 cosmological hydrodynamical simulation and its merger tree to identify backsplash galaxies. We find that backsplashers as massive (≥4.0 × 1010M⊙) and distant (≥1.2 Mpc) as NGC 3109 are extremely rare, with none having also gained energy during the interaction with their previous host. This is likely due to dynamical friction. Since we identified 13225 host galaxies similar to the Milky Way or M31, we conclude that postulating NGC 3109 is a backsplash galaxy causes >3.96σ tension with the expected distribution of backsplashers in ΛCDM. We show that the dark matter only version of TNG300 yields much the same result, demonstrating its robustness to how the baryonic physics is modelled. If instead NGC 3109 is not a backsplasher, consistency with ΛCDM would require the timing argument analysis to be off by 105 km/s for this rather isolated dwarf, which we argue is unlikely. We discuss a possible alternative scenario for NGC 3109 and the Local Group satellite planes in the context of MOND, where the Milky Way and M31 had a past close flyby 7 − 10 Gyr ago.

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The Orientation of Galaxies in Nearby Galaxy Groups

Symposium - International Astronomical Union ◽

10.1017/s0074180900197256 ◽

2004 ◽

Vol 217 ◽

pp. 116-117

Author(s):

P. Flin ◽

M. Biernacka ◽

J. Krywult

Keyword(s):

Statistical Analysis ◽

Milky Way ◽

Random Distribution ◽

Local Group ◽

Dwarf Galaxies ◽

Nearby Galaxy ◽

Groups Of Galaxies ◽

Galaxy Groups ◽

Isotropic Distribution ◽

Local Supercluster

The statistical analysis of six nearby groups of galaxies, connected with the Milky Way, M31, M81, M101, NGC5128 and NGC5236 shows an isotropic distribution of galaxy planes, similarly to galaxies within the Local Group. Also planes of galaxies in the nearby (Vr < 500 km s−1) region of the Local Supercluster exhibit random distribution, disregarding their membership to groups. The result shows that strong environmental effects observed among dwarf galaxies do not change generally random distribution of galaxy planes in this region.

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Distance to the nearby dwarf galaxy [TT2009] 25 in the NGC 891 group using the tip of the red giant branch

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936392 ◽

2019 ◽

Vol 629 ◽

pp. L2 ◽

Cited By ~ 1

Author(s):

Oliver Müller ◽

Rodrigo Ibata ◽

Marina Rejkuba ◽

Lorenzo Posti

Keyword(s):

Milky Way ◽

Local Group ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Small Scale ◽

Accurate Information ◽

Standard Candle ◽

Stellar Halo ◽

Red Giant ◽

Small Field Of View

Dwarf galaxies are key objects for small-scale cosmological tests like the abundance problems or the planes-of-satellites problem. A crucial task is therefore to get accurate information for as many nearby dwarf galaxies as possible. Using extremely deep, ground-based V and i-band Subaru Suprime Cam photometry with a completeness of i = 27 mag, we measure the distance of the dwarf galaxy [TT2009] 25 using the tip of the red giant branch as a standard candle. This dwarf resides in the field around the Milky Way-analog NGC 891. Using a Bayesian approach, we measure a distance of 10.28−1.73+1.17 Mpc, which is consistent with the distance of NGC 891, and thus confirm it as a member of NGC 891. The dwarf galaxy follows the scaling relations defined by the Local Group dwarfs. We do not find an extended stellar halo around [TT2009] 25. In the small field of view of 100 kpc covered by the survey, only one bright dwarf galaxy and the giant stream are apparent. This is comparable to the Milky Way, where one bright dwarf resides in the same volume, as well as the Sagittarius stream – excluding satellites which are farther away but would be projected in the line-of-sight. It is thus imperative to survey for additional dwarf galaxies in a larger area around NGC 891 to test the abundance of dwarf galaxies and compare this to the number of satellites around the Milky Way.

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The Formation Chronology of Local Group Spiral Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900223401 ◽

2002 ◽

Vol 207 ◽

pp. 73-82

Author(s):

Ata Sarajedini

Keyword(s):

Globular Clusters ◽

Milky Way ◽

Local Group ◽

Spiral Galaxies ◽

Dwarf Galaxy ◽

Additional Parameter ◽

Horizontal Branch ◽

The Galaxy ◽

Metal Abundance ◽

Cluster Age

The ‘Second Parameter Effect’ (2ndPE) has long been recognized as an important probe into the formation of spiral galaxies. The concept that the horizontal branch morphologies of globular clusters are primarily affected by metal abundance in the inner halo (RGC<8 kpc) of the Galaxy but require an additional parameter (probably cluster age) to explain their behavior in the outer halo (RGC > 8 kpc), suggests that the former experienced a rapid monotonic collapse while the latter underwent a slower chaotic formation scenario. As such, in the Milky Way, the so-called second parameter boundary is located at 8 kpc. We find that, in the other Local Group spirals — M31 and M33 — this boundary lies at ∼40 kpc and ∼0 kpc, respectively. We therefore speculate that the boundary delimiting rapid monotonic halo collapse from the chaotic accretion of dwarf galaxy fragments is inversely related to the mass of the spiral galaxy.

