We report a possible discovery of a relic star cluster in the Sextans dwarf spheroidal galaxy. Using the \textit{hk} index ($\equiv$($Ca-b$)$-$($b-y$)) as a photometric metallicity indicator, we discriminate the metal-poor and metal-rich stars in the galaxy and find unexpected number density excess of metal-poor stars located 7'.7 ($\sim$190 pc in projected distance) away from the known galactic center. The $V-I$ color$-$magnitude diagram (CMD) for stars around the density excess reveals that both the main sequence and the giant branch are considerably narrower and redder than the bulk of field stars in Sextans. Our stellar population models show (a) that the narrow CMD is best reproduced by a simple stellar population with an age of $\sim$13 Gyr and [Fe/H] of $\sim$$-$2.3 dex, and (b) that the redder $V-I$ color of the $hk$-weak population is explained $only$ if it is $\sim$2 Gyr older than the field stars. The results lead us to conclude that the off-centered density peak is likely associated with an old, metal-poor globular cluster. The larger spatial extent ($>$ 80 pc in radius) and the smaller number of stars ($\sim$1000) than typical globular clusters point to a star cluster that is in the process of dissolution. The finding serves as the first detection of a surviving star cluster in Sextans, supporting previous suggestions of the presence of star cluster remnants in the galaxy. If confirmed, the survival of a relic star cluster until now implies a $cored$ dark matter halo profile for this dwarf galaxy.
The Bose-Einstein condensate/scalar field dark matter model, considers that the dark matter is composed by spinless-ultra-light particles which can be described by a scalar field. This model is an alternative model to the $Λ$-cold dark matter paradigm, and therefore should be studied at galactic and cosmological scales. Dwarf spheroidal galaxies have been very useful when studying any dark matter theory, because the dark matter dominates their dynamics. In this paper we study the Sextans dwarf spheroidal galaxy, embedded in a scalar field dark matter halo. We explore how the dissolution time-s…
We present wide-field $g$ and $i$ band stellar photometry of the Sextans dwarf spheroidal galaxy and its surrounding area out to four times its half-light radius ($r_h=695\,$pc), based on images obtained with the Dark Energy Camera at the 4-m Blanco telescope at CTIO. We find clear evidence of stellar substructure associated with the galaxy, extending to a distance of $82\arcmin$ (2\,kpc) from its centre. We perform a statistical analysis of the over-densities and find three distinct features, as well as an extended halo-like structure, to be significant at the $99.7\%$ confidence level or hig…
We present the star formation history (SFH) of the Sextans dwarf spheroidal galaxy based on deep archive $B$,$I$ photometry taken with Suprime-Cam at Subaru telescope focusing our analysis on the inner region of the galaxy, fully located within the core radius. Within the errors of our SFH we have not detected any metallicity gradient along the considered radial distance interval. As a main result of this work we can state that the Sextans dwarf spheroidal stopped forming stars less than $\sim1.3$ Gyr after Big Bang in correspondance to the end of the reionization epoch. We have been able to c…
We report the discovery of two Mira variable stars (Miras) toward the Sextans dwarf spheroidal (dSph) galaxy. We performed optical long-term monitoring observations for two red stars in the Sextans dSph. The light curves of both stars in the $I_{\rm c}$ band show large-amplitude (3.7 and 0.9 mag) and long-period ($326\pm 15$ and $122\pm 5$ days) variations, suggesting that they are Miras. We combine our own infrared data with previously published data to estimate the mean infrared magnitudes. The distances obtained from the period-luminosity relation of the Miras ($75.3^{+12.8}_{-10.9}$ and $7…
We have measured the absolute proper motion of the Sextans dwarf spheroidal galaxy using Subaru Suprime-Cam images taken at three epochs, with a time baseline of ~ 10 years. We astrometrically calibrate each epoch by constructing distortion-correction maps from the best available Subaru Suprime-Cam dithered data sets and from Gaia DR1 positions. The magnitude limit of the proper-motion study is V ~ 24. The area covered is 26.7 x 23.3 arcmin, which is still within the core radius of Sextans. The derived proper motion is (mu_a, mu_d) = (-0.409 +/- 0.050, -0.047 +/- 0.058) mas/yr. The direction o…
