The intrinsic reddening of the Magellanic Clouds as traced by background galaxies -- I. The bar and outskirts of the Small Magellanic Cloud
Cameron P. M. Bell, Maria-Rosa L. Cioni, A. H. Wright, Stefano Rubele, David L. Nidever, Ben L. Tatton, Jacco Th. van Loon, Valentin D. Ivanov, Smitha Subramani… 展开作者
Cameron P. M. Bell, Maria-Rosa L. Cioni, A. H. Wright, Stefano Rubele, David L. Nidever, Ben L. Tatton, Jacco Th. van Loon, Valentin D. Ivanov, Smitha Subramanian, Joana M. Oliveira, Richard de Grijs, Clara M. Pennock, Yumi Choi, Dennis Zaritsky, Knut Olsen, Florian Niederhofer, Samyaday Choudhury, David Martínez-Delgado, Ricardo R. Muñoz
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Accepted for publication in MNRAS, 21 pages, 13 figures and 4 tables
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 $χ^{2}$-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.
We present a map of the total intrinsic reddening across ~90 deg$^{2}$ of the Large Magellanic Cloud (LMC) derived using optical (ugriz) and near-infrared (IR; YJKs) spectral energy distributions (SEDs) of background galaxies. The reddening map is created from a sample of 222,752 early-type galaxies based on the LEPHARE $χ^{2}$ minimisation SED-fitting routine. We find excellent agreement between the regions of enhanced intrinsic reddening across the central (4x4 deg$^2$) region of the LMC and the morphology of the low-level pervasive dust emission as traced by far-IR emission. In addition, we…
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 $χ^{2}$ 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 [$ΔE(B-V)\simeq 0.3$ mag]. A comparison with l…
Red clump stars are commonly used to map the reddening and morphology of the inner regions of the Milky Way. We use the new photometric catalogues of the VISTA Variables in the Vía Láctea survey to achieve twice the spatial resolution of previous reddening maps for Galactic longitudes $-10^{\circ}<l<10^{\circ}$ and latitudes $-1.5^{\circ}<b<1.5^{\circ}$. We use these de-reddened catalogues to construct the $K_{s}$ luminosity function around the red clump in the Galactic plane. We show that the secondary peak (fainter than the red clump) detected in these regions does not correspond to the bulg…
We present our recent results on the properties of the outskirts of disk galaxies. In particular, we focus on spiral galaxies with stellar disk truncations in their radial surface brightness profiles. Using SDSS, UDF and GOODS data we show how the position of the break (i.e., a direct estimator of the size of the stellar disk) evolves with time since z~1. Our findings agree with an evolution on the radial position of the break by a factor of 1.3+/-0.1 in the last 8 Gyr for galaxies with similar stellar masses. We also present radial color gradients and how they evolve with time. At all redshif…
Context: Deep GALEX UV data show that the extreme outskirts of some spiral galaxies are teeming with star formation. Such young stellar populations evolving so far away from the bulk of their host galaxies challenge our overall understanding of how star formation proceeds at galactic scales. It is at present unclear whether our own Milky Way may also exhibit ongoing and recent star formation beyond the conventional edge of the disk ($\sim 15$ kpc). Aims: Using \textit{Gaia} DR2 data, we aim to determine if such a population is present in the Galactic halo, beyond the nominal radius of the Milk…
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 LM…
The structure and evolution of the disk of the Small Magellanic Cloud (SMC) are traced by studying the Cepheids. We aim to estimate the orientation measurements of the disk, such as the inclination and the position angle of the line of nodes, and the depth of the disk. We used the V and I band photometric data of the fundamental and first-overtone Cepheids from the Optical Gravitational Lensing Experiment survey. The period-luminosity relations were used to estimate the relative distance and reddening of each Cepheid. A weighted least-square plane fitting method was then applied to estimate th…
We present the most extensive and detailed reddening maps of the Magellanic Clouds (MCs) derived from the color properties of Red Clump (RC) stars. The analysis is based on the deep photometric maps from the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV), covering approximately 670 deg2 of the sky in the Magellanic System region. The resulting maps provide reddening information for 180 deg2 in the Large Magellanic Cloud (LMC) and 75 deg2 in the Small Magellanic Cloud (SMC), with a resolution of 1.7x1.7 arcmin in the central parts of the MCs, decreasing to approximately …
