The AGORA High-resolution Galaxy Simulations Comparison Project. III: Cosmological Zoom-in Simulation of a Milky Way-mass halo

We present a suite of high-resolution cosmological zoom-in simulations to z = 4 of a 10^(12) Mꙩ halo at z = 0, obtained using seven contemporary astrophysical simulation codes (ART-I, ENZO, RAMSES, CHANGA, GADGET3, GEAR, and GIZMO) widely used in the numerical galaxy formation community. Physics prescriptions for gas cooling, heating and star formation are similar to the ones used in our previous AGORA disk comparison (Kim et al. 2016) but now account for the effects of cosmological processes such as the expansion of the Universe, intergalactic gas inflow, and the cosmic ultraviolet background radiation emitted by massive stars and quasars. In this work, we introduce the most careful comparison yet of galaxy formation simulations run by different code groups, together with a series of four calibration steps each of which is designed to reduce the number of tunable simulation parameters adopted in the final run. In the first two steps, we methodically calibrate the gas physics such as cooling and heating, in simulations without star formation. In the third, we seek an agreement on the total stellar mass produced with the common star formation prescription used in the AGORA disk comparison, in stellar feedback-free simulations. In the last calibration step, we activate stellar feedback, where each code group is asked to set the feedback prescriptions to be as close to the most used one in each code community as possible, while aiming for convergence in the stellar mass at z = 4 to the values predicted by semi-empirical models. After all the participating code groups successfully completed the calibration steps, we reach a suite of cosmological simulations with similar mass assembly histories down to z = 4. With numerical accuracy that resolves the internal structure of a target halo (˂̰ 100 physical pc at z = 4), we find that the codes overall agree well with one another in e.g., gas and stellar properties, but also show differences in e.g., circumgalactic medium (CGM) properties. We argue that, if adequately tested in accordance with our proposed calibration steps and common parameters, the results of high-resolution cosmological zoom-in simulations can be robust and reproducible. New code groups are invited to join and enrich this comparison by generating equivalent models or to test the code’s compatibility on their own, by adopting the common initial conditions, the common easy-to-implement physics package, and the proposed calibration steps. Further analyses of the zoom-in simulations presented here will be in forthcoming reports from the AGORA Collaboration, including studies of the CGM, simulations by additional codes, and results at lower redshift

Phase spirals in cosmological simulations of Milky Way-sized galaxies

The authors wish to thank the anonymous Referee for her/his comments and suggestions that improved this work. BGC and SRF work has been supported by the Madrid Government (Comunidad de Madrid-Spain) under the Multiannual Agreement with Complutense University in the line Program to Stimulate Research for Young Doctors in the context of the V PRICIT. They also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2016-75808-R, AYA2017-90589-REDT, and S2018/NMT-429, and from the CAMUCM under grant number PR65/19-22462. SRF acknowledges support from a Spanish postdoctoral fellowship, under grant number 2017-T2/TIC-5592. TA acknowledges the grant RYC2018-025968I funded by MCIN/AEI/10.13039/501100011033 and by `ESF Investing in your future'. This work was (partially) funded by the Spanish MICIN/AEI/10.13039/501100011033 and by `ERDF A way of making Europe' by the `European Union' through grant RTI2018095076-B-C21, and the Institute of Cosmos Sciences University of Barcelona (ICCUB, Unidad de Excelencia 'María de Maeztu') through grant CEX2019-000918-M. PR acknowledges support by the Agence Nationale de la Recherche (ANR project SEGAL ANR19-CE31-0017 and project ANR-18-CE31-0006) as well as from the European Research Council (ERC grant agreement No. 834148). Simulations were performed on the MIZTLI supercomputer at the DGTIC, UNAM, within the research project LANCAD-UNAMDGTIC-151.We study the vertical perturbations in the galactic disc of the Milky Way-size high-resolution hydrodynamical cosmological simulation named GARROTXA. We detect phase spirals in the vertical projection Z - V-Z of disc's stellar particles for the first time in this type of simulations. Qualitatively similar structures were detected in the recent Gaia data, and their origin is still under study. In our model, the spiral-like structures in the phase space are present in a wide range of times and locations across the disc. By accounting for an evolving mix of stellar populations, we observe that, as seen in the data, the phase spirals are better observed in the range of younger-intermediate star particles. We measure the intensity of the spiral with a Fourier decomposition and find that these structures appear stronger near satellite pericentres. Current dynamical models of the phase spiral considering a single perturber required a mass at least of the order of 10(10) M-circle dot, but all three of our satellites have masses of the order of similar to 10(8) M-circle dot. We suggest that there are other mechanisms at play which appear naturally in our model such as the physics of gas, collective effect of multiple perturbers, and a dynamically cold population that is continuously renovated by the star formation. Complementing collisionless isolated N-body models with the use of fully cosmological simulations with enough resolution can provide new insights into the nature/origin of the phase spiral.Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEUnión Europea. Horizonte 2020Ministerio de Economía y Competitividad (MINECO)Ministerio de Ciencia e Innovación (MICINN)/FEDERComunidad de MadridUniversidad Complutense de Madrid/Comunidad de MadridInstitut de Ciènces del Cosmos (Universidad de Barcelona)Agence Nationale de la Recherche (ANR) French National Research Agency (ANR)pu

