Universitaets Sternwarte Munich

München, Germany

Universitaets Sternwarte Munich

München, Germany

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Rubin R.H.,NASA | Simpson J.P.,Search for Extraterrestrial Intelligence Institute | Colgan S.W.J.,NASA | Dufour R.J.,Rice University | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

Using the short-high module of the Infrared Spectrograph on the Spitzer Space Telescope, we have measured the [S IV] 10.51, [Ne II] 12.81, [Ne III] 15.56, and [S III] 18.71-μm emission lines in nine HII regions in the dwarf irregular galaxy NGC 6822. These lines arise from the dominant ionization states of the elements neon (Ne++, Ne+) and sulphur (S3+, S++), thereby allowing an analysis of the neon to sulphur abundance ratio as well as the ionic abundance ratios Ne+/Ne++ and S3+/S++. By extending our studies of HII regions in M83 and M33 to the lower metallicity NGC 6822, we increase the reliability of the estimated Ne/S ratio. We find that the Ne/S ratio appears to be fairly universal, with not much variation about the ratio found for NGC 6822: the median (average) Ne/S ratio equals 11.6 (12.2±0.8). This value is in contrast to Asplund et al.'s currently best estimated value for the Sun: Ne/S = 6.5. In addition, we continue to test the predicted ionizing spectral energy distributions (SEDs) from various stellar atmosphere models by comparing model nebulae computed with these SEDs as inputs to our observational data, changing just the stellar atmosphere model abundances. Here, we employ a new grid of SEDs computed with different metallicities: solar, 0.4 solar, and 0.1 solar. As expected, these changes to the SED show similar trends to those seen upon changing just the nebular gas metallicities in our plasma simulations: lower metallicity results in higher ionization. This trend agrees with the observations. © 2016 The Authors.


Dilday B.,Rutgers University | Dilday B.,University of Chicago | Smith M.,University of Cape Town | Smith M.,University of Portsmouth | And 41 more authors.
Astrophysical Journal | Year: 2010

We present a measurement of the volumetric TypeIa supernova (SN Ia) rate based on data from the Sloan Digital Sky Survey II (SDSS-II) Supernova Survey. The adopted sample of supernovae (SNe) includes 516 SNe Ia at redshift z ≲ 0.3, of which 270(52%) are spectroscopically identified as SNe Ia. The remaining 246 SNe Ia were identified through their light curves; 113 of these objects have spectroscopic redshifts from spectra of their host galaxy, and 133 have photometric redshifts estimated from the SN light curves. Based on consideration of 87 spectroscopically confirmed non-Ia SNe discovered by the SDSS-II SN Survey, we estimate that 2.04+1.61 -0.95% of the photometric SNeIa may be misidentified. The sample of SNe Ia used in this measurement represents an order of magnitude increase in the statistics for SN Ia rate measurements in the redshift range covered by the SDSS-II Supernova Survey. If we assume an SN Ia rate that is constant at low redshift (z < 0.15), then the SN observations can be used to infer a value of the SN rate of rV= (2.69+0.34+0.21 -0.30-0.01)×10-5SNe yr-1Mpc-3(H0/(70kms-1Mpc-1))3at a mean redshift of 0.12, based on 79 SNe Ia of which 72 are spectroscopically confirmed. However, the large sample of SNe Ia included in this study allows us to place constraints on the redshift dependence of the SN Ia rate based on the SDSS-II Supernova Survey data alone. Fitting a power-law model of the SN rate evolution, rV(z) = Ap× ((1 + z)/(1 + z0))ν, over the redshift range 0.0 < z < 0.3 with z0= 0.21, results in Ap= (3.43+0.15 -0.15) × 10-5SNe yr-1Mpc-3(H0/(70kms-1Mpc-1))3and ν = 2.04+0.90 -0.89. © 2010. The American Astronomical Society. All rights reserved..


Dilday B.,Rutgers University | Dilday B.,University of Chicago | Bassett B.,University of Cape Town | Bassett B.,South African Astronomical Observatory | And 40 more authors.
Astrophysical Journal | Year: 2010

We present measurements of the Type Ia supernova (SN) rate in galaxy clusters based on data from the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. The cluster SN Ia rate is determined from 9 SN events in a set of 71 C4 clusters at z ≤ 0.17 and 27 SN events in 492 maxBCG clusters at 0.1 ≤ z ≤ 0.3. We find values for the cluster SN Ia rate of (0.37 +0.17+0.01 -0.12-0.01) SNur h 2 and (0.55 +0.13+0.02 -0.11-0.01) SNur h 2 (SNux = 10 -12 L -1 x⊙ yr-1) in C4 and maxBCG clusters, respectively, where the quoted errors are statistical and systematic, respectively. The SN rate for early-type galaxies is found to be (0.31+0.18+0.01 -0.12-0.01) SNur h 2 and (0.49+0.15+0.02 -0.11-0.01) SNur h 2 in C4 and maxBCG clusters, respectively. The SN rate for the brightest cluster galaxies (BCG) is found to be (2.04+1.99+0.07 -1.11-0.04) SNur h 2 and (0.36+0.84+0.01 -0.30-0.01) SNur h 2 in C4 and maxBCG clusters, respectively. The ratio of the SN Ia rate in cluster early-type galaxies to that of the SNIa rate in field early-type galaxies is 1.94+1.31+0.043 -0.91-0.015 and 3.02 +1.31+0.062 -1.03-0.048, for C4 and maxBCG clusters, respectively. The SN rate in galaxy clusters as a function of redshift, which probes the late time SN Ia delay distribution, shows only weak dependence on redshift. Combining our current measurements with previous measurements, we fit the cluster SN Ia rate data to a linear function of redshift, and find r L = [(0.49+0.15 -0.14)+(0.91+0.85 -0.81) × z] SNuB h 2. A comparison of the radial distribution of SNe in cluster to field early-type galaxies shows possible evidence for an enhancement of the SN rate in the cores of cluster early-type galaxies. With an observation of at most three hostless, intra-cluster SNe Ia, we estimate the fraction of cluster SNe that are hostless to be (9.4 +8.3 -5.1)%. © 2010. The American Astronomical Society. All rights reserved.

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