How Galaxies form Stars

22 Aug 2016, 08:00 → 26 Aug 2016, 18:00 Europe/Stockholm

AlbaNova University Center, Stockholm University, Stockholm, Sweden

The scaling between star formation and gas content follows a tight relation when considering whole galaxies (the Schmidt-Kennicutt Law), but quickly unravels when zooming into galaxies. The relation is now being investigated on two fronts: that of high redshift galaxies, finding that it appears to hold at least in general; and that of increasingly smaller regions within galaxies, finding that the physics increases in complexity and the scaling may present many different forms. The goal of this conference is to bring together experts of both the stellar and gas distributions in galaxies, and explore avenues for reconciling the global and local scaling of star formation.

Issues to discuss include:

• how stellar population evolution and dynamics affect measurements of local star formation. Stars evolve both in time (ageing) and space (migration, structure dissolution), and stellar populations survive over much longer timescales than the gas structures they are born from. Currently, it is unclear how lifetimes and migration affect local measurements of star formation and gas content. Topics for discussion will be how to reconcile these measurements, and how to link the local to the global measurements.
• the role of feedback. Mechanical, thermal, etc. feedback is likely to regulate the process of star formation over multiple scales, from those of small star groupings to those of large galactic structures (arms, bars, etc.). The collective effects of multiple discrete sources act to possibly both trigger and quench star formation. Feedback-driven turbulence may even be one of the key ingredients, together with magnetic fields, responsible for the low efficiency of star formation. Predictions from models of feedback, however, still need to be fully tested against observations, over the multiple scales that range from clumps and cores to those of whole galaxies. The role of feedback in initiating, sustaining, and suppressing star formation will be a topic of debate, together with other mechanisms, both from a modeling and observational point of view.
• how the above physical processes evolve with redshift. Almost all physical quantities used to parametrize high redshift galaxies are derived from calibrations on nearby galaxies (or even the Galaxy itself). Observations of distant galaxies are subject to the limited range of physical scales that can be probed, thus direct calibrations are often not possible. The robustness of local calibrations for high redshift applications is an open question, given that physical processes may operate on different scales as we probe younger galaxies. The answer to this question is key for addressing how accurately we can probe the evolution of gas and stars over cosmic times. The current understanding of the star formation in the high redshift Universe, including the promise of gravitational lensing, will be reviewed.

Invited speakers (confirmed):

• Ralf Klessen (Institute of Theoretical Astrophysics) - Theory of star formation and feedback
• Chang-Goo Kim (Princeton University) - Theory of star formation and feedback
• Oscar Agertz (University of Surrey) - Sub-galactic scale modelling of Star Formation
• Diederik Kruijssen (University of Heidelberg) - Stellar cluster formation from galactic to small scales simulations/theoretical
• Francoise Combes (Observatoire de Paris) - effect of galaxy dynamics on star formation
• Anne Jaskot (Smith College) - Feedback on sub-galactic scales
• Amelie Saintonge (University College London) - The Scaling Laws of Star Formation
• Amanda Heiderman (University of Virginia) - Cloud-scale star formation relations
• Steve Longmore (Liverpool John Moore University)- Small-scale star formation/clusters
• Stijn Wuyts (University of Bath) - High-z galaxies
• Janice Lee (Space Telescope Science Institute) - Star formation in galaxies

Format: 5-day conference.

Conference fee: Conference fee is 1200 sek and includes receptions, coffee breaks, 4 lunch, social event (boat trip including dinner).

Important dates:

• Abstract submission deadline: 12 June 2016
• Registration deadline: 12 June 2016

Scientific organizing committee: Daniela Calzetti (University of Massachusetts) Angela Adamo (Stockholm University) Goeran Ostlin (Stockholm University) Matthew Hayes (Stockholm University) Rob Kennicutt (University of Cambridge) Natasha Forster-Schreiber (Max-Planck-Institut für extraterrestrische) Kelsey Johnson (University of Virginia) Alberto Bolatto (University of Maryland)

Local organizing committee: Goeran Ostlin (Stockholm University), Garrelt Mellema (Stockholm University), Rocio Mendoza de Andersson (Stockholm University), Emily Freeland (Stockholm University), Matteo Messa (Stockholm University), Johannes Puschnig (Stockholm University), Veronica Menacho Menacho (Stockholm University)

Supported by: Stockholm University, The Oskar Klein Centre, Vetenskapsrådet

Monday 22 August

09:00 → 09:10 Welcome

Speaker: Angela Adamo

09:10 → 09:45 Opening Remarks, Setting the Stage (I)

Speaker: Göran Östlin (Stockholm University)

09:45 → 17:15 The Smallest Scales of Star Formation

Conveners: Angela Adamo (Stockholm University), Arjan Bik (Stockholm University), Daniela Calzetti (UMASS)

09:45 Theory of star formation and feedback (I)

Stars and star clusters are the fundamental visible building blocks of galaxies at present days as well as in the early universe. They form by gravitational collapse in regions of high density in the complex multi-phase interstellar medium (ISM). The process of stellar birth is controlled by the intricate interplay between the self-gravity of the star-forming gas and various opposing agents, such as supersonic turbulence, magnetic fields, radiation pressure, and gas pressure. Turbulence plays a dual role. On global scales it provides support, while at the same time it can promote local collapse. This process is modified by the thermodynamic response of the gas, which is determined by the balance between various heating and cooling processes, which in turn depend on the chemical composition of the material. Feedback is essential. The momentum and energy input from stars (via outflows, winds and supernovae) is an important driver of ISM turbulence, similar holds for stellar radiation which influences the thermal and chemical make-up of the ISM. I will review the current status of the field and discuss a few examples of recent progress.

Speaker: Ralf Klessen (Heidelberg University, Center for Astronomy)

10:30 Coffee break + Registration

11:15 Small-scale star formation/clusters (I)

The formation environment of stars in massive, dense stellar clusters is similar to the environment of stars forming in galaxies at a redshift of 1 - 3, at the peak star formation rate density of the Universe. As massive clusters are still forming at the present day at a fraction of the distance to high-redshift galaxies they offer an opportunity to understand the processes controlling star formation and feedback in conditions similar to those in which most stars in the Universe formed. In this talk I will outline recent efforts trying to understand massive cluster formation in the Milky Way. In particular I will describe a system of massive, dense clusters and their progenitor gas clouds in the centre of the Milky Way, and outline how detailed observations of this and similar systems may be able to: (i) help answer some of the fundamental open questions in star formation, and (ii) quantify how stellar feedback couples to the surrounding interstellar medium in this high-pressure, high-redshift analogue environment.

Speaker: Steve Longmore (Liverpool John Moore University)

Slides Longmore_Stockholm_web.pdf

12:00 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 SF physics as a function of the cosmic environment.

