We present new extinction maps and high-resolution Paschen alpha images of G-0.02-0.07, a complex of compact HII regions located adjacent to the M-0.02-0.07 giant molecular cloud, 6 parsecs in projection from the center of the Galaxy. These HII regions, which lie in projection just outside the boundary of the Sgr A East supernova remnant, represent one of the most recent episodes of star formation in the central parsecs of the Galaxy. The 1.87 micron extinctions of regions A, B and C are almost identical, approximately 1.5 magnitudes. Region D, in contrast, has a peak 1.87 micron extinction of 2.3 magnitudes. Adopting the Nishiyama et al. (2008) extinction law, we find these extinctions correspond to visual extinctions of A_V = 44.5 and A_V = 70, respectively. The similar and uniform extinctions of regions A, B and C are consistent with that expected for foreground extinction in the direction of the Galactic center, suggesting that they lie at the front side of the M-0.02-0.07 molecular cloud. Region D is more compact, has a higher extinction and is thus suspected to be younger and embedded in a dense core in a compressed ridge on the western edge of this cloud.
We present new criteria for selecting HII regions from the Infrared Astronomical Satellite (IRAS) Point Source catalogue (PSC), based on an HII region catalogue derived manually from the all-sky Wide-field Infrared Survey Explorer (WISE). The criteria are used to augment the number of HII region candidates in the Milky Way. The criteria are defined by the linear decision boundary of two samples: IRAS point sources associated with known HII regions, which serve as the HII region sample, and IRAS point sources at high Galactic latitudes, which serve as the non-HII region sample. A machine learni…
Large-scale radio continuum surveys provide data to get insights into the physical properties of radio sources. HII regions are prominent radio sources produced by thermal emission of ionised gas around young massive stars. We identify and analyse HII regions in the Sino-German 6cm polarisation survey of the Galactic plane. Objects with flat radio continuum spectra together with infrared and/or Halpha emission were identified as HII regions. For HII regions with small apparent sizes, we cross-matched the 6cm small-diameter source catalogue with the radio HII region catalogue compiled by Paladi…
We evaluate the role of radiation pressure in the dynamics of HII regions. We first determine under what conditions radiation pressure is significant in comparison to gas pressure and show that, while radiation pressure is generally unimportant for HII regions driven by a handful of massive stars, it is dominant for the larger HII regions produced by the massive star clusters found near the Galactic center and in starburst environments. We then provide a solution for the problem of how HII regions expand when radiation pressure influences their behavior. Finally, we compare radiation-dominated…
We use the three-dimensional Athena ionizing radiation-magnetohydrodynamics (IRMHD) code to simulate blister-type HII regions driven by stars on the edge of magnetized gas clouds. We compare these to simulations of spherical HII regions where the star is embedded deep within a cloud, and to non-magnetized simulations of both types, in order to compare their ability to drive turbulence and influence star formation. We find that magnetized blister HII regions can be very efficient at injecting energy into clouds. This is partly a magnetic effect: the magnetic energy added to a cloud by an HII re…
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 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…
NGC 7538 IRS2 is a compact HII region and recent star formation source, with a shell morphology, lying on the border of the visible HII region NGC 7538. We present a spectral cube of the [NeII] 12.8 micron emission line obtained with the TEXES spectrometer on Gemini North with velocity resolution approximately 4 km/s and angular resolution 0.3". The kinematics of the data cube show ionized gas flowing along multiple cavity walls. We have simulated the kinematics and structure of IRS2 with a model of superimposed cavities created by outflows from embedded stars in a cloud with density gradients…
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…
Given the rarity of young O star candidates, compact HII regions embedded in dense molecular cores continue to serve as potential sites to peer into the details of high-mass star formation. To uncover the ionizing sources of the most luminous and compact HII regions embedded in the RCW106 and RCW122 giant molecular clouds, known to be relatively nearby (2-4 kpc) and isolated, thus providing an opportunity to examine spatial scales of a few hundred to a thousand AU in size. High spatial resolution (0.3"), mid-infrared spectra (R=350), including the fine structure lines [ArIII] and [NeII], were …
Radiation pressure acting on gas and dust causes HII regions to have central densities that are lower than the density near the ionized boundary. HII regions in static equilibrium comprise a family of similarity solutions, parametrized by 3 parameters: beta, gamma, and the product (Q_0 n_rms); beta characterizes the stellar spectrum, gamma characterizes the dust/gas ratio, Q_0 is the ionizing output from the star (photons/s), and n_rms is the rms density within the ionized region. Adopting standard values for beta and gamma, varying (Q_0 n_rms) generates a one-parameter family of density profi…
