Download Physics of Star Formation: Milky Way and Beyond

Physics of Star Formation:
Milky Way and Beyond
3rd Harvard-Heidelberg workshop
November 8th −10th 2016
Tuesday 8th November
Eric Keto - Foresight talk: Low- and high-mass disks
Aida Ahmadi - CORE: A NOEMA large program to investigate fragmentation and disk kinematics during
high-mass star formation
Many questions remain unanswered in the field of high-mass star formation. Among them are those pertaining
to the fragmentation properties of high-mass gas clumps and the disk-like structures that form within them. To investigate such topics, we have undertaken a NOEMA large program (CORE, PI: Henrik Beuther) for 18 high-mass
star forming clumps in the northern sky, resolving structures at mm wavelength on scales of ∼600AU (∼0.3′′ ). Our
observations are complemented with data from the 30m telescope in order to recover missing flux and probe large
scale structures. In this talk, I will give an overview of the setup of the CORE project and its current status, along with
preliminary results of a case study for W3(H2 O). With a broad range of observed molecules, we are able to disentangle different disk/core contributions and see two fragments within W3(H2 O). A stability analysis of the larger rotating
structure around this clump furthermore proves it to be Toomre-unstable in parts, explaining the fragmentation we
observe.
Chat Hull - Probing magnetic fields in protostellar cores with ALMA observations and next-generation simulations
The first polarization data from ALMA were delivered to PIs last (northern) spring. The data are already both
expanding and confounding our understanding of the role of magnetic fields in low-mass star formation. Here I will
show the highest resolution and highest sensitivity polarization images ever made of a Class 0 protostellar source.
These new ALMA observations achieve ∼150 AU resolution, allowing us to probe polarization – and thus magnetic
field orientation – in the innermost regions surrounding the protostar. The ALMA data reveal magnetic fields that are
parallel with filamentary structures in the source; these fields lead to the central source, indicating that we may be
witnessing magnetized accretion flows onto a protostar for the first time. We compare these observations with cuttingedge AREPO simulations that match the ALMA resolution, and find not only that the source most likely originated
in a weakly magnetized, turbulent envirnoment; but also that the initial conditions at the parsec scales of clouds can
greatly influence source morphology at protostellar scales.
Eric Pellegrini - EvoHII: Observing the Simulations of Massive Star Forming Regions
We present the most realistic MHD simulations of the evolution of star forming regions ever computed with: stellar
winds, super novae, and multi-band radiation transport and pressure. As our understanding of stellar feedback is tied
to interpreting observations, we also present OPIATE, an Optimal Post-processing Iterative Approach to Emissivities,
a general purpose, publicly available code and data base for live or post processing observables from any type of numeric simulation. We will discuss the observational bias to quantifying the impact of various forms of stellar feedback.
Sarah Sadavoy - Embedded Binaries and Their Dense Cores
Several studies have identified higher binary fractions in young, embedded systems than in their older, unembedded stellar counterparts. While these studies have characterized the binaries themselves, the properties of their
parent cores and their connection to the embedded stars remains unclear. To explore the relationship between young,
embedded binaries and their parent cores, we combine the uniform binary database from the VANDAM survey with
core properties obtained from SCUBA-2 observations at 850 µm for the Perseus molecular cloud. We show that most
binary systems are found toward the centres of their parent cores, although several systems have one or more components along the core edge. We separate our systems into tight binaries (<500 AU separations) and wide binaries (>500
AU separations), such that the wide binaries show a preferred alignment with the semi-major axis of their parent core,
whereas the tight binaries show no preferred orientations. We conduct several simple evolutionary models to explain
the observed populations of binaries and individual stars, finding that a model where all stars form as aligned, wide
binaries best explains our observations. Based on this simple model, we predict that the timescale for wide binaries
to shrink into tight orbits is similar to the Class 0 lifetime and the timescale for the wide binaries to breakup into
individual stars is half the Class 0 lifetime. We also obtain a star formation rate in Perseus of 93 M⊙ /Myr, assuming
a Class 0 lifetime of 0.2 Myr, in agreement with previous estimates. If our simple model provides a good fit to other
clouds, then the mass fraction of dense cores that become stars is double what is currently believed.
Roy van Boekel - The distribution of gas and dust in the disk of TW Hya
TW Hya harbors the nearest still gas-rich protoplanetary disk and we see it nearly face-on. Recent ALMA observations with a linear resolution of ∼1 AU revealed numerous bright and dark rings, i.e. much radial structure and
nearly perfect azimuthal symmetry in the distribution of (sub-) mm sized dust grains near the disk midplane. The distribution of gas is much more difficult to constrain using mm observations, even with ALMA it requires exorbitantly
long integrations to map the relevant lines with a resolution better than 10-20 AU.
We present SPHERE images that show the disk in scattered light at optical and near-infrared wavelengths, tracing
the small dust grains in the disk surface at a linear resolution of 1-2 AU. The small grains are dynamically strongly
coupled to the gas, and we use them to infer the bulk gas distribution. To this end, we developed a radiative transfer
model with self-consistent temperature - vertical structure iteration and grain size-dependent dust settling.
The observations show the two known radial depressions at ∼80 and ∼20 AU in unprecedented detail, and reveal
a third ”gap” at ∼5 AU.
