Search

We analyse the quenched fractions, gas content, and star formation histories of ~1200 satellite galaxies with $M_* \geq 5 \times 10^6~{\rm M}_\odot$ around 198 Milky Way- (MW) and Andromeda-like (M31) hosts in TNG50, the highest-resolution simulation of IllustrisTNG. Satellite quenched fractions are larger for smaller masses, for smaller distances to their host galaxy, and in the more massive M31-like compared to MW-like hosts. As satellites cross their host's virial radius, their gas content drops: most satellites within 300 kpc lack detectable gas reservoirs at $z=0$, unless they are massive like the Magellanic Clouds and M32. Nevertheless, their stellar assembly exhibits a large degree of diversity. On average, the cumulative star formation histories are more extended for brighter, more massive satellites with a later infall, and for those in less massive hosts. Based on these relationships, we can even infer infall periods for observedMWand M31 dwarfs: e.g. 0-4 Gyr ago for the Magellanic Clouds and Leo I, 4-8 and 0-2 Gyr ago for M32 and IC 10, respectively. Ram pressure stripping (in combination with tidal stripping) deprives TNG50 satellites of their gas reservoirs and ultimately quenches their star formation, even though only a few per cent of the present-day satellites around the 198 TNG50 MW/M31-like hosts appear as jellyfish. The typical time since quenching for currently quenched TNG50 satellites is $6.9^{+2.5}_{-3.3}~{\rm Gyr}$ ago. The TNG50 results are consistent with the quenched fractions and stellar assembly of observed MW and M31 satellites, however, satellites of the SAGA survey with $M_* \sim 10^{8-9}~{\rm M}_\odot$ exhibit lower quenched fractions than TNG50 and other, observed analogues., Comment: Accepted for publication in MNRAS

We report the spectroscopic analysis of 20 halo ab-type RR Lyrae stars with heliocentric distances between 15 and 165 kpc, conducted using medium-resolution spectra from the Magellan Inamori Kyocera Echelle (MIKE) spectrograph. We obtain the systemic line-of-sight velocities of our targets with typical uncertainties of 5–10 km s−1 and compute orbital parameters for a subsample out to 50 kpc from the Galactic centre, including proper motion data from Gaia DR3. The orientation of our stars’ orbits, determined for an isolated Milky Way and for a model perturbed by the Large Magellanic Cloud, appears to suggest an accreted origin for at least half of the sample. In addition, we derive atmospheric parameters and chemical abundance ratios for seven stars beyond 20 kpc. The derived α-abundances of five of these stars follow a Milky Way halo-like trend, while the other two display an underabundance of α-elements for their [Fe/H], indicating an association with accretion events. Furthermore, based on the [Sr/Ba] ratio, we can speculate about the conditions for the formation of a potential chemically peculiar carbon-enhanced metal-poor (CEMP) RR Lyrae star. By analysing the stars’ orbital parameters and abundance ratios, we find hints of association of two of our stars with two massive satellites, namely the Large Magellanic Cloud and Sagittarius. Overall, our results are in line with the suggestion that the accretion of sub-haloes largely contributes to the outer halo stellar populations.

We present a pilot library of synthetic NUV, U, B, V, and I photometry of star clusters with stochastically sampled IMFs and ionized gas for initial masses, Mi = 103, 104, and 105 M⊙; t = 1, 3, 4, and 8 Myr; Z = 0.014 and Z = 0.002; and log(US) = −2 and −3. We compare the library with predictions from deterministic models and observations of isolated low-mass (1.0 mag more luminous than the median stochastic magnitude without gas; and (b) nebular emission lines can contribute with $\gt 50{{\ \rm per\ cent}}$ and $\gt 30{{\ \rm per\ cent}}$ to the total emission in the V and I bands, respectively. (3) Age-dating OB-star clusters via deterministic tracks in the U-B versus V-I plane is highly uncertain at Z = 0.014 for Mi ∼ 103 M⊙ and Z = 0.002 for Mi ∼ 103–105 M⊙. (4) For low-mass clusters, the V-band extinction derived with stochastic models significantly depends on the value of log(US). (5) The youngest clusters tend to have higher extinction. (6) The majority of clusters have multi-peaked age PDFs. (7) Finally, we discuss the importance of characterizing the true variance in the number of stars per mass bin in nature.

Using MUSE spectra, we investigate how pre-processing and accretion onto a galaxy cluster affect the integrated stellar population properties of dwarf early-type galaxies (dEs). We analyze a sample of nine dEs with stellar masses of $\rm \sim 10^9 \, M_\odot$, which were accreted ($\sim$ 2-3 Gyr ago) onto the Virgo cluster as members of a massive galaxy group. We derive their stellar population properties, namely age, metallicity ([M/H]), and the abundance ratio of $\alpha$ elements ([$\alpha$/Fe]), by fitting observed spectral indices with a robust, iterative procedure, and infer their star formation history (SFH) by means of full spectral fitting. We find that these nine dEs are more metal-poor (at the 2-3$\sigma$ level) and significantly more $\alpha$-enhanced than dEs in the Virgo and Coma clusters with similar stellar mass, cluster-centric distance, and infall time. Moreover, for six dEs, we find evidence for a recent episode of star formation during or right after the time of accretion onto Virgo. We interpret the high [$\alpha$/Fe] of our sample of dEs as the result of the previous exposure of these galaxies to an environment hostile to star formation, and/or the putative short burst of star formation they underwent after infall into Virgo. Our results suggest that the stellar population properties of low-mass galaxies may be the result of the combined effect of pre-processing in galaxy groups and environmental processes (such as ram-pressure triggering star formation) acting during the early phases of accretion onto a cluster., Comment: 17 pages, 10 figures, Accepted for publication in MNRAS

It has been well established that dwarf early-type galaxies (ETGs) can often exhibit a complex morphology, whereby faint spiral arms, bars, edge-on disks or clumps are embedded in their main, brighter diffuse body. In our first paper (Brought to Light I: Michea et al. 2021), we developed a new method for robustly identifying and extracting substructures in deep imaging data of dwarf ETGs in the Virgo galaxy cluster. Here we apply our method to a sample of 23 dwarf ETGs in the Fornax galaxy cluster, out of which 9 have disk-like and 14 have clump-like substructures. According to Fornax Deep Survey (FDS) data, our sample constitutes $12\%$ of all dwarf ETGs in Fornax brighter than $\text{M}_{r}=-13$ mag, and contains all cases that unequivocally exhibit substructure features. We use $g$ and $r$-band FDS images to measure the relative contribution of the substructures to the total galaxy light and to estimate their $g-r$ colors. We find that substructures typically contribute $8.7\%$ and $5.3\%$ of the total galaxy light in the $g$ and $r$ bands, respectively, within two effective radii. Disk substructures are usually found in dwarf ETGs with redder global colors, and they can be either as red as or bluer than their galaxy's diffuse component. In contrast, clump substructures are found in comparatively bluer dwarf ETGs, and they are always bluer than their galaxy's diffuse component. These results provide further evidence that dwarf ETGs can hide diverse complex substructures, with stellar populations that can greatly differ from those of the dominant diffuse light in which they are embedded., Comment: 35 pages, 12 figures, 5 tables. Accepted to AJ

The stellar mass assembly of galaxies can be affected by both secular and environmental processes. In this study, for the first time, we investigate the stellar mass assembly of $\sim90,000$ low redshift, central galaxies selected from SDSS group catalogues (M$_{\rm Stellar}\gtrsim10^{9.5}$M$_{\odot}$, M$_{\rm Halo}\gtrsim10^{12}$M$_{\odot}$) as a function of both stellar and halo mass. We use estimates of the times at which 10, 50 and 90 per cent of the stellar mass was assembled from photometric spectral energy distribution fitting, allowing a more complete investigation than single stellar ages alone. We consider trends in both stellar and halo mass simultaneously, finding dependencies of all assembly times on both. We find that galaxies with higher stellar masses (at constant halo mass) have on average older lookback times, similar to previous studies of galaxy assembly. We also find that galaxies at higher halo mass (at constant stellar mass) have younger lookback times, possibly due to a larger reservoir of gas for star formation. An exception to this is a sub sample with high stellar-to-halo mass ratios, which are likely massive, field spirals. We compare these observed trends to those predicted by the TNG300 simulation, finding good agreement overall as a function of either stellar or halo mass. However, some differences in the assembly times (of up to $\sim 3$ Gyr) appear when considering both stellar and halo mass simultaneously, noticeably at intermediate stellar masses (M$_{\rm Stellar} \sim 10^{11}$ M$_{\odot}$). These discrepancies are possibly linked to the quenched fraction of galaxies and the kinetic mode AGN feedback implemented in TNG300., 14 pages, 9 figures, Accepted for publication MNRAS

