Formation of an Extended Stellar Halo around an Ultra-faint Dwarf Galaxy Following One of the Earliest Mergers from Galactic Building Blocks

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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Stellar Populations of the Outer Milky-Way Halo

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317009279 ◽

2017 ◽

Vol 13 (S334) ◽

pp. 29-33

Author(s):

Baslio Santiago ◽

Elmer Luque ◽

Adriano Pieres ◽

Anna Bárbara Queiroz

Keyword(s):

Galaxy Evolution ◽

Galaxy Formation ◽

Milky Way ◽

Galactic Halo ◽

Dwarf Galaxy ◽

Building Blocks ◽

Early Stages ◽

Dark Energy Survey ◽

Stellar Streams ◽

The Galaxy

AbstractThe stellar spheroidal components of the Milky-Way contain the oldest and most metal poor of its stars. Inevitably the processes governing the early stages of Galaxy evolution are imprinted upon them. According to the currently favoured hierarchical bottom-up scenario of galaxy formation, these components, specially the Galactic halo, are the repository of most of the mass built up from accretion events in those early stages. These events are still going on today, as attested by the long stellar streams associated to the Sagittarius dwarf galaxy and several other observed tidal substructure, whose geometry, extent, and kinematics are important constraints to reconstruct the MW gravitational potential and infer its total (visible + dark) mass. In addition, the remaining system of MW satellites is expected to be a fossil record of the much larger population of Galactic building blocks that once existed and got accreted. For all these reasons, it is crucial to unravel as much of this remaining population as possible, as well as the current stellar streams that orbit within the halo. The best bet to achieve this task is to carry out wide, deep, and multi-band photometric surveys that provide homogeneous stellar samples. In this contribution, we summarize the results of several years of work towards detecting and characterizing distant MW stellar systems, star clusters and dwarf spheroidals alike, with an emphasis on the analysis of data from the Dark Energy Survey (DES). We argue that most of the volume in distance, size and luminosity space, both in the Galaxy and in the Clouds, is still unprobed. We then discuss the perspectives of exploring this outer MW volume using the current surveys, as well as other current and future surveys, such as the Large Synoptic Survey Telescope (LSST).

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N-body Self-consistent Stellar-halo Modeling of the Fornax Dwarf Galaxy

The Astrophysical Journal ◽

10.3847/1538-4357/abdd24 ◽

2021 ◽

Vol 909 (2) ◽

pp. 147

Author(s):

Galina Shchelkanova ◽

Kohei Hayashi ◽

Sergei Blinnikov

Keyword(s):

Dwarf Galaxy ◽

Self Consistent ◽

Stellar Halo ◽

Body Self

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Kinematics of highly r-process-enhanced halo stars: Evidence for origins in now-destroyed ultra-faint dwarf galaxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319008755 ◽

2019 ◽

Vol 14 (S353) ◽

pp. 71-74

Author(s):

Kaley Brauer ◽

Alexander P. Ji ◽

Kohei Hattori ◽

Sergio Escobar ◽

Anna Frebel

Keyword(s):

Milky Way ◽

Dwarf Galaxies ◽

Building Blocks ◽

Specific Chemical ◽

Halo Stars ◽

Novel Approach ◽

Chemical Signatures ◽

Formation History ◽

Stellar Halo ◽

R Process

AbstractThe Milky Way’s stellar halo preserves a fossil record of smaller dwarf galaxies that merged with the Milky Way throughout its formation history. Currently, though, we lack reliable ways to identify which halo stars originated in which dwarf galaxies or even which stars were definitively accreted. Selecting stars with specific chemical signatures may provide a way forward. We investigate this theoretically and observationally for stars with r-process nucleosynthesis signatures. Theoretically, we combine high-resolution cosmological simulations with an empirically-motivated treatment of r-process enhancement. We find that around half of highly r-process-enhanced metal-poor halo stars may have originated in early ultra-faint dwarf galaxies that merged into the Milky Way during its formation. Observationally, we use Gaia DR2 to compare the kinematics of highly r-process-enhanced halo stars with those of normal halo stars. R-process-enhanced stars have higher galactocentric velocities than normal halo stars, suggesting an accretion origin. If r-process-enhanced stars largely originated in accreted ultra-faint dwarf galaxies, halo stars we observe today could play a key role in understanding the smallest building blocks of the Milky Way via this novel approach of chemical tagging

