Daniel Angles-Alcazar will join GalForm@NU as a CIERA Postdoctoral Fellow

We are proud and thrilled to have recruited Daniel Angles-Alcazar to join our group as a CIERA Postdoctoral Fellow in fall 2014!

Daniel is currently finishing his Ph.D in Physics from the University of Arizona. Daniel is an expert on cosmological simulations and has pioneered the implementation more physical models of black hole accretion in such simulations. In particular, Daniel has shown that when a physically realistic gravitational torque-driven black hole accretion model is adopted, the main black hole scaling relations can be explained without the need for a feedback loop that stops black hole accretion. In the future, Daniel plans to extend his studies to include self-consistent black hole feedback and to lead cosmological studies of black hole growth with a realistic ISM and stellar feedback as part of the FIRE project.

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Research opportunities for undergraduates

We are actively looking for one or more motivated undergraduate students to carry out research in our group. Our state-of-the-art cosmological simulations are particularly well suited for important contributions by undergraduate researchers and enable a variety of projects.

Interested students should contact Claude-André Faucher-Giguère by email (x@northwestern.edu; x=cgiguere). Please include a CV, summary of interests and experience, and (if possible) a copy of your transcript. Candidates with a strong computational background are especially encouraged to apply.

Funding for undergraduate research is available through the Office for Undergraduate Research at Northwestern and the Weinberg College of Arts & Science.

U.S. citizens enrolled in any undergraduate program may also be funded by the Illinois Space Grant College Summer Research Program.

Note that many funding opportunities have early deadlines for application, so interested candidates should be in touch well in advance.

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Postdoctoral fellowship opportunities

This year, CIERA is particularly interested in postdoctoral fellows working in the broad area of galaxy formation and evolution, including star formation, stellar feedback, black hole-galaxy co-evolution, and the connection with the intergalactic medium. We anticipate to make several offers.

Apply here before Dec. 1, 2013!

Candidates interested in interacting with my group are encouraged to contact me ( x@northwestern.edu; x=cgiguere) with any questions they may have. In addition to competitive compensation and research budget, the fellows will have access to state-of-the-art computing facilities.

Candidates are encouraged to propose Northwestern as the host institution for their application to external fellowships – such as the Hubble, Einstein, or NSF — and fellows who attract external funding may be offered an extended term.

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GalForm @ NU group launch

I am excited to join the Northwestern faculty, where I am starting a new effort in galaxy formation modeling!

During the academic year 2013-2014, the Einstein Fellowship is allowing me to focus on research, after which I will officially become Assistant Professor of Physics & Astronomy at Northwestern.

My group will be part of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), an endowed center that promotes research and education through the support of postdoctoral fellows, advanced graduate and undergraduate research, and seminar series.

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Feedback-regulated star formation and the FIRE simulations

Galaxies convert their gas into stars at a rate which is typically only a few percent of what unimpeded gravitational collapse would imply. Understanding why star formation is so slow in galaxies is a central problem in astrophysics. Equivalently, what is the origin of the Kennicutt-Schmidt law?

We address this question in a recently-published paper,

Faucher-Giguère, C.-A., Quataert, E., & Hopkins,P.F., “Feedback-Regulated Star Formation in Molecular Clouds and Galactic Discs,” MNRAS, 433, 1970 [arXiv:1301.3905].

We compile observations showing that the relationship between star formation rate surface density and gas surface density in galaxies is set by a global balance between the gravitational weight of disk gas and the momentum per unit time returned by stellar feedback.

Critically, we show that the star formation efficiency per free fall time in galactic disks scales with the gas mass fraction in the disk, in agreement with a key prediction of our model for feedback-regulated star formation in galactic disks. This finding is important because competing theories of the Kennicutt-Schmidt law based on the small-scale properties of supersonic turbulence, on the other hand, predict that the star formation efficiency per free fall time is a near-universal constant of order one percent.

In our theory, favored by observations and numerical experiments, the rate-limiting step for star formation in galaxies is the formation of the most massive gravitationally-bound clouds — the giant molecular clouds (GMCs) – and the small-scale star formation prescription has only a weak effect on global star formation properties within a galaxy.

We are making use of this fact in our new simulations from the FIRE project (“Feedback In Realistic Environments”), in which we explicitly resolve the formation of GMCs in galaxies that form self-consistently in a cosmological simulation and implement stellar feedback directly based on the energy and momentum return predicted by stellar population synthesis models.

By directly resolving the rate-limiting step for star formation and implementing the feedback processes that set the galactic star formation law, we are freeing ourselves of commonly used sub-resolution prescriptions and dramatically improving the predictive power of galaxy formation simulations in a fully cosmological environment.

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Galactic winds driven by active galactic nuclei

Our paper on the physics of galactic winds driven by massive black holes has been published:

Faucher-Giguère, C.-A. & Quataert, E., “The Physics of Galactic Winds Driven by Active Galactic Nuclei,” MNRAS, 425, 605 [arXiv:1204.2547].

In this work, we show that outflows from massive black holes, with launch speed of several thousand km/s or more, are generically in the energy-conserving limit. During the energy-conserving expansion, the momentum of the swept-up gas in the galaxy is boosted, thus providing an explanation for the large momentum fluxes >>L/c that have been recently of galaxy-scale outflows by Herschel, as well as by a number of ground-based telescopes.

We also estimate the emission from shock wind bubbles, including from cosmic rays accelerated at the shocks. We find that shock-accelerated particles can give rises to observable radio and gamma-ray emission. The “Fermi bubbles” observed toward the center of the Milky Way, in particular, may be the result of an epoch ~10 Myr ago when Sgr A* was active and drove a wind into the Galaxy. In addition, a significant fraction of the radio emission that we observe from quasars could originate from this processes rather than radio jets or star formation.

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The galaxy formation group at Northwestern University is led by Claude-André Faucher-Giguère and part of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA).

We are interested in all aspects of galaxy formation and evolution, including star formation, massive black holes, and the connection with the intergalactic medium.

We address these problems using a combination of analytic modeling, numerical simulation, and comparison with observations, with an emphasizing on expanding our understanding of the fundamental physical processes involved and leveraging data from new astronomical facilities.