We have identified 453 compact dense cores in 3 mm continuum emission maps in the ATOMS (ALMA Three-millimeter Observations of Massive Star-forming regions) survey, and compiled three catalogues of high-mass star forming cores. One catalogue, referred to as H/UC-HII catalogue, includes 89 cores that enshroud hyper/ultra compact (H/UC) HII regions as characterized by associated compact H40alpha emission. A second catalogue, referred to as pure s-cHMC, includes 32 candidate Hot Molecular Cores (HMCs) showing rich spectra (N>20lines) of complex organic molecules (COMs) but not associated with H/U…
ATOMS: ALMA three-millimeter observations of massive star-forming regions -- XVIII. On the origin and evolution of dense gas fragments in molecular shells of compact HII regions
We present molecular line and 1.4 mm continuum observations towards five massive star forming regions at arcsecond resolution using the Submillimeter Array (SMA). We find that the warm molecular gas surrounding each HII region (as traced by SO_2 and OCS) appears to be undergoing bulk rotation. From the molecular line emission and thermal component of the continuum emission, we independently derived gas masses for each region which are consistent with each other. From the free-free component of the continuum emission we estimate the minimum stellar mass required to power the HII region and find…
In this contribution we discuss about numerical modeling of nebulae. In particular we emphasize on the dynamical evolution of an HII region and the chemical structure of a Photodissociation region. We do this using the Smoothed Particles Hydrodynamics code SEREN and the recently developed astrochemistry code 3D-PDR, respectively. We show an example application by simulating a cometary globule using these two codes.
We have modelled the evolution of cometary HII regions produced by zero-age main-sequence stars of O and B spectral types, which are driving strong winds and are born off-centre from spherically symmetric cores with power-law ($α= 2$) density slopes. A model parameter grid was produced that spans stellar mass, age and core density. Exploring this parameter space we investigated limb-brightening, a feature commonly seen in cometary HII regions. We found that stars with mass $M_\star \geq 12\, \mathrm{M}_\odot$ produce this feature. Our models have a cavity bounded by a contact discontinuity sep…
Atomic ionised regions with strong continuum emission are often associated with regions of high-mass star formation and low-frequency (<2GHz) observations of these regions are needed to help build star formation models. The region toward the Vela Supernova Remnant is particularly interesting as it is a complex structure of recent supernova explosions and molecular clouds containing a number of HII regions that are not well characterised. We searched publicly available catalogues for HII regions, both candidate and identified, which also have low-frequency emission. In the area of ~400 square d…
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…
As part of our ongoing HII Region Discovery Survey (HRDS), we report the Green Bank Telescope detection of 148 new angularly-large Galactic HII regions in radio recombination line (RRL) emission. Our targets are located at a declination greater than -45deg., which corresponds to 266deg. > l > -20deg. at b = 0deg. All sources were selected from the WISE Catalog of Galactic HII Regions, and have infrared angular diameters >260''. The Galactic distribution of these "large" HII regions is similar to that of the previously-known sample of Galactic HII regions. The large HII region RRL line width an…
The Southern HII Region Discovery Survey (SHRDS) is a 900 hour Australia Telescope Compact Array 4-10 GHz radio continuum and radio recombination line (RRL) survey of Galactic HII regions and infrared-identified HII region candidates in the southern sky. For this data release, we reprocess all previously published SHRDS data and include an additional ~450 hours of observations. The search for new HII regions is now complete over the range 259 deg < Galactic longitude < 346 deg, |Galactic latitude| < 4 deg for HII region candidates with predicted 6 GHz continuum peak brightnesses >30 mJy/beam. …
Using data from the all-sky Wide-Field Infrared Survey Explorer (WISE) satellite, we made a catalog of over 8000 Galactic HII regions and HII region candidates by searching for their characteristic mid-infrared (MIR) morphology. WISE has sufficient sensitivity to detect the MIR emission from HII regions located anywhere in the Galactic disk. We believe this is the most complete catalog yet of regions forming massive stars in the Milky Way. Of the ~8000 cataloged sources, ~1500 have measured radio recombination line (RRL) or H$α$ emission, and are thus known to be HII regions. This sample impro…
Dessart et al., demonstrated that type II supernova (SN II) model spectra present increasing metal line strength with increasing progenitor metallicity. To confront these models with observations, we obtained a large sample of SN II host HII region emission line spectroscopy. We show that inferred SN II host HII region metallicities have a statistically significant correlation with the strength of SN II metal lines, specifically FeII 5018A.
