Star counts in the Galaxy

Abstract

Abstract. We describe TRILEGAL, a new populations synthesis code for simulating the stellar photometry of any Galaxy field. The code attempts to improve upon several technical aspects of star count models, by: dealing with very complete input libraries of evolutionary tracks; using a stellar spectral library to simulate the photometry in virtually any broad-band system; being very versatile allowing easy changes in the input libraries and in the description of all of its ingredients -like the star formation rate, age-metallicity relation, initial mass function, and geometry of Galaxy components. In a previous paper (Groenewegen et al. 2002, Paper I), the code was first applied to describe the very deep star counts of the CDFS stellar catalogue. Here, we briefly describe its initial calibration using EIS-deep and DMS star counts, which, as we show, are adequate samples to probe both the halo and the disc components of largest scale heights (oldest ages). We then present the changes in the calibration that were necessary to cope with some improvements in the model input data, and the use of more extensive photometry datasets: now the code is shown to successfully simulate also the relatively shallower 2MASS catalogue, which probes mostly the disc at intermediate ages, and the immediate solar neighbourhood as sampled by Hipparcos -in particular its absolute magnitude versus colour diagram -, which contains a somewhat larger fraction of younger stars than deeper surveys. Remarkably, the same model calibration can reproduce well the star counts in all the above-mentioned data sets, that span from the very deep magnitudes of CDFS (16 < R < 23) to the very shallow ones of Hipparcos (V < 8). Significant deviations (above 50 percent in number counts) are found just for fields close to the Galactic Center (since no bulge component was included) and Plane, and for a single set of South Galactic Pole data. The TRILEGAL code is ready to use for the variety of wide-angle surveys in the optical/infrared that will become available in the coming years.

A Hubble Space Telescope Study of the Enigmatic Milky Way Halo Globular Cluster Crater*

“…Such stars are also likely to overlap with other parts of the CMD, notably the RGB, which can lead to confused interpretation of the stellar populations. However, the number and CMD distribution of putative foreground sources appear wellmatched to models of distribution of MW stars (e.g., Girardi et al 2005;de Jong et al 2010), allowing for straightforward accounting of intervening sources.…”

The progenitors of the Milky Way stellar halo: big bricks favoured over little bricks

“…The selection region for BHB and BS stars are shown with the blue and red polygons, respectively. We use the Trilegal Galaxy model (Girardi et al 2005) to estimate the foreground contamination included in our A-type star samples. The estimated foreground in the BHB and BS CMD selection regions is subtracted before the BS-to-BHB fractions are computed.…”

The MAGellanic Inter-Cloud (MAGIC) project – II. Slicing up the Bridge

“…We integrated the flux in the CMD subtracting the flux contribution from foreground MW halo giants and metal-poor MW dwarfs and from background galaxies. In order to estimate and remove the contamination, we used the predictions from the TRILEGAL Galaxy model (Girardi et al 2005) scaling the number of predicted MW stars to the number observed in our fields in those parts of the CMDs that were clearly devoid of MB InterCloud stars (see Gallart et al 2004 andNoël & for more details). The upper y-axis shows redshift for our current cosmology.…”