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Full list of authors: Dey, Arjun; Najita, Joan R.; Koposov, Sergey E.; Josephy-Zack, J.; Maxemin, Gabriel; Bell, Eric F.; Poppett, C.; Patel, E.; Beraldo e Silva, L.; Raichoor, A.; Schlegel, D.; Lang, D.; Meisner, A.; Myers, Adam D.; Aguilar, J.; Ahlen, S.; Allende Prieto, C.; Brooks, D.; Cooper, A. P.; Dawson, K. S.; de la Macorra, A.; Doel, P.; Font-Ribera, A.; Garcia-Bellido, Juan; Gontcho, S. Gontcho A.; Guy, J.; Honscheid, K.; Kehoe, R.; Kisner, T.; Kremin, A.; Landriau, M.; Le Guillou, L.; Levi, Michael E.; Li, T. S.; Martini, Paul; Miquel, R.; Moustakas, J.; Nie, Jundan; Palanque-Delabrouille, N.; Prada, F.; Schlafly, E. F.; Sharples, Ray M.; Tarle, Gregory; Ting, Yuan-Sen; Tyas, L.; Valluri, M.; Wechsler, Risa H.; Zou, H.--This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., We present Dark Energy Spectroscopic Instrument (DESI) observations of the inner halo of M31, which reveal the kinematics of a recent merger—a galactic immigration event—in exquisite detail. Of the 11,416 sources studied in 3.75 hr of on-sky exposure time, 7438 are M31 sources with well-measured radial velocities. The observations reveal intricate coherent kinematic structure in the positions and velocities of individual stars: streams, wedges, and chevrons. While hints of coherent structures have been previously detected in M31, this is the first time they have been seen with such detail and clarity in a galaxy beyond the Milky Way. We find clear kinematic evidence for shell structures in the Giant Stellar Stream, the Northeast Shelf, and Western Shelf regions. The kinematics are remarkably similar to the predictions of dynamical models constructed to explain the spatial morphology of the inner halo. The results are consistent with the interpretation that much of the substructure in the inner halo of M31 is produced by a single galactic immigration event 1–2 Gyr ago. Significant numbers of metal-rich stars ([Fe/H] > − 0.5) are present in all of the detected substructures, suggesting that the immigrating galaxy had an extended star formation history. We also investigate the ability of the shells and Giant Stellar Stream to constrain the gravitational potential of M31, and estimate the mass within a projected radius of 125 kpc to be ${\mathrm{log}}_{10}\,{M}_{\mathrm{NFW}}(\lt 125\,\mathrm{kpc})/{M}_{\odot }={11.80}_{-0.10}^{+0.12}$. The results herald a new era in our ability to study stars on a galactic scale and the immigration histories of galaxies. © 2023. The Author(s). Published by the American Astronomical Society., A.D. and J.N.'s research activities are supported by the NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. A.D. and J.N.'s research is also supported in part by Fellowships from the John Simon Guggenheim Memorial Foundation and by the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics. J.N. also acknowledges support from the Harvard Radcliffe Fellowship Program of the Radcliffe Institute for Advanced Study at Harvard University. J.N., G.M., and J.J.-Z. acknowledge support from the Harvard University's Radcliffe Research Partners Program of the Radcliffe Institute for Advanced Study. E.F.B. is grateful for support from the National Science Foundation through grant NSF-AST 2007065. L.B.S. acknowledges NASA-ATP award 80NSSC20K0509 and Science Foundation AAG grant AST-2009122. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under contract No. DE-AC02-05CH11231, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under contract No. AST-0950945 to the NSF's National Optical-Infrared Astronomy Research Laboratory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology of Mexico (CONACYT); the Ministry of Science and Innovation of Spain (MICINN), and by the DESI Member Institutions: https://www.desi.lbl.gov/collaborating-institutions. The authors are honored to be permitted to conduct scientific research on Iolkam Du'ag (Kitt Peak), a mountain with particular significance to the Tohono O'odham Nation. This work was performed in part at Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. This work was partially supported by a grant from the Simons Foundation., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001131-S).

