Optical detection of the emission nebulae in nearby galaxies

1. Optical detection of the emission nebulae in nearby galaxies DEJAN UROŠEVIĆ collaborators: Milica Vučetić, Bojan Arbutina, Konstantin Stavrev, Dragana Ilić, Aleksandra Dobardžić, Marko Pavlović, Dušan Onić, Branislav Vukotić Department of Astronomy, Faculty of Mathematics, University of Belgrade, Serbia Institute of Astronomy, Bulgarian Academy of Sciences, Bulgaria Astronomical Observatory Belgrade, Serbia

3. Emission nebula detectionin opticalrange • by recombination lines • by forbidden lines: collisional excitation→ radiative de-excitation • [SII]/Hα emission-line ratios • shock-heated SNRs> 0.4 • photoionized nebulae< 0.4 (Blair & Long 2004, Matonick & Fesen 1997) • Observations in red continuum, [SII] and Hα narrow band filters • Data reduction • low fluxes – long exposures – tracking problems • continuum subtraction from emission-line • absolute calibration with non-standard narrow-band filters • IRAF and IRIS software

4. Goal – the detectionof supernova remnants (SNRs) and HII regions in narrow band filters • M81galaxy group – interacting galaxies • Higher star formation rates (SFRs) • Enlarged HI concentration (radio observations) • Higher supernova rates expected • distance3.7 Mpc • Holmberg IX – dwarf, irregular galaxy, possibly youngest nearby dwarf galaxy (Sabbi et al. 2008) • Numerous HII regions (Miller and Hodge 1994) • 1 X-ray source, possible hypernova remnant or super-shell (Miller 1995, Grise et al. 2006) • Observed by our group in 2008 (Arbutina et al. 2009) • 20 HII region candidates

5. ROZHEN observatory • Telescope characteristics • 2 m Ritchey-Chrétien-Coudé telescope at National Astronomical • Observatory Rozhen, Bulgaria • Fokus 16m • CCD camera: VersArray1300B, 1340x1300 px, scale 0”.257732/px • Field of view5’45”x5’35” • Observations and total • exposure times • 2008 March 3 • 2008 November 30 • 190min in red continuum • 140minin Hα filter • 140minin[SII]filter Filter characteristics

6. Star formation rate • Can be found from recombination lines in HII regions around (young) massive stars – from Hα luminosity of HII regions • SFR can be calculated by formula given by Kennicutt et al. (1994):

7. Contamination of Hα luminosity • Sources of Hα luminosity which are not HII regions –other emission nebulae (planetary nebulae and SNRs!!!) • [NII] lines on both sides of Hα line (654.8nm and 658.4nm) • Host galaxy extinction

9. Results • Hα flux from HII regions in Homberg IX is: • Calculated star formation rate is: • This SFR (Andjelić 2011) is 10 times less than given by James at al. (2004), and 6 times less than given by Karachentsev and Kaisin (2007)

10. NGC 3077 – dwarf galaxy rich with molecular and atomic hydrogen • 6 SNR candidates, detected in radio and X range (Rosa-Gonzales 2005) • numerous HII region candidates (Walter et al. 2006)

11. ROZHEN • Observations • 28th ofFebruary 2011 • Exposure time 200s • 23 imagesthrough red cont. filter • 23 imagesthrough [SII] filter • 19 imagesthrough Hα filter

12. Results • No SNR candidates • 12 HII region candidates Andjelić et al. (2011)

13. IC342galaxy – nearby galaxy • large spiral, almost face-on galaxy, app. diameter ~20’ • near Galactic plane, b≈ 10º • heavily obscured by Galactic extinction (A ~ 1.5mag) • the most distance determinations are between 2 - 4 Mpc

14. Previous observations • 4SNR candidates, detected inopticalrange (D’Odorico et al. 1980) • Numerous observations in radio and X range, a few SNR candidates (Hummel & Grave 1990, Kong 2003, Mak et al. 2011) • Numerous HII regions (Hodge & Kennicutt 1983) • Tooth nebula – ultra-luminous X-ray source with optical, shock-heated counterpart

15. ROZHEN Observations 27th & 28th ofNovember 2011 Exposure time15 minutes 3 exposuresthrough each filter Three fields of view

17. Results • 13 SNR candidates • 11 new SNR candidates • Tooth-nebula • SNR2 from D’Odorico et al. (1980) • Note: SNR3 from D’Odorico et al. (1980) is HII region candidate!!! • 374 HII region candidates in two fields of view (5’x5’) 666 HII region candidates in entire IC 342 (20’x20’), only positions, without fluxes (Hodge & Kennicutt 1983)

18. Optical SNR candidates in IC 342 galaxy

19. FOV1 Hα image, continuum substracted

20. FOV2 Hα image, continuum substracted

21. Future prospects • Completing galactic and extragalactic SNR and HII region samples • Evolution of SNRs and HII regions • Star formation rate • … • Opticalobservations are convenient method for this purpose (1 - 2 m telescopes are enough for observations of nearby galaxies) – Rozen, Vidojevica, Antalia

22. Regards from the Belgrade ISM gang!!!!!

23. THANK YOU FOR YOUR ATTENTION!