Massive Star Formation In NGC Research Articles

PHANGS–JWST First Results: Duration of the Early Phase of Massive Star Formation in NGC 628

The earliest stages of star formation, when young stars are still deeply embedded in their natal clouds, represent a critical phase in the matter cycle between gas clouds and young stellar regions. Until now, the high-resolution infrared observations required for characterizing this heavily obscured phase (during which massive stars have formed, but optical emission is not detected) could only be obtained for a handful of the most nearby galaxies. One of the main hurdles has been the limited angular resolution of the Spitzer Space Telescope. With the revolutionary capabilities of the James Webb Space Telescope (JWST), it is now possible to investigate the matter cycle during the earliest phases of star formation as a function of the galactic environment. In this Letter, we demonstrate this by measuring the duration of the embedded phase of star formation and the implied time over which molecular clouds remain inert in the galaxy NGC 628 at a distance of 9.8 Mpc, demonstrating that the cosmic volume where this measurement can be made has increased by a factor of >100 compared to Spitzer. We show that young massive stars remain embedded for Myr ( Myr of which being heavily obscured), representing ∼20% of the total cloud lifetime. These values are in broad agreement with previous measurements in five nearby (D < 3.5 Mpc) galaxies and constitute a proof of concept for the systematic characterization of the early phase of star formation across the nearby galaxy population with the PHANGS–JWST survey.

Herschel-HOBYS study of the earliest phases of high-mass star formation in NGC 6357

Aims. To constrain models of high-mass star formation it is important to identify the massive dense cores (MDCs) that are able to form high-mass star(s). This is one of the purposes of the Herschel/HOBYS key programme. Here, we carry out the census and characterise of the properties of the MDCs population of the NGC 6357 H II region. Methods. Our study is based on the Herschel/PACS and SPIRE 70−500 μm images of NGC 6357 complemented with (sub-)millimetre and mid-infrared data. We followed the procedure established by the Herschel/HOBYS consortium to extract ~0.1 pc massive dense cores using the getsources software. We estimated their physical parameters (temperatures, masses, luminosities) from spectral energy distribution (SED) fitting. Results. We obtain a complete census of 23 massive dense cores, amongst which one is found to be IR-quiet and twelve are starless, representing very early stages of the star-formation process. Focussing on the starless MDCs, we have considered their evolutionary status, and suggest that only five of them are likely to form a high-mass star. Conclusions. We find that, contrarily to the case in NGC 6334, the NGC 6357 region does not exhibit any ridge or hub features that are believed to be crucial to the massive star formation process. This study adds support for an empirical model in which massive dense cores and protostars simultaneously accrete mass from the surrounding filaments. In addition, the massive star formation in NGC 6357 seems to have stopped and the hottest stars in Pismis 24 have disrupted the filaments.

ONGOING MASSIVE STAR FORMATION IN NGC 604

NGC 604 is the second most massive H II region in the Local Group, thus an important laboratory for massive star formation. Using a combination of observational and analytical tools that include Spitzer spectroscopy, Herschel photometry, Chandra imaging, and Bayesian Spectral Energy Distribution fitting, we investigate the physical conditions in NGC 604, and quantify the amount of massive star formation currently taking place. We derive an average age of 4 +/- 1 Myr and a total stellar mass of 1.6 (+1.6)(-1.0) x 10^5 M_sun for the entire region, in agreement with previous optical studies. Across the region we find an effect of the X-ray field on both the abundance of aromatic molecules and the [Si II] emission. Within NGC 604 we identify several individual bright infrared sources with diameters of about 15 pc and luminosity weighted masses between 10^3 M_sun and 10^4 M_sun. Their spectral properties indicate that some of these sources are embedded clusters in process of formation, which together account for ~8% of the total stellar mass in the NGC 604 system. The variations of the radiation field strength across NGC 604 are consistent with a sequential star formation scenario, with at least two bursts in the last few million years. Our results indicate that massive star formation in NGC 604 is still ongoing, likely triggered by the earlier bursts.

