Distance biases in the estimation of the physical properties of Hi-GAL compact sources-I. Clump properties and the identification of high-mass star forming candidates
Adriano Baldeschi, Davide Elia, Sergio Molinari, Stefano Pezzuto, Eugenio Schisano, Marco Gatti, Andrea Serra, Milena Benedettini, Anna Maria Di Giorgio, John S… 展开作者
Adriano Baldeschi, Davide Elia, Sergio Molinari, Stefano Pezzuto, Eugenio Schisano, Marco Gatti, Andrea Serra, Milena Benedettini, Anna Maria Di Giorgio, John Scige Liu, Manuel Merello
备注：
32 pages, 42 figures, accepted for publication in MNRAS
The degradation of spatial resolution in star-forming regions observed at large distances ($d\gtrsim1$ kpc) with Herschel,can lead to estimates of the physical parameters of the detected compact sources (clumps) which do not necessarily mirror the properties of the original population of cores. This paper aims at quantifying the bias introduced in the estimation of these parameters by the distance effect. To do so, we consider Herschel maps of nearby star-forming regions taken from the Herschel-Gould-Belt survey, and simulate the effect of increased distance to understand what amount of information is lost when a distant star-forming region is observed with Herschel resolution. In the maps displaced to different distances we extract compact sources, and we derive their physical parameters as if they were original Hi-GAL maps of the extracted source samples. In this way, we are able to discuss how the main physical properties change with distance. In particular, we discuss the ability of clumps to form massive stars: we estimate the fraction of distant sources that are classified as high-mass stars-forming objects due to their position in the mass vs radius diagram, that are only "false positives". We give also a threshold for high-mass star-formation $M>1282 \ \left(\frac{r}{[\mathrm{pc}]}\right)^{1.42} M_{\odot}$. In conclusion, this paper provides the astronomer dealing with Herschel maps of distant star-forming regions with a set of prescriptions to partially recover the character of the core population in unresolved clumps.
An Indication of Gas Inflow in Clumpy Star-Forming Galaxies near $z\sim1$: Lower Gas-Phase Metallicities in Clumpy Galaxies Compared to Non-Clumpy Galaxies
We investigate how the properties of Galactic giant molecular clouds (GMCs) and their denser substructures (clumps) correlate with the local star formation rate. We trace clouds using the $^{12}$CO(3-2) transition, as observed by the CO High Resolution Survey (COHRS). We identify their constituent clumps using thermal dust emission, as observed by the Herschel infrared GALactic plane survey (Hi-GAL). We estimate star formation rates in these clouds using 70 $μ$m emission. In total, we match 3,674 clumps to 473 clouds in position-position-velocity space spanning the Galactic longitude range $10…
Massive, star-forming clumps are a common feature of high-redshift star-forming galaxies. How they formed, and why they are so rare at low redshift, remains unclear. In this paper we identify the largest yet sample of clumpy galaxies (7,052) at low redshift using data from the citizen science project \textit{Galaxy Zoo: Clump Scout}, in which volunteers classified over 58,000 Sloan Digital Sky Survey (SDSS) galaxies spanning redshift $0.02 < z < 0.15$. We apply a robust completeness correction by comparing with simulated clumps identified by the same method. Requiring that the ratio of clump-t…
Luminous compact blue galaxies (LCBGs) have enhanced star formation rates and compact morphologies. We combine Sloan Digital Sky Survey data with HI data of 29 LCBGs at redshift z~0 to understand their nature. We find that local LCBGs have high atomic gas fractions (~50%) and star formation rates per stellar mass consistent with some high redshift star forming galaxies. Many local LCBGs also have clumpy morphologies, with clumps distributed across their disks. Although rare, these galaxies appear to be similar to the clumpy star forming galaxies commonly observed at z~1-3. Local LCBGs separate…
We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at 0.5 $\leq z \leq$ 1.5 in the rest-frame far-ultraviolet (FUV) using HST WFC3 broadband imaging in F225W, F275W, and F336W. An analysis of 1,404 galaxies yields 209 galaxies that host 403 kpc-scale clumps. These host galaxies appear to be typical star-forming galaxies, with an average of 2 clumps per galaxy and reaching a maximum of 8 clumps. We measure the photometry of the clumps, and determine the mass, age, and star formation rates (SFR) utilizing the SED-fitting code FAST. We find that clumps make an average c…
