Context. According to radiative models, radio galaxies may produce gamma-ray emission from the first stages of their evolution. However, very few such galaxies have been detected by the Fermi Large Area Telescope (LAT) so far.
Aims. NGC 3894 is a nearby (z = 0.0108) object that belongs to the class of compact symmetric objects (CSOs, i.e., the most compact and youngest radio galaxies), which is associated with a gamma-ray counterpart in the Fourth Fermi-LAT source catalog. Here we present a study of the source in the gamma-ray and radio bands aimed at investigating its high-energy emission and assess its young nature.
Methods. We analyzed 10.8 years of Fermi-LAT data between 100 MeV and 300 GeV and determined the spectral and variability characteristics of the source. Multi-epoch very long baseline array (VLBA) observations between 5 and 15 GHz over a period of 35 years were used to study the radio morphology of NGC 3894 and its evolution.
Results. NGC 3894 is detected in gamma-rays with a significance >9 sigma over the full period, and no significant variability has been observed in the gamma-ray flux on a yearly time-scale. The spectrum is modeled with a flat power law ($Γ$ = 2.0$\pm$0.1) and a flux on the order of 2.2 $\times$ 10$^{-9}$ ph cm$^{-2}$ s$^{-1}$. For the first time, the VLBA data allow us to constrain with high precision the apparent velocity of the jet and counter-jet side to be $β_{\mathrm{app,NW}}$ = 0.132$\pm$0.004 and $β_{\mathrm{app,SE}}$ = 0.065$\pm$0.003, respectively.
Conclusions. Fermi-LAT and VLBA results favor the youth scenario for the inner structure of this object, with an estimated dynamical age of 59$\pm$5 years. The estimated range of viewing angle (10° < $θ$ < 21°) does not exclude a possible jet-like origin of the gamma-ray emission.
We investigate the spatial regularity in the distribution of the young stellar population along spiral arms of three late type spiral galaxies: NGC 895, NGC 5474, and NGC 6946. This study is based on an analysis of photometric properties of spiral arms using {\it GALEX} ultraviolet, optical UBVRI, Halpha, and 8mum {IRAC} infrared surface photometry data. Using the Fourier analysis approach, we found features of spatial regularity or quasi-regularity in the distribution of the young stellar population or (and) regular chains of star formation regions in all arms of NGC 895, NGC 5474, and NGC 69…
The relative contribution of various physical processes to the spatial and temporal distribution of molecular clouds and star-forming regions in the disks of galaxies has not been fully studied. The spatial regularity in the distribution of the young stellar population in spiral and ring structures is a good test to study this contribution. We investigate photometric properties of the ring and spiral arms in the barred spiral galaxy NGC 6217 based on analysis of GALEX ultraviolet, optical UBVRI and Halpha surface photometry data. The ring in the galaxy is located near the corotation area. A sp…
The conventional picture of coeval, chemically homogeneous, populous star clusters -- known as `simple stellar populations' (SSPs) -- is a view of the past. Photometric and spectroscopic studies reveal that almost all ancient globular clusters in the Milky Way and our neighbouring galaxies exhibit star-to-star light-element abundance variations, typically known as 'multiple populations' (MPs). Here, we analyse photometric $\it Hubble$ $\it Space$ $\it Telescope$ observations of three young ($<$2 Gyr-old) Large and Small Magellanic Cloud clusters, NGC 411, NGC 1718 and NGC 2213. We measure the …
NGC 1866: First Spectroscopic Detection of Fast Rotating Stars in a Young LMC Cluster
利用麦哲伦-克莱6.5米望远镜上的密歇根/麦哲伦光纤系统和MSpec摄谱仪，对年轻（$\sim$ 2亿年）大麦哲伦星系团NGC 1866中的29颗扩展主序星进行了高分辨率光谱观测。这些光谱揭示了第一次直接探测到快速旋转的恒星，这些恒星的存在只能从光度研究中推断出来。eMSTO恒星呈现H-α发射（指示Be星递减盘），其他恒星具有浅宽H-α吸收（与旋转$\gtrsim $ 150 km s $^{-1}$一致），或深H-α核心吸收信号较低的旋转速度（$ \lesssim $ 150 km s $^{-1}$）。这些光谱似乎与两个恒星群体一致-一个快速旋转，另一个年轻且缓慢旋转。
Multiple stellar populations (MPs) representing star-to-star light-element abundance variations are common in nearly all ancient Galactic globular clusters. Here we provide the strongest evidence yet that the populous, ~ 1.7 Gyr-old Large Magellanic Cloud cluster NGC 2173 also exhibits light-element abundance variations. Thus, our results suggest that NGC 2173 is the youngest cluster for which MPs have been confirmed to date. Our conclusion is based on the distinct bifurcation at the tip of its red-giant branch in high-quality color--magnitude diagrams generated from Hubble Space Telescope ima…
