Currently, much of my research concentrates on the dynamics of satellite galaxies in the Sloan Digital Sky Survey (SDSS). More specifically, I'm using the motions of satellites galaxies to constrain the relationship between galaxy and dark matter halo properties. For example, we have analyzed the motions of brightest halo galaxies with respect to other halo members to infer the fraction of halos in which the brightest galaxy is not the central galaxy. We find that more brightest galaxies are actually satellite galaxies than expected from theoretical models, such as semi-analytic galaxy formation models. This could signal an actual shortcoming in our current understanding of galaxy formation. Furthermore, we are now using satellite kinematics to infer average halo masses of galaxies in SDSS. We show that such an analysis is on par with constraints derived from galaxy clustering and galaxy-galaxy lensing.
I also have a strong interest in galaxy assembly bias. I'm part of a research collaboration between the groups of Frank van den Bosch and Andrew Zentner. We work on ways to detect, quantify and mitigate the effect of galaxy assembly bias when modelling the galaxy-halo connection in large-scale structure surveys. We have recently analyzed the galaxy clustering in SDSS DR7 using decorated HOD models that specifically include the possibility of galaxy assembly bias. Our results show that SDSS clustering data alone cannot rule out large amounts of galaxy assembly bias and sometimes even prefers it. To study galaxy assembly bias our groups have developed the open-source halotools project to which I'm also actively contributing. Finally, I'm also working on cosmological constraints derived from an analysis of clustering and lensing in SDSS-III's Baryon Oscillation Spectroscopic Survey (BOSS).
More generally, I have a broad interesting in many areas of astrophysical research. For example, I previously published work on the high-energy emission of Gamma-Ray bursts, the detectability of anisotropies in the diffuse gamma-ray background induced by dark matter annihilation and the near-infrared emission of high-redshift galaxies.
- Lange, J.U. et al., 2018, "Maturing Satellite Kinematics into a Competitive Probe of the Galaxy-Halo Connection", submitted to MNRAS
- Campbell, D. et al., including Lange, J. U., 2018, "The Galaxy Clustering Crisis in Abundance Matching", Monthly Notices of the Royal Astronomical Society
- Lange, J.U. et al., 2018, "Brightest galaxies as halo centre tracers in SDSS DR7", Monthly Notices of the Royal Astronomical Society
- Villareal, A. S. et al., including Lange, J. U., 2017, "The Immitigable Nature of Assembly Bias: The Impact of Halo Definition on Assembly Bias", Monthly Notices of the Royal Astronomical Society
- Zentner, A.R., Hearin, A., van den Bosch, F.C., Lange, J.U. and Villarreal, A., 2016, "Constraints on Assembly Bias from Galaxy Clustering", arXiv:1606.07817
- Nelson, E. J. et al., including Lange, J. U., 2016, "Where Stars Form: Inside-out Growth and Coherent Star Formation from HST Hα Maps of 3200 Galaxies across the Main Sequence at 0.7 < z < 1.5", The Astrophysical Journal
- Momcheva, I. et al., including Lange, J. U., 2016, "The 3D-HST Survey: Hubble Space Telescope WFC3/G141 Grism Spectra, Redshifts, and Emission Line Measurements for ∼ 100,000 Galaxies", The Astrophysical Journal Supplement Series
- Lange, J. U. et al., 2016, "Evidence for Non-stellar Rest-frame Near-IR Emission Associated with Increased Star Formation in Galaxies at z ∼ 1", The Astrophysical Journal Letters
- Lange, J. U. and Chu, M.-C., 2014, "Can galactic dark matter substructure contribute to the cosmic gamma-ray anisotropy?", Monthly Notices of the Royal Astronomical Society
- Lange, J. and Pohl, M., 2013, "The average GeV-band Emission from Gamma-Ray Bursts", Astronomy & Astrophysics