We model the large kinematic data sets for the four Milky Way dwarf spheroidal (dSph) satellites: Carina, Fornax, Sculptor and Sextans, recently published by Walker et al. The member stars are selected using a reliable dynamical interloper removal scheme tested on simulated data. Our member selection is more restrictive than the one based on metallicity indicators as it removes not only contamination due to Milky Way stars but also the unbound stars from the tidal tails. We model the cleaned data sets by adjusting the solutions of the Jeans equations to the profiles of the projected velocity d…
We present tentative evidence for the existence of a dissolved star cluster in the Sextans dwarf spheroidal galaxy. In a sample of six stars, we identify three (possibly four) stars around [Fe/H] =-2.7 that are highly clustered in a multi-dimensional chemical abundance space. The estimated initial stellar mass of the cluster is M*,init = 1.9^+1.5_-0.9 (1.6^+1.2_-0.8)*10^5 Msol assuming a Salpeter (Kroupa) initial mass function (IMF). If corroborated by follow-up spectroscopy, this ancient star cluster at [Fe/H] =-2.7 is the most metal-poor system identified to date. Inspired by this finding, w…
A large extension of the Sextans dwarf spheroidal galaxy, 7 sq degrees, has been surveyed for variable stars using the Dark Energy Camera at the Blanco Telescope in Cerro Tololo Inter-American Observatory, Chile. We report 7 Anomalous Cepheids, 199 RR Lyrae stars and 16 dwarf Cepheids in the field. This is only the fifth extra-galactic systems in which dwarf Cepheids have been systematically searched. Henceforth, the new stars increase the census of stars coming from different environments that can be used to asses the advantages and limitations of using dwarf Cepheids as standard candles in p…
A few dozen dwarf satellite galaxies of the Milky Way have been discovered, which are often viewed as the remaining building blocks of our Galaxy. The follow-up spectroscopy showed that dwarf galaxies have a sizeable spread in their metallicities. Several scenarios were suggested to explain the metallicity spread, which can be tested by the structural patterns of stellar subpopulations with distinct metallicities. However, such chemical plus structural examination, to which we refer to as "chemostructural study" is hindered by the lack of stars with spectroscopic metallicity. Here we propose t…
We present the analysis of the FLAMES dataset targeting the central 25 arcmin region of the Sextans dSph. This dataset is the third major part of the high resolution spectroscopic section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team (DART). Our sample is composed of red giant branch stars down to the level of the horizontal branch in Sextans. It allows to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide [Fe/H]=$-$3.2 to $-$1.5 dex range. The ab…
Feedback from massive stars shapes the ISM and affects the evolution of galaxies, but its mechanisms acting at the small scales ($\sim 10$ pc) are still not well constrained observationally, especially in the low-metallicity environments. We present the analysis of the ionized gas (focusing on its kinematics, which were never studied before), and its connection to the massive stars in the nearby ($D \sim 1.4$ Mpc) star-forming very metal-poor ($Z\sim 0.07 Z_\odot$) galaxy Sextans A. The analysis is based on the observations with a scanning Fabry-Perot interferometer, long-slit spectroscopy and…
We present the high-resolution spectroscopic analysis of two new extremely metal-poor stars (EMPS) candidates in the dwarf spheroidal galaxy Sextans. These targets were pre-selected from medium resolution spectra centered around the Ca II triplet in the near-infrared and followed-up at higher resolution with VLT/UVES. We confirm their low metallicities with [Fe/H]=-2.95 and [Fe/H]=-3.01, placing them among the most metal-poor stars known in Sextans. The abundances of 18 elements, including C, Na, the alpha-elements, Fe-peak, and neutron capture elements, are determined. In particular, we prese…
