Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userGalaxies as seen through the most Energetic Explosions in the Universe
97
0
0.0
(
0
)
Authors
Sandra Savaglio
Ask ChatGPT about the research
No Arabic abstract
A gamma-ray burst (GRB) is a strong and fast gamma-ray emission from the explosion of stellar systems (massive stars or coalescing binary compact stellar remnants), happening at any possible redshift, and detected by space missions. Although GRBs are the most energetic events after the Big Bang, systematic search (started after the first localization in 1997) led to only 374 spectroscopic redshift measurements. For less than half, the host galaxy is detected and studied in some detail. Despite the small number of known hosts, their impact on our understanding of galaxy formation and evolution is immense. These galaxies offer the opportunity to explore regions which are observationally hostile, due to the presence of gas and dust, or the large distances reached. The typical long-duration GRB host galaxy at low redshift is small, star-forming and metal poor, whereas, at intermediate redshift, many hosts are massive, dusty and chemically evolved. Going even farther in the past of the Universe, at z > 5, long-GRB hosts have never been identified, even with the deepest NIR space observations, meaning that these galaxies are very small (stellar mass < 10^7 M_sun). We considered the possibility that some high-z GRBs occurred in primordial globular clusters, systems that evolved drastically since the beginning, but would have back then the characteristics necessary to host a GRB. At that time, the fraction of stellar mass contained in proto globular clusters might have been orders of magnitude higher than today. Plus, these objects contained in the past many massive fast rotating binary systems, which are also regarded as a favorable situation for GRBs. The common factor for all long GRBs at any redshift is the stellar progenitor: it is a very massive rare/short-lived star, present in young regions, whose redshift evolution is closely related to the star-formation history of the Universe.
rate research
Read More
The Italian communities engaged in Gamma-Ray Burst (GRB) and supernova research have been using actively the ESO telescopes and have contributed to improve and refine the observing techniques and even to guide the characteristics and performances of the instruments that were developed. Members of these two communities have recently found ground for a close collaboration on the powerful supernovae that underlie some GRBs. I will review the programs that have led to some important discoveries and milestones on thermonuclear and core-collapse supernovae and on GRBs.
We report on the Herschel/PACS observations of OH in Mrk 231, with detections in 9 doublets observed within the PACS range, and present radiative transfer models for the outflowing OH. Signatures of outflowing gas are found in up to 6 OH doublets with different excitation requirements. At least two outflowing components are identified, one with OH radiatively excited, and the other with low excitation, presumably spatially extended. Particularly prominent, the blue wing of the absorption detected in the in-ladder 2Pi_{3/2} J=9/2-7/2 OH doublet at 65 um, with E_lower=290 K, indicates that the excited outflowing gas is generated in a compact and warm (circum)nuclear region. Because the excited, outflowing OH gas in Mrk 231 is associated with the warm, far-IR continuum source, it is likely more compact (diameter of 200-300 pc) than that probed by CO and HCN. Nevertheless, its mass-outflow rate per unit of solid angle as inferred from OH is similar to that previously derived from CO, >~70x(2.5x10^{-6}/X_{OH}) Msun yr^{-1} sr^{-1}, where X_{OH} is the OH abundance relative to H nuclei. In spherical symmetry, this would correspond to >~850x(2.5x10^{-6}/X_{OH}) Msun yr^{-1}, though significant collimation is inferred from the line profiles. The momentum flux of the excited component attains ~15 L_{AGN}/c, with an OH column density of (1.5-3)x10^{17} cm^-2 and a mechanical luminosity of ~10^{11} Lsun. The detection of very excited OH peaking at central velocities indicates the presence of a nuclear reservoir of gas rich in OH, plausibly the 130-pc scale circumnuclear torus previously detected in OH megamaser emission, that may be feeding the outflow. An exceptional ^{18}OH enhancement, with OH/^{18}OH<~30 at both central and blueshifted velocities, is likely the result of interstellar-medium processing by recent starburst/SNe activity.
Here I present results from individual galaxy studies and galaxy surveys in the Local Universe with particular emphasis on the spatially resolved properties of neutral hydrogen gas. The 3D nature of the data allows detailed studies of the galaxy morphology and kinematics, their relation to local and global star formation as well as galaxy environments. I use new 3D visualisation tools to present multi-wavelength data, aided by tilted-ring models of the warped galaxy disks. Many of the algorithms and tools currently under development are essential for the exploration of upcoming large survey data, but are also highly beneficial for the analysis of current galaxy surveys.
With appropriate spatial resolution, images of spiral galaxies in thermal infrared (~10 micron and beyond) often reveal a bright central component, distinct from the stellar bulge, superimposed on a disk with prominent spiral arms. ISO and Spitzer studies have shown that much of the scatter in the mid-infrared colors of spiral galaxies is related to changes in the relative importance of these two components, rather than to other modifications, such as the morphological type or star formation rate, that affect the properties of the galaxy as a whole. With the Herschel imaging capability from 70 to 500 micron, we revisit this two-component approach at longer wavelengths, to see if it still provides a working description of the brightness distribution of galaxies, and to determine its implications on the interpretation of global far-infrared properties of galaxies.
Here we present new ALMA observations of polarized dust emission from six of the most massive clumps in W43-Main. The clumps MM2, MM3, MM4, MM6, MM7, and MM8, have been resolved into two populations of fragmented filaments. From these two populations we extracted 81 cores (96 with the MM1 cores) with masses between 0.9 Msun to 425 Msun and a mass sensitivity of 0.08 M$_{odot}$. The MM6, MM7, and MM8 clumps show significant fragmentation, but the polarized intensity appears to be sparse and compact. The MM2, MM3, and MM4 population shows less fragmentation, but with a single proto-stellar core dominating the emission at each clump. Also, the polarized intensity is more extended and significantly stronger in this population. From the polarized emission, we derived detailed magnetic field patterns throughout the filaments which we used to estimate field strengths for 4 out of the 6 clumps. The average field strengths estimations were found between 500 $mu$G to 1.8 mG. Additionally, we detected and modeled infalling motions towards MM2 and MM3 from single dish HCO$^{+}(J=4 rightarrow 3)$ and HCN$(J=4 rightarrow 3)$ data resulting in mass infall rates of $dot{mathrm{M}}_{mathrm{MM2}} = 1.2 times 10^{-2}$ Msun yr$^{-1}$ and $dot{mathrm{M}}_{mathrm{MM3}} = 6.3 times 10^{-3}$ Msun yr$^{-1}$. By using our estimations, we evaluated the dynamical equilibrium of our cores by computing the total virial parameter $alpha_{mathrm{total}}$. For the cores with reliable field estimations, we found that 71% of them appear to be gravitationally bound while the remaining 29% are not. We concluded that these unbound cores, also less massive, are still accreting and have not yet reached a critical mass. This also implies different evolutionary time-scales, which essentially suggests that star-formation in high mass filaments is not uniform.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
