1205.0542
Driving outflows with relativistic jets and the dependence of AGN feedback efficiency on ISM inhomogeneity
Wagner, Bicknell, Umemura
Detailed physics of the feedback mechanism by relativistic AGN jets interacting with 2-phase fractal ISM. Negative feedback efficiency (cloud-dispersal generated by jet-ISM interactions) sensitive to maximum size of loads in the fractal cloud distribution; distribution of smaller clouds lead to higher outflow velocities. Systems with cloud complexes > 50pc require jets of Eddington ratio > 1e-2 to disperse the clouds appreciably. Find: acceleration of dense embedded cloud provided by the ram pressure (rather than thermal pressure) of the high velocity flow through the porous channels of the warm phase, flow that has fully entrained the shocked hot-phase gas it has swept up, and is accidtionally mass-loaded by ablated cloud material. This mechanism, reminiscent of a two-stage feedback scenario, transfers 10 to 40% of the jet energy to the cold and warm gas, accelerating it to several 100 to several 1000 km/s within a few 10 to 100 Myr. Predicted velocities match those observed in a range of high and low redshift radio galaxies hosting powerful radio jets.
1205.0544
Solving the mode identification problem in astroseismology of F stars observed with Kepler
White et al
Astroseismology of F-type stars hindered by ambiguity in identification of their oscillation modes; the regular mode pattern that makes this task trivial in cooler stars is masked by increased line widths. The absolute mode frequencies can help solve this impasse because the values of epsilon implied by the two possible mode identifications are distinct. Find that the correct epsilon can be deduced from the effective temperature and the line widths; apply methods to a sample of solar-like oscillators observed with Kepler.
1205.0546
Kinematic groups beyond the Solar neighborhood with RAVE
Antoja et al
The main local kinematic groups are large scale features, surviving at least up to ~1 kpc from the Sun in the direction of anti-rotation, and at least ~700 pc below the Galactic plane [MW thickness is ~300 pc]. Also find: for known regions located at different radii than the Sun, the groups appear shifted in the velocity plane.
1205.0547
The star-formation mass sequence out to z=2.5
Whitaker, van Dokkum, Brammer, Franx
Study the SFR-M* relation from 0<z<2.5 with NEWFIRM; find SFR propto M*^0.7, and a constant observed scatter of 0.34 dex independent of redshift and M*. For only blue galaxies, SFR propto M*, similar to z=0 results; red, dusty, SF galaxies with higher masses brings down the slope. SF galaxies form in 3 distinct regions of the log(SFR)-log(M*) plane: (1) actively SF galaxies with "normal" dust obscuration and associated colors--53%, (2) red SF galaxies with low levels of dust obscuration and low sSFRs--12%, and (3) dusty, blue SF galaxies with high sSFRs--6%. The remaining 29% comprises quiescent galaxies. Galaxies on the "normal" star formation sequence show strong trends of increasing dust attenuation and decreasing sSFR with stellar mass, with an observed scatter of 0.26 dex (0.19 dex intrinsic scatter). The dusty, blue galaxies reside in the upper envelope of the SF sequence with remarkably similar spectral shapes at all masses, suggesting that the same physical process is dominated the stellar light. The red, low-dust SF galaxies may be in the process of shutting off and migrating to the quiescent population.
1205.0555
The characteristic star formation histories of galaxies at redshifts z~2-7
Reddy, Pettini, Steidel, Shapley, Erb, Law
The average SFH is such that SFRs increase with time from z>4 to z=2-3. Consequence: (a) a substantial fraction of UV-bright z~2-3 galaxies had faint sub-L* progenitors at z>4, and (b) gas masses must increase with time from z=7 to 2, over which time the net cold gas accretion rate--as inferred from the sSFR and the Kennicutt-Schmidt relation---is ~2-3x larger than the SFR. If evolved to higher redshift, the SFHs and masses of the halos that are expected to host L* galaxies at z~2: find that <10% of baryons accreted onto typical haloes at z > 4 actually contribute to SF at those epochs. These results highlight the relative inefficiency of SF even at early cosmic times when galaxies were first assembling.
1205.0563
Constraining promordial non-Gaussianity with CMB-21cm cross-correlations?
Tashiro, Ho
Investigate the effect of primordial non-Gaussianity on the cross-correlation between the CMB anisotropies and the 21cm fluctuations from the epoch of reionization. S/N~3 for f_NL~50-100. Auto-correlatons of 21cm is a better probe of f_NL than the cross-correlations; but cross-correlations rids of systematics.
1205.0588
The production rate of SN Ia events in globular clusters
Washabaugh, Bregman
In globular clusters, dynamical evolution produces luminous X-ray emitting binaries at a rate about 200 times greater than in the field. Can it also enhance SN Ia events in early type galaxies, and provide insight into their formation? Use archival HST images; of 36 nearby galaxies, 21 had good data to search for globular cluster hosts; none of the 21 SNe have a definite globular cluster counterpart (but some cases ambiguous). Upper limit to the enhancement rate of SN Ia production in globular clusters of about 40 (order of magnitude lower than luminous x-ray binary enhancement). Conclude that globular clusters are not responsible for producing a significant fraction of the SN Ia events in early-type galaxies.
1205.0647
A simplified view of blazers: why BL Lacertae is actually a quasar in disguise
Padovani, Giommi, Polenta, Turriziani, D'Elia, Piranomonte
* BL Lac object: A type of active galaxy with an AGN and characterized by rapid and large amplitude flux variability, and significant optical polarization. Compared to quasars, BL Lacs have a spectra dominated by featureless non-thermal continuum. In the unified scheme, BL Lacs have its relativistic jet aligned with LoS---a blazar subtype.
It turns out tat sources so far classified as BL Lacs on the basis of their observed weak, or undetectable, remission lines are actually of two physically different classes: intrinsically weak-lined objects, more common in X-ray selected samples, and heavily diluted broad-lined sources, more frequent in radio selected samples, which explains some of the confusion in the literature.
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