We present the deep and wide $V$ and $I_c$ photometry of the Sextans dwarf spheroidal galaxy (dSph) taken by Suprime-Cam imager on the Subaru Telescope, which extends out to the tidal radius. The colour-magnitude diagram (CMD) reaches two magnitudes below the main sequence (MS) turn-off, showing a steep red giant branch, blue and red horizontal branch (HB), sub-giant branch (SGB), MS, and blue stragglers (BS). We construct the radial profile of each evolutionary phase and demonstrate that blue HB stars are more spatially extended, while red HB stars are more centrally concentrated than the oth…
We present results from deep and very spatially extended CTIO/DECam $g$ and $r$ photometry (reaching out to $\sim$ 2 mag below the oldest MSTO and covering $\sim$ 20 deg$^2$) around the Sextans dSph. We use this data-set to study the structural properties of Sextans overall stellar population and its different stellar evolutionary phases, as well as to search for signs of tidal disturbance from the MW, which would indicate departure from dynamical equilibrium. We perform the most accurate structural analysis to-date of Sextans' stellar components by applying Bayesian MCMC methods to the indivi…
Metal-poor components of dwarf galaxies around the Milky Way could be remnants of the building blocks of the Galactic halo structure. Low-mass stars that are currently observed as metal-poor stars are expected to have formed in chemically homogeneous clusters in the early phases of galaxy formation. They should have already disintegrated and should exhibit large scatter in abundance ratios of some sets of elements (e.g., Sr/Ba) in the Milky Way field stars. However, chemical abundance ratios are expected to cluster in very metal-poor stars in dwarf galaxies because the number of clusters forme…
We introduce a likelihood analysis of multi-epoch stellar line-of-sight velocities to constrain the binary fractions and binary period distributions of dwarf spheroidal galaxies. This method is applied to multi-epoch data from the Magellan/MMFS survey of the Carina, Fornax, Sculptor and Sextans dSph galaxies, after applying a model for the measurement errors that accounts for binary orbital motion. We find that the Fornax, Sculptor, and Sextans dSphs are consistent with having binary populations similar to that of Milky Way field binaries to within 68% confidence limits, whereas the Carina dSp…
We present tentative evidence for the existence of a dissolved star cluster at [Fe/H]=-2.7 in the Sextans dwarf spheroidal galaxy. We use the technique of chemical tagging to identify stars that are highly clustered in a multi-dimensional chemical abundance space (C-space). In a sample of six stars, three, possibly four stars are identified as potential cluster stars. The initial stellar mass of the parent cluster is estimated from two independent observations to M*,init=1.9^{+1.5}_{-0.9} (1.6^{+1.2}_{-0.8}) x 10^5 M_sol, assuming a Salpeter (Kroupa) initial mass function (IMF). If corroborate…
Massive Star Population in the Sextans A Dwarf Galaxy from HST UV Photometry
Khalifa University of Science and Technology（哈利法科技大学）；Polar Research Center, Khalifa University of Science and Technology（哈利法科技大学极地研究中心）；Instituto de Astrofisica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉各拉纳大学）
Dwarf galaxies are missing nearly all of their baryons and metals from the stellar disk, presumed to be in a bound halo or expelled beyond the virial radius. The virial temperature for galaxies with $M_{\rm h} \sim 10^9 - 10^{10}$ $M_{\odot}$ is similar to the collisional ionization equilibrium temperature for the C IV ion. We searched for UV absorption from C IV in six sightlines toward three dwarf galaxies in the anti-M31 direction and at the periphery of the Local Group ($D \approx$ 1.3 Mpc; Sextans A, Sextans B, and NGC 3109). The C IV doublet is detected in only one of six sightlines, tow…
Ram-pressure signatures in the dwarf irregular galaxy SextansB revealed by deep MeerKAT HI observations
