We study the two main constituent galaxies of a constrained simulation of the Local Group as candidates for the Milky Way (MW) and Andromeda (M31). We focus on the formation of the stellar discs and its relation to the formation of the group as a rich system with two massive galaxies, and investigate the effects of mergers and accretion as drivers of morphological transformations. We use a state-of-the-art hydrodynamical code which includes star formation, feedback and chemical enrichment to carry out our study. We run two simulations, where we include or neglect the effects of radiation pressure from stars, to investigate the impact of this process on the morphologies and star formation rates of the simulated galaxies. We find that the simulated M31 and MW have different formation histories, even though both inhabit, at z=0, the same environment. These differences directly translate into and explain variations in their star formation rates, in-situ fractions and final morphologies. The M31 candidate has an active merger history, as a result of which its stellar disc is unable to survive unaffected until the present time. In contrast, the MW candidate has a smoother history with no major mergers at late times, and forms a disc that grows steadily; at z=0 the simulated MW has an extended, rotationally-supported disc which is dominant over the bulge. Our two feedback implementations predict similar evolution of the galaxies and their discs, although some variations are detected, the most important of which is the formation time of the discs: in the model with weaker/stronger feedback the discs form earlier/later. In summary, by comparing the formation histories of the two galaxies, we conclude that the particular merger/accretion history of a galaxy rather than its environment at the LG-scales is the main driver of the formation and subsequent growth or destruction of galaxy discs.
Our Milky Way provides a unique test case for galaxy evolution models, thanks to our privileged position within the Milky Way's disc. This position also complicates comparisons between the Milky Way and external galaxies, due to our inability to observe the Milky Way from an external point of view. Milky Way analog galaxies offer us a chance to bridge this divide by providing the external perspective that we otherwise lack. However, over-precise definitions of "analog" yield little-to-no galaxies, so it is vital to understand which selection criteria produce the most meaningful analog samples.…
A Mote in Andromeda's Disk: a Misidentified Periodic AGN Behind M31
我们在M31的盘面上发现了一个以前被认为是恒星的天体J0045+41，它是通过M31的低吸收区看到的背景$z\approx0.215$活动星系核。我们提出了中等分辨率光谱的J0045+41获得GMOS在Gemini北。光谱包含了归属于宿主星系的特征。我们的光谱模型来估计活动星系核的贡献，从我们估计的中心引擎的光度和维里质量。我们的拟合显示了一个蓝移的组件，以广泛的H $α$和H $β$在相对速度为$\sim4800$ km s $^{-1}$。我们还检测到\ion{Na}{1}吸收银河系restframe。我们使用Palomar瞬变工厂的$g$波段测光来寻找周期性的证据，并找到了从$\sim80-350$天到多个周期性的证据。两个检测到的周期是在一个1：4的比例，这是相同的流体动力学模拟的双超大质量黑洞系统的预测。如果这些信号是由于这样的系统而产生的，那么J0045+41就处于引力波范围内。我们计算的时间，直到螺旋由于引力辐射，假设合理的值的质量比的两个黑洞。我们讨论了我们的研究结果和即将开展的工作，以确定其他这样的闯入者在即将到来的光度调查，如Zwicky瞬态设施（ZTF）或大型综合巡天望远镜（LSST）项目的影响。
We present the properties of Milky Way- and Andromeda-like (MW/M31-like) galaxies simulated within TNG50, the highest-resolution run of the IllustrisTNG suite of $Λ$CDM magneto-hydrodynamical simulations. We introduce our fiducial selection for MW/M31 analogs, which we propose for direct usage as well as for reference in future analyses. TNG50 contains 198 MW/M31 analogs, i.e. galaxies with stellar disky morphology, with a stellar mass in the range of $M_* = 10^{10.5 - 11.2}$ Msun, and within a MW-like Mpc-scale environment at z=0. These are resolved with baryonic (dark matter) mass resolution…
Half of the satellite galaxies of Andromeda form a narrow plane termed the Great Plane of Andromeda (GPoA), and their line-of-sight velocities display correlation reminiscent of a rotating structure. Recently reported first proper motion measurements for the on-plane satellites NGC 147 and NGC 185 indicate that they indeed co-orbit along the GPoA. This provides a novel opportunity to compare the M31 satellite system to $Λ$CDM expectations. We perform the first detailed comparison of the orbital alignment of two satellite galaxies beyond the Milky Way with several hydrodynamical and dark-matter…
