Day 1036

Tuesday.  Wednesday.  Thursday.


1601.02023
Cluster mass profile reconstruction with size and flux magnification on the HST STAGES survey
Duncan, Heymans, Heavens, Joachimi

Present the first measurement of individual cluster mass estimates using WL size and flux magnification.  Using data from the HST-STAGES survey of the A901/902 supercluster, detect the 4 known groups in the supercluster at high significance using magnification alone.  Discuss the application of a fully Bayesian inference analysis, and investigate a broad range of potential systematics in the application of the method.  Compare the results to a previous WL shear analysis of the same field finding the recovered signal-to-noise of the magnification-only analysis to range from 45% o 110% of the S/N in the shear-only analysis.  On a case-by-case basis find consistent magnification and shear constraints on cluster viral radius, and find magnification constraints to be a factor 0.77±0.18 lower than the shear measurements for the the full sample.


1601.02091
AGN host galaxy mass function in COSMOS: is AGN feedback responsible for the mass-quenching of galaxies?
Bongiorno, et al

Investigate the role of SMBH in the global context of galaxy evolution by measuring the host galaxy stellar mass function (HGMF) and the specific accretion rate i.e., lambda_SAR, distribution function (SARDF) up to z~2.5 with ~1000 X-ray selected AGN from XMM-COSMOS.  Using a maximum likelihood approach, jointly fit the stellar mass function and specific accretion rate distribution function, with the X-ray luminosity function as an additional constraint.  The best fit model characterizes the SARDF as a double power-law with mass dependent but z independent break whose low lambda_SAR slope flattens with increasing redshift while the normalization increases.  This implies that, for a given stellar mass, higher lambda_SAR objects have a peak in their space density at earlier epoch compared to the lower lambda_SAR ones, following and mimicking the well known AGN cosmic downsizing as observed in the AGN luminosity function.  The mass function of active galaxies is described by a Schechter function with an almost constant Mstar* and a low mass slope alpha that flattens with redshift.  Compared to the stellar MF, find that the HGMF has a similar shape and that, up to log(Mstar/Msun)~11.5 the ratio of AGN host galaxies to star forming galaxies is basically constant (~10%).  Finally, the comparison of the AGN HGMF for different luminosity and specific accretion ratio sub-classes with the phenomenological model prediction by Peng+2010 for the "transient" population, i.e., galaxies in the process of being mass-quenched, reveals that low-luminosity AGN do not appear to be able to contribute significantly to the quenching and that at least at higher masses, i.e., Mstar>1e10.7 Msun, feedback from luminous AGN (log(Lbol) >~46 [erg/s]) may be responsible for the quenching of SF in the host galaxy.


1601.02266
The most luminous H$\alpha$ emitters at z~0.8-2.23 from HiZELS: evolution of AGN and star-forming galaxies
Sorbet et al

Find little to no evolution in the AGN fraction with redshift within errors, but the AGN fraction increases strongly with Ha luminosity and correlates best with L_Ha/L*_Ha(z).  While L_Ha<L*_Ha(z) Ha emitters are largely dominated by SF galaxies (>80%), the most luminous Ha emitters (L_Ha>10 L*_Ha(z)) at any cosmic time are essentially all BL-AGN.  Using the AGN-decontaminated sample of luminous SF galaxies, and integrating down to a fixed Ha luminosity, find a factor of ~1300x evolution in the SFR density from z=0 to z=2.23.  This is much stronger than the evolution from typical Ha SF galaxies and in line with the evolution seen for constant luminosity cuts used to select "Ultra-luminous" infrared galaxies and/or sub-millietre galaxies.  By taking in to account the evolution in the typical Ha luminosity, show that the most strongly SF Ha-selected galaxies at any epoch contribute the same fractional amount  of 15% to the total SFR density, at least up to z=2.23.


