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Stellar Properties for a Comprehensive Collection of Star-forming Regions in the SDSS APOGEE-2 Survey
(ASTRONOMICAL JOURNAL, 2023-01-01) Román-Zúñiga, CG; Kounkel, M; Hernández, J; Ramírez, KP; [et al.]
The Sloan Digital Sky Survey IV APOGEE-2 primary science goal was to observe red giant stars throughout the Galaxy to study its dynamics, morphology, and chemical evolution. The APOGEE instrument, a high-resolution 300fiber H-band (1.55-1.71 mu m) spectrograph, is also ideal to study other stellar populations in the Galaxy, among which are a number of star-forming regions and young open clusters. We present the results of the determination of six stellar properties (Teff, log g, [Fe/H], L/L-circle dot, M/M-circle dot, and age) for a sample that is composed of 3360 young stars, of subsolar to supersolar types, in 16 Galactic star formation and young open cluster regions. Those sources were selected by using a clustering method that removes most of the field contamination. Samples were also refined by removing targets affected by various systematic effects of the parameter determination. The final samples are presented in a comprehensive catalog that includes all six estimated parameters. This overview study also includes parameter spatial distribution maps for all regions and Hertzsprung-Russell (log L/L-circle dot vs. T-eff) diagrams. This study serves as a guide for detailed studies on individual regions and paves the way for the future studies on the global properties of stars in the pre-main-sequence phase of stellar evolution using more robust samples.
Light elements Na and Al in 58 bulge spheroid stars from APOGEE
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-09-29) Barbuy, B; Friaça, ACS; Ernandes, H; Moura, T; Masseron, T; Cunha, K; Smith, VV; Souto, D; Pérez-Villegas, A; Souza, SO; Chiappini, C; Queiroz, ABA; Fernández-Trincado, JG; [et al.]
We identified a sample of 58 candidate stars with metallicity [Fe/H]less than or similar to-0.8 that likely belong to the old bulge spheroid stellar population, and analyse their Na and Al abundances from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. In a previous work, we inspected APOGEE-Stellar Parameter and Chemical Abundance Pipeline abundances of C, N, O, Mg, Al, Ca, Si, and Ce in this sample. Regarding Na lines, one of them appears very strong in about 20percent of the sample stars, but it is not confirmed by other Na lines, and can be explained by sky lines, which affect the reduced spectra of stars in a certain radial velocity range. The Na abundances for 15 more reliable cases were taken into account. Al lines in the H band instead appear to be very reliable. Na and Al exhibit a spread in abundances, whereas no spread in N abundances is found, and we found no correlation between them, indicating that these stars could not be identified as second-generation stars that originated in globular clusters. We carry out the study of the behaviour of Na and Al in our sample of bulge stars and literature data by comparing them with chemodynamical evolution model suitable for the Galactic bulge. The Na abundances show a large spread, and the chemodynamical models follow the main data, whereas for aluminum instead, the models reproduce very satisfactorily the nearly secondary-element behaviour of aluminum in the metallicity range below [Fe/H]less than or similar to-1.0. For the lower-metallicity end ([Fe/H<-2.5), hypernovae are assumed to be the main contributor to yields.
CLASSY VII Lyα Profiles: The Structure and Kinematics of Neutral Gas and Implications for LyC Escape in Reionization-era Analogs
(ASTROPHYSICAL JOURNAL, 2023-10-01) Hu, WD; Martin, CL; Gronke, M; Gazagnes, S; Hayes, M; Chisholm, J; Heckman, T; Mingozzi, M; [et al.]
Ly alpha line profiles are a powerful probe of interstellar medium (ISM) structure, outflow speed, and Lyman-continuum escape fraction. In this paper, we present the Ly alpha line profiles of the Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY, a sample rich in spectroscopic analogs of reionization-era galaxies. A large fraction of the spectra show a complex profile, consisting of a double-peaked Ly alpha emission profile in the bottom of a damped, Ly alpha absorption trough. Such profiles reveal an inhomogeneous ISM. We successfully fit the damped Ly alpha absorption and the Ly alpha emission profiles separately, but with complementary covering factors, a surprising result because this approach requires no Ly alpha exchange between high-N-H I and low-N-H I paths. The combined distribution of column densities is qualitatively similar to the bimodal distributions observed in numerical simulations. We find an inverse relation between Ly alpha peak separation and the [O III]/[O II] flux ratio, confirming that the covering fraction of Lyman-continuum-thin sightlines increases as the Ly alpha peak separation decreases. We combine measurements of Ly alpha peak separation and Ly alpha red peak asymmetry in a diagnostic diagram, which identifies six Lyman-continuum leakers in the COS Legacy Archive Spectrocopy SurveY (CLASSY) sample. We find a strong correlation between the Ly alpha trough velocity and the outflow velocity measured from interstellar absorption lines. We argue that greater vignetting of the blueshifted Ly alpha peak, relative to the redshifted peak, is the source of the well-known discrepancy between shell-model parameters and directly measured outflow properties. The CLASSY sample illustrates how scattering of Ly alpha photons outside the spectroscopic aperture reshapes Ly alpha profiles because the distances to these compact starbursts span a large range.
