ترغب بنشر مسار تعليمي؟ اضغط هنا

The young stellar population in NGC 247 Main properties and hierarchical clustering

98   0   0.0 ( 0 )
 نشر من قبل Mar\\'ia Jimena Rodr\\'iguez
 تاريخ النشر 2019
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

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) slopes. We also performed a fractal analysis to determinate the clustering properties of this population. We build a stellar density map and the corresponding dendrograms corresponding to the galactic young population to detect large structures and draw their main characteristics. We detected 339 young star groups, for which we computed a mean radius of $sim$ 60 pc and a maximum in the size distribution between 30 and 70 pc. We also obtained LF slopes with a bimodal distribution showing peaks at $sim$ 0.1 and $sim$ 0.2. We identified several candidates to HII regions which follow an excellent spatial correlation with the young groups found by the PLC. We observed that the young population are hierarchically organized, where the smaller and denser structures are within larger and less dense ones. We noticed that all these groups presented a fractal subclustering, following the hierarchical distribution observed in the corresponding stellar density map. For the large young structures observed in this map, we obtained a fractal dimension of $sim$ 1.6-1.8 using the perimeter-area relation and the cumulative size distribution. These values are consistent with a scenario of hierarchical star formation.

قيم البحث

اقرأ أيضاً

We present a comprehensive study of massive young stellar objects (YSOs) in the metal-poor galaxy NGC 6822 using IRAC and MIPS data obtained from the {em Spitzer Space Telescope}. We find over 500 new YSO candidates in seven massive star-formation re gions; these sources were selected using six colour-magnitude cuts. Via spectral energy distribution fitting to the data with YSO radiative transfer models we refine this list, identifying 105 high-confidence and 88 medium-confidence YSO candidates. For these sources we constrain their evolutionary state and estimate their physical properties. The majority of our YSO candidates are massive protostars with an accreting envelope in the initial stages of formation. We fit the mass distribution of the Stage I YSOs with a Kroupa initial mass function and determine a global star-formation rate of 0.039 $M_{odot} yr^{-1}$. This is higher than star-formation rate estimates based on integrated UV fluxes. The new YSO candidates are preferentially located in clusters which correspond to seven active high-mass star-formation regions which are strongly correlated with the 8 and 24 $mu$m emission from PAHs and warm dust. This analysis reveals an embedded high-mass star-formation region, Spitzer I, which hosts the highest number of massive YSO candidates in NGC 6822. The properties of Spitzer I suggest it is younger and more active than the other prominent H,{sc ii} and star-formation regions in the galaxy.
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 spatial regularity in the distribution of the young stellar population along the galaxy ring was found. The characteristic scale of spacing is about 700 pc. At the same time, we did not find a similar regularity in the distribution of the young stellar population along the spiral arms of NGC 6217. The spatial regularity in concentration of young stellar groupings along spiral arms is a quite rare phenomenon, and it has never been found before in galactic rings.
We use Hyper Suprime-Cam on the Subaru Telescope to investigate the structural and photometric properties of early-type dwarf galaxies and young stellar systems at the center of the M81 Group. We have mapped resolved stars to $sim2$ magnitudes below the tip of the red giant branch over almost 6.5 square degrees, corresponding to a projected area of $160times160 rm{kpc}$ at the distance of M81. The resulting stellar catalogue enables a homogeneous analysis of the member galaxies with unprecedented sensitivity to low surface brightness emission. The radial profiles of the dwarf galaxies are well-described by Sersic and King profiles, and show no obvious signatures of tidal disruption. The measured radii for most of these systems are larger than the existing literature values and we find the total luminosity of IKN ($rm{M_{V,0}}=-14.29$) to be almost 3 magnitudes brighter than previously-thought. We identify new dwarf satellite candidates, d1006+69 and d1009+68, which we estimate to lie at a distance of $4.3pm0.2$ Mpc and $3.5pm0.5$ Mpc. With $rm{M_{V,0}}=-8.91pm0.40$ and $rm{[M/H]}=-1.83pm0.28$, d1006+69 is one of the faintest and most metal-poor dwarf satellites currently-known in the M81 Group. The luminosity functions of young stellar systems in the outlying tidal HI debris imply continuous star formation in the recent past and the existence of populations as young as 30 Myr old. We find no evidence for old RGB stars coincident with the young MS/cHeB stars which define these objects, supporting the idea that they are genuinely new stellar systems resulting from triggered star formation in gaseous tidal debris.
Continuing the attempt to understand the properties of the stellar content in the young cluster NGC 1893 we have carried out a comprehensive multi-wavelength study of the region. The present study focuses on the X-ray properties of T-Tauri Stars (TTS s) in the NGC 1893 region. We found a correlation between the X-ray luminosity, $L_X$, and the stellar mass (in the range 0.2$-$2.0 msun) of TTSs in the NGC 1893 region, similar to those reported in some other young clusters, however the value of the power-law slope obtained in the present study ($sim$ 0.9) for NGC 1893 is smaller than those ($sim$1.4 - 3.6) reported in the case of TMC, ONC, IC 348 and Chameleon star forming regions. However, the slope in the case of Class III sources (Weak line TTSs) is found to be comparable to that reported in the case of NGC 6611 ($sim$ 1.1). It is found that the presence of circumstellar disks has no influence on the X-ray emission. The X-ray luminosity for both CTTSs and WTTSs is found to decrease systematically with age (in the range $sim $ 0.4 Myr - 5 Myr). The decrease of the X-ray luminosity of TTSs (slope $sim$ -0.6) in the case of NGC 1893 seems to be faster than observed in the case of other star-forming regions (slope -0.2 to -0.5). There is indication that the sources having relatively large NIR excess have relatively lower $L_X$ values. TTSs in NGC 1893 do not follow the well established X-ray activity - rotation relation as in the case of main-sequence stars.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا