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

Using the 1.6μm bump to study rest-frame H-band selected galaxies at redshift 2

ii, 73 leaves : ill. ; 29 cm.Includes bibliographical references (leaves 68-73)In this work, we set out to test the feasibility and limitations of using the 1.6[mu]m bump as a photometric redshift indicator and selection technique using publicly available Spitzer/IRAC images in the GOODS fields. We find that color selection with IRAC bandpasses is comparable in completeness and contamination to BzK selection. Using model SEDs, we find that the shape of the 1.6[mu]m bump is robust, and photometric redshifts are not greatly affected by choice of model parameters. Comparison with spectroscopic redshifts shows photometric redshifts to be reliable. We create a rest-frame NIR selected catalog of galaxies at z ~ 2 and construct a galaxy stellar mass function (SMF). Comparisons with other SMFs at approximately the same redshift show similar results. This suggests that selection at bluer wavelengths does not miss a significant amount of stellar mass in passive galaxies. Comparison with SMFs at other redshifts shows evidence for the downsizing scenario of galaxy evolution

Extremely sub-wavelength THz metal-dielectric wire microcavities

We demonstrate minimal volume wire THz metal-dielectric micro-cavities, in which all but one dimension have been reduced to highly sub-wavelength values. The smallest cavity features an effective volume of 0.4 µm(3), which is ~5.10(-7) times the volume defined by the resonant vacuum wavelength (λ = 94 µm) to the cube. When combined with a doped multi-quantum well structure, such micro-cavities enter the ultra-strong light matter coupling regime, even if the total number of electrons participating to the coupling is only in the order of 10(4), thus much less than in previous studies

Using the 1.6um Bump to Study Rest-frame NIR Selected Galaxies at Redshift 2

We explore the feasibility and limitations of using the 1.6um bump as a photometric redshift indicator and selection technique and use it to study the rest-frame H-band galaxy luminosity and stellar mass functions at redshift z~2. We use publicly available Spitzer/IRAC images in the GOODS fields and find that color selection in the IRAC bandpasses alone is comparable in completeness and contamination to BzK selection. We find that the shape of the 1.6um bump is robust, and photometric redshifts are not greatly affected by choice of model parameters. Comparison with spectroscopic redshifts shows photometric redshifts to be reliable. We create a rest-frame NIR selected catalog of galaxies at z~2 and construct a galaxy stellar mass function (SMF). Comparisons with other SMFs at approximately the same redshift but determined using shorter wavelengths show good agreement. This agreement suggests that selection at bluer wavelengths does not miss a significant amount of stellar mass in passive galaxies. Comparison with SMFs at other redshifts shows evidence for the downsizing scenario of galaxy evolution. We conclude by pointing out the potential for using the 1.6um technique to select high-redshift galaxies with the JWST, whose lambda > 0.6 um coverage will not be well suited to selecting galaxies using techniques that require imaging at shorter wavelengths.Comment: Accepted for publication in Ap

Using model spectral energy distributions to study galaxy masses : now and in the future

xv, 222 leaves : col. ill. ; 29 cmIncludes abstract and appendices.Includes bibliographical references (leaves 136-152).The determination of galaxy masses is an essential tool for our understanding of galaxy evolution. Looking at 67 local galaxies, we find that galaxy stellar masses are underestimated using traditional methods that assume homogeneous stellar populations as compared to spatially resolved methods. The underestimate is correlated with specific star-formation rate (sSFR), and is as high as 25% in high-SFR nearby galaxies. At higher redshifts we find a similar effect, except the linear trend with sSFR becomes much more dramatic: unresolved mass measurements may be too low by factors of two to five for the highest sSFR galaxies. The increasing mass correction with sSFR resolves a long-standing discrepancy between the directly observed star-formation rate density and that implied by the stellar mass density. A definitive confirmation of this trend will require observations with JWST. We use the spatially resolved data of our high redshift galaxies to create simulations of the JWST's NIRISS instrument, and find that analysis tools need to ensure they can account for spatially inhomogeneous spectra within a galaxy in order to obtain the most accurate line emission measurements. Additionally, we examine how photometric redshifts can be improved for future space-based weak lensing missions such as Euclid. Weak lensing tomography depends critically upon accurate redshift estimation in order to map the three dimensional mass distribution of the universe. We demonstrate the poor quality of photometric redshifts these missions would expect without optical bandpasses and show how the addition of a U and/or G filter could remove their reliance on ground-based surveys

LARgE Survey – I. Dead monsters: the massive end of the passive galaxy stellar mass function at cosmic noon

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LARgE Survey – I. Dead monsters: the massive end of the passive galaxy stellar mass function at cosmic noon

Published VersionWe introduce the largest to date survey of massive quiescent galaxies at redshift z ∼ 1.6. With these data, which cover 27.6 deg2, we can find significant numbers of very rare objects such as ultra-massive quiescent galaxies that populate the extreme massive end of the galaxy mass function, or dense environments that are likely to become present-day massive galaxy clusters. In this paper, the first in a series, we apply our gzKs adaptation of the BzK technique to select our z ∼ 1.6 galaxy catalogue and then study the quiescent galaxy stellar mass function with good statistics over M⋆ ∼ 1010.2–1011.7 M⊙ – a factor of 30 in mass – including 60 ultra-massive z ∼ 1.6 quiescent galaxies with M⋆ > 1011.5 M⊙. We find that the stellar mass function of quiescent galaxies at z ∼ 1.6 is well represented by the Schechter function over this large mass range. This suggests that the mass-quenching mechanism observed at lower redshifts must have already been well established by this epoch, and that it is likely due to a single physical mechanism over a wide range of mass. This close adherence to the Schechter shape also suggests that neither merging nor gravitational lensing significantly affects the observed quenched population. Finally, comparing measurements of M∗ parameters for quiescent and star-forming populations (ours and from the literature), we find hints of an offset (⁠M∗SF>M∗PE⁠), which could suggest that the efficiency of the quenching process evolves with time