We present a new approach to measuring the thickness of a partially face-on stellar disk, using dust geometry. In a moderately-inclined disk galaxy, the fraction of reddened stars is expected to be 50% everywhere, assuming that dust lies in a thin midplane. In a thickened disk, however, a wide range of radii project onto the line of sight. Assuming stellar density declines with radius, this geometrical projection leads to differences in the numbers of stars on the near and far sides of the thin dust layer. The fraction of reddened stars will thus differ from the 50% prediction, with a deviation that becomes larger for puffier disks. We map the fraction of reddened red giant branch (RGB) stars across M31, which shows prominent dust lanes on only one side of the major axis. The fraction of reddened stars varies systematically from 20% to 80%, which requires that these stars have an exponential scale height h_z that is 0.14+/-0.015 times the exponential scale length (h_r~5.5kpc). M31's RGB stars must therefore have h_z=770+/-80pc, which is far thicker than the Milky Way's thin disk, but comparable to its thick disk. The lack of a significant thin disk in M31 is unexpected, but consistent with its interaction history and high disk velocity dispersion. We suggest that asymmetric reddening be used as a generic criteria for identifying ``thick disk'' dominated systems, and discuss prospects for future 3-dimensional tomographic mapping of the gas and stars in M31.
We construct a catalog of star clusters from Hubble Space Telescope images of the inner disk of the Triangulum Galaxy (M33) using image classifications collected by the Local Group Cluster Search, a citizen science project hosted on the Zooniverse platform. We identify 1214 star clusters within the Hubble Space Telescope imaging footprint of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. Comparing this catalog to existing compilations in the literature, 68% of the clusters are newly identified. The final catalog includes multi-band aperture photometry …
We present the Bayesian Extinction And Stellar Tool (BEAST), a probabilistic approach to modeling the dust extinguished photometric spectral energy distribution of an individual star while accounting for observational uncertainties common to large resolved star surveys. Given a set of photometric measurements and an observational uncertainty model, the BEAST infers the physical properties of the stellar source using stellar evolution and atmosphere models and constrains the line of sight extinction using a newly developed mixture model that encompasses the full range of dust extinction curves …
We measure the mass function for a sample of 840 young star clusters with ages between 10-300 Myr observed by the Panchromatic Hubble Andromeda Treasury (PHAT) survey in M31. The data show clear evidence of a high-mass truncation: only 15 clusters more massive than $10^4$ $M_{\odot}$ are observed, compared to $\sim$100 expected for a canonical $M^{-2}$ pure power-law mass function with the same total number of clusters above the catalog completeness limit. Adopting a Schechter function parameterization, we fit a characteristic truncation mass of $M_c = 8.5^{+2.8}_{-1.8} \times 10^3$ $M_{\odot}…
We use the Panchromatic Hubble Andromeda Treasury (PHAT) survey dataset to perform spatially resolved measurements of star cluster formation efficiency ($Γ$), the fraction of stellar mass formed in long-lived star clusters. We use robust star formation history and cluster parameter constraints, obtained through color-magnitude diagram analysis of resolved stellar populations, to study Andromeda's cluster and field populations over the last $\sim$300 Myr. We measure $Γ$ of 4-8% for young, 10-100 Myr old populations in M31. We find that cluster formation efficiency varies systematically across t…
