Post on 18-Jan-2016
transcript
Anomalously Blue Elliptical Galaxies in the Sloan Survey
Mentor:
Dr. Mike Fanelli, UNT
Collaborators:
Dr. Pam Marcum, TCU & NASA Headquarters
Dr. Christian Aars, San Angelo State U.
Curtis Mitchell
Department of PhysicsUniversity of North Texas
March 31, 2005
Galaxies• Elliptical galaxies are on the left side of the Hubble
“tuning fork”
Hubble’s Galaxy Classification Scheme
Edwin Hubble (1889-1953)
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 2997NGC 3310
Blueness
• OB stars lie along the upper end of main sequence
• Mark the location of recent star formation
NGC 3603Hertzsprung-Russell Diagram
Blue Galaxies
• “Starburst” galaxies
• Causes of star formation– Galactic interactions
NGC 4314
NGC 4038/4039
Typical Ellipticals
• “Old” red galaxies– Little or no star formation in the last several billion years– Spherically shaped
M 87
M 49
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
NGC 4038/4039
Compact Group
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 Wavelength (Angstroms)
Ultraviolet (u) 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/
ImagesAnglo-Australian ObservatoryNOAO (National Optical Astronomy Observatory)Hubble Space Telescope
LiteratureR. Michard and P. Prugniel, “Peculiarities and Populations in Elliptical Galaxies”
Astronomy and Astrophysics Vol. 423 N. 3L.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. 3F. 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. 2P.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