Day 534

Wednesday.

1310.5145
A new stellar chemo-kinematic relation reveals the merger history of the Milky Way disc
Minchev et al

Velocity dispersions of stars near the Sun are known to increase with stellar age, but age can be difficult to determine so a proxy like the abundance of alpha elements (e.g., Mg) with respect to iron, [alpha/Fe], is used.  Here, report an unexpected behavior found in the velocity dispersion of a sample of giant stars in the RAVE survey with high quality chemical and kinematical information, in that it decreases strongly for stars with [Mg/Fe]>0.4 dex (i.e., those that formed in the first Gyr of the Galaxy's life).  THese findings are explained by perturbations from massive mergers in the early Universe, which have affected more strongly the outer parts o the disc, and the subsequent radial migration of stars with cooler kinematics from the inner disc.  Similar reversed trends in velocity dispersion are also found for different metallicity subpopulations.  Results suggest that the MW disc merger history can be recovered by relating the observed chemo-kinematic relations to the properties of past merger events.  
1310.5148
Star formation and AGN activity in interacting galaxies: a near-UV perspective
Scott, Kaviraj

Study nearby (<500 km/s), close (<30 kpc) galaxy pairs in SDSS to study key factors affecting SF and AGN activity triggered during galaxy interactions.  GALEX UV flux used to estimate sSFRs, find a factor of ~5.3 increase in sSFR for low mass 1e8-11 Msun close pair galaxies and a factor of ~2.1 increase in sSFR for high mass (1e11-13 Msun) close pairs compared to the general galaxy population.  Considering galaxies of all masses, find a factor of ~1.8 enhancement in sSFR for close pairs in field environments compared to non-pairs, with no significant increase for pairs in group and cluster environments.  A modest decrease of a factor of ~1.4 is found in the Seyfert fraction in close pair galaxies when compared to isolated galaxies, which suggests that mergers may not trigger AGN activity at the close-pair stage or may trigger a different class of AGN.  This becomes a factor of ~4.2 decrease when analysis is restricted to high mass close pairs in group or cluster environments.

1310.5151
Dilution in elliptical galaxies: implications for the relation between metallicity, stellar mass and star formation rate
Yates, Kauffmann

Investigate whether gradual dilution of the gas in some elliptical galaxies is the cause of a positive correlation between SFR and gas-phase metallicity (Zg) at high stellar mass (M*) in the local Universe.  Two classes of massive (M*>=1e10.5 Msun) galaxy are selected by high sSFRs and high Zg, and the second class by low sSFR and low Zg.  These criteria roughly distinguish disc-dominant galaxies from metal-poor, elliptical galaxies.  In SAM, the second class of galaxies obtain low sSFR and low Zg due to gradual dilution of the ISM by accretion of metal-poor gas via infalling clumps and low-mass satellites.  This occurs after a merger-induced SB and the associated SN feedback have quenched most of the original gas reservoir.  A number of signatures of this evolution are present in these model galaxies at z=0, including low gas fractions, large central BHs, elliptical morphologies, old ages, and importantly, low (Zg-Z*) indicating dilution after SF.  All of these properties are also found in low sSFR, low-Zg, massive galaxies in the SDSS-DR7.  This provides strong, indirect evidence that some elliptical galaxies are undergoing gradual dilution after a gas-rich merger in the local Universe.  This dilution scenario also explains the positive correlation between SFR and Zg measured in high-M* galaxies, and therefore has consequences for the local fundamental metallicity relation, which assumes a weak anti-correlation between SFR and Zg above 1e10.5 Msun.

