A rich harvest of RR Lyrae stars has been identified for the first time in B514, a metal-poor ([Fe/H] = 1.95 +/- 0.10 dex) globular cluster of the Andromeda galaxy (M31), based on Hubble Space Telescope Wide Field Planetary Camera 2 and Advanced Camera for Surveys time-series observations. We have detected and derived periods for 89 RR Lyrae stars (82 fundamental-mode -RRab- and 7 first-overtone -RRc- pulsators, respectively) among 161 candidate variables identified in the cluster. The average period of the RR Lyrae variables (<Pab> = 0.58 days and <Pc> = 0.35 days, for RRab and RRc pulsators, respectively) and the position in the period-amplitude diagram both suggest that B514 is likely an Oosterhoff type I cluster. This appears to be in disagreement with the general behaviour of the metal-poor globular clusters in the Milky Way, which show instead Oosterhoff type II pulsation properties. The average apparent magnitude of the RR Lyrae stars sets the mean level of the cluster horizontal branch at <V(RR)> = 25.18 +/- 0.02 (sigma=0.16 mag, on 81 stars). By adopting a reddening E(B-V) = 0.07 +/- 0.02 mag, the above metallicity and M_V=0.44 +/- 0.05 mag for the RR Lyrae variables of this metallicity, we derive a distance modulus of mu_0=24.52 +/- 0.08 mag, corresponding to a distance of about 800 +/- 30 kpc, based on a value of M_V that sets mu_0(LMC)=18.52.
Based upon a metallicity selection, we identify a significant sub-population of the inner halo globular clusters in the Andromeda Galaxy which we name the Dulais Structure. It is distinguished as a co-rotating group of 10-20 globular clusters which appear to be kinematically distinct from, and on average more metal-poor than, the majority of the inner halo population. Intriguingly, the orbital axis of this Dulais Structure is closely aligned with that of the younger accretion event recently identified using a sub-population of globular clusters in the outer halo of Andromeda, and this is stron…
Water Masers in the Andromeda Galaxy: The First Step Toward Proper Motion
我们用绿岸望远镜在仙女座星系（M31）中探测并确认了五个水脉泽复合体。这些脉泽将为M31的自行研究提供所需的高亮度温度点源，从而能够通过适当的旋转测量其完整的三维速度矢量和几何距离。M31的运动是本星系群动力学的基石，也是研究星系暗物质分布的重要途径。我们对水脉泽的调查选择了M31中的206个发光致密的24微米发射区，它们的灵敏度足以探测到任何对每年约10微弧秒天体测量有用的脉泽。新发现的脉泽在单光谱分量中的各向同性光度范围为0.3-1.9 x 10^-3 L（太阳），与发光的银河脉泽类似。脉泽分布在分子环周围，包括靠近长轴和短轴的位置，这对于自行研究来说几乎是理想的。我们发现24微米亮度和水脉泽亮度之间没有相关性，这表明虽然水脉泽出现在恒星形成区域，但水脉泽的非线性放大路径和光束性质意味着它们无法仅根据红外亮度来预测。这意味着在M31中还有其他明亮的脉泽。我们预测，利用现有的设备，在2-3年内可以测量M31的几何距离和系统自行。从长远来看，随着M31接近银河系，对发散脉泽的“移动星团”观测是可能的。
We probe the feasibility of describing the structure of a multi-component axisymmetric galaxy with a dynamical model based on the Jeans equations while taking into account a third integral of motion. We demonstrate that using the third integral in the form derived by G. Kuzmin, it is possible to calculate the stellar kinematics of a galaxy from the Jeans equations by integrating the equations along certain characteristic curves. In cases where the third integral of motion does not describe the system exactly, the derived kinematics would describe the galaxy only approximately. We apply our met…
We report the discovery of an ultra-faint dwarf in the constellation of Pegasus. Pegasus~V (Peg~V) was initially identified in the public imaging data release of the DESI Legacy Imaging Surveys and confirmed with deep imaging from Gemini/GMOS-N. The colour-magnitude diagram shows a sparse red giant branch (RGB) population and a strong over-density of blue horizontal branch stars. We measure a distance to Peg~V of $D=692^{+33}_{-31}$~kpc, making it a distant satellite of Andromeda with $M_V=-6.3\pm0.2$ and a half-light radius of $r_{\rm half}=89\pm41$~pc. It is located $\sim260$~kpc from Androm…