We present the results of our study of starforming regions in the lenticular galaxy NGC 4324. During a complex analysis of multiwavelength observational data -- the narrow-band emission-line images obtained with the 2.5-m telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University and the archival images in the broad bands of the SDSS, GALEX and WISE surveys -- we have detected young starforming complexes (clumps) located in the inner ring of the lenticular galaxy NGC 4324, and we have established a regular pattern of their distribution…
The aim of this work is to investigate the characteristics of the young stellar population in the spiral galaxy NGC 247. In particular, we focused our attention in its hierarchical clustering distributions and the properties of the smallest groups. We used multiband Hubble Space Telescope (HST) data from three fields covering more than half of NGC 247 to select the young population. Then, through the path linkage criterion (PLC), we found compact young star groups, and estimated their fundamental parameters, such as their stellar densities, sizes, amount of members and luminosity function (LF)…
A primordial group of open clusters containing NGC 6871 is confirmed and described through Gaia DR3 data and the previous literature. It is a star-forming complex containing at least six young OCs, including Teutsch 8, FSR 198 and Biurakan 2. Two nearby OCs (Casado 82 and Casado-Hendy 1) are newly identified and studied in detail and found to be also members of the cited group. The parameters of the components are sufficiently similar to postulate the case of at least six clusters born from a single GMC. None of the cluster pairs of the group seems to be an authentic binary cluster, with the p…
We analyze spectroscopic observations of five young massive clusters (YMCs) in the barred spiral galaxy NGC 1313 to obtain detailed abundances from their integrated light. Our sample of YMCs was observed with the X-Shooter spectrograph on the Very Large Telescope (VLT). We make use of theoretical isochrones to generate synthetic integrated-light spectra, iterating on the individual elemental abundances until converging on the best fit to the observations. We measure abundance ratios for [Ca/Fe], [Ti/Fe], [Mg/Fe], [Cr/Fe], and [Ni/Fe]. We estimate an Fe abundance gradient of $-$0.124 $\pm$ 0.03…
The blue compact dwarf galaxy NGC 5253 hosts a very young central starburst. The center contains intense radio thermal emission from a massive ultracompact H II region (or "supernebula") and two massive and very young super star clusters (SSCs), which are seen at optical and infrared wavelengths. The spatial correspondence between these three objects over an area of < 0.5 arcsec is very uncertain, and it is usually assumed that one of the optically-detected SSCs coincides with the supernebula. Using the Gaia Data Release 2 catalog, we improve the absolute astrometry of Hubble Space Telescope u…
Near-ultraviolet (NUV) spectroscopic studies have suggested that passively evolving massive, early-type galaxies host sub-one percent fractions of young stars in their innermost regions. We shed light on the origin of these stars by analysing NGC 1277, a widely studied nearby prototypical massive compact relic galaxy. These are rare galaxies that have survived without experiencing significant size evolution via accretion and mergers since their formation at high redshift. We obtain a spectrum in the UV range within the central 1 kpc region of NGC 1277. We compare a carefully selected set of op…
Galactic star clusters are known to harbour a significant amount of binary stars, yet their role in the dynamical evolution of the cluster as a whole is not comprehensively understood. We investigated the influence of binary stars on the total mass estimate for the case of the moderately populated Galactic star cluster NGC 225. The analysis of multi-epoch radial velocities of the 29 brightest cluster members, obtained over two observational campaigns, in 1990-1991 and in 2019-2020, yields a value of binary fraction of $α=0.52$ (15 stars out of 29). Using theoretical isochrones and Monte Carlo …