1310.5177
The SWELLS survey. VI. hierarchical inference of the initial mass functions of bulges and discs
Brewer, Marshall, Auger, Treu, Dutton, Barnabè

"IMF is universal" being challenged: "Heavy" IMF preferred for massive early-type galaxies, while this IMF is inconsistent with the properties of less massive, later-type galaxies.  These discoveries motivate the hypothesis that the IMF may vary (possibly very slightly) across galaxies and across components of individual galaxies (e.g. bulges vs disks).  In this paper, use a sample of 19 late-type SL from the SWELLS survey to investigate the IMFs of the bulges and discs in late-type galaxies.  Perform a joint analysis of the galaxies' total masses (constrained by SL) and stellar masses (constrained by optical and NIR colors in the context of a SPS model, up to an IMF normalization parameter).  Using minimal assumptions apart form the physical constraint that the total stellar mass within any aperture must be less than the total mass within the aperture, find that the bulges of the galaxies cannot have IMFs heavier (i.e., implying high mass per unit luminosity) than Salpeter, while the disc IMFs are not well constrained by this data set.  Also discuss the necessity for hierarchical modeling when combining incomplete information about multiple astronomical objects.  This modeling approach allows us to place upper limits on the size of any departures from universality.  More data, including spatially resolved kinematics and stellar population diagnostics over a range of bulge and  disc masses, are needed to robustly quantify how the IMF varies within galaxies.

1310.5412
Transient weak-lensing by cosmological dark matter microhaloes
Rahvar, Baghram, Afshordi

Study of the time variation of the apparent flux of cosmological point sources due to the transient WL by DM microhaloes.  Derive correspondence between the temporal PS of WL magnification and the spatial PS of density on small scales.  Considering different approximations for the small scale structure of DM, predict the apparent magnitude of cosmological point sources to vary by as much as 1e-4 to 1e-3 due to this effect, within a period of a few months.  This red photometric noise has an almost perfect gaussian statistics, to one part in ~1e4.  Also compare the transient weak lensing PS with the BG effects such as the stellar microlensing on cosmological scales.  A quasar lensed by a galaxy or cluster with multiple images, is a suitable system for this study as: (i) using the time-delay method between different images, can remove the intrinsic variations of the quasar, and (ii) strong lensing enhances signals from the transient WL.  Also require the images to form at large angular separations from the center of the lensing structure, in order to minimize contamination by the stellar microlensing.  With long-term monitoring of quasar SL systems with a 10 m class telescope, can examine the existence of dark microhaloes as the building blocks of DM structures.  Failure to detect this signal may either be caused by a breakdown of CDM hierarchy on small scales, or rather interpreted as evidence against CDM paradigm, e.g. in favor of modified gravity models.

1310.5450
The origin of cold gas in giant elliptical galaxies and its role in fueling radio-mode AGN feedback
Werner et al

Eight nearby, X-ray and optically bright, giant elliptical galaxies studied in multi-wavelength.  All systems with extended Ha emission (6/8) display significant [CII] line emission indicating the presence of cold gas.  This emission is co-spatial with the Ha+[NII] emitting nebulae and the lowest entropy X-ray emitting plasma.  The entropy profiles of the hot galactic atmospheres show a clear dichotomy, with the systems displaying extended emission line nebulae having lower entropies beyond r~1 kpc than the cold-gas-poor systems.  Show that while the hot atmospheres of the cold-gas-poor galaxies are thermally stable outside of their innermost cores, the atmospheres of the cold-gas-rich systems are prone to cooling instabilities.  This result indicates that the cold gas is produced chiefly by thermally unstable cooling from the hot phase.  Show that cooling instabilities may develop more easily in rotating systems and discuss an alternative conditions for thermal instability for this case.  The hot atmospheres of cold-gas-rich galaxies display disturbed morphologies indicating that the accretion of clumpy multiphase gas in these systems may result in variable power output of the AGN jets, potentially triggering sporadic, larger outbursts.  In the two cold-gas-poor, X-ray morphologically relaxed galaxies of this sample, powerful AGN outbursts may have destroyed or removed most of the cold gas from the cores, allowing the jets to propagate and deposit most of their energy further out, increasing the entropy of the hot galactic atmospheres and leaving their cores relatively undisturbed.

