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Álgebras y fibrados de Clifford con aplicaciones
(Universidad de La Serena, 2012) Notte-Cuello, Eduardo
Light pollution indicators for all the major astronomical observatories
(Oxford Academic, 2022-12-20) Fabio Falchi; Felipe Ramos; Salvador Bará; Pedro Sanhueza; Marcelo Jaque Arancibia; Guillermo Damke; Pierantonio Cinzano
Light pollution at astronomical observatories is one of the main factors to be taken into account to preserve their scientific productivity and their useful lifetime. Using the Garstang–Cinzano model applied to the Visible Infrared Imaging Radiometer Suite (VIIRS) 2021 satellite radiance data, we have compared 28 sites, all hosting telescopes with apertures larger than 3 m, plus some additional selected sites. We computed and analysed five indicators of light pollution: radiance at zenith; averaged at 60° zenith distance; averaged over all the sky; averaged in the first 10° above the horizon; and horizontal irradiance. We found large variations of the values of the indicators, with a factor greater than 600 for the zenith artificial radiance between the least and most polluted major observatories. The results show that two-thirds of all large observatories have already surpassed the critical 10 per cent increase in radiance over the assumed natural levels. The results presented and the method described here can help to plan countermeasures in order to lower the impact of light pollution on observatories. These same methods can be also used to protect the night environment from the impact of artificial light (e.g. on biodiversity, on animal behaviour and physiology, on human health).
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.
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.
The Low-redshift Lyman Continuum Survey: Optically Thin and Thick Mg ii Lines as Probes of Lyman Continuum Escape
(ASTROPHYSICAL JOURNAL, 2023-01-01) Xu, XF; Henry, A; Heckman, T; Chisholm, J; [et al.]
The Mg ii lambda lambda 2796, 2803 doublet has been suggested as a useful indirect indicator for the escape of Ly alpha and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg ii or strong LyC emission. Here, we present the first study of Mg ii to probe a large dynamic range of galaxy properties, using newly obtained high-signal-to-noise, moderate-resolution spectra of Mg ii, for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg ii profiles ranging from strong emission to P-Cygni profiles to pure absorption. We find that there is a significant trend (with a possibility of spurious correlations of similar to 2%) that galaxies that are detected as strong LyC emitters (LCEs) show larger equivalent widths of Mg ii emission, while non-LCEs tend to show evidence of more scattering and absorption features in Mg ii. We then find that Mg ii strongly correlates with Ly alpha in both equivalent width and escape fraction, regardless of whether emission or absorption dominates the Mg ii profiles. Furthermore, we show that, for galaxies that are categorized as Mg ii emitters, one can use the information of Mg ii, metallicity, and dust to estimate the escape fraction of LyC within a factor of similar to 3. These findings confirm that Mg ii lines can be used as a tool for selecting galaxies as LCEs and thus serve as an indirect indicator for the escape of Ly alpha and LyC.
Taking a break: Paused accretion in the symbiotic binary RT Cru
(ASTRONOMY & ASTROPHYSICS, 2023-01-02) Pujol, A; Luna, GJM; Mukai, K; Sokoloski, JL; [et al.]
Symbiotic binaries sometimes hide their symbiotic nature for significant periods of time. There is mounting observational evidence that, in symbiotics that are powered solely by the accretion of the red giant's wind material onto a white dwarf, without any quasisteady shell burning on the surface of the white dwarf, the characteristic emission lines in the optical spectrum can vanish, leaving the semblance of an isolated red giant spectrum. Here we present compelling evidence that this disappearance of optical emission lines from the spectrum of RT Cru in 2019 was due to a decrease in the accretion rate, which we derived by modeling the X-ray spectrum. This drop in accretion rate leads to a lower flux of ionizing photons and thus to faint or absent photoionization emission lines in the optical spectrum. We observed the white dwarf symbiotic RT Cru with XMM-Newton and Swift in X-rays and UV and collected ground-based optical spectra and photometry obtained over the last 33 yr. This long-term coverage shows that, during most of the year 2019, the accretion rate onto the white dwarf was so low,. M = (3 :2 +/- 0 :06) x 10(-1)1 M fi yr(-1) (d /2.52 kpc)(2), that the historically detected hard X-ray emission almost vanished, the UV flux faded by roughly 5 mag, the U, B, and V flickering amplitude decreased, and the Balmer lines virtually disappeared from 2019 January through March. Long-lasting low-accretion episodes such as the one reported here may hamper the chances of RT Cru experiencing a nova-type outburst despite the high mass of the accreting white dwarf.
