Early-type galaxies -- slow and fast rotating ellipticals (E-SRs and E-FRs) and S0s/lenticulars -- define a Fundamental Plane (FP) in the space of half-light radius $R_e$, enclosed surface brightness $I_e$ and velocity dispersion $σ_e$. Since $I_e$ and $σ_e$ are distance-independent measurements, the thickness of the FP is often expressed in terms of the accuracy with which $I_e$ and $σ_e$ can be used to estimate sizes $R_e$. We show that: 1) The thickness of the FP depends strongly on morphology. If the sample only includes E-SRs, then the observed scatter in $R_e$ is $\sim 16\%$, of which only $\sim 9\%$ is intrinsic. Removing galaxies with $M_*<10^{11}M_\odot$ further reduces the observed scatter to $\sim 13\%$ ($\sim 4\%$ intrinsic). The observed scatter increases to the $\sim 25\%$ usually quoted in the literature if E-FRs and S0s are added. If the FP is defined using the eigenvectors of the covariance matrix of the observables, then the E-SRs again define an exceptionally thin FP, with intrinsic scatter of only $5\%$ orthogonal to the plane. 2) The structure within the FP is most easily understood as arising from the fact that $I_e$ and $σ_e$ are nearly independent, whereas the $R_e-I_e$ and $R_e-σ_e$ correlations are nearly equal and opposite. 3) If the coefficients of the FP differ from those associated with the virial theorem the plane is said to be `tilted'. If we multiply $I_e$ by the global stellar mass-to-light ratio $M_*/L$ and we account for non-homology across the population by using Sérsic photometry, then the resulting stellar mass FP is less tilted. Accounting self-consistently for $M_*/L$ gradients will change the tilt. The tilt we currently see suggests that the efficiency of turning baryons into stars increases and/or the dark matter fraction decreases as stellar surface brightness increases.
We present integral field spectroscopy of 10 early-type galaxies in the nearby, low-mass, Fornax cluster, from which we derive spatially resolved stellar kinematics. Based on the morphologies of their stellar velocity maps we classify 2/10 galaxies as slow rotators, with the remaining 8 galaxies fast rotators. Supplementing our integral field observations with morphological and kinematic data from the literature, we analyse the `kinematic' type of all 30 galaxies in the Fornax cluster brighter than M_K = -21.5 mag (M_* ~ 6 x 10^9 M_sun). Our sample's slow rotator fraction within one virial rad…
For early-type galaxies, the ability to sustain a corona of hot, X-ray emitting gas could have played a key role in quenching their star-formation history. Yet, it is still unclear what drives the precise amount of hot gas around these galaxies. By combining photometric and spectroscopic measurements for the early-type galaxies observed during the Atlas3D integral-field survey with measurements of their X-ray luminosity based on X-ray data of both low and high spatial resolution we conclude that the hot-gas content of early-type galaxies can depend on their dynamical structure. Specifically, w…
Galaxy interactions leave imprints in the motions of their stars, and so observing the two-dimensional stellar kinematics allows us to uncover their formation process. Slow rotators, which have stellar orbits dominated by random motions, are thought to be the fossil relics of a sequence of multiple gas-poor mergers, in an environment where the cold gas required to form new stars is nearly absent. Indeed, observations of a handful of nearby galaxy clusters have indicated that slow rotators are preferentially found in the gas-poor, dense cores of clusters, which themselves must form by merging o…
Do the theorised different formation mechanisms of fast and slow rotators produce an observable difference in their star formation histories? To study this we identify quenching slow rotators in the MaNGA sample by selecting those which lie below the star forming sequence and identify a sample of quenching fast rotators which were matched in stellar mass. This results in a total sample of 194 kinematically classified galaxies, which is agnostic to visual morphology. We use u-r and NUV-u colours from SDSS and GALEX and an existing inference package, STARPY, to conduct a first look at the onset …
We study the evidence for a diversity of formation processes in early-type galaxies by presenting the first complete volume-limited sample of slow rotators with both integral-field kinematics from the ATLAS3D Project and high spatial resolution photometry from the Hubble Space Telescope. Analysing the nuclear surface brightness profiles of 12 newly imaged slow rotators, we classify their light profiles as core-less, and place an upper limit to the core size of ~10 pc. Considering the full magnitude and volume-limited ATLAS3D sample, we correlate the presence or lack of cores with stellar kinem…
We present interferometric observations of HI in nine slow rotator early-type galaxies of the Atlas3D sample. With these data, we now have sensitive HI searches in 34 of the 36 slow rotators. The aggregate detection rate is 32\% $\pm$ 8\%, consistent with previous work; however, we find two detections with extremely high HI masses, whose gas kinematics are substantially different from what was previously known about HI in slow rotators. These two cases (NGC 1222 and NGC 4191) broaden the known diversity of HI properties in slow rotators. NGC 1222 is a merger remnant with prolate-like rotation …