1310.5486
Three-dimensional microlensing
Mao, Witt, An

Lensing where 2 lenses are located at different distances along the LoS.  Formulate the lens equation in complex notations and recover several previous results.  There are 4~6 images, with an equal number of images with positive and negative parities.  Find that the sum of signed magnifications for six image configurations is unity.  Furthermore, show that the light curves can be qualitatively different from those for binary lensing in a single plane.  In particular, the magnifications between a 'U'-shaped caustic crossing can be close to unity, rather than having a minimum magnification of 3 as in the single plane binary lensing.  THere is only a small probability 3-dimentionsl microlensing events will be seen in microlensing toward the Galactic centre.  It is more likely they will be first seen in cosmological microlensing.

1310.5662
Snowmass cosmic frontiers 6 (CF6) working group summary --The bright side of the cosmic frontier: cosmic probes of fundamental physics
Beatty et al, Snowmass 2013

Topics addressed include ultra-high energy cosmic rays, neutrinos, gamma rays, baryogenesis, and experiments probing the fundamental nature of space-time.

1310.5702
A CANDES - 3d-HST synergy: resolved star formation patterns at 0.7<z<1.5
Wuyts, ... van Dokkum, ... Genzel, Grogin, Koekemoer, ... et al

Analyze the resolved stellar populations of 473 massive SF galaxies at 0.7<z<1.5, with multi-wavelength broad-band imaging from CANDELS and Ha surface brightness profiles at the same kiloparsec resolution from 3D-HST.  Together they shed line on how the assembled stellar mass is distributed within galaxies, and where new stars are being formed.  Find the Ha morphologies to resemble more closely those observed in the ACS I band than in the WFC3 H band, especially for the larger systems.  Next derive a novel prescription for Ha dust corrections, which accounts for extra extinction towards HII regions.  The prescription leads to consistent SFR estimates and reproduces the observed relation between the Ha/UV luminosity ratio and visual extinction, both on a pixel-by-pixel and on a galaxy-integrated level.  Find the surface density of SF to correlate with the surface density of assembled stellar mass for spatially resolved regions within galaxies, akin to the so-called 'MS of SF' established on a galaxy-integrated level.  Deviations from this relation towards lower equivalent widths are found in the inner regions of galaxies.  Clumps and spiral features are associated with enhanced Ha equivalent widths, bluer colors, and higher sSFRs compared to the underlying disk.  Their Ha/UV luminosity ratio is lower than that of the underlying disk, suggesting the ACS clump selection preferentially picks up those regions of elevated SF activity that are the least obscured by dust.  Analysis emphasizes that monochromatic studies of galaxy structure can be severely limited by mass-to-light ratio variations due to dust and spatially inhomogeneous SFH.

1310.5711
X-ray bright active galactic nuclei in massive galaxy clusters II: the fraction of galaxies hosting active nuclei
Ehlert, von der Linden, Allen, Brandt, Xue, Luo, Mantz, Morris, Applegate, Kelly

Measurement of the fraction of cluster galaxies hosting X-ray bright AGN as a function of clusterc entric distance in units of r_500.  Analysis employs high quality Chandra X-ray and Subaru optical imaging for 42 massive X-ray selected galaxy cluster fields spanning the redshift range of 0.2<z<0.7.  In total, study involves 176 AGN with R<23 optical counterparts above 0.5-8.0 keV flux limit of 1e-14 erg/cm^2/s.  When excluding central dominant galaxies from the calculation, measure a cluster-galaxy AGN fraction in the central regions of the clusters that is ~3x lower that the field value.  This fraction increases with cluster centric distance before becoming consistent with the field at ~2.5 r500.  Data exhibit similar radial trends to those observed for star formation and optically selected AGN in cluster member galaxies, both of which are also suppressed near cluster centers to a comparable extent.  These results strongly support the idea that X-ray AGN activity and strong SF are linked through their common dependence on available reservoirs of cold gas.

