| 1. |
- Wang, Xiaofeng, et al.
(författare)
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Evidence for type ia supernova diversity from ultraviolet observations with the hubble space telescope
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 749:2, s. 126-
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Tidskriftsartikel (refereegranskat)abstract
- We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This data set provides unique spectral time series down to 2000 angstrom. Significant diversity is seen in the near-maximum-light spectra (similar to 2000-3500 angstrom) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminositiesmeasured in the uvw1/F250W filter are found to correlate with the B-band light-curve shape parameter Delta m(15)(B), but with much larger scatter relative to the correlation in the broadband B band (e.g., similar to 0.4 mag versus similar to 0.2 mag for those with 0.8 mag < Delta m(15)(B) < 1.7 mag). SN 2004dt is found as an outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia such as SN 2005cf by similar to 0.9 mag and similar to 2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects.
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| 2. |
- Clayton, Geoffrey C., et al.
(författare)
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THE CIRCUMSTELLAR ENVIRONMENT OF R CORONAE BOREALIS : WHITE DWARF MERGER OR FINAL-HELIUM-SHELL FLASH?
- 2011
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 743:1, s. 44-
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Tidskriftsartikel (refereegranskat)abstract
- In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 mu m with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 mu m. The spectral energy distribution of R CrB can be well fitted by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10(-4) and 2M(circle dot), respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white dwarf merger.
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| 3. |
- Harrison, Craig D., et al.
(författare)
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THE XMM CLUSTER SURVEY : THE STELLAR MASS ASSEMBLY OF FOSSIL GALAXIES
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 752:1, s. 12-
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents both the result of a search for fossil systems (FSs) within the XMM Cluster Survey and the Sloan Digital Sky Survey and the results of a study of the stellar mass assembly and stellar populations of their fossil galaxies. In total, 17 groups and clusters are identified at z < 0.25 with large magnitude gaps between the first and fourth brightest galaxies. All the information necessary to classify these systems as fossils is provided. For both groups and clusters, the total and fractional luminosity of the brightest galaxy is positively correlated with the magnitude gap. The brightest galaxies in FSs (called fossil galaxies) have stellar populations and star formation histories which are similar to normal brightest cluster galaxies (BCGs). However, at fixed group/cluster mass, the stellar masses of the fossil galaxies are larger compared to normal BCGs, a fact that holds true over a wide range of group/cluster masses. Moreover, the fossil galaxies are found to contain a significant fraction of the total optical luminosity of the group/cluster within 0.5 R-200, as much as 85%, compared to the non-fossils, which can have as little as 10%. Our results suggest that FSs formed early and in the highest density regions of the universe and that fossil galaxies represent the end products of galaxy mergers in groups and clusters.
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| 4. |
- Hilton, Matt, et al.
(författare)
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THE XMM CLUSTER SURVEY : ACTIVE GALACTIC NUCLEI AND STARBURST GALAXIES IN XMMXCS J2215.9-1738 AT z=1.46
- 2010
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 718:1, s. 133-147
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Tidskriftsartikel (refereegranskat)abstract
- We use Chandra X-ray and Spitzer infrared (IR) observations to explore the active galactic nucleus (AGN) and starburst populations of XMMXCS J2215.9-1738 at z = 1.46, one of the most distant spectroscopically confirmed galaxy clusters known. The high-resolution X-ray imaging reveals that the cluster emission is contaminated by point sources that were not resolved in XMM-Newton observations of the system, and have the effect of hardening the spectrum, leading to the previously reported temperature for this system being overestimated. From a joint spectroscopic analysis of the Chandra and XMM-Newton data, the cluster is found to have temperature T = 4.1(-0.9)(+0.6) keV and luminosity LX = (2.92(-0.35)(+0.24)) x 1044 erg s(-1), extrapolated to a radius of 2 Mpc. As a result of this revised analysis, the cluster is found to lie on the sigma(v)-T relation, but the cluster remains less luminous than would be expected from self-similar evolution of the local L-X-T relation. Two of the newly discovered X-ray AGNs are cluster members, while a third object, which is also a prominent 24 mu m source, is found to have properties consistent with it being a high-redshift, highly obscured object in the background. We find a total of eight > 5 sigma 24 mu m sources associated with cluster members (four spectroscopically confirmed and four selected using photometric redshifts) and one additional 24 mu m source with two possible optical/near-IR counterparts that may be associated with the cluster. Examining the Infrared Array Camera colors of these sources, we find that one object is likely to be an AGN. Assuming that the other 24 mu m sources are powered by star formation, their IR luminosities imply star formation rates similar to 100 M-circle dot yr(-1). We find that three of these sources are located at projected distances of <250 kpc from the cluster center, suggesting that a large amount of star formation may be taking place in the cluster core, in contrast to clusters at low redshift.
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| 5. |
- Viana, Pedro T. P., et al.
(författare)
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The XMM Cluster Survey : predicted overlap with the Planck Cluster Catalogue
- 2012
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 422:2, s. 1007-1013
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Tidskriftsartikel (refereegranskat)abstract
- We present a list of 15 clusters of galaxies, serendipitously detected by the XMM Cluster Survey (XCS), that have a high probability of detection by the Planck satellite. Three of them already appear in the Planck Early Sunyaev-Zel'dovich (ESZ) catalogue. The estimation of the Planck detection probability assumes the flat Lambda cold dark matter (Lambda CDM) cosmology most compatible with 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) data. It takes into account the XCS selection function and Planck sensitivity, as well as the covariance of the cluster X-ray luminosity, temperature and integrated Comptonization parameter, as a function of cluster mass and redshift, determined by the Millennium gas simulations. We also characterize the properties of the galaxy clusters in the final data release of the XCS that we expect Planck will have detected by the end of its extended mission. Finally, we briefly discuss possible joint applications of the XCS and Planck data.
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