A search for stellar tidal streams around Milky Way analogues from the SAGA sample

© The Authors 2023. We want to thank to Yao-Yuan Mao, Marla Geha and Risa Wechsler for providing the original SAGA sample for this paper and useful comments. We also thank Dustin Lang and John Moustakas for running the modified Legacypipe code to produce the images used here. DMD acknowledges financial support from the Talentia Senior Program (through the incentive ASE-136) from Secretaría General de Universidades, Investigación y Tecnología, de la Junta de Andalucía. DMD acknowledges funding from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017- 0709) and project (PDI2020-114581GB-C21/ AEI / 10.13039/501100011033). MAGF acknowledges financial support from the Spanish Ministry of Science and Innovation through the project PID2020-114581GB-C22. SRF acknowledges financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2016-75808-R, AYA2017-90589- REDT and S2018/NMT-429, and from the CAM-UCM under grant number PR65/19-22462. SRF acknowledges support from a Spanish postdoctoral fellowship, under grant number 2017-T2/TIC-5592. APC is supported by the Taiwan Ministry of Education Yushan Fellowship and Taiwan National Science and Technology Council grant 109-2112-M-007-011-MY3. The photometry analysis in this work was partly done using GNU Astronomy Utilities (Gnuastro, ascl.net/1801.009) version 0.17. Work on Gnuastro has been funded by the Japanese MEXT scholarship and its Grant-in-Aid for Scientific Research (21244012, 24253003), the European Research Council (ERC) advanced grant 339659-MUSICOS, and from the Spanish Ministry of Economy and Competitiveness (MINECO) under grant number AYA2016-76219-P. The Leiden Observatory has provided facilities and computer infrastructure for carrying out part of this work. MA acknowledges the financial support from the Spanish Ministry of Science and Innovation and the European Union - NextGenerationEU through the Recovery and Resilience Facility project ICTS-MRR-2021-03-CEFCA.Context. Stellar tidal streams are the result of tidal interactions between a central galaxy and lower mass systems such as satellite galaxies or globular clusters. For the Local Group, many diffuse substructures have been identified and their link to the galaxy evolution has been traced. However, it cannot simply be assumed that the Milky Way or M 31 are representative of their galaxy class. Thus, a larger sample of analogue galaxies beyond the Local Group is required to bolster a broader generalisation of the underlying theory. Aims. We want to detect and photometrically characterise stellar streams around Milky Way (MW-) analogues in the local Universe in order to extend the observational evidence of interactions between this class of host galaxies and their satellites. This information will be applicable in a more general context around future studies on galaxy formation and evolution processes. Methods. In the present work, we identified and analysed stellar tidal streams around MW-analogue galaxies from the SAGA sample, using deep images of the DESI Legacy Imaging Surveys. For this sample, we obtained a range of r-band surface brightness limit between 27.8 and 29 mag arcsec^(−2) . We measured the surface brightness and colours of the detected streams using GNU Astronomy Utilities software. Results. We identified 16 new stellar tidal streams around MW-analogue galaxies at distances between 25 and 40 Mpc. In applying a statistical analysis to our findings for the SAGA II galaxy sample, we obtained a frequency of 12.2% ± 2.4% for these stellar streams. We measured the surface brightness and colours of the detected streams and carried out a comparison to the dwarf satellite galaxies population around galaxies belonging to the same SAGA sample. We show that the mean colour of the streams is 0.20 mag redder than that of the SAGA satellites; in addition, the streams are, on average, 0.057 ± 0.021 mag redder that their progenitor (for cases where a likely progenitor could be identified). Conclusions. The frequency of streams detected around MW-analogues in the Local Universe is in agreement with previous studies. The difference in colour between detected streams and satellites within the SAGA host galaxy sample could be explained by a combination of both selection biases in the SAGA study and physical processes.Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUETalentia Senior Program (through the incentive ASE-136) from Secretaría General de Universidades, Investigación y Tecnología, de la Junta de AndalucíaCentro de Excelencia Severo OchoaMinisterio de Ciencia, Innovación y Universidades (MCIU)Ministerio de Economía y Competitividad (MINECO)CAM-UCMSpanish postdoctoral fellowshipTaiwan Ministry of Education Yushan FellowshipTaiwan National Science and Technology CouncilJapanese MEXT scholarshipEuropean Research Council (ERC)European Union - NextGeneration through the Recovery and Resilience Facility projectInstituto de Astrofísica de Andalucíapu

