Day 404

Friday.

1304.1152
The role of relativistic jets in the heaviest and most active supermassive black holes at high redshift
Ghisellini, Haardt, Della Ceca, Volonteri, Sbarrato

The ratio of active radio-loud to radio-quiet AGN hosting heavy black holes is a rather strong function of redshift.  Report on evidence of this from BAT and LAT.  Suggest that the more frequent occurrence of relativistic jets in the most massive BHs at high z (~4), compared to later times (~1.5-2) could be due to the average BH spin being greater in the distant past, or else to the jet helping a fast accretion rate (or some combination of the 2 scenarios).  Emphasize that the large total accretion efficiency of rapidly spinning BHs inhibits a fast growth, unless a large fraction of the available gravitational energy of the accreted mass is not converted into radiation, but used to form and maintain a powerful jet.

1304.1154
The star formation rate and stellar mass limits for submillimetre galaxies implied by recent interferometric observations
Hayward

Explaining the observed number counts of submm galaxies (SMGs) has been a longstanding challenge for theoretical models.  Surprisingly, recent observations have suggested that the brightest SMBs are almost exclusively multiple fainter sources blended into a single source in the single-dish surveys.  This result is in contrast with the predictions of our previously presented theoretical model, which includes some effects of blending.  In this Letter, consider the implications of an upper limit on the submm flux density for the demographics of the SMG population.  Using a relation amongst submm flux, SFR, and dust mass (M_d) from previous work, infer the maximum SFR for a range of flux density limits.  For a given M_d, the corresponding SFR limits are calculated [numbers given in abstract].  The SFR limit implies a correspondingly sharp, z-dependent cutoff in the M_star function, the value predicted using the S_870-M_star relation predicted by the model.  The M_star limit decreases with increasing redshift: for an S_870 limit of 9-12.5 mJy, the M_star limit ranges from 4-7e12 Msun at z~1 to 3-5e11 Msun at z~6 [rather massive?].  Discuss the few interferometrically detected SMGs that may be brighter than the proposed cutoff.  Although such objects are certainly interesting, inferences based on such objects may not apply to most SMGs.

1304.1170
Detection of a nearby halo debris stream in the WISE and 2MASS surveys
Grillmair et al

As the title says.

1304.1178
Evidence for two distinct stellar initial mass functions : revisiting the effets of cluster dynamical evolution
Zaritsky, Colucci, Pessev, Bernstein [Rebecca!], Chandar

Measure velocity dispersions of 6 galactic globular clusters with spectra, to test for the effects of internal dynamical eovlution in the stellar M/L ratios, Upsilon*, of star clusters.  Combine with 5 previous measurements; find no relation between cluster mass, or relaxation time, and Upsilon*.  (bimodality of Upsilon* indicates 2 stellar populations, which relaxation can artificially depress).  Because relaxation is mass dependent, conclude that the values of Upsilon* for these clusters are not strongly affected by dynamical effects, and so confirm the presence of the population of clusters with low Upsilon*.