Giant, star-forming clumps are a common feature prevalent amongst high-redshift star-forming galaxies and play a critical role in shaping their chaotic morphologies and yet, their nature and role in galaxy evolution remains to be fully understood. A majority of the effort to study clumps has been focused at high redshifts, and local clump studies have often suffered from small sample sizes. In this work, we present an analysis of clump properties in the local universe, and for the first time, performed with a statistically significant sample. With the help of the citizen science-powered Galaxy…
Many massive star forming disc galaxies in the redshift range 3 to 0.5 are observed to have a clumpy morphology showing giant clumps of size $\sim$1 kpc and masses of about $10^7M_{\odot}$ to $10^{10} M_{\odot}$. The nature and fate of these giant clumps is still under debate. In this work we use 19 high-resolution simulations of disc galaxies from the NIHAO sample to study the formation and the evolution of clumps in the discs of high redshift galaxies. We use mock HST - CANDELS observations created with the radiative transfer code GRASIL-3D to carry out, for the first time, a quantitative co…
(Abridged) The properties of stellar clumps in star forming galaxies and their evolution over the redshift range $2\lesssim z \lesssim 6$ are presented and discussed in the context of the build-up of massive galaxies at early cosmic times. We use HST/ACS images of galaxies with spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS) to identify clumps within a 20 kpc radius. We find that the population of galaxies with more than one clump is dominated by galaxies with two clumps, representing $\sim21-25$\% of the population, while the fraction of galaxies with 3, or 4 and more, clumps …
We study young star-forming clumps on physical scales of 10-500 pc in the Lyman-Alpha Reference Sample (LARS), a collection of low-redshift (z = 0.03-0.2) UV-selected star-forming galaxies. In each of the 14 galaxies of the sample, we detect clumps for which we derive sizes and magnitudes in 5 UV-optical filters. The final sample includes $\sim$1400 clumps, of which $\sim$600 have magnitude uncertainties below 0.3 in all filters. The UV luminosity function for the total sample of clumps is described by a power-law with slope $α= -2.03^{+0.11}_{-0.13}$. Clumps in the LARS galaxies have on avera…
We analyse stellar masses of clumps drawn from a compilation of star-forming galaxies at 1.1<z<3.6. Comparing clumps selected in different ways, and in lensed or blank field galaxies, we examine the effects of spatial resolution and sensitivity on the inferred stellar masses. Large differences are found, with median stellar masses ranging from ~10^9 Msun for clumps in the often-referenced field galaxies to ~10^7 Msun for fainter clumps selected in deep-field or lensed galaxies. We argue that the clump masses, observed in non-lensed galaxies with a limited spatial resolution of ~1 kpc, are arti…
Although giant clumps of stars are crucial to galaxy formation and evolution, the most basic demographics of clumps are still uncertain, mainly because the definition of clumps has not been thoroughly discussed. In this paper, we study the basic demographics of clumps in star-forming galaxies (SFGs) at 0.5<z<3, using our proposed physical definition that UV-bright clumps are discrete star-forming regions that individually contribute more than 8% of the rest-frame UV light of their galaxies. Clumps defined this way are significantly brighter than the HII regions of nearby large spiral galaxies,…
To indirectly study the internal structure of giant clumps in main sequence galaxies at $z \sim 1-3$, we target very turbulent and gas-rich local analogues from the DYNAMO sample with the Hubble Space Telescope, over a wavelength range of $\sim 200-480$ nm. We present a catalog of 58 clumps identified in six DYNAMO galaxies, including the WFC3/UVIS F225W, F336W, and F467M photometry where the ($225-336$) and ($336-467$) colours are sensitive to extinction and stellar population age respectively. We measure the internal colour gradients of clumps themselves to study their age and extinction pro…
