Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDYNAMO-HST Survey: Clumps in Nearby Massive Turbulent Disks and the Effects of Clump Clustering on Kiloparsec Scale Measurements of Clumps
81
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present $sim$100 pc resolution Hubble Space Telescope H$alpha$ images of 10 galaxies from the DYnamics of Newly-Assembled Massive Objects (DYNAMO) survey of low-$z$ turbulent disk galaxies, and use these to undertake the first detailed systematic study of the effects of resolution and clump clustering on observations of clumps in turbulent disks. In the DYNAMO-{em HST} sample we measure clump diameters spanning the range $d_{clump} sim 100-800$~pc, and individual clump star formation rates as high as $sim5$~M$_{odot}$~yr$^{-1}$. DYNAMO clumps have very high SFR surface densities, $Sigma_{SFR}sim 15$~M$_{odot}$~yr$^{-1}$~kpc$^{-2}$, $sim100times$ higher than in H{sc ii} regions of nearby spirals. Indeed, SFR surface density provides a simple dividing line between massive star forming clumps and local star forming regions, where massive star forming clumps have $Sigma_{SFR}> 0.5$~M$_{odot}$~yr$^{-1}$~kpc$^{-2}$. When degraded to match the observations of galaxies in $zsim 1-3$ surveys, DYNAMO galaxies are similar in morphology and measured clump properties to clumpy galaxies observed in the high-$z$ Universe. Emission peaks in the simulated high-redshift maps typically correspond to multiple clumps in full resolution images. This clustering of clumps systematically increases the apparent size and SFR of clumps in 1~kpc resolution maps, and decreases the measured SFR surface density of clumps by as much as a factor of 20$times$. From these results we can infer that clump clustering is likely to strongly effect the measured properties of clumps in high-$z$ galaxies, which commonly have kiloparsec scale resolution.
rate research
Read More
We perform a suite of 3D radiation hydrodynamics simulations of photoevaporation of molecular gas clumps illuminated by external massive stars. We study the fate of solar-mass clumps and derive their lifetimes with varying the gas metallicity over a range of $10^{-3} ,Z_odot leq Z leq Z_odot $. Our simulations incorporate radiation transfer of far ultraviolet (FUV) and extreme ultraviolet (EUV) photons, and follow atomic/molecular line cooling and dust-gas collisional cooling. Nonequilibrium chemistry is coupled with the radiative transfer and hydrodynamics in a self-consistent manner. We show that radiation-driven shocks compress gas clumps to have a volume that is set by the pressure-equilibrium with the hot ambient gas. Radiative cooling enables metal-rich clumps to condense and to have small surface areas, where photoevaporative flows are launched. For our fiducial set-up with an O-type star at a distance of 0.1 parsec, the resulting photoevaporation rate is as small as $sim 10^{-5} M_{odot}/{rm yr}$ for metal-rich clumps, but is larger for metal-poor clumps that have larger surface areas. The clumps are continuously accelerated away from the radiation source by the so-called rocket effect, and can travel over $sim$1 parsec within the lifetime. We also study photoevaporation of clumps in a photo-dissociation region. Photoelectric heating is inefficient for metal-poor clumps that contain a smaller amount of grains, and thus they survive for over $10^5$ years. We conclude that the gas metallicity strongly affects the clump lifetime and thus determines the strength of feedback from massive stars in star-forming regions.
We study the evolution of dense clumps and provide argument that the existence of the clumps is not limited by the crossing time of the clump. We claim that the lifetimes of the clumps are determined by the turbulent motions on larger scale and predict the correlation of the clump lifetime and its column density. We use numerical simulations and successfully test this relation. In addition, we study the morphological asymmetry and the magnetization of the clumps as a function of their masses.
The azimuthal substructure observed in some debris disks, as exemplified by epsilon Eridani, is usually attributed to resonances with embedded planets. In a standard scenario, the Poynting-Robertson force, possibly enhanced by the stellar wind drag, is responsible for the delivery of dust from outer regions of the disk to locations of external mean-motion planetary resonances; the captured particles then create characteristic ``clumps. Alternatively, it has been suggested that the observed features in systems like epsilon Eri may stem from populations of planetesimals that have been captured in resonances with the planet, such as Plutinos and Trojans in the solar system. A large fraction of dust produced by these bodies would stay locked in the same resonance, creating the dusty clumps. To investigate both scenarios and their applicability limits for a wide range of stars, planets, disk densities, and planetesimal families we construct simple analytic models for both scenarios. In particular, we show that the first scenario works for disks with the pole-on optical depths below about ~10^{-4}-10^{-5}. Above this optical depth level, the first scenario will generate a narrow resonant ring with a hardly visible azimuthal structure, rather than clumps. The efficiency of the second scenario is proportional to the mass of the resonant planetesimal family, as example, a family with a total mass of ~0.01 to 0.1 Earth masses could be sufficient to account for the clumps of epsilon Eridani.
We tested the validity of the three Larson relations in a sample of 213 massive clumps selected from the Herschel Hi-GAL survey and combined with data from the MALT90 survey of 3mm emission lines. The clumps have been divided in 5 evolutionary stages to discuss the Larson relations also as function of evolution. We show that this ensemble does not follow the three Larson relations, regardless of clump evolutionary phase. A consequence of this breakdown is that the virial parameter $alpha_{vir}$ dependence with mass (and radius) is only a function of the gravitational energy, independent of the kinetic energy of the system, and $alpha_{vir}$ is not a good descriptor of clump dynamics. Our results suggest that clumps with clear signatures of infall motions are statistically indistinguishable from clumps with no such signatures. The observed non-thermal motions are not necessarily ascribed to turbulence acting to sustain the gravity, but they may be due to the gravitational collapse at the clump scales. This seems particularly true for the most massive (M$geq$1000 M$_{odot}$) clumps in the sample, where also exceptionally high magnetic fields may not be enough to stabilize the collapse.
Systematic surveys of massive clumps have been carried out to study the conditions leading to the formation of massive stars. These clumps are typically at large distances and unresolved, so their physical properties cannot be reliably derived from the observations alone. Numerical simulations are needed to interpret the observations. To this end, we generate synthetic Herschel observations using our large-scale star-formation simulation, where massive stars explode as supernovae driving the interstellar-medium turbulence. From the synthetic observations, we compile a catalog of compact sources following the exact same procedure as for the Hi-GAL compact source catalog. We show that the sources from the simulation have observational properties with statistical distributions consistent with the observations. By relating the compact sources from the synthetic observations to their three-dimensional counterparts in the simulation, we find that the synthetic observations overestimate the clump masses by about an order of magnitude on average due to line-of-sight projection, and projection effects are likely to be even worse for Hi-GAL Inner Galaxy sources. We also find that a large fraction of sources classified as protostellar are likely to be starless, and propose a new method to partially discriminate between true and false protostellar sources.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
