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تسجيل مستخدم جديدThe properties of the Malin 1 galaxy giant disk: A panchromatic view from the NGVS and GUViCS surveys
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Low surface brightness galaxies (LSBGs) represent a significant percentage of local galaxies but their formation and evolution remain elusive. They may hold crucial information for our understanding of many key issues (i.e., census of baryonic and dark matter, star formation in the low density regime, mass function). The most massive examples - the so called giant LSBGs - can be as massive as the Milky Way, but with this mass being distributed in a much larger disk. Malin 1 is an iconic giant LSBG, perhaps the largest disk galaxy known. We attempt to bring new insights on its structure and evolution on the basis of new images covering a wide range in wavelength. We have computed surface brightness profiles (and average surface brightnesses in 16 regions of interest), in six photometric bands (FUV, NUV, u, g, i, z). We compared these data to various models, testing a variety of assumptions concerning the formation and evolution of Malin 1. We find that the surface brightness and color profiles can be reproduced by a long and quiet star-formation history due to the low surface density; no significant event, such as a collision, is necessary. Such quiet star formation across the giant disk is obtained in a disk model calibrated for the Milky Way, but with an angular momentum approximately 20 times larger. Signs of small variations of the star-formation history are indicated by the diversity of ages found when different regions within the galaxy are intercompared.For the first time, panchromatic images of Malin 1 are used to constrain the stellar populations and the history of this iconic example among giant LSBGs. Based on our model, the extreme disk of Malin 1 is found to have a long history of relatively low star formation (about 2 Msun/yr). Our model allows us to make predictions on its stellar mass and metallicity.
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Since its discovery, Malin 1 has been considered the prototype and most extreme example of the class of giant low surface brightness disk galaxies. Examination of an archival Hubble Space Telescope I-band image reveals that Malin 1 contains a normal
stellar disk that was not previously recognized, having a central I-band surface brightness of mu_0 = 20.1 mag arcsec^-2 and a scale length of 4.8 kpc. Out to a radius of ~10 kpc, the structure of Malin 1 is that of a typical SB0/a galaxy. The remarkably extended, faint outer structure detected out to r~100 kpc appears to be a photometrically distinct component and not a simple extension of the inner disk. In terms of its disk scale length and central surface brightness, Malin 1 was originally found to be a very remote outlier relative to all other known disk galaxies. The presence of a disk of normal size and surface brightness in Malin 1 suggests that such extreme outliers in disk properties probably do not exist, but underscores the importance of the extended outer disk regions for a full understanding of the structure and formation of spiral galaxies.
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We present a detailed investigation of the Large Magellanic Cloud (LMC) disk using classical Cepheids. Our analysis is based on optical (I,V; OGLE-IV), near-infrared (NIR: J,H,Ks) and mid-infrared (MIR: w1; WISE) mean magnitudes. By adopting new temp
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