Multi-generation massive star-formation in NGC 3576

<i>Context. <i/>Recent 1.2-mm continuum observations have shown the giant H II region NGC 3576 to be embedded in the centre of an extended filamentary dust-cloud. The bulk of the filament away from the H II region contains a number of clumps seen only at (sub-)millimetre wavelengths. Infrared and radio observations of the central star cluster have uncovered evidence of sequential star-formation leading us to believe that the adjacent clumps may host massive protostellar objects at a very early stage of evolution.<i>Aims. <i/>We have investigated the physical and chemical conditions in the dusty clumps with the goal of characterising their star-forming content.<i>Methods. <i/>We have used the Australia Telescope Compact Array (ATCA) to image the cloud for the NH<sub>3<sub/> (1,1), (2,2) and (4,4) transitions, 22 GHz H<sub>2<sub/>O masers, and 23 GHz continuum emission. The 70-m Tidbinbilla dish was used to estimate the total integrated intensity of NH<sub>3<sub/>. We also utilised the 22-m Mopra antenna to map the region for the molecular lines <sup>13<sup/>CO (1 – 0), C<sup>18<sup/>O (1 – 0), HCO<sup>+<sup/> (1 – 0), H<sup>13<sup/>CO<sup>+<sup/> (1 – 0), CS (1 – 0) and N<sub>2<sub/>H<sup>+<sup/> (1 – 0). <i>Results. <i/>Emission from dense molecular gas follows the morphology of the 1.2-mm dust emission, except towards the central ionised region. The H II region is observed to be expanding into the molecular cloud, sweeping up a clumpy shell of gas, while the central star cluster is dispersing the molecular gas to the east. Analysis of the NH<sub>3<sub/> data indicates that temperature and linewidth gradients exist in the western arm of the filament. Temperatures are highest adjacent to the central H II region, indicating that the embedded cluster of young stars there is heating the gas. Six new H<sub>2<sub/>O masers were detected in the arms of the filament, all associated with NH<sub>3<sub/> emission peaks, confirming that star-formation has begun within these cores. Core masses range from 5 to 516 and most appear to be gravitationally bound. Complementary results by André et al. (2008) imply that seven cores will go on to form massive stars between 15 and 50 . The large scale velocity structure of the filament is smooth, but at least one clump shows the signature of inward gas motions via asymmetries in the NH<sub>3<sub/> (1,1) line profiles. The same clump exhibits an enhanced abundance of N<sub>2<sub/>H<sup>+<sup/>, which coupled with an absence of CO indicates depletion onto the dust grain surface. <i>Conclusions. <i/>The HII region at the heart of NGC 3576 is potentially triggering the formation of massive stars in the bulk of the associated cloud.

Ionized gas kinematics and massive star formation in NGC 1530

We present emission line mapping of the strongly barred galaxy NGC 1530 obtained using Fabry-Perot interferom- etry in Hα, at significantly enhanced angular resolution compared with previously published studies. The main point of the work is to examine in detail the non-circular components of the velocity field of the gas, presumably induced by the strongly non-axisymmetric gravitational potential of the bar. To do this we first derive a model rotation curve making minimum assump- tions about kinematic symmetry, and go on to measure the non-circular component of the full radial velocity field. This clearly reveals the streaming motions associated with the spiral density wave producing the arms, and the quasi-elliptical motions with speeds of order 100 km s −1 aligned with the bar. It also shows in some detail how these flows swing in towards and around the nucleus as they cross a circumnuclear resonance, from the dominant x1 orbits outside the resonance to x2 orbits within it. Comparing cross-sections of this residual velocity map along and across the bar with the surface brightness map in Hα indicates a systematic offset between regions of high non-circular velocity and massive star formation. To investigate further we produce maps of velocity gradient along and across the bar. These illustrate very nicely the shear compression of the gas, revealed by the location of the dust lanes along loci of maximum velocity gradient perpendicular to the bar. They also show clearly how shear, seen in our data as velocity gradient perpendicular to the flow, acts to inhibit massive star formation, whereas shocks, seen as strong velocity gradients along the flow vector, act to enhance it. Although the inhibiting effect of gas shear flow on star formation has long been predicted, this is the clearest observational illustration so far of the effect, thanks to the strong shock-induced counterflow system in the bar. It is also the clearest evidence that dust picks out shock-induced inflow along bars. These observations should be of considerable interest to those modelling massive star formation in general.

