Blue Compact Dwarfs:

Blue Compact Dwarfs: is internal dynamics the key? I Zw 18 1 Federico Lelli 1 Marc Verheijen Filippo Fraternali1,2 Renzo Sancisi1,3 1 Kapteyn Institute, University of Groningen 2 Astronomy Dept., University of Bologna 3 INAF Observatory of Bologna

BCDs = Starbursting Dwarf Galaxies NGC 4068 (HST) StarStar Formation History Formation History <SFR> McQuinn et al. (2009, 2010) Questions: What triggers the starburst? (external vs internal mechanisms) What are the progenitors/descendants? (evolutionary links with other types of dwarfs)

Striking HI properties of BCDs Meurer et al. (1996, 1998); van Zee et al. (1998, 2001) Optical + HI map Mrk 900 Strong Concentration of HI How does gas concentrate in the centre? van Zee et al. (2001) Postion-Velocity diagram Steep Velocity Gradients Fast Rotation? Inflows/Outflows?

Sample of 18 BCDs (resolved into single stars by HST) HST studies: Galaxy Distance Distribution stellar pop. Star Formation History - mass in young & old stars - starburst timescales - energies from SN 21-cm line obs: HI distribution HI kinematics Gravitational Potential 1 kpc (baryons & dark matter) M* ~ 107-109 M Ropt ~ 0.5-5 kpc

Sample of 18 BCDs (resolved into single stars by HST) HST studies: Galaxy Distance Distribution stellar pop. Star Formation History - mass in young & old stars - starburst timescales - energies from SN 21-cm line obs: HI distribution HI kinematics Gravitational Potential 1 kpc (baryons & dark matter) M* ~ 107-109 M Ropt ~ 0.5-5 kpc

Example 1: UGC 4483 Lelli et al. 2012, A&A, submitted 7 M* ~ 10 M Rd ~ 200 pc 7 MHI ~ 2.5 x 10 M Vr ot ~ 20 km/s

HI kinematics of UGC 4483 Rotation curve: Lelli et al. 2012, A&A, submitted

HI kinematics of UGC 4483 Rotation curve: Vrad ~5 km/s Lelli et al. 2012, A&A, submitted

BCDs vs HI map UGC 4483 dirrs HI Surface Density UGC 4483 DDO 125 DDO 125 Surface Brightness ~10 M /pc2 ~3 M /pc2 Swaters et al. (2002, 2009) Optical 1 kpc Mdyn ~ 1-2 x 108 M Lelli et al. 2012, A&A, submitted Rotation Curve

Mass Models of BCDs Lelli et al. (2012), A&A, submitted M*/LR(HST) = 1.1 UGC 4483 mass budget: Mdyn = (15 ± 3) x 107 M M*(HST) = (1.0 ± 0.3) x 107 M assuming Salpeter IMF Mgas = (3.3 ± 0.4) x 107 M M*(young) ~ 0.2 x 107 M M(molecules) ~ 107 M? XCO ~20 XCO(MW)? ~30% of the total mass is baryonic (gas + old stars)

Example 2: I Zw 18 Lelli et al. (2012), A&A, 537 HST + HI map HI Surface Density Velocity Field Surface Brightness Velocity Field I Zw 18 (BCD) UGC 7232 (dirr) Rotation Curve

V(R0)/R0 BCDs vs dirrs N4068 N4068 dirrs from Swaters et al. (2009)

V(R0)/R0 BCDs vs dirrs N4068 N4068 UGC 4483 DDO 125

V(R0)/R0 BCDs vs dirrs N4068 Starburst N4068 Gravitational Potential + HI concentration dirrs from Swaters et al. (2009)

V(R0)/R0 BCDs vs dirrs N4068 Starburst N4068 Gravitational Potential + HI concentration dirrs from Swaters et al. (2009)

Progenitors/Descendants of BCDs? (Swaters 2002, 2009) Optical Luminosity Profile Luminosity Profile Compact dirr Photometry: HSB profile! μ0 ~ 20 mag arcsec-2 Maximum Disk Fit Position-Velocity Rotation Curve R0 ~ 450 pc HI kinematics: Steeply-rising rotation curve!

BCDs are different from dirrs: steeply-rising rotation curves strong concentration of mass (old stars & dark matter)

BCDs are different from dirrs: steeply-rising rotation curves strong concentration of mass (old stars & dark matter) dirrs UGC 7232 BCDs mass redistribution?...but there are also compact dirrs! I Zw 18

Large-scale HI Emission: clue to the triggering mechanism

Typical dirr: WLM Optical HI map Massey et al. (2007) Velocity Field M* = 2 x 107 M (Lee et al. 2006) Kepley et al. (2007) MHI = 6 x 107 M (Kepley et al. 2007)

I Zw 18 Optical + HI Velocity Field ~13 kpc M*(max) = 0.9 x 108 M ΣSFR = 0.16 M /yr/ kpc2 MHI = 2 x 108 M Lelli et al. (2012), A&A, 537

NGC 1569 Optical + HI Data from THINGS Velocity Field ~10 kpc M* = 7 x 108 M ΣSFR = 4 M /yr/ kpc2 MHI = 4 x 108 M Lelli et al. (in preparation)

NGC 4068 Optical + HI Data from WHISP Velocity Field ~3 kpc M* = 7 x 107 M ΣSFR = 0.002 M /yr/ kpc2 MHI = 2 x 107 M Lelli et al. (in preparation)

Distrubed, outer HI morphologies: dirrs (Swaters et al. 2002, 73 objects) ~35% of the cases BCDs (our sample, 16 objects) ~80% of the cases Interactions/mergers? Cold gas accretion? I Zw 18 NGC 1569 NGC 4068

Conclusions: BCDs have steeply-rising rotation curves --> strong concentration of mass (~30% in baryons) Starburst BCDs Gravitational Potential + HI concentration? dirrs requires redistribution of mass...or link with compact dirrs

Conclusions: BCDs have steeply-rising rotation curves --> strong concentration of mass (~30% in baryons) Starburst BCDs Gravitational Potential + HI concentration? dirrs requires redistribution of mass...or link with compact dirrs BCDs have disturbed, outer HI morphologies: Interactions/mergers? Gas accretion?

More Slides

Optical Structure of BCDs (Papaderos et al. 1996): B-band Luminosity Profile Starburst Old Stellar Pop. BLUE RED Color Profile

Starbursting vs Quiescent Dwarfs: Optical Gas Poor Gas Rich Papaderos et al. (2002) Starburst Underlying, Old Component of BCDs: μ0 ~ 21 mag arcsec-2 (Freeman value for HSB disks)

UGC 4483 Asymmetric Drift Assumptions: Constant scale-height Constant σhi = 8 km/s ΣHI (R) = Σ0 exp(-r2/2s2) V2asym = V2rot + σhi 2 (R2/s2)

I Zw 18 Disk Subtraction (Lelli et al. 2012) Optical + HI map Velocity Field Position Velocity? A C

I Zw 18 Hα/HI connection Hα Position Velocity HI-Hα arc Martin (1996) 60 km/s Hα + HI map 2'' Superbubble (R ~ 2 kpc, V ~ 60 km/s) Inner Shell (R ~ 0.2 kpc, V ~ 200 km/s)