The four HII regions in the Sgr A East complex: A, B, C, and D, represent evidence of recent massive star formation in the central ten parsecs. Using Paschen-alpha images taken with HST and 8.4 GHz VLA data, we construct an extinction map of A-D, and briefly discuss their morphology and location.
We present and discuss a new catalogue of 52 compact HII regions in the Small Magellanic Cloud (SMC) and a newly created deep 1420 MHz (λ=20 cm) radio-continuum image of the N19 region located in the southwestern part of the SMC. The new images were created by merging 1420 MHz radio-continuum archival data from the Australian Telescope Compact Array. The majority of these detected radio compact HII regions have rather flat spectral indices which indicates, as expected, that the dominant emission mechanism is of thermal nature.
The statistical shape analysis method developed for probing the link between physical parameters and morphologies of Galactic HII regions is applied here to a set of synthetic observations (SOs) of a numerically modelled HII region. The systematic extraction of HII region shape, presented in the first paper of this series, allows for a quantifiable confirmation of the accuracy of the numerical simulation, with respect to the real observational counterparts of the resulting SOs. A further aim of this investigation is to determine whether such SOs can be used for direct interpretation of the obs…
Using the Very Large Array (VLA) at 3.6~cm we identify four new compact radio sources in the vicinity of the cometary HII region G78.4+2.6 (VLA~1). The four compact radio sources (named VLA~2 to VLA~5), have near-infrared counterparts, as seen in the 3.6 $μ$m Spitzer image. One of them (VLA~5) clearly shows evidence of radio variability in a timescale of hours. We explore the possibility that these radio sources are associated with pre-main sequence (PMS) stars in the vicinity of the UC HII region G78.4+2.6. Our results favor the smaller distance value of 1.7 kpc for G78.4+2.6. In addition to …
Context. The derived physical parameters for young HII regions are normally determined assuming the emission region to be optically thin. However, this assumption is unlikely to hold for young HII regions such as hyper-compact HII(HCHII) and ultra-compact HII(UCHII) regions and leads to the underestimation of their properties. This can be overcome by fitting the SEDs over a wide range of radio frequencies. Aims. The two primary goals of this study are (1) to determine the physical properties of young HII regions from radio SEDs in the search for potential HCHII regions, and (2) to use these ph…
Using Green Bank Telescope radio recombination line (RRL) data, we analyze the role of leaking radiation from HII regions in maintaining the ionization of the interstellar medium. We observed a sample of eight Galactic HII regions of various sizes, morphologies, and luminosities. For each region the hydrogen RRL intensity decreases roughly as a power-law with distance from the center of the region. This suggests that radiation leaking from the HII region is responsible for the majority of surrounding ionized gas producing RRL emission. Our results further indicate that the hydrogen RRL intensi…
The relative alignments of mid-infrared traced Galactic bubbles are compared to the orientation of the mean Galactic magnetic field in the disk. The orientations of bubbles in the northern Galactic plane were measured and are consistent with random orientations - no preferential alignment with respect to the Galactic disk was found. A subsample of HII region driven Galactic bubbles was identified, and as a single population they show random orientations. When this subsample was further divided into subthermal and suprathermal HII regions, based on hydrogren radio recombination linewidths, the …
We have observed the compact HII region complex nearest to the dynamical center of the Galaxy, G-0.02-0.07, using ALMA in the H42a recombination line, CS J=2-1, H13CO+ J=1-0, and SiO v=0, J=2-1 emission lines, and 86 GHz continuum emission. The HII regions HII-A to HII-C in the cluster are clearly resolved into a shell-like feature with a bright-half and a dark-half in the recombination line and continuum emission. The absorption features in the molecular emission lines show that HII-A, B and C are located on the near side of the 50 km/s Molecular Cloud (50MC) but HII-D is located on the far s…
The Southern HII Region Discovery Survey (SHRDS) is a survey of the third and fourth quadrants of the Galactic plane that will detect radio recombination line and continuum emission at cm-wavelengths from several hundred HII region candidates using the Australia Telescope Compact Array. The targets for this survey come from the WISE Catalog of Galactic HII Regions, and were identified based on mid-infrared and radio continuum emission. In this pilot project, two different configurations of the Compact Array Broad Band receiver and spectrometer system were used for short test observations. The …
The ngVLA will create a Galaxy-wide, volume-limited sample of HII regions; solve some long standing problems in the physics of HII regions; and provide an extinction-free star formation tracer in nearby galaxies.
