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Bruce G Elmegreen - One of the best experts on this subject based on the ideXlab platform.
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mass functions in fractal clouds the role of cloud structure in the stellar initial mass function
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: Mohsen Shadmehri, Bruce G ElmegreenAbstract:The possibility that the stellar initial mass function (IMF) arises mostly from cloud structure is investigated with fractal Brownian motion (fBm) clouds that have power-law power spectra. An fBm cloud with a realistic projected power spectrum slope of β = 2.8 is found to have a mass function for Clumps exceeding a threshold density that is a power law with a slope of α = 2.35, the same as in the Salpeter IMF. Any hierarchically structured cloud has a clump mass function with about the same slope. This result implies that turbulent interstellar clouds produce dense substructure with the observed pre-stellar core mass function built in from the start. Details of the clump formation processes are not critical. The conversion of Clumps into stars involves a second step. A one-to-one correspondence between clump mass and star mass is not necessary to convert the clump mass spectrum into an IMF with the same power-law slope. As long as Clumps have an internal stellar IMF from sub-fragmentation, protostellar accretion, coalescence and other processes, and the characteristic mass for this internal IMF scales with the clump mass, then the IMF slope above the minimum characteristic mass will equal the clump mass slope. A detailed review of IMF models illustrates the prominence of cloud structure as a major component in a wide class of theories. Tests are proposed to determine the relative importance of cloud structure and competitive accretion in the IMF.
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mass functions in fractal clouds the role of cloud structure in the stellar initial mass function
arXiv: Astrophysics of Galaxies, 2010Co-Authors: Mohsen Shadmehri, Bruce G ElmegreenAbstract:The possibility that the stellar initial mass function (IMF) arises mostly from cloud structure is investigated with fractal Brownian motion (fBm) clouds that have power-law power spectra. An fBm cloud with a realistic projected power spectrum slope of $\beta=2.8$ is found to have a mass function for Clumps exceeding a threshold density that is a power-law with a slope of $\alpha=2.35$, the same as in the Salpeter IMF. Any hierarchically structured cloud has a clump mass function with about the same slope. This result implies that turbulent interstellar clouds produce dense substructure with the observed pre-stellar core mass function built in from the start. Details of the clump formation processes are not critical. The conversion of Clumps into stars involves a second step. A one-to-one correspondence between clump mass and star mass is not necessary to convert the clump mass spectrum into an IMF with the same power-law slope. As long as Clumps have an internal stellar IMF from sub-fragmentation, protostellar accretion, coalescence and other processes, and the characteristic mass for this internal IMF scales with the clump mass, then the IMF slope above the minimum characteristic mass will equal the clump mass slope. A detailed review of IMF models illustrates the prominence of cloud structure as a major component in a wide class of theories. Tests are proposed to determine the relative importance of cloud structure and competitive accretion in the IMF.
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the thick disks of spiral galaxies as relics from gas rich turbulent clumpy disks at high redshift
The Astrophysical Journal, 2009Co-Authors: Frederic Bournaud, Bruce G Elmegreen, Marie MartigAbstract:The formation of thick stellar disks in spiral galaxies is studied. Simulations of gas-rich young galaxies show formation of internal Clumps by gravitational instabilities, clump coalescence into a bulge, and disk thickening by strong stellar scattering. The bulge and thick disks of modern galaxies may form this way. Simulations of minor mergers make thick disks too, but there is an important difference. Thick disks made by internal processes have a constant scale height with galactocentric radius, but thick disks made by mergers flare. The difference arises because in the first case, perpendicular forcing and disk-gravity resistance are both proportional to the disk column density, so the resulting scale height is independent of this density. In the case of mergers, perpendicular forcing is independent of the column density and the low-density regions get thicker; the resulting flaring is inconsistent with observations. Late-stage gas accretion and thin-disk growth are shown to preserve the constant scale heights of thick disks formed by internal evolution. These results reinforce the idea that disk galaxies accrete most of their mass smoothly and acquire their structure by internal processes, in particular through turbulent and clumpy phases at high redshift.