The morphology of massive star-forming galaxies at high redshift is often dominated by giant clumps of mass ~10^8-10^9 Msun and size ~100-1000 pc. Previous studies have proposed that giant clumps might have an important role in the evolution of their host galaxy, particularly in building the central bulge. However, this depends on whether clumps live long enough to migrate from their original location in the disc or whether they get disrupted by their own stellar feedback before reaching the centre of the galaxy. We use cosmological hydrodynamical simulations from the FIRE (Feedback in Realist…
Studying giant star-forming clumps in distant galaxies is important to understand galaxy formation and evolution. At present, however, observers and theorists have not reached a consensus on whether the observed "clumps" in distant galaxies are the same phenomenon that is seen in simulations. In this paper, as a step to establish a benchmark of direct comparisons between observations and theories, we publish a sample of clumps constructed to represent the commonly observed "clumps" in the literature. This sample contains 3193 clumps detected from 1270 galaxies at $0.5 \leq z < 3.0$. The clumps…
The Clusters, Clumps, Dust, and Gas in Extreme Star-Forming Galaxies (CCDG) survey with the Hubble Space Telescope includes multi-wavelength imaging of 13 galaxies less than 100 Mpc away spanning a range of morphologies and sizes, from Blue Compact Dwarfs (BCDs) to luminous infrared galaxies (LIRGs), all with star formation rates in excess of hundreds of solar masses per year. Images of 7 merging galaxies in the CCDG survey were artificially redshifted to compare with galaxies at z=0.5, 1, and 2. Most redshifted tails have surface brightnesses that would be visible at z=0.5 or 1 but not at z=2…
Compact star-forming clumps observed in distant galaxies are often suggested to play a crucial role in galaxy assembly. In this paper, we use a novel approach of applying finite resolution deconvolution on ground-based images of the COSMOS field to resolve 20,185 star-forming galaxies (SFG) at 0.5<z<2 to an angular resolution of 0.3", and study their clumpy fractions. A comparison between the deconvolved and HST images across four different filters shows good agreement and validates the deconvolution. We model spectral energy distributions using the deconvolved 14-band images to provide resolv…
We present a study of molecular structures (clumps and clouds) in the dwarf galaxy NGC 404 using high-resolution (0.86x0.51 pc^2) Atacama Large Millimeter/sub-millimeter Array ^{12}CO(2-1) observations. We find two distinct regions in NGC 404: a gravitationally-stable central region (Toomre parameter Q=3-30) and a gravitationally-unstable molecular ring (Q<=1). The molecular structures in the central region have a steeper size -- linewidth relation and larger virial parameters than those in the molecular ring, suggesting gas is more turbulent in the former. In the molecular ring, clumps exhibi…
We present $\sim$100 pc resolution Hubble Space Telescope H$α$ 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, $Σ_{SFR}\…
As the precursors to stellar clusters, it is imperative that we understand the distribution and physical properties of dense molecular gas clouds and clumps. Such a study has been done with the ground-based Bolocam Galactic Plane Survey (BGPS). Now the Herschel infrared GALactic plane survey (Hi-GAL) allows us to do the same with higher quality data and complete coverage of the Galactic plane. We have made a pilot study comparing dense molecular gas clumps identified in the Hi-GAL and BGPS surveys, using six $2^\circ \times 2^\circ$ regions centered at Galactic longitudes of $\ell = 11^\circ$,…
In this paper we use HST/WFC3 observations of 6 galaxies from the DYNAMO survey, combined with stellar population modelling of the SED, to determine the stellar masses of DYNAMO clumps. The DYNAMO sample has been shown to have properties similar to $z\approx1.5$ turbulent, clumpy disks. DYNAMO sample clump masses offer a useful comparison for studies of $z>1$ in that the galaxies have the same properties, yet the observational biases are significantly different. Using DYNAMO we can more easily probe rest-frame near-IR wavelengths and also probe finer spatial scales. We find that the stellar ma…