The stellar halo in Local Group Hestia simulations
(ASTRONOMY & ASTROPHYSICS, 2023-09-11) Khoperskov, S; Minchev, I; Libeskind, N; Haywood, M; Di Matteo, P; Belokurov, V; Steinmetz, M; Gomez, FA; [et al.]
Recent progress in understanding the assembly history of the Milky Way (MW) is driven by the tremendous amount of high-quality data delivered by Gaia (ESA), revealing a number of substructures potentially linked to several ancient accretion events. In this work we aim to explore the phase-space structure of accreted stars by analysing six M31 /MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We find that all HESTIA galaxies experience a few dozen mergers but only between one and four of those have stellar mass ratios > 0 :2, relative to the host at the time of the merger. Depending on the halo definition, the most massive merger contributes from 20% to 70% of the total stellar halo mass. Individual merger remnants show diverse density distributions at z = 0, significantly overlapping with each other and with the in situ stars in the L-z - E, (V-R , V-phi) and (R; v(phi)) coordinates. Moreover, merger debris often shifts position in the Lz E space with cosmic time due to the galactic mass growth and the non-axisymmetry of the potential. In agreement with previous works, we show that even individual merger debris exhibit a number of distinct L-z-E features. In the (V-R,V-phi) plane, all HESTIA galaxies reveal radially hot, non-rotating or weakly counter-rotating, Gaia-Sausage-like features, which are the remnants of the most recent significant mergers. We find an age gradient in L-z - E space for individual debris, where the youngest stars, formed in the inner regions of accreting systems, deposit to the innermost regions of the host galaxies. The bulk of these stars formed during the last stages of accretion, making it possible to use the stellar ages of the remnants to date the merger event. In action space ( J(r),J(z),J(phi)), merger debris do not appear as isolated substructures, but are instead scattered over a large parameter area and overlap with the in situ stars. We suggest that accreted stars can be best identified using root J(r) > 0.2-0.3 (10(4) kpc km s (-1))(0.5). We also introduce a new, purely kinematic space ( J(z) /J(r)-orbital eccentricity), where di fferent merger debris can be disentangled better from each other and from the in situ stars. Accreted stars have a broad distribution of eccentricities, peaking at epsilon approximate to 0.6 0.9, and their mean eccentricity tends to be smaller for systems accreted more recently.
The stellar halo in Local Group Hestia simulations I. The in situ component and the effect of mergers
(ASTRONOMY & ASTROPHYSICS, 2023-09-11) Khoperskov, S; Minchev, I; Libeskind, N; Haywood, M; Di Matteo, P; Belokurov, V; Steinmetz, M; Gomez, FA; [et al.]
Theory suggests that mergers play an important role in shaping galactic discs and stellar haloes, which was observationally confirmed in the Milky Way (MW) thanks to Gaia data. In this work, aiming to probe the contribution of mergers to the in situ stellar halo formation, we analyse six M31 and MW analogues from the HESTIA suite of cosmological hydrodynamical zoom-in simulations of the Local Group. We found that all the HESTIA galaxies experience between one to four mergers with stellar mass ratios between 0.2 and 1 relative to the host at the time of the merger. These significant mergers, with a single exception, happened 7 11 Gyr ago. The overall impact of the most massive mergers in HESTIA is clearly seen as a sharp increase in the orbital eccentricity (and a corresponding decrease in the rotational velocity V-phi) of pre-existing disc stars of the main progenitor, thus nicely reproducing the Splash-, Plume-like feature that was discovered in the MW. We do find a correlation between mergers and close pericentric passages of massive satellites and bursts of the star formation in the in situ component. Massive mergers sharply increase the disc velocity dispersion of the in situ stars; however, the latest significant merger often heats up the disc up to the numbers when the contribution of the previous ones is less prominent in the age-velocity dispersion relation. In HESTIA galaxies, the in situ halo is an important component of the inner stellar halo where its fraction is about 30 40%, while in the outer parts it typically does not exceed approximate to 5% beyond 15 kpc from the galactic centre. The simulations suggest that this component of the stellar haloes continues to grow well after mergers conclude; however, the most significant contribution comes from stars that formed recently before the merger. The orbital analysis of the HESTIA galaxies suggests that wedges in R-max Z(max) (apocentre - maximum height from the mid-plane) space are mainly populated by the stars born in between significant mergers.