We present a new model of the optical nebular emission from HII regions by combin- ing the results of the Binary Population and Spectral Synthesis (bpass) code with the photoion- ization code cloudy (Ferland et al. 1998). We explore a variety of emission-line diagnostics of these star-forming HII regions and examine the effects of metallicity and interacting binary evo- lution on the nebula emission-line production. We compare the line emission properties of HII regions with model stellar populations, and provide new constraints on their stellar populations and supernova progenitors. We find t…
We present high-resolution HI data obtained using the Australia Telescope Compact Array to resolve the near/far distance ambiguities towards a sample of compact HII regions from the Red MSX Source (RMS) survey. The high resolution data are complemented with lower resolution archival HI data extracted from the Southern and VLA Galactic Plane surveys. We resolve the distance ambiguity for nearly all of the 105 sources where the continuum was strong enough to allow analysis of the HI absorption line structure. This represents another step in the determination of distances to the total RMS sample,…
The census of Galactic HII regions is vastly incomplete in the Southern sky. We use the Australia Telescope Compact Array (ATCA) to observe 4-10 GHz radio continuum and hydrogen radio recombination line (RRL) emission from candidate HII regions in the Galactic zone 259 deg < l < 344 deg, |b| < 4 deg. In this first data release, we target the brightest HII region candidates and observe 282 fields in the direction of at least one previously-known or candidate HII region. We detect radio continuum emission and RRL emission in 275 (97.5%) and 258 (91.5%) of these fields, respectively. We catalog t…
An investigation of dust emission associated with a large sample of HII regions has been carried out. Stacked results from this sample suggest that each HII region is at or near the center of a cluster of dense cores, that extends far beyond the HII region, and has volume density that decreases as r^(-3). The data also shows evidence for enhanced numbers of cores near the boundary of the HII regions. At the same time, a significant decrease in the number of cores, consistent with no cores, is observed in the interior of these HII regions. Neither these HII regions, nor their associated massive…
We have compiled a catalogue of HII regions detected with the Murchison Widefield Array (MWA) between 72 and 231MHz. The multiple frequency bands provided by the MWA allow us identify the characteristic spectrum generated by the thermal Bremsstrahlung process in HII regions. We detect 302 HII regions between 260 < l < 340 and report on the positions, sizes, peak, integrated flux density, and spectral indices of these HII regions. By identifying the point at which HII regions transition from the optically thin to thick regime we derive the physical properties including the electron density, ion…
Ultracompact and hypercompact HII regions appear when a star with a mass larger than about 15 solar masses starts to ionize its own environment. Recent observations of time variability in these objects are one of the pieces of evidence that suggest that at least some of them harbor stars that are still accreting from an infalling neutral accretion flow that becomes ionized in its innermost part. We present an analysis of the properties of the HII regions formed in the 3D radiation-hydrodynamic simulations presented by Peters et al. as a function of time. Flickering of the HII regions is a natu…
HII regions and planetary nebulae (PNe) both emit at radio and infrared (IR) wavelengths, and angularly small HII regions can be mistaken for PNe. This problem of classification is most severe for HII regions in an early evolutionary stage, those that are extremely distant, or those that are both young and distant. Using data from the Herschel Hi-GAL survey, as well as WISE and the Spitzer MIPSGAL and GLIMPSE surveys, we wish to establish characteristic IR colors that can be used to distinguish between HII regions and PNe. We perform aperture photometry measurements for a sample of 126 HII reg…
A number of giant cometary HII regions (GCH) sheathed inside molecular bow shocks (MBS) are found along spiral arms of the barred galaxy M83. The open cone structure is explained by a model of expanded HII front in a gaseous arm with steep density gradient, and the bow shock is shown to be formed by encounter of an HII region with the supersonic gas flow across the arm. It is suggested that dual-side compression of molecular gas at the bow head between the MBS and GCH enhances star formation along the spiral arms.