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clumpy galaxies in goods and gems massive analogs of local dwarf irregulars
The Astrophysical Journal, 2009Co-Authors: Debra Meloy Elmegreen, Bruce G Elmegreen, Max T Marcus, Karlen Shahinyan, Andrew Yau, Michael PetersenAbstract:Clumpy galaxies in the Galaxy Evolution from Morphology and SEDs and Great Observatories Origins Deep Survey fields are examined for clues to their evolution into modern spirals. The magnitudes of the Clumps and the surface brightnesses of the interclump regions are measured and fitted to models of stellar age and mass. There is an evolutionary trend from clump clusters with no evident interclump emission to clump clusters with faint red disks, to spiral galaxies of the flocculent or grand design types. Along this sequence, the interclump surface density increases and the mass surface density contrast between the Clumps and the interclump regions decreases, suggesting a gradual dispersal of Clumps to form disks. Also along this sequence, the bulge-to-clump mass ratios and age ratios increase, suggesting a gradual formation of bulges. All of these morphological types occur in the same redshift range, indicating that the clump cluster morphology is not the result of bandshifting. This redshift range also includes clear examples of interacting galaxies with tidal tails and other characteristic features, indicating that clump clusters, which do not have these features, are not generally interacting. Comparisons to local galaxies with the same rest wavelength and spatial resolution show that clump clusters are unlike local flocculent and spiral galaxies primarily because of the high clump/interclump contrasts in the clump clusters. They bear a striking resemblance to local dwarf irregulars, however. This resemblance is consistent with a model in which the clumpy morphology comes from gravitational instabilities in gas with a high turbulent speed compared to the rotation speed and a high mass fraction compared to the stars. The morphology does not depend on galaxy mass as much as it depends on evolutionary stage: clump clusters are 100 times more massive than local dwarfs. The apparent lack of star formation in damped Lyman alpha absorbers may result from fast turbulence.
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clumpy galaxies in goods and gems massive analogs of local dwarf irregulars
arXiv: Cosmology and Nongalactic Astrophysics, 2009Co-Authors: Debra Meloy Elmegreen, Bruce G Elmegreen, Max T Marcus, Karlen Shahinyan, Andrew Yau, Michael PetersenAbstract:Clumpy galaxies in the GEMS and GOODS fields are examined for clues to their evolution into modern spirals. The magnitudes of the Clumps and the surface brightnesses of the interclump regions are measured and fitted to models of stellar age and mass. There is an evolutionary trend from clump clusters with no evident interclump emission to clump clusters with faint red disks, to spiral galaxies of the flocculent or grand design types. Along this sequence, the interclump surface density increases and the mass surface density contrast between the Clumps and the interclump regions decreases, suggesting a gradual dispersal of Clumps to form disks. Also along this sequence, the bulge-to-clump mass ratios and age ratios increase, suggesting a gradual formation of bulges. All of these morphological types occur in the same redshift range, indicating that the clump cluster morphology is not the result of bandshifting. Comparisons to local galaxies with the same rest wavelength and spatial resolution show that clump clusters resemble local dwarf Irregulars. This resemblance is consistent with a model in which the clumpy morphology comes from gravitational instabilities in gas with a high turbulent speed compared to the rotation speed and a high mass fraction compared to the stars.
Debra Meloy Elmegreen - One of the best experts on this subject based on the ideXlab platform.
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clumpy galaxies in goods and gems massive analogs of local dwarf irregulars
The Astrophysical Journal, 2009Co-Authors: Debra Meloy Elmegreen, Bruce G Elmegreen, Max T Marcus, Karlen Shahinyan, Andrew Yau, Michael PetersenAbstract:Clumpy galaxies in the Galaxy Evolution from Morphology and SEDs and Great Observatories Origins Deep Survey fields are examined for clues to their evolution into modern spirals. The magnitudes of the Clumps and the surface brightnesses of the interclump regions are measured and fitted to models of stellar age and mass. There is an evolutionary trend from clump clusters with no evident interclump emission to clump clusters with faint red disks, to spiral galaxies of the flocculent or grand design types. Along this sequence, the interclump surface density increases and the mass surface density contrast between the Clumps and the interclump regions decreases, suggesting a gradual dispersal of Clumps to form disks. Also along this sequence, the bulge-to-clump mass ratios and age ratios increase, suggesting a gradual formation of bulges. All of these morphological types occur in the same redshift range, indicating that the clump cluster morphology is not the result of bandshifting. This redshift range also includes clear examples of interacting galaxies with tidal tails and other characteristic features, indicating that clump clusters, which do not have these features, are not generally interacting. Comparisons to local galaxies with the same rest wavelength and spatial resolution show that clump clusters are unlike local flocculent and spiral galaxies primarily because of the high clump/interclump contrasts in the clump clusters. They bear a striking resemblance to local dwarf irregulars, however. This resemblance is consistent with a model in which the clumpy morphology comes from gravitational instabilities in gas with a high turbulent speed compared to the rotation speed and a high mass fraction compared to the stars. The morphology does not depend on galaxy mass as much as it depends on evolutionary stage: clump clusters are 100 times more massive than local dwarfs. The apparent lack of star formation in damped Lyman alpha absorbers may result from fast turbulence.