Jouni Kainulainen - Foresight talk: Filaments
Phil Myers - Star-forming potential of filamentary clouds
In the Milky Way and in nearby galaxies, star-forming molecular clouds have filamentary structure. How does
this structure affect their production of stars? This paper presents new models of axisymmetric star-forming filaments
having no cores, one low-mass core, and one cluster-forming core. The models resemble observed clouds in their
column density maps and radial profiles, and their N-pdf distributions tend to pole-free power laws at high N, as seen
in filamentary regions. The star-forming potential of each cloud estimated by identifying its ”star-forming zone” and
by modelling its thermal fragmentation.This analysis indicates that the Musca Center filament has enough dense gas
to make its first ∼ 3 protostars, the Coronet filament can add ∼ 8 protostars to its ∼20 known stars, but L43 does not
have enough dense gas to add any protostars to its 2 already known.
Lightening Talk Session 1 - Posters 1-15
Wednesday 9th November
Cara Battersby - TBD
Stefanie Walch - Foresight talk: The physics of the ISM
Michael Rugel - THOR - The H I,OH, Recombination Line survey of the Milky Way
How does cloud formation proceed from atomic to molecular gas? How do the ionized, atomic and molecular
phases of the interstellar medium interact, e.g. in photodissociation regions or around high mass star forming clusters
or supernovae remnants?
To address these questions, the THOR (THOR - The H I,OH, Recombination Line survey of the Milky Way) maps
the HI 21 cm line, the continuum from 1-2 GHz, the four OH ground stat transitions and 19 Radio Recombination
lines in the northern part of the Milky Way (l = 15◦ −67◦ , |b|<1◦ ). The resolution of 15′′ - 25′′ allows us to combine
our data with existing surveys on similar scales in different wavelengths.
I will provide an overview on the THOR project and present early results on different aspects of the survey: We
determine accurately the column density of atomic hydrogen by accounting for optical depth effects and trace the
conversion of atomic to molecular gas by comparison with complementary archival dust continuum and CO data.
New OH maser sites tracing star-forming regions, evolved stars and supernovae remnants, are discovered and set into
the Galactic context. Thermal OH absorption against Galactic HII regions as well as extragalactic sources allow us to
investigate phase transitions of the ISM in more diffuse gas and around photon-dominated regions. In addition to this,
the radio recombination line data enables investigations of the kinematics of ionized gas and feedback processes back
into the ISM.
Lightening Talk Session 2 - Posters 16-30
Andreas Burkert - Gravity versus Turbulence
Structure formation in the interstellar medium is believed to be driven by irregular gas flows, often interpreted
as turbulence and gravitational collapse. Filamentary scaling laws might provide more insight into these processes.
I currently plan to present a new scaling relation for filaments in the ISM and will interpret that in the context of
turbulent versus gravitational flows.
Javier Ballesteros-Paredes - Gravity or Turbulence? On the origin of molecular clouds non-thermal motions
The so-called Larson scaling laws found empirically in molecular clouds (MCs) have been generally interpreted
as one of the main evidences that the clouds are turbulent, that such turbulence is scale-free, and that MCs are in
Virial equilibrium, implying in the collective imagination of astronomers that turbulence provides support to molecular clouds against collapse. Moreover, the origin of MC turbulence is still not properly understood, since it appears
to be homogeneous and ubiquitous along the galaxy, while the sources of turbulence are mostly pointlike (stars or
supernova), and turbulence is highly dissipative. In this presentation I will discuss why recent molecular cloud observations, and models of cloud formation suggest that a) Larsons relations are the result of strong observational biases,
b) they can be replaced by a single, more general relation, which in any event, still has a large scatter, and c) the main
source of non-thermal motions in molecular clouds is a disordered, chaotic and hierarchical gravitational collapse of
MCs. In other words, the supersonic, apparently turbulent but certainly chaotic motions is only a by-product of MC
collapse, and it cannot be considered as the source for support of molecular clouds against collapse. This, furthermore,
explains in a simple, natural way why MCs appear to be in virial equilibrium. As a corollary, the scale-free nature of
the motions, if exists, has a gravitational origin, rather than a turbulent one.
Marco Lombardi - Herschel-Planck view of local molecular clouds
Herschel and Planck dust emission maps, together with the robust near-infrared extinction maps, are among the
best tools we have at the moment to study the structure of dark molecular clouds and their relationship to starformation. In this talk I will present newly reduced Herschel-Planck maps of nearby (< 500 pc) molecular clouds
and highlights a few scientific results that have been obtained from them: the structure of clouds as described by the
column density probability distribution, the cloud star formation efficiency (local Schmidt law), and the distribution
of protostar clusters in the clouds.
Thursday 10th November
Simon Glover - Does chemistry matter?
Many numerical simulations of molecular cloud formation or of star cluster formation within clouds make the
simplifying assumption that the chemical evolution of the gas can be neglected. However, it is not immediately obvious that this is true, since the chemical state of the gas can significantly influence its ability to cool. In this talk,
I review what we know about the influence of chemistry on the formation of clouds and clusters and highlight the
circumstances in which chemistry matters.
Eva Schinnerer - Foresight talk: Extragalactic star formation
Kathryn Kreckel - The impact of galactic environment on star formation
While spiral arms are the most prominent sites for star formation in disk galaxies, interarm star formation contributes significantly to the overall star formation budget. However, it is still an open question if the star formation
proceeds differently in the arm and inter-arm environment. We use deep VLT/MUSE optical IFU spectroscopy to
resolve and fully characterize the physical properties of 428 interarm and arm HII regions in the nearby grand design
spiral galaxy NGC 628. Unlike molecular clouds (the fuel for star formation) which exhibit a clear dependence on
galactic environment, we find that most H II region properties (luminosity, size, metallicity, ionization parameter) are
independent of environment. One clear exception is the diffuse ionized gas (DIG) contribution to the arm and interarm
flux (traced via the temperature sensitive [SII]/Hα line ratio inside and outside of the HII region boundaries). We find
a systematically higher DIG background within H II regions, particularly on the spiral arms. Correcting for this DIG
contamination can result in significant (70%) changes to the star formation rate measured. We also show preliminary
results comparing well-corrected star formation rates from our MUSE HII regions to ALMA CO(2−1) molecular gas
observations at matched 1′′ =35pc resolution, tracing the Kennicutt-Schmidt star formation law at the scales relevant
to the physics of star formation. We estimate the timescales relevant for GMC evolution using distance from the spiral
arm as a proxy for age, and test whether star formation feedback or galactic-scale dynamical processes dominate
GMC disruption.