We present high angular and spectral resolution HI 21~cm line observations toward the cometary-shaped compact HII region G213.880-11.837 in the GGD~14 complex.The kinematics and morphology of the photodissociated region, traced by the HI line emission, reveal that the neutral gas is part of an expanding flow. The kinematics of the HI gas along the major axis of G213.880-11.837 shows that the emission is very extended toward the SE direction, reaching LSR radial velocities in the tail of about 14 km/s. The ambient LSR radial velocity of the molecular gas is 11.5 km/s, which suggests a champagne…
We make a comprehensive study of HI absorption toward HII regions located within Galactic longitudes less than 10 degrees. Structures in the extreme inner Galaxy are traced using the longitude-velocity space distribution of this absorption. We find significant HI absorption associated with the Near and Far 3kpc Arms, the Connecting Arm, Banias Clump 1 and the H I Tilted Disk. We also constrain the line of sight distances to HII regions, by using HI absorption spectra together with the HII region velocities measured by radio recombination lines.
High mass star formation and the evolution of HII regions have a substantial impact on the morphology and star formation history of molecular clouds. The HII region Gum 48d, located in the Centaurus Arm at a distance of 3.5 kpc, is an old, well evolved HII region whose ionizing stars have moved off the main sequence. As such, it represents a phase in the evolution of HII regions that is less well studied than the earlier, more energetic, main sequence phase. In this paper we use multi-wavelength archive data from a variety of sources to perform a detailed study of this interesting region. Morp…
Many more supernova remnants (SNRs) are now known in external galaxies than in the Milky Way. Most of these SNRs have been identified using narrow-band imaging, separating SNRs from HII regions on the basis of [SII]:H-alpha ratios that are elevated compared to HII regions. However, the boundary between SNRs and HII regions is not always distinct, especially at low surface brightness. Here we explore velocity structure as a possible criterion for separating SNRs from HII regions, using a sample of well-studied SNRs in the Large Magellanic Cloud (LMC) as well as a small number of SNRs in the gal…
We derive infrared and radio flux densities of all ~1000 known Galactic HII regions in the Galactic longitude range 17.5 < l < 65 degree. Our sample comes from the Wide-Field Infrared Survey Explorer (WISE) catalog of Galactic \hii regions \citep{anderson2014}. We compute flux densities at six wavelengths in the infrared (GLIMPSE 8 microns, WISE 12 microns and 22 microns, MIPSGAL 24 microns, and Hi-GAL 70 microns and 160 microns) and two in the radio (MAGPIS 20 cm and VGPS 21 cm). All HII region infrared flux densities are strongly correlated with their ~20 cm flux densities. All HII regions u…
We present radio and infrared observations of 4 hyper-compact HII regions and 4 ultra-compact HII regions in the southern Galactic plane. These objects were selected from a blind survey for UCHII regions using data from two new radio surveys of the southern sky; the Australia Telescope 20 GHz survey (AT20G) and the 2nd epoch Molonglo Galactic Plane Survey (MGPS-2) at 843 MHz. To our knowledge, this is the first blind radio survey for hyper- and ultra-compact HII regions. We have followed up these sources with the Australia Telescope Compact Array to obtain H70-alpha recombination line measurem…
The size-velocity dispersion relationship of Galactic HII regions
The Key Laboratory of Cosmic Rays (Xizang University), Ministry of Education（西藏大学宇宙射线教育部重点实验室）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）
Rich young stellar clusters produce HII regions whose expansion into the nearby molecular cloud is thought to trigger the formation of new stars. However, the importance of this mode of star formation is uncertain. This investigation seeks to quantify triggered star formation (TSF) in IC 1396A (a.k.a., the Elephant Trunk Nebula), a bright rimmed cloud (BRC) on the periphery of the nearby giant HII region IC 1396 produced by the Trumpler 37 cluster. X-ray selection of young stars from Chandra X-ray Observatory data is combined with existing optical and infrared surveys to give a more complete c…
I present recent and forthcoming works to model the CALIFA HII region using photoionization models. The first results are obtained with ad-hoc models (combining parameter determination by model fitting and strong line methods) while the next ones will use a Genetic Algorithm to fit the observations in a multi-dimensional space.
