Population effects on the red giant clump absolute magnitude, and distance determinations to nearby galaxies

By L. Girardi, Maurizio Salaris DipAst Padova, Liverpool Jmu, Mpa Garching. 2000

230 citations recorded by the source corpus.

The red giant clump has been recently argued to be a reliable distance indicator for the galaxies in the Local Group. The accuracy of distance determinations based on this method, however, depends on the possible presence of systematic magnitude differences (ΔMIRC) between the local clump revealed by the Hipparcos colour–magnitude diagram (CMD), and the clump stars observed in distant galaxies. In this paper, we re-address the problem of these systematic ‘population’ effects. First, we present tables with the theoretically predicted I-band clump magnitude as a function of age and metallicity. Simple equations, taken from basic population synthesis theory, are provided for the easy computation of the mean clump magnitude for any given galaxy model. We use our models to explain in some detail what determines the distribution of masses, ages and metallicities of clump stars in a galaxy. Such an approach has so far been neglected in the analysis of clump data related with distance determinations. We point out that, in galaxies with recent/ongoing star formation (e.g. the discs of spirals), the age distribution of clump stars is strongly biased towards younger (∼1–3 Gyr) ages, and hence towards higher metallicities. Obviously, this does not happen in galaxies with predominantly old stellar populations (e.g. ellipticals and bulges). We construct detailed models for the clump population in the local (Hipparcos) sample, the bulge, Magellanic Clouds and Carina dSph galaxy. In all cases, star formation rates and chemical enrichment histories are taken from the literature. The Hipparcos model is shown to produce distributions of metallicities, colours, and magnitudes, that are similar to those derived from spectroscopic and Hipparcos data. The bulge, Magellanic Clouds, and Carina dSph models are used to analyse the values of ΔMIRC for these different stellar systems. We show how the clump–RR Lyrae data from Udalski are well reproduced by the models. However, despite the similarity between the models and data, the models indicate that the linear ΔMIRC versus [Fe/H] relations that have been derived from the same data (such as by Udalski and Popowski) are not general. In fact, the distribution of clump stars has several factors hidden in it – e.g. the age–metallicity relation, the rate of past star formation – that cannot be described by such relations. The model behaviour is also supported by empirical data for open clusters by Sarajedini and Twarog et al. We argue that Udalski's data for Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) star clusters do not allow a good assessment of the age dependence of the clump magnitude. Moreover, we remark that similar analyses of cluster data should better include clump stars with ages 1–2 Gyr, which turn out to be very important in determining the mean clump in galaxies with recent star formation. Finally, we provide revised clump distances to the bulge, Magellanic Clouds and Carina dSph, and further comment on their reliability. The largest ΔMIRC values are found for the Magellanic Clouds and Carina dSph, which turn out to be located at distance moduli ∼0.2–0.3 mag longer than indicated by works which ignore population effects. The Galactic bulge, instead, may be slightly closer (up to 0.1 mag in distance modulus) than indicated by previous works based on the red clump, the exact result depending on the use of either scaled-solar or α-enhanced stellar models.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/233e6f9ab9348db7a909821c27bd64bf32a5a6a4

