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Register a new userA new near-IR window of low extinction in the Galactic plane
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The windows of low extinction in the Milky Way (MW) plane are rare but important because they enable us to place structural constraints on the opposite side of the Galaxy, which has hitherto been done rarely. We use the near-infrared (near-IR) images of the VISTA Variables in the Via Lactea (VVV) Survey to build extinction maps and to identify low extinction windows towards the Southern Galactic plane. Here we report the discovery of VVV WIN 1713$-$3939, a very interesting window with relatively uniform and low extinction conveniently placed very close to the Galactic plane. The new window of roughly 30 arcmin diameter is located at Galactic coordinates (l,b)= (347.4,-0.4) deg. We analyse the VVV near-IR colour-magnitude diagrams in this window. The mean total near-IR extinction and reddening values measured for this window are A_Ks=0.46 and E(J-Ks)=0.95. The red clump giants within the window show a bimodal magnitude distribution in the Ks band, with peaks at Ks=14.1 and 14.8 mag, corresponding to mean distances of D=11.0+/-2.4 and 14.8+/-3.6 kpc, respectively. We discuss the origin of these red clump overdensities within the context of the MW disk structure.
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Supernova remnants (SNRs) embody the information of the influence on dust properties by the supernova explosion. Based on the color indexes from the 2MASS photometric survey and the stellar parameters from the SDSS$-$DR12$/$APOGEE and LAMOST$-$DR2$/$LEGUE spectroscopic surveys, the near-infrared extinction law and the distance of the Monoceros SNR are derived together with its nearby two nebulas -- the Rosette Nebula and NGC 2264. The distance is found at the position of the sharp increase of interstellar extinction with distance and the nebular extinction is calculated by subtracting the foreground interstellar extinction. The distance of the Monoceros SNR is determined to be $1.98,$kpc, larger than previous values. Meanwhile, the distance of the Rosette Nebula is $1.55,$kpc, generally consistent with previous work. The distance between these two nebulas suggests no interaction between them. The distance of NGC 2264, $1.20,$kpc, exceeds previous values. The color excess ratio, $E_{rm JH}/E_{rm JK_S}$, is 0.657 for the Monoceros SNR, consistent with the average value 0.652 for the Milky Way (Xue et al. 2016). The consistency is resulted from that the SNR material is dominated by interstellar dust rather than the supernova ejecta. $E_{rm JH}/E_{rm JK_S}$ equals to 0.658 for the Rosette Nebula, further proving the universality of the near-infrared extinction law.
We report H$alpha$ filter photometry for 197 northern hemisphere planetary nebulae (PNe) obtained using imaging data from the IPHAS survey. H$alpha$+[N II] fluxes were measured for 46 confirmed or possible PNe discovered by the IPHAS survey and for 151 previously catalogued PNe that fell within the area of the northern Galactic Plane surveyed by IPHAS. After correcting for [N II] emission admitted by the IPHAS H$alpha$ filter, the resulting H$alpha$ fluxes were combined with published radio free-free fluxes and H$beta$ fluxes, in order to estimate mean optical extinctions to 143 PNe using ratios involving their integrated Balmer line fluxes and their extinction-free radio fluxes. Distances to the PNe were then estimated using three different 3D interstellar dust extinction mapping methods, including the IPHAS-based H-MEAD algorithm of Sale (2014). These methods were used to plot dust extinction versus distance relationships for the lines of sight to the PNe; the intercepts with the derived dust optical extinctions allowed distances to the PNe to be inferred. For 17 of the PNe in our sample reliable Gaia DR2 distances were available and these have been compared with the distances derived using three different extinction mapping algorithms as well as with distances from the nebular radius vs. H$alpha$ surface brightness relation of Frew et al. (2016). That relation and the H-MEAD extinction mapping algorithm yielded the closest agreement with the Gaia DR2 distances.
We present optical and near-infrared (NIR, $YJH$-band) observations of 42 Type Ia supernovae (SNe Ia) discovered by the untargeted intermediate Palomar Transient Factory (iPTF) survey. This new data-set covers a broad range of redshifts and host galaxy stellar masses, compared to previous SN Ia efforts in the NIR. We construct a sample, using also literature data at optical and NIR wavelengths, to examine claimed correlations between the host stellar masses and the Hubble diagram residuals. The SN magnitudes are corrected for host galaxy extinction using either a global total-to-selective extinction ratio, $R_V$=2.0 for all SNe, or a best-fit $R_V$ for each SN individually. Unlike previous studies which were based on a narrower range in host stellar mass, we do not find evidence for a mass-step, between the color- and stretch-corrected peak $J$ and $H$ magnitudes for galaxies below and above $log(M_{*}/M_{odot}) = 10$. However, the mass-step remains significant ($3sigma$) at optical wavelengths ($g,r,i$) when using a global $R_V$, but vanishes when each SN is corrected using their individual best-fit $R_V$. Our study confirms the benefits of the NIR SN Ia distance estimates, as these are largely exempted from the empirical corrections dominating the systematic uncertainties in the optical.
We determine the slope of the near infrared extinction power law (A$_{lambda} propto lambda^{-alpha}$) for 8 regions of the Galaxy between l$sim27^{circ}$ and $sim100^{circ}$. UKIDSS Galactic Plane Survey data are compared, in colour-colour space, with Galactic population synthesis model data reddened using a series of power laws and convolved through the UKIDSS filter profiles. Monte Carlo simulations allow us to determine the best fit value of $alpha$ and evaluate the uncertainty. All values are consistent with each other giving an average extinction power law of $alpha$=2.14$^{+0.04}_{-0.05}$. This is much steeper than most laws previously derived in the literature from colour excess ratios, which are typically between 1.6 and 1.8. We show that this discrepancy is due to an inappropriate choice of filter wavelength in conversion from colour excess ratios to $alpha$ and that effective rather than isophotal wavelengths are more appropriate. In addition, curved reddening tracks, which depend on spectral type and filter system, should be used instead of straight vectors.
We use near-infrared (J-K)-colours of bright 2MASS galaxies, measured within a 7-radius aperture, to calibrate the Schlegel et al. (1998) DIRBE/IRAS Galactic extinction map at low Galactic latitudes ($|b| < 10^{rm o}$). Using 3460 galaxies covering a large range in extinction (up to $A_K$ = 1.15 or E(B-V) ~ 3.19), we derive a correction factor $f = 0.83 pm 0.01$ by fitting a linear regression to the colour-extinction relation, confirming that the Schlegel et al. maps overestimate the extinction. We argue that the use of only a small range in extinction (e.g., $A_K$ < 0.4) increases the uncertainty in the correction factor and may overestimate it. Our data confirms the Fitzpatrick (1999) extinction law for the J- and K-band. We also tested four all-sky extinction maps based on Planck satellite data. All maps require a correction factor as well. In three cases the application of the respective extinction correction to the galaxy colours results in a reduced scatter in the colour-extinction relation, indicating a more reliable extinction correction. Finally, the large galaxy sample allows an analysis of the calibration of the extinction maps as a function of Galactic longitude and latitude. For all but one extinction map we find a marked offset between the Galactic Centre and Anticentre region, but not with the dipole of the Cosmic Microwave Background. Based on our analysis, we recommend the use of the GNILC extinction map by Planck Collaboration (2016b) with a correction factor $f = 0.86 pm 0.01$.
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