In the local volume all the galaxies are considered to be at roughly the same cosmic epoch, but the local density field varies by a factor of ~100, thus it seems that the large-scale evolutionary effects are driven mainly by the underlying density than by cosmic epoch variation. LUCA will enable us to map the bulge, disk, and halo properties with unprecedented high spatial resolution, and to study the effects of the environment on these galaxy components at different levels of field density, isolated galaxies, galaxy groups, and the nearest galaxy cluster. In this context we aim to perform a peculiar velocity galaxy survey named LoRCA (Low Redshift Calar Alto) to map the matter distribution, velocity flows, and environment that surround our Local Volume on larger scales (< 400Mpc).  Peculiar velocities arise from inhomogeneities in the large-scale mass distribution, with coherent bulk flows determined by the gravitational field of the large overdensities (galaxy clusters and super-clusters) and underdensities (voids). Their radial component vpec can be determined by independent measurements of the distance D and redshift z of sources via the approximate relationship vpec ~ c z - H0 D, valid in the nearby universe (z<0.01), or via the exact (non-relativistic) formula needed for deeper and nearby surveys, vpec = c (z-z)/(1+z), with z calculated from D for a fixed cosmology.

The 3D velocity field, reconstructed using e.g. Bayesian or deterministic techniques, is a unique means to map the density field in the nearby Universe. Moreover, its statistical properties and the relationship with the underlying density field reconstructed from redshift surveys, namely the velocity-velocity and velocity-density correlations, provide key tests of the cosmological model. Peculiar velocity surveys constraint the normalized linear-growth-rate at low-redshift from Redshift Space Distortions and velocity-velocity comparison techniques, allowing tests of general relativity that are complementary and competitive with those based on redshift surveys. The most recent peculiar velocity surveys and compilations such as SFI++, 2M++ , 6dFGSv, and Cosmicflows-3, in which distances are obtained from the Tully-Fisher relation (TFR) or Fundamental Plane (FP) extending up to z ~ 0.055, overcome the sparsity, noise, and observational selection effects that affected the earliest surveys. Despite this amazing progress, which led so far to the discovery of the Laniakea supercluster and Dipole Repeller, several issues remain poorly known that will greatly benefit from a deeper survey, e.g. the source of the Local Group motion with respect to the CMB, a low-redshift determination of parameters like f 𝜎8 and, most relevant for the success of the LUCA science program, it provides a deep knowledge on the matter distribution, velocity flows, and environment that determines the properties of the galaxies in the Local Group. To make progress on these key questions improved sky coverage and improved data quantity and quality are required. For these reasons we propose to carry out the Low Redshift survey at Calar Alto (LoRCA) at the Schmidt telescope taking advantage of his huge field of view of 50 sq. deg. This requires building a second generation instrumentation for the Schmidt, a robotic system that will place 200 fibers over such huge f.o.v. with high-precision (5µm). These fibers will feed the IFU-850 spectrograph, which will incorporate two observing modes to allow both IFU and MOS spectroscopy, independently.

An all-sky Peculiar Velocity survey: TAIPAN + LoRCA. The Fundamental Plane for early-type galaxies is the observed relationship between the central velocity dispersion sigma and two photometric parameters: the effective (half-light) radius Reff and the mean surface brightness within that radius 𝜇eff. While Reff is distance dependent, apart from relatively small well-known corrections sigma and 𝜇eff are distance independent. The Fundamental Plane is a particularly powerful distance indicator because fiber spectroscopy sigma measurements can be efficiently gathered for large numbers of early-type galaxies, see e.g. 6dFGSv which measured FP distances for ~ 9,000 early-type galaxies with z < 0.055. The prospects for constructing ~ 150,000 high-quality (high S/N and low systematic error) FP-based peculiar velocities over the full extra-galactic sky (~ 34,000 sq, deg.) are now particularly promising. For the southern hemisphere, the TAIPAN survey (da Cunha et al. 2017) starting in early 2019 will obtain redshifts for ~ 2 million galaxies with limiting magnitude i<17, optimised for low-z BAO/cosmology science, with FP distances measured for ~ 75,000 early-type galaxies with rfibre < 17.5 up to z < 0.1 and covering 20,600 sq. deg. In the northern hemisphere SDSS provides a FP dataset over the northern galactic cap, i.e. about half the northern hemisphere, which in total is ~ 45,000 galaxies. However, the usefulness of SDSS velocity dispersion data for FP work is limited by the fibre plate-to-plate systematics at the ~ 0.02dex level, which restrict the quality of the derived FP distances particularly for z>0.04. The Low Redshift survey at Calar Alto (LoRCA) will target ~ 30,000 early-type galaxies over 15,000 sq. deg outside the SDSS footprint, hence completing the coverage of the northern sky, and will calibrate the SDSS sigma systematics by re-observing a sizeable number ~ 10,000 of the SDSS galaxies. While TAIPAN aims to have a large (~ 5,000) overlap with SDSS in the equatorial region, this is limited to Dec <+15deg. The merging of the TAIPAN, SDSS, and LoRCA datasets will be particularly crucial for assessing and minimizing the sky-position systematics of the velocity dispersion measurements that have limited all previous studies. These second-generation surveys will substantially improve the local FP dataset both in terms of data quality (sigma systematics less than 0.01dex), redshift depth (to z = 0.1), the number of objects (~ 20 times the existing studies) and provide nearly the entire 4𝜋 sky coverage. It is worth noting that peculiar velocity studies largely benefit from an isotropic sky coverage, which allows for a controlled modelling of the bulk flow.

The other data input needed for the FP are the photometric parameters (Reff and 𝜇eff). The recently available high-quality optical and NIR image surveys, i.e. Pan-STARRS, DES, DECaLS, Skymapper, VHS, and UHS, will allow the construction of a very homogeneous morphologically clean FP input catalogue from which reliable multi-band measurements of the FP photometric parameters can be derived. The combined TAIPAN, SDSS, and LoRCA dataset will map a volume that is about 8 times larger than existing studies, with denser sampling and improved velocity precision. Both the cosmography and statistics (characterizing the properties of the fields through power spectra and other measurements) will be greatly improved. These new surveys will constraint f 𝜎8  with 3% precision at low-redshift and allow tests of modified gravity. Focusing on using the most massive galaxies on the full sky (34,000 sq. deg.), i.e. a K < 14 magnitude-limited sample, one can measure the BAO scale up to a precision of 4% or lower using reconstruction. Moreover, such a large volume will be capital for the understanding of the source of the Local Volume and our Local Group's motion with respect to the CMB, the knowledge of flows on large scales being inevitably modulated by the extent of the data. The new maps of the mass distribution and motions in the local universe will quantify the contributions from the dominant large nearby structures, e.g. Great Attractor, Norma, Perseus-Pisces, etc, and reach out far enough to adequately map the influence of the richest superclusters like Shapley (z=0.05) and Horologium-Reticulum (z=0.06) in the South, and Corona Borealis (z=0.07) in the north. Hence, its impact on understanding the properties and unveiling the physical processes that drives the galaxies living in our Local Volume will be fundamental.

More details on target selection and survey strategy will follow.