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clumpy galaxies in goods and gems massive analogs of local dwarf irregulars
arXiv: Cosmology and Nongalactic Astrophysics, 2009Co-Authors: Debra Meloy Elmegreen, Bruce G Elmegreen, Max T Marcus, Karlen Shahinyan, Andrew Yau, Michael PetersenAbstract:Clumpy galaxies in the GEMS and GOODS fields are examined for clues to their evolution into modern spirals. The magnitudes of the Clumps and the surface brightnesses of the interclump regions are measured and fitted to models of stellar age and mass. There is an evolutionary trend from clump clusters with no evident interclump emission to clump clusters with faint red disks, to spiral galaxies of the flocculent or grand design types. Along this sequence, the interclump surface density increases and the mass surface density contrast between the Clumps and the interclump regions decreases, suggesting a gradual dispersal of Clumps to form disks. Also along this sequence, the bulge-to-clump mass ratios and age ratios increase, suggesting a gradual formation of bulges. All of these morphological types occur in the same redshift range, indicating that the clump cluster morphology is not the result of bandshifting. Comparisons to local galaxies with the same rest wavelength and spatial resolution show that clump clusters resemble local dwarf Irregulars. This resemblance is consistent with a model in which the clumpy morphology comes from gravitational instabilities in gas with a high turbulent speed compared to the rotation speed and a high mass fraction compared to the stars.
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bulge and clump evolution in hubble ultra deep field clump clusters chains and spiral galaxies
The Astrophysical Journal, 2009Co-Authors: Bruce G Elmegreen, Debra Meloy Elmegreen, Maria Ximena Fernandez, Jenna Jo LemoniasAbstract:Clump clusters and chain galaxies in the Hubble Ultra Deep Field (UDF) are examined for bulges in Near-Infrared Camera Multi-Object Spectrometer images. Approximately 50% of the clump clusters and 30% of the chains have relatively red and massive Clumps that could be young bulges. Magnitudes and colors are determined for these bulgelike objects and for the bulges in spiral galaxies, and for all of the prominent star formation Clumps in these three galaxy types. The colors are fitted to population evolution models to determine the bulge and clump masses, ages, star formation rate decay times, and extinctions. The results indicate that bulgelike objects in clump clusters and chain galaxies have similar ages and two to five times larger masses compared to the star formation Clumps, while the bulges in spirals have roughly six times larger ages and 20 to 30 times larger masses than the Clumps. All systems appear to have an underlying red disk population. The masses of star-forming Clumps are typically in a range from 107 to 108 M ?; their ages have a wide range around ~102 Myr. Ages and extinctions both decrease with redshift. Star formation is probably the result of gravitational instabilities in the disk gas, in which case the large clump mass in the UDF is the result of a high gas velocity dispersion, 30 km s?1 or more, combined with a high gas mass column density, ~100 M ? pc?2. Because clump clusters and chains dominate disk galaxies beyond z ~ 1, the observations suggest that these types represent an early phase in the formation of modern spiral galaxies, when the bulge and inner disk formed.
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rapid formation of exponential disks and bulges at high redshift from the dynamical evolution of clump cluster and chain galaxies
The Astrophysical Journal, 2007Co-Authors: Frederic Bournaud, Bruce G Elmegreen, Debra Meloy ElmegreenAbstract:Many galaxies at high redshift have peculiar morphologies dominated by 108-109 M☉ kpc-sized Clumps. Using numerical simulations, we show that these "clump clusters" can result from fragmentation in gravitationally unstable primordial disks. They appear as "chain galaxies" when observed edge-on. In less than 1 Gyr, clump formation, migration, disruption, and interaction with the disk cause these systems to evolve from initially uniform disks into regular spiral galaxies with an exponential or double-exponential disk profile and a central bulge. The inner exponential is the initial disk size, and the outer exponential is from material flung out by spiral arms and clump torques. A nuclear black hole may form at the same time as the bulge from smaller black holes that grow inside the dense cores of each clump. The properties and lifetimes of the Clumps in our models are consistent with observations of the Clumps in high-redshift galaxies, and the stellar motions in our models are consistent with the observed velocity dispersions and lack of organized rotation in chain galaxies. We suggest that violently unstable disks are the first step in spiral galaxy formation. The associated starburst activity gives a short timescale for the initial stellar disk to form.
