Tidal Dwarves in Wolf-Rayet galaxies

Ángel R. López-Sánchez & César Esteban

Instituto de Astrofísica de Canarias

1. Wolf-Rayet galaxies• Subset of emission-line and H II galaxies• Broad emission feature at 4650 Å,

attributed to Wolf-Rayet stars (WR Bump) – He II 4686 Å– CIII/CII 4650 Å– NIII 4640 Å

• Short-lived phase (< 6 Myr)• Use of population

synthesis models – STARBURST 99

(Leitherer et al, 1999)– Wolf-Rayet and O stars

populations in young starburst (Schaerer & Vacca, 1998)

NGC 3049 Vacca & Conti 1992

2. Previous workWhat is the trigger mechanism in WR galaxies?

Interactions between dwarf galaxies or dwarf companion objects? (Méndez & Esteban, 2000)

• 14 analysed galaxies, 7 interacting and 4 with probable interaction features• Bridge between 2 galaxies (Zw 0855+06) • Several candidates to tidal tails (Mrk 8, Tol 35 and Pox 4).

3. Our sample~ 15 galaxies (Schaerer & Vacca, 1998)

3.1 Mrk 1087– Long-slit spectra

(4.2m WHT – ISIS & 2.5m INT – IDS)

– Deep V image (2.2m CAHA – CAFOS)

– J, H and Ks nIR images (1.5m CST – CAIN)

3.2 HCG 31 – Long-slit spectra

(4.2m WHT – ISIS)– Deep U, B and V images

(2.6m NOT – ALFOSC)– J, H and Ks nIR images

(1.5m CST – CAIN)

MRK 1087

HCG 31

Colors: U, B, V

Colors: U, B, V

3.1 Mrk 1087S

E

50 arcsec

• Méndez & Esteban (2000)– Faint objects with bridges

and tails and interactioning

• Our new V image: – N companion in interaction– Shows nebular emission

• O/H ratios:– #1 y #3 tidal dwarves– #7 intense SF zone off-center– North companion is an

independent nearby object

nucleus companion #1 #3 #7

MB -21.9 -18.2 -16.5 -17.3 -17.4

12+log O/ H 8.70 8.30 8.70 8.70 8.55

vr2 (km/ s) 0 + 117 - 63 + 10 +144

O/H ratios from empirical calibrations

3.1 Mrk 1087• Ages using spectral

synthesis models– North companion: ~ 5 Myr– Central body: ~ 7 Myr

• It is experiencing a strong star formation event due to the interaction with at least two external galaxies:

– the relatively bright K72 103a at ~ 70 kpc and +53 km/s

– the N companion at ~ 60 kpc and +117 km/s

• Is Mrk 1087 a compact group of galaxies?

S

E

50 arcsec

3.2 HCG 31

• UV studies of its centre (Conti, Leitherer & Vacca 1996)

• Johnson et al. (1999) obtained HST images and detected SSCs

• E, F and Mrk 1090 (G) included by Rubin et al (1990)

• H I map of the group: the galaxies are gas rich (Williams 1991)

• NGC 1741 is a very luminous WR galaxy (Conti, 1991)

Johnson & Conti 2000, H and continuum

3.2 HCG 31• 3 slit-positions for spectroscopy

– Kinematics – Physical conditions:

• [OIII] 4363 Å Te

• [OII] & [SII] doublets Ne

– Chemical Abundances

• WR features detected in C, F1 & F2

Deep V image

C F1 F2

WNL 300 40 10

O7V 96600 1660 680

WR/(WR+O) 0.003 0.024 0.014

From Schaerer & Vacca (1998) models

• Ages obtained by– STARBURST 99

(using photometry) (Leitherer et al. 1999)

– Stasinska & Leitherer (1996) and Schaerer & Vacca (1998) (using spectroscopy)

• O/H ratios– Direct determination of B, C, F1– First direct determination of E, F2 and G– A and H calculated by empirical calibrations

3.2 HCG 31

A B C E F1 F2 G H

12+log(O/ H) 8.45(1) 8.14 8.22 8.13 8.07 8.03 8.15 8.37(1)

Log (O+/ N+) -1.21 -1.39 -1.12 -1.26 -1.27 -1.43 -1.31 -1.33

Age 6-8 5-8 4-6 5-6 2-3 2-3 5-7 3-5 (1) Calculated by empirical calibrations.

3.2 HCG 31: metallicity-luminosity relation

• O/H unusual taking into account the M-L relation of Richer & McCall (1995)– It is not

appropriated for starburst galaxies

– The photometric evolution could move their position toward lower luminosity (Leitherer et al. 1999)

Tidal features in HCG 31

• Two kinematic systems in E– A tidal dwarf galaxy (E)– A tidal tail with streaming

motion towards H• F1 and F2:

– Tidal dwarf galaxies • B affected by a tidal

streaming motion between it and AC

• G: fly-by encounter with the armlike H I estructure

• Hunsberger et al (1996): – A tidal tail located at the NE of AC– Other tail towards E

• Iglesias-Páramo & Vilchez (2001)– 7 candidates from E to F (H located in debris)

4. Wolf-Rayet features and tidal tails in compact systems

• Increasing number of morphological interactions signs– Mendez de Oliveira & Hickson (1994)– Vílchez & Iglesias-Páramo (1998, 1999) – Iglesias-Páramo & Vílchez (2001)– Verdes-Montenegro et al.

(1998, 2001, 2002)– Méndez & Esteban (2000)

• Finding WR features would let to study– Star formation

(specially massive star formation), – Its triggering mechanism– Tidal tails and

tidal dwarves evolution