Our Galaxy and the nearby Andromeda galaxy (M31) are the most massive members of the Local Group, and they seem to be a bound pair, despite the uncertainties on the relative motion of the two galaxies. A number of studies have shown that the two galaxies will likely undergo a close approach in the next 4$-$5 Gyr. We used direct $N$-body simulations to model this interaction to shed light on the future of the Milky Way - Andromeda system and for the first time explore the fate of the two supermassive black holes (SMBHs) that are located at their centers. We investigated how the uncertainties on…
We focus on the evidence of a past minor merger discovered in the halo of the Andromeda galaxy (M31). Previous N-body studies have enjoyed moderate success in producing the observed giant stellar stream (GSS) and stellar shells in M31's halo. The observed distribution of stars in the halo of M31 shows an asymmetric surface brightness profile across the GSS; however, the effect of the morphology of the progenitor galaxy on the internal structure of the GSS requires further investigation in theoretical studies. To investigate the physical connection between the characteristic surface brightness …
We present results from WIYN pODI imaging of Lacerta I (And XXXI), a satellite dwarf galaxy discovered in the outskirts of the Andromeda galaxy (M31) in Pan-STARRS1 survey data. Our deep, wide-field $g,i$ photometry reaches $\sim$3 magnitudes fainter than the photometry in the Pan-STARRS1 discovery paper and allows us to trace the stellar population of Lac I beyond two half-light radii from the galaxy center. We measure a Tip of the Red Giant Branch (TRGB) distance for Lac I of $(m-M)_0=24.44\pm0.11$ mag (773$\pm$40 kpc, or 264$\pm$6 kpc from M31), which is consistent with the Pan-STARRS1 dist…
Our nearest large cosmological neighbour, the Andromeda galaxy (M31), is a dynamical system, and an accurate measurement of its total mass is central to our understanding of its assembly history, the life-cycles of its satellite galaxies, and its role in shaping the Local Group environment. Here, we apply a novel approach to determine the dynamical mass of M31 using high velocity Planetary Nebulae (PNe), establishing a hierarchical Bayesian model united with a scheme to capture potential outliers and marginalize over tracers unknown distances. With this, we derive the escape velocity run of M3…
Observations are presented of the isolated dwarf irregular galaxy And IV made with the Hubble Space Telescope Advanced Camera for Surveys and the Giant Metrewave Radio Telescope in the 21 cm HI line. We determine the galaxy distance of $7.17\pm0.31$ Mpc using the Tip of Red Giant Branch method. The galaxy has a total blue absolute magnitude of -12.81 mag, linear Holmberg diameter of 1.88 kpc and an HI-disk extending to 8.4 times the optical Holmberg radius. The HI mass-to-blue luminosity ratio for And IV amounts $12.9~M_{\odot}/L_{\odot}$. From the GMRT data we derive the rotation curve for th…
We present B and V time series photometry of the M31 satellite galaxy Andromeda XXVII (And XXVII) that we observed with the Large Binocular Cameras of the Large Binocular Telescope. In the field of And XXVII we have discovered a total of 90 variables: 89 RR Lyrae stars and 1 Anomalous Cepheid. The average period of the fundamental mode RR Lyrae stars (RRab) $\langle$P$_{\rm ab}\rangle$=0.59 d ($σ$=0.05 d) and the period-amplitude diagram place And XXVII in the class of Oosterhoff I/Intermediate objects. Combining information from the color-magnitude diagram (CMD) and the variable stars we find…
Andromeda XXI (And XXI) has been proposed as a dwarf spheroidal galaxy with a central dark matter density that is lower than expected in the Standard $Λ$ Cold Dark Matter ($Λ$CDM) cosmology. In this work, we present dynamical observations for 77 member stars in this system, more than doubling previous studies to determine whether this galaxy is truly a low density outlier. We measure a systemic velocity of $v_r=-363.4\pm1.0\,{\rm kms}^{-1}$ and a velocity dispersion of $σ_v=6.1^{+1.0}_{-0.9}\,{\rm kms}^{-1}$, consistent with previous work and within $1σ$ of predictions made within the modified…
