1506.05459
ALMA and Herschel reveal that AGN and main-sequence galaxies have different star formation rate distributions
Mullaney, et al
Investigate SFR distributions of X-ray AGN host galaxies at 0.5<z<1.5 and 1.5<z<4, comparing them to that of normal, SF (MS) galaxies. Find 34-55% of AGNs have SFRs at least a factor of 2 below that of the average MS galaxy, compared to ~15% of all MS galaxies, suggesting significantly different SFR distributions. Indeed, when both are modeled as log-normal distributions, the mass and z-normalized SFR distributions of AGNs are roughly twice as broad, and peak ~0.4 dex lower, than that of MS galaxies. However, like MS galaxies, the normalized SFR distribution of AGNs appears not to evolve with redshift. Despite AGNs and MS galaxies having different SFR distributions, the linear-mean SFR of AGNs derived from our distributions is remarkably consistent with that of MS galaxies, and thus with previous results derived from stacked Herschel data. This apparent contradiction is due to the linear-mean SFR being biased by bright outliers, and thus does not necessarily represent a true characterization of the typical SFR of AGNs.
1506.05466
H-ATLAS/GAMA: quantifying the morphological evolution of the galaxy population using cosmic calorimetry
Eales, et al
Using results from H-ATLAS/GAMA, show that, for galaxy masses above approximately 1e8 Msun, 51% of the stellar mass-density in the local Uinverse is in early-type galaxies (ETGs: Sersic n>2.5) while 89% of the rate of production of stellar mass-density is occurring in late-type galaxies (LTGs: Sersic n<2.5). From this zero-redshift benchmark, use a calorimetric technique to quantify the importance of the morphological transformation of galaxies over the history of the Universe. The extragalactic background radiation contains all the energy generated by nuclear fusion in stars since the BB. By resolving this BG radiation into individual galaxies using the deepest FIR survey with Herschel and a deep NIR/optical survey with HST, and using measurements of the Sersic index of these galaxies derived from the HST images, estimate that approximately 83% of the stellar mass-density formed over the history of the universe occurred in LTGs. The difference between this and the fraction of the stellar mass-density that is in LTGs today implies there must have been a major transformation of LTGs into ETGs after the formation of most of the stars.
1506.05537
Baryonic impact on the dark matter distribution in Milky Way-size galaxies and their satellites
Zhu, ... Springel, Hernquist, et al
Study the impact of baryons on the distribution of dark matter in a MW-size halo by comparing a high-resolution, moving-mesh cosmological simulation with its DM-only counterpart. Identify 3 main processes related to baryons -- adiabatic contraction, tidal disruption and reionization -- which jointly shape the DM distribution in both the main halo and its subclass. The relative effect of each baryonic process depends strongly on the sub halo mass. For massive sub-haloes with maximum circular velocity v_max>35 km/s, adiabatic contraction increases the DM concentration, making these haloes less susceptible to tidal disruption. For low-mass subhalos with v_max<20 km/s, reionization effectively reduces their mass on average by ~30% and v_max by ~20%. For intermediate sub haloes with 20km/s<v_max<35 km/s, which share a similar mass range as the classical dSphs, strong tidal truncation induced by the main galaxy reduces their v_max. Moreover, the stellar disk of the main galaxy effectively depletes sub-haloes near the central region. As a combined result of reionization and increased tidal disruption, the total number of low-mass sub haloes in the hydrodynamic simulation is nearly halved compared to that of the N-body simulation. No DM cores in dwarf galaxies found, unlike previous studies that employed bursty feedback-driven outflows. The substantial impact of baryons on the abundance and internal structure of sub haloes suggests that galaxy formation and evolution models based on N-body sims should include these physical processes as major components.
No comments:
Post a Comment