The Elongated Structure of the Hercules Dwarf Spheroidal Galaxy from Deep Large Binocular Telescope Imaging

Coleman, Matthew G.; Jong, J. T. A. de; Martín, Nicolás F.; Rix, H. W.; Sand, David J.; Bell, Eric F.; Pogge, Richard W.; Thompson, D. J.; Hippelein, H.; Giallongo, E.; Ragazzoni, Roberto; DiPaola, Andrea; Farinato, Jacopo; Smareglia, R.; Testa, V.; Bechtold, Jill; Hill, John M.; Garnavich, P.; Green, Richard F.

doi:10.1086/522672

Cited by 82 publications

(122 citation statements)

References 18 publications

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“…6), is an essentially perfect match to the dSph satellite Hercules (see Fig. 2 in Coleman et al 2007a) discovered 10 years later by Belokurov et al (2007). The halflight radius is 180 pc in the model and 168 pc for Hercules, RS1-5 has a velocity dispersion of about 2.8 km s −1 (Table 2 in Kroupa 1997), while Hercules has a measured velocity dispersion of 3.72 ± 0.91 km s −1 (Adén et al 2009a), and the inferred mass-to-light ratio that one would deduce from velocity dispersion measurements based on the assumption of equilibrium is about 200 in both cases.…”

Section: The Evolution Of Tdgsmentioning

confidence: 77%

Local-Group tests of dark-matter concordance cosmology

Kroupa

Famaey

Boer

et al. 2010

A&A

224

301

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Predictions of the concordance cosmological model (CCM) of the structures in the environment of large spiral galaxies are compared with observed properties of Local Group galaxies. Five new, most probably irreconcilable problems are uncovered: 1) A wide variety of published CCM models consistently predict some form of relation between dark-matter-mass and luminosity for the Milky Way (MW) satellite galaxies, but none is observed.2) The mass function of luminous sub-haloes predicted by the CCM contains too few satellites with dark matter (DM) mass ≈10 7 M within their innermost 300 pc than in the case of the MW satellites.3) The Local Group galaxies and data from extragalactic surveys indicate there is a correlation between bulge-mass and the number of luminous satellites that is not predicted by the CCM. 4) The 13 new ultra-faint MW satellites define a disc-of-satellites (DoS) that is virtually identical to the DoS previously found for the 11 classical MW satellites, implying that most of the 24 MW satellites are correlated in phase-space. 5) The occurrence of two MW-type DM halo masses hosting MW-like galaxies is unlikely in the CCM. However, the properties of the Local Group galaxies provide information leading to a solution of the above problems. The DoS and bulge-satellite correlation suggest that dissipational events forming bulges are related to the processes forming phase-space correlated satellite populations. These events are well known to occur since in galaxy encounters energy and angular momentum are expelled in the form of tidal tails, which can fragment to form populations of tidal-dwarf galaxies (TDGs) and associated star clusters. If Local Group satellite galaxies are to be interpreted as TDGs then the substructure predictions of the CCM are internally in conflict. All findings thus suggest that the CCM does not account for the Local Group observations and that therefore existing as well as new viable alternatives have to be further explored. These are discussed and natural solutions for the above problems emerge.

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Section: The Evolution Of Tdgsmentioning

confidence: 77%

Local-Group tests of dark-matter concordance cosmology

Kroupa

Famaey

Boer

et al. 2010

A&A

224

301

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“…The 2007 dataset covers only the central part of the galaxy and was collected during the LBT science demonstration time (March 2007, Coleman et al 2007) with the LBC-blue, the only active "eye" at that time. Images were taken through B Bessel -and r Sloan -filters with almost no dither.…”

Section: Observationsmentioning

confidence: 99%

“…Coleman et al (2007) selected Hercules candidate members by comparing the V vs. A similar approach was followed by Simon & Geha (2007) and Deason et al (2012), who selected galaxy candidates from the SDSS data on the basis of the colours and proximity to Hercules. Figure 8 shows the spatial distribution and the CMD of our PM-selected catalogue and the evolved stars with spectroscopic measurements.…”

Section: Membership Analysis and Comparison To Previous Workmentioning

confidence: 99%

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A bag of tricks: Using proper motions of Galactic stars to identify the Hercules ultra-faint dwarf galaxy members