Upcoming large imaging surveys will allow detailed studies of the structure and morphology of galaxies aimed at addressing how galaxies form and evolve. Computational approaches are needed to characterize their morphologies over large samples. We introduce an automatic method to quantify the outer structure of galaxies. The key to our approach is the division of a galaxy image into two sections delineated by the isophote which encloses half the total brightness of the galaxy. We call the central section the inner half-flux region (IHR) and the outer section the outer half-flux region (OHR). Fr…
Neutral gas is commonly believed to dominate over stars in the outskirts of galaxies, and investigations of the disk-halo interface are generally considered to be in the domain of radio astronomy. This may simply be a consequence of the fact that deep HI observations typically probe to a lower mass surface density than visible wavelength data. This paper presents low surface brightness optimized visible wavelength observations of the extreme outskirts of the nearby spiral galaxy NGC 2841. We report the discovery of an enormous low-surface brightness stellar disk in this object. When azimuthall…
Submillimetre galaxies represent a rapid growth phase of both star formation and massive galaxies. Mapping SMGs in galaxy protoclusters provides key insights into where and how these extreme starbursts take place in connections with the assembly of the large-scale structure in the early Universe. We search for SMGs at 850$\,μm$ using JCMT/SCUBA-2 in two massive protoclusters at $z=2.24$, BOSS1244 and BOSS1542, and detect 43 and 54 sources with $S_{850}>4\,$mJy at the $4σ$ level within an effective area of 264$\,$arcmin$^2$, respectively. We construct the intrinsic number counts and find that t…
We measured the Tip of the Red Giant Branch distances to nine galaxies in the direction to the Virgo cluster using the Advanced Camera for Surveys on the Hubble Space Telescope. These distances put seven galaxies: GR 34, UGC 7512, NGC 4517, IC 3583, NGC 4600, VCC 2037 and KDG 215 in front of the Virgo, and two galaxies: IC 3023, KDG 177 likely inside the cluster. Distances and radial velocities of the galaxies situated between us and the Virgo core clearly exhibit the infall phenomenon toward the cluster. In the case of spherically symmetric radial infall we estimate the radius of the "zero-ve…
The low column density gas at the outskirts of galaxies as traced by the 21 cm hydrogen line emission (HI) represents the interface between galaxies and the intergalactic medium, i.e., where galaxies are believed to get their supply of gas to fuel future episodes of star formation. Photoionization models predict a break in the radial profiles of HI at a column density of 5x10E+19 cm^-2 due to the lack of self-shielding against extragalactic ionizing photons. To investigate the prevalence of such breaks in galactic disks and to characterize what determines the potential "edge" of the HI disks, …
We use the VVV survey observations in bulge regions close to the Galactic plane to trace the bar inclination at the Galactic latitude b\sim\pm1° and to investigate a distinct structure in the inner regions of the bar that was previously detected at positive latitude (b=+1°). We use the (J-Ks) colors of the red clump stars to obtain reddening values on 6 x 6 arcmin scale, minimizing the problems arising from differential extinction. Dereddened magnitudes are then used to build the luminosity function of the bulge in regions of ~0.4 sq deg to obtain the mean red clump magnitudes. These are used …
We have explored the capabilities of dust extinction and $γ$ rays to probe the properties of the interstellar medium in the nearby anti-centre region. We have jointly modelled the $γ$-ray intensity and the stellar reddening, E(B-V) as a combination of H$_{\rm I}$-bright, CO-bright, and ionised gas components. The complementary information from dust reddening and $γ$ rays is used to reveal the dark gas not seen, or poorly traced, by H$_{\rm I}$, free-free, and $^{12}$CO emissions. We compare the total gas column densities, $N_{\rm{H}}$, derived from the $γ$ rays and stellar reddening with those…
The Small Magellanic Cloud (SMC) provides the only laboratory to study the structure of molecular gas at high resolution and low metallicity. We present results from the Herschel Spectroscopic Survey of the SMC (HS$^{3}$), which mapped the key far-IR cooling lines [CII], [OI], [NII], and [OIII] in five star-forming regions, and new ALMA 7m-array maps of $^{12}$CO and $^{13}$CO $(2-1)$ with coverage overlapping four of the five HS$^{3}$ regions. We detect [CII] and [OI] throughout all of the regions mapped. The data allow us to compare the structure of the molecular clouds and surrounding photo…
