Colloquium Thesis Defense: Lauren Kahre
Jan 23 @ 3:00 pm – 4:00 pm
Colloquium Thesis Defense: Lauren Kahre

Extinction Mapping and Dust-to-Gas Ratios of Nearby Galaxies

Lauren Kahre, NMSU

We present a study of the dust{to{gas ratios in 31 nearby (D >
10 Mpc) galaxies. Using Hubble Space Telescope broad band WFC3/UVIS UV and
optical images from the Treasury program LEGUS (Legacy ExtraGalactic UV
Survey) combined with archival HST/ACS data, we correct thousands of
individual stars for extinction across these galaxies using an
isochrone-matching (reddening-free Q) method. We generate extinction maps
for each galaxy from the individual stellar extinctions using both
adaptive and fixed resolution techniques, and correlate these maps with
neutral HI and CO gas maps from literature, including The HI Nearby Galaxy
Survey (THINGS) and the HERA CO-Line ExtraGalactic Survey (HERACLES). We
calculate dust-to-gas ratios and investigate variations in the dust-to-gas
ratio with galaxy metallicity. We find a power law relationship between
dust-to-gas ratio and metallicity. The single power law is consistent with
other studies of dust-to-gas ratio compared to metallicity, while the
broken power law shows a significantly shallower slope for low metallicity
galaxies than previously observed. We find a change in the relation when
H_2 is not included. This implies that underestimation of N_H2 in
low-metallicity dwarfs from a too-low CO-to-H2 conversion factor X_CO
could have produced too low a slope in the derived relationship between
dust-to-gas ratio and metallicity. We also
compare our extinctions to those derived from fitting the spectral energy
distribution (SED) using the Bayesian Extinction and Stellar Tool (BEAST)
for NGC 7793 and and systematically lower extinctions from SED-fitting as
compared to isochrone matching. Finally, we compare our extinction maps of
NGC 628 to maps of the dust obtained via IR emission from Aniano et al.
(2012) and find a factor of 2 difference in dust-to-gas ratios determined
from the two maps, consistent with previous work.

Colloquium: Safe Zone Training (Host: Inclusive Astronomy Group)
Aug 23 @ 3:15 pm – 4:15 pm
Colloquium: Safe Zone Training (Host: Inclusive Astronomy Group) @ BX102

Safe Zone Training

Dr. Zooey Sophia Pook, NMSU

The SafeZone Training was established to educate and train students, faculty, and staff on how to provide safe and affirming support to members of the gay, lesbian, bisexual, transgender, and questioning community.

Planetary Group meeting
Aug 29 @ 4:00 pm – 5:00 pm
Colloquium: Lisa Young (Host: Rene Walterbos)
Aug 30 @ 3:15 pm – 4:15 pm
Colloquium: Lisa Young (Host: Rene Walterbos) @ BX102

Cold Gas and the Evolution of Early-type Galaxies

Lisa Young, New Mexico Tech

A major theme of galaxy evolution is understanding how today’s Hubble sequence was
established — what makes some galaxies red spheroidals and others blue disks, and what
drives their relative numbers and their spatial distributions. One way of addressing these
questions is that galaxies themselves hold clues to their formation in their internal
structures. Recent observations of early-type galaxies in particular (ellipticals and
lenticulars) have shown that their seemingly placid, nearly featureless optical images can
be deceptive. Kinematic data show that the early-type galaxies have a wide variety of
internal kinematic structures that are the relics of dramatic merging and accretion
events. A surprising number of the early-type galaxies also contain cold atomic and
molecular gas, which is significant because their transitions to the red sequence must
involve removing most of their cold gas (the raw material for star formation). We can now
also read clues to the evolution of early-type galaxies in the kinematics and the
metallicity of their gas, and possibly also in the rare isotope abundance patterns in the
cold gas. Numerical simulations are beginning to work on reproducing these cold gas
properties, so that we can place the early-type galaxies into their broader context.

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Colloquium: Brian Svoboda (Host: Moire Prescott)
Sep 6 @ 3:15 pm – 4:15 pm
Colloquium: Brian Svoboda (Host: Moire Prescott) @ BX102

Starless clumps and the earliest phases of high-mass star formation in the Milky Way

Brian Svoboda, NRAO Jansky Fellow

High-mass stars are key to regulating the interstellar medium, star formation activity, and overall evolution of galaxies, but their formation remains an open problem in astrophysics. In order to understand the physical conditions during the earliest phases of high-mass star formation, I will present observational studies we have carried out on dense starless clump candidates (SCCs) that show no signatures of star formation activity. We identify 2223 SCCs from the 1.1 mm Bolocam Galactic Plane Survey, systematically analyse their physical properties, and show that the starless phase is not represented by a single timescale, but evolves more rapidly with increasing clump mass. To investigate the sub-structure in SCCs at high spatial resolution, we investigate the 12 most high-mass SCCs within 5 kpc using ALMA. We find previously undetected low-luminosity protostars in 11 out of 12 SCCs, fragmentation equal to the thermal Jeans length of the clump, and no starless cores exceeding 30 solar masses. While uncertainties remain concerning the star formation efficiency in this sample, these observational facts are consistent with models where high-mass stars form from initially low- to intermediate-mass protostars that accrete most of their mass from the surrounding clump. I will also present on-going research studying gas inflow signatures with GBT/Argus and ALMA, and the dense core mass function with the JVLA.