We discuss the largest and most homogeneous spectroscopic dataset of field RR Lyrae variables (RRLs) available to date. We estimated abundances using both high-resolution and low-resolution ({\Delta S} method) spectra for fundamental (RRab) and first overtone (RRc) RRLs. The iron abundances for 7,941 RRLs were supplemented with similar literature estimates available, ending up with 9,015 RRLs (6,150 RRab, 2,865 RRc). The metallicity distribution shows a mean value of = -1.51\pm0.01, and {\sigma}(standard deviation)= 0.41 dex with a long metal-poor tail approaching [Fe/H] = -3 and a sharp metal-rich tail approaching solar iron abundance. The RRab variables are more metal-rich (ab = -1.48\pm0.01, {\sigma} = 0.41 dex) than RRc variables (c = -1.58\pm0.01, {\sigma} = 0.40 dex). The relative fraction of RRab variables in the Bailey diagram (visual amplitude vs period) located along the short-period (more metal-rich) and the long-period (more metal-poor) sequences are 80% and 20\%, while RRc variables display an opposite trend, namely 30\% and 70\%. We found that the pulsation period of both RRab and RRc variables steadily decreases when moving from the metal-poor to the metal-rich regime. The visual amplitude shows the same trend, but RRc amplitudes are almost two times more sensitive than RRab amplitudes to metallicity. We also investigated the dependence of the population ratio (Nc/Ntot) of field RRLs on the metallicity and we found that the distribution is more complex than in globular clusters. The population ratio steadily increases from ~0.25 to ~0.36 in the metal-poor regime, it decreases from ~0.36 to ~0.18 for -1.8 < [Fe/H] < -0.9 and it increases to a value of ~0.3 approaching solar iron abundance., Comment: 22 pages, 13 figures, 3 tables. Accepted for publication in ApJ

We present a kinematical study of RR~Lyrae stars associated with two Oosterhoff groups in the Galactic bulge. We used data published in the first paper of the series, plus proper motions from the {\it Gaia} Data Release 2, and radial velocities from the literature. A 6D kinematical and spatial solution was obtained for 429 RR~Lyrae stars. We use a model of the Galactic gravitational potential to infer stellar orbits. We did not find a difference between the Oosterhoff groups in the individual components of the space velocity. We report that \textit{foreground} and \textit{background} stars with respect to the Galactic bulge stand out in the mean $V$ velocity component, which we interpret as a sign of the Galactic rotation. The movement of the studied stars in the central region of the Galactic bulge is consistent with random motions expected for a classical bulge component. From the orbital integration, we estimate that 8\,\% of the RR~Lyrae stars are halo interlopers currently located in the Galactic bulge. The majority of the stars' orbits are within a 3\,kpc radius from the Galactic bulge. The fraction of Oosterhoff\,II stars increases with increasing Galactic latitude, as well as towards longer orbital periods. We found several RR~Lyrae stars with high space velocities, one of which has an extremely long orbital period of $\sim$1\,Gyr. We conclude that based on their kinematics, the vast majority of the stars in our sample do not seem to contribute to the boxy/peanut component of the Galactic bulge., Comment: 11 pages, 8 figures, Accepted for publication in MNRAS

For the classical Cepheid V1033 Cyg we have constructed an O—C diagram spanning a time interval of 117 years. The O—C diagram has the shape of a parabola, which has made it possible to determine for the first time the quadratic light elements and to calculate the rate of evolutionary increase in the period dP/dt = 18.19 (±0.08) syr−1, in agreement with the results of theoretical calculations for the first crossing of the instability strip. Thus, V1033 Cyg is the second actually observed Cepheid (after α UMi) that crosses the instability strip for the first time.

We derived surface brightness profiles in the \emph{g} band for 170 Small Magellanic Cloud (SMC) star clusters (SCs) mainly located in the central region of the galaxy. We provide a set of homogeneous structural parameters obtained by fitting Elson, Fall \& Freeman (EFF) and King models. Through a careful analysis of their colour-magnitude diagrams (CMDs) we also supply the ages for a subsample of 134 SCs. For the first time, such a large sample of SCs in the SMC is homogeneously characterized in terms of their sizes, luminosities and masses, widening the probed region of the parameter space, down to hundreds of solar masses. We used these data to explore the evolution of the SC's structural parameters with time. In particular, we confirm the existence of a physical mechanism that induces an increase of the core radius after 0.3-1.0 Gyr. We suggest that cluster mass could be the main parameter driving the inner expansion, as none of the SCs having $\log (M/M_{\odot}) \leq 3.5$~dex analysed in this work undergoes to such an expansion. We also detected a mass-size relationship almost over the entire range of SCs masses investigated here. Finally, our data suggest that globally the SMC SC system is dynamically evolved., 24 pages, 14 figures. Accepted for publication by MNRAS

We provide the largest and most homogeneous sample of $\alpha$-element (Mg, Ca, Ti) and iron abundances for field RR Lyrae (RRLs, 162 variables) by using high-resolution spectra. The current measurements were complemented with similar abundances available in the literature for 46 field RRLs brought to our metallicity scale. We ended up with a sample of old (t$\ge$ 10 Gyr), low-mass stellar tracers (208 RRLs: 169 fundamental, 38 first overtone, 1 mixed mode) covering three dex in iron abundance (-3.00$\le$[Fe/H]$\le$0.24). We found that field RRLs are $\sim$0.3 dex more $\alpha$-poor than typical Halo tracers in the metal-rich regime, ([Fe/H]$\ge$-1.2) while in the metal-poor regime ([Fe/H]$\le$-2.2) they seem to be on average $\sim$0.1 dex more $\alpha$-enhanced. This is the first time that the depletion in $\alpha$-elements for solar iron abundances is detected on the basis of a large, homogeneous and coeval sample of old stellar tracers. Interestingly, we also detected a close similarity in the [$\alpha$/Fe] trend between $\alpha$-poor, metal-rich RRLs and red giants (RGs) in the Sagittarius dwarf galaxy as well as between $\alpha$-enhanced, metal-poor RRLs and RGs in ultra faint dwarf galaxies. These results are supported by similar elemental abundances for 46 field Horizontal Branch (HB) stars. These stars share with RRLs the same evolutionary phase and the same progenitors. This evidence further supports the key role that old stellar tracers play in constraining the early chemical enrichment of the Halo and, in particular, in investigating the impact that dwarf galaxies have had in the mass assembly of the Galaxy.

RR Lyrae stars are useful chemical tracers thanks to the empirical relationship between their heavy-element abundance and the shape of their light curves. However, the consistent and accurate calibration of this relation across multiple photometric wave bands has been lacking. We have devised a new method for the metallicity estimation of fundamental-mode RR Lyrae stars in the Gaia optical G and near-infrared VISTA K s wave bands by deep learning. First, an existing metallicity prediction method is applied to large photometric data sets, which are then used to train long short-term memory recurrent neural networks for the regression of the [Fe/H] to the light curves in other wave bands. This approach allows an unbiased transfer of our accurate, spectroscopically calibrated I-band formula to additional bands at the expense of minimal additional noise. We achieve a low mean absolute error of 0.1 dex and high R 2 regression performance of 0.84 and 0.93 for the K s and G bands, respectively, measured by cross-validation. The resulting predictive models are deployed on the Gaia DR2 and VVV inner bulge RR Lyrae catalogs. We estimate mean metallicities of −1.35 dex for the inner bulge and −1.7 dex for the halo, which are significantly less than the values obtained by earlier photometric prediction methods. Using our results, we establish a public catalog of photometric metallicities of over 60,000 Galactic RR Lyrae stars and provide an all-sky map of the resulting RR Lyrae metallicity distribution. The software code used for training and deploying our recurrent neural networks is made publicly available in the open-source domain.