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Chemical abundances of field halo stars - Implications for the building blocks of the Milky Way

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007865 ◽

2019 ◽

Vol 14 (S351) ◽

pp. 24-33

Author(s):

Miho N. Ishigaki

Keyword(s):

Milky Way ◽

Building Blocks ◽

Chemical Information ◽

Wide Field ◽

Chemical Abundance ◽

Chemical Abundances ◽

Halo Stars ◽

Dimensional Phase Space ◽

Stellar Halo ◽

Detailed Chemical

AbstractI would like to review recent efforts of detailed chemical abundance measurements for field Milky Way halo stars. Thanks to the advent of wide-field spectroscopic surveys up to a several kpc from the Sun, large samples of field halo stars with detailed chemical measurements are continuously expanding. Combination of the chemical information and full six dimensional phase-space information is now recognized as a powerful tool to identify cosmological accretion events that have built a sizable fraction of the present-day stellar halo. Future observational prospects with wide-field spectroscopic surveys and theoretical prospects with supernova nucleosynthetic yields are also discussed.

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Building Blocks of the Milky Way's Stellar Halo

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315007061 ◽

2015 ◽

Vol 11 (S317) ◽

pp. 373-374

Author(s):

Pim van Oirschot ◽

Else Starkenburg ◽

Amina Helmi ◽

Gijs Nelemans

Keyword(s):

Galaxy Formation ◽

Stellar Population ◽

Milky Way ◽

Building Blocks ◽

Formation Model ◽

Halo Stars ◽

Stellar Halo ◽

History Of ◽

Dynamical Properties ◽

Star Formation Histories

AbstractWe study the assembly history of the stellar halo of Milky Way-like galaxies using the six high-resolution Aquarius dark matter simulations combined with the Munich-Groningen semi-analytic galaxy formation model. Our goal is to understand the stellar population contents of the building blocks of the Milky Way halo, including their star formation histories and chemical evolution, as well as their internal dynamical properties. We are also interested in how they relate or are different from the surviving satellite population. Finally, we will use our models to compare to observations of halo stars in an attempt to reconstruct the assembly history of the Milky Way's stellar halo itself.

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Low Luminosity Galaxies

Publications of the Astronomical Society of Australia ◽

10.1071/as04046 ◽

2004 ◽

Vol 21 (4) ◽

pp. 360-365 ◽

Cited By ~ 4

Author(s):

J. I. Davies ◽

S. Sabatini ◽

S. Roberts

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

Large Scale ◽

Dwarf Galaxies ◽

Dwarf Galaxy ◽

Building Blocks ◽

Large Mass ◽

Dark Matter Halos ◽

Cluster Environment ◽

Dense Cluster

AbstractLow luminosity (dwarf) galaxies play a crucial role in our current theories of galaxy and large scale structure formation. In the hierarchical picture they are the building blocks from which other structures form. These theories in their basic form overpredict the numbers of small dark matter halos (dwarf galaxies?) unless some form of star formation supression is invoked. In this paper we describe observations of dwarf galaxies in a range of different environments. We find that there are far too few dwarf galaxies in low density environments to be compatible with the theories. These observations are not consistent with an environment-independent mechanism suppressing dwarf galaxy formation. It is also not clear how these mechanisms can supress star formation if dwarf galaxies have large mass-to-light ratios (≈100). Either the whole idea of hierarchical galaxy formation has to be rejected or other environmentally dependent physical processes have to be invoked. We suggest that small, gas-rich dI galaxies have their evolution rapidly advanced as they move into the dense cluster environment.

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SMC in space and time: a project to study the evolution of the prototype interacting late-type dwarf galaxy

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308025118 ◽

2008 ◽

Vol 4 (S255) ◽

pp. 381-386 ◽

Cited By ~ 1

Author(s):

M. Tosi ◽

J. Gallagher ◽

E. Sabbi ◽

K. Glatt ◽

E. K. Grebel ◽

...

