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