We study the effects of passages of compact objects such as stars, star clusters, and black holes through molecular clouds, and propose that the gravitational interaction between the compact object and the ambient gas can lead to the formation of thin and collimated features made of dense gas, which we call "molecular contrails". Supercritical contrails can collapse further leading to triggered star formation. The width of a molecular contrail is determined by the mass and velocity of the compact object and the velocity dispersion of the ambient molecular medium. Under typical conditions in the Milky Way, passages of stellar-mass objects lead to the formation of width $d\gtrsim 0.01\;\rm {parsec}$ contrails, and passages of star clusters lead to the formation of $d\gtrsim 1\;\rm {parsec}$ contrails. We present a few molecular contrail candidates from both categories identified from ALMA 1.3mm continuum observations of star-forming regions and the $^{13}$CO(1-0) map from the Galactic Ring Survey respectively. The contrails represent an overlooked channel where stars and gas in the Galactic disk interact to for structures. They also present a potential way of detecting dark compact objects in the Milky Way.
Galaxy interaction is considered a key driver of galaxy evolution and star formation (SF) history. In this paper, we present an empirical picture of the radial extent of interaction-triggered SF along the merger sequence. The samples under study are drawn from the integral field spectroscopy (IFS) survey SDSS-IV MaNGA, including 205 star-forming galaxies in pairs/mergers and ~1350 control galaxies. For each galaxy in pairs, the merger stage is identified according to its morphological signatures: incoming phase, at first pericenter passage, at apocenter, in merging phase, and in final coalesce…
Elongated, bar-like galaxies without a significant disk component, with little rotation support and no gas, often form as a result of tidal interactions with a galaxy cluster, as was recently demonstrated using the IllustrisTNG-100 simulation. Galaxies that exhibit similar properties are, however, also found to be infalling into the cluster for the first time. We use the same simulation to study in detail the history of such a galaxy over cosmic time in order to determine its origin. The bar appears to be triggered at t=6.8 Gyr by the combined effect of the last significant merger with a subha…
We report the discovery of a young (${\rm age} \sim 130~{\rm Myr}$), low-mass ($M \sim 1200~{\rm M}_\odot$), metal-poor ($[{\rm Fe}/{\rm H}] \sim -1.1$) stellar association at a heliocentric distance $D \approx 29~{\rm kpc}$, placing it far into the Milky Way halo. At its present Galactocentric position $(R, z) \sim (23, 15)~{\rm kpc}$, the association is (on the sky) near the leading arm of the gas stream emanating from the Magellanic cloud system, but is located $\approx 60^\circ$ from the Large Magellanic Cloud (LMC) center on the other side of the Milky Way disk. If we assume that the clus…
Leo I is considered one of the youngest dwarf spheroidals (dSph) in the Local Group. Its isolation, extended star formation history (SFH), and recent perigalacticon passage (~1 Gyr ago) make Leo~I one of the most interesting nearby stellar systems. Here, we analyse deep photometric Hubble Space Telescope data via colour-magnitude diagram fitting techniques to study its global and radially-resolved SFH. We find global star formation enhancements in Leo I ~13, 5.5, 2.0, and 1.0 Gyr ago, after which it was substantially quenched. Within the context of previous works focused on Leo I, we interpret…
