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Tidal streams and stellar shells are naturally formed in galaxy interactions and mergers. The Giant Stellar Stream (GSS), the North-East (NE), and Western (W) stellar shelves observed in Andromeda Galaxy (M31) are examples of these structures and were formed through the merger of M31 and a satellite galaxy. Recent observational papers have provided strong evidence that the shells and GSS originate from a single progenitor. In this paper, we investigate the formation of these two stellar shelves and the detailed nature of their relationship to the GSS. We present numerical simulations of tidal disruption of a satellite galaxy assuming that it is a progenitor of the GSS and the shell system. We represent the progenitor as a dwarf spheroidal galaxy with the stellar mass of 109 M⊙ and evolve its merger with M31 for 3 Gyr to reproduce the chemodynamical properties of the NE and W shelves. We find that an initial metallicity of the progenitor with a negative radial gradient of ΔFeH  = −0.3 ± 0.2 successfully reproduces observed metallicities of the NE, W shelves, and the GSS, showing that all these structures can originate from the same merger event. [ABSTRACT FROM AUTHOR]

We use a complete sample of 211 nearby (⁠|$z< 0.08$|⁠), dwarf (10 |$^{8}$|  M |$_{\odot }$| < |$M_{\rm {\star }}$| < 10 |$^{9.5}$|  M |$_{\odot }$|⁠) galaxies in low-density environments, to study their structural properties: effective radii (⁠|$R_{\rm e }$|⁠), effective surface brightnesses (⁠|$\langle \mu \rangle _{\rm e}$|⁠), and colour gradients. We explore these properties as a function of stellar mass and the three principal dwarf morphological types identified in a companion paper – early-type galaxies (ETGs), late-type galaxies (LTGs), and featureless systems. The median |$R_{\rm e }$| of LTGs and featureless galaxies are factors of |$\sim$| 2 and |$\sim$| 1.2 larger than the ETGs. While the median |$\langle \mu \rangle _{\rm e}$| of the ETGs and LTGs is similar, the featureless class is |$\sim$| 1 mag arcsec |$^{-2}$| fainter. Although they have similar median |$R_{\rm e }$|⁠ , the featureless and ETG classes differ significantly in their median |$\langle \mu \rangle _{\rm e}$|⁠ , suggesting that their evolution is different and that the featureless galaxies are not a subset of the ETGs. While massive ETGs typically exhibit negative or flat colour gradients, dwarf ETGs generally show positive colour gradients (bluer centres). The growth of ETGs therefore changes from being 'outside-in' to 'inside-out' as we move from the dwarf to the massive regime. The colour gradients of dwarf and massive LTGs are, however, similar. Around 46 per cent of dwarf ETGs show prominent, visually identifiable blue cores which extend out to |$\sim$| 1.5 |$R_{\rm e}$|⁠. Finally, compared to their non-interacting counterparts, interacting dwarfs are larger, bluer at all radii and exhibit similar median |$\langle \mu \rangle _{\rm e}$|⁠ , indicating that interactions typically enhance star formation across the entire galaxy. [ABSTRACT FROM AUTHOR]

Using deep imaging from the CANDELS and HFF surveys, we present bulge+disc decompositions with galfitm for |$\sim$| 17 000 galaxies over |$0.2 \le z\le 1.5$|⁠. We use various model parameters to select reliable samples of discs and bulges, and derive their stellar masses using an empirically calibrated relation between mass-to-light ratio and colour. Across our entire redshift range, we show that discs follow stellar mass–size relations that are consistent with those of star-forming galaxies, suggesting that discs primarily evolve via star formation. In contrast, the stellar mass–size relations of bulges are mass-independent. Our novel data set further enables us to separate components into star-forming and quiescent based on their specific star formation rates. We find that both star-forming discs and star-forming bulges lie on stellar mass–size relations that are similar to those of star-forming galaxies, while quiescent discs are typically smaller than star-forming discs and lie on steeper relations, implying distinct evolutionary mechanisms. Similar to quiescent galaxies, quiescent bulges show a flattening in the stellar mass–size relation at |$\sim 10^{10}$|  M |$_\odot$|⁠ , below which they show little mass dependence. However, their best-fitting relations have lower normalizations, indicating that at a given mass, bulges are smaller than quiescent galaxies. Finally, we obtain rest-frame colours for individual components, showing that bulges typically have redder colours than discs, as expected. We visually derive UVJ criteria to separate star-forming and quiescent components and show that this separation agrees well with component colour. HFF bulge+disc decomposition catalogues used for these analyses are publicly released with this paper. [ABSTRACT FROM AUTHOR]

