The Galactic HII region luminosity function (LF) is an important metric for understanding global star formation properties of the Milky Way, but only a few studies have been done and all use relatively small numbers of HII regions. We use a sample of 797 first Galactic quadrant HII regions compiled from the WISE Catalog of Galactic HII Regions to examine the form of the LF at multiple infrared and radio wavelengths. Our sample is statistically complete for all regions powered by single stars of type O9.5V and earlier. We fit the LF at each wavelength with single and double power laws. Averaging the results from all wavelengths, the mean of the best-fit single power law index is $\langleα\rangle=-1.75\,\pm\,0.01$. The mean best-fit double power law indices are $\langleα_1\rangle=-1.40\,\pm\,0.03$ and $\langleα_2\rangle=-2.33\,\pm\,0.04$. We conclude that neither a single nor a double power law is strongly favored over the other. The LFs show some variation when we separate the HII region sample into subsets by heliocentric distance, physical size, Galactocentric radius, and location relative to the spiral arms, but blending individual HII regions into larger complexes does not change the value of the power law indices of the best-fit LF models. The consistency of the power law indices across multiple wavelengths suggests that the LF is independent of wavelength. This implies that infrared and radio tracers can be employed in place of H$α$.
We use an unprecedented sample of about 23,000 HII regions detected at an average physical resolution of 67pc in the PHANGS-MUSE sample to study the extragalactic HII region Ha luminosity function (LF). Our observations probe the star-forming disk of 19 nearby spiral galaxies with low inclination and located close to the star formation main sequence at z=0. The mean LF slope $α$ in our sample is =1.73 with a $σ$ of 0.15. We find that $α$ decreases with the galaxy's star formation rate surface density and argue that this is driven by an enhanced clustering of young stars at high gas surface den…
This is the first paper of a series dedicated to nebular physics and the chemical evolution of nearby galaxies by investigating large samples of HII regions with the CFHT imaging spectrograph SITELLE. We present a technique adapted to imaging spectroscopy to identify and extract parameters from 4285 HII region candidates found in the disc of NGC628. Using both the spatial and spectral capabilities of SITELLE, our technique enables the extraction of the position, dust extinction, velocity, Halpha profile, diffuse ionised gas (DIG) background, luminosity, size, morphological type, and the emissi…
This paper investigates the gravitational trapping of HII regions predicted by steady-state analysis using radiation hydrodynamical simulations. We present idealised spherically symmetric radiation hydrodynamical simulations of the early evolution of HII regions including the gravity of the central source. As with analytic steady state solutions of spherically symmetric ionised Bondi accretion flows, we find gravitationally trapped HII regions with accretion through the ionisation front onto the source. We found that, for a constant ionising luminosity, fluctuations in the ionisation front are…
Comparative internal kinematics of the HII regions in interacting and isolated galaxies: implications for massive star formation modes
我们利用位于La Palma的Observatorio del Roque de los Muchachos的$4.2\rm{m}$ William Herschel望远镜（WHT）上的法布里-珀罗干涉仪GH $α$ FaS（Galaxy H $α$ Fabry-Perot system）观测了10个相互作用的星系对。我们在这里提出的H $α$表面亮度，速度和速度色散的地图，我们以前没有观察到使用这种技术，以及物理性质（大小，H $α$光度和速度色散）的1259 HII地区从完整的样本。我们还推导出1054个HII区的物理性质的样本中的28个孤立的星系观察到同一仪器，以比较两个人口的HII区。我们发现一个人口的最亮的HII地区的缩放关系，例如H $α$光度和半径之间的关系，是明显不同的关系，较低的光度的地区。在这个明亮的群体中的区域在相互作用的星系中更常见。我们发现，在相互作用的星系中的HII区的湍流，也是恒星形成率，增强。我们还提取了两个样本的HII区的H $α$等效宽度，发现两个样本的HII区年龄分布是一致的。我们认为，SFR增强所带来的气体流动引起的相互作用，从而产生引力约束的气体云，进一步增长的吸积从流动的气体，产生有利于恒星形成的条件。
The Southern HII Region Discovery Survey (SHRDS): Pilot Survey
南HII区发现巡天（英语：Southern HII Region Discovery Survey，缩写：SHRDS）是对银河平面第三和第四象限的巡天，将使用澳大利亚望远镜紧凑阵列探测数百个HII区候选者的厘米波长射电复合线和连续辐射。这次巡天的目标来自银河系HII区域的WISE目录，并根据中红外和无线电连续辐射确定。在这一试点项目中，紧凑阵列宽带接收器和分光计系统的两种不同配置被用于短期试验观测。试验性调查从53个HII区域候选者中的36个以及7个已知的\hii区域中检测到了无线电复合线发射。这36个重组线检测证实候选者是真正的HII区域，并允许我们估计它们的距离。
The Luminosity Functions and Timescales of MYSOs and Compact HII regions
