Tuesday.
Special Topics
Detection of a SN near the center of the galaxy cluster field MACS1149 consistent wth predictions of a new image of Supernova Refsdal
www.astronomerstelegram.org
In HST WFC3-IR exposures taken on UT 2015 Dec 10 (GO-14199; PI:Kelly), a new transient source in the MACS J1149.6+2223 (Ebeling+2003) galaxy cluster field has been discovered.
The new source was not detected in WFC3-IR exposures taken during a previous visit to the field on UT 2015 Oct 30.8 nor in earlier imaging from the Frontier SN program, Frontier fields, or Grism Lens-Amplified Survey from Space (GLASS) programs.
The new image is marginally detected in data taken in November 2015. This new image coincides with a multiply imaged BG galaxy at z-1.49. This same galaxy, but seen as a different image, is the host galaxy of SN Refsdal, a SN discovered in November 2014 as four separate images in an Einstein cross configuraiont round an early-type cluster member. Multiple lensing models consistently predicted that SN Refsdal would re-appear, within several years, at the position of the other image of the host galaxy cluster to the galaxy center. The new SN, denoted 'SX', is significantly fainter than images S1-S3 of the SN Refsdal Einstein cross when they were discovered in images taken on UT 2014 November 10.
The new SN position is both approximately spatially and temporally coincident with predictions for the location and timing of the delayed image of SN Refsdal. Moreover, the brightness differences are also approximately consistent with relative magnification predictions.
Conclude that this new SN is likely the re-appearance of SN Refsdal.
1512.03834
Are the formation and abundances of metal-poor stars the result of dust dynamics?
Hopkins, Conroy
Large dust grains can fluctuate dramatically in their local density, relative to gas, in neutral, turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. Show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains under these conditions. This can have important consequences for star formation and stellar abundances in extremely metal-poor stars. Low-mass stars could form in dust-enhanced regions almost immediately after some dust forms, even if the galaxy-average metallicity is too low for fragmentation to occur. The abundances of these 'promoted' stars may contain interesting signatures, as the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced or fluctuate independently. Remarkably, otherwise puzzling abundance patterns of some metal poor stars can be well-fit by standard core-collapse SNe yeilds, if fluctuating dust-to-gas ratios are allowed. Also show that the observed log-normal-like distribution of enhancements n these species agrees with the simulations. Moreover, confirm Mg and Si are correlated in these stars, with abundance ratios similar to those in local silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure SNe yields, shows large enhancements as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. This suggests that (1) dust exists in second-generation star formation, (2) dust-to-gas ratio fluctuations occurs and can be important for star formation, and (3) light element abundances of these stars may be affected by the chemistry of dust where they formed, rather than directly tracing nucleosynthesis.
1512.03903
The XXL Survey X: K-band luminosity - weak-lensing mass relation for groups and clusters of galaxies
Ziparo, Smith, et al
Present the K-band luminosity-halomass relation (L_K,500-M_500,WL), for a subsample of 20 of the 100 brightest clusters in the XXL survey observed with WIRCam at CFHT. Measure this relation via WL down to M_500,WL=3.5e13 Msun, allowing to investigate whether the slope of the L_K-M relation is different for groups and clusters, as seen in other works. The clusters in the sample span a wide range in mass, M=0.35-12.1e14 Msun, at 0<z<0.6. The K-band luminosity scales as log10(L_K,500/1e12 Lsun) ~ beta log10 (M_500,WL/1e14 Msun) with beta = 0.85±0.3 and an intrinsic scatter of sigma_lnL_K|M = 0.37±0.18. combining the sample with some clusters in LoCuSS, obtain a slope of 1.05±0.15 and an intrinsic scatter of 0.14±0.08. The flattening in the L_K-M seen in previous works is not seen here and might be a result of a bias in the mass measurement due to assumptions on the dynamical state of the systems. Also study the richness-mass relation and find that group-sized halos have more galaxies per unit halo mass than massive clusters. However, the BCG in low-mass systems contributes a greater fraction to the total cluster light than BCGs do in massive clusters; the luminosity gap between the two brightest galaxies is more prominent for group-sized haloes. This result is a natural outcome of the hierarchical growth of structures, where massive galaxies form and gain mass within low-mass groups and are ultimately accreted into more massive clusters to become either part of the BCG or one of the brighter galaxies.
1512.04189
Intensity mapping cross-correlations: connecting the largest scales to galaxy evolution
Wolf, Tonini, Blake, Wyithe
Intensity mapping of HI is a new observational tool that can be used to efficiently map the LSS of the Universe over wide redshift ranges. The PS of the intensity maps contains cosmo info on the matter distribution and probes galaxy evolution by tracing the HI content of galaxies at different redshifts and the scale-dependence of HI clustering. The cross-correlation of intensity maps with galaxy surveys is a robust measure of the PS which diminishes systematics caused by instrumental effects and foreground removal. Examine the cross-correlation signatures at z=0.9 using a variant of the semi-analytical galaxy formation model SAGE apply to the Millennium sim in order to model the HI gas of galaxies as well as their optical magnitudes based on their SF history. Determine the clustering of the cross-correlation power for different type of galaxies determined by their colors, acting as a proxy for their SF activity. Find that the cross-correlation coefficient for red quiescent galaxies falls off more quickly on smaller scales k>0.2h/Mpc than for blue SF galaxies. Additionally, create a mock catalogue of highly SF galaxies using a select function to mimic the WiggleZ survey, and use this to predict existing and future cross-correlation measurement of the GBT and Parkes telescope. Find that the cross-power of highly SF galaxies shows a higher clustering on small scales than any other galaxy type and that this significantly alters the PS shape on sales k>0.2h/Mpc. Show that the cross-correlation coefficient is not negligible when interpreting the cosmo cross-power spectrum. On the other hand, it contains information about the HI content of the optically selected galaxies.
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