Speaker: Alex Hygate (Max Planck Institute of Astronomy (MPIA)/Astronomisches Rechen-Institut, University of Heidelberg (ARI/ZAH), Heidelberg, Germany)

12:20 [CII] as a tracer of GMC formation

The timescale over which GMCs form and disperse sets the timescale for star formation. Until recently, most observational studies of GMCs have focused on the molecular tracers, which are good probe of the cool interiors of the clouds, but have a limited ability to trace the dynamics of the transition to the warm neutral medium (WNM). In this study, we assess the ability of [CII] emission — the main coolant in the ISM — to trace the formation of GMCs from the turbulent WNM. We present the results of radiative transfer post-processed Arepo simulations, which contain a chemical and thermodynamical model of the ISM. We show that [CII] is a good tracer of the, “dark”, sub-100K H2 that surrounds the CO-bright gas. With [CII] we show that it is possible to follow the dynamics of the ISM in an around the molecular clouds, and is thus a good probe of GMC formation. We also show how it is possible to trace the different scales of the turbulent ISM with the a combination of [CII] and CO isotopes. We compare our results to those from recent SOFIA observations.

Speaker: Paul Clark (Cardiff University)

Slides clark_Stockholm_2016.key clark_Stockholm_2016.pdf

12:40 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.

Speaker: Daniel Haydon (Astronomisches Rechen-Institut, University of Heidelberg (ARI/ZAH), Germany)

13:00 Lunch break

14:30 The multi-scale physics of star and cluster formation in galaxies across cosmic time (I)

Stellar clusters are a fundamental (by)product of the galactic-scale star formation process. I will discuss how recent theoretical insights in cluster formation and evolution have led to a unified understanding of stellar clustering across cosmic time, from local open clusters and associations to old globular cluster populations. I will conclude by discussing our 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.

Speaker: Diederik Kruijssen (Heidelberg University (ARI/ZAH))

Slides Kruijssen_Stockholm_2016.pdf

15:15 The YSC’s perspective of star formation

TBD

Speaker: Angela Adamo (Stockholm University)

Slides Stockholm16_aa.pptx

15:35 The Hierarchical Distribution of Young Stellar Clusters in Nearby Galaxies

A turbulent interstellar medium will drive the hierarchical nature of star formation, resulting in a smoothly varying distribution of substructure, where bound star clusters occupy the smallest, densest regions. We use young stellar clusters to trace the unbound hierarchical star-forming structures for several nearby galaxies drawn from the Legacy ExtraGalactic UV Survey (LEGUS). We implement the angular two point correlation function to quantify the clustering among stellar clusters as a function of spatial scale and age to establish whether the clustering strength and the survival timescale of the clustered substructure depends on the properties of the stellar populations. We separate the clusters into different classes, compact (bound) clusters and associations and compare the clustering between the different classes. In all galaxies, we find that younger star clusters are more strongly clustered over small spatial scales and that the clustering disappears rapidly for ages as young as a few tens of Myr. We also find gravitationally bound clusters are systematically less clustered compared to stellar associations. Thus, compact clusters are more evolved and have traveled significantly from their birth site within a few tens of Myr and associations disperse over the same timescale.

Speaker: Kathryn Grasha (University of Massachusetts)

15:55 Coffee break

16:25 Cluster formation and evolution in M51

While star formation has been long studied on the single-star scale and on the galaxy scale, the link between these two widely separated scales still needs to be firmly established. We use the new high-resolution NUV and U band HST observations from LEGUS (Legacy Extra Galactic UV Survey) to study the nearby interacting spiral galaxy M51 at the intermediate scale of the star cluster population. It has been recently pointed out that the environment can affect the formation and evolution processes of the star clusters. The exquisite high quality multiband coverage of M51 (NUV,U,B,V,I bands) is providing luminosities, ages, masses, and extinctions of the huge cluster population sample. We analyzed this sample as function of different environments of the galaxy, in order to understand how the cluster properties change as function of the environment where they form and interact; this gives an insight on how the star formation process at this intermediate scale is affected by the galactic environment.

Speaker: Matteo Messa (Stockholm University)

Slides messa_m51_stockholm.pdf

16:45 NGC1275: A Study of Star Formation in 4-Dimensions

This talk will briefly review patterns of star formation in NGC 1275, the brightest galaxy in the Perseus cluster. NGC 1275 is of special interest as it contains examples of unusual modes of star formation in a complex environment. Young massive star clusters detected via HST UV imaging are associated with gaseous filaments that are arrayed over 10s of kpc around the center of the galaxy. Thus NGC 1275 offers an example of the formation of high stellar density systems in settings where the average baryonic densities are low. Due to their regular spatial structures, these features also allow star formation to be traced in space and time. A different class of spatially extended star formation associated with the spiral galaxy that is falling towards NGC 1275 also was observed by HST. The young stellar regions in these tidal debris differ from those associated with the gas filaments and shells in NGC 1275, and provide an additional perspective on transitory star formation in a low density setting.

Speaker: Jay Gallagher (Dept of Astronomy, University of Wisconsin-Madison)

Slides jgallagher_4DSF_Aug16.pdf

17:15 → 17:45 Panel Discussion

J. Gallagher, R. Klessen, S. Longmore, D. Kruijssen

18:00 → 19:30 Reception

Tuesday 23 August

09:00 → 17:15 From Clouds to Disks

Conveners: John Gallagher (University of Wisconsin-Madison), Rob Kennicutt (University of Cambridge)

09:00 Cloud-scale star formation relations (I)

Speaker: Amanda Heiderman (University of Virginia)

09:45 Sub-galactic scale modelling of Star Formation (I)

I will review recent advances in sub-galactic scale modelling of star formation, with a particular emphasize on the interplay between star formation and stellar feedback and how this impacts galaxy formation and evolution over cosmic time.

Speaker: Oscar Agertz (University of Surrey)

Slides agertz.pdf

10:30 Coffee break

11:00 The Gas-Star Cycle resolved from Galactic to Cloud Scale in Nearby Galaxies

State-of-the-art instrumentation is currently revolutionizing our view on the gas-star cycle in nearby galaxies by resolving individual star-forming clouds and their young stellar population. I will highlight recent results from several concerted legacy-type surveys targeting galaxies in the Local Group and Local Universe. This includes (a) the structure of the atomic and molecular gas and the separation of the atomic gas into a cold and warm neutral medium, the finding of significant diffuse molecular gas, and observational evidence what drives the atomic-molecular phase balance. (b) A characterization of the gas properties at cloud-scale reveals striking similarities (eg, a narrow range of cloud surface densities within a galaxy) but also systematic variations depending galactic properties (eg, the mean cloud surface density and gravitational boundedness). (c) The galactic gas-star formation (Schmidt-Kennicutt) relation systematically depends on the (varying) cloud-scale gas properties and changes become apparent between massive disk, low mass, and starbursting galaxies. (d) The resolved observations allow us to extract the evolutionary timescales of the gas-star cycle for different galactic environments.

Speaker: Andreas Schruba (Max-Planck-Institut für extraterrestrische Physik)

11:20 Effect of diffuse background in spatially-resolved star-formation studies

The Kennicutt-Schmidt law relating the surface densities of the star-formation rate (SFR) and gas (atomic and molecular) is a widely-accepted star-formation law. However, it is a disk-averaged law smoothing over local variations, and hence may not provide an explanation for the local relationship between SFR and gas density at the sub-galactic scale. To further probe this, various groups have carried out spatially-resolved studies of star-formation in nearby spiral galaxies using different methods. However, most of these studies do not take into account the effect of the spatially varying diffuse background which is potentially present in all star-forming galaxies and affects all the usual SFR tracers (optical, far-ultraviolet and mid-infrared). In this contribution, we present the results from an analysis of nearby spiral galaxies using aperture photometry where the effect of the diffuse background is taken into account. Making use of a novel split of the overall light distribution as a function of spatial scale allows us to subtract the diffuse background in the SFR tracers and determine the current localised SFR density. This is then combined with the gas density estimates (molecular gas from CO(2-1) and atomic gas from HI) to study the relation between SFR and gas density. Our work indicates that accounting for a diffuse background leads to a super-linear slope of the Kennicutt-Schmidt molecular star-formation law.