Keyword(s):

Star Formation ◽

Dwarf Galaxy ◽

Variable Stars ◽

Star Formation History ◽

Space And Time ◽

Deep Well ◽

Formation History ◽

Central Regions ◽

Stellar Halo ◽

Hubble Time

AbstractWe introduce the SMC in space and time, a large coordinated space and ground-based program to study star formation processes and history, as well as variable stars, structure, kinematics and chemical evolution of the whole SMC. Here, we present the Colour-Magnitude Diagrams (CMDs) resulting from HST/ACS photometry, aimed at deriving the star formation history (SFH) in six fields of the SMC. The fields are located in the central regions, in the stellar halo, and in the wing toward the LMC. The CMDs are very deep, well beyond the oldest Main Sequence Turn-Off, and will allow us to derive the SFH over the entire Hubble time.

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Multiple populations in the Sagittarius nuclear cluster M 54 and in other anomalous globular clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315008467 ◽

2015 ◽

Vol 11 (S317) ◽

pp. 170-175

Author(s):

A. P. Milone

Keyword(s):

Globular Clusters ◽

Galactic Halo ◽

Dwarf Galaxy ◽

Hubble Space Telescope ◽

Stellar System ◽

Stellar Populations ◽

Building Blocks ◽

Multi Wavelength ◽

Nuclear Cluster ◽

Different Content

AbstractM 54 is the central cluster of the Sagittarius dwarf galaxy. This stellar system is now in process of being disrupted by the tidal interaction with the Milky Way and represents one of the building blocks of the Galactic Halo. Recent discoveries, based on the synergy of photometry and spectroscopy have revealed that the color-magnitude diagram (CMD) of some massive, anomalous, Globular Clusters (GCs) host stellar populations with different content of heavy elements. In this paper, I use multi-wavelength Hubble Space Telescope (HST) photometry to detect and characterize multiple stellar populations in M 54. I provide empirical evidence that this GC shares photometric and spectroscopic similarities with the class of anomalous GCs. These findings make it tempting to speculate that, similarly to Sagittarius nuclear cluster M 54, other anomalous GCs were born in an extra-Galactic environment.

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Evidence for two early accretion events that built the Milky Way stellar halo

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1770 ◽

2019 ◽

Vol 488 (1) ◽

pp. 1235-1247 ◽

Cited By ~ 86

Author(s):

G C Myeong ◽

E Vasiliev ◽

G Iorio ◽

N W Evans ◽

V Belokurov

Keyword(s):

Globular Cluster ◽

Total Mass ◽

Globular Clusters ◽

Milky Way ◽

Dwarf Galaxy ◽

High Energy ◽

Stellar Mass ◽

Milky Way Galaxy ◽

Stellar Halo ◽

Chemical Evidence

AbstractThe Gaia Sausage is the major accretion event that built the stellar halo of the Milky Way galaxy. Here, we provide dynamical and chemical evidence for a second substantial accretion episode, distinct from the Gaia Sausage. The Sequoia Event provided the bulk of the high-energy retrograde stars in the stellar halo, as well as the recently discovered globular cluster FSR 1758. There are up to six further globular clusters, including ω Centauri, as well as many of the retrograde substructures in Myeong et al., associated with the progenitor dwarf galaxy, named the Sequoia. The stellar mass in the Sequoia galaxy is ∼5 × 10 M⊙ , whilst the total mass is ∼1010 M⊙ , as judged from abundance matching or from the total sum of the globular cluster mass. Although clearly less massive than the Sausage, the Sequoia has a distinct chemodynamical signature. The strongly retrograde Sequoia stars have a typical eccentricity of ∼0.6, whereas the Sausage stars have no clear net rotation and move on predominantly radial orbits. On average, the Sequoia stars have lower metallicity by ∼0.3 dex and higher abundance ratios as compared to the Sausage. We conjecture that the Sausage and the Sequoia galaxies may have been associated and accreted at a comparable epoch.

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