The Green Bank Telescope HII Region Discovery Survey has doubled the number of known HII regions in the Galactic zone 343deg.\leql\leq67deg. with |b|\leq1deg. We detected 603 discrete hydrogen radio recombination line (RRL) components at 9GHz (3cm) from 448 targets. Our targets were selected based on spatially coincident mid-infrared and 20cm radio continuum emission. Such sources are almost invariably HII regions; we detected hydrogen RRL emission from 95% of our target sample. The sensitivity of the Green Bank Telescope and the power of its spectrometer together made this survey possible. He…
We spectroscopically identify 101 Galactic HII regions using spectra from the Large Sky Area Multi- Object Fiber Spectroscopic Telescope (LAMOST) survey, cross-matched with an HII region catalog derived from the all-sky Wide-Field Infrared Survey Explorer(WISE) data. Among all HII regions in our sample, 47 sources are newly confirmed. Spatially, most of our identified HII regions are located in the anti-center area of the Galaxy. For each of the HII regions, we accurately extract and measure the nebular emission lines of the spectra, and estimate the oxygen abundances using the strong-line met…
There are known differences between the physical properties of HII and diffuse ionized gas (DIG), but most of the studied regions in the literature are relatively bright. We compiled a faint sample of 390 HII regions with median $\log_{10}Hα$=34.7 in the spiral galaxy NGC300, derived their physical properties in terms of metallicity, density, extinction, and kinematics, and performed a comparative analysis of the properties of the DIG. We used MUSE data of nine fields in NGC300, covering a galactocentric distance of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm reg…
We present the results of the ethynyl (C2H) emission line observations towards the HII regions S255 and S257 and the molecular cloud between them. Radial profiles of line brightness, column density, and abundance of C2H are obtained. We show that the radial profile of the ethynyl abundance is almost flat towards the HII regions and drops by a factor of two towards the molecular cloud. At the same time, we find that the abundance of ethynyl is at maximum towards the point sources in the molecular cloud -- the stars with emission lines or emitting in X-ray. The line profiles are consistent with …
We present deep Very Large Array H66$α$ radio recombination line (RRL) observations of the two cometary HII regions in DR 21. With these sensitive data, we test the "hybrid" bow shock/champagne flow model previously proposed for the DR 21 HII regions. The ionized gas down the tail of the southern HII region is redshifted by up to ~30 km/s with respect to the ambient molecular gas, as expected in the hybrid scenario. The RRL velocity structure, however, reveals the presence of two velocity components in both the northern and southern HII regions. This suggests that the ionized gas is flowing al…
We present an analysis of the structure and properties of the compact HII region Sh 2-89, and certain of the young stellar objects (YSOs) within this regime, using mid-infrared (MIR) mapping derived from the Spitzer Space Telescope (SST) and visual slit spectroscopy of the inner regions of the source. We show that the region has a bipolar structure, and contains a variety of Class I and II YSOs. Much of the MIR emission appears to be dominated by PAH emission bands, which cause strong increases in flux in the 5.8 and 8.0 microns photometric channels, whilst the variation of H_alpha, [NII] at 6…
Because of their relatively simple morphology, "bubble" HII regions have been instrumental to our understanding of star formation triggered by HII regions. With the far-infrared (FIR) spectral coverage of the Herschel satellite, we can access the wavelengths where these regions emit the majority of their energy through their dust emission. At Herschel wavelengths 70 micron to 500 micron, the emission associated with HII regions is dominated by the cool dust in their photodissociation regions (PDRs). We find average dust temperatures of 26K along the PDRs, with little variation between the HII …
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…
This review is not a compendium of strong-line methods to derive abundances in giant HII regions. It is mostly intended for readers who wish to use such methods but do not have a solid background on the physics of HII regions. It is also meant to encourage those using abundance results published in the literature to think more thoroughly about the validity of these results.
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…
The Diffuse Ionized Gas (DIG) contributes to the nebular emission of galaxies, resulting in emission line flux ratios that can be significantly different from those produced by HII regions. Comparing the emission of [SII]6717,31 between pointed observations of HII regions in nearby galaxies and integrated spectra of more distant galaxies, it has been recently claimed that the DIG can also deeply affect the emission of bright, star-forming galaxies, and that a large correction must be applied to observed line ratios to recover the genuine contribution from HII regions. Here we show instead that…