MEGARA, the R=6000-20000 IFU and MOS of GTC

MEGARA is the new generation IFU and MOS optical spectrograph built for the 10.4m Gran Telescopio CANARIAS (GTC). The project was developed by a consortium led by UCM (Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The instrument arrived to GTC on March 28th 2017 and was successfully integrated and commissioned at the telescope from May to August 2017. During the on-sky commissioning we demonstrated that MEGARA is a powerful and robust instrument that provides on-sky intermediate-to-high spectral resolutions R_(FWHM) ~ 6,000, 12,000 and 20,000 at an unprecedented efficiency for these resolving powers in both its IFU and MOS modes. The IFU covers 12.5 x 11.3 arcsec2 while the MOS mode allows observing up to 92 objects in a region of 3.5 x 3.5 arcmin^(2) . In this paper we describe the instrument main subsystems, including the Folded-Cassegrain unit, the fiber link, the spectrograph, the cryostat, the detector and the control subsystems, and its performance numbers obtained during commissioning where the fulfillment of the instrument requirements is demonstrated

CGM properties in VELA and NIHAO simulations; the OVI ionization mechanism: dependence on redshift, halo mass, and radius

Artículo firmado por 11 autoresWe study the components of cool and warm/hot gas in the circumgalactic medium (CGM) of simulated galaxies and address the relative production of OVI by photoionization versus collisional ionization, as a function of halo mass, redshift, and distance from the galaxy halo centre. This is done utilizing two different suites of zoom-in hydro-cosmological simulations, VELA (6 haloes; z > 1) and NIHAO (18 haloes; to z = 0), which provide a broad theoretical basis because they use different codes and physical recipes for star formation and feedback. In all haloes studied in this work, we find that collisional ionization by thermal electrons dominates at high redshift, while photoionization of cool or warm gas by the metagalactic radiation takes over near z ∼ 2. In haloes of ∼10^(12) Mꙩ and above, collisions become important again at z 3 × 10^(11) Mꙩ, at z ∼ 0 most of the photoionized OVI is in a warm,not cool, gas phase (T 3 × 105 K). We also find that collisions are dominant in the central regions of haloes, while photoionization is more significant at the outskirts, around Rv, even in massive haloes. This too may be explained by the presence of warm gas or, in lower mass haloes, by cool gas inflows.I-CORE Program of the PBC/ISFNational Science Foundation (NSF)DFG/DIP grantSpanish postdoctoral fellowship 'Ayudas para la atraccion del talento investigador. Modalidad 2: jovenes investigadores, financiadas por la Comunidad deMadrid'Ministerio de Economía y Competitividad (MINECO)ERC Advanced Grant, STARLIGHT: Formation of the First StarsDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasInstituto de Física de Partículas y del Cosmos (IPARCOS)TRUEpu

The bi-modal Li-7 distribution of the Milky Way's thin-disk dwarf stars The role of Galactic-scale events and stellar evolution