Instituto de Astrofísica de Andalucía (CSIC)（安达卢西亚天体物理研究所）；LIRA, Observatoire de Paris, Université PSL, CNRS（巴黎天文台）；Department of Astronomy, University of Cape Town（开普敦大学天文学系）；Département de physique, Université de Montréal（蒙特利尔大学物理系）；Observatoire d’Astrophysique de l’Université Ouaga I Pr Joseph Ki-Zerbo (ODAUO)（瓦加杜古第一大学约瑟夫·基泽博天体物理观测站）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；Centre for Radio Astronomy Techniques and Technologies (RATT), Department of Physics and Electronics, Rhodes University（罗兹大学物理与电子学院射电天文技术与技术中心）
Dwarf spheroidal galaxies (dSph) orbiting the Milky Way are complex objects often with complicated star formation histories and internal dynamics. In this work, we search for stellar substructures in four of the classical dSph satellites of the Milky Way: Sextans, Carina, Leo I, and Leo II. We apply two methods to search for stellar substructure: the minimum spanning tree method, which helps us to find and quantify spatially connected structures, and the "brute-force" method, which is able to find elongated stellar substructures. We detected the previously known substructure in Sextans, and al…
We use VLT/FLAMES intermediate resolution (R~6500) spectra of individual red giant branch stars in the near-infrared CaII triplet (CaT) region to investigate the wide-area metallicity properties and internal kinematics of the Sextans dwarf spheroidal galaxy (dSph). Our final sample consists of 174 probable members of Sextans with accurate line-of-sight velocities (+- 2 km/s) and CaT [Fe/H] measurements (+- 0.2 dex). We use the MgI line at 8806.8 Å\, as an empirical discriminator for distinguishing between probable members of the dSph (giant stars) and probable Galactic contaminants (dwarf star…
We combine the Dark Energy Camera Legacy Survey (DECaLS) DR8 photometry with Gaia photometry to study the 3-D structure of Bootes I, Draco, Ursa Minor, Sextans and Sculptor dwarf galaxies using blue horizontal branch (BHB) stars as distance indicators. We construct a new colour-absolute magnitude of BHB stars that we use to measure the distance gradients within the body of the dwarf galaxies. We detect a statistically significant non-zero gradient only in Sextans and Sculptor. Through modeling of the gradient and 2-D density of the systems by triaxial Plummer models we find that the distance g…
We present JHK$_{s}$ observations of the metal-poor ([Fe/H] $<$ -1.40) Dwarf-irregular galaxies, Leo A and Sextans A obtained with the WIYN High-Resolution Infrared Camera at Kitt Peak. Their near-IR stellar populations are characterized by using a combination of colour-magnitude diagrams and by identifying long-period variable stars. We detected red giant and asymptotic giant branch stars, consistent with membership of the galaxy's intermediate-age populations (2-8 Gyr old). Matching our data to broadband optical and mid-IR photometry we determine luminosities, temperatures and dust-productio…
We present a detailed study of the stellar and HI structure of the dwarf irregular galaxies SextansA and SextansB, members of the NGC3109 association. We use newly obtained deep (r~26.5) and wide field g,r photometry to extend the Surface Brightness (SB) profiles of the two galaxies down to mu_V~ 31.0 mag/arcsec^2. We find that both galaxies are significantly more extended than what previously traced with surface photometry, out to ~4 kpc from their centers along their major axis. Older stars are found to have more extended distribution with respect to younger populations. We obtain the first …
Identifying Red Supergiants in the Local Group Using JWST Photometry. I. NGC 6822, Sextans A, NGC 300, WLM, and IC 1613
Institute for Frontiers in Astronomy and Astrophysics, Beijing Normal University（北京师范大学天文与前沿科学研究院）；School of Physics and Astronomy, Beijing Normal University（北京师范大学物理与天文学院）；Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台空间天文与技术重点实验室）；Department of Astronomy, College of Physics and Electronic Engineering, Qilu Normal University（齐鲁师范学院物理与电子工程学院天文学系）
We present a homogeneous set of accurate atmospheric parameters for a sample of eleven very metal-poor (-3.32 <= [Fe/H] <= -2.61) stars in the Sextans dwarf spheroidal galaxy (dSph) and the non-local thermodynamic equilibrium (NLTE) abundances of, at least, seven chemical elements based on high-resolution UVES/VLT and HDS/Subaru spectra. For each star, its effective temperature and surface gravity were derived from the spectral energy distribution and the known distance, and the Fe abundance was obtained as the average from lines of Fe I and Fe II. Based on abundances of Mg, Ca, and Ti, we sho…