We measure the spatially resolved recent star formation history (SFH) of M33 using optical images taken with the Hubble Space Telescope as part of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. The area covered by the observations used in this analysis covers a de-projected area of $\sim$38 kpc$^{2}$ and extends to $\sim$3.5 and $\sim$2 kpc from the center of M33 along the major and semi-major axes, respectively. We divide the PHATTER optical survey into 2005 regions that measure 24 arcsec, $\sim$100 pc, on a side and fit color magnitude diagrams for e…
The Panchromatic Hubble Andromeda Treasury. VI. The reliability of far-ultraviolet flux as a star formation tracer on sub-kpc scales
我们利用全色哈勃仙女座宝库（PHAT）的光学观测，测量了M31中33个FUV明亮区域的最近（<5亿年）恒星形成历史（SFHS）。区域面积范围从~ $10^4$到$10^6$ pc $^2$，这使我们能够测试FUV通量作为亚千秒差距尺度上最近恒星形成示踪剂的可靠性。恒星形成率（SFR）来自于修正后的观测FUV通量，平均而言，与1亿年的平均SFR的SFH内的1 $σ$分散一致。总体而言，分散性大于SFR的不确定性，在最小区域中尤其明显。分散是一致的，甚至组合的离散采样的初始质量函数和高变异性的SFHS。这一结果表明，为获得精确的SFR估计从FUV通量满足全IMF和恒定的SFR假设的重要性。假设一个强大的FUV消光校正，我们估计，一个因素的2.5不确定性，可以预期在FUV为基础的SFR的区域小于$10^5$ pc $^2$，或几百个pc。我们还研究了年龄和质量来自紫外线通量的共同假设下，该地区是简单的恒星星族（SSP）。SFHS表明，大多数地区不是SSP，年龄和质量估计相应地从SFHS不一致。对于这些地区的SSP样SFH，我们发现平均差异10万年的年龄和3至4的质量的一个因素。基于积分FUV通量，不可能将SSP样区域与其他区域区分开。
We present synthetic far- and near-ultraviolet (FUV and NUV) maps of M31, both with and without dust reddening. These maps were constructed from spatially-resolved star formation histories (SFHs) derived from optical Hubble Space Telescope imaging of resolved stars, taken as part of the Panchromatic Hubble Andromeda Treasury program. We use stellar population synthesis modeling to generate synthetic UV maps with projected spatial resolution of $\sim$100 pc ($\sim$24 arcseconds) The predicted UV flux agrees well with the observed flux, with median ratios between the modeled and observed flux of…
We map the star formation history across M31 by fitting stellar evolution models to color-magnitude diagrams of each 83$''{\times}$83$''$ (0.3$\times$1.4 kpc, deprojected) region of the PHAT survey outside of the innermost 6$'{\times}$12$'$ portion. We find that most of the star formation occurred prior to $\sim$8 Gyr ago, followed by a relatively quiescent period until $\sim$4 Gyr ago, a subsequent star formation episode about 2 Gyr ago and a return to relative quiescence. There appears to be little, if any, structure visible for populations with ages older than 2 Gyr, suggesting significant …
We present panchromatic resolved stellar photometry for 22 million stars in the Local Group dwarf spiral Triangulum (M33), derived from Hubble Space Telescope (HST) observations with the Advanced Camera for Surveys (ACS) in the optical (F475W, F814W), and the Wide Field Camera 3 (WFC3) in the near ultraviolet (F275W, F336W) and near-infrared (F110W, F160W) bands. The large, contiguous survey area covers $\sim$14 square kpc and extends to 3.5 kpc (14 arcmin, or 1.5-2 scale lengths) from the center of M33. The PHATTER observing strategy and photometry technique closely mimic those of the Panchro…
The Panchromatic Hubble Andromeda Treasury XI: The Spatially-Resolved Recent Star Formation History of M31
我们测量最近的恒星形成历史（SFH）的M31使用的光学图像与\texit{Hubble Space Telescope}作为全色哈勃仙女座宝库（PHAT）的一部分。我们在M31东北象限的约9000个区域中拟合了色星等图，这些区域的投影大小为约100 pc $\times$ 100 pc，覆盖了0.5平方度的区域（约380 kpc $^2$，去投影）。我们表明，SFH在这些小的空间尺度上变化显着，但也有相干的银河系范围内的波动SFH回到~500百万年，最显着的是在M31的10千秒差距的恒星形成环。我们发现，10千秒差距的环至少有4亿年的历史，表明在过去的5亿年中正在进行恒星的形成。这表明在这个半径下，环中存在至少2个动力学时间的分子气体。我们还发现，环的位置是恒定的整个这段时间，是固定在1公里/秒的水平，虽然有证据扩大环由于扩散到磁盘的恒星。根据M31环特征的现有模型，环的位置缺乏演化使得纯粹的碰撞环起源非常不可能。我们发现，全球SFR在过去的5亿年中一直相当稳定，尽管它确实在5千万年时出现了小幅增长，是过去1亿年平均SFR的1.3倍。在过去的~ 5亿年中，所有SF的~60%发生在10-kpc环中。最后，我们发现在过去的1亿年中，PHAT调查区的平均SFR为$0.28\pm0.03$ M $_\odot$ yr $^{-1}$，平均去投影强度为$7.3 \times 10^{-4}$…
The Panchromatic Hubble Andromeda Southern Treasury (PHAST). II. The Spatially Resolved Recent Star Formation History in M31
University of Washington（华盛顿大学）；California State University, Los Angeles（加州州立大学洛杉矶分校）；Flatiron Institute（平顿研究所）；University of Michigan（密歇根大学）；University of Utah（犹他大学）；Raytheon（雷神公司）；University of Arizona（亚利桑那大学）；University of California Berkeley（加州大学伯克利分校）
