mar28 lh

Blue Compact Dwarfs: 

Blue Compact Dwarfs Lei Hao Mar, 28th, 2007 Astro 620: Advanced Radio Astronomy

Outline: 

Outline BCD definition and detection Metal abundances in BCDs Star-formation processes and age problem Gas content and kinematics BCGs at redshift z~1 BCD environment

BCDs -- definition: 

BCDs -- definition Compact/emission-line/UV-excess galaxies Zwicky (1966), Haro(1956) and Markarian(1967) Only a small fraction are BCGs BCDs: BCGs fainter than MB-17 Compact (andlt;~1kpc diameter)

BCDs -- definition: 

BCDs -- definition BCDs: BCGs fainter than MB-17 Compact (andlt;~1kpc diameter) Blue and bright Gil de Paz, Madore, Pedunova (2003) BLUE BRIGHT

BCDs -- definition: 

BCDs -- definition BCDs: BCGs fainter than MB-17 Compact (andlt;~1kpc diameter) Blue and bright Emission lines

BCDs -- definition: 

BCDs -- definition BCDs and dIrr (morphology of BCDs) The central morphology is often irregular Central+surrounding host galaxy: a mixed bag ---- irregular; symmetric outer envelopes (more common); isolated HII regions (e.g. POX186)

BCDs -- definition: 

BCDs -- definition BCDs and dIrr (morphology of BCDs) The central morphology is often irregular Central+surrounding host galaxy: a mixed bag irregular; symmetric outer envelopes (more common); isolated HII regions (e.g. POX186) POX 186

BCDs -- definition: 

BCDs -- definition BCDs and dIrr (morphology of BCDs) The central morphology is often irregular Central+surrounding host galaxy: a mixed bag irregular; symmetric outer envelopes (more common); isolated HII regions (e.g. POX186) If stellar emission, then suggesting of high age: the relaxation times are of the order of a few times 108 years.

BCDs -- definition: 

BCDs -- definition BCDs and other dwarfs (surface photometry of BCDs) Most dIs and LSBGs, and faint dEs: exponential like laws Normal ellipticals: r1/4 law Brighter dEs: gradually approaching ellipticals, but never become as curve as r1/4 law (Jerjen andamp; Binggeli, 1997) BCDs: not conclusive, but shape changes with radius: critically depend on the sensitivity limits.

BCDs -- detections: 

BCDs -- detections Colors: blue color or UV excess galaxies Emission-Lines: objective-prism surveys

BCDs -- detections: 

BCDs -- detections Colors: blue color or UV excess galaxies Emission-Lines: objective-prism surveys From KISS website

BCDs -- detections: 

BCDs -- detections Colors: blue color or UV excess galaxies Emission-Lines: objective-prism surveys Emission-Lines: existing large galaxy surveys (e.g. SDSS) Thuan, Izotov, Kniazev, et. al. Extremely metal-poor galaxies are rare from the SDSS (Izotov et al., 2006)

BCDs -- metallicities: 

BCDs -- metallicities BCDs: most galaxies with low abundances Gas metallicities Methods: see Amelie’s talk 1/2 Z๏~ 1/50 Z๏ Why no metallicity lower than IZw18 or SBS0335 found? Stellar metallicities Few studies Schulte-Ladbeck et al. (1999) old stellar population: [Fe/H]=−1.92 in VIIZw403 (12+log(O/H)=7.7) Mas-Hesse andamp;Kunth (1999): yound stellar population: metallicity similar to gas metallicities.

BCDs -- metallicities: 

BCDs -- metallicities Other heavy elements N/O and C/O depend on O/H except in very metal-poor galaxies

BCDs -- metallicities: 

BCDs -- metallicities Other heavy elements N/O and C/O depend on O/H except in very metal-poor galaxies Implication: these galaxies are young? Or not? Kunth andamp; Ostlin 2000

BCDs -- metallicities: 

BCDs -- metallicities Other heavy elements N/O and C/O depend on O/H except in very metal-poor galaxies Implication: these galaxies are young?(Izotov andamp; Thuan 1999) Or not (Kunth andamp; Ostlin 2000: similar patterns have been found in the outskirts of spiral galaxies with having known old stellar populations)? Ne, Si, S, and Ar do not depend on O/H -process elements

BCDs -- metallicities: 

BCDs -- metallicities Other heavy elements N/O and C/O depend on O/H except in very metal-poor galaxies Implication: these galaxies are young?(Izotov andamp; Thuan 1999) Or not (Kunth andamp; Ostlin 2000: similar patterns have been found in the outskirts of spiral galaxies with having known old stellar populations)? Ne, Si, S, and Ar do not depend on O/H -process elements Fe/O: 2.5 times smaller than in the Sun. Izotov et al., 2006

BCDs -- metallicities: 

BCDs -- metallicities Other heavy elements N/O and C/O depend on O/H except in very metal-poor galaxies Implication: these galaxies are young?(Izotov andamp; Thuan 1999) Or not (Kunth andamp; Ostlin 2000: similar patterns have been found in the outskirts of spiral galaxies with having known old stellar populations)? Ne, Si, S, and Ar do not depend on O/H -process elements Fe/O: 2.5 times smaller than in the Sun.