We describe the HST ACS Coma cluster Treasury survey, a deep two-passband imaging survey of one of the nearest rich clusters of galaxies, the Coma cluster (Abell 1656). The survey was designed to cover an area of 740 square arcmin in regions of different density of both galaxies and intergalactic medium within the cluster. The ACS failure of January 27th 2007 leaves the survey 28% complete, with 21 ACS pointings (230 square arcmin) complete, and partial data for a further 4 pointings (44 square arcmin). Predicted survey depth for 10 sigma detections for optimal photometry of point sources is g' = 27.6 in the F475W filter, and IC=26.8 mag in F814 (AB magnitudes). Initial simulations with artificially injected point sources show 90% recovered at magnitude limits of g' = 27.55 and IC = 26.65. For extended sources, the predicted 10 sigma limits for a 1 square arcsecond region are g' = 25.8 mag/sq. arcsec and IC = 25.0 mag/sq. arcsec. We highlight several motivating science goals of the survey, including study of the faint end of the cluster galaxy luminosity function, structural parameters of dwarf galaxies, stellar populations and their effect on colors and color gradients, evolution of morphological components in a dense environment, the nature of ultra compact dwarf galaxies, and globular cluster populations of cluster galaxies of a range of luminosities and types. This survey will also provide a local rich cluster benchmark for various well known global scaling relations and explore new relations pertaining to the nuclear properties of galaxies., 47 pages, 3 figures, 6 tables, accepted for publication in Astrophysical Journal supplement

Using traditional morphological classifications of galaxies in 10 intermediate-redshift (z similar to 0.5) clusters observed with WFPC2 on the Hubble Space Telescope, we derive relations between morphology and local galaxy density similar to that found by Dressier for low-redshift clusters. Taken collectively, the ''morphology-density'' relationship, T-Sigma, for these more distant, presumably younger clusters is qualitatively similar to that found for the local sample, but a detailed comparison shows two substantial differences: (1) For the clusters in our sample, the T-Sigma relation is strong in centrally concentrated ''regular'' clusters, those with a strong correlation of radius and surface density, but nearly absent for clusters that are less concentrated and irregular, in contrast to the situation for low-redshift clusters, where a strong relation has been found for both. (2) In every cluster the fraction of elliptical galaxies is as large or larger than in low-redshift clusters, but the SO fraction is 2-3 times smaller, with a proportional increase of the spiral fraction. Straightforward, though probably not unique, interpretations of these observations are (1) morphological segregation proceeds hierarchically, affecting richer, denser groups of galaxies earlier, and (2) the formation of elliptical galaxies predates the formation of rich clusters and occurs instead in the loose-group phase or even earlier, but SO's are generated in large numbers only after cluster virialization.

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, los autores pertenecientes a la UAM y el nombre del grupo de colaboración, si lo hubiere, We describe the Milky Way Survey (MWS) that will be undertaken with the Dark Energy Spectroscopic Instrument (DESI) on the Mayall 4 m telescope at the Kitt Peak National Observatory. Over the next 5 yr DESI MWS will observe approximately seven million stars at Galactic latitudes ∣b∣ > 20°, with an inclusive target selection scheme focused on the thick disk and stellar halo. MWS will also include several high-completeness samples of rare stellar types, including white dwarfs, low-mass stars within 100 pc of the Sun, and horizontal branch stars. We summarize the potential of DESI to advance understanding of the Galactic structure and stellar evolution. We introduce the final definitions of the main MWS target classes and estimate the number of stars in each class that will be observed. We describe our pipelines for deriving radial velocities, atmospheric parameters, and chemical abundances. We use ≃500,000 spectra of unique stellar targets from the DESI Survey Validation program (SV) to demonstrate that our pipelines can measure radial velocities to ≃1 km s−1 and [Fe/H] accurate to ≃0.2 dex for typical stars in our main sample. We find the stellar parameter distributions from ≈100 deg2 of SV observations with ≳90% completeness on our main sample are in good agreement with expectations from mock catalogs and previous surveys, This equipment was funded by MoE, NSTC, and National Tsing Hua University. C.A.P. acknowledges financial support from the Spanish Ministry of Science and Innovation (MICINN) projects AYA2017-86389-P and PID2020-117493GB-I00. C.J.M. acknowledges financial support from Imperial College London through an Imperial College Research Fellowship grant. M.V. and L.B.e.S. acknowledge support from NASA-ATP award 80NSSC20K0509. The work of A.D. and J.N. is supported by NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. T.S.L. acknowledges financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC) through grant RGPIN-2022-04794. B.T. G. was supported by grant ST/T000406/1 from the Science and Technology Facilities Council (STFC). This project has received funding from the European Research Council under the European Unionʼs Horizon 2020 research and innovation program (grant agreement No. 101020057). This research made use of computing time available on the high-performance computing system at the Instituto de Astrofisica de Canarias