The VANDELS survey: the ionizing properties of star-forming galaxies at 3=z=5 using deep rest-frame ultraviolet spectroscopy
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-05-11) Saldana-Lopez, A; Schaerer, D; Chisholm, J; Calabrò, A; [et al.]
The physical properties of Epoch of Reionization (EoR) galaxies are still poorly constrained by observations. To better understand the ionizing properties of galaxies in the EoR, we investigate deep, rest-frame ultraviolet (UV) spectra of similar or equal to 500 star-forming galaxies at 3 = z & = 5 selected from the public ESO-VANDELS spectroscopic survey. The absolute ionizing photon escape fraction ($f_{\rm esc}<^>{\rm abs}$, i.e. the ratio of leaking against produced ionizing photons) is derived by combining absorption line measurements with estimates of the UV attenuation. The ionizing production efficiency (?(ion), i.e. the number of ionizing photons produced per non-ionizing UV luminosity) is calculated by fitting the far-UV (FUV) stellar continuum of the VANDELS galaxies. We find that the $f_{\rm esc}<^>{\rm abs}$ and ?(ion) parameters increase towards low-mass, blue UV-continuum slopes and strong Ly a emitting galaxies, and both are slightly higher-than-average for the UV-faintest galaxies in the sample. Potential Lyman Continuum Emitters (LCEs, $f_{\rm esc}<^>{\rm abs} \ge 5{{\ \rm \, per\ cent}}$) and selected Lyman Alpha Emitters (LAEs, W-Lya <= -20 angstrom) show systematically higher ?(ion) (log ?(ion)(Hz erg(-1)) approximate to 25.38, 25.41) than non-LCEs and non-LAEs (log ?(ion)(Hz erg(-1)) approximate to 25.18, 25.14) at similar UV magnitudes. This indicates very young underlying stellar populations (approximate to 10 Myr) at relatively low metallicities (approximate to 0.2 Z(circle dot)). The FUV non-ionizing spectra of potential LCEs is characterized by blue UV slopes (<=-2), enhanced Ly a emission (<=-25 angstrom), strong UV nebular lines (e.g. high ${\rm C\, \small {IV}}$1550/${\rm C\, \small {III}}$1908 >= 0.75 ratios), and weak absorption lines (<= 1 angstrom). The latter suggests the existence of low gas-column-density channels in the interstellar medium, which enables the escape of ionizing photons. By comparing our VANDELS results against other surveys in the literature, our findings imply that the ionizing budget in the EoR was likely dominated by UV-faint, low-mass, and dustless galaxies.
Saying Hallo to M94's Stellar Halo: Investigating the Accretion History of the Largest Pseudobulge Host in the Local Universe
(ASTROPHYSICAL JOURNAL, 2023-04-01) Gozman, K.; Bell, E. F.; Smercina, A.; Price, P.; Bailin, J.; de Jong, R. S; D'Souza, R; Jang, I. S.; Monachesi, A.; Slater, C.
It is not yet settled how the combination of secular processes and merging gives rise to the bulges and pseudobulges of galaxies. The nearby (D similar to 4.2 Mpc) disk galaxy M94 (NGC 4736) has the largest pseudobulge in the local universe, and offers a unique opportunity for investigating the role of merging in the formation of its pseudobulge. We present a first ever look at M94's stellar halo, which we expect to contain a fossil record of M94's past mergers. Using Subaru's Hyper Suprime-Cam, we resolve and identify red giant branch (RGB) stars in M94's halo, finding two distinct populations. After correcting for completeness through artificial star tests, we can measure the radial profile of each RGB population. The metal-rich RGB stars show an unbroken exponential profile to a radius of 30 kpc that is a clear continuation of M94's outer disk. M94's metal-poor stellar halo is detectable over a wider area and clearly separates from its metal-rich disk. By integrating the halo density profile, we infer a total accreted stellar mass of similar to 2.8 x 10(8) M-circle dot, with a median metallicity of [M/H] = -1.4. This indicates that M94's most-massive past merger was with a galaxy similar to, or less massive than, the Small Magellanic Cloud. Few nearby galaxies have had such a low-mass dominant merger; therefore we suggest that M94's pseudobulge was not significantly impacted by merging.
