Modelling the Galactic interstellar extinction distribution in three dimensions

Abstract

Aims. The Two Micron All Sky Survey, along with the Stellar Population Synthesis Model of the Galaxy, developed in Besançon, is used to calculate the extinction distribution along different lines of sight. By combining many lines of sight, the large scale distribution of interstellar material can be deduced.Methods. The Galaxy model is used to provide the intrinsic colour of stars and their probable distances, so that the near infrared colour excess, and hence the extinction, may be calculated and its distance evaluated. Such a technique is dependent on the model used, however we are able to show that moderate changes in the model parameters result in insignificant changes in the predicted extinction.Results. This technique has now been applied to over 64 000 lines of sight, each separated by 15 , in the inner Galaxy (|l| ≤ 100• , |b| ≤ 10• ). We have projected our three dimensional results onto a two dimensional plane in order to compare them with existing two dimensional extinction maps and CO surveys. We find that although differences exist due to the different methods used or the medium traced, the same large scale structures are visible in each of the different maps. Using our extinction map, we have derived the main characteristics of the large scale structure of the dust distribution. The scale height of the interstellar matter is found to be 125 +17 −7 pc. The dust distribution is found to be asymmetrically warped, in agreement with CO and HI observations of the ISM. However, the slope of the dust warp and the galactocentric distance where it starts are found to be smaller than the values measured for the external HI disc: for positive longitudes the angle is θ = 89• , it starts at 8.7 kpc from the Galactic center and grows with a slope of 0.14, while at negative longitudes, the angle of the maximum is at θ = 272• , the starting radius 7.8 kpc and the slope 0.11. Finally, the presence of dust is detected in the Galactic bulge. It forms an elongated structure approximately 5.2 kpc long and lies at an angle of 30 ± 5• with respect to the Sun-Galactic centre direction. This may be interpreted as a dust lane along the Galactic bar. This resulting extinction map will be useful for studies of the inner Galaxy and its stellar populations.

Evidence of the Galactic outer ring R 1 R 2 ′ $R_{1}R_{2}'$ from young open clusters and OB-associations

“…Note that we found similar features in variations of extinction for classical Cepheids (Mel'nik et al 2015). Both groups of young objects, open clusters and Cepheids, show a sharp growth of extinction in the direction toward the Galactic center (see also Neckel & Klare 1980;Marshall et al 2006). This steep increase can be attributed to the presence of the Galactic outer ring R 1 at the heliocentric distance 1-2 kpc in this direction.…”

RAPID CIRCUMSTELLAR DISK EVOLUTION AND AN ACCELERATING STAR FORMATION RATE IN THE INFRARED DARK CLOUD M17 SWex

“…The numerical cutoffs for E med and A V used to separate foreground stars from PCMs were determined iteratively, starting with expectations for the foreground reddening to M17 based on its distance and location in the Galactic plane (Marshall et al 2006) and typical E med for unobscured, pre-MS stars (Broos et al 2011a;Getman et al 2011). We refined our selection criteria to visually isolate the loci of foreground stars versus PCMs in the E med versus A V SED plot of Figure 9 and in the NIR color-color and color-magnitude diagrams shown in Figure 8.…”

Near-infrared studies of V5558 Sgr: an unusually slow nova with multiple outbursts

“…The grey curve shows that the light curve can be well matched by a uniform curve, obtained from a polynomial fit, in case the data points for the secondary maxima are excluded (see text for additional details). The bottom panel shows the plot of the extinction A k in the K band versus distance towards the nova (filled dark circles; from Marshall et al 2006; Av = 11A k ). The intersection point of this extinction curve with the MMRD generated curve can be used to determine the distance and extinction to the nova simultaneously.…”