We explore the stellar mass density and colour profiles of 118 low redshift, massive, central galaxies, selected to have assembled 90 percent of their stellar mass 6 Gyr ago, finding evidence of the minor merger activity expected to be the driver behind the size growth of quiescent galaxies. We use imaging data in the $g, r, i, z, y$ bands from the Subaru Hyper Suprime-Cam survey and perform SED fitting to construct spatially well-resolved radial profiles in colour and stellar mass surface density. Our visual morphological classification reveals that $\sim 42$ percent of our sample displays tidal features, similar to previous studies, $\sim 43$ percent of the remaining sample display a diffuse stellar halo and only $\sim 14$ percent display no features, down to a limiting $\mu_{r\mathrm{-band}}$ $\sim$ 28 mag arcsec$^{-2}$. We find good agreement between the stacked colour profiles of our sample to those derived from previous studies and an expected smooth, declining stellar mass surface density profile in the central regions (< 3 R$_{\mathrm{e}}$). However, we also see a flattening of the profile ($\Sigma_* \sim 10^{7.5}$ M$_\odot$ kpc$^{-2}$) in the outskirts (up to 10 R$_{\mathrm{e}}$), which is revealed by our method of specifically targeting tidal/accretion features. We find similar levels of tidal features and behaviour in the stellar mass surface density profiles in a younger comparison sample, however a lack of diffuse haloes. We also apply stacking techniques, similar to those in previous studies, finding such procedures wash out tidal features and thereby produces smooth declining profiles. The stellar material in the outskirts contributes on average $\sim 10^{10}$ M$_\odot$ or a few percent of the total stellar mass and has similar colours to SDSS satellites of similar stellar mass., Comment: 14 pages, 9 figures, 1 table, accepted for publication in MNRAS Jan 2023

We performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured $\approx$6,300 high resolution (HR, R$\sim$35,000) spectra for 143 RRLs (111 fundamental, RRab; 32 first overtone, RRc). The atmospheric parameters were estimated by using the traditional approach and the iron abundances were measured by using an LTE line analysis. The resulting iron distribution shows a well defined metal-rich tail approaching solar iron abundance. This suggests that field RRLs experienced a complex chemical enrichment in the early halo formation. We used these data to develop a new calibration of the $\Delta$S method. This diagnostic, based on the equivalent widths of CaII K and three Balmer (H$_{\delta,\gamma,\beta}$) lines, traces the metallicity of RRLs. For the first time the new empirical calibration: i) includes spectra collected over the entire pulsation cycle; ii) includes RRc variables; iii) relies on spectroscopic calibrators covering more than three dex in iron abundance; iv) provides independent calibrations based on one/two/three Balmer lines. The new calibrations were applied to both SEGUE-SDSS and degraded HR spectra totalling 6,451 low resolution (LR, R$\sim$2,000) spectra for 5,001 RRLs (3,439 RRab, 1,562 RRc). This resulted in an iron distribution with a median of -1.55$\pm$0.01 and $\sigma$=0.51 dex, in good agreement with literature values. We also found that RRc are 0.10 dex more metal-poor than RRab variables, and have a distribution with a smoother metal-poor tail. This finding supports theoretical prescriptions suggesting a steady decrease in the RRc number when moving from metal-poor to metal-rich stellar environments., Comment: Accepted by ApJ

This paper presents results from photometric and statistical-parallax analysis of a sample of 850 field RR Lyrae (RRL) variables. The photometric and spectroscopic data for sample RRLs are obtained from (1) our new spectroscopic observations (for 448 RRLs) carried out with the Southern African Large Telescope (SALT); (2) our photometric observations using the 1.0-m telescope of the South African Astronomical Observatory (SAAO), and (3) literature. These are combined with accurate proper motion data from the second release of \textit{Gaia} mission (DR2). This study primarily determines the velocity distribution of solar neighborhood RRLs, and it also calibrates the zero points of the RRLs visual V-band luminosity-metallicity (LZ or $M_V-$[\text{Fe/H}]) relation and their period-luminosity-metallicity (PLZ) relations in the \textit{WISE} $W_1-$ and \textit{2MASS} $Ks-$band. The calibrated PLZ and LZ relations are used to estimate the Galactic Center distance and the distance modulus of the Large Magellanic Cloud (LMC), which are found to be 7.99$\pm$0.49\,kpc and 18.46$\pm$0.09 \,mag, respectively. All our results are in excellent agreement with available literature based on statistical parallax analysis, but are considerably more accurate and precise. Moreover, the zero-points of our calibrated PLZ and LZ relations are quite consistent with current results found by other techniques and yield the LMC distance modulus that is within 0.04\,mag of the current most precise estimate., 20 pages,21 figueres

Multi-wavelength images from the farUV (~0.15 micron) to the sub-millimeter of the central region of the galaxy NGC 3351 are analyzed to constrain its stellar populations and dust attenuation. Despite hosting a ~1 kpc circumnuclear starburst ring, NGC 3351 deviates from the IRX-beta relation, the relation between the infrared-to-UV luminosity ratio and the UV continuum slope (beta) that other starburst galaxies follow. To understand the reason for the deviation, we leverage the high angular resolution of archival nearUV-to-nearIR HST images to divide the ring into ~60-180 pc size regions and model each individually. We find that the UV slope of the combined intrinsic (dust-free) stellar populations in the central region is redder than what is expected for a young model population. This is due to the region's complex star formation history, which boosts the nearUV emission relative to the farUV. The resulting net attenuation curve has a UV slope that lies between those of the starburst attenuation curve (Calzetti et al. 2000) and the Small Magellanic Cloud extinction curve; the total-to-selective attenuation value, R'(V)=4.93, is larger than both. As found for other star-forming galaxies, the stellar continuum of NGC 3351 is less attenuated than the ionized gas, with E(B-V)_{star}=0.40 E(B-V)_{gas}. The combination of the `red' intrinsic stellar population and the new attenuation curve fully accounts for the location of the central region of NGC 3351 on the IRX-beta diagram. Thus, the observed characteristics result from the complex mixture of stellar populations and dust column densities in the circumnuclear region. Despite being a sample of one, these findings highlight the difficulty of defining attenuation curves of general applicability outside the regime of centrally-concentrated starbursts., 45 page, 17 figures; accepted for publication on the Astrophysical Journal, March 21st, 2021

Dwarf early-type galaxies (ETGs) display a rich diversity in their photometric, structural, and dynamical properties. In this work, we address their structural complexity by studying with deep imaging a sample of nine dwarf ETGs from the Virgo galaxy cluster, characterized by having faint disk features, such as bars and spiral arms, which lie mostly hidden within the bright diffuse light of the galaxies. We present a new, robust method that aims to identify and extract the disk substructure embedded in these dwarf ETGs. The method consists in an iterative procedure that gradually separates a galaxy image into two components; the bright, dominant diffuse component, and the much fainter, underlying disk component. By applying it to the dwarf ETG sample, we quantify their disk substructure and find that its relative contribution to the total galaxy light ranges between 2.2 to 6.4% within two effective radii. We test the reliability of the method, and prove that it is accurate in recovering the disk substructure we introduce in mock galaxy images, even at low disk-to-total light fractions of a few percent. As a potential application of the method, we perform a Fourier analysis on the extracted disk substructures and measure the orientation, length, and strength of the bars, and the pitch angle and strength of the spiral arms. We also briefly discuss a scenario based on the numerical simulations presented in our companion paper, Brought to Light II: Smith et al. 2021, in which we investigate the origins of the substructure in such dwarf systems., Comment: 31 pages, 15 figures, 6 tables. Accepted to AJ. Companion paper: Brought to Light II (Smith et al. 2021) accepted to ApJ, also listed on arXiv today (1st of April, 2021)

In this paper we revisit the problem of identifying bona fide cluster Cepheids by performing an all-sky search for Cepheids associated with open clusters and making use of state-of-the-art catalogued information for both Cepheids and clusters, based on the unparalleled astrometric precision of the second and early third data releases of the Gaia satellite. We determine membership probabilities by following a Bayesian approach using spatial and kinematic information of the potential cluster-Cepheid pairs. We confirm 19 Cepheid-cluster associations considered in previous studies as bona-fide, and question the established cluster membership of six other associations. In addition, we identify 138 cluster Cepheid candidates of potential interest, mostly in recently discovered open clusters. We report on at least two new clusters possibly hosting more than one Cepheid. Furthermore, we explore the feasibility of using open clusters hosting Cepheids to empirically determine the Cepheid period-age relation through the use of Gaia and 2MASS photometry and a semi-automated method to derive cluster ages. We conclude that the usage of cluster Cepheids as tentative probes of the period-age relations still faces difficulties due to the sparsely populated red giant branch and the stochastically sampled main-sequence turn-off of the open clusters, making age determinations a challenging task. This biases the age-dateable cluster selection for Cepheid period-age studies towards older and high-mass clusters., Comment: 28 pages, 11 figures, 5 tables. Accepted for publication in MNRAS. Accepted 2021 April 28. Received 2021 March 31; in original form 2020 October 6

