Day 814

Monday.  Tuesday.

1501.01960
How to bend galaxy disc profiles: the role of halo spin
Herpich et al

The radial density profiles of stellar galaxy disks can be well approximated as an exponential.  Compared to this canonical form, however, the profiles in the majority of disc galaxies show downward or upward breaks at large radii.  Currently, there is no coherent explanation in a galaxy formation context of the radial profiles per se, along with the two types of profiles breaks.  Using a set of controlled hydrodynamic simulations of disc galaxy formation, find a correlation between the host halo's initial angular momentum and the resulting radial profile of the stellar disc:  galaxies that live in haloes with a low spin parameter (lambda <~0.03 show an up-bending break in their disc density profiles, while galaxies in haloes of higher angular momentum show a down-bending break.  Find that the case of pure exponential profiles (lambda ~0.035) coincides with the peak of the spin parameter distribution from cosmological simulations.  The simulations not only imply an explanation of the observed behaviors, but also suggest that the physical original of this effect is related to the amount of radial redistribution of stellar mass, which is anti-correlated with lambda.

1401.01963
Green valley galaxies
Salim

The "green valley" is a wide region separating the blue and red peaks in the UV-opitcal color magnitude diagram, first revealed using GALEX UV photometry.  They highlight the discriminating power of UV to very low relative levels of ongoing SF, to which the optical colors, including u-r, are insensitive.  It corresponds to massive galaxies below the SF "main" sequence, and therefore represents a critical tool for the study of the quenching of SF and its possible resurgence in otherwise quiescent galaxies.  This article reviews the results pertaining to morphology, structure, environment, dust content and gas properties of green valley galaxies in the local universe.  Their relationship to AGN is also discussed.  Attention is given to biases emerging from defining the "green valley" using optical colors.  Review various evolutionary scenarios and present evidence for a new, quasi-static view of the green valley, in which the majority of galaxies currently in the green valley were only partially quenched in the distant past and now participate in a slow cosmic decline of SF, which also drives down the activity on the MS, presumably as a result of the dwindling accretion/cooling onto galaxy disks.

1501.01966
The stellar mass - halo mass relation for low mass X-ray groups at 0.5<z<1 in the CDFS with CSI
Patel et al

Since z~1, the stellar mass density locked in low mass groups and clusters has grown by a factor of ~8.  Make statistical measurements of the stellar mass content of low mass X-ray groups at 0.5<z<1, enabling the calibration of stellar-to-halo mass scales for wide-field optical and IR surveys.  Groups selected from Chandra and XMM-Newton observations of CDFS.  Stellar mass computed using galaxies from Carnegie-Spitzer-IMACS (CSI) spectroscopic redshift survey.  Find no evidence for any significant evolution in the stellar-halo mass relation since z<1.

1501.01973
Satellite dwarf galaxies in a hierarchical universe: infall histories, group preprocessing, and reionization
Wetzel, Deason, Garrison-Kimmel

In the LG, almost all satellite dwarf galaxies that are within the viral radius of the MW and M31 exhibit strong environmental influence.  The orbital histories of these satellite provide the key to understanding the role of the MW/M31 halo, lower mass groups, and cosmic reionization on the evolution of dwarf galaxies.  Examine the viral-infall histories of satellites with M*=1e3-9 Msun using the ELVIS suite of cosmo zoom-in dissipation's simulations of 48 MW/M31-like haloes.  Satellites at z=0 fell into the MW/M31 haloes typically 5-8 Gyr ago at z=0.5-1.  However, they first fell into any host halo typically 7-10 Gyr ago at z=0.7-1.5.  This difference arises because many satellites experienced "group preprocession" in another host halo, typically of Mvir~1e0-12 Msun, before falling into the MW/M31 haloes.  Satellites with lower-mass and/or those closer to the MW/M31 fell in earlier and are more likely to have experienced group preprocessing; half of all satellites with M*<1e6 Msun were preprocessed in a group.  Infalling groups also drive most satellite-satellite mergers within the MW/M31 haloes.  Finally, none of the surviving satellites at z=0 were within the viral radius of their MW/M31 halo during reionization (z>6), and only <4% were satellites of any other host halo during reioinization.  Thus, effects of cosmic reionization vs host-halo environment on the formation histories of surviving dwarf galaxies in the LG occurred at distance epochs and are separable in time.

1501.02047
Photometric redshift with bayesian priors on physical properties of galaxies
Tanaka

Preset a proof-of-concept analysis of photo-z with Bayesian priors on physical properties of galaxies.  This concept is particularly suited for upcoming/on-going large imaging surveys, in which only several broad-band filters are available and it is hard to break some of the degeneracies in the multi-color space.  Construct model templates of galaxies using a stellar population synthesis code and apply Bayesian priors on physical properties such as stellar mass and SFR.  These priors are a function of redshift and they effectively evolve the templates with time in an observationally motivated way.  Demonstrate that the priories help reduce the degeneracy and deliver significantly improved photometric redshifts.  Furthermore, show that a template error function, which corrects for systematic flux errors in the model templates as a function of rest-frame wavelength, delivers further improvements.  One great advantage of the technique is that they simultaneously measure z and physical properties of galaxies in a fully self-consistent manner, unlike the two-step measurements with different templates often performed.  One may worry that the physical priors bias the inferred galaxy properties, but they show that the bias is smaller than systematic uncertainties inherent in physical properties inferred from the SED fitting and hence is not a major issue.e  Extensively test and tune the priors in the on-going HSC survey and will make the code publicly available in the future.

1501.02055
Impact of baryonic processes on weak lensing cosmology: higher-order statistics and parameter bias
Osato, Shirasaki, Yoshida

Study the impact of baryonic physics on cosmological parameter estimation with WL surveys.  Run a set of cosmo hydro sims with different galaxy formation models.  Then perform ray-tracing simulations through the total matter density field to generate 100 independent convergence maps of 25 deg2 FoV, and use them to examine the ability of the following 3 lensing statistics as cosmological probes; PS, peak counts, and Minkowski Functionals.  For the upcoming wide-field observations such as HSC survey with a sky coverage of 1400 deg2, the higher-order statistics provide tight constraints on the matter density, density fluctuation amplitude, and DE EoS, but appreciable parameter bias is induced by the baryonic processes such as gas cooling and stellar feedback.  When PS, peak counts and MF are used, the relative bias in the DE EoS w is at the level of, (0.06, 0.5-0.6, and 0.01-0.1) sigma, respectively, where sigma is the overall error derived from Fisher analysis.  Find the bias is induced in different directions in the parameter space depending on the statistics employed.  While the 2pt statistics, i.e., PS, yield robust results against baryonic effects, the overall constraining power is weak compared with the other higher-order statistics.  On the other hand, using higher-order statistics alone results in significantly biased parameter estimate.  Suggest to use an optimized combination of, for example, PS and higher-order statistics so that the baryonic effects on parameter estimation are mitigated.  Such 'calibrated' combination can place stringent and robust constraints on cosmological parameters.

1501.02251
On the origin of intracluster light in massive galaxy clusters
DeMaio, Gonzalez, Zabludoff, Zaritsky

The results of this pilot study are suggestive of a formation history of these clusters in which the ICL is built-up by the stripping of >0.2 L* galaxies, and disfavor significant contribution to the ICL by dwarf disruption or major mergers with the BCG.