1601.02611
Is there a maximum mass for black holes in galactic nuclei?
Inayoshi, Haiman

The largest observed SMBHs have mass of M_BH~1e10 Msun, nearly independent of redshift, from the local (z~0) to the early (z>6) universe.  Suggest that the growth of SMBHs above a few 1e10 Msun is prevented by small scale accretion physics, independent of the properties of their host galaxies or of cosmology.  Growing more massive BHs requires a gas supply rate from galactic scales onto a nuclear region as high as >1e3Msun/yr.  At such a high accretion rate, most of the gas converts to stars at large radii (~10-100 pc), well before reaching the BH.  Adopt a simple model (Thompson+ 2005) for a SF accretion disk, and find that the accretion rate in the sub-pc nuclear region is reduced to the smaller value of at most a few Msun/yr.  This prevents SMBHs from growing above ~1e11 Msun in the age of the Universe.  Furthermore, once a SMBH recaches a sufficiently high mass, this rate falls below the critical value at which the accretion flow becomes advection dominated.  Once this transition occurs, BH feeding can be suppressed by strong outflows and jets from hot gas near the BH.  Find that the maximum SMBH mass, given by this transition, is between M_BH,max ~ (1-6)e10 Msun, depending primarily on the efficiency of angular momentum transfer inside the galactic disk and not on other properties of the host galaxy.


1510.02618
Spectral distortion of the CMB by the cumulative CO emission from galaxies throughout cosmic history
Mashian, Loeb, Sternberg

Cumulative CO emission from galaxies throughout cosmic history distorts the spectrum of the CMB at a level that is well above the detection limit of future instruments, such as PIXIE (Primordial Inflation Explorer).  Most of the CO foreground originates from modest redshifts z~2-5, and needs to be efficiently removed for more subtle distortions from the earlier universe to be detected.


1601.02624
The mass-concentration-redshift relation of cold and warm dark matter haloes
Ludlow, ... Navarro, Cole, Frenk, et al

Sims with standard LCDM models, as well as several additional simulations with sharply truncated density fluctuation power spectra, such as those expected in WDM scenario.  The c(M,z) relation of CDM haloes is monotonic: concentrations decrease with increasing viral mass at tied redshift, and decrease with increasing redshift at fixed mass.  The main-progenitor mass accretion histories (MAHs) of CDM haloes are also scale-free, a result that has been used to infer halo concentrations directly from MAHs.  These results do not apply to WDM haloes: their MAHs are not scale-free because of the characteristic scale imposed by the PS suppression.  Further, the WDM c(M,z) relation is not monotonic: concentrations peak at a halo mass scale dictated by the truncation scale, and decrease at higher and lower masses.  Show that the assembly history of a halo can still be used to infer its concentration, provided that the total mass of its collapsed progenitors is considered (the "collapsed mass history"; CMH), rather than just that of its main ancestor.  This follows the original NFW proposal, and exploits the scale-free nature of CMHs to derive a simple scaling that reproduces the mass-concentration-redshift relation of both CDM and WDM haloes in sims over a vast range of halo masses and cosmic time  The model therefore provides a robust account of the mass, redshift, cosmo and PS dependence of the concentrations of DM haloes assembled hierarchically.


1601.02664
A comparative study of knots of star formation in interacting vs. spiral galaxies
Smith, et al

Interacting galaxies are known to have higher global rates of SF on average than normal galaxies, relative to their stellar masses.  Using UV and IR photometry combined with new and published H-alpha images, compare the SFRs of ~700 SF complexes in 46 nearby interacting galaxy pairs with those of regions in 39 normal spiral galaxies.  The interacting galaxies have proportionally more regions with high SFRs than the spirals.  The most extreme regions in the interacting systems lie at the intersections of spiral/tidal structures, where gas is expected to pile up and trigger SF.  Published HST images show unusually large and luminous star clusters in the highest luminosity regions.  The SFRs of the clumps correlate with measures of the dust attenuation, consistent with the idea that regions with more interstellar gas have more SF.  For the clumps with the highest SFRs, the apparent dust attenuation is consistent with the Calzetti starburst dust attenuation law.  This suggests that the high luminosity regions are dominated by a central group of young stars surrounded by a shell of clumpy interstellar gas.  In contrast, the lower luminosity clumps are bright in the UV relative to H-alpha, suggesting either a high differential attenuation between the ionized gas and the stars, or a post-starburst population bright in the UV but faded in Ha.  The fraction of the global light of the galaxies in the clumps is higher on average for the interacting galaxies than for the spirals.  Thus the SF regions in interacting galaxies are more luminous, dustier, or younger on average.