Maria Jesus Jimenez-Donaire - First Results From the EMPIRE Nearby Galaxy Dense Gas Survey
I will present first results from our IRAM 30m large program EMPIRE, a ∼500 hr compaign to map high critical
density tracers like HCN or HCO+ across the entire star forming disks of 9 nearby galaxies. The key goal of the survey is to understand how dense gas fractions and star formation efficiencies vary across and among galaxies and how
they relate to environmental / ISM conditions, like dust-to-gas ratios, molecular fractions, pressure or rotation / shear.
In a first round of studies, we analyzed these quantities in the nearby galaxy M51 and in the inner disk of NGC4321,
where we focus on high-resolution measurements ( ∼200pc) by combining EMPIRE with follow-up ALMA data.
One key finding is a variable efficiency of the dense gas to form stars, which I will discuss in the context of Milky
Way work and theoretical expectations. EMPIRE also provides high signal-to-noise 13 CO (and C18 O) data. These
optically thin lines are important column density tracers and can be used to constrain abundance variations across our
galaxies. I will discuss these results and conclude by providing an overview of ongoing projects in EMPIRE including
several follow-up projects (excitation studies from higher-J HCN observations, complementary dense gas studies of
starburst environments).
Laura Zschaechner - The Impact on Galactic-Scale Molecular Outflows on Star Formation: ALMA Observations of Circinus and NGC 253
Galactic outflows are poorly understood although they are essential to feedback processes that quench star formation and limit the total mass of large galaxies. Thus, insufficient understanding of feedback associated with them
- in particular molecular phase - is one of the greatest shortcomings in our knowledge of galaxy evolution and star
formation across cosmic time. Multiphase outflows associated with galactic winds have been well-studied at a range
of wavelengths, but detailed observations of the molecular phase are only now feasible with new instruments such
as ALMA. We present ALMA observations and kinematic models of the molecular outflows in Circinus galaxy and
NGC 253. Using these data, we constrain the molecular mass of the winds and outflow rates - both crucial to future
star formation. We compare the AGN-driven molecular wind in Circinus to the starburst-driven wind in NGC 253 and
note key differences in the ways each type of wind impacts star formation.
Volker Springel - Foresight talk: Star formation physics in simulations on galaxy scales
Roberto Decarli - ASPECS: The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field
Multi-wavelength studies have accurately constrained the growth of galaxies through cosmic time: The rate of star
formation per unit of cosmological volume increased from the earliest epochs until z=1-3 (Universe age: 2-6 Gyr),
when it peaked (the ”epoch of galaxy assembly”), then steeply declined by more than an order of magnitude until z=0
(today). What drives this evolution? I will address this fundamental question by targeting the fuel for star formation,
i.e., the dense phase of the interstellar medium. I will do so in the context of ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field, the largest extragalactic endeavor of ALMA to date in terms of telescope time.
For the first time, observations of the interstellar medium in high-z galaxies can be pushed well beyond the tip of the
iceberg of extremely luminous galaxies, thus uncovering the bulk of the galaxy population. We can directly gauge the
molecular gas content of galaxies throughout cosmic time, and constrain the efficiency of star formation in different
galaxy types and cosmic epochs. The results of these studies provide unique constraints on empirical predictions and
theoretical models of the physics of the interstellar medium and thus of the evolution of galaxies throughout cosmic
time.
Diederik Kruijssen - The multi-scale physics of star and cluster formation in galaxies across cosmic time
I will present a broad overview of our groups recent work on the multi-scale behaviour of the star formation relation, which turns out to be an unprecedented probe of the cloud-scale physics of star/cluster formation and feedback.
In the process, I will touch on star formation in nearby galaxies, the formation and dynamical evolution of stellar
clusters, and star formation in the Central Molecular Zone of the Milky Way. We can now obtain molecular cloud
lifetimes, star formation efficiencies, feedback timescales, feedback efficiencies, and coherence length scales for the
bulk of the local galaxy population. I will connect these measurements to recent theoretical insights in the field of
cluster formation and evolution, which have led to a unified understanding of stellar clustering across cosmic time,
from local open clusters and associations to old globular cluster populations. The Central Molecular Zone of the
Milky Way offers an ideal environment to test these ideas outside of the comfort zone of the solar neighbourhood, to
which most modern theories of star and cluster formation have been calibrated. The presented results show that star
and cluster formation is governed by universal, multi-scale physics across a large range of cosmic environments. I
will conclude by discussing some major open questions and directions for future work.