The Merger-Driven Origin of the Vast Extended Stellar Disc Around the Andromeda Galaxy
National and Kapodistrian University of Athens（雅典国立卡波蒂斯坦大学）；European Southern Observatory（欧洲南方天文台）；Observatoire de Paris（巴黎天文台）；PSL Research University（PSL研究大学）；CNRS（法国国家科学研究中心）；Max-Planck-Institut für extraterrestrische Physik (MPE)（马克斯·普朗克地外物理研究所）；University Observatory Munich (USM)（慕尼黑大学天文台）
The survey of planetary nebulae in Andromeda (M31) VII. Predictions of a major merger simulation model compared with chemodynamical data of the disc and inner halo substructures
We analyse the location of extremely metal-poor stars (EMPs, [Fe/H]$ < -3$) in 198 Milky Way (MW)/M31-like galaxies at $z=0$ in the TNG50 simulation. Each system is divided into four kinematically-defined morphological stellar components based on stellar circularity and galactocentric distance, namely bulge, cold disk, warm disk, and stellar halo, in addition to satellites (with stellar mass $\ge 5\times10^6\,M_\odot$). According to TNG50 and across all simulated systems, the stellar halo of the main galaxy and satellites present the highest frequency of EMPs (largest $M_{\mathrm{EMP, comp}}$-…
Morphological estimators on Sunyaev--Zel'dovich maps of MUSIC clusters of galaxies
星系团形态的确定对星系团的宇宙学和天体物理学研究具有重要意义。在本文中，我们解决的形态特征的合成地图的Sunyaev-Zel'dovich（SZ）的影响产生的样本258个大规模的集群（$M_{vir}>5\times10^{14}h^{-1}$ M $_\odot$在$z=0$），提取的MUSIC流体动力学模拟。具体来说，我们应用五个已知的形态学参数，已经在X射线，两个新引入的，我们将它们结合在一起，在一个单一的参数。我们分析了两组模拟得到的不同处方的气体物理（非辐射和冷却，恒星形成和恒星反馈）在四个红移0.43和0.82之间。对于每个参数，我们测试其稳定性和效率，以区分真正的集群动力学状态，测量的理论指标。组合参数更有效地区分放松和干扰的集群。该参数与流体静力学质量（$\sim 0.3$）有轻度相关性，与SZ质心和群集质心之间的偏移量（$\sim 0.8$）有较强相关性。后者的数量结果作为SZ研究的动态状态的最容易和有效的指标。
We analyze the merger and assembly histories of Milky Way (MW) and Andromeda (M31)-like galaxies to quantify how, and how often, disk galaxies of this mass can survive recent major mergers (stellar mass ratio $\ge$ 1:4). For this, we use the cosmological magneto-hydrodynamical simulation TNG50 and identify 198 analog galaxies, selected based on their $z=0$ stellar mass ($10^{10.5-11.2} {\rm M_{\odot}}$), disky stellar morphology and local environment. Firstly, major mergers are common: 85 per cent (168) of MW/M31-like galaxies in TNG50 have undergone at least one major merger across their life…
The Thesis is an attempt to combine data from three previously independent areas - the structure and kinematics of stellar populations of the Galaxy, photometric and dynamical models of galaxies, and models of the dynamical and physical evolution of galaxies. This synthesis was made with the goal to understand better the vast topic of the structure and evolution of galaxies. The main results of the study can be divided into methodical and astronomical. The methodical results are 1) extrapolation of the mass distribution function beyond the Sun distance, and the determination of the circular ve…
Galaxy shapes in Magneticum. I. Connecting stellar and dark matter shapes to dynamical and morphological galaxy properties and the large-scale structure
The star formation history of NGC 2276: Comparison between SED modeling and hydrodynamical simulations
University of Zagreb（萨格勒布大学）；INAF–Padova Astronomical Observatory（意大利国家天体物理研究所帕多瓦天文台）；Universidad Tecnica Federico Santa Maria（费德里科·Santa María理工大学）；Millenium Nucleus for Galaxies (MINGAL)（星系千年核心（MINGAL））；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）；Waterloo Centre for Astrophysics, University of Waterloo（滑铁卢大学天体物理中心）；Department of Physics & Astronomy, University of Waterloo（滑铁卢大学物理与天文系）；Georgia Institute of Technology（佐治亚理工学院）；INAF–Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）
Hydrodynamical simulations of galaxy formation and evolution attempt to fully model the physics that shapes galaxies. The agreement between the morphology of simulated and real galaxies, and the way the morphological types are distributed across galaxy scaling relations are important probes of our knowledge of galaxy formation physics. Here we propose an unsupervised deep learning approach to perform a stringent test of the fine morphological structure of galaxies coming from the Illustris and IllustrisTNG (TNG100 and TNG50) simulations against observations from a subsample of the Sloan Digita…
