Multi-Element Abundance Measurements From Medium-Resolution Spectra. Ii. Catalog of Stars in Milky Way Dwarf Satellite Galaxies

Kirby, Evan N.; Guhathakurta, Puragra; Simon, Joshua D.; Geha, Marla; Rockosi, Constance M.; Sneden, Christopher; Cohen, Judith G.; Sohn, Sangmo Tony; Majewski, Steven R.; Siegel, M. H.

doi:10.1088/0067-0049/191/2/352

Cited by 185 publications

(376 citation statements)

References 127 publications

(166 reference statements)

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“…At solar metallicity, the distinction remains clear between the dwarfs and the giants, but not for the sub-giants. We note though that, given the metallicity-luminosity relation (see Kirby et al 2010, for early type dwarf galaxies in the Local Group), stars with metallicities close to solar are not expected in UFDs, which are the systems for which one often needs to target stars below the HB due to their sparsely populated RGB. The figure also shows that the distinction among the different classes of objects would not be possible if one were to collapse all data onto one axis (i.e.…”

Section: The Lines and Their Sensitivitymentioning

confidence: 93%

“…Yi et al 2001;Demarque et al 2004) Because the dwarf galaxies currently studied in large spectroscopic surveys (e.g. Walker et al 2006Walker et al , 2009bSimon & Geha 2007;Adén et al 2009a;Kirby et al 2010) are distant objects, typically only the giants above the horizontal branch (HB) will be bright enough to be followed up with spectroscopy; however, in those systems that have sparsely populated RGBs, the observations often need to be pushed to fainter magnitudes, therefore below the HB (e.g. Martin et al 2007;Simon & Geha 2007).…”

Section: The Lines and Their Sensitivitymentioning

confidence: 99%

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Cleaning spectroscopic samples of stars in nearby dwarf galaxies

Battaglia

Starkenburg

2012

A&A

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Dwarf galaxies provide insight into the processes of star formation and chemical enrichment at the low end of the galaxy mass function, as well as into the clustering of dark matter on small scales. In studies of Local Group dwarf galaxies, spectroscopic samples of individual stars are used to derive the internal kinematics and abundance properties of these galaxies. It is therefore important to clean these samples from Milky Way stars, which are not related to the dwarf galaxy, since they can contaminate analysis of the properties of these objects. Here we introduce a new diagnostic for separating Milky Way contaminant stars, which mainly consist of dwarf stars, and red giant branch stars targeted in dwarf galaxies. As discriminator we use the trends in the equivalent width of the nIR Mg I line at 8806.8 Å as a function of the equivalent width of Ca II triplet lines. This method is particularly useful for works dealing with multi-object, intermediate-resolution spectroscopy focusing in the region of the nIR Ca II triplet. We use synthetic spectra to explore how the equivalent width of these lines changes for stars with different properties (gravity, effective temperature, metallicity) and find that a distinction among giants above the horizontal branch and dwarfs can be made with this method at [Fe/H] > −2 dex. For −2 ≤ [Fe/H] ≤ −1, this method is also valid for distinguishing dwarfs and giants down to approximately one magnitude below the horizontal branch. Using a foreground model we make predictions on the use of this new discrimination method for nearby dwarf spheroidal galaxies, including the ultra-faints. We subsequently use VLT/FLAMES data for the Sextans, Sculptor, and Fornax dwarf spheroidal galaxies to verify the predicted theoretical trends.

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Section: The Lines and Their Sensitivitymentioning

confidence: 93%

Section: The Lines and Their Sensitivitymentioning

confidence: 99%

Cleaning spectroscopic samples of stars in nearby dwarf galaxies

Battaglia

Starkenburg

2012

A&A

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“…One key observable of our Milky Way system is that although its halo population is α-rich (Hawkins et al 2014;Jackson-Jones et al 2014), its (classical) satellites are predominantly α-poor, with an exception for their most metal-poor components (e.g., Shetrone et al 1998Shetrone et al , 2001Shetrone et al , 2003Tolstoy et al 2003;Venn et al 2004;Koch et al 2008;Kirby et al 2010;Starkenburg et al 2013b;Jablonka et al 2015;Frebel & Norris 2015). Several modelling efforts have already pointed out that indeed such a discrepancy could arise in a stellar halo built out of few early-accreted, massive main progenitor galaxies.…”

Section: Relation Between Iron Abundance and Supernovae Type Ia Delaymentioning

confidence: 99%

“…Numerous observational studies (Shetrone et al 1998(Shetrone et al , 2001Tolstoy et al 2003;Venn et al 2004;Koch et al 2008;Tolstoy et al 2009;Kirby et al 2010) reported discrepancies between chemical abundances of satellite galaxies of the Milky Way and field halo stars. These studies show that the present-day satellites are, at least partly, unlike the building blocks of the Milky Way's stellar spheroid.…”

Section: Introductionmentioning

confidence: 99%

Building blocks of the Milky Way's accreted spheroid

Oirschot

Starkenburg

Helmi

et al. 2016

Mon. Not. R. Astron. Soc.

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In the ΛCDM model of structure formation, a stellar spheroid grows by the assembly of smaller galaxies, the so-called building blocks. Combining the Munich-Groningen semi-analytical model of galaxy formation with the high resolution Aquarius simulations of dark matter haloes, we study the assembly history of the stellar spheroids of six Milky Way-mass galaxies, focussing on building block properties such as mass, age and metallicity. These properties are compared to those of the surviving satellites in the same models. We find that the building blocks have higher star formation rates on average, and this is especially the case for the more massive objects. At high redshift these dominate in star formation over the satellites, whose star formation timescales are longer on average. These differences ought to result in a larger α-element enhancement from Type II supernovae in the building blocks (compared to the satellites) by the time Type Ia supernovae would start to enrich them in iron, explaining the observational trends. Interestingly, there are some variations in the star formation timescales of the building blocks amongst the simulated haloes, indicating that [α/Fe] abundances in spheroids of other galaxies might differ from those in our own Milky Way.

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“…The second spectroscopic sample refers to spectroscopic metallicities derived using medium-resolution spectroscopy (MRS) combined with spectral synthesis and adopted from Kirby et al (2010). Their dSph sample includes MRS metallicities for Sculptor, Sextans, Fornax, and Leo II.…”

Section: Spectroscopic 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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Multi-Element Abundance Measurements From Medium-Resolution Spectra. Ii. Catalog of Stars in Milky Way Dwarf Satellite Galaxies

Cited by 185 publications

References 127 publications

Cleaning spectroscopic samples of stars in nearby dwarf galaxies

Cleaning spectroscopic samples of stars in nearby dwarf galaxies

Building blocks of the Milky Way's accreted spheroid

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

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