We report the discovery of clear observational signs of past accretion/merger events in one of the Milky Way satellite galaxies, the Sextans dwarf spheroidal (dSph). These were uncovered in the spatial distribution, internal kinematics and metallicity properties of Sextans stars using literature CTIO/DECam photometric and Magellan/MMFS spectroscopic catalogues. We find the spatial distribution of stars to vary as a function of the colour/metallicity, being rather regular and round for the blue (metal-poor) red giant branch and main-sequence turn-off stars but much more elliptical and irregular…
Chemical abundances of six extremely metal-poor ([Fe/H]<-2.5) stars in the Sextans dwarf spheroidal galaxy are determined based on high resolution spectroscopy (R=40,000) with the Subaru Telescope High Dispersion Spectrograph. (1) The Fe abundances derived from the high resolution spectra are in good agreement with the metallicity estimated from the Ca triplet lines in low resolution spectra. The lack of stars with [Fe/H]=<-3 in Sextans, found by previous estimates from the Ca triplet, is confirmed by our measurements, although we note that high resolution spectroscopy for a larger sample of s…
We use Gaia EDR3 data to identify stars associated with six classical dwarf spheroidals (Draco, Ursa Minor, Sextans, Sculptor, Fornax, Carina) at their outermost radii, beyond their nominal King stellar limiting radius. For all of the dSphs examined, we find radial velocity matches with stars residing beyond the King limiting radius and with $> 50\%$ astrometric probability (four in Draco, two in Ursa Minor, eight in Sextans, two in Sculptor, twelve in Fornax, and five in Carina), indicating that these stars are associated with their respective dwarf spheroidals (dSphs) at high probability. We…
Carbon monoxide (CO) is one of the primary coolants of gas and an easily accessible tracer of molecular gas in spiral galaxies but it is unclear if CO plays a similar role in metal poor dwarfs. We carried out a deep observation with IRAM 30 m to search for CO emission by targeting the brightest far-IR peak in a nearby extremely metal poor galaxy, Sextans A, with 7% Solar metallicity. A weak CO J=1-0 emission is seen, which is already faint enough to place a strong constraint on the conversion factor (a_CO) from the CO luminosity to the molecular gas mass that is derived from the spatially reso…
Recovering the infall mass for Milky Way satellite galaxy Sextans
Institute of Astronomy, School of Physics, Zhejiang University（浙江大学物理学院天体物理研究所）；Purple Mountain Observatory（紫金山天文台）；Center for Cosmology and Computational Astrophysics, Zhejiang University（浙江大学宇宙学与计算天体物理中心）
APOGEE chemical abundances of stars in the MW satellites Fornax, Sextans, Draco and Carina
Sun Yat-sen University（中山大学）；CSST Science Center for the Guangdong-Hong Kong-Macau Greater Bay Area（中国空间站科学中心粤港澳大湾区分中心）；Universidad Católica del Norte（北天主教大学）；Nanjing University（南京大学）
We report the confirmation of an old, metal-poor globular cluster in the nearby dwarf irregular galaxy Sextans A, the first globular cluster known in this galaxy. The cluster, which we designate as Sextans A-GC1, lies some 4.4 arcminutes ($\sim1.8$ kpc) to the SW of the galaxy centre and clearly resolves into stars in sub-arcsecond seeing ground-based imaging.We measure an integrated magnitude $V=18.04$, corresponding to an absolute magnitude, $M_{V,0} = -7.85$. This gives an inferred mass $M\sim$1.6$\times10^5~M\odot$, assuming a Kroupa IMF. An integrated spectrum of Sextans A-GC1 reveals a h…
As galaxy simulations increase in resolution more attention is being paid towards the evolution of dwarf galaxies and how the simulations compare to observations. Despite this increasing resolution we are however, far away from resolving the interactions of satellite dwarf galaxies and the hot coronae which surround host galaxies. We describe a new method which focuses only on the local region surrounding an infalling dwarf in an effort to understand how the hot baryonic halo will alter the chemodynamical evolution of dwarf galaxies. Using this method we examine how a dwarf, similar to Sextans…