Ca triplet metallicities and velocities for 12 globular clusters toward the galactic bulge
(ASTRONOMY & ASTROPHYSICS, 2023-01-20) Geisler, D.; Parisi, M. C.; Dias, B.; Villanova, S.; Mauro, F.; Saviane, I.; Cohen, R. E.; Bidin, C. M.; Minniti, D.
Context. Globular clusters (GCs) are excellent tracers of the formation and early evolution of the Milky Way. The bulge GCs (BGCs) are particularly important because they can reveal vital information about the oldest in situ component of the Milky Way.Aims. Our aim is to derive the mean metallicities and radial velocities for 13 GCs that lie toward the bulge and are generally associated with this component. This region is observationally challenging because of high extinction and stellar density, which hampers optical studies of these and similar BGCs, making most previous determinations of these parameters quite uncertain.Methods. We used near-infrared low-resolution spectroscopy with the FORS2 instrument on the VLT to measure the wavelengths and equivalent widths of the CaII triplet (CaT) lines for a number of stars per cluster. We derived radial velocities, ascertained membership, and applied known calibrations to determine metallicities for cluster members, for a mean of 11 members per cluster. Unfortunately, one of our targets, VVV-GC002, which is the closest GC to the Galactic center, turned out not to have any members in our sample.Results. We derive mean cluster RV values to 3 km s(-1), and mean metallicities to 0.05 dex. We find general good agreement with previous determinations for both metallicity and velocity. On average, our metallicities are 0.07 dex more metal-rich than those of Harris (2010, arXiv:1012.3224), with a standard deviation of the difference of 0.25 dex. Our sample has metallicities between -0.21 and -1.64, and the values are distributed between the traditional metal-rich BGC peak near [Fe/H] -0.5 and a more metal-poor peak around [Fe/H] -1.1, which has recently been identified. These latter are candidates for the oldest GCs in the Galaxy, if blue horizontal branches are present, and include BH 261, NGC 6401, NGC 6540, NGC 6642, and Terzan 9. Finally, Terzan 10 is even more metal-poor. However, dynamically, Terzan 10 is likely an intruder from the halo, possibly associated with the Gaia-Enceladus or Kraken accretion events. Terzan 10 is also confirmed as an Oosterhoff type II GC based on our results.Conclusions. The CaT technique is an excellent method for deriving mean metallicities and velocities for heavily obscured GCs. Our sample provides reliable mean values for these two key properties via spectroscopy of a significant number of members per cluster for this important yet previously poorly studied sample of BGCs. We emphasize that the more metal-poor GCs are excellent candidates for being ancient relics of bulge formation. The lone halo intruder in our sample, Terzan 10, is conspicuous for also having by far the lowest metallicity, and casts doubt on the possibility of any bona fide BGCs at metallicities below about -1.5.
Spatially resolved properties of the ionized gas in the H ii galaxy J084220+115000
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-01-09) Fernández-Arenas, D.; Carrasco, E.; Terlevich, R.; Terlevich, E.; Amorín, R.; Bresolin, F.; Chávez, R.; González-Morán, A. L.; Rosa-González, D.; Mayya, Y. D.; Vega, O.; Zaragoza-Cardiel, J.; Méndez-Abreu, J.; Izazaga-Pérez, R.; de Paz, A. G.; Gallego, J.; Iglesias-Páramo, J.; García-Vargas, M. L.; Gómez-Alvarez, P.; Castillo-Morales, A.; Cardiel, N.; Pascual, S.; Pérez-Calpena, A.
