Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFeedback in Forming Star Clusters: The Mass-Radius Relation and Mass Function of Molecular Clumps in the Large Magellanic Cloud
76
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We derive the mass-radius relation and mass function of molecular clumps in the Large Magellanic Cloud (LMC) and interpret them in terms of the simple feedback model proposed by Fall, Krumholz, and Matzner (FKM). Our work utilizes the dendrogram-based catalog of clumps compiled by Wong et al. from $^{12}$CO and $^{13}$CO maps of six giant molecular clouds in the LMC observed with the Atacama Large Millimeter Array (ALMA). The Magellanic Clouds are the only external galaxies for which this type of analysis is possible at the necessary spatial resolution ($sim1$ pc). We find that the mass-radius relation and mass function of LMC clumps have power-law forms, $R propto M^{alpha}$ and $dN/dM propto M^{beta}$, with indices $alpha = 0.36 pm 0.03$ and $beta= -1.8 pm 0.1 $ over the mass ranges $10^2 M_odot lesssim M lesssim 10^5 M_odot$ and $10^2 M_odot lesssim M lesssim 10^4 M_odot$, respectively. With these values of $alpha$ and $beta$ for the clumps (i.e., protoclusters), the predicted index for the mass function of young LMC clusters from the FKM model is $beta approx 1.7$, in good agreement with the observed index. The situation portrayed here for clumps and clusters in the LMC replicates that in the Milky Way.
rate research
Read More
The Large Magellanic Cloud (LMC), the closest star forming galaxy with low metallicity, provides an ideal laboratory to study star formation in such an environment. The classical dense molecular gas thermometer NH3 is rarely available in a low metallicity environment because of photoionization and a lack of nitrogen atoms. Our goal is to directly measure the gas kinetic temperature with formaldehyde toward six star-forming regions in the LMC. Three rotational transitions of para-H2CO near 218 GHz were observed with the APEX 12m telescope toward six star forming regions in the LMC. Those data are complemented by C18O 2-1 spectra. Using non-LTE modeling with RADEX, we derive the gas kinetic temperature and spatial density, using as constraints the measured para-H2CO 321-220/303-202 and para-H2CO 303-202/C18O 2-1 ratios. Excluding the quiescent cloud N159S, where only one para-H2CO line could be detected, the gas kinetic temperatures derived from the preferred para-H2CO 321-220/303-202 line ratios range from 35 to 63 K with an average of 47 K. Spatial densities of the gas derived from the paraH2CO 303-202/C18O 2-1 line ratios yield 0.4-2.9x10^5 cm^-3 with an average of 1.5x10^5 cm^-3. Temperatures derived from the para-H2CO line ratio are similar to those obtained with the same method from Galactic star forming regions and agree with results derived from CO in the dense regions of the LMC. A comparison of kinetic temperatures derived from para-H2CO with those from the dust also shows good agreement. This suggests that the dust and para-H2CO are well mixed in the studied star forming regions. A correlation between the gas kinetic temperatures derived from para-H2CO and infrared luminosity, represented by the 250um flux, suggests that the kinetic temperatures traced by para-H2CO are correlated with the ongoing massive star formation in the LMC.
We review the complications involved in the conversion of stellar luminosities into masses and apply a range of mass-to-luminosity relations to our Hubble Space Telescope observations of the young LMC star clusters NGC 1805 and NGC 1818. Both the radial dependence of the mass function (MF) and the dependence of the cluster core radii on mass indicate clear mass segregation in both clusters at radii r <= 20-30, for masses in excess of ~1.6-2.5 Msun. This result does not depend on the mass range used to fit the slopes or the metallicity assumed. It is clear that the cluster MFs, at any radius, are not simple power laws. The global and the annular MFs near the core radii appear to be characterised by similar slopes in the mass range (-0.15 <= log m/Msun <= 0.85), the MFs beyond r >= 30 have significantly steeper slopes. We estimate that while the NGC 1818 cluster core is between ~5 and ~30 crossing times old, the core of NGC 1805 is likely $lesssim 3-4$ crossing times old. However, since strong mass segregation is observed out to ~6 Rcore and ~3 Rcore in NGC 1805 and NGC 1818, respectively, it is most likely that significant primordial mass segregation was present in both clusters, particularly in NGC 1805.
Young stellar clusters across nearly five orders of magnitude in mass appear to follow a power-law mass-radius relationship (MRR), $R_{star} propto M_{star}^{alpha}$, with $alpha approx 0.2 - 0.33$. We develop a simple analytic model for the cluster mass-radius relation. We consider a galaxy disc in hydrostatic equilibrium, which hosts a population of molecular clouds that fragment into clumps undergoing cluster formation and feedback-driven expansion. The model predicts a mass-radius relation of $R_{star} propto M_{star}^{1/2}$ and a dependence on the kpc-scale gas surface density $R_{star} propto Sigma_{rm g}^{-1/2}$, which results from the formation of more compact clouds (and cluster-forming clumps within) at higher gas surface densities. This environmental dependence implies that the high-pressure environments in which the most massive clusters can form also induce the formation of clusters with the smallest radii, thereby shallowing the observed MRR at high-masses towards the observed $R_{star} propto M_{star}^{1/3}$. At low cluster masses, relaxation-driven expansion induces a similar shallowing of the MRR. We combine our predicted MRR with a simple population synthesis model and apply it to a variety of star-forming environments, finding good agreement. Our model predicts that the high-pressure formation environments of globular clusters at high redshift naturally led to the formation of clusters that are considerably more compact than those in the local Universe, thereby increasing their resilience to tidal shock-driven disruption and contributing to their survival until the present day.
We report the results of a sensitive search for 12.2 GHz methanol maser emission towards a sample of eight high-mass star formation regions in the Large Magellanic Clouds which have been detected in other maser transitions. We detected one source towards the star formation region N105a. This is the first detection of a 12.2 GHz methanol maser outside our Galaxy. We also made near-contemporaneous observations of the 6.7 GHz methanol and 22 GHz water masers towards these sources, resulting in the detection of water maser emission in six new sources, including one associated with the strongest 6.7 GHz maser in the Magellanic Clouds IRAS 05011-6815. The majority of the maser sources are closely associated with objects identified as likely Young Stellar Objects (YSO) on the basis of Spitzer Space Telescope observations. We find that the YSOs associated with masers tend to be more luminous and have redder infrared colours than the sample as a whole. SED modeling of the YSOs shows that the masers are associated with sources of higher central mass, total luminosity and ambient density than the majority of YSOs in the LMC. This is consistent with the well-established relationship between luminous methanol and water masers and young, high-mass objects observed in the Galaxy.
We used resolved star counts from Hubble Space Telescope images to determine the center of gravity and the projected density profiles of 6 old globular clusters in the Large Magellanic Cloud (LMC), namely NGC 1466, NGC 1841, NGC 1898, NGC 2210, NGC 2257 and Hodge 11. For each system, the LMC field contribution was properly taken into account by making use, when needed, of parallel HST observations. The derived values of the center of gravity may differ by several arcseconds (corresponding to more than 1 pc at the distance of the LMC) from previous determinations. The cluster density profiles are all well fit by King models, with structural parameters that may differ from the literature ones by even factors of two. Similarly to what observed for Galactic globular clusters, the ratio between the effective and the core radii has been found to anti-correlate with the cluster dynamical age.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