Galaxy morphology is inextricably linked to environment. The morphology-density relation quantifies this relationship. However, optical morphology is only loosely related to the kinematic structure of galaxies, and about two thirds of elliptical ("spheroidal") galaxies are actually misclassified face-on disks, and would appear flattened if view edge on. A more robust classification is the slow/fast rotator classification which describes the kinematic structure. Slow and fast rotators form a bimodality in galaxy properties and are thought to follow distinct evolutionary paths, and so a kinemati…
We study the radial acceleration relation (RAR) for early-type galaxies (ETGs) in the SDSS MaNGA MPL5 dataset. The complete ETG sample show a slightly offset RAR from the relation reported by McGaugh et al. (2016) at the low-acceleration end; we find that the deviation is due to the fact that the slow rotators show a systematically higher acceleration relation than the McGaugh's RAR, while the fast rotators show a consistent acceleration relation to McGaugh's RAR. There is a 1σsignificant difference between the acceleration relations of the fast and slow rotators, suggesting that the accelerat…
It has been observed that low redshift early-type galaxies can be separated into slow and fast rotators according to a proxy of specific stellar angular momentum, $λ_{R_e}$. Detailed studies of a handful of nearby clusters have shown that slow rotators are generally found at the centres of clusters where the number density is highest, whereas the fast rotators trace the trend followed by early-type galaxies of increasing in number with local density. In this paper, we study the environmental distribution of slow and fast rotators using the stellar kinematics of about 3900 galaxies from the Slo…
By inverting the distributions of galaxies' apparent ellipticities and misalignment angles (measured around the projected half-light radius $R_{\rm e}$) between their photometric and kinematic axes, we study the intrinsic shape distribution of 189 slow rotator early-type galaxies with stellar masses $2\times 10^{11} M_{\odot}<M_\ast<2\times 10^{12} M_{\odot}$, extracted from a sample of about 2200 galaxies with integral-field stellar kinematics from the DR14 of the SDSS-IV MaNGA IFU survey. Thanks to the large sample of slow rotators, Graham+18 showed that there is clear structure in the misal…
We use the Illustris simulation to study the distributions of ellipticities and kinematic misalignments of galactic projections, as well as the intrinsic shapes and rotation of the simulated galaxies. Our results for the projections of galaxies display clear trends of an overall increase of kinematic misalignment and a slight decrease of ellipticity for fast rotators with increasing masses, while revealing no clear distinction between slow rotators of different mass. It is also found that the number of very slow rotators with large ellipticities is much larger than found in observations. The i…
Two-dimensional integral field surveys such as ATLAS^3D are producing rich observational data sets yielding insights into galaxy formation. These new kinematic observations have highlighted the need to understand the evolutionary mechanisms leading to a spectrum of fast-rotators and slow-rotators in early-type galaxies. We address the formation of slow and fast rotators through a series of controlled, comprehensive hydrodynamical simulations sampling idealized galaxy merger scenarios constructed from model spiral galaxies. Idealized and controlled simulations of this sort complement the more '…
We examine the kinematic morphology of early-type galaxies (ETGs) in eight galaxy clusters in the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. The clusters cover a mass range of 14.2<log(M_200/M_odot)<15.2 and we measure spatially-resolved stellar kinematics for 315 member galaxies with stellar masses 10.0<log(M_*/M_odot)<11.7 within 1R_200 of the cluster centers. We calculate the spin parameter, lambda_R and use that to classify the kinematic morphology of the galaxies as fast or slow rotators. The total fraction of slow rotators in the early-type galaxy populatio…
One quarter of all nearby early-type galaxies (ETGs) outside Virgo host a disc/ring of HI with size from a few to tens of kpc and mass up to ~1e+9 solar masses. Here we investigate whether this HI is related to the presence of a stellar disc within the host making use of the classification of ETGs in fast and slow rotators (FR/SR). We find a large diversity of HI masses and morphologies within both families. Surprisingly, SRs are detected as often, host as much HI and have a similar rate of HI discs/rings as FRs. Accretion of HI is therefore not always linked to the growth of an inner stellar …
