Day 762

Monday.

1410.2238
Radial migration of the Sun in the Milky Way:  A Statistical study
Martínez-Barbosa, Brown, Portegies-Zwart

Find that in general it is unlikely that the Sun has migrated significantly from the inner regions of the Galactic disk to R_\odot.

1410.2244
The stellar accretion origin of stellar population gradients in massive galaxies at large radii
Hirschmann et al

Use 10 cosmological zoom sims of haloes with 6e12 Msun < Mhalo < 2e13 Msun.  The simulations follow metal cooling and enrichment from SNII, SNIa and AGB winds.  Explore the differential impact of an empirical model for galactic winds that reproduces the mass-metallicity relation and its evolution with redshift.  At larger radii the galaxies, for both models, become more dominated by stars accreted from satellite galaxies in major and minor mergers.  In the wind model, fewer stars are accreted, but they are significantly more metal poor resulting in steep global metallicity and color.  In contrast, color and metallicity gradients of the models without winds are inconsistent with observations.  Age gradients are in general mildly positive at z=0 with significant differences between the models at higher redshift.  Demonstrate that for the wind model, stellar accretion is steepening existing in-situ metallicity gradients by about 0.2 dex by the present day and helps to match observed gradients of massive early-type galaxies at large radii.  Color and metallicity gradients are significantly steeper for systems which have accreted stars in minor mergers, while galaxies with major mergers have relatively flat gradients, confirming previous results.  This study highlights the importance of stellar accretion for stellar population properties of massive galaxies at large radii, which can provide important constraints for formation models.

1410.2250
A new probe of magnetic fields in the pre-reinization epoch: I. formalism
Venumadhav, ... Hirata, etal

Propose a method of measuring extremely weak B-fields in the inter galactic medium prior to and during the epoch of cosmic reionization.  The method utilizes the Larmor precession of spin-polarized neutral hydrogen in the triplet state of the hyperfine transition.  The resulting change in the brightness temperature fluctuations encodes information about the B-field the atoms are immersed in.  The method is most suited to probing fields that are coherent on large scales. Due to the long lifetime of the triplet state of the 21-cm transition, this technique is naturally sensitive to extremely weak field strengths, of order 1e-19 G (or 1e-21 G if scaled to the present day).  Therefore, this might open up the possibility of probing primordial B-fields just prior to reionization.  Moreover, such measurements are unaffected by later B-fields since 21-cm observations preserve redshift information.  If the B-fields are much stronger, it is still possible to recover information about their orientation.  In this paper, perform detailed calculations of the microphysics behind this effect, and take into account all the processes that affect the hyperfine transition, including radiative decays, collisions, and optical pumping by Lyman-alpha photons.  Conclude with an analytic formula for the brightness temperature of linear-regime fluctuations in the presence of a B-feld, and discuss its limiting behavior for weak and strong fields.

1410.2276
The next generation Virgo cluster survey.  XV.  The photometric redshift estimation for background sources
Raichoor, Mei, Erben, Hildebrandt, ... Ilbert, et al

The NGVCS is an optical imaging survey covering 104 sq deg centered on the Virgo cluster.  The complete survey area has been observed in the u*giz-bands and one third in the r-band.  Present the photometric z estimation fro the NGVS background sources.  After a dedicated data reduction, perform accurate photometry, with special attention to precise color measurements through PSF homogenization.  Then estimate the photometric z with the LePhare and BPZ codes.  Add a new prior which extends to iAB=12.5 mag.  Using the u*giz-bands, photometric redshifts for 15.5 <= i <~ 23 mag or zphot <~1 galaxies have bias |Delta z|<0.02, less than 5% outliers, and a scatter sigma_outl.reg. and an individual error on zphot that increase with magnitude (from 0.02 to 0.05 and from 0.03 to 0.10, respectively).  When using the u*giz-bands over the same magnitude and redshift range, the lack of the r-band increases the uncertainties in the 0.3 ~ zphot <~0.8 range.  Also present a joint analysis of the photo-z accuracy as a function of z and magnitude.  Assess the quality of the photometric z by comparison to spectroscopic sample across z bins is in agreement with the expectations.

1410.2341
The size evolution of elliptical galaxies
Zie, Guo, Cooper, Frenk, Li, Gao

Possibility of the amplitude of the size mass relation of massive early type galaxies evolves with z.  Use SAM to study the size evolution of massive ETGs; find this model is able to reproduce the amplitude of present day amplitude and slope of the relation between size and stellar mass for these galaxies, as well as its evolution.  The amplitude of this relation reflects the typical compactness of dark halos at the time when most of the stars are formed.  This link between size and SF epoch is propagated in galaxy mergers.  Mergers of high or moderate mass ratio (<1:3) become increasingly important with increasing present day stellar mass for galaxies more massive than 1e11.4 Msun. At lower masses, low mass ratio mergers play a more important role.  In situ SF contribute more to the size growth than it does to stellar mass growth.  Also find that, for ETGs identified at z=2, minor mergers dominate subsequent growth both for stellar mass and in size, consistent with earlier theoretical results.

1410.2533
Gravitational lensing of cosmological 21cm emission
Pourtsidou, Metcalf

Investigate the feasibility of measuring WL using 21cm intensity mapping with emphasis on the performance of the planned SKA.  Find that the current design for SKA-Mid should be able to measure the evolution of the lensing PS at z~2-3 using this technique.  This will be a probe of the expansion history of the universe and gravity at a unique range in redshift.  The S/N is found to be highly dependent on evolution of the neutral H fraction in the universe with a higher HI density resulting in stronger signal.  With realistic models for this , SKA Phase 1 should be capable of measuring the lensing PS and its evolution.  The S/N dependence on the area and diameter of the telescope array is quantified.  Further demonstrate the applications of this technique by applying it to two specific coupled DE models that would be difficult to observationally distinguish without information from this range of z.  Also investigate measuring the lensing signal with 21cm emission from the EoR using SKA-Low and find that it is unlikely to constrain cosmo parameters because of the small survey size, but could provide a map of the DM within a small region of the sky.