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.
Colour and infall time distributions of satellite galaxies in simulated Milky-Way analogues
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-01-09) Pan, Y.; Simpson, C. M.; Kravtsov, A.; Gómez, F. A.; Grand, R. J. J.; Marinacci, F.; Pakmor, R.; Manwadkar, V.; Esmerian, C. J.
We use the Auriga simulations to probe different satellite quenching mechanisms operating at different mass scales (10(5) M-theta ? M * < 10(11) M ((R))) in Milky Way-like hosts. Our goal is to understand the origin of the satellite colour distribution and star-forming properties in both observations and simulations. We find that the satellite populations in the Auriga simulations, which was originally designed to model Milky Way-like host galaxies, resemble the populations in the Exploration of Local VolumE Satellites (ELVES) Surv e y and the Satellites Around Galactic Analogs (SAGA) survey in their luminosity function in the luminosity range -12 ? M-V ? -15 and resemble ELVES in their quenched fraction and colour-magnitude distribution in the luminosity range -12 ? M-g ? -15. We find that satellites transition from blue colours to red colours at the luminosity range -15 ? Mg ? -12 in both the simulations and observations and we show that this shift is driven by environmental effects in the simulations. We demonstrate also that the colour distribution in both simulations and observations can be decomposed into two statistically distinct populations based on their morphological type or star-forming status that are statistically distinct. In the simulations, these two populations also have statistically distinct infall time distributions. The comparison presented here seems to indicate that this tension is resolved by the impro v ed target selection of ELVES, but there are still tensions in understanding the colours of faint galaxies, of which ELVES appears to have a significant population of faint blue satellites not reco v ered in Auriga.
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.
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.
Multiple Populations in Low-mass Globular Clusters: Eridanus
(ASTROPHYSICAL JOURNAL, 2023-02-01) Wang, Y.; Tang, B. T.; Li, C. Y.; Baumgardt, H.; Muñoz, R. R.; Fernández-Trincado, J. G.; Geisler, D.; Fang, Y. Q.
Multiple populations (MPs), characterized by variations in light elemental abundances, have been found in stellar clusters in the Milky Way, Magellanic Clouds, as well as several other dwarf galaxies. Based on a large number of observations, mass has been suggested to be a key parameter affecting the presence and appearance of MPs in stellar clusters. To further investigate the existence of MPs in low-mass clusters and explore the mass threshold for the formation of MPs, we carried out a project studying the composition of the stellar population in several lowmass Galactic globular clusters. Here we present our study on the cluster Eridanus. With blue-UV low-resolution spectra obtained with the OSIRIS/Multi-object spectrograph on the Gran Telescopio Canarias, we computed the spectral indices of CH and CN for a sample of giant stars and derived their carbon and nitrogen abundances using model spectra. A significant dispersion in the initial surface abundance of nitrogen was found in the sample, indicating the existence of MPs in Eridanus. Inspecting the age-initial mass distribution of in situ clusters with MPs, we find a slight trend that initial mass increases with increasing age, and the lowest initial masses of logM(initial) similar to 4.98 and 5.26 are found at the young and old end, respectively, which might provide a rough reference for the mass threshold for clusters to form MPs. However, more observations of clusters with low initial masses are still necessary before any firm conclusion can be drawn.
Pre-main-sequence Brackett Emitters in the APOGEE DR17 Catalog: Line Strengths and Physical Properties of Accretion Columns
(ASTROPHYSICAL JOURNAL, 2023-02-01) Campbell, H; Khilfeh, E; Covey, KR; Kounkel, M; [et al.]