Posters for Lightening Talk Session 1
1. Simon Bihr - Studying atomic hydrogen during cloud formation by means of HISAs: Kinematics and probability distribution functions
Probability distribution functions (PDFs) of the column density or volume density of hydrogen are a common tool
to examine molecular clouds. Due to turbulent motion, the initial PDFs have a log-normal shape and evolve into a
power-law tail at high column densities due to collapse and gravitational forces. To date, these studies are mostly
limited to the molecular content of the cloud. On my poster, I will present a study of the cold atomic content of the
giant molecular filament GMF38.1−32.4, present column density PDFs and study the corresponding kinematics. We
extracted a long H I self absorption (HISA) feature, which correlates partly with CO emission. The peak velocity
of the HISA and CO shows a close correlation on one side of the filament, whereas a velocity step is visible on the
other side. The column density of the cold absorbing HI is on the order of 1020 −1021 cm−2 . In contrast to this, the
column density of the molecular hydrogen, traced with CO, is an order of magnitude higher. The shape of the atomic
and molecular column density PDF reveal mostly log-normal shapes, indicating turbulent motion as the main driver.
This interpretation is supported by the measured linewidth of δv = 6-8 km s−1 for the HISA. We speculate that we
observe different evolutionary stages within the filament. The left sub-region seems to be forming a molecular cloud
out of the atomic environment, whereas the right sub-region already shows high column density peaks and active star
formation. Furthermore, I will present a comparison of these results with Herschel dust observations, covering the
atomic and molecular gas. Such studies are an important characterization of the transition between the atomic and
molecular phase and influence simulations as well as theoretical studies.
2. Felix Bosco - The High-mass Star Forming Region IRAS 23033+5951
The high-mass star forming region IRAS 23033+5951 is an excellent example of comparatively isolated massive
star formation. This case study was conducted as part of the NOEMA large program CORE (PI H. Beuther, see also
overview talk by A. Ahmadi), aiming at the fragmentation of cores and at the formation of disks during high-mass
star formation. I present the latest results toward IRAS 23033+5951 combining NOEMA and IRAM 30m data. A
complex multiple outflow structure was resolved, as well as evidences for large disks revealed. The stability of these
disks is analyzed and the results will be compared to the literature.
3. Michael Butler - Regulation of Galactic Star Formation Rates by Stellar Feedback
Star formation from the interstellar medium of galactic disks is a basic process controlling the evolution of galaxies. Most stellar populations are built in this way. Understanding the star formation rate in a local patch of a disk
with a given gas mass is thus an important challenge for theoretical models. Here we simulate a kiloparsec region
of a disk, following the evolution of self-gravitating molecular clouds down to subparsec scales, as they form stars
that then inject feedback by dissociating and ionizing UV photons and supernova explosions. We assess the relative
importance of each feedback mechanism. Our fiducial models that combine all three feedback mechanisms yield,
without fine-tuning, rates that are in excellent agreement with observations, with dissociating and ionizing photons
playing a dominant role.
4. Hope Chen - Anatomy of the column density PDF
The column density PDF has been utilized to trace various physical processes. For example, the ”log-normal”
component is said to correlate with the turbulent Mach number, and the ”power-law tail” is often proposed to correlate with numbers and ratios of YSOs. In this talk, I will give a brief overview of what has been done with the column
density PDF and evaluate the ”trueness/observability” of each correlation, in both simulations and observations. I will
then present practical methods to use the column density PDF in observations to trace the star formation, including its
timescale and the kinematics involved.
5. Mélanie Chevance - Probing the multiphase ISM in an extreme star forming low-metallicity environment:
30 Doradus in the LMC
The 30 Doradus region in the Large Magellanic Cloud (LMC) offers the best laboratory to examine in detail the
interplay between stellar activity and a metal-poor interstellar medium (ISM). The main stellar source of radiation,
provided by the closest example of a super star cluster, R136, shapes the surrounding half-solar metallicity ISM.
The proximity of 30 Doradus (50kpc) makes it possible to study gas and dust over large scales in this dramatic
environment. I will present a far-infrared (FIR) view of this extreme star-forming region.
The Herschel/PACS and SPIRE/FTS observations of FIR fine structure lines, combined with Spitzer/IRS spectroscopic maps, have been used to constrain the physical conditions in the photo-dissociation regions (PDR) with the
Meudon PDR code (Le Petit et al., 2006). This allows us to construct a comprehensive, self-consistent picture of the
density, radiation field, and ISM structure (Chevance et al., 2016). We quantify the effect of intense radiation field
on this low metallicity ISM. In particular, we build a 3-dimensionnal view of the region. We bring constraints to the
fraction of molecular dark gas not traced by CO, the so-called CO-dark gas and find that a large reservoir of H2 is not
traced by CO in this extreme environment.
Our follow-up observations of [CII] 158 µm, [OI] 145 µm, [OIII] 88 µm and [OIII] 52 µm of the full 90pc*×75pc
region with SOFIA/FIFI-LS reveal a more complete picture and allow us to study the evolution of the gas conditions
and structure with the proximity of R136.
6. Roxana-Adela Chira - Fragmenting Filaments
Dust surveys, for example by Herschel, have shown the complexity of molecular clouds and how important their
filamentary structure is for the process of star formation. One of the key questions in this context is how filaments
fragment and condensate into pre-stellar cores. We address this question by investigating the evolution in time of filaments that formed within FLASH AMR simulations of a self-gravitating, magnetized, supernova-driven, ISM, and the
criteria that lead to their fragmentation. We discuss the results in context of the underlying physics of the simulations.
7. Douglas Finkbeiner - 3-D Dust Mapping with Stellar Reddenings
Our recent work with mapping dust in 3-D with Pan-STARRS1 and 2MASS advances our knowledge of the 3-D
arrangement of dust features in the MW. I will show what we have done and discuss future improvements with Gaia
and LSST.