In this letter, we investigate the impact of environment on integrated and spatially-resolved stellar kinematics of a sample of massive, quiescent galaxies at intermediate redshift ($0.6<z<1.0$). For this analysis, we combine photometric and spectroscopic parameters from the UltraVISTA and Large Early Galaxy Astrophysics Census (LEGA-C) surveys in the COSMOS field and environmental measurements. We analyze the trends with overdensity (1+$δ$) on the rotational support of quiescent galaxies and find no universal trends at either fixed mass or fixed stellar velocity dispersion. This is consistent…
We present estimates of stellar population (SP) gradients from stacked spectra of slow (SR) and fast (FR) rotator elliptical galaxies from the MaNGA-DR15 survey. We find that: 1) FRs are $\sim 5$ Gyrs younger, more metal rich, less $α$-enhanced and smaller than SRs of the same luminosity $L_r$ and central velocity dispersion $σ_0$. This explains why when one combines SRs and FRs, objects which are small for their $L_r$ and $σ_0$ tend to be younger. Their SP gradients are also different. 2) Ignoring the FR/SR dichotomy leads one to conclude that compact galaxies are older than their larger coun…
The kinematic morphology-density relation of galaxies is normally attributed to a changing distribution of galaxy stellar masses with the local environment. However, earlier studies were largely focused on slow rotators; the dynamical properties of the overall population in relation to environment have received less attention. We use the SAMI Galaxy Survey to investigate the dynamical properties of $\sim$1800 early and late-type galaxies with $\log(M_*/M_{\odot})>9.5$ as a function of mean environmental overdensity ($Σ_{5}$) and their rank within a group or cluster. By classifying galaxies int…
We use spatially resolved two-dimensional stellar velocity maps over a $107"\times 107"$ field of view to investigate the kinematic features of 90 early-type galaxies above stellar mass $10^{11.5}M_\odot$ in the MASSIVE survey. We measure the misalignment angle $Ψ$ between the kinematic and photometric axes and identify local features such as velocity twists and kinematically distinct components. We find 46% of the sample to be well aligned ($Ψ< 15^{\circ}$), 33% misaligned, and 21% without detectable rotation (non-rotators). Only 24% of the sample are fast rotators, the majority of which (91%…
We analyze the stellar kinematics of 39 dwarf early-type galaxies (dEs) in the Virgo cluster. Based on the specific stellar angular momentum lambda_e and the ellipticity, we find 11 slow rotators and 28 fast rotators. The fast rotators in the outer parts of the Virgo cluster rotate significantly faster than fast rotators in the inner parts of the cluster. Moreover, 10 out of the 11 slow rotators are located in the inner 3 degrees (D < 1 Mpc) of the cluster. The fast rotators contain subtle disky structures that are visible in high-pass filtered optical images, while the slow rotators do not ex…
Using Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy, we analyse the stellar kinematics of 18 brightest group early-type (BGEs) galaxies, selected from the Complete Local-Volume Groups Sample (CLoGS). We analyse the kinematic maps for distinct features, and measure specific stellar angular momentum within one effective radius ($λ_{e}$). We classify the BGEs as fast (10/18) or slow (8/18) rotators, suggesting at least two different evolution paths. We quantify the anti-correlation between higher-order kinematic moment $h_{3}$ and V/$σ$ (using the $ξ_{3}$ parameter), and the kinematic mis…
We use the Atlas3D sample to perform a study of the intrinsic shapes of early-type galaxies, taking advantage of the available combined photometric and kinematic data. Based on our ellipticity measurements from the Sloan Digital Sky Survey Data Release 7, and additional imaging from the Isaac Newton Telescope, we first invert the shape distribution of fast and slow rotators under the assumption of axisymmetry. The so-obtained intrinsic shape distribution for the fast rotators can be described with a Gaussian with a mean flattening of q=0.25 and standard deviation sigma_q = 0.14, and an additio…
The fraction of galaxies supported by internal rotation compared to galaxies stabilized by internal pressure provides a strong constraint on galaxy formation models. In integral field spectroscopy surveys, this fraction is biased because survey instruments typically only trace the inner parts of the most massive galaxies. We present aperture corrections for the two most widely used stellar kinematic quantities $V/σ$ and $λ_{R}$. Our demonstration involves integral field data from the SAMI Galaxy Survey and the ATLAS$^{\rm{3D}}$ Survey. We find a tight relation for both $V/σ$ and $λ_{R}$ when m…
In this contribution I show that by combining imaging and integral-field spectroscopy it is possible to unravel the internal structure of galaxies. In particular, I will present the photometric and kinematic evidence for discs linking them with stellar angular momentum content of early-type galaxies. Furthermore, I show that the existence of both fast rotators with core and slow rotators with core-less nuclear light profiles challenges the standard formation scenarios for fast and slow rotators and suggests new pathways of mass assembly.