The cold dark matter model predicts cuspy dark matter halos. However, it has been found that, in some low-mass galaxies, cored dark halos provide a better description of their internal dynamics. Here we give constraints on the dark halo profile in the Sextans dwarf spheroidal galaxy by studying the longevity of two cold kinematic substructures detected in this galaxy. We perform N-body simulations of a stellar clump in the Sextans dwarf galaxy, including a live dark matter halo and the main stellar component. We find that, if the dark halo is cuspy, stellar clumps orbiting with semi-major axis…
Spatially resolved star formation history of Sextans dSph
Instituto Interdisciplinario de Ciencias Básicas (ICB), CONICET-UNCuyo（基础科学跨研究所 (ICB)，CONICET-UNCuyo）；Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)（国家科学研究委员会 (CONICET)）
We present sensitive CO (J = 1 - 0) emission line observations of three metal-poor dwarf irregular galaxies Leo P (Z ~ 3% Z_Solar), Sextans A (Z ~ 7.5% Z_Solar), and Sextans B (Z ~ 7.5% Z_Solar), all obtained with the Combined Array for Millimeter-wave Astronomy (CARMA) interferometer. While no CO emission was detected, the proximity of the three systems allows us to place very stringent (4 sigma) upper limits on the CO luminosity (L_CO) in these metal-poor galaxies. We find the CO luminosities to be L_CO < 2900 K km/s pc^2 for Leo P, L_CO < 12400 K km/s pc^2 for Sextans A, and L_CO < 9700 K k…
With both nebular- and stellar-derived abundances of $\lesssim$ 1/10 Zsun and low foreground extinction, Sextans A is a prime candidate to replace the Small Magellanic Cloud as reservoir of metal-poor massive stars and reference to study the metal-poor Universe. We report the discovery of two early-O type stars in Sextans A, the earliest O-stars with metallicity < 1/7 Zsun known to date, and two additional O9 stars. Colour-excess estimates towards individual targets, enabled by spectral typing, manifest that internal reddening is neither uniform nor negligible. The four targets define a new re…
We study the evolved stellar population of the galaxy Sextans A. This galaxy is one of the lowest metallicity dwarfs in which variable asymptotic giant branch stars have been detected, suggesting that little metal enrichment took place during the past history. The analysis consists in the characterization of a sample of evolved stars, based on evolutionary tracks of asymptotic giant branch and red super giant stars, which include the description of dust formation in their winds. Use of mid-infrared and near-infrared data allowed us to identify carbon-rich sources, stars undergoing hot bottom b…
Using a flexible galactic model with variable stellar velocity anisotropy, I apply the classical Jeans mass modeling approach to the five dwarf spheroidal galaxies with the largest homogeneous datasets of stellar line-of-sight velocities (between 330 and 2500 stars per galaxy) -- Carina, Fornax, Leo~I, Sculptor, and Sextans. I carry out an exhaustive model parameter search, assigning absolute probabilities to each parameter combination. My main finding is that there is a well defined radius (unique for each galaxy) where the Jeans analysis constraints on the enclosed mass are tightest, and are…
Increasing the statistics of evolved massive stars in the Local Group enables investigating their evolution at different metallicities. During the late stages of stellar evolution, the physics of some phenomena, such as episodic and systematic mass loss, are not well constrained. For example, the physical properties of red supergiants (RSGs) in different metallicity regimes remain poorly understood. Thus, we initiated a systematic study of RSGs in dwarf irregular galaxies (dIrrs) in the Local Group. The target selection is based on 3.6 $μ$m and 4.5 $μ$m photometry from archival Spitzer Space T…
We present a new chemical evolution model for dwarf spheroidal galaxies (dSphs) in the Local Universe. Our main aim is to explain both their observed star formation histories and metallicity distribution functions simultaneously. Applying our new model for the four local dSphs, that is, Fornax, Sculptor, Leo II, and Sextans, we find that our new model reproduces the observed chemical properties of the dSphs consistently. Our results show that the dSphs have evolved with both a low star formation efficiency and a large gas outflow efficiency compared with the Milky Way, as suggested by previous…
