Starbursts in Dwarf Galaxy Evolution Introduction and Overview

1
Starbursts in Dwarf Galaxy Evolution
Introduction and Overview
Robert Kennicutt Institute of Astronomy
University of Cambridge
2
Issues, Questions

• 0. What is a starburst?
• 1. What fraction of stars in DGs are formed in
  SBs?
• - does this fraction vary among DGs or with
  galaxy mass?
• - was the fraction different in the past?
• 2. Are SBs the tip of the iceberg of a
  continuous range in SFRs, or a physically
  distinct mode of SF?
• 3. Are SBs singular events, episodic, or
  stochastic?
• 4. Are SBs ubiquitous in DGs, or are some
  galaxies prone to SBs, while others are immune?
• - then what properties promote or trigger
  the SBs?
• 5. Do SBs manufacture dSph/dE galaxies?
• 6. What is the role (if any) of massive star
  cluster formation in producing a SB?

3
The Starburst Bestiary.
nuclear starbursts circumnuclear
starbursts clumpy irregular galaxies Ly-a
galaxies EA galaxies KA galaxies LBGs DRGs EROs
SCUBA galaxies extreme starbursts

• GEHRs
• SSCs
• HII galaxies
• ELGs
• CNELGs
• W-R galaxies
• BCGs
• BCDs
• LIGs, LIRGs
• ULIGs, ULIRGs
• LUVGs, UVLGs

4
Complete Inventories of SF Dwarfs

• First Generation color-selected surveys
  (Zwicky, Markarian/Byurakan, Kiso)
• Second Generation emission-line prism surveys
• (Haro, UM, Case, UCM, KISS surveys
• - robust volume-complete inventories of SB
  galaxies
• - first quantitative measures of comological SF
  density
• - first measure of SFR distribution function
• - but incomplete for low SFR, SFR/mass,
  surface brightness systems, minimal treatment of
  dust

5
Gronwall 1998
Hopkins 2004, ApJ, 615, 209
6

• Third Generation follow-up of complete samples
• SINGG/SUNGG (Meurer et al. 2006)
• Helmboldt et al. (2004, 2005)
• - deep Ha, UV imaging of HIPASS-selected
  samples
• 11MPC/11HUGS (Kennicutt et al. 2006, Lee 2006)
• - deep Ha, UV imaging of volume-complete 11
  Mpc samples
• - Spitzer followup proposed
• SDSS-selected samples (e.g., Blanton et al.
  2005)
• HALFALFA (Brosch, Salzer et al)
• - Ha imaging followup of Arecibo
  ALFALFA HI survey
• Fourth Generation blind DG/SF galaxy surveys
• MOSAIC Abell cluster survey (Sakai et al.
  2006)
• SMUDGES survey (van Zee et al.)

7
U681
11 Mpc Ha/Ultraviolet Survey (11HUGS) Distributi
on of Specific SFRs
U9240 UA106
M81 U7559
Cen A N7090
Sex A
N4826 M83
N3432 N4449 GR8
IC4662
gt

8
SINGG Survey for Ionization in Neutral-Gas
Galaxies
SINGG Survey for Ionization in Neutral-Gas
Galaxies
M83 NGC 5236 (Sc)
9
The SMUDGES Survey
L. van Zee D. Schade M. Iyer
(Systematic Multiwavelength Unbiased catalog of
Dwarf Galaxies and Evolution of Structure )

• Key goals
• Determine the fraction of dwarf galaxies that go
  through a starburst phase.
• Investigate trigger mechanisms for the
  starburst, and measure the duty cycle.
• Calculate the luminosity function for faint
  galaxies and compare with predictions for number
  counts from cosmological models.
• Investigate if there are intrinsic differences
  between starbursting and quiescent dwarf galaxies.

• Observations
• Imaging of 134 square degrees in B,V, and I
  with the WIYN 0.9m
• COMPLETED January 2006!
• Optical spectroscopy of 13,000 galaxies with
  the WIYN 3.5m
• On-going 2004-2007(?)
• Imaging in Ha of thousands of galaxies with the
  WIYN 0.9m
• First observations November 2005

10
CGCG 97-125/114 Group in Abell 1367

• starbursting dwarfs associated with tidal
  interactions and/or IGM interactions
• similar objects seen in Stephans quintet (Mendez
  de Oliveira et al 2004)

Ha
Sakai et al. 2002, ApJ, 578, 842
11
Results (so far)

• 0. Previously classified dwarf SB galaxies
  really are a physically distinct
  class.
• 1. Star formation is ubiquitous in DGs with cold
  gas (gt98). Nondetections are rare!
• 2. SBs produce a significant fraction of stars
  in DGs, but steady-state SF dominates.
• - the burst fraction changes with galaxy
  mass
• - the overall SF history is a strong
  function of galaxy mass
• 3. The present-day frequency of SBs is much
  higher than tSB/tHubble so bursts must be
  repetitive (10-100x!).

12
11MPC Sample HaGS Goldmine Virgo Sample
(Kennicutt et al 2006, James et al. 2003,
Gavazzi et al. 2003)
SFRarea
Absolute SFR
13
(No Transcript)
14
108
109
1010
1011 Mo
15
Janice Lees talk coming
16
Contributions to the global star formation budget
IR-luminous 5-8 circumnuclear
3-4 BCGs, ELGs 5-8
Total fraction 10-20
17
Results (so far)

• 0. Previously classified dwarf SB galaxies
  really are a physically distinct
  class.
• 1. Star formation is ubiquitous in DGs with cold
  gas (gt98). Nondetections are rare!
• 2. SBs produce a significant fraction of stars
  in DGs, but steady-state SF dominates.
• - the burst fraction changes with galaxy
  mass
• - the overall SF history is a strong
  function of galaxy mass
• 3. The present-day frequency of SBs is much
  higher than tSB/tHubble so bursts must be
  repetitive (10-100x!).

18
NGC 1744 SB(s)d MB -17.9
19
ESO302-G14 Im pec MB -15.1
20
DDO 210 IB(s)m MB -12
21
Results/Propositions (TBD)

• - There is strong evidence connecting some SBs
  to interactions/mergers (as with massive
  galaxies). But whether interactions/mergers
  are the dominant trigger remains unclear.
• - There is no convincing evidence yet (to me,
  at least) to suggest that SBs arise from a
  distinct subpopulation of dwarf galaxies.
• - There are hints of connections between DG
  physical properties and SFHs, but more work is
  needed.
• - We are only beginning to learn about the
  cosmic evolution of SBs and SFHs of DGs. Future
  work in this area should be very productive.
• - dIrr ? dSph connection (if any) remains
  mysterious.