Speaker: Nimisha Kumari (Institute of Astronomy, Cambridge, United Kingdom)

11:40 Linking Galactic structure to star formation in the Milky Way

In the era of multi-wavelength surveys of the Milky Way, we are well-equipped to observationally characterise the conditions necessary for star formation on parsec size-scales. With this wealth of information, we can now not only ask the question of what these conditions are, but also why they arise where they do. I employ the Herschel Galactic Plane survey (Hi-GAL) to study the connection between the properties of compact pre-stellar or star-forming objects and large scale Galactic features. I show that the prevalence of star formation decreases gradually with Galactocentric radius and explore how the properties of Hi-GAL sources vary spatially across spiral arms and into inter-arm regions. I will discuss these findings in the context of Galactic dynamical theory and extragalactic star formation studies.

Speaker: Sarah Ragan (University of Leeds)

Slides ragan_stockholm.pdf

12:00 Using CO line ratios to trace the physical properties of molecular clouds

Over the past decade, there has been a move to better connect observations with numerical simulations. In this work we focus on mimicking the CO emission for simulated Giant Molecular Clouds (GMCs). We performed a set of smooth particle hydrodynamics (SPH) simulations with time-dependent chemistry, in which environmental conditions such as mass, density, size, metallicity and Interstellar Radiation Field were systematically varied. The simulations were then post-processed using radiative transfer (via RADMC-3D) to create synthetic integrated emission maps. Synthetic emission maps are created for different lines of CO’s rotational ladder as well as different CO isotopes. We show how various CO lines trace different regions in the GMCs. For example comparing the ratio between CO’s first two rotational emission lines allows the differentiation between regions of different temperatures and densities, as shown in the following figure.

Speaker: Camilo Penaloza (Cardiff University)

Slides Peñaloza_Stockholm.pptx

12:20 The transition from atomic to molecular gas in M33: a large scale investigation on the formation of molecular clouds in a low metalicity environment

M33 was mapped in the CO 2-1 transition with a resolution of 50 pc. The IRAM M33 mapping project covers a complete area out to galactic radii of 7 kpc. Combining these data with HI and and FIR dust measurements on similar scales allows to extend the method used by Sandstroem 2011 by introducing an additional local CO dark molecular gas column density. We discuss potential influence of key parameters such galactic radius, metalicity and radiation field on the results and compare them with star formation tracers.

Speaker: Karl Schuster

Slides K-Schuster-Stockholm-2016.pdf

12:40 Lunch break

14:30 The effect of galaxy dynamics on star formation (I)

Beyond the observed proportionality between surface densities of molecular gas and star formation, the efficiency of star formation varies significantly with environment. I will review the situations where the star formation is triggered by dynamical processes, such as bars or spirals, tidal interactions, ram-pressure due to AGN feedback or in groups and clusters.

Speaker: Francoise Combes (Observatoire de Paris, LERMA)

Slides FCombes-Stockholm-16.pdf

15:15 State-of-the-art diagnostics for detecting gravitational instabilities in galaxy discs

Gravitational instabilities play a primary role in shaping the structure and powering the star formation activity of disc galaxies. We review the effort made by theorists to provide the astronomical community with reliable disc stability diagnostics. The most well-known diagnostic is Toomre's Q parameter, but there are newer and more powerful tools for detecting gravitational instabilities in galaxy discs. And a few of them are almost as easy to use as Toomre's Q. In this talk, you will learn how to use such diagnostics in a variety of applications.

Speaker: Alessandro Romeo (Chalmers University of Technology)

Slides romeo.pdf

15:45 Unveiling the role of galactic rotation on star formation

Knowing how efficiently stars are formed in galaxies is fundamental to understand the evolution of our universe. Unfortunately, several physical processes governing star formation are dynamically coupled in the non-linear regime, complicating the study of their independent effects. Here we use numerical experiments to study the effects of galactic rotation, employing the Adaptive Mesh Refinement code Enzo. By studying the Kennicutt-Schmidt and Silk-Elmegreen laws, and the dimensionally homogeneous equation proposed by Escala (2015) we find that galactic rotation decreases the efficiency of star formation in disk galaxies. We find that the relation formulated by Escala (2015) gets the correct effects of the concentration along the line-of-sight, suppressing the bi-modality of the Kennicutt-Schmidt law. Finally we show that the dimensionless efficiency of star formation is well represented by a exponentially decreasing function of Ωτ, where Ω is the orbital frequency and τ is the initial free-fall time, leading to a unique galactic star formation law.

Speaker: Jose Utreras (Universidad de Chile)

Slides Stockholm.pdf

16:05 Coffee break

16:35 The evolution of star-formation efficiency during galaxy interactions - lessons from SDSS-selected post-mergers

The bimodal distribution of galaxy-integrated star-formation efficiencies (SFE) in the Schmidt-Kennicutt plane (i.e. the SFR vs. M(H2) diagram) has been the subject of much debate in recent years. Is the proposed split into a ‘sequence of disks’ and a ‘sequence of starbursts’ a genuine effect or rather an artefact of selection effects or assumptions underlying the calculation of molecular gas masses? Is this split the consequence of the time-scales on which galaxies switch from a low-efficiency to a high-efficiency mode of star formation during, e.g., galaxy interactions or mergers? I will report on H2+HI gas measurements for a sample of ~40 morphologically selected SDSS post-merger galaxies which we recently observed with a dedicated program at the IRAM/30m telescope. By using a careful mass- and SFR-matching technique we are able to compare the SFE-distribution of our post-mergers with ‘normal’ galaxies from, e.g., the COLD GASS project, with post-starburst galaxies (e.g., French et al. 2015; Alatalo et al. 2016), and with close kinematic pair galaxies from SDSS (Violino et al., in prep.). I will discuss our findings in the context of (a) the evolution of simulated mergers in the Schmidt-Kennicutt plane, and (b) empirical expectations for unbiased SFE-distributions we derived using the 2-Star Formation Mode framework (2-SFM, Sargent et al. 2014).

Speaker: Mark Sargent

Slides Stockholm_MTSargent.ppt

17:15 → 17:45 Panel Discussion

A. Heiderman, R. Kennicutt, F. Combes, O. Agertz

Wednesday 24 August

09:00 → 13:20 Star Formation and Feedback

Convener: Matthew Hayes (Stockholm University)

09:00 Feedback on Sub-Galactic Scales: Insights from Starburst Regions (I)

Although few in number, massive stars play an outsize role in reshaping their local and global environments. Using observations of starburst regions in low-redshift galaxies, I will highlight the importance of Wolf-Rayet stellar winds, binary stellar populations, supernovae, and geometry in clearing out neutral gas from star-forming environments. This feedback from sub-galactic scales ultimately affects the galaxy as a whole by regulating galactic-scale outflows and gas cycles.

