We review the results of high-dispersion spectroscopy of 17 circumnuclear star-forming regions (CNSFRs) in 3 nearby early spiral galaxies, NGC 2903, NGC 3310 and NGC 3351. We find that ...single-Gaussian fitting to the Hβ and O iiiλ5007 Å line profiles results in velocity dispersions around 32 and 52 km s−1, respectively, while the IR Ca ii triplet cross-correlation technique provides stellar velocity dispersion values close to 50 km s−1. Even though multiple kinematical components are present, the relation between gas velocity dispersion and Balmer emission line luminosity (L-σ relation) reproduces the correlation for disc giant H ii regions albeit with a larger scatter. The scatter in the L-σ relation is considerably reduced when theoretical evolutionary corrections are applied suggesting that an age range is present in the sample of CNSFRs. To analyse the observed complex profiles, we performed multiple Gaussian component fits to the Hβ and O iiiλ5007 Å lines obtaining optimal fits with two Gaussians of different widths. These best fits indicate that the narrower component has average velocity dispersion close to 23 km s−1 while the broader component shows average values in the range 50-60 km s−1 for both lines, close to the observed stellar velocity dispersions. The fluxes of the broad and narrow Hβ components are similar. This is not the case for O iiiλ5007 Å for which the broad components have higher fluxes than the narrow ones, thus producing a clear segregation in their O iii/Hβ ratios. We suggest a possible scenario for understanding the behaviour of CNSFRs in the L-σ and σgas-σ* diagrams involving an inner gaseous disc responsible for the narrow component of the emission lines. Our main conclusion is that the presence of different kinematical components with similar total fluxes in the emission line spectrum of CNSFRs raises important doubts regarding the properties of the ionized gas derived from global line ratios obtained with low-resolution spectroscopy in star-forming regions in the central regions of early-type galaxies. Given the ubiquity of these star-forming systems, ionized gas analyses should be done preferably from high-dispersion spectra with high spatial resolution.
We present a near-infrared study focused on the detection and characterization of the youngest stellar component of the NGC 604 giant star-forming region in the Triangulum galaxy (M 33). By means of ...color-color diagrams derived from the photometry of JHK sub(s) images taken with the Gemini Near Infrared Imaging and Spectrometer (NIRI), we have found 68 candidate massive young stellar objects. The spatial distribution of these sources matches the areas where previous studies suggested that star formation might be taking place, and the high spatial resolution of our deep NIRI imaging allows us to pinpoint the star-forming knots. An analysis of the fraction of objects that show infrared excess suggests that the star formation is still active, supporting the presence of a second generation of stars being born, although the evidence for or against sequential star formation does not seem to be conclusive.
The Onfp Class in the Magellanic Clouds Walborn, Nolan R; Howarth, Ian D; Evans, Christopher J ...
The Astronomical journal,
03/2010, Letnik:
139, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The Onfp class of rotationally broadened, hot spectra was defined some time ago in the Galaxy, where its membership to date numbers only eight. The principal defining characteristic is a broad, ...centrally reversed He II Delta *l 4686 emission profile; other emission and absorption lines are also rotationally broadened. Recent surveys in the Magellanic Clouds (MCs) have brought the class membership there, including some related spectra, to 28. We present a survey of the spectral morphology and rotational velocities, as a first step toward elucidating the nature of this class. Evolved, rapidly rotating hot stars are not expected theoretically, because the stellar winds should brake the rotation. Luminosity classification of these spectra is not possible, because the principal criterion (He II Delta *l4686) is peculiar; however, the MCs provide reliable absolute magnitudes, which show that they span the entire range from dwarfs to supergiants. The Onfp line-broadening distribution is distinct and shifted toward larger values from those of normal O dwarfs and supergiants with >99.99% confidence. All cases with multiple observations show line-profile variations, which even remove some objects from the class temporarily. Some of them are spectroscopic binaries; it is possible that the peculiar profiles may have multiple causes among different objects. The origin and future of these stars are intriguing; for instance, they could be stellar mergers and/or gamma-ray-burst progenitors.