Our main goal is to derive a new extinction map of the OMC-1, obtaining information about the structure of the OMC-1 and the Orion Nebula Cluster. The most recent near-infrared catalog of stars is used to study the distribution of reddening across a ~0.3 deg^2 area covering the Orion Nebula Cluster. On the basis of the observed (H,H-K_S) diagram, we establish a criterion for disentangling contaminants from bona-fide cluster members. For contaminant stars, interstellar reddenings are estimated by comparison with a synthetic galactic model. A statistical analysis is then performed to consistentl…
We present a detailed study of the stellar and HI structure of the dwarf irregular galaxies SextansA and SextansB, members of the NGC3109 association. We use newly obtained deep (r~26.5) and wide field g,r photometry to extend the Surface Brightness (SB) profiles of the two galaxies down to mu_V~ 31.0 mag/arcsec^2. We find that both galaxies are significantly more extended than what previously traced with surface photometry, out to ~4 kpc from their centers along their major axis. Older stars are found to have more extended distribution with respect to younger populations. We obtain the first …
We define a new morphology metric called "patchiness" ($P$) that is sensitive to deviations from the average of a resolved distribution, does not require the galaxy center to be defined, and can be used on the spatially-resolved distribution of any galaxy property. While the patchiness metric has a broad range of applications, we demonstrate its utility by investigating the distribution of dust in the interstellar medium of 310 star-forming galaxies at spectroscopic redshifts $1.36<z<1.66$ observed by the MOSFIRE Deep Evolution Field (MOSDEF) survey. The stellar continuum reddening distributio…
The new data for Cepheids and RR Lyrae stars of the Optical Gravitational Lensing Experiment (OGLE-III) survey allow us to study the three-dimensional distribution of stars corresponding to young (a few tens to a few hundreds of millions of years) and old (typically older than ~9 Gyr) populations of the Large Magellanic Cloud (LMC) traced by these variable stars. We estimate the distance to 16949 RR Lyrae stars by using their photometrically estimated metallicities. Furthermore the periods of 1849 Cepheids are used to determine their distances. Three-dimensional maps are obtained by using indi…
We report on the extinction properties in the fields around the clusters NGC 1854, NGC 1856, and NGC 1858 in the bar of the Large Magellanic Cloud. The colour-magnitude diagrams of the stars in all these regions show an elongated red giant clump that reveals a variable amount of extinction across these fields, ranging from Av~0.2 to Av~1.9, including Galactic foreground extinction. The extinction properties nonetheless are remarkably uniform. The slope of the reddening vectors measured in the (V-I,V) and (B-I,B) colour-magnitude planes is fully in line with the Av/E(B-V)~5.5 value found in the…
The periphery of the Small Magellanic Cloud (SMC) can unlock important information regarding galaxy formation and evolution in interacting systems. Here, we present a detailed study of the extended stellar structure of the SMC using deep colour-magnitude diagrams (CMDs), obtained as part of the Survey of the MAgellanic Stellar History (SMASH). Special care was taken in the decontamination of our data from MW foreground stars, including from foreground globular clusters NGC 362 and 47 Tuc. We derived the SMC surface brightness using a ``conservative'' approach from which we calculated the gener…
The VISCACHA (VIsible Soar photometry of star Clusters in tApii and Coxi HuguA\footnote{LMC and SMC names in the Tupi-Guarani language spoken by native people in Brazil}) Survey is an ongoing project based on deep and spatiallyresolved photometric observations of Magellanic Cloud star clusters, collected using the SOuthern Astrophysical Research (SOAR) telescope together with the SOAR Adaptive Module Imager. So far we have used $>$300h of telescope time to observe $\sim$150 star clusters, mostly with low mass ($M < 10^4 M_{\odot}$) on the outskirts of the LMC and SMC. With this high-quality da…
We analyse deep images from the VISTA survey of the Magellanic Clouds in the YJKs filters, covering 14 sqrdeg (10 tiles), split into 120 subregions, and comprising the main body and Wing of the Small Magellanic Cloud (SMC). We apply a colour--magnitude diagram reconstruction method that returns their best-fitting star formation rate SFR(t), age-metallicity relation (AMR), distance and mean reddening, together with 68% confidence intervals. The distance data can be approximated by a plane tilted in the East-West direction with a mean inclination of 39 deg, although deviations of up to 3 kpc sug…