Structure and Star Formation in NGC 925

We present the results from an optical study of the stellar and star formation properties of NGC 925 using the WIYN 3.5 m telescope. Images in B, V, R, and Hα reveal a galaxy that is fraught with asymmetries. From isophote fits we discover that the bar center is not coincident with the center of the outer isophotes or with the dynamical center (from Paper I in this series). Cuts across the spiral arms reveal that the northern arms are distinctly different from the southern arm. The southern arm not only appears more coherent, but the peaks in stellar and Hα emission are found to be coincident with those of the H I distribution, while no such consistency is present in the northern disk. We also examine the gas surface density criterion for massive star formation in NGC 925, and we find that its behavior is more consistent with that for irregular galaxies than with late-type spirals. In particular, star formation persists beyond the radius at which the gas surface density falls below the predicted critical value for star formation for late-type spirals. Such properties are characteristic of Magellanic spirals but are present at a less dramatic level in NGC 925, a late-type spiral.

The Amorphous Galaxy NGC 2777: H [CSC]i[/CSC] Evidence for Tidal Interaction with a Faint Companion

NGC 2777 is an amorphous galaxy possessing the classic signature of an A-type spectrum with superposed emission lines. There is no optical evidence for an interaction, but observations of the neutral hydrogen in this system reveal an H I bridge between NGC 2777 and U3, a companion that is 3 mag fainter. Far-infrared observations indicate that the current rate of massive star formation in NGC 2777 is low, but the optical spectra indicate that it must have been significantly higher in the recent past. We were unable to detect CO in either galaxy. We also consider a sample of 10 amorphous galaxies, all showing A-type absorption spectra: nine from the Revised Shapley-Ames Catalog, plus NGC 2777. All show optical/H I interaction and/or peculiar velocity fields, supporting the view that amorphous characteristics are the result of interaction. For some of the galaxies, the interacting companion is much fainter than the amorphous system, which indicates that previous concerns raised by the existence of isolated amorphous galaxies may have been premature.

ITAL]VRI[/ITAL] CCD Photometry of Supergiant Stars in the Barred Galaxies NGC 925 and NGC 1637

?????V, R, and I CCD images obtained with the Canada-France-Hawaii Telescope are used to investigate the bright stellar content of the barred spiral galaxies NGC 925 and NGC 1637. Not counting objects located in H II regions, we detect 295 supergiants in NGC 925 and 266 in NGC 1637. Comparisons with theoretical isochrones indicate that massive star formation in NGC 925 has been ongoing for at least a few tens of millions of years. Most of the supergiants in NGC 925 are younger than 20 Myr and have masses between 10 and 60 M?. The majority of supergiants in NGC 1637 appear to be younger than 40 Myr and have initial masses between 8 and 60 M?. The luminosity functions of supergiants in both galaxies follow power laws with exponents d log n/d log V = 0.50 ? 0.05 for NGC 925 and 0.62 ? 0.04 for NGC 1637. These values are shallower than what is seen in most spiral galaxies, although there are some exceptions. Archival Hubble Space Telescope images of NGC 925 are used to assess the effects of blending on our photometric measurements. We conclude that crowding could cause a flattening of the luminosity function and bias the brightnesses of the most luminous stars. The brightest red supergiants are used to estimate the distance moduli of these galaxies. After applying corrections for blending, we find that ?0 = 29.67 for NGC 925 and ?0 = 29.47 for NGC 1637, corresponding to linear distances of 8.6 and 7.8 Mpc, respectively. The distance computed for NGC 925 is in good agreement with that recently derived from Cepheids.