We address the nature of the giant clumps in high-z galaxies that undergo Violent Disc Instability, attempting to distinguish between long-lived clumps that migrate inward and short-lived clumps that disrupt by feedback. We study the evolution of clumps as they migrate through the disc using an analytic model tested by simulations and confront theory with CANDELS observations. The clump ``bathtub" model, which considers gas and stellar gain and loss, is characterized by four parameters: the accretion efficiency, the star-formation-rate (SFR) efficiency, and the outflow mass-loading factors for…
Clumps in spiral galaxies at $z \lesssim 3$: Disentangling two spatial modes of star formation
Pulkovo Astronomical Observatory, Russian Academy of Sciences（俄罗斯科学院普尔科沃天文台）；Sternberg Astronomical Institute, Lomonosov Moscow State University（莫斯科国立大学斯滕伯格天文研究所）；Saint Petersburg State University（圣彼得堡国立大学）
When the cosmic star formation history peaks (z ~ 2), galaxies vigorously fed by cosmic reservoirs are gas dominated and contain massive star-forming clumps, thought to form by violent gravitational instabilities in highly turbulent gas-rich disks. However, a clump formation event has not been witnessed yet, and it is debated whether clumps survive energetic feedback from young stars, thus migrating inwards to form galaxy bulges. Here we report spatially resolved spectroscopy of a bright off-nuclear emission line region in a galaxy at z = 1.987. Although this region dominates the star formatio…
In the quest to understand high-mass star formation, it is necessary to understand that from which the high-mass stars will form -- the dense molecular gas clouds and clumps. The Herschel infrared GALactic plane survey (Hi-GAL) is a comprehensive survey of thermal dust emission that can be used to characterize the properties and Galactic distribution of molecular gas. We have analyzed the survey maps within the Galactic longitude range $10^\circ < \ell < 56^\circ$ and have transformed these 2D maps into a 3D dense gas map of the Galactic plane using distance probability density functions. This…
We study influence by models of inter-stellar medium (ISM) on properties of galaxies in cosmological simulations. We examine three models widely used in previous studies. The ISM models impose different equations of state on dense gas. Using zoom-in simulations, we demonstrate that switching the ISM models can control formation of giant clumps in massive discs at redshifts $z\sim1$--$2$ while their initial conditions and the other settings such as stellar feedback are unchanged. Thus, not only feedback but ISM models can also be responsible for clumpy morphologies of simulated galaxies. We fin…
We study the effect of sub-grid physics, galaxy mass, structural parameters and resolution on the fragmentation of gas-rich galaxy discs into massive star forming clumps. The initial conditions are set up with the aid of the ARGO cosmological hydrodynamical simulation. Blast-wave feedback does not suppress fragmentation, but reduces both the number of clumps and the duration of the unstable phase. Once formed, bound clumps cannot be destroyed by our feedback model. Widespread fragmentation is promoted by high gas fractions and low halo concentrations. Yet giant clumps $M > 10^8 M_{\odot}$ last…
We examine the nature of kpc-scale clumps seen in high-redshift galaxies using a suite of cosmological simulations of galaxy formation. We identify rest-frame UV clumps in mock HST images smoothed to 500 pc resolution, and compare them with the intrinsic 3D clumps of young stars identified in the simulations with 100 pc resolution. According to this comparison, we expect that the stellar masses of the observed clumps are overestimated by as much as an order of magnitude, and that the sizes of these clumps are also overestimated by factor of several, due to a combination of spatial resolution a…
Red clump stars are commonly used to map the reddening and morphology of the inner regions of the Milky Way. We use the new photometric catalogues of the VISTA Variables in the Vía Láctea survey to achieve twice the spatial resolution of previous reddening maps for Galactic longitudes $-10^{\circ}<l<10^{\circ}$ and latitudes $-1.5^{\circ}<b<1.5^{\circ}$. We use these de-reddened catalogues to construct the $K_{s}$ luminosity function around the red clump in the Galactic plane. We show that the secondary peak (fainter than the red clump) detected in these regions does not correspond to the bulg…