We study the abundance of satellite galaxies around 198 Milky Way- (MW) and M31-like hosts in TNG50, the final instalment in the IllustrisTNG suite of cosmological magnetohydrodynamical simulations. MW/M31-like analogues are defined as disky galaxies with stellar masses of Mstar = 10^10.5-11.2 Msun in relative isolation at z = 0. By defining satellites as galaxies with Mstar > 5*10^6 Msun within 300 kpc (3D) of their host, we find a remarkable level of diversity and host-to-host scatter across individual host galaxies. The median (16th - 84th percentiles) TNG50 MW/M31-like galaxy hosts a total of 5 (2-11) satellites with Mstar > 5*10^6 Msun, reaching up to Mstar ~ 10^8.5 Msun (10^7.4-9.4 Msun). The abundance of subhaloes with Mdyn > 5*10^7 Msun is larger by a factor of more than 10. The number of all satellites (subhaloes) ever accreted is larger by a factor of 4-5 (3-5) than those surviving to z = 0. Hosts with larger galaxy stellar mass, brighter K-band luminosity, larger total halo mass, and more recent halo assembly typically have a larger number of surviving satellites. The satellite abundances around TNG50 MW/M31-like galaxies are consistent with similar hosts from observational surveys (e.g. SAGA) and previous simulations (e.g. Latte). While the observed MW satellite system falls within the TNG50 scatter across all stellar masses considered, M31 is slightly more satellite-rich than our 1 sigma scatter, possibly due to volume and mass limitations. We find a handful of systems with both a Large and a Small Magellanic Cloud-like satellite. There is no missing satellites problem with TNG50., Accepted by MNRAS. TNG50 is publicly available at https://www.tng-project.org/

We attempt to identify RR Lyrae (RRL) stars in stellar streams that might have escaped from seven globular clusters (GCs) based on proper motions, distances, color-magnitude diagrams, and other properties extracted from the Gaia Early Data Release 3 (EDR3) database. Specifically, we cross-match two large RRL stars catalogs (from Gaia DR2 and Catalina Sky Survey) with each other and with the EDR3 database and we end up with a sample of ~ 150,000 unique RRL stars. We calculate distances to RRL stars using the (M_G-[Fe/H]) and (M_V-[Fe/H]) absolute magnitude-metallicity relations and adopt [Fe/H] values for the GCs from different spectroscopic studies. We also constrain our search in areas where stellar streams associated with GCs were previously suggested or identified in other studies. We identify 24 RRL stars that might have escaped from the following seven GCs: Palomar 13 (Pal 13), NGC 6341 (M92), NGC 5904 (M5), NGC 5466, NGC 1261, NGC 288, and NGC 1851. We list our findings in Table 2., Comment: Accepted for publication in ApJ, 14 pages, 6 figures, 1 table

We use the angular Two Point Correlation Function (TPCF) to investigate the hierarchical distribution of young star clusters in 12 local (3--18 Mpc) star-forming galaxies using star cluster catalogues obtained with the \textit{Hubble Space Telescope} (\textit{HST}) as part of the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey). The sample spans a range of different morphological types, allowing us to infer how the physical properties of the galaxy affect the spatial distribution of the clusters. We also prepare a range of physically motivated toy models to compare with and interpret the observed features in the TPCFs. We find that, conforming to earlier studies, young clusters ($T \la 10\, \mathrm{Myr}$) have power-law TPCFs that are characteristic of fractal distributions with a fractal dimension $D_2$, and this scale-free nature extends out to a maximum scale $l_{\mathrm{corr}}$ beyond which the distribution becomes Poissonian. However, $l_{\mathrm{corr}}$, and $D_2$ vary significantly across the sample, and are correlated with a number of host galaxy physical properties, suggesting that there are physical differences in the underlying star cluster distributions. We also find that hierarchical structuring weakens with age, evidenced by flatter TPCFs for older clusters ($T \ga 10\, \mathrm{Myr}$), that eventually converges to the residual correlation expected from a completely random large-scale radial distribution of clusters in the galaxy in $\sim 100 \, \mathrm{Myr}$. Our study demonstrates that the hierarchical distribution of star clusters evolves with age, and is strongly dependent on the properties of the host galaxy environment., 19 pages, 8 figures. Accepted for publication in MNRAS. Code for analysis and reproducing results available at https://github.com/shm-1996/legus-tpcf

[Context] Data-driven methods play an increasingly important role in the field of astrophysics In the context of large spectroscopic surveys of stars, data-driven methods are key in deducing physical parameters for millions of spectra in a short time. Convolutional neural networks (CNNs) enable us to connect observables (e.g. spectra, stellar magnitudes) to physical properties (atmospheric parameters, chemical abundances, or labels in general)., [Aims] We test whether it is possible to transfer the labels derived from a high-resolution stellar survey to intermediate-resolution spectra of another survey by using a CNN., [Methods] We trained a CNN, adopting stellar atmospheric parameters and chemical abundances from APOGEE DR16 (resolution R = 22 500) data as training set labels. As input, we used parts of the intermediate-resolution RAVE DR6 spectra (R ∼ 7500) overlapping with the APOGEE DR16 data as well as broad-band ALL_WISE and 2MASS photometry, together with Gaia DR2 photometry and parallaxes., [Results] We derived precise atmospheric parameters Teff, log(g), and [M/H], along with the chemical abundances of [Fe/H], [α/M], [Mg/Fe], [Si/Fe], [Al/Fe], and [Ni/Fe] for 420 165 RAVE spectra. The precision typically amounts to 60 K in Teff, 0.06 in log(g) and 0.02−0.04 dex for individual chemical abundances. Incorporating photometry and astrometry as additional constraints substantially improves the results in terms of the accuracy and precision of the derived labels, as long as we operate in those parts of the parameter space that are well-covered by the training sample. Scientific validation confirms the robustness of the CNN results. We provide a catalogue of CNN-trained atmospheric parameters and abundances along with their uncertainties for 420 165 stars in the RAVE survey., [Conclusions] CNN-based methods provide a powerful way to combine spectroscopic, photometric, and astrometric data without the need to apply any priors in the form of stellar evolutionary models. The developed procedure can extend the scientific output of RAVE spectra beyond DR6 to ongoing and planned surveys such as Gaia RVS, 4MOST, and WEAVE. We call on the community to place a particular collective emphasis and on efforts to create unbiased training samples for such future spectroscopic surveys., Funding for RAVE has been provided by: the Leibniz-Institut für Astrophysik Potsdam (AIP); the Australian Astronomical Observatory; the Australian National University; the Australian Research Council; the French National Research Agency (Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES); the German Research Foundation (SPP 1177 and SFB 881); the European Research Council (ERC-StG 240271 Galactica); the Istituto Nazionale di Astrofisica at Padova; The Johns Hopkins University; the National Science Foundation of the USA (AST-0908326); the W. M. Keck foundation; the Macquarie University; the Netherlands Research School for Astronomy; the Natural Sciences and Engineering Research Council of Canada; the Slovenian Research Agency (research core funding no. P1-0188); the Swiss National Science Foundation; the Science & Technology Facilities Council of the UK; Opticon; Strasbourg Observatory; and the Universities of Basel, Groningen, Heidelberg, and Sydney. TZ acknowledges financial support of the Slovenian Research Agency (research core funding No. P1-0188) and of the ESA project PHOTO2CHEM (C4000127986). FA is grateful for funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 800502. This work has made use of data from the European Space Agency (ESA) mission Gaia (http://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, http://www.cosmos.esa. int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

