A maximum-likelihood method for fitting colour–magnitude diagrams

Naylor, T.; Jeffries, R. D.

doi:10.1111/j.1365-2966.2006.11099.x

Cited by 131 publications

(193 citation statements)

References 24 publications

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“…By doing it for all observed stars, one can recover the SFRs, which maximise the likelihood between data and model. It is interesting to note that in recent years there have been an increasing number of papers applying this kind of technique to a wide range of problems, which include determinating the physical parameters of stellar clusters (Jørgensen & Lindegren 2005;Naylor & Jeffries 2006;Hernandez & Valls-Gabaud 2008) and of individual stars (Nordström et al 2004;da Silva et al 2006).…”

Section: Recovering the Sfhmentioning

confidence: 99%

Recovery of the star formation history of the LMC from the VISTA survey of the Magellanic system

Kerber

Girardi

Rubele

et al. 2009

A&A

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The VISTA near infrared survey of the Magellanic System (VMC) will provide deep Y JK s photometry reaching stars in the oldest turn-off point throughout the Magellanic Clouds (MCs). As part of the preparation for the survey, we aim to access the accuracy in the star formation history (SFH) that can be expected from VMC data, in particular for the Large Magellanic Cloud (LMC). To this aim, we first simulate VMC images containing not only the LMC stellar populations but also the foreground Milky Way (MW) stars and background galaxies. The simulations cover the whole range of density of LMC field stars. We then perform aperture photometry over these simulated images, access the expected levels of photometric errors and incompleteness, and apply the classical technique of SFH-recovery based on the reconstruction of colour-magnitude diagrams (CMD) via the minimisation of a chi-squared-like statistics. We verify that the foreground MW stars are accurately recovered by the minimisation algorithms, whereas the background galaxies can be largely eliminated from the CMD analysis due to their particular colours and morphologies. We then evaluate the expected errors in the recovered star formation rate as a function of stellar age, SFR(t), starting from models with a known age-metallicity relation (AMR). It turns out that, for a given sky area, the random errors for ages older than ∼0.4 Gyr seem to be independent of the crowding. This can be explained by a counterbalancing effect between the loss of stars from a decrease in the completeness and the gain of stars from an increase in the stellar density. For a spatial resolution of ∼0.1 deg 2 , the random errors in SFR(t) will be below 20% for this wide range of ages. On the other hand, due to the lower stellar statistics for stars younger than ∼0.4 Gyr, the outer LMC regions will require larger areas to achieve the same level of accuracy in the SFR(t). If we consider the AMR as unknown, the SFHrecovery algorithm is able to accurately recover the input AMR, at the price of an increase of random errors in the SFR(t) by a factor of about 2.5. Experiments of SFH-recovery performed for varying distance modulus and reddening indicate that these parameters can be determined with (relative) accuracies of Δ(m− M) 0 ∼ 0.02 mag and ΔE B−V ∼ 0.01 mag, for each individual field over the LMC. The propagation of these errors in the SFR(t) implies systematic errors below 30%. This level of accuracy in the SFR(t) can reveal significant imprints in the dynamical evolution of this unique and nearby stellar system, as well as possible signatures of the past interaction between the MCs and the MW.

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Section: Recovering the Sfhmentioning

confidence: 99%

Recovery of the star formation history of the LMC from the VISTA survey of the Magellanic system

Kerber

Girardi

Rubele

et al. 2009

A&A

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“…For example, Naylor & Jeffries (2006) used a MLE to fit colour-magnitude diagrams, Arzner et al (2007) to improve the determination of faint X-ray spectra, Makarov et al (2006) to improve distance estimates using red giant branch stars, and López-Sanjuan et al (2008, 2009a,b, 2010b) to estimate reliable merger fractions from morphological criteria. The MLEs are based on the estimation of the most probable values of a set of parameters, which define the probability distribution that describes an observational sample.…”

Section: Of the Cosmic Variance σ Vmentioning

confidence: 99%

The ALHAMBRA survey: An empirical estimation of the cosmic variance for merger fraction studies based on close pairs

López-Sanjuan¹,

Cenarro²,

Hernández-Monteagudo³

et al. 2014

A&A

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Aims. Our goal is to estimate empirically the cosmic variance that affects merger fraction studies based on close pairs for the first time. Methods. We compute the merger fraction from photometric redshift close pairs with 10 h −1 kpc ≤ r p ≤ 50 h −1 kpc and Δv ≤ 500 km s −1 and measure it in the 48 sub-fields of the ALHAMBRA survey. We study the distribution of the measured merger fractions that follow a log-normal function and estimate the cosmic variance σ v as the intrinsic dispersion of the observed distribution. We develop a maximum likelihood estimator to measure a reliable σ v and avoid the dispersion due to the observational errors (including the Poisson shot noise term). Results. The cosmic variance σ v of the merger fraction depends mainly on (i) the number density of the populations under study for both the principal (n 1 ) and the companion (n 2 ) galaxy in the close pair and (ii) the probed cosmic volume V c . We do not find a significant dependence on either the search radius used to define close companions, the redshift, or the physical selection (luminosity or stellar mass) of the samples. Conclusions. We have estimated the cosmic variance that affects the measurement of the merger fraction by close pairs from observations. We provide a parametrisation of the cosmic variance with n 1 , n 2 , and V c , σ v ∝ n −0.54(n 2 /n 1 ) −0.37 . Thanks to this prescription, future merger fraction studies based on close pairs could properly account for the cosmic variance on their results.

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“…Several distance estimates, from 360-480 pc, are available in the literature (Claria 1982;Shobbrook 1986;Lyra et al 2006;Naylor & Jeffries 2006;van Leeuwen 2009). An accurate age of 35 ± 3 Myr has been derived from the lithium-depletion boundary (Jeffries & Oliveira 2005).…”

Section: Introductionmentioning

confidence: 99%

TheGaia-ESO survey: Discovery of a spatially extended low-mass population in the Vela OB2 association

Sacco

Jeffries

Randich

et al. 2015

A&A

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The nearby (distance ∼ 350-400 pc), rich Vela OB2 association, includes γ 2 Velorum, one of the most massive binaries in the solar neighbourhood and an excellent laboratory for investigating the formation and early evolution of young clusters. Recent Gaia-ESO survey observations have led to the discovery of two kinematically distinct populations in the young (10-15 Myr) cluster immediately surrounding γ 2 Velorum. Here we analyse the results of Gaia-ESO survey observations of NGC 2547, a 35 Myr cluster located two degrees south of γ 2 Velorum. The radial velocity distribution of lithium-rich pre-main sequence stars shows a secondary population that is kinematically distinct from and younger than NGC 2547. The radial velocities, lithium absorption lines, and the positions in a colour-magnitude diagram of this secondary population are consistent with those of one of the components discovered around γ 2 Velorum. This result shows that there is a young, low-mass stellar population spread over at least several square degrees in the Vela OB2 association. This population could have originally been part of a cluster around γ 2 Velorum that expanded after gas expulsion or formed in a less dense environment that is spread over the whole Vela OB2 region.

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A maximum-likelihood method for fitting colour–magnitude diagrams

Cited by 131 publications

References 24 publications

Recovery of the star formation history of the LMC from the VISTA survey of the Magellanic system

Recovery of the star formation history of the LMC from the VISTA survey of the Magellanic system

The ALHAMBRA survey: An empirical estimation of the cosmic variance for merger fraction studies based on close pairs

TheGaia-ESO survey: Discovery of a spatially extended low-mass population in the Vela OB2 association

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