Speaker: Anne Jaskot (Smith College)

Slides jaskot_stockholm.pdf

09:45 How do supernovae regulate star formation and launch galactic winds? (I)

Supernova (SN) explosions inject a prodigious amount of energy into the interstellar medium (ISM). This powerful feedback implies that SNe are a major driver of turbulence and galactic winds, and may be the dominant regulator of star formation (SF) in disk galaxies. Our understanding of the interaction of SN(e) with the ISM have gradually improved over many decades. However, a complete and self-consistent gas-dynamical model of the ISM including SN(e) is still numerically challenging, and for many years the effect of SN feedback has been both underestimated (based on poorly resolved numerical simulations) and overestimated (based on classical analytic theories with unconfirmed assumptions). In this talk, I first revisit the evolution of radiative SN remnants in the two phase ISM driven by single and multiple SN(e) and provide the condition for SNR evolution to be numerically resolved. This shows that (1) the inability of SNe to limit SF in many galaxy formation simulations has been due to lack of resolution, and (2) classical analytic models do not properly account for cooling during post-Sedov SNR evolution. I then present a theoretical and numerical framework for self-regulation of the star formation rates (SFRs) in disk galaxies. The theory assumes (1) force balance between pressure support and the weight of the ISM, (2) thermal balance between radiative cooling in the ISM and heating via FUV radiation from massive young stars, and (3) turbulent energy balance between dissipation in the ISM and driving by momentum injection of SNe. Numerical simulations show vigorous dynamics in the ISM at all times, but with proper temporal and spatial averages, all the expected balances hold. This leads to a scaling relation between mean SFRs and galactic gas and stellar properties, arising from the fundamental relationship between SFR surface density and the total midplane pressure. Finally, I shall show results from a new ISM/SF simulation of the solar neighborhood that follows space-time correlation of SNe with dense and diffuse gas realistically, resolves all thermal phases of the ISM, and fully captures the circulation of the galactic “fountain.” A fast, ``hot’’ galactic wind is launched with a mass loading factor of 0.1-1, while the SFR is self-regulated consistent with expectations within the warm and cold ISM.

Speaker: Chang-Goo Kim (Princeton University)

Slides changgookim.pdf

10:30 Superbubbles, Supernovae, and Deregulating Galaxies: Too Big Not to Fail

M* galaxies, with halo masses ~10^12 Msun, live in an interesting part of parameter space. Not only are they the "turnover" in the galaxy mass Schecter function, they also have the highest stellar mass (and baryon) fraction, very low bulge-to-disk ratios, and dominate the star formation of the epoch they live in. In this talk I will present the results of a sample of 18 cosmological M* galaxies, simulated using the state-of-the-art superbubble method for handling feedback from Type II Supernovae. I will show that the key to obtaining a realistic stellar mass to halo mass relation (SMHMR) is preventing the runaway growth of a massive bulge by driving outflows with large mass-loadings. If this happens, SN feedback alone can no longer effectively drive outflows from the galaxy, and star formation becomes unregulated. This is a key piece of evidence that the peak of the SMHMR is due to the shut down of SN regulation and the beginning of AGN regulation in more massive halos. I will also show how the interaction between hot outflows and the disk ISM, together with the potential well they live within, sets how much mass is entrained in a galactic wind/fountain, and how this can halt SN-driven winds in high- mass galaxies.

Speaker: Ben Keller (McMaster University)

Slides BW_Keller.pdf

10:50 Coffee break

11:20 The feedback of super star clusters on the ISM

The feedback of massive stars and star clusters has a dramatic effect on the surrounding interstellar matter (ISM), affecting the shape and fate of galaxies as a whole. The molecular ISM in which the stars are formed is transformed to a warm ionized medium by means of the Lyman continuum output as well as the stellar wind and supernovae of the massive stars in the galaxy. The large amounts of energy put in by the massive stars can lead to galactic scale outflows and to changes in the star-formation activity of galaxies. We present high quality VLT/MUSE observations of ESO 338-IG04. The super star clusters in this Blue Compact Galaxy have strongly altered the state of the ISM. Analysis of the optical emission lines reveals the physical conditions of the ionized gas in the large halo surrounding this galaxy. Several large scale outflows are identified. This is compared to the properties of the star clusters as derived from SED fitting. We find that the youngest and most massive clusters are responsible for the highest ionization gas. Typically, the youngest clusters are surrounded by higher density (and pressure) gas, suggesting they are still partly embedded in their natal HII region. Our analysis suggests that the central starburst in ESO 338 highly ionized the entire central part of the galaxy and which is expanding into the lower-ionization outskirts of the galaxy giving rise to shocked gas.

Speaker: Arjan Bik (Stockholm University)

Slides Bik_Stockholm16.pdf

11:40 Feedback efficiency in young stellar clusters in M83

The initial stages of star cluster formation (the first 10 Myr) are still not entirely clear, though this age is highly important for understanding their subsequent evolution and that of the galaxy itself. We have studied a sample of young massive clusters (<10 Myr, >5000 solar masses) in nearby spiral galaxy M83, using archival HST WFC3 data available on the HST Legacy Archive. By looking at images of the clusters using the Halpha filter, which traces ionised gas, we find that these clusters have expelled all of the extra gas from initial star formation by ~3-4 Myr. This very rapid removal of gas is seen across all mass scales on the same timescales, as we find cluster 23 in ESO 338-IG04 at ~5x10^6 solar masses and 6 Myr shows the same result. We also find that some clusters in M83 could potentially contain Wolf-Rayet stars (though definite membership is difficult to determine) which could contribute to the rapid removal of gas, though we hope to expand on this with future MUSE data of M83.

Speaker: Katherine HOLLYHEAD (Astrophysics Research Institute)

Slides khollyhead.pdf

12:00 Blustering and Blasting - Stellar feedback and its Chemical Tracers

The mechanisms of feedback in which Milky-Way and smaller galaxies are regulated by events on scales of parsecs and below is still poorly understood. In this talk I will look at hydrodynamical simulations on cosmological and interstellar medium scales and tease out some of the dynamical and chemical indicators at small and large (galaxy population) scales that can be used to identify the culprits of the low efficiency of star formation.

Speaker: Peter Creasey (University of California at Riverside (UCR))

Slides pcreasey_Stockholm_export.pdf

12:20 Simulations of realistic dwarf galaxies including Population III feedback

Dwarf galaxies occupy the faint end of the galaxy mass function and their properties are often regarded as strong tests for cosmological and galaxy evolution models. Indeed, their shallow gravitational potential makes them very susceptible to both external and internal processes, such as ram-pressure stripping and supernova feedback. Using computer simulations, the effects of such processes can be tested (e.g. Mayer et al. 2006, Governato et al. 2010). To do this, the properties of the simulated galaxies need to be closely compared to a broad range of observed galaxy properties and scaling relations. We present the results of N-body/SPH simulations including radiative cooling, star formation, chemical enrichment, stellar feedback, heating by the cosmic UV background, and feedback from Population III stars (Verbeke et al. 2015) and show that these compare very well to observed galaxies over the entire dwarf galaxy regime, unlike simulations without Population III feedback. We therefore conclude that Population III stars played a crucial role in the evolution of (dwarf) galaxies. Furthermore, we stress the importance of the way simulations are analyzed. The more in line these mock observations are with real observational techniques, the more reliable the comparison. Obtaining for example the rotational velocity from HI kinematics and metallicities from RGB stars (Kirby et al. 2013) are thus very important and can greatly affect the interpretation of the simulations. As a recent result, we use these realistic simulated dwarf galaxies and investigate different mechanisms to trigger a starburst in them. We then compare whether these simulations have similar properties as observed blue compact dwarfs, for example in terms of compactness, similar to what was done in Verbeke et al. 2014.