Context. We present a large homogeneous set of stellar parameters and abundances across a broad range of metallicities, involving 13 classical dwarf spheroidal (dSph) and ultra-faint dSph (UFD) galaxies. In total, this study includes 380 stars in Fornax, Sagittarius, Sculptor, Sextans, Carina, Ursa Minor, Draco, Reticulum II, Bootes I, Ursa Major II, Leo I, Segue I, and Triangulum II. This sample represents the largest, homogeneous, high-resolution study of dSph galaxies to date. Aims. With our homogeneously derived catalog, we are able to search for similar and deviating trends across different galaxies. We investigate the mass dependence of the individual systems on the production of α-elements, but also try to shed light on the long-standing puzzle of the dominant production site of r-process elements. Methods. We used data from the Keck observatory archive and the ESO reduced archive to reanalyze stars from these 13 classical dSph and UFD galaxies. We automatized the step of obtaining stellar parameters, but ran a full spectrum synthesis (1D, local thermal equilibrium) to derive all abundances except for iron to which we applied nonlocal thermodynamic equilibrium corrections where possible. Results. The homogenized set of abundances yielded the unique possibility of deriving a relation between the onset of type Ia supernovae and the stellar mass of the galaxy. Furthermore, we derived a formula to estimate the evolution of α-elements. This reveals a universal relation of these systems across a large range in mass. Finally, we show that between stellar masses of 2.1 × 107 M⊙ and 2.9 × 105 M⊙, there is no dependence of the production of heavy r-process elements on the stellar mass of the galaxy. Conclusions. Placing all abundances consistently on the same scale is crucial to answering questions about the chemical history of galaxies. By homogeneously analyzing Ba and Eu in the 13 systems, we have traced the onset of the s-process and found it to increase with metallicity as a function of the galaxy’s stellar mass. Moreover, the r-process material correlates with the α-elements indicating some coproduction of these, which in turn would point toward rare core-collapse supernovae rather than binary neutron star mergers as a host for the r-process at low [Fe/H] in the investigated dSph systems.

The Radial Velocity Experiment (Rave) is a magnitude-limited (9 < I < 12) spectroscopic survey of Galactic stars randomly selected in Earth's southern hemisphere. The Rave medium-resolution spectra (R ∼ 7500) cover the Ca-triplet region (8410-8795 Å). The sixth and final data release (DR6) is based on 518,387 observations of 451,783 unique stars. Rave observations were taken between 2003 April 12 and 2013 April 4. Here we present the genesis, setup, and data reduction of Rave as well as wavelength-calibrated and flux-normalized spectra and error spectra for all observations in Rave DR6. Furthermore, we present derived spectral classification and radial velocities for the Rave targets, complemented by cross-matches with Gaia DR2 and other relevant catalogs. A comparison between internal error estimates, variances derived from stars with more than one observing epoch, and a comparison with radial velocities of Gaia DR2 reveals consistently that 68% of the objects have a velocity accuracy better than 1.4 km s-1, while 95% of the objects have radial velocities better than 4.0 km s-1. Stellar atmospheric parameters, abundances and distances are presented in a subsequent publication. The data can be accessed via the Rave website (http://rave-survey.org) or the Vizier database., Funding for Rave has been provided by: the Leibniz-Institut f¨ur Astrophysik Potsdam (AIP); the Australian Astronomical Observatory; the Australian National University; the Australian Research Council; the French National Research Agency (Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES); the German Research Foundation (SPP 1177 and SFB 881); the European Research Council (ERC-StG 240271 Galactica); the Istituto Nazionale di Astrofisica at Padova; The Johns Hopkins University; the National Science Foundation of the USA (AST-0908326); the W. M. Keck foundation; the Macquarie University; the Netherlands Research School for Astronomy; the Natural Sciences and Engineering Research Council of Canada; the Slovenian Research Agency (research core funding no. P1-0188); the Swiss National Science Foundation; the Science & Technology Facilities Council of the UK; Opticon; Strasbourg Observatory; and the Universities of Basel, Groningen, Heidelberg, and Sydney. PJM is supported by grant 2017-03721 from the Swedish Research Council. LC is the recipient of the ARC Future Fellowship FT160100402. RAG acknowledges the support from the PLATO CNES grant. SM would like to acknowledge support from the Spanish Ministry with the Ramon y Cajal fellowship number RYC-2015-17697. MS thanks the Research School of Astronomy & Astrophysics in Canberra for support through a Distinguished Visitor Fellowship. RFGW thanks the Kavli Institute for Theoretical Physics and the Simons Foundation for support as a Simons Distinguished Visiting Scholar. This research was supported in part by the National Science Foundation under Grant No. NSF PHY-1748958 to KITP.

We present part 2 of the sixth and final Data Release (DR6) of the Radial Velocity Experiment (Rave), a magnitude-limited spectroscopic survey of Galactic stars randomly selected in Earth's southern hemisphere. The Rave medium-resolution spectra (R ∼ 7500) cover the Ca triplet region (8410-8795 Å) and span the complete time frame from the start of Rave observations on 2003 April 12 to their completion on 2013 April 4. In the second of two publications, we present the data products derived from 518,387 observations of 451,783 unique stars using a suite of advanced reduction pipelines focusing on stellar atmospheric parameters, in particular purely spectroscopically derived stellar atmospheric parameters, and the overall metallicity), enhanced stellar atmospheric parameters inferred via a Bayesian pipeline using Gaia DR2 astrometric priors, and asteroseismically calibrated stellar atmospheric parameters for giant stars based on asteroseismic observations for 699 K2 stars. In addition, we provide abundances of the elements Fe, Al, and Ni, as well as an overall [α/Fe] ratio obtained using a new pipeline based on the GAUGUIN optimization method that is able to deal with variable signal-to-noise ratios. The Rave DR6 catalogs are cross-matched with relevant astrometric and photometric catalogs, and are complemented by orbital parameters and effective temperatures based on the infrared flux method. The data can be accessed via the Rave website (http://rave-survey.org) or the Vizier database., Funding for Rave has been provided by: the Leibniz-Institut f¨ur Astrophysik Potsdam (AIP); the Australian Astronomical Observatory; the Australian National University; the Australian Research Council; the French National Research Agency (Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES); the German Research Foundation (SPP 1177 and SFB 881); the European Research Council (ERC-StG 240271 Galactica); the Istituto Nazionale di Astrofisica at Padova; The Johns Hopkins University; the National Science Foundation of the USA (AST-0908326); the W. M. Keck foundation; the Macquarie University; the Netherlands Research School for Astronomy; the Natural Sciences and Engineering Research Council of Canada; the Slovenian Research Agency (research core funding no. P1-0188); the Swiss National Science Foundation; the Science & Technology Facilities Council of the UK; Opticon; Strasbourg Observatory; and the Universities of Basel, Groningen, Heidelberg, and Sydney. PJM is supported by grant 2017-03721 from the Swedish Research Council. LC is the recipient of the ARC Future Fellowship FT160100402. RAG acknowledges the support from the PLATO CNES grant. SM would like to acknowledge support from the Spanish Ministry with the Ramon y Cajal fellowship number RYC-2015-17697. MS thanks the Research School of Astronomy & Astrophysics in Canberra for support through a Distinguished Visitor Fellowship. RFGW thanks the Kavli Institute for Theoretical Physics and the Simons Foundation for support as a Simons Distinguished Visiting Scholar. This research was supported in part by the National Science Foundation under Grant No. NSF PHY-1748958 to KITP.