We present a spatially resolved spectroscopic study for the metal poor H ii galaxy J084220+115000 using MEGARA Integral Field Unit observations at the Gran Telescopio Canarias. We estimated the gas metallicity using the direct method for oxygen, nitrogen, and helium and found a mean value of 12 + log (O/H) = 8.03 +/- 0.06, and integrated electron density and temperature of similar to 161 cm(-3) and similar to 15400 K, respectively. The metallicity distribution shows a large range of Delta(O/H) = 0.72 dex between the minimum and maximum (7.69 +/- 0.06 and 8.42 +/- 0.05) values, unusual in a dwarf star-forming galaxy. We derived an integrated log (N/O) ratio of -1.51 +/- 0.05 and found that both N/O and O/H correspond to a primary production of metals. Spatially resolved maps indicate that the gas appears to be photoionized by massive stars according to the diagnostic line ratios. Between the possible mechanisms to explain the starburst activity and the large variation of oxygen abundance in this galaxy, our data support a possible scenario where we are witnessing an ongoing interaction triggering multiple star-forming regions localized in two dominant clumps.
An ever-present Gaia snail shell triggered by a dark matter wake
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-07-04) Grand, R. J. J.; Pakmor, R.; Fragkoudi, F.; Gómez, F. A.; Trick, W.; Simpson, C. M.; van de Voort, F.; Bieri, R.
We utilize a novel numerical technique to model star formation in cosmological simulations of galaxy formation - called SUPERSTARS - to simulate a Milky Way-like galaxy with greater than or similar to 10(8) star particles to study the formation and evolution of out-of-equilibrium stellar disc structures in a full cosmological setting. In the plane defined by the coordinate and velocity perpendicular to the mid-plane [vertical phase space, (Z, V-Z)], stars in solar- like volumes at late times exhibit clear spirals qualitatively similar in shape and amplitude to the Gaia 'snail shell' phase spiral. We show that the phase spiral forms at a lookback time of similar to 6 Gyr during the pericentric passage of an similar to 10(10) M-circle dot satellite on a polar orbit. This satellite stimulates the formation of a resonant wake in the dark matter halo while losing mass at a rate of similar to 0.5-1 dex per orbit loop. The peak magnitude of the wake-induced gravitational torque at the solar radius is similar to 8 times that from the satellite, and triggers the formation of a disc warp that wraps up into a vertical phase spiral over time. As the wake decays, the phase spiral propagates several gigayears to present day and can be described as `ever-present' once stable disc evolution is established. These results suggest an alternative scenario to explain the Gaia phase spiral, which does not rely on a perturbation from bar buckling or a recent direct hit from a satellite.
The spectroscopic orbit of HD 168112 A,B in NGC 6604: another massive binary target for interferometry
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-09-11) Putkuri, C.; Gamen, R.; Morrell, N.; Apellániz, J. M.; Arias, J.; Simón-Díaz, S.; Ferrero, G. A.; Rodríguez, C. N.; Sota, A.; Benvenuto, O. G.; Barbá, R. H.
We present the first spectroscopic orbit of the O-type double-lined star HD 168112 A,B. We analyse 101 high-resolution optical spectra identifying the absorption lines of both components. The orbital solution presents a relatively long period, P = 513.52 +/- 0.01 d, and a high eccentricity, e = 0.743 +/- 0.005. The binary system consists of two very similar stars of minimum masses of similar to 25 M-circle dot, effective temperatures of similar to 40 000 K, and surface gravities of similar to 3.7 dex. The system has a minimum semimajor axis a sin i similar to 1000 R-circle dot. We confirm that the A and B visual components identified via interferometry do correspond to the spectroscopic ones. We also analyse the underlying stellar groups using Gaia DR3 data and ground-based spectroscopy as part of the Villafranca project, determining that NGC 6604 is at a distance of 1942(-36)(+38) pc and giving spectral classifications for 23 massive stellar systems in Villafranca O-035 and the surrounding Ser OB2 association, for which we provide the most complete census of massive stars to date.
The Three Hundred Project: Connection between star formation quenching and dynamical evolution in and around simulated galaxy clusters
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-01) Hough, T.; Cora, S. A.; Haggar, R.; Vega-Martinez, C.; Kuchner, U.; Pearce, F.; Gray, M.; Knebe, A.; Yepes, G.