1310.5712
Anomalous anisotropies of cosmic rays from turbulent magnetic fields
Ahlers

Propagation of CRs in turbulent interstellar B-fields is typically described as a spatial diffusion process.  This formalism predicts only a small deviation from an isotropic CR distribution in the form of a dipole in the direction of the CR density gradient or relative BG flow.  Show that the existence of a global CR dipole moment necessarily generates a spectrum of higher multipole moments in the local CR distribution.  These "anomalous" anisotropies are a direct consequence of Liouville's theorem in the presence of a local turbulent B-field. Show that the predictions of this model are in excellent agreement with the observed PS of multi-TeV CRs.

1310.5721
Detection of warm and diffuse baryons in large scale structure from the cross-correlation of gravitational lensing and the thermal Sunyaev-Zeldovich effect
Van Waerbeke, Hinshaw, Murray

Correlation between GL by LSS and the tSZ effect.  Using mass map from CFHTLenS and a newly-constructued tSZ map from Planck, measure a non-zero correlation between the two maps out to one degree angular separation on the sky, with an overall significance of 6 sigma.  The tSZ maps are formed in a manner that removes primary CMB fluctuations and minimizes residual contamination by galactic and extragalactic dust emission, and by CO line emission.  Perform numerous test to show that meausrement is immune to these residual contaminants.  The resulting correlation function is consistent with the existsence of a warm baryonic gas tracing the LSS with a bias b_gas.  Given the shape of the lensing kernel, signal sensitivity peaks at z~0.4, where half a degree separation on the sky corresponds toa a physical scale of ~10 Mpc.  The amplitude of the signal constrains the product (b_gas/1)(Te/1 keV)(n_e/1 m^-3)=2.01 pm 0.31 pm 0.21, at z=0.  Study suggests that a substantial fraction of the "missing" baryons in the universe may reside in a low density warm plasma that traces DM.

1310.5739
Super cosmic variance from mode-coupling: a worked example
LoVerde

If the entire post-inflationary patch is large compared to our Hubble volume, even a small level of non-Gaussianity can cause statistics of the primordial curvature field in our Hubble volume to be biased by mode-coupling.  Explicitly compute the variation of locally measured statistics of the primordial curvature zeta from non-Gaussian mode coupling within a specific inflationary scenario: the curvaton model with a quadratic curvaton potential.  This "super cosmic variance" is calculated in two ways: (i) as a super observer who has access to the curvature perturbation field across the entire post-inflationary patch and therefore sees local statistics as biased by mode coupling and (ii) as a local observer who sees the statistics of zeta determined by the local values of quantities in their Hubble patch.  The two calculations agree, and show that in the quadratic curvaton model, patch-to-patch differences in statistics of zeta can be interpreted entirely as a shift in the value of the curvaton field at freeze out.  Applying the same arguments to single-field slow-roll inflation gives a simple picture of how non-Gaussian mode-coupling between the curvature perturbations on very different physical scales must vanish in the attractor limit.

1310.5825
Effects of plasma on gravitational lensing
Er, Mao

Study GL when plasma surrounds the lens: easily observable at ~100th of an arcsec when an inhomogeneous plasma distribution exists.  Can use the position difference in different frequencies to estimate the density of plasma in the lens.  THe magnification ratios between multiple images are mainly determined by other properties of the lens, and are only weakly affected by the plasma.  Find that the SL time delay will be affected by the plasma.  Estimation of the Hubble constant from the time delay in low radio frequency observation may be slightly biased due to plasma in the lens.  Unfortunately, the ionosphere of the Earth strongly affects low frequency radio observations; thus ability to detect the effect depends on how well the ionosphere can be calibrated out.

1310.5926
How secret interactions can reconcile sterile neutrinos with cosmology
Hannestad, Hansen, Tram

Short baseline neutrino oscillation experiments have shown hints of the existence of additional sterile neutrinos in the eV mass range.  However, such neutrinos seem incompatible with cosmology because they have too large an impact on cosmic structure formation.  Here, show that new interactions in the sterile neutrino sector can prevent their production in the early Universe and reconcile short baseline oscillation experiments with cosmology.