Speaker: Robbert Verbeke (Ghent University)

Slides verbekel_talkHowGalaxiesFormStars.pptx

12:40 Triggered formation of cold gas from superbubbles

The large-scale shocks formed by the clustered feedback of young stars are considered an important source of mechanical energy for the interstellar medium and a trigger of molecular cloud formation. Their interaction sites are locations where kinetic energy and magnetic field are redistributed between ISM phases. In this work we study the role of turbulence and magnetic fields in the dynamics of supershells and their interactions. On the one hand, we study the effect of the magnetic field on the expansion and fragmentation of supershells and on the other, we look for the signatures of supershell collisions on the kinetic and magnetic energy distribution of the ISM. We perform a series of high-resolution, three-dimensional simulations of expanding and colliding supershells. These simulations are compared to observations of Galactic supershells and supershell collision sites in HI and CO to examine the dynamical stability of the shocks and the efficiency of shock collisions for molecular cloud formation. In general, we find that supershell collisions are not effective in converting atomic to molecular gas. We also find that, a magnetic field either in the direction of the collision or perpendicular to it alters the expansion and the stability of the shocks significantly.

Speaker: Evangelia Ntormousi (CEA/Saclay)

Slides ntormousi_hgfs16.pdf

13:00 How black hole feedback may trigger star formation in galaxies

Black hole feedback is often invoked to suppress star formation in galaxies by driving galaxy-scale outflows. However, radiative feedback from the central black hole may actually trigger star formation within those galactic outflows. In our picture, new stars are formed at increasingly larger radii in the outflowing shell, with young stellar populations gradually populating the outer regions of the galaxy. This particular form of star formation may be most relevant in high redshift galaxies, affecting spatial scales ranging from the central nucleus to the galaxy outskirts. Following the episode of star formation triggering, the remaining dusty gas may be cleared out of the galaxy. I will discuss how the interplay between such positive and negative feedback may both trigger and quench star formation in galaxies.

Speaker: Wako Ishibashi (ETH Zurich)

13:20 → 18:00 Free Lunch & Afternoon

18:00 → 22:00 Boat trip and Conference Dinner

Thursday 25 August

09:00 → 13:05 Star Formation Properties in The Local Universe

Convener: Nils Bergvall (Uppsala University)

09:00 The scaling laws of star-formation on galactic scales (I)

Over the past 5 years, it has become possible to assemble measurements of molecular gas in large samples of normal star-forming galaxies up to z=2. These observations have been key in establishing the currently favoured model for galaxy evolution, which is centered around the cycling of gas in and out of galaxies and the efficiency of the star formation process. While star formation is a physical process taking place on very small scales, significant insights can be gained by systematic studies of the scaling relations between gas, star formation, and global galaxy properties. In this talk I will review some of these key observations at both low and high redshifts, and how they are shaping our understanding of how, when and where galaxies form their stars.

Speaker: Amelie Saintonge (University College London)

Slides Saintonge.pdf

09:45 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 HII 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]/Halpha line ratio inside and outside of the HII region boundaries). We find a systematically higher DIG background within HII 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.

Speaker: Kathryn Kreckel (MPIA)

Slides Kreckel_Stockholm.pdf

10:05 Spatially-resolved Star Formation Rate and Stellar Mass of Spiral Galaxies in the Local Universe : Quantifying The Inside-out Scenario of Disk Galaxies Formation

According to Lambda CDM paradigm of hierarchical galaxy formation, galactic disks were form gradually from inside to outside (“inside-out” scenario of galaxy formation). In spite of this being a long-known prediction, but very few observational evidences have been brought forward to support it. In order to sought the indication of this “inside-out” scenario in the local universe and also to test it, in this research the distribution of SFR and stellar mass of 118 local massive spiral galaxies (with log(M*)>10.5 located at 0.01<z<0.02) are resolved. The method so called “pixel-to-pixel SED fitting” is established to obtained the resolved SFR and stellar mass of galaxy by fitting observed resolved-7bands photometric SEDs (using data from GALEX and SDSS) with set of constructed Model SEDs. Fitting is done by using Bayesian Inference statistic. Analysis on resolved SFRs and stellar masses of galaxies sample found that SFR distribution in the galaxy is typically follow stellar mass distribution but more extended (as expected from "inside-out" scenario); sSFR radial profiles are relatively flat in the outskirt but suppressed in the central region (indication of inside-out quenching); majority of galaxies have total SFR outside (of half-mass radius) larger than total SFR inside (of half-mass radius), and majority of those which have large ratio of total SFR outside/total SFR inside are bar galaxies. We also found that bar structure in galaxies suppress SFR around it. In addition to this results, we also found the indication of resolved "Downsizing" scenario, where more massive galaxies tend to be quenched faster in all radii than less massive galaxies; and the consistency between integrated and resolved star formation main sequence (SFMS) which indicates that integrated SFMS might be derived from local SFMS relation. Overall, this results confirm the inside-out scenario of disk galaxies formation.

Speaker: Abdurrouf Abdurrouf (Astronomical Institute, Tohoku University)

Slides Abdurrouf_SpatiallyresolvedSFRSM.pdf

10:25 The outer filaments of Centaurus A

Recent studies suggest that AGN can regulate the gas accretion and thus slow down star formation (negative feedback). However, evidence of AGN positive feedback is also invoked in a few radio galaxies (eg. Centaurus A, Minkowski's Object, 3C 285, ...). I will present a multi-wavelength study of the northern filaments of Centaurus A. These filaments of gas and young stars extend on scales up to 15 kpc, aligned with the radio-jet. Along the radio jet, CO emission has been detected in a HI shell (Schiminovich et al. 1994, Charmandaris et al. 2000). We also detected CO in a large area along the filaments. By confronting the CO data to archival Herschel-FIR and GALEX-FUV data, we determine that the gas in the filaments is very inefficient to form stars (with depletion time of a few Gyr). This is strengthened by archival ALMA data that revealed the presence of unresolved CO(2-1) emitting clumps. We showed that these clumps are probably not gravitationally bound. From our recent APEX data, we can now constrain the molecular gas dynamics in the filaments. By comparison with neutral HI (from VLA) and ionised gas (from VIMOS and MUSE), we confirm evidences of a dynamical effect of the radio jet on the gas along the jet direction. We also lay the foundations for upcoming high angular resolution ALMA data at large scales (in the scheduling queue).