Dust in the very metal-poor galaxy Sextans A with JWST. I: Characterizing the evolved stellar population of Sextans A based on JWST observations and stellar evolution models
Università degli Studi Roma Tre（罗马第三大学）；INAF - Osservatorio Astronomico di Roma（罗马天文台（意大利国家天体物理研究所））；Space Telescope Science Institute（太空望远镜科学研究所）；Open University（开放大学）；Keele University（基尔大学）；Instituto de Astrofísica de Canarias（加那利天体物理学研究所）；Universidad de La Laguna（拉古纳大学）；Koninklijke Sterrenwacht van België（比利时皇家天文台）；National Centre for Nuclear Research（国家核研究中心）
The detection and characterization of supermassive black holes (SMBHs) in local low mass galaxies is crucial to our understanding of the origins of SMBHs. This statement assumes that low mass galaxies have had a relatively quiet cosmic history, so that their black holes have not undergone significant growth and therefore can be treated as relics of the original SMBH seeds. While recent studies have found optical signatures of active galactic nuclei (AGNs) in a growing population of dwarf galaxies, these studies are biased against low metallicity and relatively merger-free galaxies, thus missin…
This work establishes the most complete sample of red supergiants (RSGs) in twelve low-mass galaxies (WLM, IC 10, NGC 147, NGC 185, IC 1613, Leo A, Sextans B, Sextans A, NGC 6822, Pegasus Dwarf, SMC and LMC) of the Local Group, which forms the solid basis to study the properties of RSGs as well as the star formation rate (SFR) and initial mass function (IMF) of the galaxies. After removing the foreground dwarf stars by their obvious branch in the near-infrared color-color diagram ($(J-H)_0/(H-K)_0$) with the UKIRT/WFCAM and 2MASS photometry as well as the Gaia/EDR3 measurements of proper motio…
University of Chicago（芝加哥大学）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理研究所）；NSF NOIRLab（美国国家科学基金会NOIR天文台实验室）；University of Virginia（弗吉尼亚大学）；NSF-Simons AI Institute for the Sky (SkAI)（美国国家科学基金会-西蒙斯天空人工智能研究所）；Department of Astronomy/Steward Observatory, University of Arizona（亚利桑那大学天文学系/斯图沃德天文台）；Yale University（耶鲁大学）；Center for Astrophysics and Space Astronomy, University of Colorado Boulder（科罗拉多大学博尔德分校天体物理学与空间天文中心）
Observational bias against finding Milky Way (MW) dwarf galaxies at low Galactic latitudes (b < 20 deg) and at low surface brightnesses (fainter than 29 mag arcsec^-2, in the V-band) currently limits our understanding of the faintest limits of the galaxy luminosity function. This paper is a proof-of-concept that groups of two or more RR Lyrae stars reveal MW dwarf galaxies at d > 50 kpc in these unmined regions of parameter space, with only modest contamination from interloper groups when large halo structures are excluded. For example, a friends-of-friends (FOF) search with a linking length o…
Co-evolution of baryons and dark matter halos of LYRA dwarf galaxies
Durham University（杜伦大学）；European Southern Observatory（欧洲南方天文台）；Stockholm University（斯德哥尔摩大学）；University of Hawaii（夏威夷大学）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）
Unveiling Massive Main-Sequence Stars in Sextans A through Panchromatic Photometry
The Observatories of the Carnegie Institution for Science（卡内基科学研究所天文台）；California Institute of Technology（加州理工学院）；University of California, Berkeley（加州大学伯克利分校）；NSF National Optical-Infrared Astronomy Research Laboratory（美国国家光学-红外天文研究实验室）；University of Washington（华盛顿大学）；Space Telescope Science Institute（太空望远镜科学研究所）；Johns Hopkins University（约翰斯·霍普金斯大学）；Flatiron Institute（平托研究所）；University of California, Santa Cruz（加州大学圣克鲁兹分校）
New observations indicate that ultrafaint dwarf galaxies (UFD) -- the least luminous systems bound by dark matter halos (<10^5 Lsun) -- may have formed before reionization. The extrapolated virial masses today are uncertain with estimates ranging from 10^8 Msun to 10^9 Msun. We show that the progenitor halo masses of UFDs can be as low as Mvir = 10^7 Msun. Under the right conditions, such a halo can survive the energy input of a supernova and its radiative progenitor. A clumpy medium is much less susceptible to both internal and external injections of energy. It is less prone to SN sweeping be…
