These are the latest articles published in The Astrophysical Journal Letters.

• Open/close CLASH: Discovery of a Bright z 6.2 Dwarf Galaxy Quadruply Lensed by MACS J0329.6-0211

  A. Zitrin et al. 2012 ApJ 747 L9 Tag this article

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  We report the discovery of a z _phot = 6.18 ^+0.05 _{– 0.07} (95% confidence level) dwarf galaxy, lensed into four images by the galaxy cluster MACS J0329.6-0211 ( z _l = 0.45). The galaxy is observed as a high-redshift dropout in HST/ACS/WFC3 CLASH and Spitzer/IRAC imaging. Its redshift is securely determined due to a clear detection of the Lyman break in the 18-band photometry, making this galaxy one of the highest-redshift multiply lensed objects known to date with an observed magnitude of F125W =24.00 ± 0.04 AB mag for its most magnified image. We also present the first strong-lensing analysis of this cluster uncovering 15 additional multiply imaged candidates of five lower-redshift sources spanning the range z _s 2-4. The mass model independently supports the high photometric redshift and reveals magnifications of 11.6 ^+8.9 _{– 4.1}, 17.6 ^+6.2 _{– 3.9}, 3.9 ^+3.0 _{– 1.7}, and 3.7 ^+1.3 _{– 0.2}, respectively, for the four images of the high-redshift galaxy. By delensing the most magnified image we construct an image of the source with a physical resolution of ~200 pc when the universe was ~0.9 Gyr old, where the z 6.2 galaxy occupies a source-plane area of approximately 2.2 kpc ². Modeling the observed spectral energy distribution using population synthesis models, we find a demagnified stellar mass of , subsolar metallicity ( Z/ Z _☉ ~ 0.5), low dust content ( A _V ~ 0.1 mag), a demagnified star formation rate (SFR) of yr ^–1, and a specific SFR of ~3.4 Gyr ^–1, all consistent with the properties of local dwarf galaxies.

• Open/close Detection of the Second r-process Peak Element Tellurium in Metal-poor Stars

  Ian U. Roederer et al. 2012 ApJ 747 L8 Tag this article

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  Using near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, we detect neutral tellurium in three metal-poor stars enriched by products of r-process nucleosynthesis, BD +17 3248, HD 108317, and HD 128279. Tellurium (Te, Z = 52) is found at the second r-process peak ( A 130) associated with the N = 82 neutron shell closure, and it has not been detected previously in Galactic halo stars. The derived tellurium abundances match the scaled solar system r-process distribution within the uncertainties, confirming the predicted second peak r-process residuals. These results suggest that tellurium is predominantly produced in the main component of the r-process, along with the rare earth elements.

• Open/close Spectroscopic Detection of Carbon Monoxide in the Young Supernova Remnant Cassiopeia A

  J. Rho et al. 2012 ApJ 747 L6 Tag this article

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  We report the detection of carbon monoxide (CO) emission from the young supernova remnant Cassiopeia A (Cas A) at wavelengths corresponding to the fundamental vibrational mode at 4.65 μm. We obtained AKARI Infrared Camera spectra toward four positions which unambiguously reveal the broad characteristic CO ro-vibrational band profile. The observed positions include unshocked ejecta at the center, indicating that CO molecules form in the ejecta at an early phase. We extracted a dozen spectra across Cas A along the long 1' slits and compared these to simple CO emission models in local thermodynamic equilibrium to obtain first-order estimates of the excitation temperatures and CO masses involved. Our observations suggest that significant amounts of carbon may have been locked up in CO since the explosion 330 years ago. Surprisingly, CO has not been efficiently destroyed by reactions with ionized He or the energetic electrons created by the decay of the radiative nuclei. Our CO detection thus implies that less carbon is available to form carbonaceous dust in supernovae than is currently thought and that molecular gas could lock up a significant amount of heavy elements in supernova ejecta.

• Open/close Evidence for a Compact Wolf-Rayet Progenitor for the Type Ic Supernova PTF 10vgv

  A. Corsi et al. 2012 ApJ 747 L5 Tag this article

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  We present the discovery of PTF 10vgv, a Type Ic supernova (SN) detected by the Palomar Transient Factory, using the Palomar 48 inch telescope (P48). R-band observations of the PTF 10vgv field with P48 probe the SN emission from its very early phases (about two weeks before R-band maximum) and set limits on its flux in the week prior to the discovery. Our sensitive upper limits and early detections constrain the post-shock-breakout luminosity of this event. Via comparison to numerical (analytical) models, we derive an upper-limit of R 4.5 R _☉ ( R 1 R _☉) on the radius of the progenitor star, a direct indication in favor of a compact Wolf-Rayet star. Applying a similar analysis to the historical observations of SN 1994I yields R 1/4 R _☉ for the progenitor radius of this SN.

• Open/close First Cosmological Constraints on the Proton-to-electron Mass Ratio from Observations of Rotational Transitions of Methanol

  S. P. Ellingsen et al. 2012 ApJ 747 L7 Tag this article

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  We have used the Australia Telescope Compact Array to measure the absorption from the 2 ₀ → 3 _–1 E 12.2 GHz transition of methanol toward the z = 0.89 lensing galaxy in the PKS B1830–211 gravitational lens system. Comparison of the velocity of the main absorption feature with the published absorption spectrum from the 1 ₀ → 2 _–1 E transition of methanol shows that they differ by –0.6 ± 1.6 km s ^–1. We can use these observations to constrain the changes in the proton-to-electron mass ratio μ from z = 0.89 to the present to 0.8 ± 2.1 × 10 ^–7. This result is consistent, and of similar precision to recent observations at z = 0.68 achieved through comparison of a variety of rotational and inversion transitions, and approximately a factor of two better than previous constraints obtained in this source. Future more sensitive observations that incorporate additional rotational methanol transitions offer the prospect of improving current results by a factor of 5-10.