An Ultraviolet and Near‐Infrared View of NGC 4214: A Starbursting Core Embedded in a Low Surface Brightness Disk

During the Astro-2 Spacelab mission in 1995 March, the Ultraviolet Imaging Telescope (UIT) obtained far-UV (λ = 1500 A) imagery of the nearby Sm/Im galaxy NGC 4214. The UIT images have a spatial resolution of ~3'' and a limiting surface brightness, μ1500 > 25 mag arcsec-2, permitting detailed investigation of the intensity and spatial distribution of the young, high-mass stellar component. These data provide the first far-UV imagery covering the full spatial extent of NGC 4214. Comparison with a corresponding I-band image reveals the presence of a starbursting core embedded in an extensive low surface brightness disk. In the far-UV (FUV), NGC 4214 is resolved into several components: a luminous, central knot; an inner region (r 2.5 kpc) with ~15 resolved sources embedded in bright, diffuse emission; and a population of fainter knots extending to the edge of the optically defined disk (r ≈ 5 kpc). The FUV light, which traces recent massive star formation, is observed to be more centrally concentrated than the I-band light, which traces the global stellar population. The FUV radial light profile is remarkably well represented by an R1/4 law, providing evidence that the centrally concentrated massive star formation in NGC 4214 is the result of an interaction, possibly a tidal encounter, with a dwarf companion(s). The brightest FUV source produces ~8% of the global FUV luminosity. This unresolved source, corresponding to the Wolf-Rayet knot described by Sargent & Filippenko, is located at the center of the FUV light distribution, giving NGC 4214 an active galactic nucleus-like morphology. Another strong source is present in the I band, located 19'' west, 10'' north of the central starburst knot, with no FUV counterpart. The I-band source may be the previously unrecognized nucleus of NGC 4214 or an evolved star cluster with an age greater than ~200 Myr. The global star formation rate derived from the total FUV flux is consistent with rates derived using data at other wavelengths and lends support to the scenario of roughly constant star formation during the last few hundred million years at a level significantly enhanced relative to the lifetime averaged star formation rate. The hybrid disk/starburst-irregular morphology evident in NGC 4214 emphasizes the danger of classifying galaxies based on their high surface brightness components at any particular wavelength.

Differential efficiency of massive star formation in NGC 628

The efficiency ratio of massive star formation in the arms of the spiral NGC 628 to that in the interarm region has been determined from the sizes and positions of itsHii regions following the method described in Cepa and Beckman (1989a, b). The variation of this relative star formation efficiency with radius shows a very similar behaviour for each of the three arms of this galaxy with a minimum at 100 arc sec from the centre, which can be identified with the corotation radius distances at which the arms show bifurcations or sudden changes in their pitch angles. This result, together with the higher star formation efficiency in the arms than that in the interarm zones, is evidence supporting the hypothesis that the spiral arms of NGC 628 are driven by a density wave which triggers the star formation according to the spiral density wave theory.

Massive star formation in NGC 6946

view Abstract Citations (70) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Massive star formation in NGC 6946. Degioia-Eastwood, K. ; Grasdalen, G. L. ; Strom, S. E. ; Strom, K. M. Abstract H-alpha measurements of the late-type spiral galaxy NGC 6946 are presented. Assuming an initial mass function, the H-alpha data are used to calculate the total star formation rate and efficiency of massive star formation as a function of galactocentric radius. An attempt is made to determine the factors influencing these quantities by comparing them to the surface densities of H I and H 2 and the degree of compression suffered by the gas in spiral density wave theory. The rate of star formation is very closely correlated with the first power of the surface density of H2, and somewhat less correlated with the degree of compression of the gas predicted by density wave theory. In contrast, the efficiency of massive star formation is roughly constant across the face of the galaxy. Publication: The Astrophysical Journal Pub Date: March 1984 DOI: 10.1086/161823 Bibcode: 1984ApJ...278..564D Keywords: Density Wave Model; Spiral Galaxies; Star Formation; Stellar Mass; Galactic Evolution; Galactic Nuclei; Gas Density; H Alpha Line; Interstellar Matter; Radii; Rates (Per Time); Star Formation Rate; Astrophysics full text sources ADS | data products SIMBAD (1) NED (1)