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stellar populations in 10 clump cluster galaxies of the hubble ultra deep field
The Astrophysical Journal, 2005Co-Authors: Bruce G Elmegreen, Debra Meloy ElmegreenAbstract:Color-color diagrams for the clump and interclump emission in 10 clump-cluster galaxies of the Hubble Ultra Deep Field (UDF) are made from B,V, i, and z images and compared with models to determine redshifts, star formation histories, and galaxy masses. These galaxies are members of a class dominated by 5-10 giant Clumps, with no exponential disk or bulge. The redshifts are found to be in the range from 1.6 to 3. The clump emission is typically 40% of the total galaxy emission, and the luminous clump mass is 19% of the total galaxy mass. The clump colors suggest declining star formation over the last ~0.3 Gyr, while the interclump emission is redder than the Clumps, corresponding to a greater age. The clump luminous masses are typically 6 × 108 M☉, and their diameters average 1.8 kpc, making their average density ~0.2 M☉ pc-3. Including the interclump populations, assumed to begin forming at z = 6, the total galaxy luminous masses average 6.5 × 1010 M☉ and their diameters average 19 kpc to the 2 σ noise level. The expected galaxy rotation speeds average ~150 km s-1 if they are uniformly rotating disks. The ages of the Clumps are longer than their internal dynamical times by a factor of ~8, so they are stable star clusters, but the clump densities are only ~10 times the limiting tidal densities, so they could be deformed by tidal forces. This is consistent with the observation that some Clumps have tails. The Clumps could form by gravitational instabilities in accreting disk gas and then disperse on a ~1 Gyr timescale, building up the interclump disk emission, or they could be captured as gas-rich dwarf galaxies, flaring up with star formation at first and then dispersing. Support for this second possibility comes from the high abundance of nearly identical Clumps in the UDF, smaller than 6 pixels, whose distributions on color-magnitude and color-color plots are the same as the galaxy Clumps studied here. The distribution of axial ratios for the combined population of chain and clump-cluster galaxies in the UDF is compared with models and shown to be consistent with a thick-disk geometry. If these galaxies evolve into today's disk galaxies, then we are observing a stage in which accretion and star formation are extremely clumpy and the resulting high velocity dispersions form thick disks. Several clump-clusters have disk densities that are much larger than in local disks, however, suggesting an alternate model in which they do not survive until today, but get converted into ellipticals by collisions.
R Genzel - One of the best experts on this subject based on the ideXlab platform.
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rotational support of giant Clumps in high z disc galaxies
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Daniel Ceverino, Frederic Bournaud, Nir Mandelker, R Genzel, Avishai Dekel, Andreas Burkert, Joel R PrimackAbstract:We address the internal support against total free-fall col lapse of the giant Clumps that form by violent gravitational instability in high-z disc galaxies. Guidance is provided by an analytic model, where the proto-Clumps are cut from a rotating disc and collapse to equilibrium while preserving angular momentum. This model predicts prograde clump rotation, which dominates the support if the clump has contracted to a surface-density contrast > ∼10. This is confirmed in hydro-AMR zoom-in simulations of galaxies in a cosmological context. In most high-z Clumps, the centrifugal force dominates the support, R ≡ V 2 rot/V 2 circ > 0.5, where Vrot is the rotation velocity and the circular velocity Vcirc measures the potential well. The clump spin indeed tends to be in the sense of the global disc angular momentum, but substantial tilts are frequent, reflecting the highly wa rped nature of the high-z discs. Most Clumps are in Jeans equilibrium, with the rest of the support provided by turbulence, partly driven by the gravitational instability itself. The general agreement between model and simulations indicates that angular-momentum loss or gain in most Clumps is limited to a factor of two. Simulations of isolated gas-rich discs that resolve the clump substructure reveal that the cosmological simulations may overestimate R by ∼30%, but the dominance of rotational support at high z is not a resolution artifact. In turn, isolated gas-poor dis c simulations produce at z = 0 smaller gaseous non-rotating transient clouds, indicatin g that the difference in rotational support is associated with the fra ction of cold baryons in the disc. In our current cosmological simulations, the clump rotation velocity is typically more than twice the disc dispersion, Vrot ∼100kms −1 , but when beam smearing of >0.1 arcsec is imposed, the rotation signal is reduced to a small gradient of 6 30kms −1 kpc −1 across the clump. The velocity dispersion in the simulated Clumps is comparable to the disc dispersion so it is expected to leave only a marginal signal for any beam smearing. Retrograde minor-merging galaxies could lead to massive Clumps that do not show rotation even when marginally resolved. Testable predictions of the scenario as simulate d are that the mean stellar age of the Clumps, and the stellar fraction, are declining linearl y with distance from the disc center.
