An inverse method to interpret colour-magnitude diagrams

Vergely, Jean‐Luc; Köppen, J.; Egret, D.; Bienaymé, O.

doi:10.1051/0004-6361:20020334

Cited by 52 publications

(77 citation statements)

References 27 publications

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“…By assuming the hypothesis that the two stars are physically associated, i.e. have the same distance, the latter E(b − y) value is coherent with the results of the analysis by Vergely et al (1998) of the interstellar extinction in the solar neighbourhood.…”

Section: Photometrysupporting

confidence: 75%

HD 174005: Another binary classified asλBootis

Faraggiana

Gerbaldi

Bonifacio

2001

A&A

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Section: Photometrysupporting

confidence: 75%

HD 174005: Another binary classified asλBootis

Faraggiana

Gerbaldi

Bonifacio

2001

A&A

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“…This correction for radiative transfer depends logarithmically on 1/τ ⊥ at low optical depth (yielding a variation ∝ R if Σ is an exponential -see Elmegreen & Parravano (1994)), varying by ∼ 50% for τ ⊥ ∼ 0.1 − 1. For simplicity, we neglect variations in J FUV associated with the radiative transfer here; we shall simply assume Fuchs et al (2009) (see also Bertelli & Nasi 2001;Vergely et al 2002) find that the Solar-neighborhood value of the surface star formation rate Σ SFR,0 is 2.5 × 10 −9 M ⊙ pc −2 yr −1 , which then yields…”

Section: Thermal Equilibrium Of Diffuse Gasmentioning

confidence: 99%

“…This simply reflects the fact that Σ SF R,0 < ∼ 10 −9 M ⊙ pc −2 yr −1 if Σ GBC < ∼ 2 M ⊙ pc −2 and t SF = 2 × 10 9 yr, whereas observational estimates of Σ SF R,0 are higher by a factor ∼ 2 (Bertelli & Nasi 2001;Vergely et al 2002;Fuchs et al 2009). It is uncertain whether this discrepancy is the result of an underestimate of the local Σ GBC , an overestimate of the local Σ SFR , or a lower local value for t SF than the mean extragalactic value.…”

mentioning

confidence: 98%

Regulation of Star Formation Rates in Multiphase Galactic Disks: A Thermal/Dynamical Equilibrium Model

Ostriker¹,

McKee²,

Leroy³

2010

ApJ

373

544

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We develop a model for the regulation of galactic star formation rates Σ SFR in disk galaxies, in which ISM heating by stellar UV plays a key role. By requiring that thermal and (vertical) dynamical equilibrium are simultaneously satisfied within the diffuse gas, and that stars form at a rate proportional to the mass of the self-gravitating component, we obtain a prediction for Σ SFR as a function of the total gaseous surface density Σ and the midplane density of stars + dark matter ρ sd . The physical basis of this relationship is that the thermal pressure in the diffuse ISM, which is proportional to the UV heating rate and therefore to Σ SFR , must adjust until it matches the midplane pressure value set by the vertical gravitational field. Our model applies to regions where Σ < ∼ 100 M ⊙ pc −2 . In low-Σ SFR (outer-galaxy) regions where diffuse gas dominates, the theory predicts that Σ SFR ∝ Σ √ ρ sd . The decrease of thermal equilibrium pressure when Σ SFR is low implies, consistent with observations, that star formation can extend (with declining efficiency) to large radii in galaxies, rather than having a sharp cutoff at a fixed value of Σ. The main parameters entering our model are the ratio of thermal pressure to total pressure in the diffuse ISM, the fraction of diffuse gas that is in the warm phase, and the star formation timescale in self-gravitating clouds; all of these are (at least in principle) direct observables. At low surface density, our model depends on the ratio of the mean midplane FUV intensity (or thermal pressure in the diffuse gas) to the star formation rate, which we set based on Solar neighborhood values. We compare our results to recent observations, showing good agreement overall for azimuthally-averaged data in a set of spiral galaxies. For the large flocculent spiral galaxies NGC 7331 and NGC 5055, the correspondence between theory and observation is remarkably close.

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“…Additionally, for the stars between the limits and outside the orange regions, a 3σ clipping in color-at fixed magnitude-is used to exclude outliers. We use this new technique instead of the one described in the above work or CMD template fitting (see e.g., Harris & Zaritsky 2001;Dolphin 2002;Ng et al 2002;Vergely et al 2002;Cignoni et al 2006;Aparicio & Hidalgo 2009) because for our problem, repeatedly simulating individual CMDs is less computationally intensive than computing the tables of likelihood functions required for the Gennaro et al (2015) approach or the CMD templates required for the template fitting approach. The mechanics of the fitting procedure can be broken into two largely independent parts: a function for quantitatively comparing CMDs, and an algorithm for using that comparison to explore a probability distribution.…”

Section: Fitting Techniquementioning

confidence: 99%

Evidence of a Non-universal Stellar Initial Mass Function. Insights from HST Optical Imaging of Six Ultra-faint Dwarf Milky Way Satellites^∗

Gennaro

Tchernyshyov

Brown

et al. 2018

ApJ

103

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Using deep observations obtained with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST), we demonstrate that the sub-solar stellar initial mass function (IMF) of six ultra-faint dwarf Milky Way satellites (UFDs) is more bottom light than the IMF of the Milky Way disk. Our data have a lowermass limit of ∼0.45 M e , while the upper limit is ∼0.8 M e , set by the turnoff mass of these old, metal-poor systems. If formulated as a single power law, we obtain a shallower IMF slope than the Salpeter value of −2.3, ranging from −1.01 for Leo IV to −1.87 for BoötesI. The significance of these deviations depends on the galaxy and is typically 95% or more. When modeled as a log-normal, the IMF fit results in a higher peak mass than in the Milky Way disk, but a Milky Way disk value for the characteristic system mass (∼0.22 M e ) is excluded at only 68% significance, and only for some UFDs in the sample. We find that the IMF slope correlates well with the galaxy mean metallicity, and to a lesser degree, with the velocity dispersion and the total mass. The strength of the observed correlations is limited by shot noise in the number of observed stars, but future space-based missions like the James Webb Space Telescope (JWST) and the Wide-Field Infrared Survey Telescope (WFIRST) will enhance both the number of dwarf Milky Way satellites that can be studied in such detail and the observation depth for individual galaxies.

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An inverse method to interpret colour-magnitude diagrams

Cited by 52 publications

References 27 publications

HD 174005: Another binary classified asλBootis

HD 174005: Another binary classified asλBootis

Regulation of Star Formation Rates in Multiphase Galactic Disks: A Thermal/Dynamical Equilibrium Model

Evidence of a Non-universal Stellar Initial Mass Function. Insights from HST Optical Imaging of Six Ultra-faint Dwarf Milky Way Satellites^∗

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An inverse method to interpret colour-magnitude diagrams

Cited by 52 publications

References 27 publications

HD 174005: Another binary classified asλBootis

HD 174005: Another binary classified asλBootis

Regulation of Star Formation Rates in Multiphase Galactic Disks: A Thermal/Dynamical Equilibrium Model

Evidence of a Non-universal Stellar Initial Mass Function. Insights from HST Optical Imaging of Six Ultra-faint Dwarf Milky Way Satellites∗

Contact Info

Product

Resources

About

Evidence of a Non-universal Stellar Initial Mass Function. Insights from HST Optical Imaging of Six Ultra-faint Dwarf Milky Way Satellites^∗