Day 975

Friday.


1509.07121
Photometric redshifts and clustering of emission line galaxies selected jointly by DES and eBOSS
Jouvel, et al

Present the results of the first test plates of eBOSS.  This paper focuses on the emission line galaxies (ELG) population targeted from DES photometry.  Analyze the success rate, efficiency, redshift distribution, and clustering properties of the targets.  From the 9000 spectroscopic redshifts targeted, 4600 have been selected from the DES photometry.  The total success rate for redshifts between 0.6 and 1.2 is 71% and 68% respectively for a bright and faint, on average more distant, samples including redshifts measured from a single strong emission line.  Find a mean redshift of 0.8 and 0.87, with 15 and 13% of unknown redshifts respectively for the bright and faint samples.  In the redshift range 0.6<z<1.2, for the most secure spectroscopic redshifts, the mean redshift for the bright and faint sample is 0.85 and 0.9 respectively.  Star contamination is lower than 2%.  Measure a galaxy bias averaged on scales of 1 and 10 Mpc/h of 1.72±0.1 for the bright sample end of 1.78±0.12 for the faint sample.  The error on the galaxy bias have been obtained propagating the errors in the correlation function to the fitted parameters.  This redshift evolution for the galaxy bias is in agreement with theoretical expectations for a galaxy population with MB-5logh<-21.0.  Note that biasing is derived from the galaxy clustering relative to a model for the mass fluctuations.  Investigate the quality of the DES photometric redshifts and find that the outlier fraction can be reduced using a comparison between template fitting and neural network, or using a random forest algorithm.


1509.07124
The spectral SN-GRB connrection: systematic spectral comparisons between type Ic supernovae, broad-lined Type Ic supernovae with and without Gamma-ray bursts
Modjaz, Liu, Bianco, Graur

Present the first systematic investigation of spectral properties of 17 SNe Ic, 10 broad-lined SNe Ic (SNe Ic-bl) without observed GRBs and 10 SNe Ic-bl with GRBs (SN-GRBs) as a function of time in order to probe their explosion conditions and progenitors.  Analyze a total of 396 spectra, which were drawn from published spectra of individual SNe as well as from the densely time-sampled spectra data of Modjaz+2014.  In order to quantify the diversity of the SN spectra as a function of SN subtype, construct average spectra of SNe Ic, SNe Ic-bl without GRBs, and SNe Ic-bl with GRBs, along with standard deviation and maximum deviation contours.  Find that SN1994I is not a typical SN Ic, in contrast to common belief, while the spectra of SN 1998bw/GRB 980425 are representative of mean spectra of SNe Ic-bl.  Measure the ejecta absorption and width  and find that SNe Ic-bl with GRBs, on average, have quantifiably higher absorption velocities, as well as broader line widths than SNe without observed GRBs.  Interpret this to indicate that SNe Ic-bl without observed GRBs may have had lower energy, chocked jets that imparted lower velocities to the SN ejecta.  Moreover, address the He-problem in SNe Ic-bl, namely whether the puzzling lack of He lines in SN Ic-bl spectra could be due to their He lines being too broadened by the high velocities present, and thus smeared out.  Show that the absence of clear He lines in optical spectra of all SNe Ic-bl, and in particular of SN-GRBs, is not due to them being too smeared out.  This implies that the progenitor stars of SN-GRBs are probably He-free, in addition to being H-free, which puts strong constraints on the stellar evolutionary paths needed to produce such SN-GRB progenitor stars at the observed low metallicities.