Very young (t less than or similar to 10 Myr) stars possess strong magnetic fields that channel ionized gas from the interiors of their circumstellar disks to the surface of the star. Upon impacting the stellar surface, the shocked gas recombines and emits hydrogen spectral lines. To characterize the density and temperature of the gas within these accretion streams, we measure equivalent widths of Brackett (Br) 11-20 emission lines detected in 1101 APOGEE spectra of 326 likely pre-main-sequence accretors. For sources with multiple observations, we measure median epoch-to-epoch line strength variations of 10% in Br11 and 20% in Br20. We also fit the measured line ratios to predictions of radiative transfer models by Kwan & Fischer. We find characteristic best-fit electron densities of n ( e ) = 10(11)-10(12) cm(-3), and excitation temperatures that are inversely correlated with electron density (from T similar to 5000 K for n ( e ) similar to 10(12) cm(-3) to T similar to 12,500 K at n ( e ) similar to 10(11) cm(-3)). These physical parameters are in good agreement with predictions from modeling of accretion streams that account for the hydrodynamics and radiative transfer within the accretion stream. We also present a supplementary catalog of line measurements from 9733 spectra of 4255 Brackett emission-line sources in the APOGEE Data Release 17 data set.
A MUSE/VLT spatially resolved study of the emission structure of Green Pea galaxies
(Edp Sciences, 2023-02-20) Arroyo-Polonio; J. Iglesias-Páramo; C. Kehrig; J. M. Vílchez; R. Amorín; I. Breda; E. Pérez-Montero; B. Pérez-Díaz; M. Hayes
Green Pea galaxies (GPs) present among the most intense starbursts known in the nearby Universe. These galaxies are regarded as local analogs of high-redshift galaxies, making them a benchmark in the understanding of the star formation processes and the galactic evolution in the early Universe. In this work, we performed an integral field spectroscopic (IFS) study for a set of 24 GPs to investigate the interplay between its ionized interstellar medium (ISM) and the massive star formation that these galaxies present. Observations were taken in the optical spectral range (λ4750 Å–λ9350 Å) with the MUSE spectrograph attached to the 8.2 m telescope VLT. Spatial extension criteria were employed to verify which GPs are spatially resolved in the MUSE data cubes. We created and analyzed maps of spatially distributed emission lines (at different stages of excitation), continuum emission, and properties of the ionized ISM (e.g., ionization structure indicators, physical-chemical conditions, dust extinction). We also took advantage of our IFS data to produce integrated spectra of selected galactic regions in order to study their physical-chemical conditions. Maps of relevant emission lines and emission line ratios show that higher-excitation gas is preferentially located in the center of the galaxy, where the starburst is present. The continuum maps, with an average angular extent of 4″, exhibit more complex structures than the emission line maps. However, the [O III]λ5007 Å emission line maps tend to extend beyond the continuum images (the average angular extent is 5.5″), indicating the presence of low surface brightness ionized gas in the outer parts of the galaxies. Hα/Hβ, [S II]/Hα, and [O I]/Hα maps trace low-extinction, optically thin regions. The line ratios [O III]/Hβ and [N II]/Hα span extensive ranges, with values varying from 0.5 dex to 0.9 dex and from −1.7 dex to −0.8 dex, respectively. Regarding the integrated spectra, the line ratios were fit to derive physical properties including the electron densities ne = 30 − 530 cm−3, and, in six GPs with a measurable [O III]λ4363 Å line, electron temperatures of Te = 11 500 K–15 500 K, so the direct method was applied in these objects to retrieve metallicities 12 + log(O/H)≃8. We found the presence of the high-ionizing nebular He IIλ4686 Å line in three GPs, where two of them present among the highest sSFR values (> 8 × 108 yr−1) in this sample. Non-Wolf-Rayet (WR) features are detected in these galaxy spectra.
On monotone pseudocontractive operators and Krasnoselskij iterations in an ordered Hilbert space
(Springer Open, 2023-02-22) Jorquera Alvarez, Eduardo Daniel
The aim of this work is to establish fixed point results in ordered Hilbert spaces for monotone operators with a pseudocontractive property. We state monotone versions of Theorem 12 in [F. E. Browder, W. V. Petryshyn, Construction of fixed points of nonlinear mappings in Hilbert space, J. Math. Anal. Appl. 20 (1967), 197–228] and Theorem 2.1 in [Berinde, Vasile. Weak and strong convergence theorems for the Krasnoselskij iterative algorithm in the class of enriched strictly pseudocontractive operators, Annals of West University of Timisoara-Mathematics and Computer Science, vol. 56, no. 2, 2018, pp. 13–27], as well as, several related results. Further results, in Hilbert spaces without a partial order, are stated too.
