Carlesi, E., Hoffman, Y., Gottlöber, S., Libeskind, N. I., Knebe, A., Yepes, G., Pilipenko, S. V., 2020, Monthly Notices of the Royal Astronomical Society
, 491, 2 , 1531 Published: January 2020
In this work, an ensemble of simulated Local Group (LG) analogues is used to constrain the properties of the mass assembly history of the Milky Way (MW) and Andromeda (M31) galaxies. These objects have been obtained using the constrained simulation technique, which ensures that simulated LGs live within a large-scale environment akin to the observed one. Our results are compared against a standard Λ Cold Dark Matter (ΛCDM) series of simulations that use the same cosmological parameters. This allows us to single out the effects of the constraints on the results. We find that (I) the median constrained merging histories for M31 and MW live above the standard ones at the 1σ level, (II) the median formation time takes place ≈0.5 Gyr earlier than unconstrained values, while the latest major merger happens on average 1.5 Gyr earlier, and (III) the probability for both LG haloes to have experienced their last major merger in the first half of the history of the Universe is ≈ 50 per cent higher for the constrained pairs. These results have been estimated to be significant at the 99 per cent confidence level by means of a Kolmogorov-Simirnov test. These results suggest that the particular environment in which the MW and M31 form plays a role in shaping their properties, and favours earlier formation and last major merger time values in agreement with other observational and theoretical considerations.
Libeskind, N. I., Carlesi, E., Müller, O., Pawlowski, M. S., Hoffman, Y., Pomarède, D., Courtois, H. M., Tully, R., Gottlöber, S., Steinmetz, M., Sorce, J., Knebe, A., 2019, Monthly Notices of the Royal Astronomical Society
, 490, 3 , 3786 Published: December 2019
To date at least 10 highly flattened planes of dwarf galaxies are claimed to have been discovered in the Local Universe. The origin of these planes of galaxies remains unknown. One suggestion is that they are related to the large-scale structure of the cosmic web. A recent study found that the normal of a number of these dwarf galaxy planes is very closely aligned with the eigenvector of the shear tensor corresponding to the direction of greatest collapse obtained by reconstructing the full velocity field in the linear regime. Here we extend that work by both considering an additional 5 planes beyond the five examined previously and examining the alignment with respect to the quasi-linear field, a more sophisticated reconstruction, which is a better approximation on smaller (quasi-linear) scales. Our analysis recovers the previous result while not finding a significantly tight alignment with the additional five planes. However, the additional five plane normals also do not appear to be randomly oriented. We conclude that this could be due either to the normals of the new planes being poorly defined and described; the quasi-linear field at those locations being poorly constrained; or different formation mechanisms for the orientation of planes of dwarf galaxies.
Graziani, R., Courtois, H. M., Lavaux, G., Hoffman, Y., Tully, R. B., Copin, Y., Pomarède, D., 2019, Monthly Notices of the Royal Astronomical Society
, 488, 4 , 5438 Published: October 2019
A hierarchical Bayesian model is applied to the Cosmicflows-3 catalogue of galaxy distances in order to derive the peculiar velocity field and distribution of matter within z ∼ 0.054. The model assumes the ΛCDM model within the linear regime and includes the fit of the galaxy distances together with the underlying density field. By forward modelling the data, the method is able to mitigate biases inherent to peculiar velocity analyses, such as the Homogeneous Malmquist bias or the lognormal distribution of peculiar velocities. The statistical uncertainty on the recovered velocity field is about 150 km s-1 depending on the location, and we study systematics coming from the selection function and calibration of distance indicators. The resulting velocity field and related density fields recover the cosmography of the Local Universe which is presented in an unprecedented volume of our Universe 10 times larger than previously reached. This methodology opens the doors to reconstruction of initial conditions for larger and more accurate constrained cosmological simulations. This work is also preparatory to larger peculiar velocity data sets coming from Wallaby, TAIPAN, or LSST.
Tully, R. B., Pomarède, D., Graziani, R., Courtois, H. M., Hoffman, Y., Shaya, E. J., 2019, The Astrophysical Journal
, 880, 1 , 24 Published: July 2019
Cosmicflows-3 distances and inferred peculiar velocities of galaxies have permitted the reconstruction of the structure of overdensities and underdensities within the volume extending to 0.05c. This study focuses on the underdense regions, particularly the Local Void that lies largely in the zone of obscuration and consequently has received limited attention. Major overdense structures that bound the Local Void are the Perseus-Pisces and Norma-Pavo-Indus filaments separated by 8500 km s-1. The void network of the universe is interconnected and void passages are found from the Local Void to the adjacent very large Hercules and Sculptor voids. Minor filaments course through voids. A particularly interesting example connects the Virgo and Perseus clusters, with several substantial galaxies found along the chain in the depths of the Local Void. The Local Void has a substantial dynamical effect, causing a deviant motion of the Local Group of 200-250 km s-1. The combined perturbations due to repulsion from the Local Void and attraction toward the Virgo Cluster account for ∼50% of the motion of the Local Group in the rest frame given by the cosmic microwave background.
Mostoghiu, R., Di Cintio, A., Knebe, A., Libeskind, N. I., Minchev, I., Brook, C., 2018, Monthly Notices of the Royal Astronomical Society
, 480, 4 , 4455 Published: November 2018
HST/ACS observations along the major axis of M33 show that the mean age of its stars decreases with increasing distance from the galaxy centre. Such a behaviour is consistent with an inside-out growth of the disc. However, in the outermost observed field, at r ≃ 11.6 kpc, a reversal of this gradient is detected, with old stars found in high percentages beyond this radius. In this work, we investigate the origin of such a reversal in stellar age gradient, by using a simulated M33 analogue from the Constrained Local UniversE Simulations (CLUES). The simulated M33 is similar to the observed one in terms of mass, rotation velocity, surface brightness, and, similar to what has been reported in observations, shows a stellar age turnaround at large radii. We demonstrate that this reversal is mostly a result of stellar accretion from old satellite galaxies and, to a lesser extent, of stellar migration of in-situ stars. The old accreted stars, with formation times tf < 4 Gyrs, are kinematically hot and can be differentiated from the in-situ stars by their high velocity dispersion and the fact that they do not have rotationally supported orbits. In the future, obtaining kinematic information of the stars in the outskirt of M33 will help to verify this scenario.