8. Sam Green - Regulating Star Formation with Radiative Feedback
Massive stars produce a large quantity of ionising radiation. In this talk I present work comprising numerical simulations and analytic theory that allows us to interpret the dynamics of star-forming molecular clouds and provides
insights into observed relations in star-forming regions. We find that the ram pressure inside molecular clouds is a
key parameter for determining the evolution of HII regions, and hence the star formation efficiency of clouds and the
subsequent evolution of supernova remnants from the embedded cluster. Ionising radiation feedback is also important
in explaining the observed star formation efficiencies in nearby star-forming regions.
9. Matthias Gritschneder - The Formation and Fragmentation of Filaments
We analyze the stability of filaments in equilibrium between gravity and internal as well as external pressure using the grid based AMR-code RAMSES. It is well known that a straight marginable stable cylinder fragments into
cores if the density is slightly perturbed. The cores form on the length scale of the fastest growing mode, set by the
mass-to-line ratio of the filament. However, we discovered that a homogenous cylinder in a stable configuration starts
to oscillate, is triggered into fragmentation, and collapses when it is bent, e.g. with a slight sinusoidal perturbation.
This previously unstudied behaviour is important as it allows a filament to fragment at any given scale, as long as it
has slight bends. In our realization in the figure below, the spacing between the cores matches the wavelength of the
sinusoidal perturbation. We then continue to investigate the formation of filaments by studying infall onto a filament
and the created sub(sonic) turbulence. This enables us to address the question if quiescent, Ostriker-like filaments can
be formed easily or if the initial conditions already set the future fragmentation properties.
10. Lionel Haemmerlé - Impact of initial conditions and variable accretion rates on the pre-main-sequence
evolution of massive and intermediate-mass stars
Despite the crucial importance of massive stars in the evolution of the interstellar medium, of galaxies and of the
whole Universe, the process of their formation is still far from being understood. In particular, the pre-main-sequence
evolution of objects destined to become massive stars by accretion, and the properties of their radiative feedback
remain open issues. We present pre-main-sequence tracks for massive and intermediate-mass stars, using the Geneva
code with variable accretion rates, and focusing on the impact of the initial conditions on the evolution of stellar
radius, effective temperature and ionizing luminosity. We show that the magnitude of the swelling of the protostar for
high accretion rates depends sensitively on the initial conditions. For radiative initial structures, the star reacts quickly
to accretion bursts, leading to considerable changes in photospheric properties on timescales as short as 100 - 1000
yr. The evolution for convective initial structures is much less influenced by the instantaneous accretion rate, and
produces a monotonically increasing ionizing flux that can be many orders of magnitude smaller than in the radiative
case. For massive stars, it results in a delay of the HII region expansion by up to 10,000 yr. In the radiative case, the
HII region can potentially be engulfed by the star during the swelling, which never happens in the convective case.
We conclude that the early stellar structure has a large impact on the radiative feedback during the pre-main-sequence
evolution of massive protostars and introduces an important uncertainty that should be taken into account in models
of massive star formation. Because of their lower effective temperatures, our convective initial models may hint at
a solution to an observed discrepancy between the luminosity distribution functions of massive young stellar objects
and compact HII regions.
11. Daniel Haydon - Synthetic observations of star formation tracers in disc galaxy simulations the validation
of a new method to constrain the cloud-scale physics of star formation and feedback
A major problem in star/cluster formation and feedback is to constrain the cloud-scale physics across galactic environment and cosmic time. A promising solution has been put forward by Kruijssen & Longmore (2014), who present
a statistical method for measuring ill-constrained cloud-scale quantities such as the cloud lifetime, star formation /
feedback time-scales, star formation efficiencies, feedback velocities, and mass loading factors, using galaxy-scale
observations. I will use detailed hydrodynamical simulations of disc galaxies to demonstrate that the method accurately retrieves the above quantities down to an uncertainty of just a few 10%, but only if the characteristic ”reference
timescale” of the star formation tracer is known. I will then use synthetic H alpha, NUV, and FUV maps of the simulated galaxies to measure their reference timescales and demonstrate that we constrain them to high accuracy. I will
also show that these time scales are environmentally dependent as predicted by IMF theory. These results enable the
first observational census of cloud-scale star formation / feedback physics in galaxies across cosmic time.
12. Alex Hygate - Constraining the cloud-scale physics of star formation and feedback in galaxies across cosmic
time
In this contribution, I will discuss a new method of observationally measuring the key quantities describing the
cloud-scale physics of star formation and feedback, such as the cloud lifetime, feedback timescale, star formation
efficiency, mass loading factor, etc. (Kruijssen & Longmore, 2014). This method for the first time allows us to probe
these physics over a large galaxy sample and across cosmic time. I will present results from the first sample of galaxies
that the method has been applied to: the two flocculent disc galaxies NGC300 (Kruijssen+ in prep.) and M33 (Hygate+ in prep.), as well as the massive spiral galaxy M31 (Schruba+ in prep.). Using these results, I will compare the
lifecycle of molecular clouds, star formation, and feedback in these three galaxies. Furthermore, I will discuss how,
using the increased resolving power of modern instruments such as ALMA and MUSE, this method will be applied
to a large number of galaxies in differing environments from the local Universe out to redshift z ∼4, i.e. across a
cosmologically representative part of the galaxy population rather than the limited sample of Local Group galaxies
where such measurements were previously possible. This enables the systematic study of star formation physics as a
function of the cosmic environment.