Aims: The purpose of this work is to study the properties of the spatial distribution of the young population in three nearby galaxies in order to better understand the first stages of star formation. Methods: We used ACS/HST photometry and the "path-linkage criterion" in order to obtain a catalog of young stellar groups (YSGs) in the galaxy NGC 2403. We studied the internal distribution of stars in these YSGs using the Q parameter. We extended these analyses to the YSGs detected in in NGC 300 and NGC 253 our previous works. We built the young stars' density maps for these three galaxies. Thro…
Aims. We present positions and velocities for 796 planetary nebulae (PNe) in the Fornax Brightest Cluster Galaxy NGC 1316 (Fornax A). The planetary nebulae and existing kinematics are used to explore the rotation of this merger remnant and constrain dynamical models. Methods. Using FORS2 on the VLT, the PN velocities were measured using a counter-dispersed slitless-spectroscopy technique that produced the largest-to-date sample outside of the Local Group. Spherical, non-rotating, constant-anisotropy Jeans models were con- strained by observations of the planetary nebulae and existing integrate…
NGC 602 is a young, low-metallicity star cluster in the "Wing" of the Small Magellanic Cloud. We reveal the recent evolutionary past of the cluster through analysis of high-resolution ($\sim$0.4 pc) Atacama Large Millimeter/submillimeter Array observations of molecular gas in the associated $\textrm{H}\scriptstyle\mathrm{II}$ region N90. We identify 110 molecular clumps ($R <$ 0.8 pc) traced by CO emission, and study the relationship between the clumps and associated young stellar objects (YSOs) and pre-main-sequence (PMS) stars. The clumps have high virial parameters (typical $α_{\rm{vir}} = …
The spectroscopic and photometric signals of the star-to-star abundance variations found in globular clusters seem to be correlated with global parameters like the cluster's metallicity, mass and age. Understanding this behaviour could bring us closer to the origin of these intriguing abundance spreads. In this work we use deep HST photometry to look for evidence of abundance variations in the main sequence of a young massive cluster NGC 419 ($\sim10^5$ M$_{\odot}$, $\sim1.4$ Gyr). Unlike previous studies, here we focus on stars in the same mass range found in old globulars ($\sim0.75-1$ M$_{\…
We present a detailed chemical abundance analysis of the young massive cluster (YMC) NGC 1569-B. The host galaxy, NGC~1569, is a dwarf irregular starburst galaxy at a distance of 3.36$\pm$0.20 Mpc. We determined the abundance ratios from the analysis of an optical integrated-light spectrum of NGC 1569-B, obtained with the HIRES echelle spectrograph on the Keck I telescope. We considered different red-to-blue supergiant ratios, namely: the ratio obtained from a theoretical isochrone, the ratio obtained from a resolved colour-magnitude diagram of the YMC, and the ratio that minimises the $χ^2$ w…
Young Star Clusters In The Circumnuclear Region Of NGC 2110
近红外高分辨率观测显示，在塞弗特1号NGC 2110的活动星系核（AGN）周围有星团，在其核周围有一个90 x 35 pc的冲击气体物质棒。这些都是第一次看到我们的成像和气体运动学的中央100 pc与凯克OSIRIS仪器与自适应光学。这些星团中的每一个都比靠近银河系中心的拱门星团亮2-3倍。核心恒星形成率（SFR）为0.3 M $_\odot$ /年。光电离气体（He I）动力学意味着封闭质量为3-4 x 10 $^8$ M $_\odot$。这些观测结果证明了活动星系核反馈（触发大质量星团中的恒星形成）与由此产生的恒星风（和SNe）之间的物理联系，后者导致观测到的[Fe II]发射并为黑洞提供能量。
Young planetary nebulae (PNe) retain a large amount of neutral material that was shed in the previous asymptotic giant branch stage. The thick H I region in young PNe can be effectively probed by illuminating far UV radiation that may be inelastically scattered to appear in the optical region. Raman-scattered features are unique spectroscopic tracers of neutral regions that can be used to investigate the mass-loss process in young PNe. We conduct high resolution spectroscopy of young PNe using BOES (the Bohyunsan Observatory Echelle Spectrograph) and report the discovery of a Raman-scattered H…
We report the detection of a black hole (NGC 1850 BH1) in the $\sim$100 Myr-old massive cluster NGC~1850 in the Large Magellanic Cloud. It is in a binary system with a main-sequence turn-off star (4.9 $\pm$ 0.4 M${_\odot}$), which is starting to fill its Roche Lobe and becoming distorted. Using 17 epochs of VLT/MUSE observations we detected radial velocity variations exceeding 300 km/s associated to the target star, linked to the ellipsoidal variations measured by OGLE-IV in the optical bands. Under the assumption of a semi-detached system, the simultaneous modelling of radial velocity and lig…
