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The genus of the isodensity contours is a robust measure of the topology of a large-scale structure, and it is relatively insensitive to nonlinear gravitational evolution, galaxy bias, and redshift-space distortion. We show that the growth of density fluctuations is scale dependent even in the linear regime in some modified gravity theories, which opens a new possibility of testing the theories observationally.We propose to use the genus of the isodensity contours, an intrinsic measure of the topology of the large-scale structure, as a statistic to be used in such tests. In Einstein's general theory of relativity, density fluctuations grow at the same rate on all scales in the linear regime, and the genus per comoving volume is almost conserved as structures grow homologously, so we expect that the genus--smoothing-scale relation is basically time independent. However, in some modified gravity models where structures grow with different rates on different scales, the genus--smoothing-scale relation should change over time. This can be used to test the gravity models with large-scale structure observations. We study the cases of the f (R) theory, DGP braneworld theory as well as the parameterized post-Friedmann models. We also forecast how the modified gravity models can be constrained with optical/IR or redshifted 21 cm radio surveys in the near future. [ABSTRACT FROM AUTHOR]

We measure the bivariate luminosity function (BLF) of galaxy pairs and use it to probe and characterize the galaxy–galaxy interaction between pair members. The galaxy pair sample is selected from the main galaxy sample of Sloan Digital Sky Survey and supplied with a significant number of redshifts from the LAMOST spectral and GAMA surveys. We find the BLFs depend on the projected distance dp between pair members. At large separation dp > 150 h−1 kpc, the BLF degenerates into a luminosity function of single galaxies, indicating few interactions between pair members. At 100 h−1 kpc ≤ dp ≤ 150 h−1 kpc, the BLF starts to show a correlation between pair members, in the sense that the shape of the conditional luminosity function (CLF) of one member galaxy starts to depend on the luminosity of the other member galaxy. Specifically, the CLF with a brighter companion has a steeper faint-end slope, which becomes even more significant at 50 h−1 kpc ≤ dp ≤ 100 h−1 kpc. This behavior is consistent with the scenario—and also is the observational evidence—that dynamic friction drives massive major merger pairs to merge more quickly. At close distance dp ≤ 50 h−1 kpc, aside from the merging timescale effect, the BLF also shows an overall brightening of ΔMr ≥ 0.04 mag, which reveals the enhanced star formation of the close-pair phase. By combining this with the statistical conclusion that the star formation rate of late-type galaxies in close pairs is enhanced at a level of about 40%, we further conclude that the average starburst timescale of close pairs is as long as 0.4 Gyr. [ABSTRACT FROM AUTHOR]

We introduce the OSIRIS Lens-Amplified Survey (OLAS), a kinematic survey of gravitationally lensed galaxies at cosmic noon taken with Keck adaptive optics. In this paper, we present spatially resolved spectroscopy and nebular emission kinematic maps for 17 star-forming galaxies with stellar masses 8 < log(M*/M⊙) < 9.8 and redshifts 1.2 < z < 2.3. OLAS is designed to probe the stellar mass (M*) and specific star formation rate (sSFR) range where simulations suggest that stellar feedback is most effective at driving gaseous outflows that create galaxy-wide potential fluctuations, which can generate dark matter cores. We compare our kinematic data with the trend among sSFR, M*, and Hα velocity dispersion, σ, from the Feedback In Realistic Environments (FIRE) simulations. Our observations reveal a correlation between sSFR and σ at fixed M* that is similar to the trend predicted by simulations: feedback from star formation drives star-forming gas and newly formed stars into more dispersion-dominated orbits. The observed magnitude of this effect is in good agreement with the FIRE simulations, in which feedback alters the central density profiles of low-mass galaxies, converting dark matter cusps into cores over time. Our data support the scenario that stellar feedback drives gaseous outflows and potential fluctuations, which in turn drive dark matter core formation in dwarf galaxies. [ABSTRACT FROM AUTHOR]

The tomographic Alcock–Paczynski (AP) test is a robust large-scale structure (LSS) measurement that receives little contamination from the redshift space distortion. It has placed tight cosmological constraints by using small and intermediate clustering scales of the LSS data. However, previous works have neglected the cross-correlation among different redshift bins, which could cause the statistical uncertainty being underestimated by ∼20%. In this work, we further improve this method by including this multi-redshift’s full correlation. We apply it to the SDSS DR12 galaxies sample and find out that, for ΛCDM, the combination of AP with the Planck+BAO data set slightly reduces (within 1σ) Ωm to 0.304 ± 0.007 (68.3% CL). This then leads to a larger H0 and also mildly affects Ωbh2 and ns as well as the derived parameters z*, r*, and zre but not τ, As, and σ8. For the flat wCDM model, our measurement gives Ωm = 0.301 ± 0.010 and w = −1.090 ± 0.047, where the additional AP measurement reduces the error budget by ∼25%. When including more parameters into the analysis, the AP method also improves the constraints on Ωk, , and Neff by 20%–30%. Early universe parameters such as and r, however, are unaffected. Assuming the dark energy equation of state , the Planck+BAO+SNe Ia+H0+AP data sets prefer a dynamical dark energy at ≈1.5σ CL. Finally, we forecast the cosmological constraints expected from the DESI galaxy survey and find that combining AP with the CMB+BAO method would improve the w0–wa constraint by a factor of ∼10. [ABSTRACT FROM AUTHOR]