It is crucial for a deeper understanding of the formation and evolution of galaxies in the Universe to study stellar mass (M *) and star formation rate (SFR). Traditionally, astronomers infer the properties of galaxies from spectra, which are highly informative, but expensive and hard to be obtained. Fortunately, modern sky surveys obtained a vast amount of high-spatial-resolution photometric images. The photometric images are obtained relatively economically than spectra, and it is very helpful for related studies if M * and SFR can be estimated from photometric images. Therefore, this paper conducted some preliminary researches and explorations on this regard. We constructed a deep learning model named Galaxy Efficient Network (GalEffNet) for estimating integrated M * and specific star formation rate (sSFR) from Dark Energy Spectroscopic Instrument galaxy images. The GalEffNet primarily consists of a general feature extraction module and a parameter feature extractor. The research results indicate that the proposed GalEffNet exhibits good performance in estimating M * and sSFR, with σ reaching 0.218 and 0.410 dex. To further assess the robustness of the network, prediction uncertainty was performed. The results show that our model maintains good consistency within a reasonable bias range. We also compared the performance of various network architectures and further tested the proposed scheme using image sets with various resolutions and wavelength bands. Furthermore, we conducted applicability analysis on galaxies of various sizes, redshifts, and morphological types. The results indicate that our model performs well across galaxies with various characteristics and indicate its potentials of broad applicability. [ABSTRACT FROM AUTHOR]

Young stellar clusters are predominantly the hub of star formation and hence, ideal to perform comprehensive studies over the least explored substellar regime. Various unanswered questions like the mass distribution in brown dwarf regime and the effect of diverse cluster environment on brown dwarf formation efficiency still plague the scientific community. The nearby young cluster, IC 1396 with its feedback-driven environment, is ideal to conduct such study. In this paper, we adopt a multiwavelength approach, using deep Subaru HSC along with other data sets and machine learning techniques to identify the cluster members complete down to ∼ 0.03 M⊙ in the central 22 arcmin area of IC 1396. We identify 458 cluster members including 62 brown dwarfs which are used to determine mass distribution in the region. We obtain a star-to-brown dwarf ratio of ∼ 6 for a stellar mass range 0.03–1 M⊙ in the studied cluster. The brown dwarf fraction is observed to increase across the cluster as radial distance from the central OB-stars increases. This study also compiles 15 young stellar clusters to check the variation of star-to-brown dwarf ratio relative to stellar density and ultraviolet (UV) flux ranging within 4–2500 stars pc−2 and 0.7–7.3  G 0, respectively. The brown dwarf fraction is observed to increase with stellar density but the results about the influence of incident UV flux are inconclusive within this range. This is the deepest study of IC 1396 as of yet and it will pave the way to understand various aspects of brown dwarfs using spectroscopic observations in future. [ABSTRACT FROM AUTHOR]

The fraction of ionizing photons that escape their host galaxies to ionize hydrogen in the intergalactic medium (IGM) is a critical parameter in analyses of the reionization era. In this paper, we use the meraxes semi-analytic galaxy formation model to infer the mean ionizing photon escape fraction and its dependence on galaxy properties through joint modelling of the observed high redshift galaxy population and existing constraints on the reionization history. Using a Bayesian framework, and under the assumption that escape fraction is primarily related to halo mass, we find that the joint constraints of the ultraviolet luminosity function, cosmic microwave background optical depth, and the Ly α forest require an escape fraction of |$(18\pm 5)$| per cent for galaxies within haloes of M ≲ 109 M⊙ and |$(5\pm 2)$| per cent for more massive haloes. In terms of galaxy properties, this transition in escape fraction occurs at stellar masses of M ⋆ ∼ 107 M⊙, nearly independent of redshift. As a function of redshift, reionization is dominated by the smaller M ⋆ ≲ 107 M⊙ galaxies with high escape fractions at z ≳ 6 and by the larger M ⋆ ≳ 107 M⊙ galaxies with lower escape fractions at z ≲ 6. Galaxies with star formation rates of 10−2.5 M⊙yr−1 to 10−1.5 M⊙yr−1 provide the dominant source of ionizing photons throughout reionization. Our results are consistent with recent direct measurements of a |$\sim 5~{{\ \rm per\ cent}}$| escape fraction from massive galaxies at the end of reionization and support the picture of low mass galaxies being the dominant sources of ionizing photons during reionization. [ABSTRACT FROM AUTHOR]

