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Title: The LMC geometry and outer stellar populations from early DES data

Abstract

The Dark Energy Camera has captured a large set of images as part of Science Verification (SV) for the Dark Energy Survey (DES). The SV footprint covers a large portion of the outer Large Magellanic Cloud (LMC), providing photometry 1.5 mag fainter than the main sequence turn-off of the oldest LMC stellar population. We derive geometrical and structural parameters for various stellar populations in the LMC disc. For the distribution of all LMC stars, we find an inclination of i = -38 degrees.14 +/- 0 degrees.08 (near side in the north) and a position angle for the line of nodes of theta(0) = 129 degrees.51 +/- 0 degrees.17. We find that stars younger than similar to 4 Gyr are more centrally concentrated than older stars. Fitting a projected exponential disc shows that the scale radius of the old populations is R->4Gyr = 1.41 +/- 0.01 kpc, while the younger population has R-<4Gyr = 0.72 +/- 0.01 kpc. However, the spatial distribution of the younger population deviates significantly from the projected exponential disc model. The distribution of old stars suggests a large truncation radius of R-t = 13.5 +/- 0.8 kpc. If this truncation is dominated by the tidal field ofmore » the Galaxy, we find that the LMC is similar or equal to 24(-6)(+9) times less massive than the encircled Galactic mass. By measuring the Red Clump peak magnitude and comparing with the best-fitting LMC disc model, we find that the LMC disc is warped and thicker in the outer regions north of the LMC centre. Our findings may either be interpreted as a warped and flared disc in the LMC outskirts, or as evidence of a spheroidal halo component.« less

Authors:
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Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
OSTI Identifier:
1342914
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Monthly Notices of the Royal Astronomical Society; Journal Volume: 449; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS

Citation Formats

Balbinot, E., Santiago, B. X., Girardi, L., Pieres, A., da Costa, L. N., Maia, M. A. G., Gruendl, R. A., Walker, A. R., Yanny, B., Drlica-Wagner, A., Benoit-Levy, A., Abbott, T. M. C., Allam, S. S., Annis, J., Bernstein, J. P., Bernstein, R. A., Bertin, E., Brooks, D., Buckley-Geer, E., Rosell, A. C., Cunha, C. E., DePoy, D. L., Desai, S., Diehl, H. T., Doel, P., Estrada, J., Evrard, A. E., Neto, A. F., Finley, D. A., Flaugher, B., Frieman, J. A., Gruen, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Lahav, O., March, M., Marshall, J. L., Miller, C., Miquel, R., Ogando, R., Peoples, J., Plazas, A., Scarpine, V., Schubnell, M., Sevilla-Noarbe, I., Smith, R. C., Soares-Santos, M., Suchyta, E., Swanson, M. E. C., Tarle, G., Tucker, D. L., Wechsler, R., and Zuntz, J.. The LMC geometry and outer stellar populations from early DES data. United States: N. p., 2015. Web. doi:10.1093/mnras/stv356.
Balbinot, E., Santiago, B. X., Girardi, L., Pieres, A., da Costa, L. N., Maia, M. A. G., Gruendl, R. A., Walker, A. R., Yanny, B., Drlica-Wagner, A., Benoit-Levy, A., Abbott, T. M. C., Allam, S. S., Annis, J., Bernstein, J. P., Bernstein, R. A., Bertin, E., Brooks, D., Buckley-Geer, E., Rosell, A. C., Cunha, C. E., DePoy, D. L., Desai, S., Diehl, H. T., Doel, P., Estrada, J., Evrard, A. E., Neto, A. F., Finley, D. A., Flaugher, B., Frieman, J. A., Gruen, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Lahav, O., March, M., Marshall, J. L., Miller, C., Miquel, R., Ogando, R., Peoples, J., Plazas, A., Scarpine, V., Schubnell, M., Sevilla-Noarbe, I., Smith, R. C., Soares-Santos, M., Suchyta, E., Swanson, M. E. C., Tarle, G., Tucker, D. L., Wechsler, R., & Zuntz, J.. The LMC geometry and outer stellar populations from early DES data. United States. doi:10.1093/mnras/stv356.
Balbinot, E., Santiago, B. X., Girardi, L., Pieres, A., da Costa, L. N., Maia, M. A. G., Gruendl, R. A., Walker, A. R., Yanny, B., Drlica-Wagner, A., Benoit-Levy, A., Abbott, T. M. C., Allam, S. S., Annis, J., Bernstein, J. P., Bernstein, R. A., Bertin, E., Brooks, D., Buckley-Geer, E., Rosell, A. C., Cunha, C. E., DePoy, D. L., Desai, S., Diehl, H. T., Doel, P., Estrada, J., Evrard, A. E., Neto, A. F., Finley, D. A., Flaugher, B., Frieman, J. A., Gruen, D., Honscheid, K., James, D., Kuehn, K., Kuropatkin, N., Lahav, O., March, M., Marshall, J. L., Miller, C., Miquel, R., Ogando, R., Peoples, J., Plazas, A., Scarpine, V., Schubnell, M., Sevilla-Noarbe, I., Smith, R. C., Soares-Santos, M., Suchyta, E., Swanson, M. E. C., Tarle, G., Tucker, D. L., Wechsler, R., and Zuntz, J.. Sat . "The LMC geometry and outer stellar populations from early DES data". United States. doi:10.1093/mnras/stv356.
@article{osti_1342914,
title = {The LMC geometry and outer stellar populations from early DES data},
author = {Balbinot, E. and Santiago, B. X. and Girardi, L. and Pieres, A. and da Costa, L. N. and Maia, M. A. G. and Gruendl, R. A. and Walker, A. R. and Yanny, B. and Drlica-Wagner, A. and Benoit-Levy, A. and Abbott, T. M. C. and Allam, S. S. and Annis, J. and Bernstein, J. P. and Bernstein, R. A. and Bertin, E. and Brooks, D. and Buckley-Geer, E. and Rosell, A. C. and Cunha, C. E. and DePoy, D. L. and Desai, S. and Diehl, H. T. and Doel, P. and Estrada, J. and Evrard, A. E. and Neto, A. F. and Finley, D. A. and Flaugher, B. and Frieman, J. A. and Gruen, D. and Honscheid, K. and James, D. and Kuehn, K. and Kuropatkin, N. and Lahav, O. and March, M. and Marshall, J. L. and Miller, C. and Miquel, R. and Ogando, R. and Peoples, J. and Plazas, A. and Scarpine, V. and Schubnell, M. and Sevilla-Noarbe, I. and Smith, R. C. and Soares-Santos, M. and Suchyta, E. and Swanson, M. E. C. and Tarle, G. and Tucker, D. L. and Wechsler, R. and Zuntz, J.},
abstractNote = {The Dark Energy Camera has captured a large set of images as part of Science Verification (SV) for the Dark Energy Survey (DES). The SV footprint covers a large portion of the outer Large Magellanic Cloud (LMC), providing photometry 1.5 mag fainter than the main sequence turn-off of the oldest LMC stellar population. We derive geometrical and structural parameters for various stellar populations in the LMC disc. For the distribution of all LMC stars, we find an inclination of i = -38 degrees.14 +/- 0 degrees.08 (near side in the north) and a position angle for the line of nodes of theta(0) = 129 degrees.51 +/- 0 degrees.17. We find that stars younger than similar to 4 Gyr are more centrally concentrated than older stars. Fitting a projected exponential disc shows that the scale radius of the old populations is R->4Gyr = 1.41 +/- 0.01 kpc, while the younger population has R-<4Gyr = 0.72 +/- 0.01 kpc. However, the spatial distribution of the younger population deviates significantly from the projected exponential disc model. The distribution of old stars suggests a large truncation radius of R-t = 13.5 +/- 0.8 kpc. If this truncation is dominated by the tidal field of the Galaxy, we find that the LMC is similar or equal to 24(-6)(+9) times less massive than the encircled Galactic mass. By measuring the Red Clump peak magnitude and comparing with the best-fitting LMC disc model, we find that the LMC disc is warped and thicker in the outer regions north of the LMC centre. Our findings may either be interpreted as a warped and flared disc in the LMC outskirts, or as evidence of a spheroidal halo component.},
doi = {10.1093/mnras/stv356},
journal = {Monthly Notices of the Royal Astronomical Society},
number = 1,
volume = 449,
place = {United States},
year = {Sat Mar 14 00:00:00 EDT 2015},
month = {Sat Mar 14 00:00:00 EDT 2015}
}
  • The Dark Energy Camera has captured a large set of images as part of Science Verification (SV) for the Dark Energy Survey. The SV footprint covers a large portion of the outer Large Magellanic Cloud (LMC), providing photometry 1.5 magnitudes fainter than the main sequence turn-off of the oldest LMC stellar population. We derive geometrical and structural parameters for various stellar populations in the LMC disc. For the distribution of all LMC stars, we find an inclination of i = –38.14°±0.08° (near side in the North) and a position angle for the line of nodes of θ₀ = 129.51°±0.17°. Wemore » find that stars younger than ~4 Gyr are more centrally concentrated than older stars. Fitting a projected exponential disc shows that the scale radius of the old populations is R >4Gyr = 1.41 ± 0.01 kpc, while the younger population has R <4Gyr = 0.72 ± 0.01 kpc. However, the spatial distribution of the younger population deviates significantly from the projected exponential disc model. The distribution of old stars suggests a large truncation radius of R t = 13.5 ± 0.8 kpc. If this truncation is dominated by the tidal field of the Galaxy, we find that the LMC is ≃24 +9 –6 times less massive than the encircled Galactic mass. By measuring the Red Clump peak magnitude and comparing with the best-fit LMC disc model, we find that the LMC disc is warped and thicker in the outer regions north of the LMC centre. As a result, our findings may either be interpreted as a warped and flared disc in the LMC outskirts, or as evidence of a spheroidal halo component.« less