We use a large sample of isolated dark matter halo pairs drawn from cosmological N-body simulations to identify candidate systems whose kinematics match that of the Local Group of Galaxies (LG). We find, in agreement with the "timing argument" and earlier work, that the separation and approach velocity of the Milky Way (MW) and Andromeda (M31) galaxies favour a total mass for the pair of $\sim 5\times 10^{12} \,M_{\odot}$. A mass this large, however, is difficult to reconcile with the small relative tangential velocity of the pair, as well as with the small deceleration from the Hubble flow ob…
The optical morphology of galaxies is strongly related to galactic environment, with the fraction of early-type galaxies increasing with local galaxy density. In this work we present the first analysis of the galaxy morphology-density relation in a cosmological hydrodynamical simulation. We use a convolutional neural network, trained on observed galaxies, to perform visual morphological classification of galaxies with stellar masses $M_\ast > 10^{10} \, \mathrm{M}_\odot$ in the EAGLE simulation into elliptical, lenticular and late-type (spiral/irregular) classes. We find that EAGLE reproduces …
The existence of mutually correlated thin and rotating planes of satellite galaxies around both the Milky Way (MW) and Andromeda (M31) calls for an explanation. Previous work in Milgromian dynamics (MOND) indicated that a past MW-M31 encounter might have led to the formation of these satellite planes. We perform the first-ever hydrodynamical MOND simulation of the Local Group using Phantom of RAMSES. We show that an MW-M31 encounter at $z \approx 1$, with a perigalactic distance of about 80 kpc, can yield two disc galaxies at $z=0$ oriented similarly to the observed galactic discs and separate…
Multi-wavelength features of Fermi Bubbles as signatures of a Galactic wind
使用流体动力学模拟，我们第一次表明，在银河系中心的恒星形成的插曲，与恒星形成率（SFR）$\sim 0.5$ M $_\odot$年$^{-1}$为$\sim 30$万年，可以产生类似于费米泡（FB）的泡沫，当从太阳的位置。FB的形态，范围和多波长观测，特别是X射线，限制了各种物理参数，如SFR，年龄和环银河系介质（CGM）密度。我们表明，CGM与银河风驱动的恒星形成在中心区域的相互作用可以解释所观察到的表面亮度和形态特征的X射线与费米泡。此外，假设宇宙射线电子通过冲击和/或湍流被加速{ \it in situ}，可以解释伽马射线发射的亮度和形态以及微波雾。在我们的模型中，冷团和暖团的运动学也与最近通过气泡观察到的吸收线相匹配。
We study the morphologies of 3,964 galaxies and their progenitors with $M_\star > 10^{10} M_\odot$ in the reference EAGLE hydrodynamical simulation from redshifts $z=1$ to $z=0$, concentrating on the redshift evolution of the bar fraction. We apply two convolutional neural networks (CNNs) to classify 35,082 synthetic g-band images across 10 snapshots in redshift. We identify galaxies as either barred or unbarred, while also classifying each sample into one of four morphological types: elliptical (E), lenticular (S0), spiral (Sp), and irregular/miscellaneous (IrrM). We find that the bar fractio…
We investigate the spatially-resolved morphology of galaxies in the early Universe. We consider a typical redshift z = 6 Lyman Break galaxy, "Althaea" from the SERRA hydrodynamical simulations. We create mock rest-frame ultraviolet, optical, and far-infrared observations, and perform a two-dimensional morphological analysis to de-blend the galaxy disk from substructures (merging satellites or star-forming regions). We find that the [CII]158um emitting region has an effective radius 1.5 - 2.5 times larger than the optical one, consistent with recent observations. This [CII] halo in our simulate…
In our hierarchical structure-formation paradigm, the observed morphological evolution of massive galaxies -- from rotationally-supported discs to dispersion-dominated spheroids -- is largely explained via galaxy merging. However, since mergers are likely to destroy discs, and the most massive galaxies have the richest merger histories, it is surprising that any discs exist at all at the highest stellar masses. Recent theoretical work by our group has used a cosmological, hydrodynamical simulation to suggest that extremely massive (M* > 10^11.4 MSun) discs form primarily via minor mergers betw…
