Characterisation of the open cluster M67

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2016, Tutors: Carme Jordi Nebot, Eduard Masana Fresno, Lola Balaguer NúñezIn this study a characterisation of the physical parameters of the open cluster M67 is made by using empirical calibrations in the Ströomgren-Crawford filter system. A group of 316 stars contributed to the results. The photometric analysis leads to an extinction of Eb-y = 0:03 +- 0:03, a distance modulus V0 - Mv = 9:6 +- 0:3 (or 830 +- 60 pc), a metallicity [Fe=H] = 0:0 +- 0:3 and the age of the cluster is approximated to be log t(yr) = 9:57 +- 0:05 (or 3:72 +- 0:19 Gyr

The Magellanic Puzzle: origin of the periphery

In this paper, we analyse the metallicity structure of the Magellanic Clouds using parameters derived from the Gaia DR3 low-resolution XP spectra, astrometry and photometry. We find that the qualitative behavior of the radial metallicity gradients in the LMC and SMC are quite similar, with both of them having a metallicity plateau at intermediate radii and a second at larger radii. The LMC has a first metallicity plateau at [Fe/H]$\approx$-0.8 for 3$-$7\degr, while the SMC has one at [Fe/H]$\approx$-1.1 at 3$-$5\degr. The outer LMC periphery has a fairly constant metallicity of [Fe/H]$\approx$-1.0 (10$-$18\degr), while the outer SMC periphery has a value of [Fe/H]$\approx$-1.3 (6$-$10\degr). The sharp drop in metallicity in the LMC at $\sim$8\dgr and the marked difference in age distributions in these two regions suggests that there were two important evolutionary phases in the LMC. In addition, we find that the Magellanic periphery substructures, likely Magellanic debris, are mostly dominated by LMC material stripped off in old interactions with the SMC. This presents a new picture in contrast with the popular belief that the debris around the Clouds had been mostly stripped off from the SMC due to having a lower mass. We perform a detailed analysis for each known substructure and identify its potential origin based on metallicities and motions with respect to each galaxy.Comment: 11 pages, 7 figures. Submitted to MNRAS. Comments welcome

Revealing the Chemical Structure of the Magellanic Clouds with APOGEE. III. Abundance Gradients of the Small Magellanic Cloud

We determine radial- and age-abundance gradients of the Small Magellanic Cloud (SMC) using spectra of 2,062 red giant branch (RGB) field stars observed by SDSS-IV / APOGEE-2S. With coverage out to $\sim$9 kpc in the SMC, these data taken with the high resolution ($R \sim 22,500$) APOGEE $H$-band spectrograph afford the opportunity to measure extensive radial gradients for as many as 24 abundance ratios. The SMC is found to have an overall metallicity gradient of $-$0.0546 $\pm$ 0.0043 dex/kpc. Ages are calculated for every star to explore the evolution of the different abundance gradients. As a function of age, many of the gradients show a feature 3.66--5.58 Gyr ago, which is especially prominent in the [X/H] gradients. Initially many gradients flatten until about $\sim$5.58 Gyr ago, but then steepen in more recent times. We previously detected similar evolutionary patterns in the Large Magellanic Cloud (LMC) which are attributed to a recent interaction between the LMC and SMC. It is inferred that the feature in the SMC gradients was caused by the same interaction. The age-[X/Fe] trends, which track average [X/Fe] over time, are flat, demonstrating a slow enrichment history for the SMC. When comparing the SMC gradients to the LMC and MW, normalized to disk scale length ($R_\text{d}$), the [X/Fe] and [X/Mg] gradients are similar, but there is a dichotomy between the dwarfs and the Milky Way (MW) for the [X/H] gradients. The median MW [X/H] gradient around $-$0.125 dex/$R_\text{d}$ whilst the Clouds have gradients of about $-$0.075 dex/$R_\text{d}$.Comment: 27 pages, 22 figures, and 11 table

SMASHing the LMC: A Tidally-induced Warp in the Outer LMC and a Large-scale Reddening Map

We present a study of the three-dimensional (3D) structure of the Large Magellanic Cloud (LMC) using ~2.2 million red clump (RC) stars selected from the Survey of the MAgellanic Stellar History. To correct for line-of-sight dust extinction, the intrinsic RC color and magnitude and their radial dependence are carefully measured by using internal nearly dust-free regions. These are then used to construct an accurate 2D reddening map (165 square degrees with ~10 arcmin resolution) of the LMC disk and the 3D spatial distribution of RC stars. An inclined disk model is fit to the 2D distance map yielding a best-fit inclination angle i = 25.86(+0.73,-1.39) degrees with random errors of +\-0.19 degrees and line-of-nodes position angle theta = 149.23(+6.43,-8.35) degrees with random errors of +/-0.49 degrees. These angles vary with galactic radius, indicating that the LMC disk is warped and twisted likely due to the repeated tidal interactions with the Small Magellanic Cloud (SMC). For the first time, our data reveal a significant warp in the southwestern part of the outer disk starting at rho ~ 7 degrees that departs from the defined LMC plane up to ~4 kpc toward the SMC, suggesting that it originated from a strong interaction with the SMC. In addition, the inner disk encompassing the off-centered bar appears to be tilted up to 5-15 degrees relative to the rest of the LMC disk. These findings on the outer warp and the tilted bar are consistent with the predictions from the Besla et al. simulation of a recent direct collision with the SMC.Comment: 25 pages, 15 figures, published in Ap