A cluster intermediate in age between the Pleiades (150 Myr) and the Hyades (600 Myr) is needed to probe the rotational evolution, especially the transition between fast and slow rotation that occurs between the two ages. We study the rich 300 Myr-old open cluster NGC 3532 to provide constraints on angular momentum loss. Measuring the rotation periods builds on our prior work of providing spectroscopic membership information for the cluster, and it supports the chromospheric activity measurements of cluster stars that we provide in a companion paper. Using 42 d-long photometric time series obs…
We measure $λ_{R_e}$, a proxy for galaxy specific stellar angular momentum within one effective radius, and the ellipticity, $ε$, for about 2300 galaxies of all morphological types observed with integral field spectroscopy as part of the MaNGA survey, the largest such sample to date. We use the $(λ_{R_e}, ε)$ diagram to separate early-type galaxies into fast and slow rotators. We also visually classify each galaxy according to its optical morphology and two-dimensional stellar velocity field. Comparing these classifications to quantitative $λ_{R_e}$ measurements reveals tight relationships bet…
We use a sample of $z=0$ galaxies visually classified as slow rotators (SRs) in the EAGLE hydrodynamical simulations to explore the effect of galaxy mergers on their formation, characterise their intrinsic galaxy properties, and study the connection between quenching and kinematic transformation. SRs that have had major or minor mergers (mass ratios $\ge 0.3$ and $0.1-0.3$, respectively) tend to have a higher triaxiality parameter and ex-situ stellar fractions than those that had exclusively very minor mergers or formed in the absence of mergers ("no-merger" SRs). No-merger SRs are more compac…
We use the complete Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey to determine the contribution of slow rotators, as well as different types of fast rotators, to the stellar mass function of galaxies in the local Universe. We use stellar kinematics not only to discriminate between fast and slow rotators, but also to distinguish between dynamically cold systems (i.e., consistent with intrinsic axis ratios$<0.3$) and systems including a prominent dispersion-supported bulge. We show that fast rotators account for more than $80\%$ of the stellar mass budget of nearby gal…
We investigate the anisotropy of the stellar velocity dispersions within the effective radius, $R_{\rm e}$, in 24 ATLAS$^{\rm 3D}$ pure-bulge galaxies, 16 of which are kinematic slow rotators (SRs). We allow the spherical anisotropy parameter $β$ to be radially varying and allow a radial gradient in the stellar mass-to-light ratio ($M_\star/L$) through the parameter $K$ introduced earlier. The median anisotropy for SRs depends on $K$ as follows: $\langleβ_{\rm m}\rangle = a + b K$ with $a=0.19\pm 0.05$, $b=-0.13\pm 0.07$ ($Λ$CDM) or $a=0.21\pm 0.05$, $b=-0.26\pm 0.08$ (MOND), where $β_{\rm m}$…
Using the Illustris simulation, we follow thousands of elliptical galaxies back in time to identify how the dichotomy between fast and slow rotating ellipticals (FRs and SRs) develops. Comparing to the $\textrm{ATLAS}^\textrm{3D}$ survey, we show that Illustris reproduces similar elliptical galaxy rotation properties, quantified by the degree of ordered rotation, $λ_\textrm{R}$. There is a clear segregation between low-mass ($M_{\rm *} < 10^{11} M_{\rm \odot}$) ellipticals, which form a smooth distribution of FRs, and high-mass galaxies ($M_{\rm *} > 10^{11.5} M_{\rm \odot}$), which are mostly…
Observations of galaxy isophotes, longs-slit kinematics and high-resolution photometry suggested a possible dichotomy between two distinct classes of E galaxies. But these methods are expensive for large galaxy samples. Instead, integral-field spectroscopic can efficiently recognize the shape, dynamics and stellar population of complete samples of early-type galaxies (ETGs). These studies showed that the two main classes, the fast and slow rotators, can be separated using stellar kinematics. We showed there is a dichotomy in the dynamics of the two classes. The slow rotators are weakly triaxia…