13. Nico Krieger - Molecular Cloud Evolution in the Central Molecular Zone
The Central Molecular Zone (CMZ) in the Galactic Center (GC) contains large amounts of dense molecular gas,
but observed star formation rates are lower than expected by a factor of 10-100 (Longmore et al. 2013a). Longmore
et al. (2013b) and Kruijssen et al. (2015) model this gas as streams which pass close (60 pc) to the Galactic Center
near Sgr A∗ where cloud collapse is expected to be triggered by tidal interactions. Downstream of these pericenter
passages, a sequence of advancing star formation tracers is observed, the star formation sequence (SFS), while it is
unknown how the gas behaves along the sequence.
Based on ammonia temperature maps of the Survey of Water and Ammonia in the Galactic Center (SWAG, see
poster by J. Ott for details) and the dynamical model of Kruijssen et al. (2015), the absolute time dependence of
kinematic gas temperature is inferred along the molecular clouds orbit. It is found that gas temperatures increase
as a function of time in both regimes before and after the corresponding cloud passes pericenter where its collapse
is presumably triggered. Other investigated quantities (line width, column density, opacity) show no strong sign of
time dependence (i.e. offset) but are likely dominated by cloud-to-cloud variations. The results are discussed in the
framework of tidal triggering of cloud collapse and orbital kinematics and found to generally match the predictions,
i.e. the observation of a tidally triggered star formation sequence in the Galactic center supports the proposed model.
14. Hendrik Linz - Filleting the filament
At MPIA, we have followed a strategy to scrutinise a pre-selected sample of very young high-mass star-forming
clumps (IRDCs and ISOSS-sources) in great detail within our Herschel programme ”EPOS”. While the population of
Herschel point sources embedded in these regions has been addressed earlier, we discuss here the morphological FIR
fine-structure of the regions and their relation to the gas properties. Especially the interferometer studies reveal the
complex dynamics within the more filamentary clumps on linear scales < 10,000 AU. For one grand-design IRDC
filament we managed to secure 3-mm mosaicking data with ALMA over an extent of > 7 pc, which reveals a mazy
composition of sub-filaments in dense-gas tracers like N2H+ and HCO+ that is not obvious in the IRDC’s mid- and
far-IR continuum appearance. Putting our results together, we discuss to what extent this multi-facetted phenomenology can also be retrieved from current models of early (higher-mass) star formation.
15. Johanna Malinen - Comparing Herschel dust emission structures, magnetic fields observed by Planck, and
dynamics: high-latitude star forming cloud L1642
The nearby high-latitude cloud L1642 is one of only two known very high latitude (|b| > 30◦ ) clouds actively
forming stars. This cloud is a rare example of star formation in isolated conditions, and can reveal important details
of star formation in general, e.g., of the effect of magnetic fields. This cloud has been mapped as part of our Herschel
Key Programme Galactic Cold Cores where we made Herschel observations of over 100 cold objects detected with
Planck and scattered over the whole sky. We compare Herschel dust emission structures and magnetic field orientation
revealed by Planck polarization maps in L1642, and also combine these with dynamic information from molecular
line observations. The high-resolution Herschel data reveal a complex structure including a dense, compressed central clump, and low density striations. The Planck polarization data reveal an ordered magnetic field that pervades the
cloud and is aligned with the surrounding low density striations. We show that there is a complex interplay between
the cloud structure and large scale magnetic fields revealed by Planck polarization data at 10′ resolution. This suggests
that the magnetic field is closely linked to the formation and evolution of the cloud. We see a clear transition from
aligned to perpendicular structures approximately at a column density of NH = 2x×1021 cm−2 . We conclude that
Planck polarization data revealing the large scale magnetic field orientation can be very useful even when comparing
to the finest structures in higher resolution data, e.g. Herschel at ∼18′′ resolution.
Posters for Lightening Talk Session 2
16. Tomonari Michiyama - Investigating the Relation between CO (3–2) and Far Infrared Luminosities for
Nearby Merging Galaxies Using ASTE
We review the Michiyama et al., (2016 PASJ accepted; 2016arXiv160805075M), which investigate the relation
between the CO(32) luminosity and the far Infrared luminosity in a sample of 29 early stage and 31 late stage merging
galaxies, and 28 nearby isolated spiral galaxies. We find that normal isolated spiral galaxies and merging galaxies
have different slopes (alpha) in the logL’CO(32)-logLFIR plane (alpha ∼0.79 for spirals and ∼1.12 for mergers).
Comparing our results with sub-kpc scale local star formation and global starburst activity in the high-z Universe, we
find deviations from the linear relationship in the logL’CO(32)-logLFIR plane for the late stage mergers and high-z
star forming galaxies. By comparing our findings with the results from simulations, we suggest; (1) inefficient starbursts triggered by disk-wide dense clumps occur in the early stage of interaction and (2) efficient starbursts triggered
by central concentration of gas occur in the final stage. A systematic high spatial resolution survey of diffuse and
dense gas tracers is a key to confirm this scenario.
17. Joseph Mottram - CORE: linking sites of high mass star formation with their surroundings
Very few individual protostars form in isolation. Instead, most (and almost all in high mass star forming regions)
form in regions of molecular gas and dust which will give birth to many stars. These clouds or cloud complexes often
contain sources at a range of evolutionary stages, from starless cores to revealed surrounding main-sequence stars, all
of which deliver feed-back in a range of forms to the region. It is therefore important to consider and quantify the
context within which protostars form and evolve, and what effect environment may have on their current and final
properties. I will present the current status of such efforts within the context of a NOEMA large program studying 18
regions of high mass star formation (CORE, PI H. Beuther, see overview talk by A. Ahmadi) which includes observations using multiple interferometric configurations plus single-dish data from the IRAM 30m. As such this dataset
will allow these regions of high-mass star formation to be studied on spatial scales from 0.3 to 18′′ , with information
on even larger scales available from publicly available datasets (e.g. GLIMPSE, WISE etc.). With such studies, we
can begin to understand how the star formation is linked to the properties of the local region and neighbouring sources.