Assessing model-based carbon and oxygen abundance derivation from ultraviolet emission lines in AGNs
(Oxford Academic, 2023-03-02) E Pérez-Montero; R Amorín; B Pérez-Díaz; J M Vílchez; R García-Benito
We present an adapted version of the code HII-CHI-MISTRY-UV to derive chemical abundances from emission lines in the ultraviolet, for use in narrow line regions (NLR) of active galactic nuclei (AGN). We evaluate different ultraviolet emission line ratios and how different assumptions about the models, including the presence of dust grains, the shape of the incident spectral energy distribution, or the thickness of the gas envelope around the central source, may affect the final estimates as a function of the set of emission lines used. We compare our results with other published recipes for deriving abundances using the same emission lines and show that deriving the carbon-to-oxygen abundance ratio using C III] λ 1909 Å and O III] λ 1665 Å emission lines is a robust indicator of the metal content in AGN that is nearly independent of the model assumptions, similar to the case of star-forming regions. Moreover, we show that a prior determination of C/O allows for a much more precise determination of the total oxygen abundance using carbon UV lines, as opposed to assuming an arbitrary relationship between O/H and C/O, which can lead to non-negligible discrepancies.
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.
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.
A MUSE view of the multiple interacting system HCG 31
(Oxford academic, 2023-04-14) Diego A Gómez-Espinoza; S Torres-Flores; V Firpo; Philippe Amram; Benoit Epinat; Thierry Contini; Claudia Mendes de Oliveira
We present, for the first time, spatially resolved spectroscopy for the entire Hickson Compact Group 31 obtained with the MUSE instrument at the VLT and an in-depth analysis of this compact group. To obtain a complete understanding of the system, we derived radial velocity and dispersion velocity maps, maps of the ionization mechanism of the system, chemical abundances and their distribution over the whole system, star formation rates and ages of the different star-forming regions, and the spatial distribution of the Wolf–Rayet stellar population. We also reconstructed the star formation history of the galaxies HCG 31 A, C, B, and F, measured the emission-line fluxes, and performed a stellar population synthesis. Our main findings are: (i) that there is clearly disturbed kinematics due to the merger event that the system is experiencing; (ii) that the ionization is produced exclusively via star formation except for the nucleus of the galaxy HCG 31 A, where there is a small contribution of shocks; (iii) that there is low oxygen abundance distributed homogeneously through the system; (iv) that there is a prominent population of carbon Wolf–Rayet stars in the central zone of the group; and (v) that there are clear evidences of the tidal origin of the galaxies HCG 31 E, HCG 31 H, and HCG 31 F because they show quite high oxygen abundances for their stellar mass. All these findings are clear evidence that HCG 31 is currently in an early merging phase and manifesting a starburst in its central region.
Spatially resolved chemodynamics of the starburst dwarf galaxy CGCG 007-025: evidence for recent accretion of metal-poor gas
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-04-21) del Valle-Espinosa, M. G.; Sánchez-Janssen, R.; Amorín, R.; Fernández, V.; Almeida, J. S.; Lorenzo, B. G.; Papaderos, P.
Nearby metal-poor starburst dwarf galaxies present a unique opportunity to probe the physics of high-density star formation with a detail and sensitivity unmatched by any observation of the high-z Universe. Here, we present the first results from a chemodynamical study of the nearby, gas-rich starburst dwarf CGCG 007-025. We use VLT/MUSE integral field spectroscopy to characterize the properties of the star-forming (SF) gas, from its metal content to its kinematics. The star formation rate (SFR) surface density presents a clumpy distribution, with the brightest knot hosting a 5 Myr young, Wolf-Rayet (WR) population (revealed by the presence of the characteristic 5808 angstrom WR bump). The ionized gas kinematics are dominated by disordered motions. A superposition of a narrow (sigma approximate to 30km s(-1)), intermediate (150 km s(-1)), and broad (1000 km s(-1)) kinematic components are needed to model the emission-line profiles in the brightest SF region, suggesting the presence of energetic outflows from massive stars. The gas-phase metallicity of the galaxy spans 0.6 dex and displays a strong anticorrelation with SFR surface density, dropping to 12 + log(O/H) = 7.7 in the central SF knot. The spatially resolved BPTs indicate the gas is being ionized purely by SF processes. Finally, the anticorrelation between the SFR and the gas metallicity points out to accretion of metal-poor gas as the origin of the recent off-centre starburst, in which the infalling material ignites the SF episode.
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.