In this work, we combine the semi-analytic model of galaxy formation and evolution SAG with the 102 relaxed simulated galaxy clusters from THE THREE HUNDRED project, and we study the link between the quenching of star formation (SF) and the physical processes that galaxies experience through their dynamical history in and around clusters. We classify galaxies in four populations based on their orbital history: recent and ancient infallers, and backsplash and neighbouring galaxies. We find that similar to 85 per cent of the current population of quenched galaxies located inside the clusters are ancient infallers with low or null content of hot and cold gas. The fraction of quenched ancient infallers increases strongly between the first and second pericentric passage, due to the removal of hot gas by the action of ram-pressure stripping (RPS). The majority of them quenches after the first pericentric passage, but a non-negligible fraction needs a second passage, specially galaxies with M-* <= 10(10.5) M-circle dot. Recent infallers represent similar to 15 per cent of the quenched galaxies located inside the cluster and, on average, they contain a high proportion of hot and cold gas; moreover, pre-processing effects are responsible for quenching the recent infallers prior to infall onto the main cluster progenitor. The similar to 65 per cent of quenched galaxies located around clusters are backsplash galaxies, for which the combination of RPS acting during a pre-processing stage and inside the cluster is necessary for the suppression of SF in this population.
A trail of the invisible: blue globular clusters trace the radial density distribution of the dark matter – case study of NGC 4278
(Oxford Academic, 2023-03-22) Matthias Kluge; Rhea-Silvia Remus; Iurii V Babyk; Duncan A Forbes; Arianna Dolfi
We present new, deep optical observations of the early-type galaxy NGC 4278, which is located in a small loose group. We find that the galaxy lacks fine substructure, that is, it appears relaxed, out to a radius of ∼70 kpc. Our g- and i-band surface brightness profiles are uniform down to our deepest levels of ∼28 mag arcsec−2. This spans an extremely large radial range of more than 14 half-mass radii. Combined with archival globular cluster (GC) number density maps and a new analysis of the total mass distribution obtained from archival Chandra X-ray data, we find that the red GC subpopulation traces well the stellar mass density profile from 2.4 out to even 14 half-mass radii, while the blue GC subpopulation traces the total mass density profile of the galaxy over a large radial range. Our results reinforce the scenario that red GCs form mostly in situ along with the stellar component of the galaxy, while the blue GCs are more closely aligned with the total mass distribution in the halo and were accreted along with halo matter. We conclude that for galaxies where the X-ray emission from the hot halo is too faint to be properly observable and as such is not available to measure the dark matter profile, the blue GC population can be used to trace this dark matter component out to large radii.
Backsplash galaxies and their impact on galaxy evolution: a three-stage, four-type perspective
(Oxford Academic, 2023-07-31) Andrés N Ruiz; Héctor J Martínez; Valeria Coenda; Hernán Muriel; Sofía A Cora; Martín de los Rios; Cristian A Vega-Martínez
We study the population of backsplash galaxies at z = 0 in the outskirts of massive, isolated clusters of galaxies taken from the MDPL2-SAG semi-analytical catalogue. We consider four types of backsplash galaxies according to whether they are forming stars or passive at three stages in their lifetimes: before entering the cluster, during their first incursion through the cluster, and after they exit the cluster. We analyse several geometric, dynamic, and astrophysical aspects of the four types at the three stages. Galaxies that form stars at all stages account for the majority of the backsplash population (58 per cent) and have stellar masses typically below
that avoid the innermost cluster’s regions and are only mildly affected by it. In a similar mass range, galaxies that become passive after exiting the cluster (26 per cent) follow orbits characterized by small pericentric distance and a strong deflection by the cluster potential well while suffering a strong loss of both dark matter and gas content. Only a small fraction of our sample (4 per cent) becomes passive while orbiting inside the cluster. These galaxies have experienced heavy pre-processing and the cluster’s tidal stripping and ram pressure provide the final blow to their star formation. Finally, galaxies that are passive before entering the cluster for the first time (12 per cent) are typically massive and are not affected significantly by the cluster. Using the bulge/total mass ratio as a proxy for morphology, we find that a single incursion through a cluster does not result in significant morphological changes in all four types.
The stellar halo in Local Group Hestia simulations
(ASTRONOMY & ASTROPHYSICS, 2023-09-11) Khoperskov, S; Minchev, I; Libeskind, N; Belokurov, V; [et al.]