18. Camilo Penaloza - ??
19. Paul Rohde - Protostellar episodic outflows
There is growing evidence that the accretion of protostars is not continuous but occurs in short episodic outburst
(Herbig, 1977; Hartmann & Kenyon, 1996). Protostellar Outflows are known to accompany the star formation process (Shu & Adams, 1987) in the very early phase, such as for Class 0-1 stars. Moreover, protostellar outflows are
potentially able to drive turbulence in the whole cluster (Arce et al., 2010, 2011) and thereby eventually control the
star formation rate in a self-consistent manner Federrath (2016). More recent observations suggest, that outflows are
not continuous, but episodic (Staff et al., 2010; Bally et al., 2011; Ninan et al., 2016). It is generally agreed today that
outflows are proportional to the accretion rate onto the protostar (Ninan et al., 2016). Here we present a completely
new episodic outflow feedback model for SPH simulations. Stamatellos et al. (2011) use the semi analytic model
by (Zhu et al., 2009, 2010) to mimic the accretion behavior of FU Orion type stars. We extended this model by an
outflow mechanism, that is coupled to the intrinsic accretion rate. We compare the velocity dispersion and momentum injection for continuous and episodic accretion feedback for initially turbulent Bonnor-Ebert spheres with 1.8 M.
Furthermore, we discuss the impact of episodic outflows on the star formation rate and the multiplicity.
20. Dimitry Semenov - Towards the detection of emission of complex organics in disks
21. Somayeh Sheikhnezami - Wobbling and Precessing Jets from Warped Disks in Binary Systems
I will present results of the first ever three-dimensional (3D) magnetohydrodynamics (MHD) simulations of the
accretion-ejection structure.In our recent work, we investigate the 3D evolution of jets launched symmetrically from
single stars but also jets from warped disks in binary systems.We have applied various model setups and tested them
by simulating a stable and bipolar symmetric 3D structure from a single stardiskjet system. Our reference simulation
maintains a good axial symmetry and also a bipolar symmetry for more than 500 rotations of the inner disk, confirming the quality of our model setup. We have then implemented a 3D gravitational potential (Roche potential) due by a
companion star and run a variety of simulations with different binary separations and mass ratios. These simulations
show typical 3D deviations from axial symmetry, such as jet bending outside the Roche lobe or spiral arms forming in
the accretion disk. In order to find indications of precession effects, we have also run an exemplary parameter setup,
essentially governed by a small binary separation of only sime200 inner disk radii. This simulation shows a strong
indication that we observe the onset of a jet precession caused by the wobbling of the jet-launching disk. We estimate
the opening angle of the precession cone defined by the lateral motion of the jet axis to be about 4◦ after about 5000
dynamical time steps.
22. Christine Simpson - The role of cosmic ray pressure in accelerating galactic outflows
I will present simulations of galactic outflows in a stratified column of gas driven by supernova explosions from
a realistic, multi-phase interstellar medium that includes molecular cooling performed with the moving-mesh code
AREPO. I will compare different simulation models for supernova placement and energy feedback, including cosmic
rays (CR), and will demonstrate that models that place SNe in dense gas and account for CR diffusion are able to drive
outflows with similar mass loading as obtained from a random placement of supernovae with no CRs. Despite this
similarity, CR-driven outflows differ in several other key properties including their overall clumpiness and velocity.
Moreover, the forces driving these outflows originate in different sources of pressure, with the CR diffusion model
relying on non-thermal pressure gradients to create an outflow driven by internal pressure and the random-placement
model depending on kinetic pressure gradients to propel a ballistic outflow. CRs therefore appear to be non-negligible
physics in the formation of outflows from the interstellar medium. Time permitting, I will also discuss the application
of our model to a variety of galactic environments, including starbursting systems and galactic centers and future work
simulating full galactic disks.
23. Kazimierz Sliwa - A Tale of Woe for 13 CO in Luminous Infrared Galaxies
Major mergers such as Luminous Infrared Galaxies (LIRGs) are extremely bright in 12 CO; however, to get a better
understanding of the molecular gas physical conditions, an optically thin tracer such as 13 CO is required. Unfortunately, 13 CO is unusually weak relative to 12 CO (>20 times weaker) in LIRGs which made observations difficult.
Now with ALMA, these observations are more routine. We present new ALMA observations of 13 CO (and C18 O)
for four major mergers: VV 114, Arp 240, NGC 2623 and the second closest ULIRG, IRAS 13120-5453 (nicknamed
”The Yo-Yo”). In addition to the four sources, we analyzed three other major mergers and we find that an enhanced
abundance of 12 CO-to-13 CO ([12 CO]/[13 CO] >90) is the most likely explanation for the advanced mergers. For relatively younger mergers, we find the most likely [12 CO]/[13 CO] value to be similar to the value near the Galactic
center ( 30). We suggest that stellar nucleosynthesis the culprit in the enhanced abundance value in advanced. This is
evident in the Yo-Yo, as a hole is observed in 13 CO emission but not in 12 CO and C18 O.