The Andromeda Galaxy (M31) has been observed with the UltraViolet Imaging Telescope (UVIT) instrument onboard the AstroSat Observatory. The M31 sky area was covered with 19 fields, in multiple UV filters per field, over the period of 2017 to 2019. The entire galaxy was observed in the FUV F148W filter, and more than half observed in the NUV filters. A new calibration and data processing is described which improves the astrometry and photometry of the UVIT data. The high spatial resolution of UVIT ($\simeq$1 arcsec) and new astrometry calibration ($\simeq$0.2 arcsec) allow identification of UVI…
The Panchromatic Hubble Andromeda Treasury IV. A Probabilistic Approach to Inferring the High Mass Stellar Initial Mass Function and Other Power-law Functions
We analyze the kinematics of Andromeda's disk as a function of stellar age by using photometry from the Panchromatic Hubble Andromeda Treasury (PHAT) survey and spectroscopy from the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) survey. We use HI 21-cm and CO ($\rm J=1 \rightarrow 0$) data to examine the difference between the deprojected rotation velocity of the gas and that of the stars. We divide the stars into four stellar age bins, from shortest lived to longest lived: massive main sequence stars (0.03 Gyr), more luminous intermediate mass asymptotic giant b…
Stellar kinematics and metallicity are key to exploring formation scenarios for galactic disks and halos. In this work, we characterized the relationship between kinematics and photometric metallicity along the line-of-sight to M31's disk. We combined optical HST/ACS photometry from the Panchromatic Hubble Andromeda Treasury (PHAT) survey with Keck/DEIMOS spectra from the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) survey. The resulting sample of 3512 individual red giant branch stars spans 4-19 projected kpc, making it a useful probe of both the disk and inner…
Hubble Tarantula Treasury Project: Unraveling Tarantula's Web. II. Optical and Near Infrared Star Formation History of the Starburst Cluster NGC 2070 in 30 Doradus
The radiation of stars heats dust grains in the diffuse interstellar medium and in star-forming regions in galaxies. Modelling this interaction provides information on dust in galaxies, a vital ingredient for their evolution. It is not straightforward to identify the stellar populations heating the dust, and to link attenuation to emission on a sub-galactic scale. Radiative transfer models are able to simulate this dust-starlight interaction in a realistic, three-dimensional setting. We investigate the dust heating mechanisms on a local and global galactic scale, using the Andromeda galaxy (M3…
A New Approach to Detailed Structural Decomposition: Kicked-up Disk Stars in Andromeda's Halo?
我们在0.4 < R < 225 kpc的径向范围内描述了仙女座星系（M31）的球、盘和晕子成分。这些子成分的共空间性质使得它们难以单独使用表面亮度（SB）信息来解开，特别是在~20 kpc的内部。我们的新分解技术结合了来自超过150万明亮的亮度函数（LF）的信息，（20 < I < 22）颗恒星来自全色哈勃仙女座宝藏（PHAT）巡天，超过5000颗红巨星分支恒星的径向速度来自仙女座恒星晕的光谱和光度景观（SPLASH）巡天，以及来自各种来源的集成I波段SB配置文件。我们使用一个仿射不变的马尔可夫链蒙特卡罗算法，以适应这三个数据集的一个适当的玩具模型。凸起，磁盘和晕SB配置文件被建模为Sersic，指数，和核心的幂律，分别，和LF被建模为破幂律。我们发现，与盘状LF的恒星的数量是~5%的数量大于在动态冷组件，这表明，一些恒星出生在磁盘已动态加热的点，他们是运动学上无法区分的晕成员。这是第一个运动学证据，证明在M31的恒星晕中存在着一个“被踢起的盘”。被踢出的盘星的比例与模拟中发现的一致。更多信息见Dorman et al.（2013，已提交）。
We present results from a 2-epoch HST H$α$ emission line survey of the Andromeda Galaxy that overlaps the footprint of the Panchromatic Hubble Andromeda Treasury (PHAT) survey. We find 552 (542) classical Be stars and 8429 (8556) normal B-type stars in epoch # 1 (epoch # 2), yielding an overall fractional Be content of 6.15% $\pm$0.26% (5.96% $\pm$0.25%). The fractional Be content decreased with spectral sub-type from $\sim$23.6% $\pm$2.0% ($\sim$23.9% $\pm$2.0%) for B0-type stars to $\sim$3.1% $\pm$0.34% ($\sim$3.4% $\pm$0.35%) for B8-type stars in epoch # 1 (epoch # 2). We observe a clear po…
We present a near-complete catalog of the metal-rich population of Thermally-Pulsing Asymptotic Giant Branch stars in the northwest quadrant of M31. This metal-rich sample complements the equally complete metal-poor Magellanic Cloud AGB catalogs produced by the SAGE program. Our catalog includes HST wide-band photometry from the Panchromatic Hubble Andromeda Treasury survey, HST medium-band photometry used to chemically classify a subset of the sample, and Spitzer mid- and far-IR photometry that we have used to isolate dust-producing AGB stars. We have detected 346,623 AGB stars; these include…