Speaker: Quentin SALOME (LERMA, Observatoire de Paris)

Slides QSalome-CenA.pdf

10:45 Coffee break

11:15 Star Formation in the outer M83 XUV disk

The spatially resolved star formation law has been studied in great detail in galaxies in recent years. At high surface density, when most of the gas is molecular, the Kennicutt-Schmidt relation is almost linear providing a constant gas consumption time-scale of about 3Gyr (e.g Bigiel et al. 2011, Saintonge et al 2011). However the star formation efficiency (SFE) falls very quickly when the surface density drops below 10Mo/pc2, and the gas is mainly atomic. The star formation rate (SFR) becomes a highly non-linear function of gas density, and the depletion time-scale is several Gyrs up to Hubble time. This is the case for dwarf galaxies and the most external parts of disk galaxies (Bigiel et al 2010), where the low gas density, low temperature and low metallicity conditions resemble early galaxies in the universe. Recent star formation within such environments was detected in H-alpha (one of the main star formation tracer). However, the Galaxy Evolution Explorer (GALEX) data demonstrate that H-alpha observations, tracing ~10Myr SF, still fail to detect a significant population of moderate-age stars in the outermost disks of spiral galaxies. Our aim is to detect the corresponding molecular gas expected in these regions. One remarkable example is M83, a nearby galaxy with an extend XUV disk reaching 2 times the optical major radius (Gil de Paz et al. 2007). However, our progress in understanding these XUV disks has been halted by the difficulty of detecting molecular gas via CO emission. In particular, no highly significant (>5sigma) CO emission was detect in ALMA maps of the XUV disk of M83 when we expected to detect 20-30 molecular clouds with SNR > 17. We hypothesize that the molecular clouds in the ALMA data are CO-dark, caused by the strong UV radiation field, which dissociates CO preferentially, keeping the H2 gas intact.

Speaker: Isadora Chaves Bicalho (Observatoire de Paris)

Slides Isadora_Bicalho.pdf

11:35 Using far-infrared transitions to study star formation activity in galaxies

The [CII] 158 um and [NII] 122 and 205 um far-infrared transitions are powerful tracers of the neutral and ionized gas in the interstellar medium of local and high-z galaxies. In this talk I will discuss the ability of these lines to trace the star formation activity in a wide range of environments that include low metallicity, normal, star-forming galaxies, AGN, LIRGS and high-z galaxies. Our work is based on a sample of resolved regions from nearby galaxies observed by Herschel as part of the KINGFISH, "Beyond the Peak" and SHINING surveys. For the [CII] transition, we conclude that it can be used for measurements of star formation rates (SFRs) on both, global and kiloparsec scales, in normal star-forming galaxies in the absence of strong AGNs. The main source of scatter in the correlation is associated with regions that exhibit warm IR colors. For the [NII] transitions, we find nearly linear correlations between the [NII] emission and SFR. The scatter in the correlation can be understood as a property of the electron density distribution. For regions with electron densities close to or higher than the [NII] line critical densities, the [NII] based SFR calibration systematically underestimates the SFR since the [NII] emission is collisionally quenched. Finally, I will review how the [CII] line can be used to measure the thermal pressure of the diffuse, neutral gas and discuss its connection to the star formation activity in the context of a galactic disk that evolves into a state of dynamical, thermal, and star formation equilibrium (e.g. Ostriker et al. 2010, Kim et al. 2013). As predicted by this model, the ratio between the thermal pressure and the vertical weight of the overlying ISM is about 0.3 and has a weak dependence with star formation activity.

Speaker: Rodrigo Herrera-Camus (Max Planck Institute for Extraterrestrial Physics)

Slides Herrera-Camus_pdf.pdf

11:55 Resolved stellar populations studied with MUSE crowded field 3D spectroscopy

We present first results from a study of resolved stellar populations in the 2 Mpc distant sculptor group disk galaxy NGC300 using integral field spectroscopy with MUSE. From data cubes obtained under conditions of excellent seeing we are able to extract on the order of 1500 stellar spectra per pointing of 1.5 hours observing time, using the PampelMuse code that has already revolutionized the spectroscopy of globular cluster stars. Thanks to high throughput, excellent image quality, and decent spatial sampling, we are able to disentangle stellar spectra from nebular contamination in environments of bright gaseous emission. We find rare objects like WR stars, LBV candidates, and other blue emission line stars. We detect normal and compact HII regions, superbubbles, giant shells, planetary nebulae, and SNRs down to limiting flux levels of a few 10e-18 erg/cm^2/s. We measure the diffuse ionized gas and find spatial patterns in the ISM with hints of ancient supernova explosions. We detect planetary nebulae 6 mag below the bright cutoff of the PNLF as a potential new diagnostic for intermediate age stellar populations. In summary, we argue that MUSE has opened a new era for detailed studies of resolved stellar populations in nearby galaxies with great benefits for calibrating integrated light observations at higher redshift.

Speaker: Martin Roth (Leibniz Institute for Astrophysics Potsdam (AIP))

12:25 Tidal Tales of Minor Mergers: Star Formation in the Tidal Tails of Minor Mergers

While major mergers and their tidal debris are well studied, equal mass galaxy mergers are relatively rare compared to minor mergers (mass ratio <0.3). Minor mergers are less energetic than major mergers, but more common in the observable universe, and thus likely played a pivotal role in the formation of most large galaxies. Tidal debris regions have large amounts of neutral gas but a lower gas density and may have higher turbulence. We use star formation tracers such as young star cluster populations and H-alpha and CII emission to determine the different factors that may influence star formation in tidal debris. These tracers were compared to the reservoirs of molecular and neutral gas available for star formation to estimate the star formation efficiency (SFE). The SFR in tidal debris can reach up to 50% of the total star formation in the system. The SFE of tidal tails in minor mergers can range over orders of magnitude on both local and global scales. From the tidal debris environments in our study, this variance appears to stem from the formation conditions of the debris. Current surveys of the 2.12 micron line of molecular hydrogen, CO(1-0), and HI for 15 minor mergers, are providing a larger sample of environments to study the threshold for star formation that can inform star formation models, particularly at low densities.

Speaker: Karen Knierman (Arizona State University)

Slides Knierman_ttales.key Knierman_ttales.pdf

12:45 Radial variations in elliptical galaxy stellar populations - constraints on mass-assembly from infrared spectroscopy

Massive elliptical galaxies are thought to form in two stages - first, the formation of a central core via fast dissipative processes by z~2, followed by the accumulation of mass through (mostly minor) dry mergers. A combination of evidence from spectroscopy, lensing, and stellar dynamics appears to suggest that in the most massive central cores stars form according to a 'bottom-heavy' IMF (i.e. an excess of dwarf stars are formed relative to the Milky-Way stellar populations). This has implications for the inferred M/L ratio (and thus the SFR estimated for these systems at high redshift), and also for the future evolution of these systems since the IMF controls e.g. the SNe rate. The accumulation of mass via minor mergers ought to introduce radial gradients in the inferred IMF for present-day massive ellipticals (since lower mass systems are thought to form stars according to a Milky-Way-like IMF). Likewise, both dissipative collapse and minor mergers should introduce e.g. radial metallicity gradients. Both of these are in principle detectable through spatially-resolved spectroscopy. I will present infrared spectroscopy from VLT-KMOS for a sample of local massive ellipticals (Alton et al. 2016 - submitted to MNRAS), showing that IMF gradients are not significant within the half-light radii of these systems (although chemical abundance gradients are present). Taken in concert with evidence for a bottom-heavy IMF in these systems, this appears to indicate that minor mergers deposit mass primarily beyond the present-day half-light radii. Meanwhile, the stellar population within the effective radius is inferred to be dwarf-enriched throughout.

