Internal Kinematics of the Fornax Dwarf Spheroidal Galaxy

Walker, Matthew G.; Mateo, Mario; Olszewski, Edward W.; Bernstein, R. A.; Wang, Xiao; Woodroofe, Michael

doi:10.1086/500193

Cited by 216 publications

(298 citation statements)

References 65 publications

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“…The ratio between the stellar and dark core radii r stars c /r halo c ranges between 0.2 and 0.5, indicating a spatial segregation of the stars relative to the dark halo, as discussed in (Peñarrubia et al 2008). Additionally, the line-of-sight stellar velocity dispersion profiles are flat in the enclosed within the core radii, with 6 to 10 km/s, corresponding to the least and the most massive dSph, respectively, hence well within the observed range (Walker et al 2006a;Muñoz et al 2006;Battaglia et al 2008a;Walker et al 2006b). …”

Section: Mass Profiles and Velocity Dispersionssupporting

confidence: 70%

The dynamical and chemical evolution of dwarf spheroidal galaxies

Revaz¹,

Jablonka

Sawala

et al. 2009

A&A

124

168

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We present a large sample of fully self-consistent hydrodynamical Nbody/Tree-SPH simulations of isolated dwarf spheroidal galaxies (dSphs). It has enabled us to identify the key physical parameters and mechanisms at the origin of the observed variety in the Local Group dSph properties. The initial total mass (gas + dark matter) of these galaxies is the main driver of their evolution. Star formation (SF) occurs in series of short bursts. In massive systems, the very short intervals between the SF peaks mimic a continuous star formation rate, while less massive systems exhibit well separated SF bursts, as identified observationally. The delay between the SF events is controlled by the gas cooling time dependence on galaxy mass. The observed global scaling relations, luminosity-mass and luminosity-metallicity, are reproduced with low scatter. We take advantage of the unprecedentedly large sample size and data homogeneity of the ESO Large Programme DART, and add to it a few independent studies, to constrain the star formation history of five Milky Way dSphs, Sextans, LeoII, Carina, Sculptor and Fornax. For the first time, [Mg/Fe] vs [Fe/H] diagrams derived from high-resolution spectroscopy of hundreds of individual stars are confronted with model predictions. We find that the diversity in dSph properties may well result from intrinsic evolution. We note, however, that the presence of gas in the final state of our simulations, of the order of what is observed in dwarf irregulars, calls for removal by external processes.

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Section: Mass Profiles and Velocity Dispersionssupporting

confidence: 70%

The dynamical and chemical evolution of dwarf spheroidal galaxies

Revaz¹,

Jablonka

Sawala

et al. 2009

A&A

124

168

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“…We then estimated the RV spreads σ RA and σ Dec as a function of distance from the GC center with their errors. We used the maximum likelihood estimation method (MLE) with the likelihood formulation described by Pryor & Meylan (1993), Walker et al (2006) and Martin et al (2007), which takes into account the errors on measurements as well. The actual errors on the RV dispersions in each radial bin are of about 0.4-1.4 km s −1 .…”

Section: Measurement Of Derived Quantitiesmentioning

confidence: 99%

“…We employed an MLE analysis of the 18 simulated GCs using the strict and loose membership criteria described above. We used the likelihood estimator described by Pryor & Meylan (1993), Walker et al (2006), and Martin et al (2007), which takes into account the highly variable errors, and we computed the most probable parallax and its error δ . The result is displayed in Table 4.…”

Section: Parallaxesmentioning

confidence: 99%

Globular clusters with Gaia

Pancino

Bellazzini

Giuffrida

et al. 2017

Mon. Not. R. Astron. Soc.