Giant clumps are a characteristic feature of observed high-redshift disk galaxies. We propose that these kpc-sized clumps have a complex substructure and are the result of many smaller clumps self-organizing themselves into clump clusters (CC). This bottom-up scenario is in contrast to the common top-down view that these giant clumps form first and then sub fragment. Using a high resolution hydrodynamical simulation of an isolated, fragmented massive gas disk and mimicking the observations from Genzel et al. (2011) at $z \sim 2$, we find remarkable agreement in many details. The CCs appear as …
We present a pixelized source reconstruction method applied on Integral Field Spectroscopic (IFS) observations of gravitationally lensed galaxies. We demonstrate the effectiveness of this method in a case study on the clumpy morphology of a $z \sim 2$ lensed galaxy behind a group-scale lens. We use a Bayesian forward source modelling approach to reconstruct the surface brightness distribution of the source galaxy on a uniformly pixelized grid while accounting for the image point spread function (PSF). The pixelated approach is sensitive to clump sizes down to 100 pc and resolves smaller clump …
Stars form in molecular complexes that are visible as giant clouds ($\sim 10^{5-6} \mathrm{M}_\odot$) in nearby galaxies and as giant clumps ($\sim 10^{8-9}\mathrm{M}_\odot$) in galaxies at redshifts $z\approx1$$-$$3$. Theoretical inferences on the origin and evolution of these complexes often require robust measurements of their characteristic size, which is hard to measure at limited resolution and often ill-defined due to overlap and quasi-fractal substructure. We show that maximum and luminosity-weighted sizes of clumps seen in star formation maps (e.g.\ H$α$) can be recovered statisticall…
We utilize zoom-in cosmological simulations to study the nature of violent disc instability (VDI) in clumpy galaxies at high redshift, $z=1$--$5$. Our simulated galaxies are not in the ideal state assumed in Toomre instability, of linear fluctuations in an isolated, uniform, rotating disk. There, instability is characterised by a $Q$ parameter below unity, and lower when the disk is thick. Instead, the high-redshift discs are highly perturbed. Over long periods they consist of non-linear perturbations, compact massive clumps and extended structures, with new clumps forming in inter-clump regio…
High-resolution simulations of star-forming massive galactic discs have shown that clumps form with a characteristic baryonic mass in the range $10^7-10^8~M_{\odot}$, with a small tail exceeding $10^9~M_{\odot}$ produced by clump-clump mergers. This is in contrast with the observed kpc-size clumps with masses up to $10^{10}~M_{\odot}$ in high-redshift star-forming galaxies. In this paper we show that the comparison between simulated and observed star-forming clumps is hindered by limited observational spatial resolution and sensitivity. We post-process high-resolution hydrodynamical simulation…
Giant stellar clumps are ubiquitous in high-redshift galaxies. They are thought to play an important role in the build-up of galactic bulges and as diagnostics of star formation feedback in galactic discs. Hubble Space Telescope (HST) blank field imaging surveys have estimated that these clumps have masses up to 10$^{9.5}$ M$_{\odot}$ and linear sizes larger than ~1 kpc. Recently, gravitational lensing has also been used to get higher spatial resolution. However, both recent lensed observations and models suggest that the clumps properties may be overestimated by the limited resolution of stan…
Giant star-forming regions (clumps) are widespread features of galaxies at $z \approx 1-4$. Theory predicts that they can play a crucial role in galaxy evolution if they survive to stellar feedback for > 50 Myr. Numerical simulations show that clumps' survival depends on the stellar feedback recipes that are adopted. Up to date, observational constraints on both clumps' outflows strength and gas removal timescale are still uncertain. In this context, we study a line-emitting galaxy at redshift $z \simeq 3.4$ lensed by the foreground galaxy cluster Abell 2895. Four compact clumps with sizes $\l…