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short lived star forming giant Clumps in cosmological simulations of z 2 disks
The Astrophysical Journal, 2012Co-Authors: Shy Genel, Thorsten Naab, R Genzel, Natascha Forster M Schreiber, Amiel Sternberg, Ludwig Oser, Peter H Johansson, Romeel Dave, Benjamin D OppenheimerAbstract:Many observed massive star-forming z 2 galaxies are large disks that exhibit irregular morphologies, with 1 kpc, 108-1010M⊙ Clumps. We present the largest sample to date of high-resolution cosmological smoothed particle hydrodynamics simulations that zoom-in on the formation of individual M * 1010.5M⊙ galaxies in 1012M⊙ halos at z 2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions (f g 50%), and high specific star formation rates (1 Gyr–1). In accord with recent models, giant Clumps (M clump (5 × 108-109)M⊙) form in situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant Clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialize or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual Clumps, our simulations reproduce well new observational constraints on clump kinematics and clump ages. In particular, the observation that older Clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside-out formation of the disks rather than inward clump migration.
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constraints on the assembly and dynamics of galaxies ii properties of kiloparsec scale Clumps in rest frame optical emission of z 2 star forming galaxies
The Astrophysical Journal, 2011Co-Authors: N Forster M Schreiber, Shy Genel, R Genzel, Alice E Shapley, N Bouche, G Cresci, R Davies, Dawn K Erb, D Lutz, S NewmanAbstract:We study the properties of luminous stellar "Clumps" identified in deep, high-resolution Hubble Space Telescope NIC2/F160W imaging at 1.6 μm of six z ~ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. Individual Clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ≈5000 A emission, with median of ≈2%; the total contribution of clump light ranges from 10% to 25%. The median intrinsic clump size and stellar mass are ~1 kpc and ~10^9 M_☉, in the ranges for Clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation through gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with Advanced Camera for Surveys (ACS)/F814W imaging available for one source, and adaptive-optics-assisted SINFONI Hα data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of Clumps identified at different wavelengths do not fully overlap; NIC2-identified Clumps tend to be redder/older than ACS- or Hα-identified Clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the Clumps, consistent with scenarios where inward migration of Clumps transports material toward the central regions. From constraints on a bulge-like component at radii ≾1-3 kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the buildup of stellar bulges and the role of Clumps in this process.
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rotational support of giant Clumps in high z disc galaxies
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Daniel Ceverino, Frederic Bournaud, Nir Mandelker, R Genzel, Avishai Dekel, Andreas Burkert, Joel R PrimackAbstract:We address the internal support against total free-fall collapse of the giant Clumps that form by violent gravitational instability in high-z disc galaxies. Guidance is provided by an analytic model, where the proto-Clumps are cut from a rotating disc and collapse to equilibrium while preserving angular momentum. This model predicts prograde clump rotation. This is confirmed in hydro-AMR zoom-in simulations of galaxies in a cosmological context. In most high-z Clumps, the centrifugal force dominates the support, R=Vrot^2/Vcirc^2 > 0.5, where Vrot is the rotation velocity and Vcirc is the circular velocity. The clump spin indeed tends to be in the sense of the global disc angular momentum, but substantial tilts are frequent. Most Clumps are in Jeans equilibrium, with the rest of the support provided by turbulence. Simulations of isolated gas-rich discs that resolve the clump substructure reveal that the cosmological simulations may overestimate R by ~30%, but the dominance of rotational support at high-z is not a resolution artifact. In turn, isolated gas-poor disc simulations produce at z=0 smaller gaseous non-rotating transient clouds, indicating that the difference in rotational support is associated with the fraction of cold baryons in the disc. In our current cosmological simulations, the clump rotation velocity is typically Vrot~100 km/s, but when beam smearing of \geq 0.1 arcsec is imposed, the rotation signal is reduced to a small gradient of \leq 30 km/s/kpc across the clump. The velocity dispersion in the simulated Clumps is comparable to the disc dispersion so it is expected to leave only a marginal signal. Retrograde minor-merging galaxies could lead to massive Clumps that do not show rotation.Testable predictions of the scenario as simulated are that the mean stellar age of the Clumps, and the stellar fraction, are declining linearly with distance from the disc center.
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constraints on the assembly and dynamics of galaxies ii properties of kiloparsec scale Clumps in rest frame optical emission of z 2 star forming galaxies
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: N Forster M Schreiber, Shy Genel, R Genzel, Alice E Shapley, N Bouche, G Cresci, R Davies, Dawn K Erb, D Lutz, S NewmanAbstract:We study the properties of luminous stellar Clumps identified in deep, high resolution HST/NIC2 F160W imaging at 1.6um of six z~2 star-forming galaxies with existing near-IR integral field spectroscopy from SINFONI at the VLT. Individual Clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ~5000A emission, with median of about 2%; the total contribution of clump light ranges from 10%-25%. The median intrinsic clump size and stellar mass are ~1kpc and log(Mstar[Msun])~9, in the ranges for Clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation via gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with ACS/F814W imaging available for one source, and AO-assisted SINFONI Halpha data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of Clumps identified at different wavelengths do not fully overlap; NIC2-identified Clumps tend to be redder/older than ACS- or Halpha-identified Clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the Clumps, consistent with scenarios where inward migration of Clumps transports material towards the central regions. From constraints on a bulge-like component at radii <1-3kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the build-up of stellar bulges and the role of Clumps in this process.