Galaxy environment has been shown to play an important role in transforming late-type, star-forming galaxies to quiescent spheroids. This transformation is expected to be more severe for low-mass galaxies (M < $10^{10}$ \(M_\odot\)) in dense galaxy groups and clusters, mostly due to the influence of their past host halos (also known as pre-processing) and their present-day environments. For the first time, in this study, we investigate a sample of nine early-type dwarf galaxies (dEs) that were accreted as a likely bound group onto the Virgo galaxy cluster about 2-3 Gyr ago. Considering this special condition, these nine dEs may provide a test bed for distinguishing between the influence of the Virgo galaxy cluster and the effects of the previous host halo on their current properties. Specifically, we use VLT/MUSE integral-field unit spectra to derive their kinematics and specific angular momentum ($\lambda_{R}$) profiles. We observe a spread in the $\lambda_{R}$ profiles of our sample dEs, finding that the $\lambda_{R}$ profiles of half of them are as high as those of low-mass field galaxies. The remaining dEs exhibit $\lambda_{R}$ profiles as low as those of Virgo dEs that were likely accreted longer ago. Moreover, we detect nebular emission in one dE with a gas velocity offset suggesting ongoing gas stripping in Virgo. We suggest that the low-$\lambda_{R}$ dEs in our sample were processed by their previous host halo, prior to their infall to Virgo, and that the high-$\lambda_{R}$ dEs may be experiencing ram pressure stripping in Virgo., Comment: 23 pages, 16 figures, Accepted for publication in MNRAS

This compilation is the fourth data release from the $R$-Process Alliance (RPA) search for $r$-process-enhanced stars, and the second release based on "snapshot" high-resolution ($R \sim 30,000$) spectra collected with the du Pont 2.5m Telescope. In this data release, we propose a new delineation between the $r$-I and $r$-II stellar classes at $\mathrm{[Eu/Fe]} = +0.7$, instead of the empirically chosen $\mathrm{[Eu/Fe]} = +1.0$ level previously in use, based on statistical tests of the complete set of RPA data released to date. We also statistically justify the minimum level of [Eu/Fe] for definition of the $r$-I stars, [Eu/Fe] $> +0.3$. Redefining the separation between $r$-I and $r$-II stars will aid in analysis of the possible progenitors of these two classes of stars and whether these signatures arise from separate astrophysical sources at all. Applying this redefinition to previous RPA data, the number of identified $r$-II and $r$-I stars changes to 51 and 121, respectively, from the initial set of data releases published thus far. In this data release, we identify 21 new $r$-II, 111 new $r$-I (plus three re-identified), and 7 new (plus one re-identified) limited-$r$ stars out of a total of 232 target stars, resulting in a total sample of 72 new $r$-II stars, 232 new $r$-I stars, and 42 new limited-$r$ stars identified by the RPA to date., 17 pages, 7 figures, 6 tables; accepted to ApJS

We collected over 6000 high-resolution spectra of four dozen field RR Lyrae (RRL) variables pulsating either in the fundamental (39 RRab) or in the first overtone (9 RRc) mode. We measured radial velocities (RVs) of four strong metallic and four Balmer lines along the entire pulsational cycle and derived RV amplitudes with accuracies better than 1$-$2~\kmsec. The new amplitudes were combined with literature data for 23~RRab and 3~RRc stars (total sample 74 RRLs) which allowed us to investigate the variation of the Bailey diagram (photometric amplitude versus period) when moving from optical to mid-infrared bands and to re-cast the Bailey diagram in terms of RV amplitudes. We found that RV amplitudes for RRab are minimally affected by nonlinear phenomena (shocks) and multi-periodicity (Blazhko effect). The RV slope ($\log P$--A(V$_r$)) when compared with the visual slope ($\log P$--A($V$)) is shallower and the dispersion, at fixed period, decreases by a factor of two. We constructed homogeneous sets of Horizontal Branch evolutionary models and nonlinear, convective pulsation models of RRLs to constrain the impact of evolutionary effects on their pulsation properties. Evolution causes, on the Bailey diagram based on RV amplitudes, a modest variation in pulsation period and a large dispersion in amplitude. The broad dispersion in period of the Bailey diagram is mainly caused by variation in RRL intrinsic parameters (stellar mass, chemical composition). Empirical evidence indicates that RV amplitudes are an optimal diagnostic for tracing the mean effective temperature across the RRab instability strip., 14 pages, 4 figures, 1 table, Accepted on ApJ Letter

Clues to the formation and evolution of Nuclear Star Clusters (NSCs) lie in their stellar populations. However, these structures are often very faint compared to their host galaxy, and spectroscopic analysis of NSCs is hampered by contamination of light from the rest of the system. With the introduction of wide-field IFU spectrographs, new techniques have been developed to model the light from different components within galaxies, making it possible to cleanly extract the spectra of the NSCs and study their properties with minimal contamination from the light of the rest of the galaxy. This work presents the analysis of the NSCs in a sample of 12 dwarf galaxies in the Fornax Cluster observed with MUSE. Analysis of the stellar populations and star-formation histories reveal that all the NSCs show evidence of multiple episodes of star formation, indicating that they have built up their mass further since their initial formation. The NSCs were found to have systematically lower metallicities than their host galaxies, which is consistent with a scenario for mass-assembly through mergers with infalling globular clusters, while the presence of younger stellar populations and gas emission in the core of two galaxies is indicative of in-situ star formation. We conclude that the NSCs in these dwarf galaxies likely originated as globular clusters that migrated to the core of the galaxy which have built up their mass mainly through mergers with other infalling clusters, with gas-inflow leading to in-situ star formation playing a secondary role., 18 pages, 13 figures. Accepted for publication in MNRAS

We have revisited the problem of metallicity prediction of RR Lyrae stars from their near-infrared light curves in the Cousins I waveband. Our study is based on high-quality time-series photometry and state-of-the-art high-resolution spectroscopic abundance measurements of 80 fundamental-mode (RRab) and 24 first-overtone (RRc) stars, spanning $\sim$[$-2.7$,$+0.18$] dex and $\sim$[$-3$,$-0.5$] dex ranges, respectively. Employing machine-learning methods, we investigated various light-curve representations and regression models to identify their optimal form for our objective. Accurate new empirical relations between the [Fe/H] iron abundance and the light-curve parameters have been obtained using Bayesian regression for both RRab and RRc stars with mean absolute prediction errors of 0.16 and 0.18 dex, respectively. We found that earlier $I$-band [Fe/H] estimates had a systematic positive bias of up to $\sim 0.4$ dex in the metal-poor regime. Our new predictive models were deployed on large ensembles of RR Lyrae stars to obtain photometric metallicity distribution functions (MDFs) for various old stellar populations in and around the Milky Way. We find that the mode of the old bulge component's MDF is approximately $-1.4$ dex, in remarkable agreement with the latest spectroscopic result. Furthermore, we derive MDF modes of $-1.83$, $-2.13$, and $-1.77$ dex for the Large and Small Magellanic Clouds, and the Sagittarius dwarf galaxy, respectively., Accepted for publication in The Astrophysical Journal. Data and codes are available at https://github.com/idekany/ifeh

Westerlund 2 (Wd2) is one of the most massive young star clusters known in the Milky Way. The close proximity (4.16 kpc) to the Sun, and the young age (2.0 Myr) allow us to study star formation in detail at a high spatial resolution. We present results from our recent deep multi-band survey in the optical and near-infrared obtained with the Hubble Space Telescope. We demonstrated that, as expected, the region is affected by significant differential reddening with a median value of E(B − V)g = 1.87 mag. The distance was inferred from the dereddened color-magnitude diagrams using Padova isochrones. Analyzing the spatial distribution of stars we found that Wd2 consists of two sub-clumps, namely the main cluster of Westerlund 2 and a less well populated clump located to the North. We estimated the same age of 0.1–2.0 Myr for both sub-clumps, thus we conclude that they are likely coeval.

We present a new catalog and results for the cluster system of the starburst galaxy NGC 4449, based on multiband imaging observations taken as part of the LEGUS and H_α-LEGUS surveys. We improve the spectral energy fitting method used to estimate cluster ages, and find that the results, particularly for older clusters, are in better agreement with those from spectroscopy. The inclusion of H_α measurements, the role of stochasticity for low-mass clusters, the assumptions about reddening, and the choices of SSP model and metallicity all have important impacts on the age dating of clusters. A comparison with ages derived from stellar color–magnitude diagrams for partially resolved clusters shows reasonable agreement, but large scatter in some cases. The fraction of light found in clusters relative to the total light (i.e., T_L) in the U, B, and V filters in 25 different ≈ kiloparsec-size regions throughout NGC 4449 correlates with both the specific region luminosity, R_L , and the dominant age of the underlying stellar population in each region. The observed cluster age distribution is found to decline over time as dN/dτ ∝ τ^γ , with γ = −0.85 ± 0.15, independent of cluster mass, and is consistent with strong, early cluster disruption. The mass functions of the clusters can be described by a power law with dN/dM ∝ M^β and β = −1.86 ± 0.2, independent of cluster age. The mass and age distributions are quite resilient to differences in age-dating methods. There is tentative evidence for a factor of 2–3 enhancement in both the star and cluster formation rate ≈100–300 Myr ago, indicating that cluster formation tracks star formation generally. The enhancement is probably associated with an earlier interaction event.