This paper presents the third data release of the INvestigating Stellar Population In RElics (INSPIRE) project, comprising 52 ultra-compact massive galaxies (UCMGs) observed with the X-Shooter spectrograph. We measure integrated stellar velocity dispersion, [Mg/Fe] abundances, ages, and metallicities for all the INSPIRE objects. We thus infer star formation histories and confirm the existence of a degree of relicness (DoR), defined in terms of the fraction of stellar mass formed by z  = 2, the time at which a galaxy has assembled 75 per cent of its mass, and the final assembly time. Objects with a high DoR assembled their stellar mass at early epochs, while low-DoR objects show a non-negligible fraction of later formed populations and hence a spread in ages and metallicities. A higher DoR correlates with larger [Mg/Fe], supersolar metallicity, and larger velocity dispersion values. The 52 UMCGs span a large range of DoR from 0.83 to 0.06, with 38 of them having formed more than 75  per cent of their mass by z  = 2. Of these, nine are extreme relics (DoR>0.7), since they formed the totality (⁠|$\gt 99~{{\ \rm per\ cent}}$|⁠) of their stellar mass by redshift z  = 2. The remaining 14 UCMGs cannot be considered relics, as they are characterized by more extended star formation histories. With INSPIRE  we built the first sizeable sample of relics outside the local Universe, up to z ∼ 0.4, increasing the number of confirmed relics by a factor of >10, and opening up an important window to explain the mass assembly of massive galaxies in the high- z Universe. [ABSTRACT FROM AUTHOR]

With the launch of JWST and other scheduled missions aimed at probing the distant universe, we are entering a new promising era for high- z astronomy. One of our main goals is the detection of the first population of stars (Population III or Pop III stars), and models suggest that Pop III star formation is allowed well into the Epoch of Reionization (EoR), rendering this an attainable achievement. In this paper, we focus on our chance of detecting massive Pop IIIs at the moment of their death as Pair-Instability Supernovae (PISNe). We estimate the probability of discovering PISNe during the EoR in galaxies with different stellar masses (7.5 ≤ Log(M ⋆/M⊙) ≤ 10.5) from six dustyGadget simulations of 50  h −1 cMpc per side. We further assess the expected number of PISNe in surveys with JWST/NIRCam and Roman/WFI. On average, less than one PISN is expected in all examined JWST fields at z ≃ 8 with Δ z  = 1, and O(1) PISN may be found in a ∼1 deg2 Roman field in the best-case scenario, although different assumptions on the Pop III IMF and/or Pop III star formation efficiency can decrease this number substantially. Including the contribution from unresolved low-mass haloes holds the potential for increased discoveries. JWST/NIRCam and Roman/WFI allow the detection of massive-progenitor (∼250 M⊙) PISNe throughout all the optimal F200W-F356W, F277W-F444W, and F158-F213 colours. PISNe are also pre-dominantly located at the outskirts of their hosting haloes, facilitating the disentangling of underlying stellar emission thanks to the spatial-resolution capabilities of the instruments. [ABSTRACT FROM AUTHOR]

The estimation of galaxy stellar masses depends on the assumed prior of the star-formation history (SFH) and spatial scale of the analysis (spatially resolved versus integrated scales). In this paper, we connect the prescription of the SFH in the spectral energy distribution (SED) fitting to spatially resolved scales (∼kpc) to shed light on the systematics involved when estimating stellar masses. Specifically, we fit the integrated photometry of ∼970 massive (log (M⋆/M⊙) = 9.8–11.5), intermediate redshift (z  = 0.5–2.0) galaxies with PROSPECTOR , assuming both exponentially declining tau model and flexible SFHs. We complement these fits with the results of spatially resolved SFH estimates obtained by pixel-by-pixel SED fitting, which assume tau models for individual pixels. These spatially resolved SFHs show a large diversity in shapes, which can largely be accounted for by the flexible SFHs with PROSPECTOR. The differences in the stellar masses from those two approaches are overall in good agreement (average difference of ∼0.07 dex). Contrarily, the simpler tau model SFHs typically miss the oldest episode of star formation, leading to an underestimation of the stellar mass by ∼0.3 dex. We further compare the derived global specific star-formation rate (sSFR), the mass-weighted stellar age (t50), and the star-formation time-scale (τSF) obtained from the different SFH approaches. We conclude that the spatially resolved scales within galaxies motivate a flexible SFH on global scales to account for the diversity of SFHs and counteract the effects of outshining of older stellar populations by younger ones. [ABSTRACT FROM AUTHOR]