We present a sample of 224 stars that emit H$α$ (H$α$ stars) in the Andromeda galaxy (M31). The stars were selected from $\sim$ 5000 spectra, collected as part of the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey using Keck II/DEIMOS. We used six-filter Hubble Space Telescope photometry from the Panchromatic Hubble Andromeda Treasury survey to classify and investigate the properties of the H$α$ stars. We identified five distinct categories of H$α$ star: B-type main sequence (MS) stars, `transitioning'-MS (T-MS) stars, red core He burning (RHeB) stars, non-C-rich as…
We present Period-Luminosity Relations (PLRs) for 55 Cepheids in M31 with periods ranging from 4 to 78 days observed with the Hubble Space Telescope (HST) using the same three-band photometric system recently used to calibrate their luminosities. Images were taken with the Wide Field Camera 3 in two optical filters (F555W and F814W) and one near-infrared filter (F160W) using the Drift And SHift (DASH) mode of operation to significantly reduce overheads and observe widely-separated Cepheids in a single orbit. We include additional F160W epochs for each Cepheid from the Panchromatic Hubble Andro…
As galaxies evolve, they must enrich and exchange gas with the surrounding medium, but the timing of these processes and how much gas is involved remain poorly understood. In this work, we leverage metals as tracers of past gas flows to constrain the history of metal ejection and redistribution in M31. This roughly $L*$ galaxy is a unique case where spatially resolved measurements of the gas-phase and stellar metallicity, dust extinction, and neutral ISM gas content are all available, enabling a census of the present metal mass. We combine spatially resolved star formation histories from the P…
A galaxy's stellar mass-to-light ratio ($M_\star/L$) is a useful tool for converting luminosity to stellar mass ($M_\star$). However, the practical utility of $M_\star/L$ inferred from stellar population synthesis (SPS) models is limited by mismatches between the real and assumed models for star formation history (SFH) and dust geometry, both of which vary within galaxies. Here, we measure spatial variations in $M_\star/L$ and their dependence on color, star formation history, and dust across the disk of M31, using a map of $M^\mathrm{CMD}_\star$ derived from color-magnitude diagrams of resolv…
Extinction Distributions in Nearby Star-resolved Galaxies. II. M33
Qilu Normal University（齐鲁师范学院）；Shandong Key Laboratory of Space Environment and Exploration Technology（山东省空间环境与探月技术重点实验室）；Beijing Normal University（北京师范大学）；Yunnan University（云南大学）
The presence of AGB stars in clusters provides key constraints for stellar models, as has been demonstrated with historical data from the Magellanic Clouds. In this work, we look for candidate AGB stars in M31 star clusters from the Panchromatic Hubble Andromeda Treasury (PHAT) survey. Our photometric criteria selects stars brighter than the tip of the red giant branch, which includes the bulk of the thermally-pulsing AGB stars as well as early-AGB stars and other luminous cool giants expected in young stellar populations (e.g. massive red supergiants, and intermediate-mass red helium-burning …
Carbon Stars as Standard Candles: An Empirical Test for the Reddening, Metallicity, and Age Sensitivity of the J-region Asymptotic Giant Branch (JAGB) Method
Aims: We use new deep XMM-Newton observations of the northern disk of M 31 to trace the hot interstellar medium (ISM) in unprecedented detail and to characterise the physical properties of the X-ray emitting plasmas. Methods: We used all XMM-Newton data up to and including our new observations to produce the most detailed image yet of the hot ISM plasma in a grand design spiral galaxy such as our own. We compared the X-ray morphology to multi-wavelength studies in the literature to set it in the context of the multi-phase ISM. We performed spectral analyses on the extended emission using our n…