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The treatment of crowded fields in Gaia data will only be a reality in a few years from now. In particular, for globular clusters, only the end-of-mission data (public in 2022-2023) will have the necessary full crowding treatment and will reach sufficient quality for the faintest stars. As a consequence, the work on the deblending and decontamination pipelines is still ongoing. We describe the present status of the pipelines for different Gaia instruments, and we model the end-of-mission crowding errors on the basis of available information. We then apply the nominal post-launch Gaia performances, appropriately worsened by the estimated crowding errors, to a set of 18 simulated globular clusters with different concentration, distance, and field contamination. We conclude that there will be 10 3 -10 4 stars with astrometric performances virtually untouched by crowding (contaminated by <1 mmag) in the majoritiy of clusters. The most limiting factor will be field crowding, not cluster crowding: the most contaminated clusters will only contain 10-100 clean stars. We also conclude that: (i) the systemic proper motions and parallaxes will be determined to 1% or better up to 15 kpc, and the nearby clusters will have radial velocities to a few km s −1 ; (ii) internal kinematics will be of unprecendented quality, cluster masses will be determined to 10% up to 15 kpc and beyond, and it will be possible to identify differences of a few km s −1 or less in the kinematics (if any) of cluster sub-populations up to 10 kpc and beyond; (iii) the brightest stars (V 17 mag) will have space-quality, wide-field photometry (mmag errors), and all Gaia photometry will have 1-3% errors on the absolute photometric calibration.

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“…We refer to these works for further details on the photometric observations and analysis. In all the studied dSphs the final photometric datasets are placed on a common V, I photometry scale in the Johnsons-Cousins photometric system (Carina: Walker et al 2007; Fornax: Walker et al 2006;Leo II: Bellazzini et al 2005; Sextans: Lee et al 2003;Sculptor: Walker et al 2006;Coleman et al 2005). We note that for Carina, Fornax, and 5 Gyr, a range in metallicities from −2.5 to −1 dex, and a step size of 0.5 dex.…”

Section: Photometric Samplementioning

confidence: 99%

Spectroscopic versus photometric metallicities: Milky Way dwarf spheroidal companions as a test case

Lianou

Grebel

Koch

2011

A&A

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Aims. The method of deriving photometric metallicities using red giant branch stars is applied to resolved stellar populations under the common assumption that they mainly consist of single-age old stellar populations. We explore the effect of the presence of mixed-age stellar populations on deriving photometric metallicities. Methods. We use photometric data sets for the five Galactic dwarf spheroidals Sculptor, Sextans, Carina, Fornax, and Leo II in order to derive their photometric metallicity distribution functions from their resolved red giant branches using isochrones of the Dartmouth Stellar Evolutionary Database. We compare the photometric metallicities with published spectroscopic metallicities based on the analysis of the near-infrared Ca triplet (Ca T), both on the metallicity scale of Carretta & Gratton and on the scale defined by the Dartmouth isochrones. In addition, we compare the photometric metallicities with published spectroscopic metallicities based on spectral synthesis and medium-resolution spectroscopy, and on high resolution spectra where available. Results. The mean properties of the spectroscopic and photometric metallicity samples are comparable within the intrinsic scatter of each method although the mean metallicities of dSphs with pronounced intermediate-age population fractions may be underestimated by the photometric method by up to a few tenths of dex in [Fe/H]. The star-by-star differences of the spectroscopic minus the photometric metallicities show a wide range of values along the fiducial spectroscopic metallicity range, with the tendency to have systematically lower photometric metallicities for those dwarf spheroidals with a higher fraction of intermediate-age populations. Such discrepancies persist even in the case of the purely old Sculptor dSph, where one would naïvely expect a very good match when comparing with medium or low resolution metallicity measurements. Overall, the agreement between Ca T metallicities and photometric metallicities is very good in the metallicity range from ∼−2 dex to ∼−1.5 dex. We find that the photometric method is reliable in galaxies that contain small (less than 15%) intermediate-age stellar fractions. Therefore, in the presence of mixed-age stellar populations, one needs to quantify the fraction of the intermediate-age stars in order to assess their effect on determining metallicities from photometry alone. Finally, we note that the comparison of spectroscopic metallicities of the same stars obtained with different methods reveals similarly large discrepancies as the comparison with photometric metallicities.

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Internal Kinematics of the Fornax Dwarf Spheroidal Galaxy

Cited by 216 publications

References 65 publications

The dynamical and chemical evolution of dwarf spheroidal galaxies

The dynamical and chemical evolution of dwarf spheroidal galaxies

Globular clusters with Gaia

Spectroscopic versus photometric metallicities: Milky Way dwarf spheroidal companions as a test case

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