K M Menten - One of the best experts on this subject based on the ideXlab platform.
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atlasgal selected massive Clumps in the inner galaxy v temperature structure and evolution
arXiv: Astrophysics of Galaxies, 2017Co-Authors: C. König, A. Giannetti, S. Leurini, J S Urquhart, T Csengeri, F Wyrowski, K M Menten, Rolf GustenAbstract:(Abridged) Aims: We aim to use the progressive heating of the gas caused by the feedback of high-mass young stellar objects (YSOs) to prove the statistical validity of the most common schemes used to define an evolutionary sequence for high-mass Clumps, and characterise the sensitivity of different tracers to this process. Methods: From the spectroscopic follow-ups of the ATLASGAL TOP100 sample, we selected several multiplets of CH3CN, CH3CCH, and CH3OH emission lines to derive and compare the physical properties of the gas in the Clumps along the evolutionary sequence. Our findings are compared with results obtained from CO isotopologues, dust, and NH3 from previous studies on the same sample. Results: The chemical properties of each species have a major role on the measured physical properties. Low temperatures are traced by NH3, CH3OH, and CO (in the early phases), the warm and dense envelope can be probed with CH3CN, CH3CCH, and, in evolved sources via CO isotopologues. CH3OH and CH3CN are also abundant in the hot cores, and their high-excitation transitions may be good tools to study the kinematics in the hot gas surrounding the YSOs that these Clumps are hosting. All tracers show, to different degrees, progressive warming with evolution. The relation between gas temperature and L/M is reproduced by a toy model of a spherical, internally heated clump. Conclusions: The evolutionary sequence defined for the Clumps is statistically valid and we could identify the processes dominating in different intervals of L/M. For L/M 40Lsun/Msun HII regions become common, showing that dissipation of the parental clump dominates.
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the rate and latency of star formation in dense massive Clumps in the milky way
Astronomy and Astrophysics, 2016Co-Authors: Mark H Heyer, S. Leurini, J S Urquhart, T Csengeri, K M Menten, R A Gutermuth, M Wienen, F WyrowskiAbstract:Context. Newborn stars form within the localized, high density regions of molecular clouds. The sequence and rate at which stars form in dense Clumps and the dependence on local and global environments are key factors in developing descriptions of stellar production in galaxies. Aims. We seek to observationally constrain the rate and latency of star formation in dense massive Clumps that are distributed throughout the Galaxy and to compare these results to proposed prescriptions for stellar production. Methods. A sample of 24 ?m-based Class I protostars are linked to dust Clumps that are embedded within molecular clouds selected from the APEX Telescope Large Area Survey of the Galaxy. We determine the fraction of star-forming Clumps, f?, that imposes a constraint on the latency of star formation in units of a clump’s lifetime. Protostellar masses are estimated from models of circumstellar environments of young stellar objects from which star formation rates are derived. Physical properties of the Clumps are calculated from 870 ?m dust continuum emission and NH3 line emission. Results. Linear correlations are identified between the star formation rate surface density, ?SFR, and the quantities ?H2/?ff and ?H2/?cross, suggesting that star formation is regulated at the local scales of molecular clouds. The measured fraction of star forming Clumps is 23%. Accounting for star formation within Clumps that are excluded from our sample due to 24 ?m saturation, this fraction can be as high as 31%, which is similar to previous results. Dense, massive Clumps form primarily low mass (<1–2 M?) stars with emergent 24 ?m fluxes below our sensitivity limit or are incapable of forming any stars for the initial 70% of their lifetimes. The low fraction of star forming Clumps in the Galactic center relative to those located in the disk of the Milky Way is verified.
