The Panchromatic Hubble Andromeda Treasury V: Ages and Masses of the Year 1 Stellar Clusters
Morgan Fouesneau, L. Clifton Johnson, Daniel R. Weisz, Julianne J. Dalcanton, Eric F. Bell, Luciana Bianchi, Nelson Caldwell, Dimitrios A. Gouliermis, Puragra G… 展开作者
Morgan Fouesneau, L. Clifton Johnson, Daniel R. Weisz, Julianne J. Dalcanton, Eric F. Bell, Luciana Bianchi, Nelson Caldwell, Dimitrios A. Gouliermis, Puragra Guhathakurta, Jason Kalirai, Søren S. Larsen, Hans-Walter Rix, Anil C. Seth, Evan D. Skillman, Benjamin F. Williams, PHAT collaboration
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19 pages, 13 figures, catalog available as online material. Accepted for publication in ApJ
We present ages and masses for 601 star clusters in M31 from the analysis of the six filter integrated light measurements from near ultraviolet to near infrared wavelengths, made as part of the Panchromatic Hubble Andromeda Treasury (PHAT). We derive the ages and masses using a probabilistic technique, which accounts for the effects of stochastic sampling of the stellar initial mass function. Tests on synthetic data show that this method, in conjunction with the exquisite sensitivity of the PHAT observations and their broad wavelength baseline, provides robust age and mass recovery for clusters ranging from $\sim 10^2 - 2 \times 10^6 M_\odot$. We find that the cluster age distribution is consistent with being uniform over the past $100$ Myr, which suggests a weak effect of cluster disruption within M31. The age distribution of older ($>100$ Myr) clusters fall towards old ages, consistent with a power-law decline of index $-1$, likely from a combination of fading and disruption of the clusters. We find that the mass distribution of the whole sample can be well-described by a single power-law with a spectral index of $-1.9 \pm 0.1$ over the range of $10^3-3 \times 10^5 M_\odot$. However, if we subdivide the sample by galactocentric radius, we find that the age distributions remain unchanged. However, the mass spectral index varies significantly, showing best fit values between $-2.2$ and $-1.8$, with the shallower slope in the highest star formation intensity regions. We explore the robustness of our study to potential systematics and conclude that the cluster mass function may vary with respect to environment.
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 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 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 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
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…
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…
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 …
