Day 690

Wednesday.

1407.0002
Stellar population gradients in galaxy discs from the CALIFA survey
Sanchez-Blazquez et al

While studies of gas-phase metallicity gradients in disc galaxies are common, very little has been done in the acquisition of stellar abundance gradients in the same regions.  Present a comparative study of the stellar metallicity and age distributions in a sample of 62 nearly face-on, spiral galaxies with and without bars, using data from the CALIFA survey.  Measure the slopes of the gradients and study their relation with other properties of the galaxies.  Find that the mean stellar age and metallicity gradients in the disc are shallow and negative.  Furthermore, when normalized to the effective radius of the disc, the slope of the stellar population gradients does not correlate with the mass or with the morphological type of the galaxies.  Contrary to this, the values of both age and metallicity at ~2.5 scale-lengths correlate with the central velocity dispersion in a similar manner to the central values of the bulges, although bulges show, on average, older ages and higher metallicities than the disks.  One of the goals of the present paper is to test the theoretical prediction that NL coupling between the bar and the spiral arms is an efficient mechanism for producing radial migrations across significant distances within discs.  The process of radial migration should flatten the stellar metallicity gradient with time and, therefore, would expect flatter stellar metallicity gradients in barred galaxies.  However, do not find any difference in the metallicity or age gradients in galaxies with [or] without bars.  Discuss possible scenarios that can lead to this absence of difference.

1407.0022
Faint dwarfs as a test of DM models: WDM vs. CDM
Governato, ... Madau, et al

Use high resolution Hydro+N-body cosmological simulations to compare the assembly and evolution of a small field dwarf (stellar mass ~1e6-7 Msun, goal mass 1e10 Msun) in LCDM and 2keV WDM cosmologies.  Find that SF in the WDM model is reduced and delayed by 1-2 Gyr relative to the CDM model, independently of the details of SF and feedback.  Independent of the DM model, but proportionally to the SF efficiency, gas outflows owed the central mass density through 'dynamical heating', such that all realization have circular velocities < 20 km/s at 500 pc, in agreement with local kinematic constraints.  As a result of dynamical heating, older stars are less centrally concentrated than younger stars, similar to stellar population gradients observed in nearby dwarf galaxies.  Translate simulations into artificial color-magnitude diagrams and SFHs in order to directly compare to available observations.  The simulated galaxies formed most of their stars in many ~10 Myr long bursts.  The CDM galaxy has a global SFH, HI abundance and Fe/H and alpha-element distribution well matched to current observations of dwarf galaxies.  These results highlight the importance of directly including 'baryon physics' in simulations when 1) comparing predictions of galaxy formation models with the kinematics and number density of local dwarf galaxies and 2) differentiating between CDM and non-standard models with different DM or power spectra.

1407.0031
Inferring the redshift distribution of the cosmic infrared background
Schmidt, Ménard, Scranton, Morrison, Rahman, Hopkins

Cross-correlating the Planck HFI maps against quasars from the SDSS DR7, determine the intensity distribution of CIB over 0<z<5.  Detect redshift-dependent spatial cross-correlations between the two datasets using the 3 channels and obtain upper limits at 1 channel consistent with expectations.  At all frequencies with detectable signal, infer a redshift distribution peaking around z~1.2 and find the recovered spectrum to be consistent with emission arising from SF galaxies.  However, lacking mid-IR coverage, we are not able to make an accurate determination of the mean temperature for the dust responsible for the CIB. By assuming simple modified BB and Kennicutt relations, able to determine dust and SF density as a function of z, finding results consistent with earlier measurements over a large portion of cosmic history.