我们提出了一个确定的光度函数的大规模的年轻恒星对象（MYSO）和紧凑的（C）HII地区的银河系内使用的大型，精心挑选的样本，这些来源确定的红色MSX源（RMS）的调查。MYSO光度函数单调减小，使得在$L\gtrsim 10^{5}$ Lsol的情况下几乎没有，当CHII区域被检测到高达~10个$^{6}Lsol. The lifetimes of these phases are also calculated as a function of luminosity by comparison with the luminosity function for local main-sequence OB stars. These indicate that the MYSO phase has a duration ranging from 4x10$ ^{5} $ yrs for 10$ ^{4} $Lsol to ~7x10$ ^{4} $ yrs at 10$ ^{5} $Lsol, whilst the CHII region phase lasts of order 3x10$ ^{5} $ yrs or ~3-10% of the exciting star's main-sequence lifetime. MYSOs between 10$ ^{4} Lsol和~…
We presented a multi-wavelength study of AFGL 333-Ridge. The molecular line data reveals that the AFGL 333-Ridge has two independent velocity components at -50.5 km/s and -48.0 km/s. In the Position-Velocity diagram, the bridge feature connects with two parts that are spatially correlated but separated in velocity. These observational evidences support the scenario that the two velocity components have collided and merged into one molecular cloud. The majority of Class I YSOs are distributed within the collision region, suggesting that the cloud-cloud collision has induced the YSOs formation i…
The tight correlation between turbulence and luminosity in Giant HII Regions is not well understood. While the luminosity is due to the UV radiation from the massive stars in the ionizing clusters, it is not clear what powers the turbulence. Observations of the two prototypical Giant HII Regions in the local Universe, 30 Doradus and NGC604, show that part of the kinetic energy of the nebular gas comes from the combined stellar winds of the most massive stars - the cluster winds, but not all. We present a study of the kinematics of 30 Doradus based on archival VLT FLAMES/GIRAFFE data and new hi…
Star formation activity in the southern Galactic HII region G351.63-1.25
银河系南部的高质量恒星形成区G351.6-1.3是一个HII区-分子云复合体，光度为2.0 x 10^5 L_sun，距离2.4 kpc。本文主要研究G351.6-1.3附近的HII区、嵌入星系团和星际介质。我们解决的激励源的识别以及人口普查的恒星星族。电离气体的分布已被映射使用巨型米波射电望远镜（GMRT），印度在三个连续频率：1280，610和325兆赫。HII区域显示出细长的形态，1280 MHz图包括6个分辨的高密度区域，由跨越1.4 pc x 1.0 pc的扩散发射包围。最亮的射电核心的零龄主序（ZAMS）谱型为O7.5。我们进行了近红外观测在JHKs波段使用SIRIUS仪器的1.4米红外测量设施（IRSF）望远镜。近红外图像揭示了一个嵌入星云状扇形辐射中的星团的存在。嵌入星团K波段光度函数的对数正态斜率为0.27 ± 0.03，近红外多余星的比例估计为43%。这表明星团的年龄与100万年一致。香槟流模型从一个平坦的，薄的分子云被用来解释相对于毫米云和红外亮度的无线电发射的形态。
We present a new catalog of HII regions based on the integral field spectroscopy (IFS) data of the extended CALIFA and PISCO samples. The selection of HII regions was based on two assumptions: a clumpy structure with high contrast of H$α$ emission and an underlying stellar population comprising young stars. The catalog provides the spectroscopic information of 26,408 individual regions corresponding to 924 galaxies, including the flux intensities and equivalent widths of 51 emission lines covering the wavelength range between 3745-7200A. To our knowledge, this is the largest catalog of spectro…
The NGC 346 young stellar system and associated N66 giant HII region in the Small Magellanic Cloud are the nearest example of a massive star forming event in a low metallicity ($Z\approx0.2Z_{\odot}$) galaxy. With an age of $\lesssim$3Myr this system provides a unique opportunity to study relationships between massive stars and their associated HII region. Using archival data, we derive a total H$α$ luminosity of L(H$α$)=4.1$\times$10$^{38}$ergs$^{-1}$ corresponding to an H-photoionization rate of 3$\times$10$^{50}$s$^{-1}$. A comparison with a predicted stellar ionization rate derived from th…
We discuss the first results from our mid-infrared imaging survey of Milky Way Giant HII regions with our detailed analysis of W51A, which is one of the largest GHII regions in our Galaxy. We used the FORCAST instrument on SOFIA to obtain 20 and 37$μ$m images of the central $10' \times 20'$ area, which encompasses both of the G49.5-0.4 and G49.4-0.3 sub-regions. Based on these new data, and in conjunction with previous multi-wavelength observations, we conjecture on the physical nature of several individual sources and sub-components within W51A. We find that extinction seems to play an import…
The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Halpha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the Canada-French-Hawaii telescope (CFHT). We use a new set of data extracted from VESTIGE to study the impact of the hostile cluster environment on the star formation process down to the scale of HII regions (~ 50 pc). HII regions are identified and their parameters measured using the HIIphot code on a sample of 114 late-type galaxies spanning a wide range in morphological type (Sa-Sd, Im, BCD), stellar mass (10^6.5 <= M_star…