We present spatially-resolved two-dimensional stellar kinematics for the 41 most massive early-type galaxies (MK <~ -25.7 mag, stellar mass M* >~ 10^11.8 Msun) of the volume-limited (D < 108 Mpc) MASSIVE survey. For each galaxy, we obtain high-quality spectra in the wavelength range of 3650 to 5850 A from the 246-fiber Mitchell integral-field spectrograph (IFS) at McDonald Observatory, covering a 107" x 107" field of view (often reaching 2 to 3 effective radii). We measure the 2-D spatial distribution of each galaxy's angular momentum (lambda and fast or slow rotator status), velocity dispersi…
Recent cosmological hydrodynamical simulations suggest that integral field spectroscopy can connect the high-order stellar kinematic moments h3 (~skewness) and h4 (~kurtosis) in galaxies to their cosmological assembly history. Here, we assess these results by measuring the stellar kinematics on a sample of 315 galaxies, without a morphological selection, using 2D integral field data from the SAMI Galaxy Survey. A proxy for the spin parameter ($λ_{R_e}$) and ellipticity ($ε_e$) are used to separate fast and slow rotators; there exists a good correspondence to regular and non-regular rotators, r…
Recent observations from integral field spectroscopy (IFS) indicate that the fraction of galaxies that are slow rotators, $F_{\rm SR}$, depends primarily on stellar mass, with no significant dependence on environment. We investigate these trends and the formation paths of slow rotators (SRs) using the EAGLE and Hydrangea hydro-dynamical simulations. EAGLE consists of several cosmological boxes of volumes up to $(100\,\rm Mpc)^3$, while Hydrangea consists of $24$ cosmological simulations of galaxy clusters and their environment. Together they provide a statistically significant sample in the st…
We examine the kinematic morphology of early-type galaxies (ETGs) in three galaxy clusters Abell 85, 168 and 2399. Using data from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) we measured spatially-resolved kinematics for 79 ETGs in these clusters. We calculate $λ_{R}$, a proxy for the projected specific stellar angular momentum, for each galaxy and classify the 79 ETGs in our samples as fast or slow rotators. We calculate the fraction of slow rotators in the ETG populations ($f_{SR}$) of the clusters to be $0.21\pm0.08$, $0.08\pm0.08$ and $0.12\pm0.06$ for Abell 85, 168 and …
In this contribution we report on a kinematic study for 33 early type galaxies (ETGs) into their outer halos (average 6 effective radii, Re). We use planetary nebulae (PNe) as tracers of the main stellar population at large radii, where absorption line spectroscopy is no longer feasible. The ePN.S survey is the largest survey to-date of ETG kinematics with PNe, based on data from the Planetary Nebula Spectrograph (PN.S), counter-dispersed imaging, and high-resolution PN spectroscopy. We find that ETGs typically show a kinematic transition between inner regions and halos. Slow rotators have inc…
A massive and evolved slow-rotating galaxy in the early Universe
University of California, Davis（加州大学戴维斯分校）；York University（约克大学）；Tufts University（塔夫茨大学）；University of Toronto（多伦多大学）；University of California, Riverside（加州大学河滨分校）；University of California, Irvine（加州大学尔湾分校）；W. M. Keck Observatory（W·M·凯克天文台）；Ludwig-Maximilians-Universität München（慕尼黑大学）
State-of-the-art integral field surveys like $\mathrm{ATLAS^{3D}}$, SLUGGS, CALIFA, SAMI, and MaNGA provide large data sets of kinematical observations of early-type galaxies (ETGs), yielding constraints on the formation of ETGs. Using the cosmological hydrodynamical \textit{Magneticum Pathfinder} simulations, we investigate the paradigm of fast and slow rotating ETGs in a fully cosmological context. We show that the ETGs within the \textit{Magneticum} simulation are in remarkable agreement with the observations, revealing fast and slow rotators quantified by the angular momentum proxy $λ_{\ma…
We present near-infrared observations of 35 of the most massive early-type galaxies in the local universe. The observations were made using the infrared channel of the Hubble Space Telescope Wide Field Camera 3 in the F110W (1.1 $μ$m) filter. We measured surface brightness profiles and elliptical isophotal fit parameters from the nuclear regions out to a radius of ~10 kpc in most cases. We find that 37% (13) of the galaxies in our sample have isophotal position angle rotations greater than 20 degrees over the radial range imaged by WFC3/IR, which is often due to the presence of neighbors or mu…