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Citations in the corpus

On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk (2014, background): “…might be affected by larger uncertainties, since we are dealing with stellar populations covering a broad range in ages and in metal abundances (Girardi & Salaris 2001; Salaris & Girardi 2002). ii) Gradients – Recent spectroscopic investigations indicate that the use of homogeneous and…”
Kinematics and history of the solar neighbourhood revisited (2009, result): “This result is similar to that of Girardi & Salaris (2001), who found that the metallicity distribution for K giants is well represented by a Gaussian with a mean of −0.12 and a dispersion of 0.18 dex.”
Evolution of Stars and Stellar Populations (2005, background): “The effect of the SFH on the HB brightness is expected to be generally smaller if one employs the I , and especially the K (when metallicities are around solar) filters, but some knowledge of the SFH is absolutely necessary for a meaningful distance determination using HB stars ([83], [179]).”
New Cepheid Period-Luminosity Relations for the Large Magellanic Cloud: 92 Near-Infrared Light Curves (2004, methodology): “The absolute astrometric calibration for the red clump method is based on a large sample of stars and is statistically more reliable than the Cepheid zero point, but this method is still relatively new, and the effects of systematics are only beginning to be explored (e.g., Girardi & Salaris 2001).”
The Milky Way Tomography with SDSS. II. Stellar Metallicity (2008, background): “A difficulty with the former hypothesis is that the implied thin-disk metallicity distribution has a mean of about −0.55, which is too metal poor by about 0.4 dex, compared to local measurements (Girardi & Salaris 2001; Nordström et al. 2004).”
Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data: Revisiting the concept of superclusters (2004, background): “15) as expected for a sample of disk giants: Girardi & Salaris (2001) found an average metallicity of [Fe/H]=−0.12 ± 0.18, while for their sample of F and G dwarfs, Nordström et al. (2004) found [Fe/H]=−0.14± 0.19.”
REDDENING AND EXTINCTION TOWARD THE GALACTIC BULGE FROM OGLE-III: THE INNER MILKY WAY'S RV ∼ 2.5 EXTINCTION CURVE (2012, methodology): “It also cannot plausibly be due to a difference in absolute magnitude, as RC stars have a metallicity-dependence of ∼0.2 mag dex−1 in I (Girardi & Salaris 2001; Pietrzyński et al. 2010), whereas from Equation 17 and as such an unphysical mean metallicity of [Fe/H]≈+1.20 would be required to…”
The Adequacy of Stellar Evolution Models for the Interpretation of the Color-Magnitude Diagrams of Resolved Stellar Populations (2005, methodology): “These data, together with that of Twarog, Anthony-Twarog & Bricker (1999) and Corsi et al. (1994), are rediscussed by Girardi (1999) and Girardi & Salaris (2001).”
The structure of the Milky Way's bar outside the bulge (2015, background): “For reference, to have formed RCGs the stars must still be & 500Myr old but galaxies with ongoing star formation have a strong bias to younger RCGs with c© 2015 RAS, MNRAS 000, 1–18 a peak of age ∼ 1Gyr (Girardi & Salaris 2001; Salaris & Girardi 2002).”
NEW OPTICAL REDDENING MAPS OF THE LARGE AND SMALL MAGELLANIC CLOUDS (2011, methodology): “The point source catalogues1 are divided into 40 fields for the SMC and 116 fields for the LMC.”
THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY. X. ULTRAVIOLET TO INFRARED PHOTOMETRY OF 117 MILLION EQUIDISTANT STARS (2014, background): “Some of the additional scatter is likely attributable to real changes in the stellar populations, since the red clump does change somewhat in brightness with metallicity, age, and He content (e.g., Cole 1998; Girardi & Salaris 2001).”
Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS II. The complete high resolution extinction map and implications for Galactic bulge studies (2012, unknown): “The influence of population effects on the RC magnitudes and color has been investigated both theoretically (Girardi & Salaris 2001; Salaris & Girardi 2002) and observationally (Alves 2000; Grocholski & Sarajedini 2002; Pietrzyński et al. 2003; Laney et al. 2012).”
Calibration of the Tip of the Red Giant Branch (2003, background): “Unlike the case for TRGB stars, the evolutionary tracks for red clump stars are well known to be strong functions of both age and metallicity (see, for example, Girardi & Salaris 2001; Williams et al. 2009).”
A RADIAL AGE GRADIENT IN THE GEOMETRICALLY THICK DISK OF THE MILKY WAY (2016, background): “The age distribution of RC and RGB stars tends to be biased toward younger ages, but the strength of the effect depends on the stellar evolutionary phase and the local star formation history (Girardi & Salaris 2001; Bovy et al. 2014; Hayden et al. 2015).”
A COLD NEPTUNE-MASS PLANET OGLE-2007-BLG-368Lb: Cold neptunes are common (2009, methodology): “…adopt the intrinsic RCG magnitude MI,RC,0 = −0.25±0.05, MV,RC,0 = 0.79±0.08 and color (V −I)RC,0 = 1.04±0.08 from Bennett et al. (2008) which is based on Girardi & Salaris (2001) and Salaris & Girardi (2002), where the error is assigned based on the size of the theoretical corrections to the RCG…”
ARGOS - III. Stellar populations in the Galactic bulge of the Milky Way (2012, result): “We note that theory predicts a metallicity dependence of the absolute magnitude of the clump (i.e. Girardi & Salaris 2001) and this has been supported by earlier observations (i.e. Sarajedini 1999; Twarog, Anthony-Twarog, & Bricker 1999).”