Stellar chemical abundances and kinematics provide key information for recovering the assembly history of galaxies. In this work we explore the chemo-chrono-kinematics of accreted and in situ stellar populations, by analyzing six M31 /Milky Way (MW) analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We show that elemental abundances ([Fe =H], [Mg =Fe]) of merger debris in the stellar haloes are chemically distinct from the survived dwarf galaxies, in that they are [ alpha/Fe]-enhanced and have lower metallicity in the same stellar mass range. Therefore, mergers debris have abundances expected for stars originating from dwarfs that had their star formation activity quenched at early times. Accreted stellar haloes, including individual debris, reveal [Fe=H] and [Mg=Fe] gradients in the E - L-z plane, with the most metal-rich, [alpha/Fe]-poor stars, which have formed in the inner parts of the disrupted systems before the merger, contributing mainly to the central regions of the host galaxies. This results in negative metallicity gradients in the accreted components of stellar haloes at z = 0, seen also for the individual merger debris. We suggest, therefore, that abundance measurements of halo stars in the inner MW will allow constraining better the parameters, such as the mass and merger time, of MW ' s most massive merger Gaia-Sausage-Enceladus. The metallicity distribution functions (MDFs) of the individual debris show several peaks and the majority of debris have lower metallicity than the in situ stars in the prograde part of the E-L-z space. At the same time, non-rotating and retrograde accreted populations are very similar to the in situ stars in terms of [Fe=H] abundance. Prograde accreted stars show a prominent knee in the [Fe=H]-[Mg=Fe] plane, reaching up to solar [Mg=Fe], while retrograde stars typically contribute to the high-[Mg=Fe] sequence only. We find that the most metal-poor stars ([Fe=H]less than or similar to -1) of the HESTIA galaxies exhibit net rotation up to 80 km s (-1), which is consistent with the Aurora population recently identified in the MW. At higher metallicities ([Fe=H] approximate to -0.5 +/- 0.1) we detect a sharp transition (spin-up) from the turbulent phase to a regular disk-like rotation. Di fferent merger debris appear similar in the [Fe=H]-[Mg=Fe] plane, thus making it di fficult to identify individual events. However, combining a set of abundances, and especially stellar age, makes it possible to distinguish between di fferent debris.
The VVV near-IR galaxy catalogue in a Northern part of the Galactic disc
(Oxford Academic, 2023-06-16) I V Daza-Perilla; M A Sgró; L D Baravalle; M V Alonso; C Villalon; M Lares; M Soto; J L Nilo Castellón; C Valotto; P Marchant Cortés; D Minniti; M Hempel
The automated identification of extragalactic objects in large surveys provides reliable and reproducible samples of galaxies in less time than procedures involving human interaction. However, regions near the Galactic disc are more challenging due to the dust extinction. We present the methodology for the automatic classification of galaxies and non-galaxies at low Galactic latitude regions using both images and photometric and morphological near-IR data from the VISTA Variables in the Vía Láctea eXtended (VVVX) survey. Using the VVV NIR Galaxy Catalogue (VVV NIRGC), we analyse by statistical methods the most relevant features for galaxy identification. This catalogue was used to train a convolutional neural network with image data and an XGBoost model with both photometric and morphological data and then to generate a data set of extragalactic candidates. This allows us to derive probability catalogues used to analyse the completeness and purity as a function of the configuration parameters and to explore the best combinations of the models. As a test case, we apply this methodology to the Northern disc region of the VVVX survey, obtaining 172 396 extragalactic candidates with probabilities of being galaxies. We analyse the performance of our methodology in the VVV disc, reaching an F1-score of 0.67, a 65 per cent purity, and a 69 per cent completeness. We present the VVV NIRGC: Northern part of the Galactic disc comprising 1003 new galaxies, with probabilities greater than 0.6 for either model, with visual inspection and with only two previously identified galaxies. In the future, we intend to apply this methodology to other areas of the VVVX survey.
ABYSS. I. Targeting Strategy for the APOGEE and BOSS Young Star Survey in SDSS-V
(ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 2023-05-01) Kounkel, M; Zari, E; Covey, K; Tkachenko, A; [et al.]
The fifth iteration of the Sloan Digital Sky Survey is set to obtain optical and near-infrared spectra of similar to 5 million stars of all ages and masses throughout the Milky Way. As a part of these efforts, APOGEE and BOSS Young Star Survey (ABYSS) will observe similar to 10(5) stars with ages <30 Myr that have been selected using a set of homogeneous selection functions that make use of different tracers of youth. The ABYSS targeting strategy we describe in this paper is aimed to provide the largest spectroscopic census of young stars to date. It consists of eight different types of selection criteria that take the position on the H-R diagram, infrared excess, variability, as well as the position in phase space in consideration. The resulting catalog of similar to 200,000 sources (of which a half are expected to be observed) provides representative coverage of the young Galaxy, including both nearby diffuse associations as well as more distant massive complexes, reaching toward the inner Galaxy and the Galactic center.