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Lithium and beryllium in the Gaia-Enceladus galaxy

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1653 ◽

2020 ◽

Vol 496 (3) ◽

pp. 2902-2909

Author(s):

P Molaro ◽

G Cescutti ◽

X Fu

Keyword(s):

Milky Way ◽

Local Group ◽

Galactic Halo ◽

Dwarf Galaxy ◽

Chemical Abundances ◽

Dwarf Stars ◽

Evolution Experiment ◽

External Galaxies ◽

Low Metallicity ◽

Gaia Dr2

ABSTRACT Data from Gaia DR2 and The Apache Point Observatory Galactic Evolution Experiment surveys revealed a relatively new component in the inner Galactic halo, which is likely the dynamical remnant of a disrupted dwarf galaxy named Gaia-Enceladus that collided with the Milky Way about 10 Gyr ago. This merging event offers an extraordinary opportunity to study chemical abundances of elements in a dwarf galaxy, since they are generally hampered in external galaxies. Here, we focus on 7Li and 9Be in dwarf stars that are out of reach even in Local Group galaxies. Searching in GALAH, Gaia-ESO survey and in literature, we found several existing 7Li abundance determinations of stars belonging to the Gaia-Enceladus galaxy. The 7Li abundances of stars at the low metallicity end overlap with those of the Galactic halo. These are effective extragalactic 7Li measurements, which suggest that the 7Li Spite plateau is universal, as is the cosmological 7Li problem. We found a 7Li-rich giant out of 101 stars, which suggests a small percentage similar to that of the Milky Way. We also collect 9Be abundance for a subsample of 25 Gaia-Enceladus stars from literature. Their abundances share the Galactic [Be/H] values at the low metallicity end but grow slower with [Fe/H] and show a reduced dispersion. This suggests that the scatter observed in the Milky Way could reflect the different 9Be evolution patterns of different stellar components that are mixed-up in the Galactic halo.

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Tidal evolution of dwarf galaxies with shallow dark matter density profiles

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314011181 ◽

2012 ◽

Vol 10 (H16) ◽

pp. 346-346

Author(s):

Ewa L. Łokas

Keyword(s):

Dark Matter ◽

Milky Way ◽

Local Group ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Morphological Evolution ◽

Matter Density ◽

Density Profiles ◽

Tidal Evolution ◽

Dark Matter Density

AbstractOne of the scenarios for the formation of dwarf spheroidal galaxies in the Local Group proposes that the objects formed from late type dwarfs via tidal interaction with bigger galaxies such as the Milky Way and Andromeda. The scenario naturally explains the morphology-density relation observed for dwarf galaxies in the Local Group. Using N-body simulations we study the long-term tidal evolution of dwarf galaxies in the vicinity of the Milky Way. The dwarf galaxies were initially composed of stellar disks embedded in dark matter haloes of different inner density slopes including shallow ones recently obtained in N-body+hydro simulations of dwarf galaxy formation in isolation. Such progenitors were placed on five different orbits around the Milky Way and their evolution was followed for 10 Gyr. The outcome of the evolution, in terms of the mass loss, morphological transformation and randomization of stellar orbits depends very sensitively on the inner density slope of dark matter. The effects of tides are stronger for dwarfs with shallower slopes; they are more heavily stripped, in some cases down to the scale of ultra-faint satellites of the Milky Way or even dissolved completely with obvious implications for the missing satellites problem. The morphological evolution of the stellar component, from rotationally supported disks to spheroids dominated by random motions, also proceeds faster. In addition, bars which usually form at the first pericenter passage are created more easily and live longer in dwarfs with shallow dark matter density profiles on extended orbits.