BCDs -- metallicities: 

BCDs -- metallicities Primordial Helium Abundances Helium is mainly produced during the first few minutes of our universe. A test of the theory of big bang nucleosynthesis The goal is to measure Y, helium mass function Methods: extrapolate from He/H vs. O/H

BCDs -- metallicities: 

BCDs -- metallicities Primordial Helium Abundances Helium is mainly produced during the first few minutes of our universe. A test of the theory of big bang nucleosynthesis The goal is to measure Y, helium mass function Methods: extrapolate from He/H vs. O/H Izotov et al., 2007

BCDs -- metallicities: 

BCDs -- metallicities Primordial Helium Abundances Better than 1%. Uncertainties Reddening Underlying stellar absorption in the HeI lines Collisional excitation of the He I lines Collisional excitation of the hydrogen lines Possible departures from case B in the emissivities of H and He I lines Temperature structure of the HII region Ionization structure

BCDs -- metallicities: 

BCDs -- metallicities Primordial Helium Abundances Latest result: Yp=0.244, consistent with the prediction of the big bang nucleosynthesis Large scatter: an indication of possible differences in the chemical evolution history of these dwarf galaxies.

BCDs -- Starformation: 

BCDs -- Starformation Two-mode: 'active' and 'passive' (e.g. Hunt et al., 2003; Hirashita andamp; Hunt, 2004)

BCDs -- Starformation: 

BCDs -- Starformation Two-mode: 'active' and 'passive' From L. Hunt

BCDs -- Starformation: 

BCDs -- Starformation Two-mode: 'active' and 'passive' From L. Hunt

Slide26: 

Two-mode: 'active' and 'passive' From L. Hunt

Slide27: 

From L. Hunt

Slide28: 

Active: dusty embedded star clusters Passive: similar to luminous starbursts From L. Hunt

BCDs – Young or Old?: 

BCDs – Young or Old? Metal poor: The first round of star formation Star formation rate low Galactic wind remove metals Observation of old stellar population Surface photometry or resolved star photometry Many degenerates Color-magnitude diagram (CMD) Very challenging Results so far: agree on the existence of old population, but disagree on how old

BCDs – Young or Old?: 

BCDs – Young or Old? BCDs are old burst phase in BCDs is a transitory event and perhaps cyclical in nature Where are quiescent-phase BCDs today? Part of dI group dE disappear

BCDs – gas content and kinematics: 

BCDs – gas content and kinematics BCDs are as gas rich as spirals and dIs, but less than LSBGs BCDs have very low CO luminosities. This doesn’t preclude the presence of H2 Need FUSE to detect cold H2 in absorption BCDs are rotation dominated

BCDs – gas content and kinematics: 

BCDs – gas content and kinematics BCDs are as gas rich as spirals and dIs, but less than LSBGs BCDs have very low CO luminosities. This doesn’t preclude the presence of H2 Need FUSE to detect cold H2 in absorption BCDs are rotation dominated Van Zee et al., 2001

BCDs – gas content and kinematics: 

BCDs – gas content and kinematics BCDs are as gas rich as spirals and dIs, but less than LSBGs BCDs have very low CO luminosities. This doesn’t preclude the presence of H2 Need FUSE to detect cold H2 in absorption BCDs are rotation dominated, while dE have little or no rotation support. BCDs can not passively evolve into dEs

BCGs – at higher redshift: 

BCGs – at higher redshift HST found many luminous blue compact galaxies at intermediate redshift. Many names like CNELGs, BNG, faint and compact galaxies Small half-light radii (1-3.5kpc) and narrow emission line velocity width (35km/s ~ 126km/s) What are they ? 1. small galaxies with starburst dwarf-like morphologies=andgt; local low-mass spheroidal or dwarf elliptical galaxies, or small disk or irregular galaxies (Koo, Guzman, Phillips) 2. bulges forming with central burst of star formation in luminous spiral galaxies =andgt; large spiral galaxies (Hammer, Barton, Van Zee)

BCDs – environment: 

BCDs – environment Basically follow the structures outlined by bright normal galaxies Tend to avoid dense environment/giant companions However, do not dominate the void Pustilnik et al. 1995; Popescu et al. 1997; Lindner et al. 1999, 1996 Hoyle et al. 2005, Binggeli et al 1990

BCDs – environment: 

BCDs – environment Dwarfs do not dominate the void Hoyle et al. 2005

BCDs – environment: 

BCDs – environment Void galaxy population is dominated by faint, late-type galaxies Hoyle et al. 2005

References: 

References Kunth andamp; Ostlin 2000, ARAA Hirashita andamp; Hunt, 2004, Aandamp;A, 421, 555 Van Zee et al., 2001, AJ, 122, 121 Noeske et al., 2006, ApJ, 640, L143 Barton andamp; Van Zee, 2001, 550, L35 Izotov, et al., 2006, Aandamp;A, 955, 970 Izotove, et al., 2007, astro-ph/0702072