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the rate and latency of star formation in dense massive Clumps in the milky way
arXiv: Astrophysics of Galaxies, 2016Co-Authors: Mark H Heyer, S. Leurini, J S Urquhart, T Csengeri, K M Menten, R A Gutermuth, M Wienen, F WyrowskiAbstract:Newborn stars form within the localized, high density regions of molecular clouds. The sequence and rate at which stars form in dense Clumps and the dependence on local and global environments are key factors in developing descriptions of stellar production in galaxies. We seek to observationally constrain the rate and latency of star formation in dense massive Clumps that are distributed throughout the Galaxy and to compare these results to proposed prescriptions for stellar production. A sample of 24 micron-based Class~I protostars are linked to dust Clumps that are embedded within molecular clouds selected from the APEX Telescope Large Area Survey of the Galaxy. We determine the fraction of star-forming Clumps, f*, that imposes a constraint on the latency of star formation in units of a clump's lifetime. Protostellar masses are estimated from models of circumstellar environments of young stellar objects from which star formation rates are derived. Physical properties of the Clumps are calculated from 870 micron dust continuum emission and NH_3 line emission. Linear correlations are identified between the star formation rate surface density, Sigma_{SFR}, and the quantities Sigma_{H2}/tau_{ff} and Sigma_{H2}/tau_{cross}, suggesting that star formation is regulated at the local scales of molecular clouds. The measured fraction of star forming Clumps is 23%. Accounting for star formation within Clumps that are excluded from our sample due to 24 micron saturation, this fraction can be as high as 31%. Dense, massive Clumps form primarily low mass (< 1-2 msun) stars with emergent 24 micron fluxes below our sensitivity limit or are incapable of forming any stars for the initial 70% of their lifetimes. The low fraction of star forming Clumps in the Galactic center relative to those located in the disk of the Milky Way is verified.
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atlasgal towards a complete sample of massive star forming Clumps
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: J S Urquhart, Toby J. T. Moore, T Csengeri, F Wyrowski, F Schuller, M G Hoare, S L Lumsden, J C Mottram, M A Thompson, K M MentenAbstract:By matching infrared-selected, massive young stellar objects (MYSOs) and compact HII regions in the RMS survey to massive Clumps found in the submillimetre ATLASGAL survey, we have identified ∼1000 embedded young massive stars between 280 ◦
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atlasgal properties of compact h ii regions and their natal Clumps
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: J S Urquhart, T Csengeri, F Wyrowski, F Schuller, M G Hoare, M A Thompson, K M Menten, T J T Moore, C R Purcell, S L LumsdenAbstract:We present a complete sample of molecular Clumps containing compact and ultracompact (UC) Hii regions betweenl = 10 ◦ and 60 ◦ and|b|< 1 ◦ , identified by combining the the ATLASGAL sub-mm and CORNISH radio continuum surveys wit h visual examination of archival infrared data. Our sample is complete to optically thin, compact and UC Hii regions driven by a zero age main sequence star of spectral type B0 or earlier embedded within a 1,000 M⊙ clump. In total we identify 213 compact and UC Hii regions, associated with 170 Clumps. Unambiguous kinematic distances are derived for these Clumps and used to estimate their masses and physical sizes, as well as the Lyman continuum fluxes and sizes of their embedded Hii regions. We find a clear lower envelope for the surface densit y of molecular Clumps hosting massive star formation of 0.05 g cm −2 , which is consistent with a similar sample of Clumps associated with 6.7 GHz masers. The mass of the most massive embedded stars is closely correlated with the mass of their natal clump. Young B stars appear to be significantly more luminous in the ultraviolet than predicted by current stellar atmosphere models. The properties of Clumps associated with compact and UC Hii regions are very similar to those associated with 6.7 GHz methanol masers and we speculate that there is little evolution in the structure of the molecular Clumps between these two phases. Finally, we identify a significant peak in the surface density of compact and UC Hii regions associated with the W49A star-forming complex, noting that this complex is truly one of the most massive and intense regions of star formation in the Galaxy.
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short lived star forming giant Clumps in cosmological simulations of z 2 disks
The Astrophysical Journal, 2012Co-Authors: Shy Genel, Thorsten Naab, R Genzel, Natascha Forster M Schreiber, Amiel Sternberg, Ludwig Oser, Peter H Johansson, Romeel Dave, Benjamin D OppenheimerAbstract:Many observed massive star-forming z 2 galaxies are large disks that exhibit irregular morphologies, with 1 kpc, 108-1010M⊙ Clumps. We present the largest sample to date of high-resolution cosmological smoothed particle hydrodynamics simulations that zoom-in on the formation of individual M * 1010.5M⊙ galaxies in 1012M⊙ halos at z 2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions (f g 50%), and high specific star formation rates (1 Gyr–1). In accord with recent models, giant Clumps (M clump (5 × 108-109)M⊙) form in situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant Clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialize or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual Clumps, our simulations reproduce well new observational constraints on clump kinematics and clump ages. In particular, the observation that older Clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside-out formation of the disks rather than inward clump migration.