  • The Dark Energy Camera has captured a large set of images as part of Science Verification (SV) for the Dark Energy Survey (DES). The SV footprint covers a large portion of the outer Large Magellanic Cloud (LMC), providing photometry 1.5 mag fainter than the main sequence turn-off of the oldest LMC stellar population. We derive geometrical and structural parameters for various stellar populations in the LMC disc. For the distribution of all LMC stars, we find an inclination of i = -38°.14 ± 0°.08 (near side in the north) and a position angle for the line of nodes of θmore » 0 = 129°.51 ± 0°.17. We also found that stars younger than ~4 Gyr are more centrally concentrated than older stars. Fitting a projected exponential disc shows that the scale radius of the old populations is R >4 Gyr = 1.41 ± 0.01 kpc, while the younger population has R <4 Gyr = 0.72 ± 0.01 kpc. However, the spatial distribution of the younger population deviates significantly from the projected exponential disc model. The distribution of old stars suggests a large truncation radius of R t = 13.5 ± 0.8 kpc. Furthermore, if this truncation is dominated by the tidal field of the Galaxy, we find that the LMC is ≃24 +9 -6 times less massive than the encircled Galactic mass. By measuring the Red Clump peak magnitude and comparing with the best-fitting LMC disc model, we find that the LMC disc is warped and thicker in the outer regions north of the LMC centre. Our findings may either be interpreted as a warped and flared disc in the LMC outskirts, or as evidence of a spheroidal halo component.« less
  • We report the discovery of an X-ray/UV stellar flare from the source LMC 335, captured by XMM-Newton in the field of the Large Magellanic Cloud. The flare event was recorded continuously in X-ray for its first 10 hr from the precursor to the late decay phases. The observed fluxes increased by more than two orders of magnitude at its peak in X-ray and at least one in the UV as compared to quiescence. The peak 0.1-7.0 keV X-ray flux is derived from the two-temperature APEC model to be {approx}(8.4 {+-} 0.6) Multiplication-Sign 10{sup -12} erg cm{sup -2} s{sup -1}. Combiningmore » astrometric information from multiple X-ray observations in the quiescent and flare states, we identify the NIR counterpart of LMC 335 as the Two Micron All Sky Survey source J05414534-6921512. The NIR color relations and spectroscopic parallax characterize the source as a Galactic K7-M4 dwarf at a foreground distance of (100-264) pc, implying a total energy output of the entire event of {approx}(0.4-2.9) Multiplication-Sign 10{sup 35} erg. This report comprises detailed analyses of this late-K/early-M dwarf flare event that has the longest time coverage yet reported in the literature. The flare decay can be modeled with two exponential components with timescales of {approx}28 minutes and {approx}4 hr, with a single-component decay firmly ruled out. The X-ray spectra during flare can be described by two components, a dominant high-temperature component of {approx}40-60 MK and a low-temperature component of {approx}10 MK, with a flare loop length of about 1.1-1.3 stellar radius.« less
  • The Large Magellanic Cloud (LMC) harbors a rich and diverse system of star clusters, whose ages, chemical abundances, and positions provide information about the LMC history of star formation. We use Science Verification imaging data from the Dark Energy Survey to increase the census of known star clusters in the outer LMC and to derive physical parameters for a large sample of such objects using a spatially and photometrically homogeneous data set. Our sample contains 255 visually identified cluster candidates, of which 109 were not listed in any previous catalog. We quantify the crowding effect for the stellar sample producedmore » by the DES Data Management pipeline and conclude that the stellar completeness is < 10% inside typical LMC cluster cores. We therefore develop a pipeline to sample and measure stellar magnitudes and positions around the cluster candidates using DAOPHOT. We also implement a maximum-likelihood method to fit individual density profiles and colour-magnitude diagrams. For 117 (from a total of 255) of the cluster candidates (28 uncatalogued clusters), we obtain reliable ages, metallicities, distance moduli and structural parameters, confirming their nature as physical systems. The distribution of cluster metallicities shows a radial dependence, with no clusters more metal-rich than [Fe/H] ~ -0.7 beyond 8 kpc from the LMC center. Furthermore, the age distribution has two peaks at ≃ 1.2 Gyr and ≃ 2.7 Gyr.« less
  • The study of stellar populations in early-type galaxies in different environments is a powerful tool for constraining their star formation histories. This study has been traditionally restricted to the optical range, where dwarfs around the turn-off and stars at the base of the red giant branch dominate the integrated light at all ages. The near-infrared spectral range is especially interesting since in the presence of an intermediate-age population, asymptotic giant branch stars are the main contributors. In this Letter, we measure the near-infrared indices Na I and D {sub CO} for a sample of 12 early-type galaxies in low-density environmentsmore » and compare them with the Fornax galaxy sample presented by Silva et al.. The analysis of these indices in combination with Lick/IDS indices in the optical range reveals that (1) the Na I index is a metallicity indicator as good as C4668 in the optical range, and (2) D {sub CO} is a tracer of intermediate-age stellar populations. We find that low-mass galaxies in low-density environments show higher Na I and D {sub CO} than those located in the Fornax cluster, which points toward a late stage of star formation for the galaxies in less dense environments, in agreement with results from other studies using independent methods.« less