A clear link between a dwarf-dwarf merger event and enhanced star formation (SF) in the recent past was recently identified in the gas-dominated merger remnant VCC 848, offering by far the clearest view of a gas-rich late-stage dwarf-dwarf merger. We present a joint analysis of JVLA HI emission-line mapping, optical imaging and numerical simulations of VCC 848, in order to examine the impact of the merger on the stellar and gaseous distributions. VCC 848 has less than 30% of its HI gas concentrated within the central high-surface-brightness star-forming region, while the remaining HI is entrai…
Star cluster formation history along the minor axis of the Large Magellanic Cloud
我们分析了华盛顿$CMT_1$测光的星团位于沿短轴的LMC，从LMC光学中心到$\sim$ 39度向外西北。利用数据库，以寻找新的星团候选人，产生集群CMD清理场星污染，并获得年龄估计的统计上完整的集群样本。我们确认了146个星团候选者是真正的物理系统，并得出结论，在调查区域中，总的$\sim$ 30%的编目星团不太可能是真正的物理系统。我们没有发现任何新的集群候选人在郊区的大麦哲伦星系（去投影距离$\ge$ 8度）。所研究的星团的年龄范围为7.2 < log（$t$ yr $^{-1}$）$\le$ 9.4，唯一的例外是球状星团NGC 1，1786（log（$t$ yr $^{-1}$）= 10.10）。我们还计算了每个地区的集群频率，从中我们确认了先前提出的外部-内部情景。此外，我们发现外LMC领域显示突然发作的团簇形成（log（$t$ yr $^{-1}$）$\sim$ 7.8-7.9），持续直到log（$t$ yr $^{-1}$）$\sim$ 7.3只在最外层LMC区域。我们链接这些功能的第一个近心点通道的LMC的MW，这可能会引发团簇形成由于冲压压力之间的相互作用的LMC和MW晕。
The Fornax dwarf spheroidal galaxy has an anomalous number of globular clusters, five, for its stellar mass. There is a longstanding debate about a potential sixth globular cluster (Fornax~6) that has recently been `rediscovered' in DECam imaging. We present new Magellan/M2FS spectroscopy of the Fornax~6 cluster and Fornax dSph. Combined with literature data we identify $\sim15-17$ members of the Fornax~6 cluster that this overdensity is indeed a star cluster and associated with the Fornax dSph. The cluster is significantly more metal-rich (mean metallicity of $\overline{\rm [Fe/H]}=-0.71\pm0.…
We report three-dimensional hydrodynamical simulations of shocks (${\cal M_{\rm shock}}\geq 4$) interacting with fractal multicloud layers. The evolution of shock-multicloud systems consists of four stages: a shock-splitting phase in which reflected and refracted shocks are generated, a compression phase in which the forward shock compresses cloud material, an expansion phase triggered by internal heating and shock re-acceleration, and a mixing phase in which shear instabilities generate turbulence. We compare multicloud layers with narrow ($σ_ρ=1.9\barρ$) and wide ($σ_ρ=5.9\barρ$) log-normal …
The Milky Way's central molecular zone (CMZ) has emerged in recent years as a unique laboratory for the study of star formation. Here we use the simulations presented in Tress et al. 2020 to investigate star formation in the CMZ. These simulations resolve the structure of the interstellar medium at sub-parsec resolution while also including the large-scale flow in which the CMZ is embedded. Our main findings are as follows. (1) While most of the star formation happens in the CMZ ring at $R\gtrsim100 {\, \rm pc}$, a significant amount also occurs closer to SgrA* at $R \lesssim 10{\, \rm pc}$. (…
Spatially resolved star-formation histories of local post-starburst galaxies: Starburst and quenching spatial patterns consistent with recent mergers
University of St Andrews（圣安德鲁斯大学）；University of Edinburgh（爱丁堡大学）；Imperial College London（帝国理工学院）；University of Hertfordshire（赫特福德大学）；Anqing Normal University（安庆师范大学）
Co-evolution of the Milky Way high- and low-α sequences with chemical evolution models
INAF, Osservatorio Astronomico di Trieste（意大利国家天体物理研究所，的里雅斯特天文台）；IFPU, Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Dipartimento di Fisica, Sezione di Astronomia, Università di Trieste（的里雅斯特大学，物理系，天文学部）；INFN Sezione di Trieste（意大利国家核物理研究所，的里雅斯特分部）
本文通过改进的化学演化模型探讨银河盘内高α和低α序列的共同演化及古老低α星的存在，解释了观测到的[α/Fe] vs [Fe/H]图谱。