The intrinsic reddening of the Magellanic Clouds as traced by background galaxies -- II. The Small Magellanic Cloud

We present a map of the total intrinsic reddening across ~34 deg$^{2}$ of the Small Magellanic Cloud (SMC) derived using optical ($ugriz$) and near-infrared (IR; $YJK_{\mathrm{s}}$) spectral energy distributions (SEDs) of background galaxies. The reddening map is created using a subsample of 29,274 galaxies with low levels of intrinsic reddening based on the LePhare $\chi^{2}$ minimisation SED-fitting routine. We find statistically significant enhanced levels of reddening associated with the main body of the SMC compared with regions in the outskirts [$\Delta E(B-V)\simeq 0.3$ mag]. A comparison with literature reddening maps of the SMC shows that, after correcting for differences in the volume of the SMC sampled, there is good agreement between our results and maps created using young stars. In contrast, we find significant discrepancies between our results and maps created using old stars or based on longer wavelength far-IR dust emission that could stem from biased samples in the former and uncertainties in the far-IR emissivity and the optical properties of the dust grains in the latter. This study represents one of the first large-scale categorisations of extragalactic sources behind the SMC and as such we provide the LePhare outputs for our full sample of ~500,000 sources.Comment: Accepted for publication in MNRAS, 13 pages, 6 figures and 4 tables. Tables 1, 3 and 4 will be available in full as Supporting Information in the online version of the articl

Stellar history of the Small Magellanic Cloud in the era of deep photometric surveys

One of the key goals in modern astrophysics is to understand the origin of galaxies. Detailed studies of the various components of our Galaxy and its satellite galaxies allow us to reconstruct past events through present day clues. Essentially, we are unpicking the past history of our close systems on a galactic scale, carrying out what astronomers call "galactic archaeology''. The Milky Way (MW), its largest companion the Andromeda (M31) galaxy, and the smaller systems around them constitute the Local Group. Given their proximity, size, and interacting nature (among others), the largest satellites of our Galaxy, the Magellanic Clouds (MCs), provide optimum tests and constraints on galaxy formation and evolution theories as well as on the Lambda Cold Dark Matter (LCDM) paradigm. The aim of the present thesis is to further disentangle the formation and evolution of galaxies using the Small and the Large Magellanic Clouds (SMC/LMC) as laboratories. To achieve this, I present a careful study of the SMC stellar populations using the Survey of the MAgellanic Stellar History (SMASH), an unprecedentedly deep and wide survey of the MCs. I derive the SMC surface brightness profile in order to calculate the general parameters of the SMC, finding it very staggered. I trace the fainter outskirts by constructing a stellar density profile, uncovering a tidally disrupted stellar feature that reaches as far out as ~13 kpc from the SMC centre. I also serendipitously identify a faint feature of unknown origin located some ~15 kpc from the SMC centre that could be associated to a more distant structure. Comparing it observed tidal debris to in-house simulations of a 10^{9} solar masses SMC, I find that its elliptical shape can be explained by its tidal disruption under the combined presence of our Galaxy and the LMC. The SMC's older stellar populations present a smooth profile while its younger component has a jump in the density followed by a flat profile, confirming the heavily disrupted nature of this galaxy. I also present a quantitative study of the SMC resolved star formation history (SFH) and compare it with that of the LMC. I devise a strong link between the SFHs of the SMC and the LMC as far backwards in time as 3.5 Gyr ago, with three peaks of star formation at around 3, 2, 1.1 Gyr ago as well as a current enhancement. I test the robustness of these results against crowding issues and line-of-sight depth spread. The resulting resolved maps of star formation prove that the peak of star formation 2 Gyr ago had a much bigger impact across the SMC than in its larger companion. This peak is also the most conspicuous of them all, suggesting a very close encounter might have occurred with the LMC at around that time. Finally, I present a preliminary work on the three dimensional structure of the SMC using photometry of red clump stars alongside astrometric data from Gaia. The combination allows us to determine distances to every part of the galaxy. The hope is to be able to fully characterise the main tidal disruption of the galaxy

Exploring the Very Extended Low-surface-brightness Stellar Populations of the Large Magellanic Cloud with SMASH

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