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The missing dwarf galaxies of the Local Group

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa375 ◽

2020 ◽

Vol 493 (2) ◽

pp. 2596-2605 ◽

Cited By ~ 3

Author(s):

Azadeh Fattahi ◽

Julio F Navarro ◽

Carlos S Frenk

Keyword(s):

Galaxy Formation ◽

Milky Way ◽

Local Group ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Wide Field ◽

Mass Relation ◽

Galaxy Masses ◽

Galaxy Population ◽

Formation Efficiency

ABSTRACT We study the Local Group (LG) dwarf galaxy population predicted by the APOSTLE ΛCDM cosmological hydrodynamics simulations. These indicate that: (i) the total mass within 3 Mpc of the Milky Way–Andromeda mid-point (M3Mpc) typically exceeds ∼3 times the sum of the virial masses (M200crit) of the two primaries and (ii) the dwarf galaxy formation efficiency per unit mass is uniform throughout the volume. This suggests that the satellite population within the virial radii of the Milky Way and Andromeda should make up fewer than one third of all LG dwarfs within 3 Mpc. This is consistent with the fraction of observed LG galaxies with stellar mass $M_*\gt 10^7\, {\rm M}_\odot$ that are satellites (12 out of 42; i.e. 28 per cent). For the APOSTLE galaxy mass–halo mass relation, the total number of such galaxies further suggests an LG mass of $M_{\rm 3 Mpc}\sim 10^{13}\, {\rm M}_\odot$. At lower galaxy masses, however, the observed satellite fraction is substantially higher (42 per cent for $M_*\gt 10^5\, { \mathrm{ M}}_\odot$). If this is due to incompleteness in the field sample, then ∼50 dwarf galaxies at least as massive as the Draco dwarf spheroidal must be missing from the current LG field dwarf inventory. The incompleteness interpretation is supported by the pronounced flattening of the LG luminosity function below $M_*\sim 10^7\, {\rm M}_\odot$, and by the scarcity of low surface brightness LG field galaxies compared to satellites. The simulations indicate that most missing dwarfs should lie near the virial boundaries of the two LG primaries, and predict a trove of nearby dwarfs that await discovery by upcoming wide-field imaging surveys.

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The edge of the Galaxy

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1711 ◽

2020 ◽

Vol 496 (3) ◽

pp. 3929-3942 ◽

Cited By ~ 3

Author(s):

Alis J Deason ◽

Azadeh Fattahi ◽

Carlos S Frenk ◽

Robert J J Grand ◽

Kyle A Oman ◽

...

Keyword(s):

Dark Matter ◽

Radial Velocity ◽

Milky Way ◽

Local Group ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Space Distribution ◽

Radial Density ◽

The Galaxy ◽

Galaxy Population

ABSTRACT We use cosmological simulations of isolated Milky Way (MW)-mass galaxies, as well as Local Group (LG) analogues, to define the ‘edge’ – a caustic manifested in a drop in density or radial velocity – of Galactic-sized haloes, both in dark matter and in stars. In the dark matter, we typically identify two caustics: the outermost caustic located at ∼1.4r200m, corresponding to the ‘splashback’ radius, and a second caustic located at ∼0.6r200m, which likely corresponds to the edge of the virialized material that has completed at least two pericentric passages. The splashback radius is ill defined in LG-type environments where the haloes of the two galaxies overlap. However, the second caustic is less affected by the presence of a companion, and is a more useful definition for the boundary of the MW halo. Curiously, the stellar distribution also has a clearly defined caustic, which, in most cases, coincides with the second caustic of the dark matter. This can be identified in both radial density and radial velocity profiles, and should be measurable in future observational programmes. Finally, we show that the second caustic can also be identified in the phase–space distribution of dwarf galaxies in the LG. Using the current dwarf galaxy population, we predict the edge of the MW halo to be 292 ± 61 kpc.

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An Analysis of M31 and its Satellite Galaxies Using RR Lyrae Variables

Proceedings of the International Astronomical Union ◽

10.1017/s1743921318006270 ◽

2018 ◽

Vol 14 (S344) ◽

pp. 147-150

Author(s):

Nahathai Tanakul ◽

Ata Sarajedini

Keyword(s):

Milky Way ◽

Local Group ◽

Hubble Space Telescope ◽

Common Type ◽

Published Data ◽

Host Galaxies ◽

Rr Lyrae Stars ◽

Rr Lyrae ◽

History Of ◽

Lyrae Stars

AbstractRR Lyrae stars are powerful tools to study their host populations. Information such as distance, metallicity, reddening, and age can be obtained from their pulsation properties. Dwarf spheroidal (dSph) galaxies are the most common type of galaxy in the Local Group. They are found around massive hosts such as the Milky Way (MW) and M31 and are suggested to be the present-day counterparts to systems from which spheroids and stellar halos of larger galaxies were assembled. By comparing RR Lyraes in these dSphs with their host galaxies, we hope to understand more about the formation of these galaxies. In order to achieve this goal, we have analyzed six fields in M31 using archival imaging from the Hubble Space Telescope. Published data for M31, M33, and several M31 dSphs are also included. The results are then compared with those in the MW to better constrain the early history of these systems.

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