We present chemodynamical links between the present-day Milky Way halo field star population and Galactic globular clusters (GCs) using a dataset that combines information from the $\rm{\it Gaia}$ space mission and the Sloan Digital Sky Survey (SDSS-IV, DR14). Moreover, we incorporated a sample of halo giant stars with a distinct chemical signature (strong CN bandheads) that resembles the light-elements anomaly otherwise only seen in the second generation of GC stellar populations. Using three different tagging techniques, we could successfully establish unique associations between 151 extratidal stars in the neighborhood of eight GCs. In addition, we traced the possible origin of about $62\%$ of the sample of CN-strong giants to their potential host clusters. Several of the involved GCs have been brought into connection with the Gaia-Enceladus and Sequoia merger events. By establishing kinematic and chemical connections between 17 CN-strong stars and their surrounding fields, we could identify co-moving groups of stars at the same [Fe/H] with a possible cluster origin. We found strong evidence that four CN-strong stars and their associates are connected to the Sagittarius stream whilst their tightly confined [Fe/H] may hint to a birth site in M 54. Finally, we provide tentative estimates for the fraction of first-generation cluster stars among all stars lost to the halo. In the immediate cluster vicinity, this value amounts to $50.0\pm16.7\%$ while the associations in the halo field rather imply $80.2_{-5.2}^{+4.9}\%$. We speculate that -- if proven real by spectroscopic follow-up -- the disparity between these numbers could indicate a major contribution of low-mass clusters to the overall number of stars escaped to the halo or, alternatively, point toward a strong mass loss from the first generation during early cluster dissolution. [abridged], Comment: 20 pages (+9 pages of appendices), 39 figures, 4 tables, accepted for publication in A&A

Context: The effective temperature is a key parameter governing the properties of a star. For stellar chemistry, it has the strongest impact on the accuracy of the abundances derived. Since Cepheids are pulsating stars, determining their effective temperature is more complicated that in the case of non-variable stars. Aims: We want to provide a new temperature scale for classical Cepheids, with a high precision and full control of the systematics. Methods: Using a data-driven machine learning technique employing observed spectra, and taking great care to accurately phase single-epoch observations, we have tied flux ratios to (label) temperatures derived using the infrared surface brightness method. Results: We identified 143 flux ratios that allow us to determine the effective temperature with a precision of a few K and an accuracy better than 150 K, which is in line with the most accurate temperature measures available to date. The method does not require a normalization of the input spectra and provides homogeneous temperatures for low- and high-resolution spectra, even at the lowest signal-to-noise ratios. Due to the lack of a dataset of sufficient sample size for Small Magellanic Cloud Cepheids, the temperature scale does not extend to Cepheids with [Fe/H] < -0.6 dex but nevertheless provides an exquisite, homogeneous means of characterizing Galactic and Large Magellanic Cloud Cepheids. Conclusions: The temperature scale will be extremely useful in the context of spectroscopic surveys for Milky Way archaeology with the WEAVE and 4MOST spectrographs. It paves the way for highly accurate and precise metallicity estimates, which will allow us to assess the possible metallicity dependence of Cepheids' period-luminosity relations and, in turn, to improve our measurement of the Hubble constant H0., 16 pages, 13 figures, accepted in A&A

We study the stellar-to-halo mass relation (SHMR) for central and satellite galaxies with total dynamical masses above 10^10.5 Msun using the suite of cosmological magneto-hydrodynamical simulations IllustrisTNG. In particular, we quantify environmental effects on satellite populations from TNG50, TNG100, and TNG300 located within the virial radius of group- and cluster-like hosts with total masses of 10^12-15.2 Msun. At fixed stellar mass, the satellite SHMR exhibits a distinct shift towards lower dynamical mass compared to the SHMR of centrals. Conversely, at fixed dynamical mass, satellite galaxies appear to have larger stellar-to-total mass fractions than centrals by up to a factor of a few. The systematic deviation from the central SHMR is larger for satellites in more massive hosts, at smaller cluster-centric distances, with earlier infall times, and that inhabit higher local density environments; moreover, it is in place already at early times (z < 2). Systematic environmental effects might contribute to the perceived galaxy-to-galaxy variation in the measured SHMR when galaxies cannot be separated into satellites and centrals. The SHMR of satellites exhibits a larger scatter than centrals, over the whole range of dynamical mass (by up to 0.8 dex). The shift of the satellite SHMR results mostly from tidal stripping of their dark matter, which affects satellites in an outside-in fashion: the departure of the satellite SHMR from the centrals' relation diminishes for measurements of dynamical mass in progressively smaller apertures. Finally, we provide a family of fitting functions for the SHMR predicted by IllustrisTNG., Published in MNRAS. Key figures: 1 & 8. Corrected Equation 1 for the SHMR fitting formula

We present our chemical abundance investigation of the metal-poor ([Fe/H]=-1.60 dex), r-process-enriched ([Eu/Fe]=0.73 dex) halo star HD 20 using novel and archival high-resolution spectra at outstanding signal-to-noise ratios. By combining one of the first asteroseismic gravity measurements in the metal-poor regime from a TESS light curve with non-LTE analyses of iron lines, we derive a set of highly accurate and precise stellar parameters. These allow us to delineate a chemical pattern comprised of solid detections of 48 elements, including 28 neutron-capture elements, which establishes HD 20 among the few benchmark stars that have almost complete patterns with low systematic dependencies on the stellar parameters. Our light-element (Z, Comment: 23 pages (+10 pages appendix), 27 figures, 8 tables, revised version resubmitted to A&A

Aiming to extend the census of RR Lyrae stars to highly reddened low-latitude regions of the central Milky Way, we performed a deep near-IR variability search using data from the VISTA Variables in the V\'ia L\'actea (VVV) survey of the bulge, analyzing the photometric time series of over a hundred million point sources. In order to separate fundamental-mode RR Lyrae (RRab) stars from other periodically variable sources, we trained a deep bidirectional long short-term memory recurrent neural network (RNN) classifier using VVV survey data and catalogs of RRab stars discovered and classified by optical surveys. Our classifier attained a ~99% precision and recall for light curves with signal-to-noise ratio above 60, and is comparable to the best-performing classifiers trained on accurate optical data. Using our RNN classifier, we identified over 4300 hitherto unknown bona fide RRab stars toward the inner bulge. We provide their photometric catalog and VVV J,H,Ks photometric time-series., Comment: Accepted for publication in The Astrophysical Journal

We present a kinematical study of 314 RR~Lyrae stars in the solar neighbourhood using the publicly available photometric, spectroscopic, and {\it Gaia} DR2 astrometric data to explore their distribution in the Milky Way. We report an overdensity of 22 RR~Lyrae stars in the solar neighbourhood at a pericenter distance of between 5--9\,kpc from the Galactic center. Their orbital parameters and their chemistry indicate that these 22 variables share the kinematics and the [Fe/H] values of the Galactic disc, with an average metallicity and tangential velocity of [Fe/H]=$-0.60$\,dex and $v_{\theta} = 241$\,km\,s$^{-1}$, respectively. From the distribution of the Galactocentric spherical velocity components, we find that these 22 disc-like RR~Lyrae variables are not consistent with the {\it Gaia} Sausage ({\it Gaia}-Enceladus), unlike almost half of the local RR~Lyrae stars. Chemical information from the literature shows that the majority of the selected pericenter peak RR~Lyrae variables are $\alpha$-poor, a property shared by typically much younger stars in the thin disc. Using the available photometry we rule out a possible misclassification with the known classical and anomalous Cepheids. The similar kinematic, chemical, and pulsation properties of these disc RR~Lyrae stars suggest they share a common origin. In contrast, we find the RR~Lyrae stars associated with the {\it Gaia}-Enceladus based on their kinematics and chemical composition show a considerable metallicity spread in the old population ($\sim$~1\,dex)., Comment: 12 pages, 9 figures, Accepted for publication in MNRAS, final version

The morphology of HII regions around young star clusters provides insight into the timescales and physical processes that clear a cluster's natal gas. We study ~700 young clusters (5Myr), consistent with the expected temporal evolution of HII regions and previous results. However, 2) similarities in the age distributions for clusters with concentrated and partially exposed H$\alpha$ morphologies imply a short timescale for gas clearing (, Comment: 20 pages, 16 figures, 7 tables; accepted for publication in MNRAS