We present our third set of results from our mid-infrared imaging survey of Milky Way Giant HII (GHII) regions with our detailed analysis of W49A, one of the most distant, yet most luminous, GHII regions in the Galaxy. We used the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) to obtain 20 and 37$μ$m images of the entire ~5.0' x 3.5' infrared-emitting area of W49A at a spatial resolution of ~3". Utilizing these SOFIA data in conjunction with previous multi-wavelength observations from the near-infrared to radio, including Spitzer-IRAC and Herschel-PACS archi…
Stellar feedback, the energetic interaction between young stars and their birthplace, plays an important role in the star formation history of the universe and the evolution of the interstellar medium (ISM). Correctly interpreting the observations of star-forming regions is essential to understand stellar feedback, but it is a non-trivial task due to the complexity of the feedback processes and degeneracy in observations. In our recent paper, we introduced a conditional invertible neural network (cINN) that predicts seven physical properties of star-forming regions from the luminosity of 12 op…
Investigating HII Regions in the Disk of NGC 7331 with the Circumgalactic H$α$ Spectrograph
Steward Observatory, University of Arizona（亚利桑那大学斯图尔德天文台）；School of Physics and Astronomy, Rochester Institute of Technology（罗切斯特理工学院物理与天文学学院）；Department of Astronomy, Columbia University（哥伦比亚大学天文学系）；Columbia Astrophysics Laboratory, Columbia University（哥伦比亚大学哥伦比亚天体物理实验室）；Department of Physics, Columbia University（哥伦比亚大学物理学系）
The star-forming activity in the HII region RCW 42 is investigated using multiple wavebands, from near-infrared to radio wavelengths. Located at a distance of 5.8 kpc, this southern region has a bolometric luminosity of 1.8 $\times$ 10$^6$ L$_{\odot}$. The ionized gas emission has been imaged at low radio frequencies of 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India and shows a large expanse of the HII region, spanning $20\times 15$ pc$^2$. The average electron number density in the region is estimated to be $\sim70$ cm$^{-3}$, which suggests an average ionization fraction o…
This is the fourth paper exploring the infrared properties of giant HII regions with the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). Our survey utilizes the census of 56 Milky Way giant HII regions identified by Conti & Crowther (2004), and in this paper we present the 20 and 37 micron imaging data we have obtained from SOFIA for sources Sgr D and W42. Based upon the SOFIA data and other multi-wavelength data, we derive and discuss the detailed physical properties of the individual compact sources and sub-regions as well as the large scale properties of …
We present our second set of results from our mid-infrared imaging survey of Milky Way Giant HII regions. We used the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy to obtain 20 and 37$μ$m images of the central ~10'X10' area of M17. We investigate the small- and large-scale properties of M17 using our data in conjunction with previous multi-wavelength observations. The spectral energy distributions of individual compact sources were constructed with Spitzer-IRAC, SOFIA-FORCAST, and Herschel-PACS photometry data and fitted with massive young stellar object (MYSO) mod…
We have carried out the largest and most unbiased search for hypercompact (HC) HII regions. Our method combines four interferometric radio continuum surveys (THOR, CORNISH, MAGPIS and White2005) with far-infrared and sub-mm Galactic Plane surveys to identify embedded HII regions with positive spectral indices. 120 positive spectrum HII regions have been identified from a total sample of 534 positive spectral index radio sources. None of these HII regions, including the known HCHII regions recovered in our search, fulfills the canonical definition of an HCHII region at 5 GHz. We suggest that th…
The role of ionization feedback on high-mass (>8 Msun) star formation (HMSF) is still highly debated. Questions remain concerning the presence of nearby HII regions changes the properties of early HMSF and whether HII regions promote or inhibit the formation of high-mass stars. To characterize the role of HII regions on the HMSF, we study the properties of a sample of candidates high-mass starless clumps (HMSCs), of which about 90% have masses larger than 100 Msun. These high-mass objects probably represent the earliest stages of HMSF; we search if (and how) their properties are modified by th…
