Day 883

Friday.


1505.01493
Testing the modern merger hypothesis via the assembly of massive blue elliptical galaxies in the local universe
Haines, McIntosh, Sánchez, Tremonti, Rudnick

The modern merger hypothesis offers a method of forming a new elliptical galaxy through merging two equal-mass, gas-rich disk galaxies fueling a nuclear starburst followed by efficient quenching and dynamical stabilization.  A key prediction of this scenario is a central concentration of young stars during the brief phase of morphological transformation from highly-disturbed remnant to new elliptical galaxy.  To test this aspect of the merger hypothesis, use integral field spectroscopy to track the stellar Balmer absorption and 4000A break strength indices as a function of galactic radius for 12 massive (M*>1e10Msun), nearby (z<0.03), visually-selected plausible new ellipticals with blue-cloud optical colors and varying degrees of morphological peculiarities.  Find that these index values and their radial dependence correlate with specific morphological features such that the most disturbed galaxies have the smallest 4000A break strengths and the largest Balmer absorption values.  Overall, two-thirds of the sample are inconsistent with the predictions of the modern merger hypothesis.  Of these eight, half exhibit signatures consistent with recent minor merger interactions.  The other half have SFHs similar to local, quiescent early-type galaxies.  Of the remaining four galaxies, three have the strong morphological disturbances and SF optical colors consistent with being remnants of recent, gas-rich major mergers, but exhibit a weak, central burst consistent with forming ~5% of their stars.  The final galaxy possesses spectroscopic signatures of a strong, centrally-concentrated starburst and quiescent core optical colors indicative of recent quenching (i.e., a post-starburst signature) as prescribed by the modern merger hypothesis.


1505.01570
The first data release (DR1) of the LAMOST general survey
Luo, et al

The LAMOST (large sky area multi-object spectroscopic telescope) general survey is a spectroscopic survey that will eventually cover approximately half of the celestial sphere and collect 10M spectra of stars, galaxies, and QSOs.  Objects both in the pilot survey and the first year general survey are included in the LAMOST DR1.  The pilot survey started in 10/2011 and ended in 06/2012, and the data have been released to the public as the LAMOST Pilot Data Release in 08/2012.  The general survey started 09/2012, and completed its first year of operation in 06/2013.  The LAMOST DR1 includes a total of 1202 plates containing 2,955,336 spectra, of which 1.7M spectra have observed S/N>10.  All data with S/N>2 are formally released as LAMOST DR1 under the LAMOST data policy.  This data release contains a total of 2.2M spectra, but also 3 stellar catalogs with measured parameters: AFGK-type stars with high quality spectra (1.0M entries), A-type stars (200k entries) and M stars (121k entries).  This paper introduces the survey design, the observational and instrumental limitations, data reduction and analysis, and some caveats.  Description of the FITS structure of spectral files and parameter catalogues is also provided.