Globular clusters (GCs) have been posited, alongside dwarf galaxies, as significant contributors to the field stellar population of the Galactic halo. In order to quantify their contribution, we examine the fraction of halo stars formed in stellar clusters in the suite of 25 present-day Milky Way-mass cosmological zoom simulations from the E-MOSAICS project. We find that a median of $2.3$ and $0.3$ per cent of the mass in halo field stars formed in clusters and GCs, defined as clusters more massive than $5\times 10^3$ and $10^5~M_{\odot}$, respectively, with the $25$-$75$th percentiles spanning $1.9$-$3.0$ and $0.2$-$0.5$ per cent being caused by differences in the assembly histories of the host galaxies. Under the extreme assumption that no stellar cluster survives to the present day, the mass fractions increase to a median of $5.9$ and $1.8$ per cent. These small fractions indicate that the disruption of GCs plays a sub-dominant role in the build-up of the stellar halo. We also determine the contributed halo mass fraction that would present signatures of light-element abundance variations considered to be unique to GCs, and find that clusters and GCs would contribute a median of $1.1$ and $0.2$ per cent, respectively. We estimate the contributed fraction of GC stars to the Milky Way halo, based on recent surveys, and find upper limits of $2$-$5$ per cent (significantly lower than previous estimates), suggesting that models other than those invoking strong mass loss are required to describe the formation of chemically enriched stellar populations in GCs., 7 pages, 2 figures; submitted to MNRAS (Oct. 10th 2019)

The combination of the final version of the RAVE spectroscopic survey data release 6 with radial velocities and astrometry from Gaia DR2 allows us to identify and create a catalog of single lined binary star candidates (SB1), their inferred orbital parameters, and to inspect possible double lined binary stars (SB2). A probability function for the detection of radial velocity (RV) variations is used for identifying SB1 candidates. The estimation of orbital parameters for main sequence dwarfs is performed by matching the measured RVs with theoretical velocity curves sampling the orbital parameter space. The method is verified by studying a mock sample from the SB9 catalogue. Studying the boxiness and asymmetry of the spectral lines allows us to identify possible SB2 candidates, while matching their spectra to a synthetic library indicates probable properties of their components. From the RAVE catalog we select 37,664 stars with multiple RV measurements and identify 3838 stars as SB1 candidates. Joining RAVE and Gaia DR2 yields 450,646 stars with RVs measured by both surveys and 27,716 of them turn out to be SB1 candidates, which is an increase by an order of magnitude over previous studies. For main sequence dwarf candidates we calculate their most probable orbital parameters: orbital periods are not longer than a few years and primary components have masses similar to the Solar mass. All our results are available via Vizier/CDS., Comment: 14 pages, 12 figures

We present results from a joint ALMA-HST study of the nearby spiral galaxy NGC 628. We combine the HST LEGUS database of over 1000 stellar clusters in NGC 628 with ALMA Cycle 4 millimeter/submillimeter observations of the cold dust continuum that span ~15 square kpc including the nuclear region and western portions of the galaxy's disk. The resolution -- 1.1" or approximately 50 pc at the distance of NGC 628 -- allows us to constrain the spatial variations in the slope of the millimeter dust continuum as a function of the ages and masses of the nearby stellar clusters. Our results indicate an excess of dust emission in the millimeter assuming a typical cold dust model for a normal star-forming galaxy, but little correlation of the dust continuum slope with stellar cluster age or mass. For the depth and spatial coverage of these observations, we cannot substantiate the millimeter/submillimeter excess arising from the processing of dust grains by the local interstellar radiation field. We detect a bright unknown source in NGC 628 in ALMA bands 4 and 7 with no counterparts at other wavelengths from ancillary data. We speculate this is possibly a dust obscured supernova., 10 pages, 8 figures, to be published in ApJ

We report the discovery of two new lithium-rich Cepheids in the Milky Way (A(Li) ≈ 2.9 dex) among the targets of the MAGIC spectroscopic survey with the Southern African Large Telescope spectrographs. The 6707 Å Li feature is usually not detectable in the atmosphere of Cepheids. Only three Cepheids (two in the Milky Way and one in the Large Magellanic Cloud) had been reported so far with high lithium abundances. We examine the possibility that the Li-rich Cepheids are evolving towards the red giant branch, crossing the instability strip for the first time, as well as other possible scenarios. The two stars are mixed-mode Cepheids pulsating simultaneously in the first and in the second overtone modes. We briefly discuss the possible connection between their unusual chemical composition and their pulsational properties.

The far side of the Milky Way's disk is one of the most concealed parts of the known Universe due to extremely high interstellar extinction and point source density toward low Galactic latitudes. Large time-domain photometric surveys operating in the near-infrared hold great potential for the exploration of these vast uncharted areas of our Galaxy. We conducted a census of distant classical and type II Cepheids along the southern Galactic mid-plane using near-infrared photometry from the VISTA Variables in the V\'ia L\'actea survey. We performed a machine-learned classification of the Cepheids based on their infrared light curves using a convolutional neural network. We have discovered 640 distant classical Cepheids with up to ~40 magnitudes of visual extinction, and over 500 type II Cepheids, most of them located in the inner bulge. Intrinsic color indices of individual Cepheids were predicted from sparse photometric data using a neural network, allowing their use as accurate reddening tracers. They revealed a steep, spatially varying near-infrared extinction curve toward the inner bulge. Type II Cepheids in the Galactic bulge were also employed to measure robust mean selective-to-absolute extinction ratios. They trace a centrally concentrated spatial distribution of the old bulge population with a slight elongation, consistent with earlier results from RR Lyrae stars. Likewise, the classical Cepheids were utilized to trace the Galactic warp and various substructures of the Galactic disk, and to uncover significant vertical and radial age gradients of the thin disk population at the far side of the Milky Way., Comment: Accepted for publication by The Astrophysical Journal

Prompted by some inconsistencies in the photometry of the VISTA Variables in the V\'ia L\'actea (VVV) survey, we conduct a revision of the standard calibration procedure of VISTA data in the $J$, $H$, and $K_S$ passbands. Two independent sources of bias in the photometric zero-points are identified: First, high sky backgrounds severely affect the $H$-band measurements, but this can mostly be minimized by strict data vetting. Secondly, during the zero-point calibration, stars serving as standards are taken from the 2MASS catalog, which can suffer from high degrees of blending in regions of high stellar density, affecting both the absolute photometric calibration, as well as the scatter of repeated observations. The former affects studies that rely on an absolute magnitude scale, while the latter can also affect the shapes and amount of scatter in the VVV light curves, thus potentially hampering their proper classification. We show that these errors can be effectively eliminated by relatively simple modifications of the standard calibration procedure, and demonstrate the effect of the recalibration on the VVV survey's data quality. We give recommendations for future improvements of the pipeline calibration of VISTA photometry, while also providing preliminary corrections to the VVV $JHK_\mathrm{S}$ observations as a temporary measure., Comment: Accepted for publication in Experimental Astronomy; Table 1 is available from the first author upon request

There is ample evidence in the Milky Way for globular cluster (GC) disruption. Hence one may expect that also part of the Galactic halo field stars may once have formed in GCs. We quantify the fraction of halo stars donated by GCs by searching for stars that bear the unique chemical fingerprints typical for a subset of GC stars often dubbed `second-generation stars'. These are stars showing light element abundance anomalies such as a pronounced CN-band strength accompanied by weak CH-bands. Based on this indicator, past studies have placed the fraction of halo stars with a GC origin between a few to up to 50%. Using low-resolution spectra from the most recent data release of the latest extension of the Sloan Digital Sky Survey (SDSS-IV), we were able to identify 118 metal-poor ($-1.8\le$[Fe/H]$\le -1.3$) CN-strong stars in a sample of 4470 halo giant stars out to 50 kpc. This results in an observed fraction of these stars of 2.6$\pm$0.2%. Using an updated formalism to account for the fraction of stars lost early on in the GCs' evolution we estimate the fraction of the halo that stems from disrupted clusters to be 11$\pm$1%. This number represents the case that stars lost from GCs were entirely from the first generation and is thus merely an upper limit. Our conclusions are sensitive to our assumptions of the mass lost early on from the first generation formed in the GCs, the ratio of first-to-second generation stars, and other GC parameters. We carefully test the influence of varying these parameters on the final result and find that, under realistic scenarios, the above fraction depends on the main assumptions at less than 10%. We further recover a flat trend in this fraction with Galactocentric radius, with a marginal indication of a rise beyond 30 kpc that could reflect the ex-situ origin of the outer halo. (abridged), 13 pages, 11 figures, accepted for publication in Astronomy & Astrophysics