We use deep learning to explore the nature of observed giant clumps in high-redshift disc galaxies, based on their identification and classification in cosmological simulations. Simulated clumps are detected using the 3D gas and stellar densities in the VELA zoom-in cosmological simulation suite, with $\sim \!\! 25\ \!\rm{pc}$ maximum resolution, targeting main sequence galaxies at $1\!<\!z\!<\!3$. The clumps are classified as long-lived clumps (LLCs) or short-lived clumps (SLCs) based on their longevity in the simulations. We then train neural networks to detect and classify the simulated clu…
We present Keck/OSIRIS adaptive optics observations with 150-400 pc spatial sampling of 7 turbulent, clumpy disc galaxies from the DYNAMO sample ($0.07<z<0.2$). DYNAMO galaxies have previously been shown to be well matched in properties to main sequence galaxies at $z\sim1.5$. Integral field spectroscopy observations using adaptive optics are subject to a number of systematics including a variable PSF and spatial sampling, which we account for in our analysis. We present gas velocity dispersion maps corrected for these effects, and confirm that DYNAMO galaxies do have high gas velocity dispers…
A new method for measuring the large-scale structure of the Galactic magnetic field is presented. The Galactic magnetic field has been probed through the Galactic disk with near-infrared starlight polarimetry, however the distance to each background star is unknown. Using red clump stars as near-infrared standard candles, this work presents the first attempt to decompose the line of sight structure of the sky-projected Galactic magnetic field. Two example lines-of-sight are decomposed: toward a field with many red clump stars and toward a field with few red clump stars. A continuous estimate o…
We present deep ALMA CO(5-4) observations of a main sequence, clumpy galaxy at z=1.5 in the HUDF. Thanks to the ~0.5" resolution of the ALMA data, we can link stellar population properties to the CO(5-4) emission on scales of a few kpc. We detect strong CO(5-4) emission from the nuclear region of the galaxy, consistent with the observed $L_{\rm IR}$-$L^{\prime}_{\rm CO(5-4)}$ correlation and indicating on-going nuclear star formation. The CO(5-4) gas component appears more concentrated than other star formation tracers or the dust distribution in this galaxy. We discuss possible implications o…
Gas accretion is an important process in the evolution of galaxies, but it has limited direct observational evidences. In this paper, we report the detection of a possible ongoing gas accretion event in a Blue Compact Dwarf (BCD) galaxy, MaNGA 8313-1901, observed by the Mapping Nearby Galaxies and Apache Point Observatory (MaNGA) program. This galaxy has a distinct off-centered blue clump to the northeast (the NE clump) that shows low metallicity and enhanced star-formation. The kinematics of the gas in the NE clump also seems to be detached from the host BCD galaxy. Together with the metallic…
We present $HST$ narrow-band near-infrared imaging of Pa$α$ and Pa$β$ emission of 48 local Luminous Infrared Galaxies (LIRGs) from the Great Observatories All-Sky LIRG Survey (GOALS). These data allow us to measure the properties of 810 spatially resolved star-forming regions (59 nuclei and 751 extra-nuclear clumps), and directly compare their properties to those found in both local and high-redshift star-forming galaxies. We find that in LIRGs, the star-forming clumps have radii ranging from $\sim90-900$ pc and star formation rates (SFRs) of $\sim1\times10^{-3}$ to 10 M$_\odot$yr$^{-1}$, with…
Star-forming clumps dominate the rest-frame ultraviolet morphology of galaxies at the peak of cosmic star formation. If turbulence driven fragmentation is the mechanism responsible for their formation, we expect their stellar mass function to follow a power-law of slope close to $-2$. We test this hypothesis performing the first analysis of the stellar mass function of clumps hosted in galaxies at $z\sim 1-3.5$. The clump sample is gathered from the literature with similar detection thresholds and stellar masses determined in a homogeneous way. To overcome the small number statistics per galax…
Stars form in dense, dusty structures, which are embedded in larger clumps of molecular clouds often showing a clear filamentary structure on large scales (> 1pc). One of the best-studied regions in the Hi-GAL survey can be observed toward the l=224deg field. Here, a filamentary region has been studied and it has been found that protostellar clumps are mostly located along the main filament, whereas starless clumps are detected off this filament and are instead found on secondary, less prominent filaments. We want to investigate this segregation effect and how it may affect the clumps properti…