Speaker: Alton Padraig (Durham University)

13:05 → 14:30 Lunch break

14:30 → 17:00 Global Properties at Low and High Redshifts

Convener: Göran Östlin (Stockholm University)

14:30 Starbursting Dwarf Galaxies: Back in the Spotlight (I)

Since the discovery of "isolated extragalactic H II regions" by Sargent & Searle in 1970, low mass dwarf galaxies experiencing intense bursts of star formation have periodically become the subject of frenetic research because of their unusual and discordant properties. Today, the study of massive star formation and its impact on the interstellar medium seems to be at a major crossroad, with starbursting dwarf galaxies back in the spotlight. Stabursting dwarfs seem to be the key to understanding a range of phenomena, from the escape of ionizing photons, to the origins of superluminous supernovae and gamma ray bursts, to the formation of the most massive stars. In this talk, I will review recent findings involving dwarf starbursting galaxies, and speculate on the propensity of their environments to favor the formation of high mass stars at increased efficiency.

Speaker: Janice Lee (Space Telescope Science Institute)

15:15 A high-z perspective on galaxy growth and star formation (I)

For many years, far-infrared and optical/near-infrared astronomers focused on largely disjoint samples of high-redshift galaxies. While the far-infrared community primarily studied luminous and dusty starbursting monsters, detailed spectroscopic analyses in the (rest-)optical preferentially targeted less obscured systems. With the increased sensitivity offered by Herschel, PdBI-NOEMA and ALMA on the one hand, and the multiplexing capabilities of new near-infrared (integral-field) spectrographs on the other hand, this divide has been rapidly closing. Complemented by resolved HST observations, we are now in the fortunate situation that we can study the physics of star formation, stellar buildup and structural growth since the peak of cosmic star formation for large samples of normal star-forming galaxies. I will present recent findings on high-z galaxies obtained by combining observations of their stellar, dust, molecular and ionized gas components.

Speaker: Stijn Wuyts (University of Bath)

Slides wuyts_stijn_Stockholm_aug2016_forweb.pdf

16:00 Coffee break

16:30 Star Formation and Feedback in Low Metallicity Galaxies at z~2

Low mass, low metallicity galaxies are the most likely source of the photons that reionized the universe, but the relationships between low metallicity star formation, galactic outflows, and the escape of ionizing radiation at high redshifts are still unclear. Using rest-frame UV and optical spectra of lensed and unlensed low metallicity galaxies at z~2, I will discuss constraints on the velocity and ionization state of outflows, the rate and geometry of star formation, and the covering fraction and column density of neutral hydrogen.

Speaker: Dawn Erb (University of Wisconsin Milwaukee)

Slides erb_stockholm2016.pdf

17:00 → 17:30 Panel Discussion

A. Jaskot, A. Saintonge, C. G. Kim, J. Lee, S. Wuyts

Friday 26 August

09:00 → 14:30 Global Properties at Low and High Redshifts (continuation)

Convener: Dawn Erb (University of Wisconsin Milwaukee)

09:00 Characterizing Dust Attenuation in Local Star Forming Galaxies

The presence of dust in galaxies can significantly alter their observed spectral energy distribution. If not properly accounted for, this effect can lead to incorrect values of derived physical quantities such as the star formation rate, stellar mass, and photometric redshift. Virtually all studies of star forming galaxies, both local and distant, make use the attenuation curve derived from a small sample of local starburst galaxies to correct for the effects of dust. However, it is not clear how reasonable the general application of this curve is for more typical star forming galaxies. In this talk, I will present results from a study utilizing ~10000 local (z<0.1) star forming galaxies to identify the extent to which attenuation varies as a function of galactic physical properties.

Speaker: Andrew Battisti (UMass Amherst)

Slides Battisti_Stockholm2016_v2.pptx

09:20 Cold gas and star formation on clump scales: an ALMA look at a prototypical z~2 galaxy

Key aspects of galaxy evolution including bulge formation and quenching may be regulated by the dynamics of large star forming clumps which are almost ubiquitous in the gas-rich ISM medium of normal high redshift galaxies. The impact of clump-driven dynamical processes on the evolution of galaxies depends crucially on whether these giant clumps are transient phenomena or not. Clump lifetimes are believed to vary with the amount of cold gas in these clumps, with the clump internal star formation efficiency and the strength of stellar feedback. I will present results from deep, 0.3 arcsecond resolution ALMA observations of the molecular gas content in a z=1.5 clumpy, main-sequence disk galaxy. Combined with HUDF imaging in the optical-NIR and integral field spectroscopy observation with VLT/SINFONI in the J+H bands, these provide a unique dataset for the study high redshift gas properties down to kpc scales. I will discuss the implications of these observations in terms of the Schmidt-Kennicutt law on clump scales, the ability of clumps to endure mass loss by outflows and local variations in gas reservoirs between the star-forming clumps and the more evolved central bulge component. I will also discuss our constraints on the level of turbulence in the clump ISM and how these lead to insight into feedback processes acting on the clumps.

Speaker: Anna Cibinel (Astronomy Centre, U. of Sussex)

09:40 Swift/UVOT Measurements of the UV Dust Extinction Curve and the Recent Star Formation History of the SMC and M33

The Swift Ultraviolet/Optical Telescope (UVOT) is uniquely suited to study star formation and dust extinction in nearby galaxies. I will discuss results from the Small Magellanic Cloud (SMC) and M33, for which we have unprecedented observations in three near-UV bands from 1700-3000 A at 2.5" resolution. We combine our UV imaging with archival optical and infrared data to model the spectral energy distributions of individual regions of each galaxy, simultaneously fitting for the dust extinction curve properties, total dust, stellar mass, and age. We have created the first-ever maps of the UV dust extinction curve, which show previously-unconfirmed spatial variation: both the slope and 2175 Angstrom bump vary considerably over the face of both the SMC and M33. In addition, we have measured a detailed star formation history over the previous ~300 Myr. These results have strong implications for studies of star formation and galaxy evolution at both low and high redshift.

Speaker: Lea Hagen (Penn State University)

Slides hagen_lea_smc_m33.pdf

10:00 New Probes of Starburst Feedback and Circumgalactic OVI in Emission

I will present the first image of an individual extragalactic object in which the coronal gas phase (T ~300,000 K) is both isolated and spatially resolved, by targeting the O VI doublet at 1032,1037 Å in emission. The combination of HST UV imaging and spectroscopy provides unique new insights into the mass, cooling, kinematics, and ultimately the fate of gas that has been heated by feedback from star formation. The O VI-bearing gas has the morphology of a significantly extended halo that has an exponential scale length ten times larger than the ionizing stellar population. COS spectroscopy confirms both the O VI nature of the gas in emission, and in absorption shows the gas is outflowing with a velocity of ~350 km/s. I will show how a large number of constraints can be placed on the conditions in the coronal phase, that for the first time come with a significantly reduced assumptions: we solve for the cloud sizes, electron density, pressure, cooling rate, and sound speed. In this presentation I will demonstrate that: (A.) this phase contains only a small amount of the mechanical energy returned by SNe explosions at any given instant, but because of a short cooling time a significant fraction of the gas will have passed through this phase over the star-forming episode; (B.) the coronal gas cannot have been lifted from the star-forming regions - it will ultimately unbind from the galaxy but will be neutral by the time it does, thereby joining and enriching the Ly-alpha absorption systems; (C.) the pressure in the clouds observationally matches that in the H II regions and, independently, the clouds must be pressure-confined in order to remain visible. I will argue that we are observing outrushing gas that is compressed - thereby undergoing rapid cooling - as it accelerates ambient gas in the galaxy halo. These data represent the first stage in an ongoing study. I will present the status of current observations of the first extended sample, that were selected to be the analogues of galaxies at >2 that produced the bulk of the metals for early cosmic enrichment. I will close with a discussion of how the results will be generalized to provide new empirical insights for galaxy formation scenarios.

