Missing Stellar Mass in SED Fitting: Spatially Unresolved Photometry can Underestimate Galaxy Masses

We fit model spectral energy distributions to each pixel in 67 nearby (=0.0057) galaxies using broadband photometry from the Sloan Digital Sky Survey and GALEX. For each galaxy, we compare the stellar mass derived by summing the mass of each pixel to that found from fitting the entire galaxy treated as an unresolved point source. We find that, while the pixel-by-pixel and unresolved masses of galaxies with low specific star formation rates (such as ellipticals and lenticulars) are in rough agreement, the unresolved mass estimate for star-forming galaxies is systematically lower then the measurement from spatially-resolved photometry. The discrepancy is strongly correlated with sSFR, with the highest sSFRs in our sample having masses underestimated by 25% (0.12 dex) when treated as point sources. We found a simple relation to statistically correct mass estimates derived from unresolved broad-band SED fitting to the resolved mass estimates: m_{resolved} = m_{unresolved}/(-0.057log(sSFR) + 0.34) where sSFR is in units of yr^{-1}. We study the effect of varying spatial resolution by degrading the image resolution of the largest images and find a sharp decrease in the pixel-by-pixel mass estimate at a physical scale of approximately 3 kpc, which is comparable to spiral arm widths. The effects we observe are consistent with the "outshining" idea which posits that the youngest stellar populations mask more massive, older -- and thus fainter -- stellar populations. Although the presence of strong dust lanes can also lead to a drastic difference between resolved and unresolved mass estimates (up to 45% or 0.3 dex) for any individual galaxy, we found that resolving dust does not affect mass estimates on average. The strong correlation between mass discrepancy and sSFR is thus most likely due to the outshining systematic bias.Comment: 13 pages, 8 figures, accepted for publication in MNRA

The numbers of z~2 star-forming and passive galaxies in 2.5 square degrees of deep CFHT imaging

We use an adaptation of the BzKs technique to select ~40,000 z~2 galaxies (to K(AB) = 24), including ~5,000 passively evolving (PE) objects (to K(AB) = 23), from 2.5 deg^2 of deep CFTH imaging. The passive galaxy luminosity function exhibits a clear peak at R = 22 and a declining faint-end slope ({\alpha} = - 0.12 [+0.16 -0.14]),while that of star-forming galaxies is characterized by a steep faint-end slope ({\alpha} = -1.43 +- [0.02] (systematic) [+0.05 -0.04] (random)). The details of the LFs are somewhat sensitive (at <25% level) to cosmic variance even in these large(~0.5 deg^2) fields, with the D2 field (located in the COSMOS field) most discrepant from the mean. The shape of the z ~ 2 stellar mass function of passive galaxies is remarkably similar to that at z ~ 0.9, save for a factor of ~4 lower number density. This similarity suggests that the same mechanism may be responsible for the formation of passive galaxies seen at both these epochs. This same formation mechanism may also operate down to z ~ 0 if the local PE galaxy mass function, known to be two-component, contains two distinct galaxy populations. This scenario is qualitatively in agreement with recent phenomenological mass-quenching models and extends them to span more than three quarters of the history of the Universe.Comment: 18 pages, 13 Figure

The build-up of mass in UV-selected sub-L* galaxies at z~2

Broadband spectral energy distribution (SED) fitting is used to study a deep sample of UV-selected sub-L* galaxies at z~2. They are found to be less dusty than L* galaxies, and to contribute more mass to the cosmic mass budget at this epoch than is inferred from shallower high-z surveys. Additionally, SFRs are found to be proportional to stellar masses over three orders of magnitude in mass; this phenomenon can be explained by assuming that new stars form out of gas that co-accretes along with dark matter onto the galaxies' dark matter halos, a scenario that naturally leads to SFRs that gradually increase with time.Comment: Proceedings of "Tracing the Ancestry of Galaxies on the Land of our Ancestors", C. Carignan, K. Freeman & F. Combes, ed

Treatment Planning in Brachytherapy HDR Based on Three‐Dimensional Image

Treatment planning in High Dose Rate (HDR) brachytherapy based on three‐dimensional (3D) imaging allows for prearranging and realization optimal treatment process. This process consists of procedure planning, the choice of applicators, adjusting the appropriate implantation technique, and planning of three‐dimensional distribution of dose in computerized treatment planning system. 3D images used in treatment planning in HDR brachytherapy allows for choosing the most appropriate application technique. This in turn allows for the best area coverage by reference dose with simultaneous protection of critical organs. Treatment planning on 3D images assures individual planning of dose dispersion in target area. Several techniques will be presented based on 3D imaging in location such as lung, skin cancer, breast, and prostate cancer. For each location, relative cases will be provided where different applicators and techniques were applied. These examples are going to present images from before and after performed application along with the pictures from computer treatment planning system. In each of described locations, relative advice and rules of conducting accurate application will be provided

Keck Deep Fields. I. Observations, Reductions, and the Selection of Faint Star-Forming Galaxies at Redshifts z~4, 3, and 2

We introduce a very deep, R_lim~27, multicolor imaging survey of very faint star-forming galaxies at z~4, z~3, z~2.2, and z~1.7. This survey, carried out on the Keck I telescope, uses the very same UGRI filter system that is employed by the Steidel team to select galaxies at these redshifts, and thus allows us to construct identically-selected, but much fainter, samples. However, our survey reaches ~1.5 mag deeper than the work of Steidel and his group, letting us probe substantially below the characteristic luminosity L* and thus study the properties and redshift evolution of the faint component of the high-z galaxy population. The survey covers 169 square arcminutes in three spatially independent patches on the sky and -- to R<~27 -- contains 427 GRI-selected z~4 LBGs, 1481 UGR-selected z~3 LBGs, 2417 UGR-selected z~2.2 star-forming galaxies, and 2043 UGR-selected z~1.7 star-forming galaxies. In this paper, the first in a series, we introduce the survey, describe our observing and data reduction strategies, and outline the selection of our z~4, z~3, z~2.2, and z~1.7 samples.Comment: To appear in Ap

Keck Deep Fields. II. The UV Galaxy Luminosity Function at z~4, 3, and 2

We use very deep UGRI multi-field imaging obtained at the Keck telescope to study the evolution of the rest-frame 1700A galaxy luminosity function as the Universe doubles its age from z~4 to z~2. The depth of our imaging allows us to constrain the faint end of the luminosity function reaching M_1700A ~ -18.5 at z~3 (equivalent to ~1M_sun/yr) accounting for both N^1/2 uncertainty in the number of galaxies and for cosmic variance. We carefully examine many potential sources of systematic bias in our LF measurements before drawing the following conclusions. We find that the luminosity function of Lyman Break Galaxies evolves with time and that this evolution is likely differential with luminosity. The result is best constrained between the epochs at z~4 and z~3, where we find that the number density of sub-L* galaxies increases with time by at least a factor of 2.3 (11sigma statistical confidence); while the faint end of the LF evolves, the bright end appears to remain virtually unchanged, indicating that there may be differential, luminosity-dependent evolution significant at the 97% level. Potential systematic biases restric our ability to draw strong conclusions about continued evolution of the luminosity function to lower redshifts, z~2.2 and z~1.7, but, nevertheless, it appears certain that the number density of z~2.2 galaxies at all luminosities we studied, -22<M_1700A<-18, is at least as high as that of their counterparts at z~3. While it is not yet clear what mechanism underlies the observed evolution, the fact that this evolution is differential with luminosity opens up new avenues of improving our understanding of how galaxies form and evolve at high redshift.Comment: Accepted for publication in ApJ. Updated preprint to reflect this final versio