Calendar

Oct
28
Fri
Colloquium: Mark Wardle
Oct 28 @ 3:15 pm – 4:15 pm
Colloquium: Mark Wardle @ Biology Annex 102

Star formation in the vicinity of the supermassive black hole at the Galactic Centre

Dr. Mark Wardle, Macquarie University

The disruptive tidal field near supermassive black holes overcomes the self-gravity of objects that are less dense than the Roche density.  This was once expected to suppress star formation within several parsecs of  Sgr A*, the four million solar mass black hole at the centre of the Galaxy.   It has since become apparent that things are not this simple:  Sgr A* is surrounded by a sub-parsec-scale orbiting disk of massive stars, indicating a star formation event occurred a few million years ago.    And on parsec scales,  star formation seems to be happening now:  there are proplyd candidates and protostellar outflow candidates,  as well as methanol and water masers that in the galactic disk would be regarded as sure-fire signatures of star formation.  In this talk, I shall consider how star formation can occur so close to Sgr A*.

The stellar disk may be created through the partial capture of a molecular cloud as it swept through the inner few parsecs of the galaxy and temporarily engulfed Sgr A*.  This rather naturally creates a disk of gas with the steep surface density profile of the present stellar disk.  The inner 0.04 pc  is so optically thick that it cannot fragment, instead accreting onto Sgr A* in a few million years; meanwhile the outer disk fragments and creates the observed stellar disk.   The isolated young stellar objects found at larger distances, on the other hand,  can be explained by stabilisation of clouds or cloud cores by the high external pressure that permeates the inner Galaxy.   A virial analysis shows that clouds are indeed tidally disrupted within 0.5 pc of Sgr A*, but outside this the external pressure allows self-gravitating clouds to survive, providing the raw material for ongoing star formation.

 

Nov
7
Mon
PDS Atmospheres Node meeting
Nov 7 @ 9:00 am – 10:00 am
Nov
11
Fri
Colloquium: Amy Simon (Host: Nancy Chanover)
Nov 11 @ 3:15 pm – 4:15 pm
Colloquium: Amy Simon (Host: Nancy Chanover) @ Biology Annex 102

Outer Planets Update

Dr. Amy Simon, NASA

The Hubble Outer Planet Atmospheres Legacy (OPAL) program is a yearly program for observing each of the outer planets over two full rotations. Observations began with Uranus in 2014, adding Neptune and Jupiter in 2015 (Saturn will be included in 2018, after the end of the Cassini mission). These observations have provided interesting new discoveries in their own right, but are also now being combined with observations from a number of facilities, including NASA’s IRTF, Keck, the VLA, as well as the Kepler and Spitzer missions to further expand the breadth of science they contain.  This talk will cover the latest observations for each of these planets and what we are learning from these data sets.

 

Nov
14
Mon
Pizza Lunch: Drew Chojnowski
Nov 14 @ 12:30 pm – 1:30 pm
Pizza Lunch: Drew Chojnowski @ AY 119

Title: H-band Spectral Variability of Classical Be Stars

Drew Chojnowski

 

Nov
18
Fri
Colloquium: Karen Olsen
Nov 18 @ 3:15 pm – 4:15 pm
Colloquium: Karen Olsen @ Biology Annex 102

Simulations of the interstellar medium at high redshift: What does [CII] trace?

Dr. Karen Olsen, Arizona State University

We are in an exciting era were simulations on large, cosmological scales meet modeling of the interstellar medium (ISM) on sub-parsec scales. This gives us a way to predict and interpret observations of the ISM, and in particular the star-forming gas, in high-redshift galaxies, useful for ongoing and future ALMA/VLA projects.

In this talk, I will walk you though the current state of simulations targeting the the fine structure line of [CII] at 158 microns, which has now been observed in several z>6 galaxies. [CII] can arise throughout the interstellar medium (ISM), but the brightness of the [CII] line depends strongly on local environment within a galaxy, meaning that the ISM phase dominating the [CII] emission can depend on galaxy type. This complicates the use of [CII] as a tracer of either SFR or ISM mass and calls for detailed modeling following the different ways in which [CII] can be excited.

I will present SÍGAME (Simulator of GAlaxy Millimeter/submillimeter emission) – a novel method for predicting the origin and strength of line emission from galaxies. Our method combines data from cosmological simulations with sub-grid physics that carefully calculates local radiation field strength, pressure, and ionizational/thermal balance. Preliminary results will be shown from recent modeling of [CII] emission from z~6 star-forming galaxies with SÍGAME. We find strong potential for using the total [CII] luminosity to derive the ISM and molecular gas mass of galaxies during the Epoch of Reionization (EoR).

 

Nov
21
Mon
PDS Atmospheres Node meeting
Nov 21 @ 9:00 am – 10:00 am
Nov
28
Mon
Planetary Group meeting
Nov 28 @ 3:00 pm – 4:00 pm
Dec
5
Mon
PDS Atmospheres Node meeting
Dec 5 @ 9:00 am – 10:00 am
Apr
7
Fri
Colloquium: Lauren Waszek (Host: Jason Jackiewicz)
Apr 7 @ 3:15 pm – 4:15 pm
Colloquium: Lauren Waszek (Host: Jason Jackiewicz) @ BX102

The growth of Earth’s inner core: a new technique to constrain seismic properties in its outermost layers

Dr. Lauren Waszek, Department of Physics, NMSU

The inner core displays a hemispherical difference in seismic velocity, attenuation, and anisotropy, which is well-established from seismic studies. Recent observations reveal increasingly complex and regional features. However, geodynamical models generally only attempt to explain the basic east-west asymmetry. Regional seismic features, such as depth-dependence anisotropy or variation in hemisphere boundaries, are difficult to reproduce and relatively poorly constrained by seismic data. Processes to generate these complex features are debated.

The structures of the inner core are suggested to be formed as the inner core grows over time. Thus, the most recently-formed outermost layers likely hold the key to understanding the geodynamical mechanisms generating the inner core properties. Current datasets of the uppermost inner core and inner core boundary are limited by uneven data coverage, however. In the very uppermost inner core, seismic waves arrive with similar travel times and interfere, making measurements difficult.

Despite the uneven coverage of current datasets, we can use them to infer a very slow inner core super-rotation. The first ever global tomographical inversion for the inner core allows us to make regional observations, and map the lateral variation in the hemispherical structures. In the uppermost inner core, we have developed a new waveform modeling technique with synthetic data to separate these seismic phases, allowing us to measure the seismic properties in the very uppermost inner core. This, in combination with geodynamical modeling, will help us determine how the inner core hemispheres and other features are generated.

 

 

 

 

 

 

Sep
28
Fri
Colloquium: Bharat Ratra (Host: Anatoly Klypin)
Sep 28 @ 3:15 pm – 4:15 pm
Colloquium: Bharat Ratra (Host: Anatoly Klypin) @ BX102

Spatial Curvature, Dark Energy Dynamics, Neither, or Both?

Bharat Ratra, Kansas State University

Experiments and observations over the two last decades have persuaded cosmologists that (as yet undetected) dark energy is by far the main component of the energy budget of the current universe. I review a few simple dark energy models and compare their predictions to observational data, to derive dark energy model-parameter constraints and to test consistency of different data sets. I conclude with a list of open cosmological questions.