Download Characteristics of Blue Elliptical Galaxies

Anomalously Blue Elliptical Galaxies in
the Sloan Survey
Curtis Mitchell
Department of Physics
University of North Texas
March 31, 2005
Mentor:
Dr. Mike Fanelli, UNT
Collaborators:
Dr. Pam Marcum, TCU & NASA Headquarters
Dr. Christian Aars, San Angelo State U.
Galaxies
• Elliptical galaxies are on the left side of the Hubble
“tuning fork”
Edwin Hubble
(1889-1953)
Hubble’s Galaxy
Classification Scheme
Stars
• Formed when interstellar gas and dust clouds collapse
and begin fusing hydrogen into helium
• Wide variations in mass, color, and size exist
Sagittarius Star Cloud
Star-Forming Systems
• Optically appear blue
• Luminosity dominated
by OB-type stars
NGC 3310
NGC 2997
Blueness
• OB stars lie along the
upper end of main
sequence
• Mark the location of
recent star formation
Hertzsprung-Russell Diagram
NGC 3603
Blue Galaxies
• “Starburst” galaxies
• Causes of star formation
– Galactic interactions
NGC 4038/4039
NGC 4314
Typical Ellipticals
• “Old” red galaxies
– Little or no star formation in the last several billion years
– Spherically shaped
M 49
M 87
Galactic Interactions
• Unlike stellar evolution, interactions are important
to galactic evolution
NGC 2207 & IC 2163
Origin of Ellipticals
• Origins not clear
– Most likely formed from
galactic mergers
– Early ellipticals possibly
came from collapsing
proto-galactic clouds
Compact Group
NGC 4038/4039
Blue Ellipticals
• Unusual objects
– Probably late-stage
mergers
– Stars have “settled
down”
– Using up remaining
gas and dust
NGC 3921
Isolated Systems
• Merger and collapse
scenarios can be tested by
looking for isolated
ellipticals
– Most ellipticals are in dense
galactic environments
KIG 557
Isolated Ellipticals
• Marcum, et al examined a sample of nine isolated ellipticals
– Contained two blue systems and two red, normal systems (possibly
oldest pristine galaxies in universe)
Questions
• What is the nature of the blue systems?
• How do these objects fit into an evolutionary sequence?
Sloan Digital Sky Survey
• Contains luminosities and positions for 100 million plus objects
• Detailed mapping of one quarter of the sky
• We will use the Sloan Survey to search for blue ellipticals
SDSS Survey Telescope
(2.5 meters)
Sloan Information
• SDSS will provide ID, redshifts, images, and spectra for
up to a million galaxies
Sloan Filters:
Filter
Ultraviolet (u)
Wavelength
(Angstroms)
3543
Green (g)
4770
Red (r)
6231
Near Infrared (i) 7625
Infrared (z)
9134
Survey Telescope Primary Mirror
Search Criteria
• We will look for objects meeting the blueness and shape
criteria
Research Method
• Data mining
– New branch of research:
Earth Sciences:
Life Sciences:
Astronomy:
Search Example
• Image of Haro 2 retrieved
from Sloan Sky Server
– Absolute blue magnitude ~ -18
– (B-V) color = +0.45
(typical E’s are +0.9 to 1.0)
– Class: intermediate luminosity
elliptical with a blue core,
probably with a starburst
nucleus
Sources
• Animation
– http://burro.astr.cwru.edu/JavaLab/
Images
Anglo-Australian Observatory
NOAO (National Optical Astronomy Observatory)
Hubble Space Telescope
Literature
R. Michard and P. Prugniel, “Peculiarities and Populations in Elliptical Galaxies” Astronomy
and Astrophysics Vol. 423 N. 3
L.M. Buson, F. Bertola, A. Bressan, D. Burstein, and M. Cappellari, “Is the giant elliptical
galaxy NGC 5018 a post-merger remnant?” Astronomy and Astrophysics v. 423 N. 3
F. Bournard, F. Combes, and C.J. Jog, “Unequal-mass galaxy merger remnants: Spiral-like
morphology but elliptical-like kinematics” Astronomy and Astrophysics, V. 418 N. 2
P.M. Marcum, C.E. Aars, M.N. Fanelli, “Early-Type Galaxies in Extremely Isolated
Environments: Typical Ellipticals?” The Astronomical Journal, Vol. 127 pp. 3213-3234
Sloan Web Page:
www.sdss.org