Context. The lithium abundance, A(Li), in stellar atmospheres suffers from various enhancement and depletion processes during the star's lifetime. While several studies have demonstrated that these processes are linked to the physics of stellar formation and evolution, the role that Galactic-scale events play in the galactic A(Li) evolution is not yet well understood. Aims. We aim to demonstrate that the observed A(Li) bi-modal distribution, in particular in the FGK-dwarf population, is not a statistical artefact and that the two populations connect through a region with a low number of stars. We also want to investigate the role that Galactic-scale events play in shaping the A(Li) distribution of stars in the thin disk. Methods. We use statistical techniques along with a Galactic chemical evolution model for A(Li) that includes most of the well-known Li-7 production and depletion channels. Results. We confirm that the FGK main-sequence stars belonging to the Milky Way's thin disk present a bi-modal A(Li) distribution. We demonstrate that this bi-modality can be generated by a particular Milky Way star formation history profile combined with the stellar evolution's Li-7 depletion mechanisms. We show that A(Li) evolution can be used as an additional proxy for the star formation history of our Galaxy

On the Dynamical Relevance of Galaxy Spiral Arm Evolution. I. Arm Density Structure

We explore the spiral arm structural properties in a large variety of simulated galaxy systems. We study spiral arms arising from isolated barred and unbarred galaxies, as well as from interactions with small satellites. In all these first models, galactic systems are all embedded in a spherical dark matter halo. We also study spiral arms arising from a galactic system embedded in a triaxial dark matter halo. Simulations used in this work have been obtained by using different N-body codes and initial conditions techniques. Our strategy is to study the 3D arm structure through the analysis of pitch angle, along/transverse/vertical density laws and their corresponding scale lengths, and spiral lifetime. Our main results are as follows. First, the radial density profile of all spiral arms analyzed in this work is exponential. This profile resembles the one of the disk but with a scale length that is systematically larger (5%-40%). This result suggests that spiral arm gravitational influence is important beyond the scale radius of the disk. Second, the vertical and transversal density laws of the spiral arms follow a sech(2). The vertical scale length is compatible with the one of the disk; this is observed in all spiral arms analyzed here, independently of their origin, i.e., bar, high-order disk perturbation, tidal interaction with satellites, or halo triaxiality. Third, in the triaxial and satellite simulations, spiral arms follow a logarithmic locus all through their lifetime; the remaining models develop transient, recurrent, and short-lived spirals with a nondefined locus. In all cases, spiral arms wind up in their lifetime with a small pitch angle reduction. It is common that newborn spirals inherit the pitch angle of the previous ones; this result challenges the dynamical relevance of arm evolution. Finally, from the analysis of public photometric observations of NGC 2543, we state that the properties of observed spiral arm structure can be consistent with our conclusions. Further and systematic comparisons with observations are needed in order to confirm our results.CONACyT Ciencia BasicaPrograma de Apoyo a Proyectos de Investigacion e Innovacion Tecnologica (PAPIIT)Fronteras de la Ciencia CONACyTDepto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasInstituto de Física de Partículas y del Cosmos (IPARCOS)TRUEpu

A feather on the hat: tracing the giant stellar stream around the Sombrero galaxy

Recent evidence of extremely metal-rich stars found in the Sombrero galaxy (M104) halo suggests that this galaxy has undergone a recent major merger with a relatively massive galaxy. In this paper, we present wide-field deep images of the M104 outskirts obtained with a 18-cm amateur telescope with the purpose of detecting any coherent tidal features from this possible major merger. Our new data, together with a model of the M104 inner halo and scattered light from stars around the field, allow us to trace for the first time the full path of the stream on both sides of the disk of the galaxy. We fully characterize the ring-like tidal structure and we confirm that this is the only observable coherent substructure in the inner halo region. This result is in agreement with the hypothesis that M104 was created by a wet major merger more than 3.5 Gyr ago that heated up the stellar population, blurring all old substructure. We generated a set of numerical models that reproduce the formation of the observed tidal structure. Our best fit model suggests the formation of this stream in the last 3 Gyr is independent of the wet major merger that created the M104 system. Therefore, the formation of the tidal stream can put a constraint on the time when the major merger occurred