24. Jonathan Stern - Is the galaxy color bi-modality driven by the thermal properties of the CGM?
The star-formation rate (SFR) of a galaxy is limited by the gas accretion rate from the circum-galactic medium
(CGM), and therefore may depend on the physical conditions in the CGM. Recent observations of quasar sightlines
through the CGM of foreground galaxies have revealed a clue for the nature of the relation between the specific SFR
and the CGM. Sightlines near blue galaxies at low redshift almost ubiquitously exhibit OVI absorption features, while
this ion is all but absent in sightlines near red galaxies at similar redshifts. I will present evidence that the gas traced
by OVI cannot co-exist with quasi-static hot gas shocked to the halo virial temperature. Hence, OVI absorption originates in regions in which most of the CGM gas has not shocked, and such regions are significantly more prevalent
in blue galaxies than in red galaxies. This result is consistent with galaxy accretion theories where the galaxy color
bi-modality is driven by the prevalence of astable virial shock in the CGM.
25. Shaye Storm - The Present and Future of Characterizing the Internal Velocity Fields of Cores
The internal velocity structure within prestellar/protostellar cores plays a crucial role in providing the initial conditions for star formation, but has not been well characterized because of small samples sizes and instrument limitations.
We will present new results on the kinematics of prestellar cores and protostellar envelopes at scales down to ∼0.01 pc
using data from the CARMA and SMA interferometers. Looking forward, we will also focus on our plan to utilize the
unique capabilities of GBT-ARGUS to probe a new regime of resolution and signal-to-noise to observationally assess
the true nature of velocity structure in dense cores; we think the improved instrumentation will let us challenge the
(often necessary) assumption that velocity gradients are simply due to bulk, solid-body rotation. Statistics from such
a study will provide new insights into the origin and distribution of core angular momentum, which are critical in developing star/binary formation theory and understanding the observed diversity in size and mass of circumstellar disks.
26. Jonas Syed - Kinematical Signatures of young high-mass star forming regions
Early formation processes of high-mass stars are still not well understood. The analysis of velocity structures and
gas temperatures in infrared dark clouds (IRDCs) could hold important insights that yield an understanding of early
evolutionary stages of these high-mass star forming regions. A VLA ammonia study of seven very young high-mass
star forming regions comprised of IRDCs along with ISO-selected far-infrared emission sources (ISOSS) was conducted. The molecular line data of ammonia allows to study velocity structures, linewidths, and gas temperatures
of cold gas clumps. It revealed temperatures in the range between 10K and 30K and different velocity gradients.
These velocity gradients are smooth in most cases, but there is one exceptional source (ISOSS23053), for which
several velocity components were found with a steep velocity gradient toward the clump center that is larger than
30 km s−1 pc−1 . Therefore follow-up observations of two interesting regions of this sample were observed with the
VLA in the C-array configuration at higher spectral and spatial resolution. Using this data, I aim to analyze the turbulent structure of the clouds by resolving the linewidth on small scales and characterize dynamical cloud collapse
signatures, such as steep velocity steps. On my poster I will present the work and progress on the VLA study to
investigate temperatures, kinematics and turbulent properties in the dense gas of these two clouds.
27. Richard Teague - Probing Planet Formation in TW Hya
I will present ALMA observations of CO, CN and CS emission in TW Hya, the nearest protoplanetary disk to
Earth which have been used to understand the planet forming properties in TW Hya. CS emission believed to trace
close to the planet forming midplane of a disk, displays a dip in emission at 80au, remarkably similar to those seen in
HST, GPI and SPHERE scattered light images. We have performed chemical modelling to test the frequently invoked
hypothesis of a planet-induced surface density perturbation as the source of this emission feature. Furthermore, the
high spectral resolutions afforded by ALMA have allowed us to spatially map the turbulent broadening in TW Hya, a
first for protoplanetary disks, with values consistent with predictions from magneto-rotational instabilities, a leading
contender for driving turbulent motions and inciting planet formation.
28. Yuan Wang - The Milky Way at radio continuum wavelengths as seen with THOR
We will present the 21cm continuum emission for the whole inner Milky Way as observed with the THOR survey.
These data provide a detailed view on the compact as well as extended radio emission of our Galaxy and thousands of
extragalactic background sources. Investigating the spectral index with the THOR data between 1 and 2 GHz allows
us to characterize the physical properties of the gas, e.g., whether they are HII regions, supernovae remnants or extragalactic synchrotron sources. Furthermore, the survey can also be employed to search for new supernovae remnants
in the Milky Way.
29. Miaomiao Zhang - An automatic PSF-fitting pipeline for the VVV survey imaging data
We improved an automatic PSF-fitting pipeline, which is based on DAOPHOT algorithm and can be used to
perform PSF-fitting photometry of VVV ESO public survey data. The pipeline is a complete command-line tool,
avoiding any user interactive operations. The pipeline can provide the photometric catalogs about 1.5-2 magnitudes
deeper than the VVV archival catalog that is obtained with aperture photometry. We also make this pipeline be able
to run in multi-core mode, which can significantly decrease the calculating time of PSF fitting.
30. Catherine Zucker - The Physical Properties of Large-Scale Galactic Filaments
In 2014, Goodman et al. showed that the 160 pc long filamentary infrared dark cloud Nessie lies directly in
the Galactic mid-plane and traces out a bone-like feature of the Scutum-Centaurus arm in position-position-velocity
space. Since then, several follow-up studies have been conducted to determine the physical properties of large-scale
(10-500 pc) Galactic filaments and their potential association with spiral structure. These studies, aimed at finding
Giant CO Molecular filaments, Large-scale Herschel filaments, ultra-dense IRDC Bones, and automated Minimum
Spanning Tree-derived filaments, have used different selection criteria and methodology. As a result, the relationship
of these classes of filaments to each other, and the properties of elongated Galactic filaments as a whole, remain
uncertain. We compile existing large-scale filament catalogs from the literature and perform a uniform analysis of
their physical properties and association with spiral arm models.