We present 107 maps of continuum emission at 350 microns from Galactic molecular clumps. Observed sources were mainly selected from the Bolocam Galactic Plane Survey (BGPS) catalog, with 3 additional maps covering star forming regions in the outer Galaxy. The higher resolution of the SHARC-II images (8.5" beam) compared with the 1.1 mm images from BGPS (33" beam) allowed us to identify a large population of smaller substructures within the clumps. A catalog is presented for the 1386 sources extracted from the 350 micron maps. The color temperature distribution of clumps based on the two wavele…
We study the survival versus disruption of the giant clumps in high-redshift disc galaxies, short-lived (S) versus long-lived (L) clumps and two L sub-types, via analytic modeling tested against simulations. We develop a criterion for clump survival, with or without their gas, based on a predictive survivability parameter $S$. It compares the energy sources by supernova feedback and gravitational contraction to the clump binding energy and losses by outflows and turbulence dissipation. The clump properties are derived from Toomre instability, approaching virial and Jeans equilibrium, and the s…
Giant clumps on ~kpc scales and with masses of 10^8-10^9 Msol are ubiquitous in observed high-redshift disc galaxies. Recent simulations and observations with high spatial resolution indicate the existence of substructure within these clumps. We perform high-resolution simulations of a massive galaxy to study the substructure formation within the framework of gravitational disc instability. We focus on an isolated and pure gas disk with an isothermal equation of state with T=10^4 K that allows capturing the effects of self-gravity and hydrodynamics robustly. The main mass of the galaxy resides…
We present spatially-resolved properties of molecular gas and dust in a gravitationally-lensed submillimeter galaxy H-ATLAS J090311.6+003906 (SDP.81) at $z=3.042$ revealed by the Atacama Large Millimeter/submillimeter Array (ALMA). We identified 14 molecular clumps in the CO(5-4) line data, all with a spatial scale of $\sim$50-300 pc in the source plane. The surface density of molecular gas ($Σ_{\rm H_2}$) and star-formation rate ($Σ_{\rm SFR}$) of the clumps are more than three orders of magnitude higher than those found in local spiral galaxies. The clumps are placed in the `burst' sequence …
We study the population of star-forming clumps in A521-sys1, a $\rm z=1.04$ system gravitationally lensed by the foreground ($\rm z=0.25$) cluster Abell 0521. The galaxy presents one complete counter--image with a mean magnification of $\rm μ\sim4$ and a wide arc containing two partial images of A521-sys1 with magnifications reaching $\rm μ>20$, allowing the investigations of clumps down to scales of $\rm R_{eff}<50$ pc. We identify 18 unique clumps with a total of 45 multiple images. Intrinsic sizes and UV magnitudes reveal clumps with elevated surface brightnesses, comparable to similar syst…
We study the dependence of fragmentation in massive gas-rich galaxy disks at $z > 1$ on feedback model and hydrodynamical method, employing the GASOLINE2 SPH code and the lagrangian mesh-less code GIZMO in finite mass mode. We compare non-cosmological galaxy disk runs with standard blastwave supernovae (SN)feedback, which introduces delayed cooling in order to drive winds, and runs with the new superbubble SN feedback, which produces winds naturally by modelling the detailed physics of SN-driven bubbles and leads to efficient self-regulation of star formation. We find that, with blastwave feed…
We present the Green Bank 100m Telescope (GBT) mapping observations of CS 1-0, and the Submillimeter Array (SMA) 157-pointings mosaic of the 0.86 mm dust continuum emission as well as several warm and dense gas tracers, in the central ~20 pc area in Galactic Center. The unprecedentedly large field-of-view and the high angular resolution of our SMA dust image allow the identification of abundant 0.1-0.2 pc scale dense gas clumps. We found that in the Galactic Center, the Class I methanol masers are excellently correlated with the dense gas clumps. However, on the ~0.1 pc scale, these dense gas …