Fabrizio

Raimondo

Brocato

et al. 2014

A&A

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Context. Discovered in the last decade as overdensities of resolved stars, the ultra-faint dwarfs (UFDs) are among the least luminous, most dark-matter dominated, and most metal-poor galaxies known today. They appear as sparse, loose objects with high mass-to-light ratios. Hercules is the prototype of the UFD galaxies. To date, there are still no firm constraints on its total luminosity due to the difficulty of disentangling Hercules bona-fide stars from the severe Galactic field contamination. Aims. To better constrain Hercules properties, we aim at removing foreground and background contaminants in the galaxy field using the proper motions of the Milky Way stars and the colour-colour diagram. Methods. We have obtained images of Hercules in the r Sloan , B Bessel and U spec bands with the Large Binocular Telescope (LBT) and LBC-BIN mode capabilities. The r Sloan new dataset combined with data from the LBT archive span a time baseline of about 5 yr, allowing us to measure proper motions of stars in the Hercules direction for the first time. The U spec data along with existing LBT photometry allowed us to use colour-colour diagram to further remove the field contamination.Results. Thanks to a highly-accurate procedure to derive the r Sloan -filter geometric distortion solution for the LBC-red, we were able to measure stellar relative proper motions to a precision of better than 5 mas yr −1 down to r Sloan 22 mag and disentangle a significant fraction (>90%) of Milky Way contaminants. We ended up with a sample of 528 sources distributed over a large portion of the galaxy body (∼0.12 deg 2 ). Of these sources, 171 turned out to be background galaxies and additional foreground stars from the analysis of the U spec − B Bessel vs. B Bessel − r Sloan colour-colour diagram. This leaves us with a sample of 357 likely members of the Hercules UFD. We compared the cleaned colour-magnitude diagram (CMD) with evolutionary models and synthetic CMDs, confirming the presence in Hercules of an old population (t = 12 ± 2 Gyr) with wide spread metallicity (−3.3 < [Fe/H] < −1.8). Conclusions. Our procedure to estimate star proper motions proved to be a very effective way to identify likely members for stellar systems as far as 130 kpc. The present selection, based on both proper motions and colour-colour diagram, provides a robust identification of Hercules members and a new target list for more spectroscopic investigations.

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“…These ultrafaint dSphs tend to have very high M/L ratios (Muñoz et al 2006b, Simon & Geha 2007) that point to a common dSph mass scale (Strigari et al 2008), which may arise from some critical scale in the formation of galaxies or a characteristic scale for the clustering of DM. But a few ultrafaints show evidence for tidal disruption and dynamical instability (e.g., Coleman et al 2007) and may represent exceptions to the common mass scale (Adén et al 2009). …”

Section: Wide Field Photometric Surveys In the Coming Decadementioning

confidence: 99%

The Future of Stellar Populations Studies in the Milky Way and the Local Group

Majewski

2009

Proc. IAU

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Abstract. The last decade has seen enormous progress in understanding the structure of the Milky Way and neighboring galaxies via the production of large-scale digital surveys of the sky like 2MASS and SDSS, as well as specialized, counterpart imaging surveys of other Local Group systems. Apart from providing snaphots of galaxy structure, these "cartographic" surveys lend insights into the formation and evolution of galaxies when supplemented with additional data (e.g., spectroscopy, astrometry) and when referenced to theoretical models and simulations of galaxy evolution. These increasingly sophisticated simulations are making ever more specific predictions about the detailed chemistry and dynamics of stellar populations in galaxies. To fully exploit, test and constrain these theoretical ventures demands similar commitments of observational effort as has been plied into the previous imaging surveys to fill out other dimensions of parameter space with statistically significant intensity. Fortunately the future of large-scale stellar population studies is bright with a number of grand projects on the horizon that collectively will contribute a breathtaking volume of information on individual stars in Local Group galaxies. These projects include: (1) additional imaging surveys, such as Pan-STARRS, SkyMapper and LSST, which, apart from providing deep, multicolor imaging, yield time series data useful for revealing variable stars (including critical standard candles, like RR Lyrae variables) and creating large-scale, deep proper motion catalogs; (2) higher accuracy, space-based astrometric missions, such as Gaia and SIM-Lite, which stand to provide critical, high precision dynamical data on stars in the Milky Way and its satellites; and (3) large-scale spectroscopic surveys provided by RAVE, APOGEE, HERMES, LAMOST, and the Gaia spectrometer, which will yield not only enormous numbers of stellar radial velocities, but extremely comprehensive views of the chemistry of stellar populations. Meanwhile, previously dust-obscured regions of the Milky Way will continue to be systematically exposed via large infrared surveys underway or on the way, such as the various GLIMPSE surveys from Spitzer's IRAC instrument, UKIDSS, APOGEE, JASMINE and WISE.

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The Elongated Structure of the Hercules Dwarf Spheroidal Galaxy from Deep Large Binocular Telescope Imaging

Cited by 82 publications

References 18 publications

Local-Group tests of dark-matter concordance cosmology

Local-Group tests of dark-matter concordance cosmology

A bag of tricks: Using proper motions of Galactic stars to identify the Hercules ultra-faint dwarf galaxy members

The Future of Stellar Populations Studies in the Milky Way and the Local Group

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