J. Snchez Almeida, C. MuozTun, - PowerPoint PPT Presentation

Title: J. Snchez Almeida, C. MuozTun,


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Search for Blue Compact Dwarf Galaxies During
Quiescence
J. Sánchez Almeida, C. Muñoz-Tuñón, R. Amorín,
J. A. Aguerri, R. Sánchez-Janssen, G.
Tenorio-Tagle
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Summary

• Motivation

• SDSS/DR6 search for QBCDs

• Results

• Future prospects metallicity problem

• Conclusions

Reference SA et al., 2008, ApJ, 684, in press,
astro-ph/0805.3298
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Motivation
Blue Compact Dwarf galaxies (BCDs) are metal poor
systems undergoing a vigorous starburst. Due to
the strength of the starburst and smallness of
the dwarf galaxy, this process can last only a
few My, i.e., a small fraction of the galaxy
lifetime (Gys).
Where are the galaxies before and after they
glow as BCDs? It is so far unknown. Evolution
connections with other dwarfs have been pointed
out and questioned
This work aims at identifying field galaxies
which could be precursors and leftovers of the
BCD phase.
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The Connection

• BCDs seems to be chemically unevolved systems,
  with record-breaking low metallicities among
  galaxies. Fossils from the early Universe.

• Ideal for cosmo-chemistry (primordial He
  abundance, first stars Pop III, primitive ISM, )?

• Hierarchical galaxy formation the closest
  examples we have of the elemental units in galaxy
  assembly. Missing dwarf galaxy problem

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Search for QBCDs
Most BCDs galaxies are known to have a red low
surface brightness component (e.g., Kunth Oslin
2000), which should exist before the starburst,
and which probably survives the BCD phase.
Caon et al (2005)?
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We search for field galaxies with luminosities,
surface brightness, and colors characteristic of
the low surface brightness component (LSB) of the
BCDs analyzed by Amorín et al. (2007, 2008).
Amorín et al. fit a Sersic profile to the
outskirts of BCD images in various filters,
masking the bright BCD core. They have a sample
of 28 BCD galaxies
Search carried out in SDSS/DR6 spectroscopic
catalog (Stoughton et al. 2002 Adelman-McCarthy
et al. 2007)?
SDSS/DR6 is unique

• 7425 sq. deg. coverage
• More than 790000 galaxies
• Complete for r lt 17.77 mag

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Search Criteria for QBCDs
(Johnsons mag ? SDSS mag according to Smith et
al. 2002 Petrosian mag. ? integrated mag.
from )?
4.- Isolated (inspired by Allam et al. 2005) no
companion brighter than 3 mag fainter than the
candidate within
5.- Others redshift gt 0.003
CASJOBS required!
21493 candidates
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Search Criteria for BCD candidates
Control sample to be compared with the QBCD
candidates
Criteria inspired by Malmberg(2005) and
quantified according to Gil de Paz et al. (2003)
4.- 12log(O/H) lt 1/3 ?
6.- No need for AGN removal
1609 BCD candidates
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BCD candidates
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BCD candidates
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QBCD candidates
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QBCD candidates
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Results

• QBCDs 30 times more abundant than BCDs. QBCD
  phase 30 times longer than BCD phase.

• Sub-solar O/H abundance, but metal rich compared
  to the BCD candidates.
  N2 method

• Surface Brightness µg 23 mag, i.e., two orders
  of magnitude fainter than the BCD candidates.

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Luminosity Functions
x4
x 27
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Future prospects metallicity problem
Hard to understandt why BCD precursors (QBCDs)
have metallicity smaller than the descendents
(BCDs).
Conjecture HII regions in QBCDs are contaminated
by previous starburst. The metallicity that they
provide is not the true metallicity of the
galaxic galaxy.
We are trying to prove of disprove it by
measuring the age and metallicity of the stellar
component, by fitting single stellar population
synthetic spectra (MILES, V4, Vazdekis et al.
2008) to the observed SDSS spectra.
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Preliminary analysis
QBCD Stellar metallicity 0.4 dex larger than
nebular metallicity
QBCD Ages lt 2 Gy
Low SFRs
Hard to explain the metallicity difference is the
full galactic gas is enriched
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Summary - Conclusions

• Some 21500 QBCD host galaxy candidates in
  SDSS/RD6. (1600 BCD candidates).

• They represent one out of 4 dwarf galaxies and,
  30 times the number of BCD candidates.

• Sub-solar O/H abundance (0.6 solar value).

• QBCD nebular metallicity gt BCD metallicity. Why?

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