Transcript High Resolution 33 GHz Observations of Embedded Star Formation

High Resolution 33 GHz
Observations of Embedded Star
Formation in NGC 6240
Antonio J. Porras1,2, Aaron Evans1, Loreto
Barcos-Muñoz2, Sean Linden2
National Radio Astronomy Observatory1
Fisk-Vanderbilt Bridge Graduate Program2
Personal Motivation
Diffuse
Molecular
clouds
Tails and Tidal bridges.
Interaction between galaxies
using deep surface photometry
Search for Binary
Supermassive Black
Holes
Understand star formation in extreme
environments
Take away: Understand galaxy evolution by
applying different experiences
Importance of (U)LIRGS
• What are Luminous Infrared Galaxies (LIRGS)?
 Galaxies with luminosities above 100 billion times that of
our Sun, or 1011 L☉
 Ultra-Luminous Infrared Galaxies (ULIRGS) have above
1012 L☉
• Giant stellar nurseries for the study of extreme star formation
• Possible way to grow Supermassive Black Holes
• About half of the emission that we see since the Big Bang
coming from the infrared
Take away: (U)LIRGS are important to study extreme star
formation environments
Why study star formation at
Radio wavelengths?
Infrared
Optical and UV
photons
x
x
Dust
(Infrared)
Stars
(optical)
Sanders & Mirabel (1996)
• Intrinsic emission from massive stars and accretion disks is
optical and ultraviolet absorbed by dust and reemitted in the IR
Take away: Radio is not affected by dust absorption
NGC6240
Late stage merger (Nuclear Separation ~ 2 kpc)
Redshift of 0.02
LIR (8-1000 μm) ~ 7x1011L☉
Star Formation Rate (SFR) ~ 87 M☉ per year (Milky Way’s
SFR ~ 1M☉ per year)
• Two Active Supermassive Black Holes (energy output weak
relative to star formation)
•
•
•
•
NGC6240
VLA Ka band. 33GHz with
resolution 0.77” x 0.61”
HST. 0.8 μm with resolution
0.08”
NGC6240
Flux density at 33GHz:
North west nucleus: 4.8 ± 0.3 mJy
South east nucleus: 13.3 ± 1.2 mJy
Flux total with 3 arcsec resolution
= 21.8 ± 0.6 mJy
Take away: Total flux density does not add up because some of the
emission was resolved out at a higher resolution.
Star Formation Rates
• Synchrotron emission (accelerating electrons associated with
Supernovae
• Free-free emission (ion-electron interaction in ionized gas, HII
regions,)
• Thermal dust (absorption of photons heat up dust)
• Assume Synchrotron and
free-free spectral slopes of 0.8 and 0.1 respectively
(Murphy 2012)
Free free
• SFR (IR) ~ 87 M☉ per year
• SFR (33GHz) ~ 121 M☉ per
year
Condon (1992)
Star Formation Rates
MRK231: High
AGN contribution
to total energy
NGC6240: Low AGN
contribution to total
energy
SFR (33GHz) ~ 121 solar
masses per year
SFR (IR) ~ 87 solar
masses per year
Barcos-Muñoz et al. To
be submitted in the Fall
2016
Take away: Although NGC6240 has a double AGN, we find that its
SFR is similar to that of normal galaxies
Thermal Fraction
Thermal fraction for
NGC6240 is 0.44 ± 0.01
Median thermal fraction
= 0.71 ± 0.25
NGC6240
Barcos-Muñoz et al. To
be submitted in the Fall
2016
MRK231
Take away: Our thermal fraction is in the low end, but not inconsistent
with what we see in star forming galaxies
Surface Density
Object
ΣIR (L☉ / kpc2)
Size
NGC6240
1.7x1012
520 pc
Orion Core
3x1012
0.3 pc
ARP220
0.4,4x1013
100,70 pc
M82
9x1011
450 x 75 pc
Soifer et al. 2000, Barcos-Muñoz et
al. 2016
Take away: NGC6240’s star formation region is similar to the Orion
core, but spread over a larger scale
Future Work
• Use ALMA data to calculate gas surface density
• Compare gas surface density to nearby normal galaxies and
starbursting objects
• Possibly look at other galaxies in our sample
Summary
• (U)LIRGS are important to study extreme star formation
environments
• Radio is not affected by dust absorption
• SF calculated in the IR is similar to what we calculated in the
radio
• NGC6240’s SFR is much more extreme than the Milky Way’s
• The thermal fraction at 33GHz is within the values that we get
from normal star forming galaxies
• NGC6240’s star formation region is similar to the Orion core,
but spread over a larger scale
NAC Experience 2015
NAC
NAC Experience 2015
Sense of Community and Diversity
Why do we matter? How do we succeed?
Where do I belong? Impostor syndrome anyone?
Exposure of New Opportunities
Graduate School paid for. Bridge programs in Astronomy
Fellowships
Jobs outside of academia
Networking
RESULT: I am part of the Fisk-Vanderbilt Bridge
Program!
NAC Experience 2016
Good things:
• I had the first African American mentor in my scientific career.
• Experienced a more diverse working environment in Charlottesville
• Was the only male at the REU office, with six other women
Bad things:
• Sense of abandonment (black killings, not much was talked about)
• A bit disorganized
• Few NAC events
Personal Feedback
• Summer talks about Diversity and Inclusion
 Let it be open to public
• Provide safe place for NAC students to discuss presentation on
 Diversity and Inclusion with mentors and presenter
• Expose common problems underrepresented minority face in
academic settings
 Let students know there is a reason underrepresented minorities
underperform and it’s NOT linked to intellectual capacity
• Suggested reading for the summer
 Whistling Vivaldi
GOALS Project
Motivation
• Dust is challenging for observations
• We don’t live long enough
GOALS survey
• Use over 200 out of 629 extragalactic objects from IRAS
• GOALS collection has objects with 60-micron, flux densities about 5.24Jy,
galactic latitude above five degrees
• Redshifts z< 0.088 Brightest 60 micron sources in the extragalactic sky
• (U)LIRGS with luminosities greater than 1011 L☉
• Our Milky Way is about 3*1010 L☉
Take away: We need to observe at multiple wavelengths to get around the issue of dust
Equations
IMF: Kroupa 2001, having a slope of -1.3 for stellar masses between
0.1-0.5 solar masses and -2.3 for stellar masses ranging between 0.5
and 100 solar.
SFR independent of extinction
Murphy et al. 2012
Equations
Calculating IR Luminosity