We present a spectroscopic study of the N159/N160 massive star-forming region south of 30 Doradus in the Large Magellanic Cloud, classifying a total of 189 stars in the field of the complex. Most of ...them belong to O and early B spectral classes; we have also found some uncommon and very interesting spectra, including members of the Onfp class, a Be P Cygni star, and some possible multiple systems. Using spectral types as broad indicators of evolutionary stages, we considered the evolutionary status of the region as a whole. We infer that massive stars at different evolutionary stages are present throughout the region, favoring the idea of a common time for the origin of recent star formation in the N159/N160 complex as a whole, while sequential star formation at different rates is probably present in several subregions.
A deep dive into NGC 604 with Gemini/NIRI imaging Fariña, Cecilia; Bosch, Guillermo L.; Barbá, Rodolfo R.
Proceedings of the International Astronomical Union,
08/2009, Letnik:
5, Številka:
S266
Journal Article
Recenzirano
Odprti dostop
The giant Hii region NGC 604 constitutes a complex and rich population to study in detail many aspects of massive star formation, such as their environments and physical conditions, the evolutionary ...processes involved, the initial mass function for massive stars and star-formation rates, among many others. Here, we present our first results of a near-infrared study of NGC 604 performed with NIRI images obtained with Gemini North. Based on deep JHK photometry, 164 sources showing infrared excess were detected, pointing to the places where we should look for star-formation processes currently taking place. In addition, the color–color diagram reveals a great number of objects that could be giant/supergiant stars or unresolved, small, tight clusters. An extinction map obtained based on narrow-band images is also shown.
We present a spectroscopic study of the N159/N160 massive star-forming region south of 30 Doradus in the Large Magellanic Cloud, classifying a total of 189 stars in the field of the complex. Most of ...them belong to O and early B spectral classes; we have also found some uncommon and very interesting spectra, including members of the Onfp class, a Be P Cygni star, and some possible multiple systems. Using spectral types as broad indicators of evolutionary stages, we considered the evolutionary status of the region as a whole. We infer that massive stars at different evolutionary stages are present throughout the region, favoring the idea of a common time for the origin of recent star formation in the N159/N160 complex as a whole, while sequential star formation at different rates is probably present in several subregions.
The goal of this study was to analyze the presenting features, natural history, and prognostic factors in 59 patients with well characterized mantle cell lymphoma (MCL).
Cases were classified as ...nodular or diffuse and as typical or blastic variants. Age, performance status (PS), histologic variants, mitotic index (MI), hematologic parameters, tumor extension data, and International Prognostic Index (IPI) were recorded and evaluated for prognosis.
The median age of the patients was 63 years (range, 39-83 years), and the male to female ratio was 3:1. Fifty-three patients had typical histology (3 nodular and 50 diffuse), and 6 had the blastic variant. Approximately 95% of patients presented with advanced stage disease (Ann Arbor Stage III-IV). Leukemic expression was observed in 58%. Complete and partial response rates were 19% and 46%, respectively. Parameters associated with lower response rate were Stage IV, high/intermediate or high risk IPI, and increased lactate dehydrogenase (LDH) level. In the logistic regression analysis, high LDH level and Stage IV disease were associated independently with lower response rate. Median survival was 49 months. Parameters associated with a short survival were: poor PS, splenomegaly, B-symptoms, MI > 2.5, leukocyte count > 10 x 10(9)/L, high LDH level, blastic variant, and high/intermediate or high risk IPI. In the Cox proportional hazards regression model, only poor PS (relative risk RR = 3.3; P = 0.002), splenomegaly (RR = 2.8; P = 0.007), and MI > 2.5 (RR = 2.4; P = 0.012) were associated with short survival.
In this series, patients with MCL presented with advanced stage and extranodal involvement. Only a minority of patients achieved a complete response. The median survival was 4 years, with PS, splenomegaly, and MI being the most important factors predicting survival. These results show clearly that more effective therapies for MCL are needed.
PDF