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constraints on the assembly and dynamics of galaxies ii properties of kiloparsec scale Clumps in rest frame optical emission of z 2 star forming galaxies
The Astrophysical Journal, 2011Co-Authors: N Forster M Schreiber, Shy Genel, R Genzel, Alice E Shapley, N Bouche, G Cresci, R Davies, Dawn K Erb, D Lutz, S NewmanAbstract:We study the properties of luminous stellar "Clumps" identified in deep, high-resolution Hubble Space Telescope NIC2/F160W imaging at 1.6 μm of six z ~ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. Individual Clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ≈5000 A emission, with median of ≈2%; the total contribution of clump light ranges from 10% to 25%. The median intrinsic clump size and stellar mass are ~1 kpc and ~10^9 M_☉, in the ranges for Clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation through gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with Advanced Camera for Surveys (ACS)/F814W imaging available for one source, and adaptive-optics-assisted SINFONI Hα data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of Clumps identified at different wavelengths do not fully overlap; NIC2-identified Clumps tend to be redder/older than ACS- or Hα-identified Clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the Clumps, consistent with scenarios where inward migration of Clumps transports material toward the central regions. From constraints on a bulge-like component at radii ≾1-3 kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the buildup of stellar bulges and the role of Clumps in this process.
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constraints on the assembly and dynamics of galaxies ii properties of kiloparsec scale Clumps in rest frame optical emission of z 2 star forming galaxies
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: N Forster M Schreiber, Shy Genel, R Genzel, Alice E Shapley, N Bouche, G Cresci, R Davies, Dawn K Erb, D Lutz, S NewmanAbstract:We study the properties of luminous stellar Clumps identified in deep, high resolution HST/NIC2 F160W imaging at 1.6um of six z~2 star-forming galaxies with existing near-IR integral field spectroscopy from SINFONI at the VLT. Individual Clumps contribute ~0.5%-15% of the galaxy-integrated rest-frame ~5000A emission, with median of about 2%; the total contribution of clump light ranges from 10%-25%. The median intrinsic clump size and stellar mass are ~1kpc and log(Mstar[Msun])~9, in the ranges for Clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation via gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with ACS/F814W imaging available for one source, and AO-assisted SINFONI Halpha data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of Clumps identified at different wavelengths do not fully overlap; NIC2-identified Clumps tend to be redder/older than ACS- or Halpha-identified Clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the Clumps, consistent with scenarios where inward migration of Clumps transports material towards the central regions. From constraints on a bulge-like component at radii <1-3kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the build-up of stellar bulges and the role of Clumps in this process.
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the sins survey of z 2 galaxy kinematics properties of the giant star forming Clumps
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: R Genzel, Shy Genel, N Forster M Schreiber, S Newman, Therese M Jones, Kristen L Shapiro, S J Lilly, A Renzini, L J TacconiAbstract:We have studied the properties of giant star forming Clumps in five z~2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. The Clumps reside in disk regions where the Toomre Q-parameter is below unity, consistent with their being bound and having formed from gravitational instability. Broad H{\alpha}/[NII] line wings demonstrate that the Clumps are launching sites of powerful outflows. The inferred outflow rates are comparable to or exceed the star formation rates, in one case by a factor of eight. Typical Clumps may lose a fraction of their original gas by feedback in a few hundred million years, allowing them to migrate into the center. The most active Clumps may lose much of their mass and disrupt in the disk. The Clumps leave a modest imprint on the gas kinematics. Velocity gradients across the Clumps are 10-40 km/s/kpc, similar to the galactic rotation gradients. Given beam smearing and clump sizes, these gradients may be consistent with significant rotational support in typical Clumps. Extreme Clumps may not be rotationally supported; either they are not virialized, or they are predominantly pressure supported. The velocity dispersion is spatially rather constant and increases only weakly with star formation surface density. The large velocity dispersions may be driven by the release of gravitational energy, either at the outer disk/accreting streams interface, and/or by the clump migration within the disk. Spatial variations in the inferred gas phase oxygen abundance are broadly consistent with inside-out growing disks, and/or with inward migration of the Clumps.
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short lived star forming giant Clumps in cosmological simulations of z 2 disks
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Shy Genel, Thorsten Naab, R Genzel, Natascha Forster M Schreiber, Amiel Sternberg, Ludwig Oser, Peter H Johansson, Romeel Dave, Benjamin D OppenheimerAbstract:Many observed massive star-forming z\approx2 galaxies are large disks that exhibit irregular morphologies, with \sim1kpc, \sim10^(8-10)Msun Clumps. We present the largest sample to date of high-resolution cosmological SPH simulations that zoom-in on the formation of individual M*\sim10^(10.5)Msun galaxies in \sim10^(12)Msun halos at z\approx2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions (f_g\sim50%) and high specific star-formation rates (\gtrsim1Gyr^(-1)). In accord with recent models, giant Clumps (Mclump\sim(5x10^8-10^9)Msun) form in-situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant Clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialise or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual Clumps, our simulations reproduce well new observational constraints on clump kinematics and clump ages. In particular, the observation that older Clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside-out formation of the disks rather than inward clump migration.