Speaker: Matthew Hayes (Stockholm University)

Slides Hayes_SthlmSF_2016.pptx

10:30 Coffee break

11:00 Galactic magnetic fields and the FIR-radio correlation at high redshifts

Magnetic fields are omnipresent in local galaxies and can affect the star formation process crucially. Observational evidence between the coupling of the magnetic field and the star formation rate (SFR) comes from the far-infrared(FIR)-radio correlation which holds over more than six orders of magnitude. While the FIR radiation is a tracer of the SFR, radio emission is typically synchrotron radiation and thus depends on the magnetic energy density. The latter can be assumed to be in equipartition with the turbulent energy density as a result of efficient small-scale dynamo amplification. With a steady-state model for cosmic ray electrons we determine the galactic synchrotron flux as a function of redshift z. Our model reproduces the observed FIR-radio correlation well at z=0. With increasing redshift we predict a decrease of the synchrotron flux. This leads to a deviation from the FIR-radio correlation from its present-day appearance which could already be detected at z \approx 2 if the gas density increases strongly with z. Our model can be tested in the near future with ultra-deep radio surveys.

Speaker: Jennifer Schober (Nordita)

11:20 FADO: a novel spectral population synthesis tool for the exploration of galaxy evolution by means of genetic optimization under self-consistency boundary conditions

Despite significant progress over the past decades, all state-of-the-art population spectral synthesis (pss) codes suffer from two major conceptual deficiencies that limit their potential of gaining sharp insights into the star formation history (SFH) of star-forming (SF) galaxies and potentially introduce substantial biases in studies of their physical properties (e.g., stellar mass and sSFR): i) the neglect of nebular continuum emission in spectral fits and ii) the lack of a mechanism that ensures consistency between the best-fitting SFH and the observed nebular emission characteristics (e.g., hydrogen Balmer-line luminosities and equivalent widths-EWs, shape of the continuum in the region around the Balmer and Paschen jump). FADO (Fitting Analysis using Differential evolution Optimization; Gomes & Papaderos 2016, submitted) is a conceptually novel, publicly available (http://www.spectralsynthesis.org) pss code with the distinctive capability of permitting identification of the SFH that best reproduces the observed nebular characteristics of a SF galaxy. This so far unique self-consistency concept allows to significantly alleviate degeneracies in spectral synthesis, thereby opening a new avenue to the detailed exploration of the assembly history of galaxies. FADO is the first pss code employing genetic Differential Evolution Optimization. This, in conjunction with various other currently unique elements in its mathematical concept and numerical realization results in key improvements with respect to computational efficiency and uniqueness of the best-fitting SFHs. An outline of FADO and illustrative examples of its application on SDSS spectra will be presented.

Speaker: Polychronis Papaderos (Instituto de Astrofísica e Ciências do Espaço, Centro de Astrofísica da Universidade do Porto)

11:40 The Lyman alpha reference sample

The Lyman apha reference sample (LARS) is a major multiwavelength imaging and spectroscopic campaign of local normal star-forming galaxies, UV-luminous starburst systems, and luminous infrared galaxies using HST and ground-based telescopes. The aim of this survey is to probe what physical conditions and processes regulate the emission of Lyα radiation on local and global galactic scales. The Ly alpha line is widely used to identify and confirm galaxies in the distant universe, close to the epoch when the first galaxies formed and when the universe was reionized. However, the fact that Ly alpha is a resonant line makes it optically thick even at relatively low neutral hydrogen column densities. This means that the radiative transport of Ly alpha photons through galaxies is a complex problem where the structure, kinematics and dust content, and neutral hydrogen content of the interstellar medium all contribute to the process. In this talk I will present the current status of the project including: unique HST Ly alpha maps and FUV spectroscopy of 44 galaxies within the LARS sample, HI observations with GBA and VLA for a subset of the sample, IFU spectroscopy using CAHA/PMAS and VLT/MUSE for a subset of the sample. The first published results of the LARS survey reveal that when Ly alpha manages to escape it does so in the form of diffuse scattering halos.

Speaker: Jens Melinder

Slides jensmelinder_Stockholm2016.pdf

12:00 Lunch break

13:30 The Star Formation-Gas Relation in NGC4449

Using recent 1.1 mm maps of the dust continuum of NGC4449 obtained with the Large Millimiter Telescope (LMT), we derive a high-angular resolution map of the gas in this nearby dwarf starburst galaxy. We combine the gas map with star formation rate tracers at optical and infrared wavelengths, and investigate the SFR-gas relation at ~250 parsec resolution.

Speaker: Daniela Calzetti (UMASS)

13:50 Of needles and haystacks: High-detail characterization of warm ISM in nearby starbursts

The ISM of starburst galaxies is well known to contain a wide variety of physical conditions and be kinematically complex. Yet, when describing it spectroscopically, a single number is often relied on to characterize each physical property, derived from data integrated over the entire slit. Here, we present a highly detailed spatial and kinematic decomposition of 2D spectra of three starburst regions in nearby Lyman Break Analogs Haro 11 and ESO 338. We identify and characterize a number of physical subsystems in the projected area covered by each slit, and perform a number of commonly used line ratio-based diagnostics on these, allowing us to study e.g temperature, density, velocity gradients, element abundances, shock vs. photoionization ratios etc. for individual subsystems. The high level of detail lets us describe the variation underlying the properties typically reported for unresolved objects and, often, even well resolved local objects. We also identify subsystems and regions with particularly interesting behavior which in previous studies have been drowned out by other components and thus gone unnoticed so far.

Speaker: Thøger Emil Rivera-Thorsen (Stockholm University)

Slides RiveraThorsenGalFormStars.pdf

14:10 Challenges and first results from CO and IR measurements in local Lyman Alpha Emitters

Carbon Monoxide has proven to be a well-calibrated tracer of the total molecular gas content in galaxies at low and high redshift. However, CO observations in galaxies of subsolar metallicity remain challenging, even in the local universe. For that reason, the dust mass is often used to infer the molecular gas in low metallicity systems. I will present first results of CO and dust measurements in the Lyman Alpha Reference Sample (LARS), a sample of local Lyman Alpha emitting starburst galaxies, all of subsolar metallicity. Using multiple-J CO transitians obtained with APEX and the IRAM 30m telescope, as well as Herschel/PACS and WISE data in combination with physical dust models and PDR codes, properties of the star forming gas could be derived and CO and dust scaling relations studied.

Speaker: Johannes Puschnig (Stockholm University)

Slides Molecular_gas_and_dust_in_LARS.pdf

14:30 → 15:15 Summary and Closing Remarks: What Next? (I)

Speaker: Robert Kennicutt (University of Cambridge)