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Colloquium Thesis Proposal: Rachel Marra
Sep 12 @ 1:30 pm – 2:30 pm
Colloquium Thesis Proposal: Rachel Marra @ Jett Hall 210

An Observer’s Examination of the Circumgalactic Medium using Cosmological Simulations

Rachel Marra, NMSU

A significant aspect to understanding galaxy evolution is having an understanding of the intricacies involving the inflow and outflow of baryons onto a galaxy. Gas needs to accrete onto the galaxy in order for star formation to occur, while stellar winds, supernovae, and radiation pressure result in the outflow of gas from the galaxy. The diffuse region around the galaxy that has gas from interstellar medium (ISM) inflows and intergalactic medium (IGM) outflows interacting is the circumgalactic medium (CGM). Studying the CGM will help us learn about the baryon cycle and give us a better understanding of galactic evolution.

The primary method to studying the CGM is through absorption, as the density is too low to detect emission. Studying these absorption features allows us to learn about the physical properties of the gas giving rise to the absorption. Other than through observations, cosmological simulations play a large role in how we learn about the CGM of galaxies. Using MOCKSPEC, the Quasar Absorption Line Analysis Pipeline, to create mock quasar sightlines through the VELA simulation suite of galaxies, we use the absorption features seen in the sightlines to study the CGM in the simulations. While there are many ions that are used to study the CGM, we focus on OVI.

We intend to study how effective our methods are for studying the CGM with both observations and simulations. The covering fraction of OVI for a sample of observed galaxies will be compared with the covering fraction that is found from a selection of LOS that probe simulated, Milky-Way type galaxies. This tells us if the simulations can reproduce the observations, and if they do not, we can gain insights as to why the simulations do not match observed data. We will also investigate if the metallicity calculated from an observed absorption feature reflects the actual metallicity of the probed gas by using mock sightlines through simulations. Additionally, we will do a comparison of different methodologies used to study the CGM in simulations, to determine if using mock quasar sightlines is a more realistic and accurate method to compare to observed data.

Planetary Group meeting
Sep 12 @ 4:00 pm – 5:00 pm
Colloquium: Eric Nielsen (Host: Moire Prescott)
Sep 13 @ 3:15 pm – 4:15 pm
Colloquium: Eric Nielsen (Host: Moire Prescott) @ BX102

Charting the Outer Reaches of Exoplanetary Systems: Wide-Separation Giant Planet Demographics with Direct Imaging

Eric Nielsen, Kavli Institute for Particle Astrophysics and Cosmology, Stanford University

Over the past decade, the combination of advances in adaptive optics, coronagraphy, and data processing has enabled the direct detection and characterization of giant exoplanets orbiting young, nearby stars. In addition to the wealth of information about exoplanetary atmospheres we obtain from spectroscopy of directly imaged planets, the demographics of these wide-separation planets allow us to directly test theories of planet formation, probing the outer planetary systems compared to transit and radial velocity techniques. In this talk I will present results from the Gemini Planet Imager Exoplanet Survey (GPIES), which surveyed 521 nearby stars for giant planet and brown dwarf companions orbiting beyond 5 AU, and is one of the largest, deepest direct imaging searches for exoplanets every conducted. The overall occurrence rate of substellar companions, and trends with companion mass, semi-major axis, and stellar mass are consistent with giant planets forming via core accretion, and point to different formation mechanisms for giant planets and brown dwarfs between 10 and 100 AU.


Planetary Group meeting
Sep 26 @ 4:00 pm – 5:00 pm
Colloquium: Mental Health Training (Host: Sarah Kovac)
Sep 27 @ 3:15 pm – 4:15 pm
Colloquium: Mental Health Training (Host: Sarah Kovac) @ BX102

Promoting Graduate Student Wellness: A Guide for Faculty and Staff

Marie Zubiate, Aggie Health and Wellness Center

As graduate students demonstrate signs of emotional and psychological distress, faculty and staff play an important role in supporting students, who may be in challenging situations. This guided discussion will outline important information to assist graduate students, including identifying warning signs of distress, and ways for faculty to address students, if concerned.