Day 1038

Tuesday.  Wednesday.  Thursday.


1601.04226
Observational evidence of a slow downfall of star formation efficiency in massive galaxies during the last 10 Gyr
Schreiber, et al

Study the causes of the reported mass-dependence of the slope of SFR-M* relation, the so-called "Main Sequence" of SF galaxies, and discuss its implication on the physical processes that shaped the SF history of massive galaxies over cosmic time.  Make use of the NIR high-res imaging from HST in the CANDELS fields to perform a careful bulge-to-disk decomposition of distant galaxies and measure for the first time the slope of the SFR-Mdisk relation at z=1.  Find that this relation follows very closely the shape of the nominal SFR-M* correlation, still with a pronounced flattening at the high-mass end.  This is clearly excluding, at least at z=1, the secular growth of quiescent stellar bulges in SF galaxies as the main driver for the change of slope of the MS.  Then, by stacking the Herschel data available in the CANDELS field, estimate the gas mass (Mgas) and the star formation efficiency SFE=SFR/Mgas at different positions on the SFR-M* relation.  Find that the relatively low SFRs observed in massive galaxies (M*>5e10 Msun) are caused by a decreased SFE, by up to a factor of 3 as compared to lower stellar mass galaxies, and not by a reduced gas content.  Argue that this stellar-mass-dependent SFE can explain the varying slope of the MS since z=1.5, hence over 70% of the Hubble time.  The drop of SFE occurs at lower masses in the local Universe (M*>2e10 Msun) and is not present at z=2.  Altogether this provides evidence for a slow downfall of the SFE in massive MS galaxies.  The resulting loss of SF is found to be rising starting from z=2 to reach a level comparable to the mass growth of the quiescent population by z=1.  Finally discuss the possible physical origin of this phenomenon.


1601.04414
On the origin of flux ratio anomaly in quadruple lens systems
Inoue

Use SAM based on N-body sims to study the origin of flux ratio anomaly.  Estimate the effect of possible magnification perturbation caused by sub haloes with a mass scale of <~1e9 Msun/h in lensing galaxy haloes.  Expected change to the flux ratios per a multiply lensed image is just a few percent and the mean of the expected convergence perturbation at the effective Einstein radius of the lensing galaxy halo is <delta kappa_sub>=0.003, corresponding to the mean of the ratio of a projected DM mass fraction in sub haloes <f_sub>=0.006 for observed 11 quadruple lens systems.  In contrast, the expected change to the flux ratio caused by LoS structures in intergalactic spaces is typically ~10% and the mean of the convergence perturbation is <|detla kappa_los|>=0.008, corresponding to <f_los>=0.017.  The contribution of magnification perturbation cased by sub haloes is ~40% of the total at a source redshift z_s=0.7 and decreases monotonically in z_s to ~20% at z_s=3.6. Assuming statistical isotropy, the convergence perturbation estimated from the 11 systems has a positive correlation with the source redshift z_s, which is much stronger than that with the lens redshift z_L.  This feature also supports the idea that the flux ratio anomaly is caused mainly by LoS structures rather than sub haloes.  Also discuss about a possible imprint of LoS structures in demagnification of minimum images due to locally underdense structures in the LoS.


Science
Evidence for a distant giant planet in the solar system
Batygin, Brown

Analysis show, within the scattered disk population of Kuiper Belt exhibit an unexpected clustering in their respective arguments of perihelion.  Show that the orbits of KBOs cluster not only in argument of perihelion, but also in physical space.  Demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance, thus requiring a dynamical origin.  Find that the observed orbital alignment can be maintained by a distant eccentric planet with mass >~10 M_earth whose orbit lies in approximately the same plane as those of the distant KBOs, but whose perihelion is 180 deg away from the perihelia of the minor bodies.  In addition to accounting for the observed orbital alignment, the existence of such a plant naturally explains the presence of high-perihelion Sedna-like objects, as well as the known collection of high semimajor axis objects with inclinations between 60 and 150 deg whose origin was previously unclear.  Continued analysis of both distant and highly include outer solar system objects provides the opportunity for testing the hypothesis as well as further constraining the orbital elements and mass of the distant planet.  


Science
ASASSN-15lh: a highly super-luminous supernova
Dong, et al

Discovery of SN 2015L: the most luminous SN yet found.  At z=0.2326, ASASSN-15lh reached an absolute magnitude of M_u,AB=-23.5±0.1 and bolometric luminosity L_bol=(2.2±0.2)e45 ergs/s, which is more than twice as luminous as any previously known SN.  It as several major features characteristic of the H-poor super-luminous SNe (SLSNe-I), whose energy sources and progenitors are currently pool understood.  In contrast to most previously known SLSNe-I that reside in SF dwarf galaxies ASASSN-15lh appears to be hosted by a luminous galaxies (MK~-25.5) with litter SF.  In the 4 months since first detection, ASASSN-15lh radiated (1.1±0.2)e52 ergs, challenging the magnetar model for its engine.


1601.04704
The formation of massive, quiescent galaxies at cosmic noon
Feldmann, Hopkins, Quataert, Faucher-Giguere, Keres

The cosmic noon (z~1.5-3) marked a period of vigorous SF for most galaxies.  However, about a 1/3 of the more massive galaxies at those times were quiescent in the sense that their observed stellar populations are inconsistent with rapid SF.  The reduced SF activity is often attributed to gaseous outflows driven by feedback from SMBHs, but the impact of BH feedback on galaxies in the young Universe is not yet definitively established.  Analyze the origin of quiescent galaxies with the help of ultra-high resolution, cosmo sims that include feedback from stars but do not model the uncertain consequences of BH feedback.  Show that DM haloes with specific accretion rates below ~0.25-0.4 per Gyr preferentially host galaxies with reduced SFRs and red broadband colors.  The fraction of such haloes in large dark matter only simulations matches the observed fraction of massive quiescent galaxies (~1e10-11 Msun).  This strongly suggests that halo accretion rate is the key parameter determining which massive galaxies at z~1.5-3 become quiescent.  Empirical models that connect galaxy and halo evolution, such as HOD or abundance matching models assume a tight link between galaxy properties and the masses of their parent haloes.  These models will benefit from adding the specific accretion rate of haloes as a second model parameter.


1501.04947
The morphologies and alignments of gas, mass and the central galaxies of CLASH clusters of galaxies
Donahue, et al

Because morphology is often used to infer the state of relaxation of galaxy clusters, analyze and present a uniformly estimated X-ray morphological statistics for quantitative characterization of all 25 clusters in CLASH.  Compare X-ray morphologies of CLASH cluster with those identically measured for a large sample of simulated clusters for the MUSIC-2 sims, selected by mass.  Confirm a threshold in X-ray surface brightness concentration of C>0.4 for cool-core clusters, where C is the ratio of X-ray emission inside 100kpc/h70 compared to inside 500 kpc/h70.  Report and compare morphologies of these clusters inferred from SZE maps of he hot gas and in from projected mass maps based on SL and WL.  Find a strong agreement in alignments of the orientation of major axis for the lensing ,X-ray and SZE maps of nearly all of the CLASH clusters at radii of 500 kpc (approximately 0.5 R500 for these clusters).  Also find a striking alignment of clusters shapes at the 500 kpc scale, as measured with X-ray, SZE, and lensing, with that of the NIR stellar light a 10 kpc scales for the 20 "relaxed" clusters.  This strong alignment indicates a powerful coupling between the cluster- and galaxy-scale galaxy formation processes.