1601.02693
The effects of assembly bias on cosmological inference from galaxy-galaxy lensing and galaxy clusters
McEwen, Weinberg

The combination of GGL and galaxy clustering is a promising route to measuring the amplitude of matter clustering and testing modified gravity theories of cosmic acceleration.  HOD modeling can extend the approach down to nonlinear scales, but galaxy assembly bias could introduce systematic errors by causing the HOD to vary with large scale environment at fixed halo mass.  Investigate this problem using the mock galaxy catalogs created by Hearin+Watson (2013), which exhibit significant assembly bias because galaxy luminosity is tied to halo peak circular velocity and galaxy color is tied to halo formation time.  The preferential placement of galaxies (especially red galaxies) in older haloes affects the cutoff of the mean occupation function <N_cen(M_min)> for central galaxies, with haloes in overdense regions more likely to host galaxies.  The effect of assembly bias on the satellite galaxy HOD is minimal.  Introduce an extended, environment dependent HOD (EDHOD) prescription to describe these results and fit galaxy correlation measurements.  Crucially, find that the galaxy-matter cross-correlation coefficient, r_gm==xi_gm/sqrt(xi_mm xi_gg), is insensitive to assembly bias on scales r>~1Mpc/h, even though xi_gm and xi_gg are both affected individually.  Can therefore recover the correct xi_mm from the HW13 gg and gm correlations using either a standard HOD or EDHOD fitting method.  For Mr<-19 or Mr<-20 samples, the recovery of xi_mm is accurate to 2% or better.  For a sample of red Mr<-20 galaxies, achieve 2% recovery at r>2 Mpc/h with EDHOD modeling but lower accuracy at smaller scales or with a standard HOD fit.


1601.03042
When the Milky Way turnoff the lights: APOGEE provides evidence of star formation "quenching" in our Galaxy
Haywood, et al

Show the first evidence that the MW experienced a generalized quenching of its SF at the end of its thick disk formation ~9 Gyr ago.  Elemental abundances of stars studied as part of the APOGEE survey reveal indeed that in less than ~2 Gyr the SFR in the Galaxy dropped by an order-of-magnitude.  Because of the tight correlation between age and alpha abundance, this event reflects in the dearth of stars along the inner disk sequence the [Fe/H]-[a/Fe] plane.  Before this phase, which lasted about 1.5 Gyr, the MW was actively forming stars.  Afterwards, the SF resumed at a much lower level to form the thin disk.  These events are very well matched by the latest observation of MW-type progenitors at high redshifts.  In late type galaxies, quenching is believed to be related to a long and secure exhaustion of gas.  In our Galaxy, it occurred on a much shorter time scale, while the chemical continuity before and after the quenching indicates that it was not due to the exhaustion of the gas.  While quenching is generally associated with spheroids, the results show that it also occurs in galaxies like the MW, possibly when they are undergoing a morphological transition from thick to thin disks.  Given the demographics of late type galaxies in the local universe, in which classical bulges are rare, suggest further that this may hold true generally in galaxies with mass lower than or approximately M*, where quenching could be directly a consequence of thick disk formation.  Emphasize that the quenching phase in MW could be contemporaneous with, and related to, the formation of the bar.  Sketch a scenario on how a strong bar may inhibit SF.


1601.03051
Gravitational lensing by ring-like structures
Lake, Zheng

Study a class of gravitational lensing systems consisting of an inclined ring/belt, with and without an added point mass at the centre.  Show that a common property of such systems is the so-called "pseudo-caustic", across which the magnification of a point source changes discontinuously and yet remains finite.  Such a magnification change can be associated with either a change in image multiplicity or a sudden change in the size of one of the images.  The existence of pseudo-caustics and the complex interplay between them and the formal caustics (corresponding to points of infinite magnification) can lead to interesting consequences, such as truncated or open caustics and the violation of Burke's theorem.  The origin of the pseudo-caustics is found to be the discontinuity in the solutions to the lens equation across the ring/belt boundaries, and the pseudo-caustics correspond to these boundaries in the image (lens) plane.  Provide a few illustrative examples to understand the pseudo-caustic features, and in a separate paper, consider a specific astronomical application of microlensing by extrasolar asteroid belts.


1601.03052
Detecting extrasolar asteroid belts through their microlensing signatures
Lake, Zheng, Dong

(see abstract directly above) Astroid belt + star lens systems create "pseudo-caustics", where the magnification exhibits a finite but discontinuous jump.  These features allow such systems to generate distinctive microlensing light curves across a wide region of belt parameter space and possess remarkably large using cross-sections.  Sample light curves for a range of mastoid bel parameters are presented.  In the near future, space-based microlensing surveys (e.g., WFIRST) may be able t discover extrasolar asteroid belts with masses of the order of 0.1 M_earth.