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Register a new userEmpirical calibration of the reddening maps in the Magellanic Clouds
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We present reddening maps of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), based on color measurements of the red clump. Reddening values of our maps were obtained by calculating the difference of the observed and intrinsic color of the red clump in both galaxies. To obtain the intrinsic color of the red clump, we used reddenings obtained from late-type eclipsing binary systems, measurements for blue supergiants and reddenings derived from Str{o}mgren photometry of B-type stars. We obtained intrinsic color of the red clump $(V-I)_0$ = 0.838 $pm$ 0.034 mag in the LMC, and $(V-I)_{0}$ = 0.814 $pm$ 0.034 mag in the SMC. We prepared our map with 3 arcmin resolution, covering the central part of the LMC and SMC. The mean value of the reddening is E$(B-V)_{mathrm{LMC}}$=0.127 mag and E$(B-V)_{mathrm{SMC}}$=0.084 mag for the LMC and SMC, respectively. The systematic uncertainty of the average reddening value assigned to each field of our maps is 0.013 mag for both Magellanic Clouds. Our reddening values are on average higher by 0.061 mag for the LMC and 0.054 mag for the SMC, compared with the maps of Haschke et al. (2011). We also compared our values with different types of reddening tracers. Cepheids, RR Lyrae stars, early-type eclipsing binaries and other reddening estimations based on the red clump color on average show reddenings consistent with our map to within a few hundredths of magnitude.
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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.
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 templates to estimate the NIR mean magnitudes from single-epoch measurements, we build the currently most accurate, largest and homogeneous multi-band dataset of LMC Cepheids. We determine Cepheid individual distances using optical and NIR Period-Wesenheit relations (PWRs), to measure the geometry of the LMC disk and its viewing angles. Cepheid distances based on optical PWRs are precise at 3%, but accurate to 7, while the ones based on NIR PWRs are more accurate (to 3%), but less precise (2%-15%), given the higher photometric error on the observed magnitudes. We found an inclination i=25.05 $pm$ 0.02 (stat.) $pm$ 0.55 (syst.) deg, and a position angle of the lines of nodes P.A.=150.76 $pm$ 0.02(stat.) $pm$ 0.07(syst.) deg. These values agree well with estimates based either on young (Red Supergiants) or on intermediate-age (Asymptotic Giant Branch, Red Clump) stellar tracers, but they significantly differ from evaluations based on old (RR Lyrae) stellar tracers. This indicates that young/intermediate and old stellar populations have different spatial distributions. Finally, by using the reddening-law fitting approach, we provide a reddening map of the LMC disk which is ten times more accurate and two times larger than similar maps in the literature. We also found an LMC true distance modulus of $mu_{0,LMC}=18.48 pm 0.10$ (stat. and syst.) mag, in excellent agreement with the currently most accurate measurement (Pietrzynski et al. 2013).
We present a method to map the total intrinsic reddening of a foreground extinguishing medium via the analysis of spectral energy distributions (SEDs) of background galaxies. In this pilot study, we implement this technique in two distinct regions of the Small Magellanic Cloud (SMC) - the bar and the southern outskirts - using a combination of optical and near-infrared $ugrizYJK_{mathrm{s}}$ broadband imaging. We adopt the LePhare $chi^{2}$-minimisation SED-fitting routine and various samples of galaxies and/or quasi-stellar objects to investigate the intrinsic reddening. We find that only when we construct reddening maps using objects classified as galaxies with low levels of intrinsic reddening (i.e. ellipticals/lenticulars and early-type spirals), the resultant maps are consistent with previous literature determinations i.e. the intrinsic reddening of the SMC bar is higher than that in the outer environs. We employ two sets of galaxy templates - one theoretical and one empirical - to test for template dependencies in the resulting reddening maps and find that the theoretical templates imply systematically higher reddening values by up to 0.20 mag in $E(B-V)$. A comparison with previous reddening maps, based on the stellar components of the SMC, typically shows reasonable agreement. There is, however, significant variation amongst the literature reddening maps as to the level of intrinsic reddening associated with the bar. Thus, it is difficult to unambiguously state that instances of significant discrepancies are the result of appreciable levels of dust not accounted for in some literature reddening maps or whether they reflect issues with our adopted methodology.
In the present study, we examine reddening distribution across the LMC and SMC through largest data on Classical Cepheids provided by the OGLE Phase IV survey. The V and I band photometric data of 2476 fundamental mode (FU) and 1775 first overtone mode (FO) Cepheids in the LMC and 2753 FU and 1793 FO Cepheids in the SMC are analyzed for their Period-Luminosity (P-L) relations. We convert period of FO Cepheids to corresponding period of FU Cepheids before combining the two modes of Cepheids. The reddening analysis is performed on 133 segments covering a total area of about 154.6 deg^2 in the LMC and 136 segments covering a total area of about 31.3 deg^2 in the SMC. By comparing with well calibrated P-L relations of these two galaxies, we determine reddening E(V-I) in each segment. Using reddening values in different segments across the LMC and SMC, reddening maps are constructed. We find clumpy structures in the reddening distributions of the LMC and SMC. From the reddening map of the LMC, highest reddening of E(V-I) = 0.466 mag is traced in the region centered at RA ~ 85.13 deg, DEC ~ -69.34 deg which is in close vicinity of the star forming HII region 30 Doradus. In the SMC, maximum reddening of E(V-I) = 0.189 mag is detected in the region centered at RA ~ 12.10 deg, DEC ~ -73.07 deg. The mean reddening values in the LMC are estimated as E(V-I) = 0.113+/-0.060 mag and E(B-V) = 0.091+/-0.050 mag; and that in the SMC are E(V-I) = 0.049+/-0.070 mag and E(B-V) = 0.038+/-0.053 mag. The period-age relations are used to derive the age of the Cepheid populations in the LMC and SMC. We investigate age and spatio-temporal distributions of Cepheids to understand the recent star formation history in the Magellanic Clouds (MCs) and found an evidence of a common enhanced Cepheid population in the MCs at around 200 Myr ago which appears to have occurred due to close encounter between the two clouds.
A zero point calibration of the Red Giant Branch Tip (TRGB) in the $I$-band is determined from OGLE photometry of the Magellanic Clouds (MCs). It is shown that TRGB measurements made in star-forming regions, with concomitantly high quantities of gas and dust, are less precise and biased to fainter magnitudes, as compared to the same measurements made in quiescent regions. Once these low accuracy fields are excluded from consideration, the TRGB can be used for the first time to constrain the three-dimensional plane geometry of the LMC. Composite CMDs are constructed for the SMC and LMC from only those fields with well-defined TRGB features, and the highest accuracy TRGB zero point calibration to date is presented. The $I$-band TRGB magnitude is measured to be flat over the color range $ 1.45 < (V-I)_0 < 1.95$ mag, with a modest slope introduced when including metal-rich (up to $(V-I)_0 = 2.2$ mag) Tip stars into the fit. Both the flat, blue zero point and the shallow slope calibration are consistent with the canonical value of $-4.05$ mag for the old, metal-poor TRGB, and would appear to resolve a recent debate in the literature over the methods absolute calibration.
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