We present a 2D kinematic analysis out to ~2-5 effective radii (Re) of 33 massive elliptical galaxies with stellar velocity dispersions larger than 150 km/s. Our observations were taken using the Mitchell Spectrograph (formerly VIRUS-P), a spectrograph with a large 107 x 107 square arcsecond field-of-view that allows us to construct robust, spatially resolved kinematic maps of the mean velocity and velocity dispersion for each galaxy extending to at least 2 Re. Using these maps we study the radial dependence of the stellar angular momentum and other kinematic properties. We see the familiar di…
The observed star formation rate of the Milky Way can be explained by applying a metallicity-dependent factor to convert CO luminosity to molecular gas mass and a star formation efficiency per free-fall time that depends on the virial parameter of a molecular cloud. These procedures also predict the trend of star formation rate surface density with Galactocentric radius. The efficiency per free-fall time variation with virial parameter plays the major role in bringing theory into agreement with observations for the total star formation rate, while the metallicity dependence of the CO luminosit…
We study the distribution of projected ellipticity n(epsilon) for galaxies in a sample of 20 rich (Richness >= 2) nearby (z < 0.1) clusters of galaxies. We find no evidence of differences in n(epsilon), although the nearest cluster in the sample (the Coma Cluster) is the largest outlier (P(same) < 0.05). We then study n(epsilon) within the clusters, and find that epsilon increases with projected cluster-centric radius R (hereafter the epsilon-R relation). This trend is preserved at fixed magnitude, showing that this relation exists over and above the trend of more luminous galaxies to be both …
We present the kinematic morphology-density relation in three galaxy clusters, Abell 85, 168 and 2399, using data from the SAMI Pilot Survey. We classify the early-type galaxies in our sample as fast or slow rotators (FRs/SRs) according to a measured proxy for their projected specific stellar angular momentum. We find each cluster contains both fast and slow rotators with and average fraction of SRs in the sample of $f_{SR}=0.15\pm$0.04. We investigate this fraction within each cluster as a function of local projected galaxy density. For Abell 85 we find that $f_{SR}$ increases at high local d…
Rotation is a directly-observable stellar property, and drives magnetic field generation and activity through a magnetic dynamo. Main sequence stars with masses below approximately 0.35Msun (mid-to-late M dwarfs) are fully-convective, and are expected to have a different type of dynamo mechanism than solar-type stars. Measurements of their rotation rates provide insights into these mechanisms, but few rotation periods are available for these stars at field ages. Using photometry from the MEarth transit survey, we measure rotation periods for 387 nearby, mid-to-late M dwarfs in the Northern hem…
It is generally assumed that galaxies are a bimodal population in both star formation and structure: star-forming galaxies are disks, while passive galaxies host large bulges or are entirely spheroidal. Here, we test this scenario by presenting a full census of the kinematic morphologies of a volume-limited sample of galaxies in the local Universe extracted from the MaNGA galaxy survey. We measure the integrated stellar line-of-sight velocity to velocity dispersion ratio ($V/σ$) for 4574 galaxies in the stellar mass range $9.75 < \log M_{\star}[\rm{M}_{\odot}] < 11.75$. We show that at fixed s…
Whether or not molecular clouds and embedded cloud fragments are stable against collapse is of utmost importance for the study of the star formation process. Only "supercritical" cloud fragments are able to collapse and form stars. The virial parameter, alpha=M_vir/M, which compares the virial to the actual mass, provides one way to gauge stability against collapse. Supercritical cloud fragments are characterized by alpha<2, as indicated by a comprehensive stability analysis considering perturbations in pressure and density gradients. Past research has suggested that virial parameters alpha>2 …