Constraining the assembly time of the stellar haloes of nearby Milky Way-mass galaxies through AGB populations
(Oxford Academic, 2023-08-25) Benjamin Harmsen; Eric F Bell; Richard D’Souza; Antonela Monachesi; Roelof S de Jong; Adam Smercina; In Sung Jang; Benne W Holwerda
The star formation histories (SFHs) of galactic stellar haloes offer crucial insights into the merger history of the galaxy and the effects of those mergers on their hosts. Such measurements have revealed that while the Milky Way’s most important merger was 8–10 Gyr ago, M31’s largest merger was more recent, within the last few Gyr. Unfortunately, the required halo SFH measurements are extremely observationally expensive outside of the Local Group. Here, we use asymptotic giant branch (AGB) stars brighter than the tip of the red giant branch (RGB) to constrain stellar halo SFHs. Both stellar population models and archival data sets show that the AGB/RGB ratio constrains the time before which 90 per cent of the stars formed, t90. We find AGB stars in the haloes of three highly inclined roughly Milky Way-mass galaxies with resolved star measurements from the Hubble Space Telescope; this population is most prominent in the stellar haloes of NGC 253 and NGC 891, suggesting that their stellar haloes contain stars born at relatively late times, with inferred t90 ∼ 6 ± 1.5 Gyr. This ratio also varies from region to region, tending towards higher values along the major axis and in tidal streams or shells. By combining our measurements with previous constraints, we find a tentative anticorrelation between halo age and stellar halo mass, a trend that exists in models of galaxy formation but has never been elucidated before, i.e. the largest stellar haloes of Milky Way-mass galaxies were assembled more recently.
The resolved chemical composition of the starburst dwarf galaxy CGCG007-025: direct method versus photoionization model fitting
(Oxford Academic, 2023-01-23) V Fernández; R Amorín; R Sanchez-Janssen; M G del Valle-Espinosa; P Papaderos
This work focuses on the gas chemical composition of CGCG007-025. This compact dwarf is undergoing a galaxy wide star-forming burst, whose spatial behaviour has been observed by VLT/MUSE. We present a new line measurement library to treat almost 7800 voxels. The direct method chemical analysis is limited to 484 voxels with good detection of the
temperature diagnostic line. The recombination fluxes are corrected for stellar absorption via a population synthesis. Additionally, we discuss a new algorithm to fit photoionization models via neural networks. The eight ionic abundances analysed show a spatial normal distribution with a
, where only half this value can be explained by the uncertainty in the measurements. The oxygen abundance distribution is 12 + log(O/H) = 7.88 ± 0.11. The
and ne[S II] are also normally distributed. However, in the central and brightest region, the ne[S II] is almost thrice the mean galaxy value. This is also reflected in the extinction measurements. The ionization parameter has a distribution of
. The parameter spatial behaviour agrees with the S2+/S+ map. Finally, the discrepancies between the direct method and the photoionization model fitting are discussed. In the latter technique, we find that mixing lines with uneven uncertainty magnitudes can impact the accuracy of the results. In these fittings, we recommend overestimating the minimum flux uncertainty one order below the maximum line flux uncertainty. This provides a better match with the direct method.
The impact of the Large Magellanic Cloud on dark matter direct detection signals
(JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 2023-10-27) Smith-Orlik, A; Ronaghi, N; Bozorgnia, N; Cautun, M; [et al.]
We study the effect of the Large Magellanic Cloud (LMC) on the dark matter (DM) distribution in the Solar neighborhood, utilizing the Auriga magneto-hydrodynamical simulations of Milky Way (MW) analogues that have an LMC-like system. We extract the local DM velocity distribution at different times during the orbit of the LMC around the MW in the simulations. As found in previous idealized simulations of the MW-LMC system, we find that the DM particles in the Solar neighborhood originating from the LMC analogue dominate the high speed tail of the local DM speed distribution. Furthermore, the native DM particles of the MW in the Solar region are boosted to higher speeds as a result of a response to the LMC's motion. We simulate the signals expected in near future xenon, germanium, and silicon direct detection experiments, considering DM interactions with target nuclei or electrons. We find that the presence of the LMC causes a considerable shift in the expected direct detection exclusion limits towards smaller cross sections and DM masses, with the effect being more prominent for low mass DM. Hence, our study shows, for the first time, that the LMC's influence on the local DM distribution is significant even in fully cosmological MW analogues.
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